Activation Of Cholinergic Receptors Research Articles

Cell-type-specific cholinergic control of granular retrosplenial cortex with implications for angular velocity coding across brain states.

Cholinergic receptor activation enables the persistent firing of cortical pyramidal neurons, providing a key cellular basis for theories of spatial navigation involving working memory, path integration, and head direction encoding. The granular retrosplenial cortex (RSG) is important for spatially-guided behaviors, but how acetylcholine impacts RSG neurons is unknown. Here, we show that a transcriptomically, morphologically, and biophysically distinct RSG cell-type - the low-rheobase (LR) neuron - has a very distinct expression profile of cholinergic muscarinic receptors compared to all other neighboring excitatory neuronal subtypes. LR neurons do not fire persistently in response to cholinergic agonists, in stark contrast to all other principal neuronal subtypes examined within the RSG and across midline cortex. This lack of persistence allows LR neuron models to rapidly compute angular head velocity (AHV), independent of cholinergic changes seen during navigation. Thus, LR neurons can consistently compute AHV across brain states, highlighting the specialized RSG neural codes supporting navigation.

Cholinergic Mechanisms in Gastrointestinal Neoplasia.

Acetylcholine-activated receptors are divided broadly into two major structurally distinct classes: ligand-gated ion channel nicotinic and G-protein-coupled muscarinic receptors. Each class encompasses several structurally related receptor subtypes with distinct patterns of tissue expression and post-receptor signal transduction mechanisms. The activation of both nicotinic and muscarinic cholinergic receptors has been associated with the induction and progression of gastrointestinal neoplasia. Herein, after briefly reviewing the classification of acetylcholine-activated receptors and the role that nicotinic and muscarinic cholinergic signaling plays in normal digestive function, we consider the mechanics of acetylcholine synthesis and release by neuronal and non-neuronal cells in the gastrointestinal microenvironment, and current methodology and challenges in measuring serum and tissue acetylcholine levels accurately. Then, we critically evaluate the evidence that constitutive and ligand-induced activation of acetylcholine-activated receptors plays a role in promoting gastrointestinal neoplasia. We focus primarily on adenocarcinomas of the stomach, pancreas, and colon, because these cancers are particularly common worldwide and, when diagnosed at an advanced stage, are associated with very high rates of morbidity and mortality. Throughout this comprehensive review, we concentrate on identifying novel ways to leverage these observations for prognostic and therapeutic purposes.

Motor behavior improvement in ischemic gerbils by cholinergic receptor activation and treadmill training

Introduction: Treadmill exercise training is one of the most investigated non-pharmacological treatment options for experimental brain ischemia. However, the cholinergic system is essential for improving motor behavior responses. Objective: To analyze the effects of a nicotinic acetylcholine receptor (nAChR) agonist (1, 2, and 4 mg/kg) on the motor behavior of ischemic gerbils subjected to forced treadmill training.Methods: In this experimental study, 72 gerbils, weighing 65–80 g, were divided into eight groups: Sal, Ni1, Ni2, Ni4, I, INi1, INi2, and INi4. Behavioral assessment was initiated 24 hours after the last motor stimulation on the treadmill. Rotarod test (RR) was employed to analyze animal behavior. The data were analyzed using one-way analysis of variance (ANOVA), and the Newman-Keuls post hoc test evidenced differences detected between groups. Results: Data regarding the RR test revealed decreased time spent on the RR apparatus for the Ni1, Ni4, and I groups compared to the Sal and Ni2 groups. However, the INi1 and INi2 groups showed increased time spent compared with the ischemia and INi4 groups (F7,64=4.63; p<0.05).Conclusions: The present study indicates that treadmill training with a concomitant 1 and 2 mg/kg of nAChR agonist effectively improves the behavior of ischemic gerbils.

Effects of Cholinergic Receptor Activation and Magnetic Fields on Motor Behavior in Ischemic Gerbils

Introduction: Ischemic stroke stands as a leading global cause of death and disability, prompting the need for animal model experiments in stroke research and the protection of motor function. Recently, magnetic fields have gained significant interest in various biological contexts, showing promise in preserving neurons and reversing behavioral and morphological changes in stroke models. This study explores the potential synergy between static magnetic field and nAChR agonist administration in safeguarding motor behavior in ischemic gerbils. Objective: To determine whether the combined use of a static magnetic field and an agonist for nicotinic acetylcholine receptors (nAChR) can preserve motor behavior in ischemic gerbils.Methods: In this experimental study, 72 Mongolian gerbils were randomly allocated into nine groups (n=8): S, SISM, SINSM, ISM, INP, ISP, INSM, INNP, INSP, distributed according to surgical procedure and treatment. The animals were trained and evaluated on the Rotarod (RR) to assess motor performance.Results: The main finding was the preservation of motor behavior in the Sham Ischemia and Nicotine and Sham Magnetic Stimulation (SINSM) and Ischemia and Nicotine and South Pole Magnetic Field (INSP) groups, as evidenced by the results of the RR test.Conclusions: The findings are consistent with previous literature and provide insight into the mechanism of potentiation, as results showed that adding a nAChR agonist to the magnetic field preserved motor performance in the RR test of ischemic animals.

