Nucleus Of The Solitary Tract Research Articles

Effects of acupuncture on gastrointestinal diseases and its underlying mechanism: a literature review of animal studies.

Acupuncture is a non-pharmacological traditional Chinese medical technique that has been used for various types of gastrointestinal (GI) diseases in Eastern medicine. However, the specific mechanisms underlying acupuncture treatment in the GI tract have not yet been elucidated. In this study, we searched the electronic databases PUBMED, EMBASE, and MEDLINE and identified 30 eligible studies that were summarized in this review. This review demonstrates that treatments, including both manual and electroacupuncture, have therapeutic mechanisms in diverse GI diseases. The underlying mechanisms are broadly divided into the following: changes in gene expression in the gastric mucosa or nuclei of the solitary tract, metabolic change induction, regulation of anti-inflammatory substances, vagal activity increase, change in functional connectivity between brain regions, and control of the number of neurons related to GI diseases. Although this study is limited in that it does not represent all types of GI diseases with different acupuncture methods, this study identified acupuncture as effective for GI diseases through various biological mechanisms. We hope that our study will reveal various mechanisms of acupuncture in GI diseases and play an important role in the therapy and treatment of GI diseases, thus advancing the field of study.

Clarification of hypertension mechanisms provided by the research of central circulatory regulation.

Sympathoexcitation, under the regulatory control of the brain, plays a pivotal role in the etiology of hypertension. Within the brainstem, significant structures involved in the modulation of sympathetic nerve activity include the rostral ventrolateral medulla (RVLM), caudal ventrolateral medulla (CVLM), nucleus tractus solitarius (NTS), and paraventricular nucleus (paraventricular). The RVLM, in particular, is recognized as the vasomotor center. Over the past five decades, fundamental investigations on central circulatory regulation have underscored the involvement of nitric oxide (NO), oxidative stress, the renin-angiotensin system, and brain inflammation in regulating the sympathetic nervous system. Notably, numerous significant findings have come to light through chronic experiments conducted in conscious subjects employing radio-telemetry systems, gene transfer techniques, and knockout methodologies. Our research has centered on elucidating the role of NO and angiotensin II type 1 (AT1) receptor-induced oxidative stress within the RVLM and NTS in regulating the sympathetic nervous system. Additionally, we have observed that various orally administered AT1 receptor blockers effectively induce sympathoinhibition by reducing oxidative stress via blockade of the AT1 receptor in the RVLM of hypertensive rats. Recent advances have witnessed the development of several clinical interventions targeting brain mechanisms. Nonetheless, Future and further basic and clinical research are needed.

The modulation effects of repeated transcutaneous auricular vagus nerve stimulation on the functional connectivity of key brainstem regions along the vagus nerve pathway in migraine patients.

Previous studies have shown a significant response to acute transcutaneous vagus nerve stimulation (taVNS) in regions of the vagus nerve pathway, including the nucleus tractus solitarius (NTS), raphe nucleus (RN) and locus coeruleus (LC) in both healthy human participants and migraine patients. This study aims to investigate the modulation effect of repeated taVNS on these brainstem regions by applying seed-based resting-state functional connectivity (rsFC) analysis. 70 patients with migraine were recruited and randomized to receive real or sham taVNS treatments for 4 weeks. fMRI data were collected from each participant before and after 4 weeks of treatment. The rsFC analyses were performed using NTS, RN and LC as the seeds. 59 patients (real group: n = 33; sham group: n = 29) completed two fMRI scan sessions. Compared to sham taVNS, real taVNS was associated with a significant reduction in the number of migraine attack days (p = 0.024) and headache pain intensity (p = 0.008). The rsFC analysis showed repeated taVNS modulated the functional connectivity between the brain stem regions of the vagus nerve pathway and brain regions associated with the limbic system (bilateral hippocampus), pain processing and modulation (bilateral postcentral gyrus, thalamus, and mPFC), and basal ganglia (putamen/caudate). In addition, the rsFC change between the RN and putamen was significantly associated with the reduction in the number of migraine days. Our findings suggest that taVNS can significantly modulate the vagus nerve central pathway, which may contribute to the potential treatment effects of taVNS for migraine.Clinical Trial Registration: http://www.chictr.org.cn/hvshowproject.aspx?id=11101, identifier ChiCTR-INR-17010559.

ID: 208947 Ultrashort Microscopic Magnetic Vagal Stimulation

Electrical stimulation of the cervical vagus nerve is an emerging treatment field for various central nervous system disorders. Invasive electrical Vagus nerve stimulation (VNS) is an FDA-approved add-on treatment to medication for refractory partial-onset seizures in patients 12 years of age and older. However, only approximately 40-50% of patients experience a marked seizure reduction of 50% or more than seizures before treatment [1]. The effects of VNS on neurotransmitter systems, including the noradrenergic system originating from the locus coeruleus and the serotonergic system from the dorsal raphe nucleus, have been reported in experimental settings. The therapeutic effect of VNS in the brain is linked to the stimulation of large diameter afferent fibers. These large myelinated afferent fibers, terminating in the nucleus tractus solitarius in the brainstem, are assumed to deliver the therapeutic effect through further projections into the other brain areas. Non-selective stimulation results in inadvertent activation of efferent fibers that innervate a wide range of peripheral organs resulting in adverse effects [2] with a rare but severe risk of bradyarrhythmia and asystole.

