Muscarinic Research Articles

Contribution of Ih to Postnatal Maturation of Muscarinic Modulation of Inspiratory Bursting at Hypoglossal Motoneurons in Neonatal Mice

Activation of hypoglossal motoneurons (XII MNs) contributes to stiffening of the upper airway during inspiration. The magnitude of this excitation is decreased during sleep, likely due to a combination of withdrawal of noradrenaline and acetylcholine release at XII MNs. Acetylcholine acts at muscarinic acetylcholine receptors (mAChRs) and surprisingly mAChR activation has an excitatory effect on inspiratory bursting in neonatal preparations, which becomes inhibitory in adult preparations. mAChRs modulate several ion channels and characterizing muscarinic effect changes at the XII nucleus will help to explain the mechanism of the inhibitory shift over postnatal maturation. The hyperpolarization activated cyclic nucleotide gated (HCN) channel is positively modulated by mAChRs. HCN channels give rise to Ih, a mixed cation current activated at hyperpolarized membrane potentials that contribute to membrane depolarization. Ihincreases dramatically with postnatal maturation in XII MNs. Thus, we hypothesize that 1) the effects of muscarinic modulation of Ih increases with postnatal maturation, and 2) that muscarinic activation of Ih contributes to the net inhibitory component of muscarinic modulation of inspiratory bursting at XII motoneurons. To test our hypotheses, we used the rhythmic medullary slice preparation to test the functional effects of muscarinic modulation of Ih on inspiratory bursting in neonatal CD1 mice (postnatal day, P0-P4) in combination with pharmacological block of Ih with ZD7288 (25 μM, 150s). Local application of muscarine (100μM, 30s) in the XII motor nucleus increased inspiratory burst amplitude (189 ± 58% of baseline, n = 9). Contrary to our hypothesis, there was no statistically significant difference between inspiratory burst amplitude elicited by muscarine in the presence of ZD7288 (192 ± 47% of baseline, n = 9) versus with the aCSF vehicle control (174 ± 43% of baseline, p = 0.098). We next tested a higher ZD7288 concentration (100 μM) and longer application times (150s, 330s) in neonatal preparations. Preliminary data (n=2) indicate that ZD7288 may increase muscarinic potentiation of inspiratory burst amplitude at XII MNs (muscarinic potentiation (100μM, 30s): control — 112 ±65 % of baseline, aCSF vehicle control - 131 ± 38% of baseline; ZD7288 100μM, 150s - 148 ± 44% of baseline; ZD7288 100μM, 330s - 107 ± 72% of baseline). Future research will elucidate whether the Ih contribution to muscarinic modulation of inspiratory bursting increases with postnatal maturation. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Development of simultaneous determination of dopamine 2, histamine 1, and muscarinic acetylcholine receptor occupancies by antipsychotics using liquid chromatography with tandem mass spectrometry

Receptor occupancy is an indicator of antipsychotic efficacy and safety. It is desirable to simultaneously determine the occupancy of multiple brain receptors as an indicator of the efficacy and central side effects of antipsychotics because many of these drugs have binding affinities for various receptors, such as dopamine 2 (D2), histamine 1 (H1), and muscarinic acetylcholine (mACh) receptors. The purpose of this study was to develop a method for the simultaneous measurement of multiple receptor occupancies in the brain by the simultaneous quantification of unlabeled tracer levels using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Rats were pre-administered with a vehicle, displacer, or olanzapine, and mixed solutions of raclopride, doxepin, and 3-quinuclidinyl benzilate (3-QNB) were administered (3, 10, and 30 μg/kg). The brain tissue and plasma tracer concentrations were quantified 45 min later using LC-MS/MS, and the binding potential was calculated. The highest binding potential was observed at 3 μg/kg raclopride, 10 μg/kg doxepin, and 30 μg/kg 3-QNB. Tracer-specific binding at these optimal tracer doses in the cerebral cortex was markedly reduced by pre-administration of displacers. D2, H1, and mACh receptor occupancy by olanzapine increased in a dose-dependent manner, reaching 70–95%, 19–43%, and 12–45%, respectively, at an olanzapine dose range of 3–10 mg/kg. These results suggest that simultaneous determination of in vivo D2, H1, and mACh receptor occupancy is possible using LC-MS/MS.