Activation of M1 cholinergic receptors in mouse somatosensory cortex enhances information processing and detection behaviour

To optimise sensory representations based on environmental demands, the activity of cortical neurons is regulated by neuromodulators such as Acetylcholine (ACh). ACh is implicated in cognitive functions including attention, arousal and sleep cycles. However, it is not clear how specific ACh receptors shape the activity of cortical neurons in response to sensory stimuli. Here, we investigate the role of a densely expressed muscarinic ACh receptor M1 in information processing in the mouse primary somatosensory cortex and its influence on the animal’s sensitivity to detect vibrotactile stimuli. We show that M1 activation results in faster and more reliable neuronal responses, manifested by a significant reduction in response latencies and the trial-to-trial variability. At the population level, M1 activation reduces the network synchrony, and thus enhances the capacity of cortical neurons in conveying sensory information. Consistent with the neuronal findings, we show that M1 activation significantly improves performances in a vibriotactile detection task.

Non-neuronal acetylcholine is causal for cardioprotection by hypoxic preconditioning in adult rat cardiomyocytes

Abstract Introduction Brief episodes of non-lethal myocardial ischemia/reperfusion preceding more sustained ischemia and reperfusion reduce lethal ischemia/reperfusion injury. The underlying protective signaling mechanisms of such ischemic preconditioning are unclear in their details. Among other protective mediators, neuronal acetylcholine (ACh) and its signaling through cholinergic receptors is involved in protection by ischemic preconditioning. Recently, a non-neuronal cardiac cholinergic system (NNCCS) has been identified, suggesting that a nervous system-independent, cardiomyocyte-derived acetylcholine signaling with signal amplification by auto- and paracrine cholinergic receptor activation could also participate in ischemic preconditioning. Aim We aimed to examine the role of NNCCS-derived ACh as a mediator of ischemic preconditioning. We therefore, in a reductionist approach, used isolated adult cardiomyocytes with hypoxic preconditioning (HPC). Methods Adult ventricular rat cardiomyocytes were isolated (from n=9 hearts), and HPC was induced by one cycle of 10 min hypoxia / 20 min reoxygenation. Thirty min normoxia served as control. Cardiomyocytes were then exposed to 30 min sustained hypoxia / 5 min reoxygenation (H/R), or a 35 min time control (TC). Cardiomyocyte viability was quantified before and after H/R or TC, respectively, by trypan blue staining. In a subgroup of experiments (cardiomyocytes from n=6 hearts) in the presence of physostigmine (0.2 mmol/L), intracellular ACh was quantified before and after HPC or normoxia and after sustained hypoxia and reoxygenation or TC, respectively, via liquid chromatography-coupled tandem mass spectrometry. Experiments on cardiomyocyte viability (from n=9 hearts) were repeated with the addition of cholinergic receptor antagonists (nicotinic: hexamethonium [1 µmol/L], muscarinic: atropine [0.1 µmol/L]) a) during the first 30 min with HPC or normoxia, b) during H/R or TC (30-65 min), or c) throughout the total 65 min protocol. Results The viability of cardiomyocytes subjected to H/R was better preserved with HPC than without (Figure A), and intracellular ACh was increased during hypoxia after prior HPC (Figure B). Cholinergic receptor antagonists during HPC did not change HPC´s protection (Figure A). However, the combination of both antagonists during sustained hypoxia abrogated HPC´s protection (Figure A), whereas nicotinic or muscarinic cholinergic receptor antagonists alone did not. Cholinergic receptor antagonists throughout the total 65 min also abrogated HPC´s protection (Figure A). Conclusion: The NNCCS is activated by HPC and causal for HPC´s protection. HPC increases intracellular acetylcholine, and cardiomyocyte protection is mediated via both nicotinic and muscarinic cholinergic receptors, suggesting an auto- and paracrine signal amplification on the cardiomyocyte level.Figure

