Increase In Acetylcholine Release Research Articles

Novel Pitolisant-Derived Sulfonyl Compounds for Alzheimer Disease.

Alzheimer's disease (AD) is a complex and multifactorial neurodegenerative disorder characterized by cognitive decline, memory loss, behavioral changes, and other neurological symptoms. Considering the urgent need for new AD therapeutics, in the present study we designed, synthesized, and evaluated multitarget compounds structurally inspired by sulfonylureas and pitolisant with the aim of obtaining multitarget ligands for AD treatment. Due to the diversity of chemical scaffolds, a novel strategy has been adopted by merging into one structure moieties displaying H3R antagonism and acetylcholinesterase inhibition. Eight compounds, selected by their binding activity on H3R, showed a moderate ability to inhibit acetylcholinesterase activity in vitro, and two of the compounds (derivatives 2 and 7) were also capable of increasing acetylcholine release in vitro. Among the tested compounds, derivative 2 was identified and selected for further in vivo studies. Compound 2 was able to reverse scopolamine-induced cognitive deficits with results comparable to those of galantamine, a drug used in clinics for treating AD. In addition to its efficacy, this compound showed moderate BBB permeation in vitro. Altogether, these results point out that the fragment-like character of compound 2 leads to an optimal starting point for a plausible medicinal chemistry approach for this novel strategy.

D-Serine Increases Release of Acetylcholine in Rat Submandibular Glands.

d-serine has been observed in submandibular gland tissue in rats, but its functions remain to be clarified. Oral administration of d-serine, but not l-serine, increased its concentrations in the submandibular gland and pilocarpine-induced salivary secretion. In vivo microdialysis was used to collect the d- and l-enantiomers of amino acids from local interstitial fluid in the rat submandibular gland. The proportion of the d-form of serine in interstitial fluid was higher than that in plasma or saliva. Perfusion of the rat submandibular gland with d-serine and l-glutamic acid via the submandibular gland artery resulted in a significant increase in salivary secretion after stimulation of muscarinic receptors with carbachol. In vivo microdialysis applied to the submandibular glands of rats showed that infusion of d-serine along with l-glutamate through the microdialysis probe significantly elevated acetylcholine levels in local interstitial fluids in the submandibular glands of anesthetized rats as compared to that with l-glutamate alone in an N-methyl-d-aspartate receptor glycine site antagonist-sensitive manner. These results indicate that d-serine augments salivary secretion by increasing acetylcholine release in the salivary glands.

PD19-11 DIABETES CAUSES TEMPORAL CHANGES IN CHOLINERGIC-MEDIATED BLADDER CONTRACTILITY DUE TO INFLAMMATION VIA THE NLRP3 INFLAMMASOME IN FEMALE AKITA MICE