Endogenous Acetylcholine Contributes to Flow-Mediated Dilation in Humans

Background & Objective. Flow-mediated dilation (FMD) is a crucial function of the vascular endothelium wherein intraluminal shear stress stimulates endothelium-dependent vasodilation mediated primarily by nitric oxide. Brachial artery FMD (baFMD) is widely evaluated in clinical research as an index of endothelial function, and impaired baFMD is an independent predictor of cardiovascular risk. Despite the physiological and clinical relevance of FMD, the mechanisms by which shear stress is transduced to endothelium-dependent vasodilation (i.e., upstream of nitric oxide production) remain unclear. baFMD corresponds closely with sensitivity to the endothelium-dependent vasodilator acetylcholine (ACh), and preclinical models suggest ACh is released from endothelial cells in response to shear stress. Therefore, the present study tested the hypothesis that activation of muscarinic ACh receptors facilitates baFMD in humans. Methods. baFMD was evaluated using Doppler ultrasound in healthy participants (n=11; 5F/6M; 23±2 y; means ± SE) under control conditions and following local inhibition of muscarinic ACh receptors via intra-arterial atropine infused proximal to the measurement site. baFMD was assessed in response to transient and sustained shear stimuli in separate trials: 1) reactive hyperemia following 5 min of arterial cuff occlusion (RH-FMD) and 2) steady-state rhythmic handgrip exercise at graded intensities (10, 15, 20, & 25% maximal voluntary contraction, MVC) to produce step increases in shear rate (EX-FMD). Blockade effcacy was confirmed via a dose-response to intra-arterial ACh infusion pre and post atropine. Results. Baseline brachial artery diameter and forearm blood flow were similar in all trials (all P>0.05). Atropine reduced peak brachial artery dilation following cuff release (RH-FMD, Δ diameter, atropine: 4.6±0.8 vs. control: 6.5±0.8%, P=0.04) and increased the shear stimulus (shear rate area under the curve, SRAUC: atropine, 29±3 vs. control: 21±3 s−1×103, P=0.01) such that the percent change in brachial diameter was diminished by 35±16% when normalized to SRAUC (baFMD:SRAUC ratio, atropine: 1.7±0.3 vs. control: 3.9±1.0, P=0.02). Similarly, in the EX-FMD trial, atropine reduced brachial artery diameter at all exercise intensities (25% MVC, percent change in diameter: atropine, 10.8±1.4 vs. control, 15.5±1.7%, P=0.04) despite a greater shear stimulus (shear rate: atropine, 10.9±1.1 vs. control, 9.3±0.9 s−1×102, P=0.01). Thus, atropine reduced the slope describing the relationship between brachial artery vasodilation (percent change) and the change in shear rate by 38±8% across all exercise intensities (slope, atropine: 1.3±0.1 vs. control: 2.4±0.4% Δ×s×10−2, P=0.007). As expected, atropine reduced brachial artery vasodilation in response to upstream infusion of ACh (1.5 μg ACh/dl forearm volume/min, Δ diameter, atropine: 2±1 vs. control: 23±4%, P=0.001). Conclusions. The results suggest endogenous ACh facilitates baFMD in response to both transient and sustained shear stimuli, which highlights a novel physiological role of endogenous ACh in vascular regulation in humans and provides insight regarding the basic mechanisms of flow-mediated vasodilation. NIH R01 HL119337 and F31 HL142240. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Sex-Dependent Regulation of Mucin Gene Transcription and Goblet Cell Secretion Machinery Following Intra-Airway IL-13 in Mice with Conditional Loss of Club Cell Creb1

IL-13 is an important effector molecule in allergic asthma, converting secretoglobin-positive club cells into mucin-secreting goblet cells and promoting mucin hypersecretion. IL-13-mediated conversion of club cells to goblet cells requires decreased gene expression of forkhead box A2 ( FOXA2) and increased gene expression of SAM pointed domain containing ETS transcription factor ( SPDEF). In addition, IL-13-mediated mucin hypersecretion may include modulation of purinergic and muscarinic receptors that control basal and stimulated mucus secretion, respectively. We recently found that the cAMP response element-binding protein (CREB), a ubiquitous transcription factor, directly binds to FOXA2 and modulates mucus secretion mechanisms in mice. Here we tested the hypothesis that conditional loss of club cell Creb1 in murine airways modulates the pro-mucin effects of IL-13. Loss of club cell Creb1 augmented IL-13-mediated increases in gene expression of the major gel-forming secreted mucins Muc5ac and Muc5b in male murine airways, with no effect on IL-13-mediated increases in Muc5ac and Muc5b in female murine airways. Examination of mucin secretion mechanisms revealed that IL-13 decreased muscarinic 3 receptor ( M3R) mRNA expression in male murine airways, whereas loss of club cell Creb1 prevented this, resulting in a significant treatment by genotype interaction. Interestingly, in female airways, a main effect of genotype was observed, with loss of club cell Creb1 reducing M3R mRNA expression in the airway. Examination of the purinergic receptor P2Y ( P2ry2) mRNA revealed a main treatment effect for IL-13 to increase P2ry2 expression in male murine airways with no impact of loss of club cell Creb1. In the females, IL-13 increased P2ry2 mRNA in both genotypes, with loss of club cell Creb1 significantly blunting the effect of IL-13 on P2ry2 mRNA. Lastly, we examined goblet cell density and mucin secretion mechanisms using Alcian Blue-PAS staining post in vivo stimulation with a muscarinic agent. We found no major effect of treatment or genotype in the density of goblet cells containing acidic mucins in either male or female airways. In contrast, both males and females showed IL-13-mediated increases in the density of goblet cells containing neutral mucins that was not impacted by genotype. Our preliminary findings suggest that loss of club cell Creb1 decreases molecular mucin secretion mechanisms in male and female airways, and increases Muc5ac and Muc5b mRNA in male airways, though a corresponding genotype-dependent increase in goblet cell density post cholinergic stimulation was not observed. Thus, we conclude that loss of club cell Creb1 causes changes to molecules important for IL-13-mediated mucin hypersecretion, without apparent functional benefit or detriment to the murine airway. This work was supported by the National Institutes of Health (OD026582, HL152101), the Cystic Fibrosis Foundation (REZNIKO20I0, REZNIKO19I0), the Katie Rose Foundation (AWD08203), and the University of Florida McKnight Career Accelerator Award. Angelina Bonilla was funded by the National institutes of Health (R25GM115298). Pedro Trevizan Bau receives the University of Florida McKnight Brain Institute Gator NeuroScholar Fellowship. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Characterizing Muscarinic Receptor Subtype Roles in Inspiratory Burst Modulation of Hypoglossal Motoneurons in Mice