GINSENOSIDE-RG3 ENHANCES SOME ANTIHYPERTENSIVE AGENTS-INDUCED INHIBITION OF ADRENAL CATECHOLAMINE SECRETION

Objective: The present study was designed to examine the influence of ginsenoside-Rg3 (Rg3), one of panaxadiol-type saponins, which is isolated from Korean Panax ginseng, in some antihypertensive agents-induced inhibition on the secretion of catecholamines (CA) from the perfused rat adrenal medullae. Design and method: The adrenal gland was isolated and perfused with Krebs-bicarbonate. CA was measured directly by using the fluorospectrophotometer. Results: Ginsenoside-Rg3 (3∼30 μM) during perfusion into an adrenal vein for 90 min significantly inhibited the CA secretion evoked by acetylcholine (ACh). Also, olmesartan (AT1 receptor blocker, 15 μM), simvastatin (an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase, 60 μM), enalapril (an inhibitor of angiotensin converting enzyme, 150 μM), and cilnidipine (a voltage-dependent L-type Ca2+ channel blocker, 3 μM) significantly reduced the CA secretion evoked by ACh and angiotensin II (Ang II), respectively. In the simultaneous presence of ginsenoside-Rg3 (10 μM) along with four antihypertensive agents (olmesartan, enalapril, simvastatin or cilnidipine), the CA secretion evoked by ACh and Ang II was more strongly inhibited compared with that of each antihypertensive agent-treatment alone. Conclusions: Collectively, these results demonstrate that ginsenoside-Rg3 as well as antihypertensive agents can inhibit the CA secretion evoked by activation of both cholinergic and AT1 receptors from the perfused rat adrenal medulla. When this ginsenoside-Rg3 was used in combination with different antihypertensive agents, their effects of antihypertensive agents on reduction of adrenal CA secretion were significantly enhanced, which may also be clinically beneficial for the treatment of cardiovascular diseases.

MP03-07 THE LACK OF MECHANOSENSITIVE TREK-1 CHANNEL MIMICS THE DEVELOPMENT OF AGING-RELATED BLADDER PHENOTYPES IN MICE

You have accessJournal of UrologyCME1 Apr 2023MP03-07 THE LACK OF MECHANOSENSITIVE TREK-1 CHANNEL MIMICS THE DEVELOPMENT OF AGING-RELATED BLADDER PHENOTYPES IN MICE Alison Xiaoqiao Xie, Nao Iguchi, and Anna Malykhina Alison Xiaoqiao XieAlison Xiaoqiao Xie More articles by this author , Nao IguchiNao Iguchi More articles by this author , and Anna MalykhinaAnna Malykhina More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000003214.07AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: Previous animal and human studies have confirmed that the potassium channel subfamily K member 2 (TREK-1), a member of two-pore domain mechanosensitive K+ channels (K2P), acts as a mechanosensor in the urinary bladder. We reported that TREK-1 is a predominantly expressed K2P channel in the human detrusor, and its expression and function are altered in patients with idiopathic detrusor overactivity (DO). TREK-1 expression in the peripheral organs and in the nervous system also declines during aging. This study aimed to investigate the role of TREK-1-related mechanosensitivity in the detrusor in aging mice. METHODS: Bladder histology, detrusor contractility, and voiding function were investigated in adult (3, 6, 9 and 12 months old) TREK-1 KO mice of both sexes and age-matched wildtype controls. Bladder weight, detrusor smooth muscle (DSM) thickness, and collagen content were compared between the groups using paraffin-embedded bladder samples. Bladder strip assay was used to evaluate detrusor muscle contractility and nerve-induced bladder contractions. Voiding spot assay (VSA) and awake cystometry recordings were performed to assess micturition patterns in vivo. RESULTS: Increased bladder weight and bladder wall thickness were observed in TREK-1 KO mice of both sexes, starting as early as at 6-month-old. and threshold volume in cystometry recordings. In comparison to age- and sex-matched controls, bladder strips isolated from TREK-1 KO mice showed significantly decreased DSM contractility including contractile responses to electric field stimulation and cholinergic receptor activation. Interestingly, while the peak forces of evoked DSM contractions decreased with aging in control mice, TREK-1 KO animals at 6-12 month-old displayed DSM contractility that was lower than in 12-month-old control animals. Increased numbers of non-voiding contractions were observed in both sexes of TREK-1 KO mice, whereas the bladder capacity, intermicturition interval, and micturition threshold volume were significantly increased in comparison to age-matched controls. CONCLUSIONS: In summary, the lack of TREK-1 expression in adult mice significantly increased a number of functional changes typically observed in underactive bladders with detrusor overactivity, including increases in bladder size, weight, capacity, and a significant decrease in DSM contractility. Our findings suggest that decreased TREK-1 expression may mimic the development of age-related voiding phenotypes in mice. Source of Funding: DK095817 (Malykhina), DK116648 (Malykhina) and Department of Surgery Academic Enrichment Fund (Xie) © 2023 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 209Issue Supplement 4April 2023Page: e23 Advertisement Copyright & Permissions© 2023 by American Urological Association Education and Research, Inc.MetricsAuthor Information Alison Xiaoqiao Xie More articles by this author Nao Iguchi More articles by this author Anna Malykhina More articles by this author Expand All Advertisement PDF downloadLoading ...