Fentanyl-Induced Respiratory Depression and Locomotor Hyperactivity Are Mediated by μ-Opioid Receptors Expressed in Somatostatin-Negative Neurons

AbstractOpioid drugs are widely used as analgesics but cause respiratory depression, a potentially lethal side effect with overdose, by acting on μ-opioid receptors (MORs) expressed in brainstem regions involved in the control of breathing. Although many brainstem regions have been shown to regulate opioid-induced respiratory depression, the types of neurons involved have not been identified. Somatostatin is a major neuropeptide found in brainstem circuits regulating breathing, but it is unknown whether somatostatin-expressing circuits regulate respiratory depression by opioids. We examined the coexpression ofSst(gene encoding somatostatin) andOprm1(gene encoding MORs) mRNAs in brainstem regions involved in respiratory depression. Interestingly,Oprm1mRNA expression was found in the majority (>50%) ofSst-expressing cells in the preBötzinger Complex, the nucleus tractus solitarius, the nucleus ambiguus, and the Kölliker–Fuse nucleus. We then compared respiratory responses to fentanyl between wild-type andOprm1full knock-out mice and found that the lack of MORs prevented respiratory rate depression from occurring. Next, using transgenic knock-out mice lacking functional MORs specifically inSst-expressing cells, we compared respiratory responses to fentanyl between control and the conditional knock-out mice. We found that respiratory rate depression by fentanyl was preserved when MORs were deleted only inSst-expressing cells. Our results show that despite coexpression ofSstandOprm1in respiratory circuits and the importance of somatostatin-expressing cells in the regulation of breathing, these cells do not mediate opioid-induced respiratory rate depression. Instead, MORs found in respiratory cell populations other thanSst-expressing cells likely contribute to the respiratory effects of fentanyl.

Non-Invasive Ultrasound Modulation of Solitary Tract Nucleus Exerts a Sustainable Antihypertensive Effect in Spontaneously Hypertensive Rats.

We applied the method of non-invasive ultrasound (US) neuromodulation to regulate blood pressure (BP) by stimulating the solitary tract nucleus (NTS) of spontaneously hypertensive rats (SHRs). The rats were exposed to US stimulation for 20 mins every day for two months. Morphology and function of the hypertensive target organs (heart and kidney) were then examined by echocardiography and immunohistochemical staining. C-fos immunofluorescence assays were used to evaluate neuronal activity in the US stimulated areas and to explore related neural pathways. Moreover, the effects of US stimulation on biochemical indicators angiotensinII (ANGII), aldosterone (Aldo), endothelin-1 (ET-1), atrial natriuretic factor (ANF), cortisol (Cor) in SHRs were detected. In addition, HE, TUNEL, and Nissl staining were performed to evaluate the safety of long-term transcranial US stimulation. After two months of US stimulation, systolic blood pressure (SBP) decreased from 170 ± 1.1 mmHg to 158 ± 1.8 mmHg, p < 0.01. What's more, US stimulation effectively inhibited the pathological process of target organs from both morphological and functional levels. With US stimulation, neuronal activities were also significantly enhanced in the NTS, ventrolateral periaqueductal gray (vlPAG), and the caudal ventrolateral medulla (CVLM) region. And US stimulation did not cause brain tissue damage. Meanwhile, the plasma levels of ANF, ANGII, Aldo, and Cor content were inhibited. US stimulation of the NTS could significantly lower BP in SHRs. Non-invasive transcranial US stimulation acting on the NTS might be a potential therapeutic intervention due to its efficacy and safety.

Evidence for a feeding related association between melanocortin in the NTS and Neuropeptide-Y in the PVN

Melanocortin and neuropeptide-Y (NPY) are both involved in feeding and energy regulation, and they have opposite effects in the paraventricular nucleus of the hypothalamus (PVN). The present study examined an interaction between melanocortin in the nucleus of the solitary tract (NTS) and NPY in the PVN. Male Sprague-Dawley rats were implanted with cannulae in the injection sites of interest. In Experiment 1, subjects received either the melanocortin 3/4-receptor (MC3/4) antagonist SHU9119 (0, 10, 50 and 100 pmol/0.5 μl) or the MC3/4 agonist MTII (0, 10, 50, 100 and 200 pmol/0.5 μl) into the NTS. Food intake was measured at 1, 2, 4, 6 and 24-h post-injection. Administration of SHU9119 into the NTS significantly and dose-dependently increased food intake at 1, 2, 4, 6 and 6-24-h, and administration of MTII into the NTS significantly and dose-dependently decreased 24-h free feeding. In Experiment 2, subjects received the MC3/4 agonist MTII (0, 10, 50, 100 and 200 pmol/0.5 μl) into the NTS just prior to NPY (0 and 1μg/0.5 μl) in the PVN. PVN injection of NPY stimulated feeding, and administration of MTII (50, 100 and 200 pmol) into the NTS significantly and dose-dependently decreased NPY-induced feeding at 2, 4, 6 and 6-24-h. These data suggest that there could be a neuronal association between melanocortin in the NTS and NPY in the PVN, and that the melanocortin system in the NTS has an antagonistic effect on NPY-induced feeding in the PVN.