Loss of tongue muscle (innervated by hypoglossal (XII) motoneurons) tone is responsible for airway obstruction during sleep. Contributing factors include loss of noradrenergic drive and activation of muscarinic acetylcholine receptors (mAChRs). While noradrenergic effects are well studied, less is known about muscarinic effects. In mice, XII motoneurons express four mAChRs; M1, M3, and M5 are excitatory while M2 is inhibitory. We hypothesize that M2 is upregulated with postnatal maturation whereas M1, M3, and M5 are downregulated. We therefore expect that activation of M1, M3, and M5 receptors will potentiate inspiratory bursting early in postnatal development whereas activation of M2 receptors will inhibit inspiratory bursting later in postnatal development. To test this, we utilized rhythmic medullary slice preparations from mice at postnatal days 0-5 (P0-5) and P9-14, which contained preBötzinger Complex (site of inspiratory rhythm generation) and XII motoneurons. Blocking M1 receptors locally with pirenzepine (10 μM & 100 μM) decreased the muscarinic potentiation of inspiratory bursting in P0-5 mice at 100 μM (168±23% at 10 μM and 129±16% at 100 μM in muscarine [p<0.05] vs 183±34% muscarine (100 μM) control response, n=9). Activating M1 receptors locally with cevimeline (1 mM) for 30s or 60s did not mediate potentiation of inspiratory bursting as seen with muscarine (116±7% at 30s and 117±7% at 60s vs 181±40% control muscarine response [n=6, p<0.05]). Bath application of M2 antagonist methoctramine (MTH) in P0-5 mice at 1 μM had no effect on muscarine-potentiation of inspiratory bursting (207±109% at 1 μM MTH in muscarine vs 212±84% muscarine control response, n=9). Preliminary analysis of the P9-14 age group using 1 μM MTH suggests there may be an increase in muscarine-mediated potentiation of inspiratory bursting with M2 blockade (170±56% at 1 μM MTH in muscarine vs 152±56% muscarine control response, n=6, p>0.5). Bath application of M3 receptor antagonist 4-DAMP in P0-5 mice at 10 nM had no effect on muscarine-potentiated inspiratory bursting (172±12% vs 178±30% muscarine control), whereas application at 100 nM decreased muscarine-mediated inspiratory burst potentiation compared to control (133±12%, n=4, p<0.05). However, bath application with another M3 receptor antagonist, J Fumarate 104129, had no significant effect on muscarinic modulation of inspiratory bursting in P0-5 mice (188±46% at 0.6 nM [n=6], 185±32% at 6 nM [n=6], and 144±24% at 60 nM [n=4] vs 176±34% muscarine control [n=6]). Overall, our data partially supports a role of M1 receptors contributing to muscarinic potentiation of inspiratory bursting in XII motoneurons, with the contributions of M2 and M3 appearing insignificant early in postnatal life. Preliminary analysis suggests that M2 has a larger contribution later in maturation. Future research will evaluate the contribution of muscarinic receptor subtypes to inspiratory burst modulation later in postnatal life. NIH/NHLBI Funding: R15HL148870. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Efficacy and Safety of Xanomeline-Trospium Chloride in Schizophrenia

A significant need exists for new antipsychotic medications with different mechanisms of action, greater efficacy, and better tolerability than existing agents. Xanomeline is a dual M1/M4 preferring muscarinic receptor agonist with no direct D2 dopamine receptor blocking activity. KarXT combines xanomeline with the peripheral muscarinic receptor antagonist trospium chloride with the goal of reducing adverse events due to xanomeline-related peripheral muscarinic receptor activation. In prior trials, xanomeline-trospium chloride was effective in reducing symptoms of psychosis and generally well tolerated in people with schizophrenia. To evaluate the efficacy and safety of xanomeline-trospium vs placebo in adults with schizophrenia. EMERGENT-3 (NCT04738123) was a phase 3, multicenter, randomized, double-blind, placebo-controlled, 5-week trial of xanomeline-trospium in people with schizophrenia experiencing acute psychosis, conducted between April 1, 2021, and December 7, 2022, at 30 inpatient sites in the US and Ukraine. Data were analyzed from February to June 2023. Participants were randomized 1:1 to receive xanomeline-trospium chloride (maximum dose xanomeline 125 mg/trospium 30 mg) or placebo for 5 weeks. The prespecified primary end point was change from baseline to week 5 in Positive and Negative Syndrome Scale (PANSS) total score. Secondary outcome measures were change from baseline to week 5 in PANSS positive subscale score, PANSS negative subscale score, PANSS Marder negative factor score, Clinical Global Impression-Severity score, and proportion of participants with at least a 30% reduction in PANSS total score. Safety and tolerability were also evaluated. A total of 256 participants (mean [SD] age, 43.1 [11.8] years; 191 men [74.6%]; 156 of 256 participants [60.9%] were Black or African American, 98 [38.3%] were White, and 1 [0.4%] was Asian) were randomized (125 in xanomeline-trospium group and 131 in placebo group). At week 5, xanomeline-trospium significantly reduced PANSS total score compared with placebo (xanomeline-trospium , -20.6; placebo, -12.2; least squares mean difference, -8.4; 95% CI, -12.4 to -4.3; P < .001; Cohen d effect size, 0.60). Discontinuation rates due to treatment-emergent adverse events (TEAEs) were similar between the xanomeline-trospium (8 participants [6.4%]) and placebo (7 participants [5.5%]) groups. The most common TEAEs in the xanomeline-trospium vs placebo group were nausea (24 participants [19.2%] vs 2 participants [1.6%]), dyspepsia (20 participants [16.0%] vs 2 participants [1.6%]), vomiting (20 participants [16.0%] vs 1 participant [0.8%]), and constipation (16 participants [12.8%] vs 5 participants [3.9%]). Measures of extrapyramidal symptoms, weight gain, and somnolence were similar between treatment groups. Xanomeline-trospium was efficacious and well tolerated in people with schizophrenia experiencing acute psychosis. These findings, together with the previously reported and consistent results from the EMERGENT-1 and EMERGENT-2 trials, support the potential of xanomeline-trospium to be the first in a putative new class of antipsychotic medications without D2 dopamine receptor blocking activity. ClinicalTrials.gov Identifier: NCT04738123.