You have accessJournal of UrologyCME1 Apr 2023PD19-11 DIABETES CAUSES TEMPORAL CHANGES IN CHOLINERGIC-MEDIATED BLADDER CONTRACTILITY DUE TO INFLAMMATION VIA THE NLRP3 INFLAMMASOME IN FEMALE AKITA MICE Michael Odom, Francis Hughes, Huixia Jin, and J. Todd Purves Michael OdomMichael Odom More articles by this author , Francis HughesFrancis Hughes More articles by this author , Huixia JinHuixia Jin More articles by this author , and J. Todd PurvesJ. Todd Purves More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000003285.11AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: The most common complication of diabetes is bladder dysfunction which is driven in the female Akita type 1 diabetic mouse by inflammation mediated by the NLRP3 inflammasome. It is unclear how diabetes affects signaling pathways responsible for bladder contractility and if this is mediated by NLRP3. Using a female Akita model that develops a temporal progression from bladder overactivity to underactivity, we investigated effects on the cholinergic signaling pathways. To accomplish this we utilized ex vivo myography to determine how neurotransmitter release from efferent nerve terminals and muscarinic receptor activation is impacted in bladders of non-diabetic and diabetic mice±the NLRP3 gene. METHODS: Akita mice were crossbred with NLRP3-/- mice to yield non-diabetics and diabetics±NLRP3 gene. Females were aged to 15 and 30 weeks when respective overactive and underactive bladder phenotypes are evident. For ex vivo myography, bladder strips with intact mucosa were used. Efferent neurotransmitter-mediated contractions were assessed using electric field stimulation (EFS)±the muscarinic receptor antagonist atropine. Contractility to carbachol, a muscarinic receptor agonist, was also assessed (n=5-10 per group). RESULTS: At 15 weeks, diabetic NLRP3+/+ mice have increased EFS contractility (p<0.05) but NLRP3 gene deletion prevented this pathology in diabetics. At 30 weeks, EFS contractions were no longer dysregulated. EFS was repeated in the presence of atropine to determine the cholinergic contribution. In the presence of atropine, no significant differences were noted in diabetic animals – indicating the increase in contractility at 15 weeks was due to upregulated cholinergic mechanisms. No changes in contractions to carbachol were noted at either time point. This indicates the increased contractility to EFS was not due to increased muscarinic receptor activity but rather an increase in acetylcholine release. CONCLUSIONS: Diabetes increases cholinergic neurotransmitter release and bladder contractility in mice with an overactive bladder as a consequence of inflammation driven by NLRP3. This suggests an NLRP3 inhibitor may be an effective therapy to prevent overactive bladder and eliminate the need for conventional anti-cholinergic treatments. Source of Funding: NIH-K12 DK100024; NIH-RO1 DK117890 © 2023 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 209Issue Supplement 4April 2023Page: e581 Advertisement Copyright & Permissions© 2023 by American Urological Association Education and Research, Inc.MetricsAuthor Information Michael Odom More articles by this author Francis Hughes More articles by this author Huixia Jin More articles by this author J. Todd Purves More articles by this author Expand All Advertisement PDF downloadLoading ...

Moving Beyond Amyloid in Alzheimer's Therapeutics

Moving Beyond Amyloid in Alzheimer's Therapeutics

Activation of medial septum cholinergic neurons restores cognitive function in temporal lobe epilepsy.

Cognitive impairment is the most common complication in patients with temporal lobe epilepsy with hippocampal sclerosis. There is no effective treatment for cognitive impairment. Medial septum cholinergic neurons have been reported to be a potential target for controlling epileptic seizures in temporal lobe epilepsy. However, their role in the cognitive impairment of temporal lobe epilepsy remains unclear. In this study, we found that patients with temporal lobe epilepsy with hippocampal sclerosis had a low memory quotient and severe impairment in verbal memory, but had no impairment in nonverbal memory. The cognitive impairment was slightly correlated with reduced medial septum volume and medial septum-hippocampus tracts measured by diffusion tensor imaging. In a mouse model of chronic temporal lobe epilepsy induced by kainic acid, the number of medial septum cholinergic neurons was reduced and acetylcholine release was reduced in the hippocampus. Furthermore, selective apoptosis of medial septum cholinergic neurons mimicked the cognitive deficits in epileptic mice, and activation of medial septum cholinergic neurons enhanced hippocampal acetylcholine release and restored cognitive function in both kainic acid- and kindling-induced epilepsy models. These results suggest that activation of medial septum cholinergic neurons reduces cognitive deficits in temporal lobe epilepsy by increasing acetylcholine release via projections to the hippocampus.

Angiotensin-Converting Enzyme Inhibitor and Angiotensin Receptor Blocker Use and ICU Delirium Incidence