Functional connectivity in central nucleus of amygdala, paraventricular hypothalamus, and nucleus tractus solitarii circuits during high-intensity endurance treadmill exercise in rats

High-intensity endurance exercise (HIE) induces negative emotions alongside fatigue, suffering, and changes in cardiovascular responses, and these regulations could be important for athletic performance. Previous studies have reported that limbic and brain stem regions, including the central nucleus of the amygdala (CeA), the paraventricular nucleus of the hypothalamus (PVH), and the nucleus tractus solitarii (NTS), play important roles in emotional response and autonomic cardiovascular regulation. However, how these brain regions interact during HIE remains unclear. In this study, Wistar rats were subjected to 90-min treadmill running sessions at different endurance exercise intensities (sedentary, low-intensity, and high-intensity: 0, 20, and 34 m/min, respectively; n = 9 per group). After exercise, brain tissues were extracted and examined for c-Fos immediate early gene expression in brain regions such as the CeA, PVH, and NTS at each exercise intensity. The c-Fos-positive cells were counted, and then a partial correlation analysis was performed to examine the functional connectivity during exercise. As a result, the numbers of c-Fos-positive cells in the CeA, PVH, and NTS increased in an exercise intensity-dependent manner. Furthermore, partial correlation analyses of c-Fos-positive cells between CeA and NTS (CeA-NTS), PVH and NTS (PVH-NTS), and CeA and PVH (CeA-PVH) exhibited significant correlation coefficients during HIE but not during sedentary and low-intensity endurance exercises. Thus, these results suggest that functional connectivity between CeA-PVH, PVH-NTS, and CeA-NTS may be enhanced during HIE. This enhanced functional connectivity may also be involved in emotional and cardiovascular regulation during exercise.

Atropine facilitates water-evoked swallows via central muscarinic receptors in anesthetized rats.

Anticholinergic medication causes impaired swallowing with hyposalivation. However, the underlying mechanisms by which these drugs modulate the swallowing reflex remain unclear. This study investigated the effects of the muscarinic acetylcholine receptor (mAChR) nonspecific antagonist atropine on the initiation of swallowing. Experiments were performed on 124 urethane-anesthetized rats. A swallow was evoked by either topical laryngeal application of a small amount of distilled water (DW), saline, citric acid, or capsaicin; upper airway distention with a continuous airflow; electrical stimulation of the superior laryngeal nerve (SLN); or focal microinjection of N-methyl-d-aspartate (NMDA) into the lateral region of the nucleus of the solitary tract (L-nTS). Swallows were identified by electromyographic bursts of the digastric and thyrohyoid muscles. Either atropine, the peripheral mAChR antagonist methylatropine, or antagonists of mAChR subtypes M1-M5 were intravenously delivered. Atropine at a dose of 1 mg/kg increased the number of DW-evoked swallows compared with baseline and did not affect the number of swallows evoked by saline, citric acid, capsaicin, or upper airway distention. Methylatropine and M1-M5 antagonists did not significantly change the number of DW-evoked swallows. Bilateral SLN transection completely abolished DW-evoked swallows, and atropine decreased the swallowing threshold of SLN electrical stimulation. Finally, microinjection of NMDA receptor antagonist AP-5 into the L-nTS inhibited DW-evoked swallows, and atropine facilitated the initiation of swallowing evoked by NMDA microinjection into this region. These results suggest that atropine facilitates DW-evoked swallows via central mAChR actions.NEW & NOTEWORTHY Atropine facilitated the distilled water (DW)-evoked swallows in anesthetized rats. Atropine decreased the swallowing threshold evoked by electrical stimulation of the superior laryngeal nerve, which is a primary sensory nerve for the initiation of DW-evoked swallows. Atropine facilitated the swallows evoked by N-methyl-d-aspartate microinjection into the lateral region of the nucleus of the solitary tract, which is involved in the DW-evoked swallows. We speculate that atropine facilitates the DW-evoked swallows via central muscarinic receptor actions.

Hypothalamic and brainstem glucose-dependent insulinotropic polypeptide receptor neurons employ distinct mechanisms to affect feeding.