Characterization of HCN channel subtypes at hypoglossal motoneurons throughout postnatal maturation in mice

The inspiratory phase of breathing includes a stiffening of the upper airway to decrease airway resistance and is mediated by excitatory motor output from hypoglossal motoneurons (XII MNs). This excitation decreases from wakefulness to sleep. This decrease in excitation is in large part due to increasing acetylcholine levels, which activate muscarinic acetylcholine receptors (mAChRs) that have a net inhibitory effect in adult preparations. By contrast, activation of mAChRs in neonatal rodent preparations has a net effect of potentiating inspiratory burst amplitude. Therefore, characterizing changes in muscarinic effects at XII MNs across postnatal maturation will help elucidate the mechanism underlying the shift from muscarinic excitation to inhibition. mAChRs modulate several effector ion channels including the hyperpolarization activated cyclic nucleotide gated (HCN) channel. HCN channels give rise to I h, a mixed cation current activated at hyperpolarized membrane potentials. I h additionally shows upregulation at XII MNs with postnatal maturation. Since there are four HCN subtypes (HCN1-4), the reported changes in I h may be caused by changes in HCN channel subtype levels. HCN1 and HCN2 are most prominent in adult XII MNs, whereas the expression of HCN1-4 in neonates is unknown. Thus, the purpose of this research is to characterize changes in HCN gene and channel expression levels at XII MNs across postnatal maturation. We hypothesis that both HCN1 and HCN2 subtypes will increase with postnatal maturation, and that HCN2 has higher levels than HCN1. To test this hypothesis, we used neuroanatomical techniques to evaluate changes in expression patterns of the four HCN proteins at the XII nuclei across postnatal maturation in CD-1 mice. We performed double-labeled immunofluorescence experiments against HCN1 and HCN2 and co-labeled with choline acetyltransferase (ChAT) on 20μm transverse brainstem slices across six postnatal age groups under identical conditions: P0-P1, P4-P6, P9-P10, P12-P14, P17-P19, and adult. Images of the XII nuclei were collected using a confocal microscope. ImageJ was used to determine the average XII MN HCN subtype intensity across postnatal maturation. Preliminary data suggest that HCN1 (n=2) channels undergo a decrease in expression at P17-19 before a final increase in adulthood (P0-1= 97-100%, P4-6= 92-100%, P9-10= 85-95%, P12-14= 77-97%, P17-19= 61-67%, adult= 71-82%). By contrast, preliminary data suggest that HCN2 (n=2) expression intensity remained relatively consistent with a decrease in labeling intensity at P4-6 (P0-1= 97-100%, P4-6=62-84%, P9-10= 45-95%, P12-14= 67-90%, P17-19= 50-93%, adult= 75-100%). These modest changes in labeling intensity of HCN channel subtypes may not contribute to the observed shift of mAChR modulation at XII MNs from excitation to inhibition with postnatal maturation. Biomedical Sciences, College of Graduate Studies; Department of Physiology, College of Graduate Studies, Midwestern University; NIH/NHLBI Funding: R15HL148870. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

SEVERITY OF NEUROLOGICAL LONG-COVID SYMPTOMS CORRELATES WITH INCREASED LEVEL OF AUTOANTIBODIES TARGETING VASOREGULATORY AND AUTONOMIC NERVOUS SYSTEM RECEPTORS

Objective: The Long-COVID syndrome is characterized by a variety of physical, cognitive and psychological symptoms. Worldwide, at least 65 million people are thought to be affected, nevertheless there is still insufficient knowledge about the pathogenesis of long-COVID. Studies on the Long-COVID related myalgicencephalomyelitis/chronic fatigue syndrome (ME/CFS) suggest autoimmune-related changes, for example the formation of autoantibodies against G protein-coupled receptors. Design and method: This monocentric, cross-sectional study included patients who suffered a mild to moderate SARS-CoV-2 infection up to 12 months prior to enrollment with (n = 72) or without (n = 58) Long-COVID diagnosis according to the German S1 guideline or with no known history of SARS-CoV-2 infection (n = 70). Autoantibodies towards the vasoregulation associated Adrenergic Receptor (ADR) B1 and B2 and the CNS and vasoregulation associated muscarinic acetylcholine receptor (CHR) M3 and M4 were measured by ELISA. Neurological disorders and fatigue were quantified by internationally standardized questionnaires including Chalder Fatigue Scale, Short-Form-36 Questionnaire and the CERAD Neurophysiological Assessment Battery. Results: The prevalence and concentrations of evaluated autoantibodies were significantly higher in Long-COVID compared to the 2 other groups (p = 2.1∗10-9) with a significantly higher number of patients with simultaneous detection of more than one autoantibody in Long-COVID group (p = 0.0419). Importantly, the overall inflammatory state was low in all 3 groups. ARB1 and ARB2 correlated negatively CERAD Trail Marking A and B (R &lt;= -0.26, p &lt;= 0.043), while CHRM3 correlated positively with Chadler Fatigue Scale (R = 0.37, p = 0.0087). Conclusions: The present study shows that autoantibodies to GPCR are highly prevalent in patients with Long-COVID. These autoantibodies occur in healthy controls as well, but the prevalence is substantially lower. Concentrations of autoantibodies correlates to intensity of neurological disorders including psychomotor speed, visual search, attention, and fatigue.