Background: Delirium is a form of acute brain dysfunction which is associated with longer hospital stays, cognitive decline, and increased risk of mortality. Angiotensin converting enzyme inhibitors (ACEI) and angiotensin receptor blockers (ARB) have been proposed to have neuroprotective effects. ACE inhibitors and ARBs both block the action of angiotensin II leading to an increase in release of acetylcholine. As acetylcholinergic failure is implicated in delirium pathophysiology, ACE inhibitors or ARBs may improve cognitive function and protect against ICU delirium.&#x0D; Objective: To study the relationship between the prescription of ACEIs or ARBs on delirium occurrence in ICU patients.Design: Observational studySetting: ICUs in three large academic hospitals in IndianapolisPatients: 4791 patients admitted to the ICU for more than 24 hours&#x0D; Methods and Main Results: The Richmond Agitation Sedation Scale (RASS) and the Confusion Assessment Method for the ICU (CAM-ICU) were used to evaluate patients for the presence of delirium while in the ICU. ACEI/ARB exposure was determined if the patient had prescription for these medications 6 months prior to ICU admission. The cohort of 4791 participants had a mean age of 60.7 years (SD: 16.1), 46% were female, and 39% were African American. The most common comorbidities were hypertension (68%), hyperlipidemia (49%), and depression (43%). Delirium incidence in this cohort was 13%. Prescription of an ACEI alone (OR: 0.91, 95% CI: 0.73, 1.15, p=0.425) or ARB alone (OR: 0.64, 95% CI: 0.38, 1.07, p=0.114) were not significantly associated with decreased odds of delirium.&#x0D; Conclusion: Prescription of an ACEI or ARB 6 months prior to ICU admission was not associated with reduced incidence of ICU delirium, although further research is needed. Larger studies with medication adherence data are needed to further study the relationship among ACEI/ARBs and delirium.

Hydromethylthionine enhancement of central cholinergic signalling is blocked by rivastigmine and memantine.

The prevention of tau protein aggregations is a therapeutic goal for the treatment of Alzheimer's disease (AD), and hydromethylthionine (HMT) (also known as leucomethylthioninium-mesylate [LMTM]), is a potent inhibitor of tau aggregation in vitro and in vivo. In two Phase 3clinical trials in AD, HMT had greater pharmacological activity on clinical endpoints in patients not receiving approved symptomatic treatments for AD (acetylcholinesterase (AChE) inhibitors and/or memantine) despite different mechanisms of action. To investigate this drug interaction in an animal model, we used tau-transgenic L1 and wild-type NMRI mice treated with rivastigmine or memantine prior to adding HMT, and measured changes in hippocampal acetylcholine (ACh) by microdialysis. HMT given alone doubled hippocampal ACh levels in both mouse lines and increased stimulated ACh release induced by exploration of the open field or by infusion of scopolamine. Rivastigmine increased ACh release in both mouse lines, whereas memantine was more active in tau-transgenic L1mice. Importantly, our study revealed a negative interaction between HMT and symptomatic AD drugs: the HMT effect was completely eliminated in mice that had been pre-treated with either rivastigmine or memantine. Rivastigmine was found to inhibit AChE, whereas HMT and memantine had no effects on AChE or on choline acetyltransferase (ChAT). The interactions observed in this study demonstrate that HMT enhances cholinergic activity in mouse brain by a mechanism of action unrelated to AChE inhibition. Our findings establish that the drug interaction that was first observed clinically has a neuropharmacological basis and is not restricted to animals with tau aggregation pathology. Given the importance of the cholinergic system for memory function, the potential for commonly used AD drugs to interfere with the treatment effects of disease-modifying drugs needs to be taken into account in the design of clinical trials.

Effects of fastigial nucleus electrostimulation on cardiac nerve regeneration, neurotransmitter release, and malignant arrhythmia inducibility in a post-infarction rat model.

The reduced density of cardiac autonomic nerves plays an important role in malignant arrhythmia after myocardial infarction (MI). Previous studies have shown that there is an interaction between the brain and the heart, and fastigial nucleus electrostimulation (FNS) promotes central nerve regeneration. Whether and how it can promote cardiac nerve regeneration after MI and the underlying mechanisms remain unknown. This study investigated whether FNS promotes cardiac nerve regeneration and reduces malignant arrhythmia inducibility in a post-infarction rat model. Ninety-eight Wistar rats were randomly assigned to Sham control, MI (left anterior descending coronary artery ligation without FNS), FNS (MI plus FNS), and FNL (fastigial nucleus lesion plus FNS plus MI) groups. The frequency of malignant arrhythmia was significantly lower in the FNS group than in the MI and FNL groups. The density of cardiac autonomic nerves was less in the MI group than in the Sham group, which was promoted by FNS. The nerve growth factor (NGF) mRNA expression was downregulated in the MI group compared to the Sham group, which was significantly enhanced by FNS. The expression levels of norepinephrine (NE) and acetylcholine (ACh) were higher and lower respectively in the MI and FNL groups than in the Sham group. After FNS, NE concentration was reduced and Ach level was elevated compared to the MI group. These data suggested that FNS promoted the regeneration of cardiac autonomic nerves and reduced the incidence of malignant arrhythmias in MI rat model. The mechanisms might involve up-regulation of NGF mRNA expression, decrease of NE release and increase of ACh release.