Cholinergic dysfunction-induced insufficient activation of alpha7 nicotinic acetylcholine receptor drives the development of rheumatoid arthritis through promoting protein citrullination via the SP3/PAD4 pathway.

Both cholinergic dysfunction and protein citrullination are the hallmarks of rheumatoid arthritis (RA), but the relationship between the two phenomena remains unclear. We explored whether and how cholinergic dysfunction accelerates protein citrullination and consequently drives the development of RA. Cholinergic function and protein citrullination levels in patients with RA and collagen-induced arthritis (CIA) mice were collected. In both neuron-macrophage coculture system and CIA mice, the effect of cholinergic dysfunction on protein citrullination and expression of peptidylarginine deiminases (PADs) was assessed by immunofluorescence. The key transcription factors for PAD4 expression were predicted and validated. Cholinergic dysfunction in the patients with RA and CIA mice negatively correlated with the degree of protein citrullination in synovial tissues. The cholinergic or alpha7 nicotinic acetylcholine receptor (α7nAChR) deactivation and activation resulted in the promotion and reduction of protein citrullination invitro and invivo, respectively. Especially, the activation deficiency of α7nAChR induced the earlier onset and aggravation of CIA. Furthermore, deactivation of α7nAChR increased the expression of PAD4 and specificity protein-3 (SP3) invitro and invivo. Our results suggest that cholinergic dysfunction-induced deficient α7nAChR activation, which induces the expression of SP3 and its downstream molecule PAD4, accelerating protein citrullination and the development of RA.

Prenatal cyanuric acid exposure induced spatial learning impairments associated with alteration of acetylcholine-mediated neural information flow at the hippocampal CA3-CA1 synapses of male rats.

Cyanuric acid (CA) is reported to induce nephrotoxicity but its toxic effect is not fully known. Prenatal CA exposure causes neurodevelopmental deficits and abnormal behavior in spatial learning ability. Dysfunction of the acetyl-cholinergic system in neural information processing is correlated with spatial learning impairment and was found in the previous reports of CA structural analogue melamine. To further investigate the neurotoxic effects and the potential mechanism, the acetylcholine (ACh) level was detected in the rats which were exposed to CA during the whole of gestation. Local field potentials (LFPs) were recorded when rats infused with ACh or cholinergic receptor agonist into hippocampal CA3 or CA1 region were trained in the Y-maze task. We found the expression of ACh in the hippocampus was significantly reduced in dose-dependent manners. Intra-hippocampal infusion of ACh into the CA1 but not the CA3 region could effectively mitigate learning deficits induced by CA exposure. However, activation of cholinergic receptors did not rescue the learning impairments. In the LFP recording, we found that the hippocampal ACh infusions could enhance the values of phase synchronization between CA3 and CA1 regions in theta and alpha oscillations. Meanwhile, the reduction in the coupling directional index and the strength of CA3 driving CA1 in the CA-treated groups was also reversed by the ACh infusions. Our findings are consistent with the hypothesis and provide the first evidence that prenatal CA exposure induced spatial learning defect is attributed to the weakened ACh-mediated neuronal coupling and NIF in the CA3-CA1 pathway.