HIV-derived Proteins induce Hypertension, Sympatho-activation, and neuroinflammation via T cell-dependent mechanisms

Combination antiretroviral therapy (cART) has markedly increased life expectancy in people living with HIV (PLWH) and induced a switch in the cause of death from opportunistic diseases to cardiovascular disease (CVD). CVD is currently the leading cause of death in PLWH and hypertension, the primary risk factor for CVD, presents in more than 65% of them. However, the mechanisms whereby hypertension develops in PLWH remain unknown. In PLWH on cART, T lymphocytes (T cells) remain a viral reservoir for HIV and continue to secrete viral proteins. Viral proteins remain in circulation and are expressed in the central nervous system. Herein, we tested the hypothesis that expression of HIV-derived proteins increases blood pressure (BP), induces sympatho-activation and inflammation of the central nervous system. We utilized the Tg26 mouse model which expresses 7/9 viral proteins. Quantitative PCR analysis of viral protein expression showed that Tat, gp120, Nef, Vif, and Vpr are primarily expressed in spleen, lung, and brain tissues in Tg26 mice. Morphometric analysis revealed slight but significant increases and decreases in lean mass and fat weights respectively in Tg26. Flow cytometry analysis showed no reduction in CD4+ T cells in Tg26 mice indicating that this mouse model does not progress to AIDS and reproduce the conditions of virally suppressed PLWH. Blood pressure (BP) measurement via telemetry revealed a hypertensive phenotype in male and female Tg26 mice. Hypertension was associated with a larger drop in BP in response to ganglionic blockade but no alterations in heart rate responses to muscarinic and β-adrenergic receptor blockade in Tg26 mice, indicating that viral proteins expression increases neurogenic control of BP but did not alter cardiac autonomic control. β-adrenergic receptor blockade did not reduce BP in Tg26 mice. Tg26 mice also display increased aortic vasoconstriction to phenylephrine. To test the contribution of T cells in BP regulation and sympatho-activation, mice were subjected to a CTLA-4 inhibitor, abatacept, which inhibits T cell activation. Abatacept treatment significantly reduced BP, sympatho-activation, and phenylephrine constriction in Tg26 mice with no effects on wild-type mice. To determine whether the increase in sympatho-activation involves central inflammation, inflammatory cytokines and T cell markers levels were measured in the brain. Levels of pro-inflammatory cytokines including IL-1α, TNFα, IL-6, and CCL2 were increased in the brain of Tg26 mice as well as levels of the T-cell marker GATA3. Altogether, our data shows that the expression of HIV-derived proteins increases BP, sympatho-activation, and vascular adrenergic contractility via T cell-dependent mechanisms likely through central mechanisms involving neuro-inflammation. R01HL147639-01A1, R01HL15526501 and 19EIA34760167 (E.J.B). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Bone Mechanical Loading Reduces Heart Rate and Increases Heart Rate Variability via the Autonomic Nervous System in Anesthetized Mice

Mechanical loading of bone creates interstitial fluid flow and shear stress within the bone lacunocanalicular system, leading to alterations of bone size and mass. Bone plays an important role as an endocrine organ, releasing endocrine signaling molecules that impact systemic physiology. Further, the central and peripheral nervous systems regulate bone mass in response to strain through alterations in autonomic tone. This suggests the potential for interplay between bone and other organs via endocrine signaling and autonomic innervation. In this study, our group investigated this potential interplay by focusing on bone and heart. We hypothesized that mechanical bone loading of mice in vivo would result in altered cardiac function. To test this hypothesis, we performed acute in vivo mechanical loading on right leg tibias of anesthetized TOPGAL and CD-1 mice. Tibias underwent compressive cyclic loading (a sine wave) that modulates between -0.3N and -9.0N for 300 cycles at 2 Hz. Cardiac function was monitored with lead II electrocardiogram (ECG) data, heart rate (HR), and heart rate variability (HRV). Immediate, transient reduction in resting HR (0.93 ± 0.013 fold change from baseline, n=6-7, p&lt;0.01 compared to control) was achieved during tibial loading in 6-month-old male and female mice, with concurrent increase in HRV (1.24 ± 0.11 fold change from baseline, n=6-7, p&lt;0.01). Both HR and HRV returned to baseline levels upon completion of the loading process. ECG measurements, QRS and corrected QT (QTc), were not found to be altered (p&gt;0.05) during loading and 30 minutes following loading. In further studies, 1N-2N did not produce a decrease in HR, while 3N (0.92 ± 0.077 fold change from baseline, n=12, p&lt;0.05) and 9N (0.93 ± 0.061 fold change from baseline, n=13, p&lt;0.05) decreased HR. There was decreased magnitude and responsiveness with aging to 11 months old at 3N and 9N (p&gt;0.05), suggesting the response may weaken with age. The immediate, transient nature of the changes to resting HR and HRV suggest a neural mechanism for this response. To test this mechanism, we inhibited local neuronal afferent activity by injecting lidocaine (2.5mg/kg) near the tibia prior to loading. In doing so, the decrease in HR during loading was significantly diminished (vehicle 0.90 ± 0.060 vs. lidocaine 0.97 ± 0.042 fold change from baseline, n=7-8, p&lt;0.05). To test the efferent arm of the response, mice were injected with the parasympathetic, muscarinic acetylcholine receptor antagonist atropine (2mg/kg), or the sympathetic, β1/β2 receptor antagonist propranolol (10mg/kg). Propranolol significantly inhibited the HR decrease during loading (vehicle 0.88 ± 0.095 vs. propranolol 0.98 ± 0.026 fold change from baseline, n=7-8, p&lt;0.05), while atropine did not (n=8-11, p&gt;0.05). These findings suggest that reductions in sympathetic tone on the heart during bone loading led to the decrease in HR. In conclusion, this study uncovered a reflexive neural connection between bone and heart that is affected by age and mediated by afferent neurons in the tibia and alterations in efferent sympathetic tone to the heart. These findings provide new knowledge that builds on the current science of bone remodeling and its regulation. This study was funded by HRSA Medical Student Education Grant T99HP39202 and NIH P01AG039355. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