Homeostatic plasticity induced by increased acetylcholine release at the mouse neuromuscular junction

At the neuromuscular junction (NMJ), changes to the size of the postsynaptic potential induce homeostatic compensation. At the Drosophila NMJ, increased glutamate release causes a compensatory decrease in quantal content, but it is unknown if this mechanism operates at the cholinergic mammalian NMJ. We addressed this question by recording endplate potentials (EPP) and muscle contraction in 3-month and 24-month ChAT-ChR2-EYFP mice that overexpress vesicular acetylcholine transporter and release more acetylcholine per vesicle. At 3 months, the quantal content of EPPs from ChAT-ChR2-EYFP mice were not different from WT controls, however tetanic depression was greater, and quantal size during high-frequency stimulation and the size of the readily releasable pool (RRP) were decreased. At 24 months of age, quantal content was reduced in ChAT-ChR2-EYFP mice, which normalized synaptic depression despite smaller RRP. The effect of pancuronium on indirect evoked muscle twitch was not different between groups. These results indicate that an increase in the amount of acetylcholine per vesicle induces two distinct age-dependent homeostatic mechanisms compensating excessive acetylcholine release.

Predicting complex spikes in striatal projection neurons of the direct pathway following neuromodulation by acetylcholine and dopamine.

The input structure of the basal ganglia, striatum, receives dense neuromodulatory input in the form of dopamine and acetylcholine. The two systems are tightly connected, for example, synchronized activity of cholinergic interneurons, leading to increased acetylcholine release, has been shown to directly trigger dopamine release from dopaminergic terminals in striatum. Both signals are further needed for induction of locomotion. High dopamine concentration leads to increased excitability of the direct pathway striatal projection neurons. High cholinergic tone inhibits various potassium channels further increasing the excitability of striatal projection neurons. Here, we investigate the combined effect of concurrent high acetylcholine and dopamine using biophysically detailed models based on rodent data. The aim of the study is to investigate how neuromodulation affects dendritic integration. The result shows that neuromodulation paired with synaptic activation of dendrites can give rise to complex spiking patterns, resembling spike shapes seen in the hippocampus. In the hippocampus, these complex spikes are associated with behavioral time scale plasticity and place cell tuning. We further investigate the mechanisms behind the complex spikes and find that there are two components, one axo-somatic and one dendritic in origin.

Dexmedetomidine-Mediated Prevention of Renal Ischemia-Reperfusion Injury Depends in Part on Cholinergic Anti-Inflammatory Mechanisms.

Organ ischemia-reperfusion injury often induces local and systemic inflammatory responses, which in turn worsen organ injury. These inflammatory responses can be regulated by the central nervous system, particularly by the vagal nerve and nicotinic acetylcholine receptors, which are the key components of cholinergic anti-inflammatory pathway. Activation of the cholinergic anti-inflammatory pathway can suppress excessive inflammatory responses and be a potential strategy for prevention of ischemia-reperfusion injury of organs including the kidney. Vagal nerve activity, plasma acetylcholine, catecholamine and inflammatory mediators, renal tissue injury, and cell death were measured in mice with bilateral renal ischemia/reperfusion with or without treatment with dexmedetomidine (Dex), an α2-adrenergic receptor agonist. Dex significantly increased the discharge frequency of the cervical vagal nerve by up to 142 Hz (mean) (P < .001), and preserved kidney gross morphology and structure and attenuated cell apoptosis after ischemia-reperfusion. Furthermore, Dex also significantly increased acetylcholine release to 135.8 pmol/L (median) when compared to that (84.7 pmol/L) in the sham group (P < .001) and reduced the levels of several inflammatory mediators induced by renal ischemia/reperfusion. All the effects were abolished by vagotomy, splenectomy, or combinative administration of atipamezole, an α2-adrenergic receptor antagonist. Our findings suggest that Dex provides renoprotection, at least in part, through anti-inflammatory effects of the parasympathetic nervous system activation in addition to its direct actions on α2-adrenergic receptors.