S-13-4: INHIBITORY IMPACTS OF CHLOROGENIC ACID ON ADRENAL CATECHOLAMINE SECRETION

(Objective) Chlorogenic acid (CGA) is one of the most available phenolic acid compounds in foods, such as coffee and tea. Thus, the present study was aimed to determine the characteristics of CGA on secretion of catecholamines (CA) in the perfused model of the rat adrenal medulla, and also to validify its mechanism of action. (Design and Methods) The adrenal gland was isolated and perfused with Krebs-bicarbonate. CA was measured directly by using the fluorospectrophotometer. (Results) CGA (30∼300 μM), administered into an adrenal vein for 90 min, reduced ACh-induced CA secretion in a dose- and time-dependent manner. CGA also time-dependently depressed the CA secretion induced by McN-A-343 (a selective muscarinic M1 receptor agonist), DMPP (a selective neuronal nicotinic receptor agonist), and angiotensin II. CGA itself failed to influence spontaneous CA secretion. Also, During the perfusion of CGA for 90 min, the CA secretory responses induced by high K+ (56 mM, a direct membrane depolarizer), veratridine (a voltage-dependent Na+ channel activator, cyclopiazonic acid (a cytoplasmic Ca2+-ATPase inhibitor, Bay-K-8644 (an L-type dihydropyridine Ca2+ channel activator were suppressed. However, in the simultaneous presence of CGA and L-NAME (an inhibitor of NO synthase), the CA secretory responses induced by ACh, Ang II, Bay-K-8644 and veratridine was restored nearly to the control level compared to those of the inhibitory effects of CGA-treatment alone. Virtually, the adrenal NO release was significantly enhanced by CGA-treatment. Also, in the coexistence of CGA and olmesartan, ACh-induced CA secretion was markedly reduced compared to that of olmesartan-treatment alone. (Conclusion) Taken together, we present the first evidence that CGA suppresses the CA secretion induced by activation of cholinergic receptors as well as AT1-receptors. This CGA-induced inhibitory effect seems to be exerted by reducing both the influx of Na+ and Ca2+ through their ionic channels into the adrenomedullary chromaffin cells as well as by suppressing the Ca2+ release from the cytoplasmic calcium store, at least through the elevated NO release by the activation of NO synthase, which is associated to the blockade of neuronal cholinergic receptors and AT1-receptors. Based on these results, the ingestion of CGA may be helpful to alleviate or prevent the cardiovascular diseases, via reduction of adrenal CA secretion and consequent decreased CA level in the circulation. Co-administration of CGA and Olmesartan (ARB) may be clinically beneficial for treatment of cardiovascular diseases, including hypertension and angina pectoris.

PS-BPB04-3: ENHANCEMENT EFFECTS OF GINSENOSIDE-RG2 ON SOME ANTIHYPERTENSIVE AGENTS-INDUCED SUPPRESSION OF ADRENAL CATECHOLAMINE RELEASE

Objective: The present study was aimed to investigate the effects of ginsenoside-Rg2 (Rg2), one of panaxadiol-type saponins, which is isolated from Korean Red ginseng, in some antihypertensive agents-induced reduction on the release of catecholamines (CA) from the perfused model of the rat adrenal medullae. Design and Methods: The adrenal gland was isolated and perfused with Krebs-bicarbonate. The CA amoiunt in the perfusate was measured directly by using the fluorospectrophotometer. Results: Ginsenoside-Rg2 (3∼30 μM) during perfusion into an adrenal vein for 90 min significantly inhibited the CA secretion evoked by acetylcholine (ACh) in a dose- and time-dependent fashion. Also, olmesartan (AT1 receptor blocker, 15 μM), simvastatin (an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase, 60 μM), enalapril (an inhibitor of angiotensin converting enzyme, 150 μM), and cilnidipine (a voltage-dependent L-type Ca2+ channel blocker, 3 μM) significantly reduced the CA secretion evoked by ACh and angiotensin II (Ang II), respectively. In the simultaneous presence of ginsenoside-Rg2 (10 μM) along with four antihypertensive agents (olmesartan, enalapril, simvastatin or cilnidipine), the CA secretion evoked by ACh and Ang II was more strongly inhibited compared with that of each antihypertensive agent-treatment alone. Conclusion: Collectively, these results demonstrate that ginsenoside-Rg2 as well as antihypertensive agents can inhibit the CA secretion evoked by activation of both cholinergic and AT1 receptors from the perfused rat adrenal medulla. When this ginsenoside-Rg2 was used in combination with different antihypertensive agents, their effects of antihypertensive agents on reduction of adrenal CA secretion were significantly enhanced, which may also be clinically beneficial for the treatment of cardiovascular diseases.

The interaction between hippocampal cholinergic and nitrergic neurotransmission coordinates NMDA-dependent behavior and autonomic changes induced by contextual fear retrieval.

Re-exposing an animal to an environment previously paired with an aversive stimulus evokes large alterations in behavioral and cardiovascular parameters. Dorsal hippocampus (dHC) receives important cholinergic inputs from the basal forebrain, and respective acetylcholine (ACh) levels are described to influence defensive behavior. Activation of muscarinic M1 and M3 receptors facilitates autonomic and behavioral responses along threats. Evidence show activation of cholinergic receptors promoting formation of nitric oxide (NO) and cyclic guanosine monophosphate (cGMP) in dHC. Altogether, the action of ACh and NO on conditioned responses appears to converge within dHC. As answer about how ACh and NO interact to modulate defensive responses has so far been barely addressed, we aimed to shed additional light on this topic. Male Wistar rats had guide cannula implanted into the dHC before being submitted to the contextual fear conditioning (3footshocks/085mA/2s). A catheter was implanted in the femoral artery the next day for cardiovascular recordings. Drugs were delivered into dHC 10min before contextual re-exposure, which occurred 48h after the conditioning procedure. Neostigmine (Neo) amplified the retrieval of conditioned responses. Neo effects (1nmol) were prevented by the prior infusion of a M1-M3 antagonist (fumarate), a neuronal nitric oxide synthase inhibitor (NPLA), a NO scavenger (cPTIO), a guanylyl cyclase inhibitor (ODQ), and a NMDA antagonist (AP-7). Pretreatment with a selective M1 antagonist (pirenzepine) only prevented the increase in autonomic responses induced by Neo. The results show that modulation in the retrieval of contextual fear responses involves coordination of the dHC M1-M3/NO/cGMP/NMDA pathway.