414. Understanding the Role of Muscarinic M1 and M4 Receptors in Neural Circuits That Modulate Negative Symptoms of Schizophrenia

414. Understanding the Role of Muscarinic M1 and M4 Receptors in Neural Circuits That Modulate Negative Symptoms of Schizophrenia

Urinary Bladder Dysfunction in a Novel Model of Neuroendocrine Stress

Chronic stress can lead to urinary bladder dysfunction and pain either through actions within the central nervous system or by mechanisms that are locally induced in the bladder. Prolonged upregulation of brain-derived neurotrophic factor (BDNF) in the paraventricular nucleus of the hypothalamus (PVN) has been shown to induce hypertension and chronically elevate activities of the sympathetic nervous system and hypothalamus-pituitary-adrenal axis. Taking advantage of this mechanism, we created a novel model of chronic neuroendocrine stress by subjecting male Sprague Dawley rats to bilateral PVN injections of AAV2 viral vectors expressing either BDNF or GFP (for control). We tested the hypothesis that model-induced chronic neuroendocrine stress would impair bladder function. Bladder activity was assessed 10 weeks post-injections by monitoring the number of urinary voids and average urinary void volume along with water intake over a 48-hour period. To further characterize changes in the urinary bladder, bladder weights were recorded, and in vitro bladder strip experiments were conducted 14 weeks after viral vector injections. BDNF overexpression in the hypothalamus led to significantly lower daily urine output even though water intake remained unaffected, suggesting that BDNF-treated animals showed a significantly higher non-urine-related fluid compared to GFP controls (daily urine output = GFP: 33.85±4.94, BDNF: 14.82±2.18, p &lt; 0.01. Interestingly, despite a lower total daily urine volume, BDNF-treated animals had a significantly higher number of urinary voids (GFP: 7.50±1.42, BDNF: 15.38±2.76; GFP vs. BDNF: p &lt; 0.001) and lower average void volume (GFP: 1.19±0.15, BDNF: 0.27±0.07; GFP vs. BDNF: p &lt; 0.01), thus emulating the overactive bladder phenotype, a common complication in humans with chronic stress. These findings were complemented by in vitro experiments where bladder strips from BDNF rats showed significantly higher contractility as tested with high K+ concentration and electric field stimulation. Moreover, Carbachol-induced stimulation of muscarinic receptors in BDNF bladder strips also trended towards higher contractility. However, urinary bladder weights were unaffected by BDNF overexpression. In summary, we demonstrated that prolonged hypothalamic BDNF overexpression, a model of chronic neuroendocrine stress, leads to significant alterations in bladder function such that BDNF-treated rats exhibited a higher number of urinary voids and lower average void volume compared to GFP controls, and bladder strip experiments suggest that enhanced smooth muscle contractility may contribute to this overactive bladder phenotype. These findings from our novel experimental model will help elucidate pathways through which neuroendocrine stress mechanisms contribute to the development of the overactive bladder syndrome. Funded by R01HL166464, R03AG072016 and R01DK125543. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Investigating the Role of Arcuate Pirt Neurons in Energy Homeostasis

The arcuate nucleus (ARC) is a critical hypothalamic region for the control of metabolism and feeding. Previous studies show that a subgroup of inhibitory ARC neurons, which express the vesicular inhibitory amino acid transporter gene ( Slc32a1) and the leptin receptor gene ( Lepr), control metabolism but not feeding. However, the identity of these neurons remains elusive. We identified a candidate neuron subtype in the ARC, marked by the expression of the phosphoinositide interacting regulator of the transient receptor potential ( Pirt) gene. We hypothesize, based on their molecular profile, that PirtARC neurons are activated by feeding to drive thermogenesis. We used the Pirt-Cre transgenic mouse to investigate the role of PirtARC neurons in energy homeostasis. To validate Cre activity, we expressed a reporter virus (AAV8-hSyn-FLEX-TVA-P2A-GFP-2A-oG) in the ARC of male and female Pirt-Cre mice (n=4; 6 injections, 50 nL each) and compared GFP (green fluorescent protein) fluorescence to Pirt expression by RNA fluorescence in situ hybridization (RNA FISH). In the absence of Cre expression, we failed to detect GFP expression, confirming the Cre dependency of the AAV. However, in Pirt-Cre mice, we found that 77% (380 of 495) of ARC Pirt RNA+neurons were GFP+ and that 79% (380 of 483) of GFP+ ARC neurons were Pirt RNA+, thereby validating the Pirt-Cre mouse for genetically targeting PirtARC neurons. Next, to investigate whether PirtARC neurons respond to metabolic states, we subjected male and female C57BL/6J mice to ad libitum feeding, 18-hour fasting, and 18-hour fasting then 2-hour refeeding (n=4 mice per condition). Using RNA FISH, we assessed the co-localization of Pirt mRNA with Fos mRNA (neuronal activity marker) across the metabolic states. We found that the percentage of PirtARC neurons co-expressing Fos mRNA is higher in ad libitum-fed mice than in fasted mice (p=0.0135; one-way ANOVA followed by Tukey’s multiple comparison test), though neither group differed significantly from post-fast re-fed mice (p &gt; 0.05). This indicates that PirtARC neurons are more active in fed mice than fasted ones, consistent with our hypothesis. Finally, to investigate whether PirtARC neurons regulate food intake, we expressed the intersectional chemogenetics (AAV-CreON/FlpON-hM3Dq-HA) in the ARC of male and female Pirt-Cre::Slc32a1-Flp mice (n=6; 6 injections, 100 nL each) to activate PirtARC neurons. We intraperitoneally injected the artificial muscarinic receptor ligand, clozapine N-oxide (CNO; 1 mg/kg), or saline vehicle in ad libitum-fed mice during the 12-hour light cycle and measured food intake after 30 minutes, 1 hour, 2 hours, and 4 hours on alternating days (CNO, 0.11 ± 0.05 g food/4 hrs.; saline, 0.11 ± 0.04 g food/4 hrs.; Two-way ANOVA, CNO vs saline, p &gt; 0.05 for all time points). Unlike other ARC inhibitory neurons, we found that activating PirtARC neurons does not increase food intake. Together, our results show that PirtARC neurons are a novel subtype of feeding-activated, non-orexigenic neurons in the arcuate hypothalamus. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Endothelial Membrane Potential Changes are Required for Propagated Vasodilation