Brain Delivery of Thyrotropin-Releasing Hormone via a Novel Prodrug Approach.

Using thyrotropin-releasing hormone (TRH) as a model, we explored whether synergistic combination of lipoamino acid(s) and a linker cleaved by prolyl oligopeptidase (POP) can be used as a promoiety for prodrug design for the preferential brain delivery of the peptide. A representative prodrug based on this design principle was synthesized, and its membrane affinity and in vitro metabolic stability, with or without the presence of a POP inhibitor, were studied. The in vivo formation of TRH from the prodrug construct was probed by utilizing the antidepressant effect of the peptide, as well as its ability to increase acetylcholine (ACh) synthesis and release. We found that the prototype prodrug showed excellent membrane affinity and greatly increased metabolic stability in mouse blood and brain homogenate compared to the parent peptide, yet a POP inhibitor completely prevented prodrug metabolism in brain homogenate. In vivo, administration of the prodrug triggered antidepressant-like effect, and microdialysis sampling showed greatly increased ACh release that was also antagonized upon a POP inhibitor treatment. Altogether, the obtained promising exploratory data warrant further investigations on the utility of the prodrug approach introduced here for brain-enhanced delivery of small peptides with neurotherapeutic potential.

Basal and Evoked Neurotransmitter Levels in Parkin, DJ-1, PINK1 and LRRK2 Knockout Rat Striatum

Parkinson’s disease (PD) is the most common neurodegenerative movement disorder and is characterized by the loss of neurons in the substantia nigra that project to the striatum and release dopamine (DA), which is required for normal movement. Common non-motor symptoms likely involve abnormalities with other neurotransmitters, such as serotonin, norepinephrine, acetylcholine, glycine, glutamate and gamma-aminobutyric acid (GABA). As part of a broad effort to provide better PD research tools, the Michael J. Fox Foundation for Parkinson’s Research funded the generation and characterization of knockout (KO) rats for genes with PD-linked mutations, including PINK1, Parkin, DJ-1 and LRRK2. Here we extend the phenotypic characterization of these lines of KO rats to include in vivo microdialysis to measure both basal and potassium-induced release of the above neurotransmitters and their metabolites in the striatum of awake and freely moving rats at ages 4, 8 and 12 months compared to wild-type (WT) rats. We found age-dependent abnormalities in basal DA, glutamate and acetylcholine in PINK1 KO rats and age-dependent abnormalities in basal DA metabolites in Parkin and LRRK2 KO rats. Parkin KO rats had increased glycine release while DJ-1 KO rats had decreased glutamate release and increased acetylcholine release compared to WT rats. All lines except DJ-1 KO rats showed age-dependent changes in release of one or more neurotransmitters. Our data suggest these rats may be useful for studies of PD-related synaptic dysfunction and neurotransmitter dynamics as well as studies of the normal and pathogenic functions of these genes with PD-linked mutations.

Scorpion venom increases acetylcholine release by prolonging the duration of somatic nerve action potentials

Scorpionism is frequently accompanied by a massive release of catecholamines and acetylcholine from peripheral nerves caused by neurotoxic peptides present in these venoms, which have high specificity and affinity for ion channels. Tityus bahiensis is the second most medically important scorpion species in Brazil but, despite this, its venom remains scarcely studied, especially with regard to its pharmacology on the peripheral (somatic and autonomic) nervous system. Here, we evaluated the activity of T. bahiensis venom on somatic neurotransmission using myographic (chick and mouse neuromuscular preparations), electrophysiological (MEPP, EPP, resting membrane potentials, perineural waveforms, compound action potentials) and calcium imaging (on DRG neurons and muscle fibres) techniques. Our results show that the major toxic effects of T. bahiensis venom on neuromuscular function are presynaptically driven by the increase in evoked and spontaneous neurotransmitter release. Low venom concentrations prolong the axonal action potential, leading to a longer depolarization of the nerve terminals that enhances neurotransmitter release and facilitates nerve-evoked muscle contraction. The venom also stimulates the spontaneous release of neurotransmitters, probably through partial neuronal depolarization that allows calcium influx. Higher venom concentrations block the generation of action potentials and resulting muscle twitches. These effects of the venom were reversed by low concentrations of TTX, indicating voltage-gated sodium channels as the primary target of the venom toxins. These results suggest that the major neuromuscular toxicity of T. bahiensis venom is probably mediated mainly by α- and β-toxins interacting with presynaptic TTX-sensitive ion channels on both axons and nerve terminals.