Dopamine plays a critical role in the olfactory adaptive learning pathway in Caenorhabditis elegans.

Encoding and consolidating information through learning and memory is vital in adaptation and survival. Dopamine (DA) is a critical neurotransmitter that modulates behavior. However, the role of DA in learning and memory processes is not well defined. Herein, we used the olfactory adaptive learning paradigm in Caenorhabditis elegans to elucidate the role of DA in the memory pathway. Cat-2 mutant worms with low DA synthesis showed a significant reduction in chemotaxis index (CI) compared to the wild type (WT) after short-term conditioning. In dat-1::ICE worms, having degeneration of DA neurons, there was a significant reduction in adaptive learning and memory. When the worms were trained in the presence of exogenous DA (10 mM) instead of food, a substantial increase in CI value was observed. Furthermore, our results suggest that both dop-1 and dop-3 DA receptors are involved in memory retention. The release of DA during conditioning is essential to initiate the learning pathway. We also noted an enhanced cholinergic receptor activity in the absence of dopaminergic neurons. The strains expressing GCaMP6 in DA neurons (pdat-1::GCaMP-6::mCherry) showed a rise in intracellular calcium influx in the presence of the conditional stimulus after training, suggesting DA neurons are activated during memory recall. These results reveal the critical role of DA in adaptive learning and memory, indicating that DA neurons play a crucial role in the effective processing of cognitive function.

Effects of Sublethal Organophosphate Toxicity and Anti-cholinergics on Electroencephalogram and Respiratory Mechanics in Mice

Organophosphates are used in agriculture as insecticides but are potentially toxic to humans when exposed at high concentrations. The mechanism of toxicity is through antagonism of acetylcholinesterase, which secondarily causes excess activation of cholinergic receptors leading to seizures, tremors, respiratory depression, and other physiological consequences. Here we investigated two of the major pathophysiological effects, seizures and respiratory depression, using subcutaneous injection into mice of the organophosphate diisopropylfluorophosphate (DFP) at sublethal concentrations (2.1 mg/Kg) alone and co-injected with current therapeutics atropine (50 mg/Kg) or acetylcholinesterase reactivator HI6 (3 mg/Kg). We also tested a non-specific cholinergic antagonist dequalinium chloride (2 mg/Kg) as a novel treatment for organophosphate toxicity. Electroencephalogram (EEG) recordings revealed that DFP causes focal delta frequency (average 1.4 Hz) tonic spikes in the parietal region that occur transiently (lasting an average of 171 ± 33 min) and a more sustained generalized theta frequency depression in both parietal and frontal electrode that did not recover the following 24 h. DFP also caused behavioral tremors that partially recovered the following 24 h. Using whole body plethysmography, DFP revealed acute respiratory depression, including reduced breathing rates and tidal volumes, that partially recover the following day. Among therapeutic treatments, dequalinium chloride had the most potent effect on all physiological parameters by reducing acute EEG abnormalities and promoting a full recovery after 24 h from tremors and respiratory depression. Atropine and HI6 had distinct effects on EEGs. Co-treatment with atropine converted the acute 1.4 Hz tonic spikes to 3 Hz tonic spikes in the parietal electrode and promoted a partial recovery after 24 h from theta frequency and respiratory depression. HI6 fully removed the parietal delta spike increase and promoted a full recovery in theta frequency and respiratory depression. In summary, while all anticholinergic treatments promoted survival and moderated symptoms of DFP toxicity, the non-selective anti-cholinergic dequalinium chloride had the most potent therapeutic effects in reducing EEG abnormalities, moderating tremors and reducing respiratory depression.

Muscarinic (M1 ) cholinergic receptor activation within the dorsal hippocampus promotes destabilization of strongly encoded object location memories.