Introduction: The coordination of blood flow in response to localized increases in metabolic activity is vital for tissue function. This adaptive response typically involves the release of vasoactive factors leading to local vasodilation. This local vasodilation must propagate upstream to proximal feed arterioles and arteries to ensure a coordinated increase in blood flow and adequate tissue perfusion. But the mechanisms underlying such propagated vasodilation remain to be fully understood. This study aims to identify the conduction pathway(s) that facilitate this response. The hypothesis is that endothelial membrane potential changes are required for propagated vasodilation to occur. Methods: To dissect the pathways involved in propagated vasodilation, we employed micropuffng techniques to locally apply vasoactive agents to precontracted rat 2nd order mesenteric arteries. Using a 50um tip micropipette activators were applied against a flowing perfusate, to limit the action of the drug, and the precise site of activators determined by co-application of the fluorophore sulforhodamine. Vasodilator responses were recorded at the site of application and at intervals upstream from the application site. Results: Local application of the muscarinic receptor agonist, acetylcholine (ACh), evoked robust vasodilator responses that propagated upstream from the site of application. The propagation of vasodilation terminated at the site of removal of a 100uM wide strip of endothelial cells. A high-potassium solution, which induces depolarization and ‘clamps’ the membrane potential, also inhibited propagated vasodilation. In contrast, the nitric oxide donor, sodium nitroprusside did not initiate propagated vasodilation in arteries with an intact endothelium. Conclusion: Collectively, these results show that the endothelium serves as the primary signalling pathways for propagated vasodilation. Furthermore, our results highlight the necessity of endothelial cell membrane potential change in the initiation of this vasodilator signal. These insights reinforce the endothelium’s pivotal role in coordinating vascular function. British Heart Foundation. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

A comprehensive assessment of the cholinergic-supporting and cognitive-enhancing effects of Rosa damascena Mill. (Damask rose) essential oil on scopolamine-induced amnestic rats.

Alzheimer's disease (AD) is a neurodegenerative condition characterized by gradual loss of cognitive abilities (dementia) and is a major public health problem. Here, we aimed at investigating the effects of Rosa damascena essential oil (RDEO) on learning and memory functions in a rat model of amnesia induced by scopolamine, as well as on changes in acetylcholinesterase (AChE) activity, M1 muscarinic acetylcholine receptor (mAChR) expression, and brain-derived neurotrophic factor (BDNF) levels in the extracted brain tissues. The control, amnesia (scopolamine, 1mg/kg/i.p.) and treatment (RDEO, 100μL/kg/p.o. or galantamine, 1.5mg/kg/i.p.) groups were subjected to Morris water maze and new object recognition tests. AChE activity was assayed by ELISA, and M1 mAChR and BDNF concentration changes were determined by western blotting. Also, using computational tools, human M1 mAChR was modeled in an active conformation, and the major components of RDEO were docked onto this receptor. According to our behavioral tests, RDEO was able to mitigate the learning and memory impairments caused by scopolamine in vivo. Our in vitro assays showed that the observed positive effects correlated well with a decrease in AChE activity and an increase in M1 mAChR and BDNF levels in amnestic rat brains. We also demonstrated in an in silico setting that the major components of RDEO, specifically -citronellol, geraniol, and nerol, could be accommodated favorably within the allosteric binding pocket of active-state human M1 mAChR and anchored here chiefly by hydrogen-bonding and alkyl-π interactions. Our findings offer a solid experimental foundation for future RDEO-based medicinal product development for patients suffering from AD.

The C-terminus of the prototypical M2 muscarinic receptor localizes to the mitochondria and regulates cell respiration under stress conditions.

Muscarinic acetylcholine receptors are prototypical G protein-coupled receptors (GPCRs), members of a large family of 7 transmembrane receptors mediating a wide variety of extracellular signals. We show here, in cultured cells and in a murine model, that the carboxyl terminal fragment of the muscarinic M2 receptor, comprising the transmembrane regions 6 and 7 (M2tail), is expressed by virtue of an internal ribosome entry site localized in the third intracellular loop. Single-cell imaging and import in isolated yeast mitochondria reveals that M2tail, whose expression is up-regulated in cells undergoing integrated stress response, does not follow the normal route to the plasma membrane, but is almost exclusively sorted to the mitochondria inner membrane: here, it controls oxygen consumption, cell proliferation, and the formation of reactive oxygen species (ROS) by reducing oxidative phosphorylation. Crispr/Cas9 editing of the key methionine where cap-independent translation begins in human-induced pluripotent stem cells (hiPSCs), reveals the physiological role of this process in influencing cell proliferation and oxygen consumption at the endogenous level. The expression of the C-terminal domain of a GPCR, capable of regulating mitochondrial function, constitutes a hitherto unknown mechanism notably unrelated to its canonical signaling function as a GPCR at the plasma membrane. This work thus highlights a potential novel mechanism that cells may use for controlling their metabolism under variable environmental conditions, notably as a negative regulator of cell respiration.

Diffusion and Oligomerization States of the Muscarinic M1 Receptor in Live Cells─The Impact of Ligands and Membrane Disruptors.