Central glucose-dependent insulinotropic polypeptide (GIP) receptor (GIPR) signaling is critical in GIP-based therapeutics' ability to lower body weight, but pathways leveraged by GIPR pharmacology in the brain remain incompletely understood. We explored the role of Gipr neurons in the hypothalamus and dorsal vagal complex (DVC) - brain regions critical to the control of energy balance. Hypothalamic Gipr expression was not necessary for the synergistic effect of GIPR/GLP-1R coagonism on body weight. While chemogenetic stimulation of both hypothalamic and DVC Gipr neurons suppressed food intake, activation of DVC Gipr neurons reduced ambulatory activity and induced conditioned taste avoidance, while there was no effect of a short-acting GIPR agonist (GIPRA). Within the DVC, Gipr neurons of the nucleus tractus solitarius (NTS), but not the area postrema (AP), projected to distal brain regions and were transcriptomically distinct. Peripherally dosed fluorescent GIPRAs revealed that access was restricted to circumventricular organs in the CNS. These data demonstrate that Gipr neurons in the hypothalamus, AP, and NTS differ in their connectivity, transcriptomic profile, peripheral accessibility, and appetite-controlling mechanisms. These results highlight the heterogeneity of the central GIPR signaling axis and suggest that studies into the effects of GIP pharmacology on feeding behavior should consider the interplay of multiple regulatory pathways.

Cholinergic projections to the preBötzinger complex.

Rhythmic inspiratory activity is generated in the preBötzinger complex (preBötC), a neuronal network located bilaterally in the ventrolateral medulla. Cholinergic neurotransmission affects respiratory rhythmogenic neurons and inhibitory glycinergic neurons in the preBötC. Acetylcholine has been extensively investigated given that cholinergic fibers and receptors are present and functional in the preBötC, are important in sleep/wake cycling, and modulate inspiratory frequency through its action on preBötC neurons. Despite its role in modulating inspiratory rhythm, the source of acetylcholine input to the preBötC is not known. In the present study, we used retrograde and anterograde viral tracing approaches in transgenic mice expressing Cre-recombinase driven by the choline acetyltransferase promoter to identify the source of cholinergic inputs to the preBötC. Surprisingly, we observed very few, if any, cholinergic projections originating from the laterodorsal and pedunculopontine tegmental nuclei (LDT/PPT), two main cholinergic, state-dependent systems long hypothesized as the main source of cholinergic inputs to the preBötC. On the contrary, we identified glutamatergic and GABAergic/glycinergic neurons in the PPT/LDT that send projections to the preBötC. Although these neurons contribute minimally to the direct cholinergic modulation of preBötC neurons, they could be involved in state-dependent regulation of breathing. Our data also suggest that the source of cholinergic inputs to the preBötC appears to originate from cholinergic neurons in neighboring regions of the medulla, the intermediate reticular formation, the lateral paragigantocellularis, and the nucleus of the solitary tract.

Brain mapping: topography of neurons and their transmitters involved in various brain functions.

Use of the demanding techniques microdialysis or push-pull superfusion makes it possible to identify neurons in distinct brain areas involved in central control of peripheral functions, thus enabling brain mapping. Investigations with the push-pull superfusion technique have shown that mainly catecholaminergic neurons of the posterior and anterior hypothalamus, the locus coeruleus, and the nucleus of the solitary tract are of crucial importance for blood pressure regulation. Experimentally induced blood pressure changes also modify the release of histamine, glutamate, and taurine in the posterior hypothalamus and of serotonin in the locus coeruleus. Furthermore, histaminergic neurons of the nucleus accumbens are involved in memory, serotonergic neurons of the locus coeruleus in response to noxious stimuli, while nitric oxide of striatum has been implicated in neurotoxicity elicited by amphetamines. The involvement of several neurons in one brain function is discussed.

Carotid body contribution to the physio-pathological consequences of intermittent hypoxia: role of nitro-oxidative stress and inflammation.

Obstructive sleep apnoea (OSA), characterized by chronic intermittent hypoxia (CIH), is considered to be an independent risk for hypertension. The pathological cardiorespiratory consequences of OSA have been attributed to systemic oxidative stress, inflammation and sympathetic overflow induced by CIH, but an emerging body of evidence indicates that a nitro-oxidative and pro-inflammatory milieu within the carotid body (CB) is involved in the potentiation of CB chemosensory responses to hypoxia, which contribute to enhance the sympathetic activity. Accordingly, autonomic and cardiovascular alterations induced by CIH are critically dependent on an abnormally heightened CB chemosensory input to the nucleus of tractus solitarius (NTS), where second-order neurons project onto the rostral ventrolateral medulla (RVLM), activating pre-sympathetic neurons that control pre-ganglionic sympathetic neurons. CIH produces oxidative stress and neuroinflammation in the NTS and RVLM, which may contribute to the long-term irreversibility of the CIH-induced alterations. This brief review is mainly focused on the contribution of nitro-oxidative stress and pro-inflammatory molecules on the hyperactivation of the hypoxic chemoreflex pathway including the CB and the brainstem centres, and whether the persistence of autonomic and cardiorespiratory alterations may depend on the glial-related neuroinflammation induced by the enhanced CB chemosensory afferent input.