Food-Induced Increase of Acetylcholine in Mouse Hypothalamus.

Using microdialysis in C57Bl6 mice, we monitored cholinergic activity in the hypothalamus. Food intake after an overnight fast caused a 3-fold increase of extracellular acetylcholine (ACh) concentrations in the hypothalamus. The effect lasted for about 30 min. Food containing no calories (kaolin pellets), or food that was presented but not accessible, also increased ACh release. In contrast, injections of glucose or β-hydroxybutyrate did not change extracellular ACh. Mice deficient in muscarinic M3 receptors had the same cholinergic response as wild-type mice. We conclude that the increase of ACh in the hypothalamus was not caused by local detection of nutrients but by anticipation of food intake. This suggests the involvement of motivational circuits in the basal forebrain which is reinforced by the fact that we found slight increases of ACh in the nucleus accumbens during feeding.

Nicotinic Receptor Dysfunction Underlies Abnormal Responses to Muscarinic Receptor Antagonist Treatment in DYT1 Dystonia

DYT1 dystonia is an inherited dystonia caused by a mutation in the TOR1A gene, which encodes the torsinA protein. Trihexyphenidyl (THP) a nonselective muscarinic receptor antagonist is the small molecule drug of choice for the treatment of DYT1 dystonia, but it is poorly tolerated due to significant side effects. A better understanding of both the underlying pathology of DYT1 dystonia and the mechanism of action of THP is needed for the development of better treatments. Abnormalities in dopamine (DA) transmission have been implicated in DYT1 and other forms of dystonia. Previous studies have shown that Dyt1 knockin mice have reduced extracellular striatal DA in vivo and reduced striatal DA release ex vivo. Acetylcholine (ACh) is known to play a key role in regulating striatal DA release, and muscarinic receptor antagonists are used to treat dystonia which suggests the hypothesis that ACh signaling mediates the DA release deficiency in DYT1 dystonia. To test this hypothesis, we used ex vivo fast scan cyclic voltammetry (FSCV) and in vivo microdialysis to investigate ACh regulation of striatal DA release in Dyt1 knockin mice. We found that THP increased striatal DA release as assessed by ex vivo FSCV and in vivo microdialysis. However, THP was less effective at enhancing DA release in DYT1 mice relative to WT mice in the ex vivo FSCV experiment (mean increase WT: 65% vs DYT1: 35%). In striatum, blocking mACh autoreceptors on cholinergic interneurons increases ACh release. ACh then activates nicotinic acetylcholine receptors (nAChRs) located on DA terminals to enhance DA release. To determine if abnormal nAChR responses could account for the attenuated response to THP in Dyt1 knockin mice, we performed a dose response experiment with the α4 nAChR subunit selective antagonist dihydro‐β‐erythroidine. We found that Dyt1 mice are more sensitive to nAChR antagonism, which reduces DA release (IC50: WT= 29.46nM, DYT1= 12.26nM). These data suggest that nAChRs mediate the differential effects of THP in Dyt1 mice. These data also suggest that nAChRs may be suitable therapeutic targets for DYT1 dystonia. Future studies will evaluate nAChR positive allosteric modulators for DA‐enhancing effects.Support or Funding InformationSupported by: DoD W81XWH‐15‐1‐0545 and NIH T32‐GM008602This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

The modulation of hippocampal theta rhythm by the vestibular system.