Following the initial consolidation process, memories can become reactivated by exposure to a reminder of the original learning event. This can lead to the memory becoming destabilized and vulnerable to disruption or other forms of modification. The memory must then undergo the protein-synthesis dependent process of reconsolidation in order to be retained. However, older and/or stronger memories resist destabilization, but can become labile when reactivated in the presence of salient novelty. We have implicated the neurotransmitter acetylcholine, acting at M1 muscarinic cholinergic receptors (mAChRs) within perirhinal cortex (PRh), in novelty-induced destabilization of remote object memories. It remains unclear, however, whether mAChRs are involved in destabilization of other forms of memory. We hypothesized that the role of M1 mAChRs previously demonstrated for PRh-dependent object memory would extend to hippocampus-dependent spatial memory. Using the object location (OL) task, which relies on the dorsal hippocampus (dHPC), we showed that (a) reactivation-dependent reconsolidation of OL memories requires protein synthesis within the dHPC; (b) destabilization of relatively weak OL memories depends on M1 mAChR activation within the dHPC; (c) salient novelty during reactivation promotes destabilization of resistant strongly encoded OL memories; (d) novelty-induced destabilization of strong OL memories requires activation of mAChRs within the dHPC; and (e) M1 mAChR activation within the dHPC in the absence of novelty during memory reactivation mimics the effect of novelty, destabilizing strongly encoded OL memories. These results implicate ACh acting at M1 mAChRs in the destabilization of dHPC-dependent spatial memories, demonstrating generalizability of this cholinergic function beyond memory for object identity. These findings therefore enhance our understanding of the dynamics of long-term memory storage and suggest implications for the treatment of human conditions such as Alzheimer's disease and aging, which are characterized by behavioral and mnemonic inflexibility.

Effects of the Partial M1 Muscarinic Cholinergic Receptor Agonist CDD-0102A on Stereotyped Motor Behaviors and Reversal Learning in the BTBR Mouse Model of Autism.

BackgroundAutism spectrum disorders (ASD) are a set of neurodevelopmental disorders marked by a lack of social interaction, restrictive interests, and repetitive behaviors. There is a paucity of pharmacological treatments to reduce core ASD symptoms. Various lines of evidence indicate that reduced brain muscarinic cholinergic receptor activity may contribute to an ASD phenotype.MethodsThe present experiments examined whether the partial M1 muscarinic receptor agonist, 5-(3-ethyl-1,2,4-oxadiazol-5-yl)-1,4,5,6-tetrahydropyrimidine hydrochloride (CDD-0102A), alleviates behavioral flexibility deficits and/or stereotyped motor behaviors in the BTBR mouse model of autism. Behavioral flexibility was tested using a reversal learning test. Stereotyped motor behaviors were measured by eliciting digging behavior after removal of nesting material in a home cage and by measuring repetitive grooming.ResultsCDD-0102A (0.2 and 0.6 mg/kg but not 1.2 mg/kg) injected prior to reversal learning attenuated a deficit in BTBR mice but did not affect performance in B6 mice. Acute CDD-0102A treatment (1.2 and 3 mg/kg) reduced self-grooming in BTBR mice and reduced digging behavior in B6 and BTBR mice. The M1 muscarinic receptor antagonist VU0255035 (3 mg/kg) blocked the effect of CDD-0102A on grooming behavior. Chronic treatment with CDD-0102A (1.2 mg/kg) attenuated self-grooming and digging behavior in BTBR mice. Direct CDD-0102A infusions (1 µg) into the dorsal striatum reduced elevated digging behavior in BTBR mice. In contrast, CDD-0102A injections in the frontal cortex were not effective.ConclusionsThe results suggest that treatment with a partial M1 muscarinic receptor agonist may reduce repetitive behaviors and restricted interests in autism in part by stimulating striatal M1 muscarinic receptors.

The Cholinergic Lateral Line Efferent Synapse: Structural, Functional and Molecular Similarities With Those of the Cochlea.

Vertebrate hair cell (HC) systems are innervated by efferent fibers that modulate their response to external stimuli. In mammals, the best studied efferent-HC synapse, the cholinergic medial olivocochlear (MOC) efferent system, makes direct synaptic contacts with HCs. The net effect of MOC activity is to hyperpolarize HCs through the activation of α9α10 nicotinic cholinergic receptors (nAChRs) and the subsequent activation of Ca2+-dependent SK2 potassium channels. A serious obstacle in research on many mammalian sensory systems in their native context is that their constituent neurons are difficult to access even in newborn animals, hampering circuit observation, mapping, or controlled manipulation. By contrast, fishes and amphibians have a superficial and accessible mechanosensory system, the lateral line (LL), which circumvents many of these problems. LL responsiveness is modulated by efferent neurons which aid to distinguish between external and self-generated stimuli. One component of the LL efferent system is cholinergic and its activation inhibits LL afferent activity, similar to what has been described for MOC efferents. The zebrafish (Danio rerio) has emerged as a powerful model system for studying human hearing and balance disorders, since LL HC are structurally and functionally analogous to cochlear HCs, but are optically and pharmacologically accessible within an intact specimen. Complementing mammalian studies, zebrafish have been used to gain significant insights into many facets of HC biology, including mechanotransduction and synaptic physiology as well as mechanisms of both hereditary and acquired HC dysfunction. With the rise of the zebrafish LL as a model in which to study auditory system function and disease, there has been an increased interest in studying its efferent system and evaluate the similarity between mammalian and piscine efferent synapses. Advances derived from studies in zebrafish include understanding the effect of the LL efferent system on HC and afferent activity, and revealing that an α9-containing nAChR, functionally coupled to SK channels, operates at the LL efferent synapse. In this review, we discuss the tools and findings of these recent investigations into zebrafish efferent-HC synapse, their commonalities with the mammalian counterpart and discuss several emerging areas for future studies.