Developing Targeted Optogenetic Stimulation Approaches to Preserve Upper Airway Function in Amyotrophic Lateral Sclerosis (ALS) Using a Translational Mouse Model

Amyotrophic lateral sclerosis (ALS) results in debilitating upper airway (swallowing and breathing) impairment that profoundly degrades quality of life while increasing the risk of death by almost eight-fold. The underlying cause has been attributed to degeneration of the hypoglossal lower motor neurons (XII LMNs) that control tongue movement; therefore, treatment efforts are focused on slowing XII LMN degeneration. However, there is growing evidence that ALS is not a pure motor neuron disease – it also affects sensory neurons, including those in the nucleus tractus solitarius (NTS) involved in autonomic regulation of swallowing and breathing. We propose that upper airway impairment in ALS may be more effectively treated using sensorimotor approaches that collectively target XII LMNs and the NTS. Here, we are leveraging a translational mouse model of ALS (low copy number SOD1-G93A; LCN-SOD1) that we have shown develops progressive tongue atrophy, XII LMN degeneration, and “motor” dysphagia (slower tongue motility and swallow rates) resembling human ALS. These mice also show clinicopathological evidence of “sensory” dysphagia, specifically a higher swallow threshold (assessed via electrical stimulation of superior laryngeal nerve afferents) and degeneration of the NTS. Using this model, we have been developing tools and procedures to investigate the therapeutic effects of optogenetic stimulation (opto-stim) of XII LMNs and the NTS during voluntary swallow-related behaviors (drinking, eating, grooming) vs. spontaneous breathing in LCN-SOD1 mice. We have already achieved robust expression of the excitatory opsin channelrhodopsin (ChR2) in XII LMNs via adeno-associated virus delivery into the genioglossus muscle or XII nucleus. ChR2 transfection of XII LMNs was well-tolerated, without adverse effects on swallowing/breathing, general health, and survival. Functionally, XII LMN opto-stim evoked robust tongue protrusion (i.e., genioglossus contraction) in anesthetized mice and slowed lick rate during voluntary drinking in awake mice, which we hypothesize is due to resistive force against tongue movement, similar to resistance exercise. Currently, we are exploring the effects of opto-stim (10 ms pulses at 40 or 80 Hz in trains of 1 s ON/OFF for up to 1 h, 2X/wk) as a tongue resistance exercise in pre-clinical LCN-SOD1 mice. In parallel, we are also developing procedures for targeted opsin expression in the NTS via direct injection vs. pharyngeal mucosa application. We hypothesize that NTS opto-stim, in contrast to XII LMN, will assist swallowing by lowering the sensory threshold to unleash higher swallow rates. We propose these novel sensorimotor opto-stim approaches could ultimately translate into minimally invasive targeted treatments for upper airway impairment in ALS patients. This project is funded by NIH R21 NS123761 This is the full abstract presented at the American Physiology Summit 2023 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.

Orexin facilitates the hypoxic ventilatory response via the activation of corticotropin-releasing hormone neurons that project to the nucleus of the solitary tract

The paraventricular nucleus of the hypothalamus (PVN) contributes significantly to the peripheral chemoreflex-mediated respiratory and sympathetic responses to hypoxia, in part via reciprocal interactions with nucleus of the solitary tract (nTS). Previously we showed that orexin neurons in the perifornical hypothalamus are activated by hypoxia and facilitate the hypoxic ventilatory response (HVR) in the active phase of the circadian cycle . The neural circuitry through which orexin facilitates the HVR is unknown. Orexin receptors (OxR) are expressed in the PVN, and we recently showed that OxR blockade reduced the activation of both corticotropin-releasing hormone neurons in the PVN as well as nTS neurons. In addition, hypoxia activated orexin neurons projecting to the PVN, but not those projecting to nTS. Here we further explored the hypothesis that orexin facilitates the HVR and arterial blood pressure (ABP) response to hypoxia via the activation of nTS-projecting CRH neurons, and that specific OxR1 knockdown in the PVN would reduce the HVR. To test these hypotheses, we nanoinjected fluorescent retrobeads bilaterally into the nTS to label nTS-projecting neurons. Rats were then exposed to hypoxia (2hrs at 11% O2 during the active phase) following injection of either suvorexant (OxR antagonist; 20 mg/kg i.p.; n=4), or vehicle (DMSO; n=4). Using immunohistochemistry (IHC) we then quantified the number of activated (i.e., Fos-immunoreactive; IR) nTS-projecting CRH neurons. In separate groups of rats we nanoinjected shRNA to knockdown Ox1R expression specifically in the PVN (n=8). PVN of control rats was nanoinjected with scrambled RNA (scRNA; n=3) or aCSF (n=2). Three weeks later, rats were exposed to graded hypoxia (from 21% to 10% inspired O2) over 3-5 minutes to assess the acute HVR and ABP response to different levels of hypoxia. OxR blockade reduced the number of Fos-IR, nTS-projecting CRH neurons by ~32% (drug: p&lt;0.0001). Images confirmed successful targeting of shRNA to PVN, and OxR1 knockdown (by ~50%) was confirmed in subsets of samples by Western Blot and IHC. Ox1R knockdown specifically in the PVN had no effect on resting ventilation, but significantly reduced the HVR (main effect: p=0.02; 22% decrease in VE/VCO2 at 13% O2), due to a reduction in the respiratory frequency response to hypoxia (main effect: p=0.004; 38 breath/min decrease at 13% O2). Ox1R knockdown also decreased ABP (~5 mmHg at all O2 levels; main effect: p=0.0015), but not its response to hypoxia. These data suggest that orexin neurons facilitate the HVR via OxR1 Grants: 5R01HL098602 (EH, DK), 5R01HL136710 (KC) This is the full abstract presented at the American Physiology Summit 2023 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.