G protein-coupled receptors (GPCRs) are a major gateway to cellular signaling, which respond to ligands binding at extracellular sites through allosteric conformational changes that modulate their interactions with G proteins and arrestins at intracellular sites. High-resolution structures in different ligand states, together with spectroscopic studies and molecular dynamics simulations, have revealed a rich conformational landscape of GPCRs. However, their supramolecular structure and spatiotemporal distribution is also thought to play a significant role in receptor activation and signaling bias within the native cell membrane environment. Here, we applied single-molecule fluorescence techniques, including single-particle tracking, single-molecule photobleaching, and fluorescence correlation spectroscopy, to characterize the diffusion and oligomerization behavior of the muscarinic M1 receptor (M1R) in live cells. Control samples included the monomeric protein CD86 and fixed cells, and experiments performed in the presence of different orthosteric M1R ligands and of several compounds known to change the fluidity and organization of the lipid bilayer. M1 receptors exhibit Brownian diffusion characterized by three diffusion constants: confined/immobile (∼0.01 μm2/s), slow (∼0.04 μm2/s), and fast (∼0.14 μm2/s), whose populations were found to be modulated by both orthosteric ligands and membrane disruptors. The lipid raft disruptor C6 ceramide led to significant changes for CD86, while the diffusion of M1R remained unchanged, indicating that M1 receptors do not partition in lipid rafts. The extent of receptor oligomerization was found to be promoted by increasing the level of expression and the binding of orthosteric ligands; in particular, the agonist carbachol elicited a large increase in the fraction of M1R oligomers. This study provides new insights into the balance between conformational and environmental factors that define the movement and oligomerization states of GPCRs in live cells under close-to-native conditions.

Urinary Incontinence Associated with Sertraline use in a Young SSRI-Naí¯ve Female Patient: a Case Report

Introductions: Urinary incontinence is a side effect of several antidepressants, especially those in the SSRI and SNRI groups. Sertraline, a popular SSRI effective against a wide range of mental disorders, is one such drug with a clear association with a new onset of UI. Case: A 20-year-old Indonesian Chinese woman, presenting with mixed anxiety and depressive symptoms, was initially treated with sertraline 50 mg. She experienced an acute onset of urinary urgency and a loss of bladder control. These symptoms resolved upon discontinuation of sertraline. She was then given 10 mg of fluoxetine, and she noted that the urinary problems did not return. The medication was gradually tapered up to 40 mg/day with no remarkable adverse events. Discussions: Sertraline tends to stimulate micturition through effects on M3 muscarinic receptors on the bladder's detrusor muscle and inhibition of the dopamine transporter in the central nervous system. On the other hand, fluoxetine acts antagonistically on 5-HT2C, inhibiting the voiding reflex and promoting urinary continence. Therefore, though both are SSRIs, sertraline and fluoxetine may exhibit different, clinically meaningful effects. Conclusions: Clinicians need to have a greater awareness of urinary incontinence as a side effect of sertraline, as it impacts patients' adherence and quality of life. When possible, switching to fluoxetine is recommended for patients with urinary problems in the event of sertraline use.

Agonist-selective activation of individual G-proteins by muscarinic receptors

Selective activation of individual subtypes of muscarinic receptors is a promising way to safely alleviate a wide range of pathological conditions in the central nervous system and the periphery as well. The flexible G-protein interface of muscarinic receptors allows them to interact with several G-proteins with various efficacy, potency, and kinetics. Agonists biased to the particular G-protein mediated pathway may result in selectivity among muscarinic subtypes and, due to the non-uniform expression of individual G-protein alpha subunits, possibly achieve tissue specificity. Here, we demonstrate that novel tetrahydropyridine-based agonists exert specific signalling profiles in coupling with individual G-protein α subunits. These signalling profiles profoundly differ from the reference agonist carbachol. Moreover, coupling with individual Gα induced by these novel agonists varies among subtypes of muscarinic receptors which may lead to subtype selectivity. Thus, the novel tetrahydropyridine-based agonist can contribute to the elucidation of the mechanism of pathway-specific activation of muscarinic receptors and serve as a starting point for the development of desired selective muscarinic agonists.

Multiple cholinergic receptor subtypes coordinate dual modulation of acetylcholine on anterior and posterior paraventricular thalamic neurons.

Paraventricular thalamus (PVT) plays important roles in the regulation of emotion and motivation through connecting many brain structures including the midbrain and the limbic system. Although acetylcholine (ACh) neurons of the midbrain were reported to send projections to PVT, little is known about how cholinergic signaling regulates PVT neurons. Here, we used both RNAscope and slice patch-clamp recordings to characterize cholinergic receptor expression and ACh modulation of PVT neurons in mice. We found ACh excited a majority of anterior PVT (aPVT) neurons but predominantly inhibited posterior PVT (pPVT) neurons. Compared to pPVT with more inhibitory M2 receptors, aPVT expressed higher levels of all excitatory receptor subtypes including nicotinic α4, α7, and muscarinic M1 and M3. The ACh-induced excitation was mimicked by nicotine and antagonized by selective blockers for α4β2 and α7 nicotinic ACh receptor (nAChR) subtypes as well as selective antagonists for M1 and M3 muscarinic ACh receptors (mAChR). The ACh-induced inhibition was attenuated by selective M2 and M4 mAChR receptor antagonists. Furthermore, we found ACh increased the frequency of excitatory postsynaptic currents (EPSCs) on a majority of aPVT neurons but decreased EPSC frequency on a larger number of pPVT neurons. In addition, ACh caused an acute increase followed by a lasting reduction in inhibitory postsynaptic currents (IPSCs) on PVT neurons of both subregions. Together, these data suggest that multiple AChR subtypes coordinate a differential modulation of ACh on aPVT and pPVT neurons.