Metaplastic Reinforcement of Long-Term Potentiation in Hippocampal Area CA2 by Cholinergic Receptor Activation.

Hippocampal CA2, an inconspicuously positioned area between the well-studied CA1 and CA3 subfields, has captured research interest in recent years because of its role in social memory formation. However, the role of cholinergic inputs to the CA2 area for the regulation of synaptic plasticity remains to be fully understood. We show that cholinergic receptor activation with the nonselective cholinergic agonist, carbachol (CCh), triggers a protein synthesis-dependent and NMDAR-independent long-term synaptic depression (CCh-LTD) at entorhinal cortical (EC)-CA2 and Schaffer collateral (SC)-CA2 synapses in the hippocampus of adult male Wistar rats. The activation of muscarinic acetylcholine receptors (mAChRs) is critical for the induction of CCh-LTD with the results suggesting an involvement of M3 and M1 mAChRs in the early facilitation of CCh-LTD, while nicotinic AChR activation plays a role in the late maintenance of CCh-LTD at CA2 synapses. Remarkably, we find that CCh priming lowers the threshold for the subsequent induction of persistent long-term potentiation (LTP) of synaptic transmission at EC-CA2 and the plasticity-resistant SC-CA2 pathways. The effects of such a cholinergic-dependent synaptic depression on subsequent LTP at EC-CA2 and SC-CA2 synapses have not been previously explored. Collectively, the results demonstrate that CA2 synaptic learning rules are regulated in a metaplastic manner, whereby modifications triggered by prior cholinergic stimulation can dictate the outcome of future plasticity events. Moreover, the reinforcement of LTP at EC inputs to CA2 following the priming stimulus coexists with concurrent sustained CCh-LTD at the SC-CA2 pathway and is dynamically scaled by modulation of SC-CA2 synaptic transmission.SIGNIFICANCE STATEMENT The release of the neuromodulator acetylcholine is critically involved in processes of hippocampus-dependent memory formation. Cholinergic afferents originating in the medial septum and diagonal bands of Broca terminating in the hippocampal area CA2 might play an important role in the modulation of area-specific synaptic plasticity. Our findings demonstrate that cholinergic receptor activation induces an LTD of synaptic transmission at entorhinal cortical- and Schaffer collateral-CA2 synapses. This cholinergic activation-mediated LTD displays a bidirectional metaplastic switch to LTP on a future timescale. This suggests that such bidirectional synaptic modifications triggered by the dynamic modulation of tonic cholinergic receptor activation may support the formation of CA2-dependent memories given the increased hippocampal cholinergic tone during active wakefulness observed in exploratory behavior.

A calcium fluorescence assay for quantification of cholinergic receptor activity of clinical drugs in serum - comparison with radioactive methods

A new approach is described for quantifying cholinergic receptor activation status human blood samples, based on M1 receptor-driven mobilization of intracellular calcium stores. The assay identifies anticholinergic as well as agonist cholinergic receptor activity. As a cell-based procedure, the assay shares the high efficiency of recently developed M1 receptor binding protocols, but differs from the latter in relying on fluorescence rather than radioactivity measurements. The assay targets a true functional effect insofar as it reflects a time-dependent process of net changes in activation of cholinergic receptors. Results from experiments with M1-expressing CHO cells exposed to a fluorogenic dye and the standard cholinergic agonist carbachol revealed the assay's ability to isolate pure agonist effects of clinical compounds as well as the net effects of serum containing agonist and antagonist factors. The new protocol thus provides two additional quantitative indices of cholinergic receptor activity in human serum, namely pure agonistic effects and net agonist/antagonist effects. As such, it could constitute a very useful addition to efforts to quantify global cholinergic status in human serum in various clinical conditions. By relying on fluorescence measures it should also prove much more accessible than radioactivity-based protocols.