Interoceptive receptive fields and functional architecture of physiological control in the mouse brainstem

Our external senses of sight, smell, sound, touch, and taste enable us to perceive the external world. In addition, our viscerosensory system monitors the physiological state of peripheral organs. This bodily sensory system orchestrates multi-organ physiological responses, regulating feeding, drinking, sickness behaviors, and generating the internal senses such as satiety, hunger, nausea, visceral malaise. In comparison to external sensory systems, the principles that define visceral sensory processing remain poorly defined. We developed a two-photon calcium imaging preparation to understand internal organ representations in the nucleus of the solitary tract (NTS), a sensory gateway in the brainstem that receives bodily signals mostly via the vagus nerve. Combining the imaging platform with stimulation of multiple visceral organs, we uncover diverse neuronal responses to internal stimuli, while functionally defined cell-types are highly organized within the NTS. Combining functional imaging with pharmacogenetic manipulations and viral tracing from genetically defined vagal sensory cell types, we show that the highly organized representations of internal senses are generated by vagal axon sorting and higher-order sensory processing within the NTS. Using a newly developed spatially patterned optogenetic stimulation system, we showed that stimulating different spatial domains of the NTS differentially modulates autonomic functions. Together, our study reveals basic coding principles used by the brain to process visceral inputs and sheds light on the treatment of viscerosensory and autonomic diseases, including obesity, diabetes, eating disorders, and neuroimmune diseases. The work was supported by NIH grants to S.D.L. (DP1 AT009497, R01 DK122976 and R01 DK103703), the Food Allergy Science Initiative, and a Leonard and Isabelle Goldenson Postdoctoral Fellowship, a Harvard Brain Science Initiative Young Investigator Transitions Award, and an American Diabetes Association Postdoctoral Fellowship to C.R. S.D.L. is an investigator of the Howard Hughes Medical Institute. This is the full abstract presented at the American Physiology Summit 2023 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 Cardiovascular Sensory Afferent Pathways to Adrenergic Groups

Cardiovascular autonomic reflexes arise from activation of peripheral glutamatergic sensory inputs terminating in brainstem’s nucleus of the solitary tract (NTS). NTS neurons process, integrate and encode information for descending neuronal groups, ultimately resulting in a homeostatic response. However, anatomical and circuit-based genetic mapping data supports distinct circuits beginning in NTS for individual sensory information. Additionally, other brain regions projecting to cardiovascular regulatory regions modify these cardiovascular homeostatic responses. In particular, central adrenergic regions send axonal projections not only to NTS, but also major cardiovascular regulatory regions throughout brainstem. Therefore, we hypothesized that activation of baroreflex or cardiopulmonary chemoreflex results in differential inhibition of a neuronal activity marker, c-Fos, production in adrenergic brain regions. To examine this, chemical stimulation of transient receptor potential vanilloid subtype 1 receptors (TRPV1) using capsaicin (5 ug/ml) or baroreceptors using phenylephrine (PE; 25 ug/ml) was performed in adult male and female mice using jugular catheterization under urethane anesthesia. After 90 minutes, mice were transcardially perfused and brain slices were processed for c-Fos and tyrosine hydroxylase (TH) immunoreactivity. As expected, PE and capsaicin both elicited significant bradycardia (PE: -362±24 bpm, capsaicin: -482.25±11 bpm) compared to controls (n=4 and p&lt;0.0001 all groups). Immunohistochemical analysis of A2 found no significant differences in total TH+ neurons (PE: 22±1; capsaicin: 26±4; controls: 23±3). However, the percent of TH+ neurons labeled with c-Fos after injection of PE was significantly lower (8±3) than the precent of c-Fos+ TH neurons after capsaicin (19±3; p=0.05) or controls (17±1; p=0.04). A2 did not demonstrate a significant difference in c-Fos expression between capsaicin and controls (p=0.9). Examination of locus coeruleus (LC) found no significant difference in total TH+ neurons (PE: 37±4; capsaicin: 43±6; controls: 39±5). In contrast to A2, LC demonstrated a significant difference in c-Fos immunoreactivity after capsaicin. Specifically, the percent of TH+ neurons labeled with c-Fos after injection of capsaicin was significantly lower (36±3) than the percent of c-Fos+ TH neurons after PE (54±6; p=0.05) or controls (56±6; p=0.04). These data indicate that activation of baroreflex elicits a significant inhibition of c-Fos production in A2, while activation of cardiopulmonary chemoreflex elicits a significant inhibition of c-Fos in LC. Therefore, in relation to adrenergic brain regions, these data provide evidence for divergence in circuits related to these two sensory inputs. Future studies will address other reflexes, but more importantly will determine specific circuits responsible for communication of sensory input to these adrenergic brain regions. NIH R01HL157366 to CRB This is the full abstract presented at the American Physiology Summit 2023 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.

Efferent network of Neuromedin B neurons in the retrotrapezoid nucleus in mice

In the parafacial region of the medulla, the peptide Neuromedin B (NMB) is expressed in retrotrapezoid nucleus (RTN) neurons that are proposed to be central respiratory chemoreceptors. The efferent network of RTN Nmb neurons has been established in rats, but has not been examined in mice in detail. To map the downstream connections of RTN Nmb neurons we performed genetically-targeted tracing using novel Nmb-Cre knock-in mice. Adult Nmb-Cre mice were injected in the RTN unilaterally with a Cre-dependent AAV producing expression of red fluorescent protein (AAV-Cre ON -mScarlet). Expression of Nmb was identified by fluorescent in situ hybridization (FISH). Injections of AAV-Cre ON -mScarlet in the RTN (N=3) transduced 58 ± 11 % of Nmb-expressing neurons with a selectivity for Nmb neurons of 98 ± 1 %. Intensely labelled axons and terminals were observed in regions overlapping with the medullary and pontine respiratory network. We observe an intra-RTN network of fibers with close appositions between RTN Nmb neurons, as well as moderate projections to areas dorso-medial to the facial nucleus and medially adjacent to the locus coeruleus. There was a modest contralateral projection to the medullary respiratory network, but none to the pontine respiratory network. No labelled fibers were found rostral of the parabrachial nucleus. Anterograde tracing of RTN Nmb neurons was complemented using retrograde transport of Cre-recombinase (AAVrg-Cre) in R26-loxSTOPlox-L10-GFP mice (eGFP-reporter) mice combined with labelling of transcript for Nmb by FISH. Small volumes (3-6 nL) of AAVrg-Cre were unilaterally injected in the Pre-Bötzinger complex (PreBöt), lateral parabrachial nucleus (LPB), caudal ventral respiratory group (cVRG), and the nucleus of the solitary tract (NTS). We determined the proportion of total RTN Nmb neurons that were retro-labelled from each target (PreBöt- 75 ± 3%, n=3; LPB- 65 ± 3%, n=4; cVRG- 54 ± 6%, n=3; NTS- 38 ± 3%, n=3). This result suggests that RTN neurons have a high degree of collateralization within the medullary and pontine respiratory network. Injections of AAVrg-Cre in the PreBöt labelled 16 ± 11% of RTN Nmb neurons contralateral to the injection site. Collectively, these neuroanatomical observations show that the efferent network of RTN Nmb neurons broadly innervate and selectively the central respiratory network in alignment with prior descriptions in rat. Furthermore, we provide evidence for novel connectivity between RTN Nmb neurons. This anatomy supports the idea that RTN neurons generate a coordinated widespread excitation of the respiratory rhythm and pattern generating network in order to promote alveolar ventilation. Funding from NIH-HLBI #HL148004 This is the full abstract presented at the American Physiology Summit 2023 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.

Corticotropin-releasing hormone and oxytocin receptors tonically influence nTS activity in rats subjected to chronic intermittent hypoxia

Chronic intermittent hypoxia (CIH) elevates basal sympathetic nervous system activity, blood pressure, respiration and augments their responses to an acute hypoxic challenge. These physiological effects are due, in part, to the integration of several central nuclei. The nucleus tractus solitarii (nTS) is the initial site of peripheral chemoafferent integration and receives input from the paraventricular nucleus of the hypothalamus (PVN) to modulate nTS activity. PVN-to-nTS projections contain oxytocin (OT) and/or corticotropin-releasing hormone (CRH), yet their contribution to nTS activity after CIH is not well understood. We sought to determine the influence of these neuropeptides on nTS synaptic and neuronal activity, hypothesizing they individually increase nTS activity, which is magnified by their co-application, and such responses are enhanced by CIH. Male Sprague-Dawley rats (~3 wks) were exposed to 10d normoxia (21% O2) or CIH (~30s of 6% O2, 10x/hr, 8 h/day). In nTS slices, spontaneous (s) and TS-evoked excitatory postsynaptic currents (EPSCs), membrane potential and action potential discharge (APD) were recorded (n=7,9). Events were examined during OT and CRH or their receptor block (OTR-x, CRHR2-x). Overall, aCSF vehicle did not alter events over the 40-min recording, confirming their stability. Network-driven sEPSCs were enhanced in normoxic slices by only CRH, whereas CRHR2-x did not alter currents. After CIH, the elevation of sEPSCs by CRH was lost and block of OTR and CRHR2-x reduced sEPSC amplitude, indicating a greater tonic activation of these receptors on the nTS neurocircuitry. Afferent (TS)- EPSCs evoked at 0.5 and 20 Hz were not altered by OT or CRH alone nor their receptor block in normoxia. However, CIH elevated TS-EPSCs in response to CRH and CRH+OT, and this effect was greater than normoxia. Block of OTR and CRHR2 after CIH did not alter TS-EPSC amplitude, indicating their minimal tonic influence on sensory integration. Membrane potential was not altered in either group in response to OT and/or CRH application, or their receptor blockade. APD was induced in both groups by current injection. The co-application of OT and CRH increased the APD in normoxic but not CIH neurons. Within the nTS, CIH decreased the expression of OT and CRH (via immunohistochemistry, n = 3-4) and increased OTR and CRHR2 mRNA (via RNA Scope, n=3-4). In agreement with the increased OTR and CRHR2 mRNA expression, calcium imaging in primary dissociated nTS neurons demonstrated enhanced responses to OT+ CRH following CIH vs normoxia (n= 15, 17). Taken together, these data suggest that following CIH, OT and CRH have modality specific effects on nTS activity. NIH R01 HL098602 &amp; R01 HL128454 (DDK). This is the full abstract presented at the American Physiology Summit 2023 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.

Transcutaneous auricular vagus nerve stimulation may elicit anti-inflammatory actions through activation of the hypothalamic-pituitary-adrenal axis in humans

Introduction: Since the discovery of the cholinergic anti-inflammatory pathway, vagus nerve stimulation (VNS) has been suggested as a treatment option for chronic inflammatory conditions. This pathway relies on efferent vagal nerve fibers. Invasive cervical VNS activates afferent and efferent vagal nerve fibers and, thus, has the potential to directly activate the cholinergic anti-inflammatory pathway. In contrast, transcutaneous auricular VNS (taVNS) activates the auricular branch of the vagus nerve that is purely afferent and projects to the nucleus of the solitary tract. Thus, any anti-inflammatory actions of taVNS are unlikely to result from a direct activation of the cholinergic anti-inflammatory pathway. The objective of this study was to investigate alternative mechanisms by which taVNS may elicit anti-inflammatory effects. The hypothesis was tested that taVNS activates the hypothalamic-pituitary-adrenal (HPA) axis, resulting in adrenal cortisol secretion that will then modulate circulatory immune cell numbers. Methods: The study was approved by the appropriate authorities (IRB# 0054_2019 and NCT04177264). Study participants were healthy adults (n=19, 6 male, 13 female). On three consecutive days either taVNS (left ear, 10 Hz, 1-2 mA, 300 μs pulse width) or sham-taVNS (stimulator off) was applied for 10 minutes. A blood sample was drawn at the end of the third day. Plasma cortisol was determined by ELISA (K003-H1W, Arbor Assays, MI). Circulating T-helper cells (CD3+, CD4+), cytotoxic T-cells (CD3+, CD8+), B-cells (CD19+), monocytes (CD14+, CD11b+), and natural killer (NK, CD3-, CD56+) cells were counted using flow cytometry. Statistical significance was assumed at P&lt;0.05 and trends are reported for P&lt;0.15 based on unpaired t-tests. Results: Plasma cortisol levels tended to be higher following taVNS (72.5±9.5 ng/mL) compared to sham-taVNS (52.3±3.8 ng/mL, P=0.09). Following taVNS, the relative number of circulatory B cells was lower (0.48±0.11 % vs. 0.82±0.11 %, P&lt;0.05), while the number of circulatory monocytes was higher (2.21±0.32 % vs 1.58±0.16 %, P=0.06) compared to sham-taVNS. T-helper cells, cytotoxic T cells, and NK cells were not significantly affected by taVNS. In conclusion, the higher plasma cortisol levels following taVNS together with the higher number of circulatory monocytes and lower number of B cells suggest that taVNS elicits anti-inflammatory actions through activation of the HPA axis, because it is known that cortisol increases circulatory monocytes and reduces B cells. The decrease in B cells following taVNS gives rise to the intriguing hypothesis that taVNS may prevent secondary treatment failure to biologic drugs in chronic inflammatory conditions by reducing production of anti-drug antibodies. Funding: This study was supported by a grant from the American Osteopathic Association (Grant No.: 19137759). This is the full abstract presented at the American Physiology Summit 2023 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.