The vestibular system is a sensory system that has evolved over millions of years to detect acceleration of the head, both rotational and translational, in three dimensions. One of its most important functions is to stabilize gaze during unexpected head movement; however, it is also important in the control of posture and autonomic reflexes. Theta rhythm is a 3- to 12-Hz oscillating EEG signal that is intimately linked to self-motion and is also known to be important in learning and memory. Many studies over the last two decades have shown that selective activation of the vestibular system, using either natural rotational or translational stimulation, or electrical stimulation of the peripheral vestibular system, can induce and modulate theta activity. Furthermore, inactivation of the vestibular system has been shown to significantly reduce theta in freely moving animals, which may be linked to its impairment of place cell function as well as spatial learning and memory. The pathways through which vestibular information modulate theta rhythm remain debatable. However, vestibular responses have been found in the pedunculopontine tegmental nucleus (PPTg) and activation of the vestibular system causes an increase in acetylcholine release into the hippocampus, probably from the medial septum. Therefore, a pathway from the vestibular nucleus complex and/or cerebellum to the PPTg, supramammillary nucleus, posterior hypothalamic nucleus, and septum to the hippocampus is likely. The modulation of theta by the vestibular system may have implications for vestibular effects on cognitive function and the contribution of vestibular impairment to the risk of dementia.

The mouse passive-transfer model of MuSK myasthenia gravis: disrupted MuSK signaling causes synapse failure.

While the majority of myasthenia gravis patients express antibodies targeting the acetylcholine receptor, the second most common cohort instead displays autoantibodies against muscle-specific kinase (MuSK). MuSK is a transmembrane tyrosine kinase found in the postsynaptic membrane of the neuromuscular junction. During development, MuSK serves as a signaling hub, coordinating the alignment of the pre- and postsynaptic components of the synapse. Adult mice that received repeated daily injections of IgG from anti-MuSK+ myasthenia gravis patients developed muscle weakness, associated with neuromuscular transmission failure. MuSK autoantibodies are predominantly of the IgG4 type. They suppress the kinase activity of MuSK and the phosphorylation of target proteins in the postsynaptic membrane. Loss of postsynaptic acetylcholine receptors is the primary cause of neuromuscular transmission failure. MuSK autoantibodies also disrupt the capacity of the motor nerve terminal to adaptively increase acetylcholine release in response to the reduced postsynaptic responsiveness to acetylcholine. The passive IgG transfer model of MuSK myasthenia gravis has been used to test candidate treatments. Pyridostigmine, a first-line cholinesterase inhibitor drug, exacerbated the disease process, while 3,4-diaminopyridine and albuterol were found to be beneficial in this mouse model.

Synergy between 5-HT4 receptor stimulation and phosphodiesterase 4 inhibition in facilitating acetylcholine release in human large intestinal circular muscle.

Gastroprokinetic properties of 5-HT4 receptor agonists, such as prucalopride, are attributed to activation of 5-HT4 receptors on cholinergic nerves innervating smooth muscle in the gastrointestinal smooth muscle layer, increasing acetylcholine release and muscle contraction. In porcine stomach and colon, phosphodiesterase (PDE) 4 has been shown to control the signaling pathway of these 5-HT4 receptors. The aim of this study was to investigate the PDE-mediated control of these 5-HT4 receptors in human large intestine. Circular smooth muscle strips were prepared from human large intestine; after incubation with [³H]-choline, electrically induced tritium outflow was determined as a measure for acetylcholine release. The influence of PDE inhibition on the facilitating effect of prucalopride on electrically induced acetylcholine release was studied. The non-selective PDE inhibitor IBMX enhanced the facilitating effect of prucalopride on electrically induced acetylcholine release. The selective inhibitors vinpocetine (PDE1), EHNA (PDE2) and cilostamide (PDE3) did not influence, while rolipram and roflumilast (PDE4) enhanced the prucalopride-induced facilitation to the same extent as IBMX. In human large intestinal circular muscle, the intracellular pathway of 5-HT4 receptors facilitating cholinergic neurotransmission to large intestinal circular smooth muscle is controlled by PDE4. If the synergy between 5-HT4 receptor agonism and PDE4 inhibition is confirmed in a functional assay with electrically induced cholinergic contractions of human large intestinal circular smooth muscle strips, combination of a selective 5-HT4 receptor agonist with a selective PDE4 inhibitor might enhance the in vivo prokinetic effect of the 5-HT4 receptor agonist in the large intestine.

Effects of muscarinic receptor antagonists on cocaine discrimination in wild-type mice and in muscarinic receptor M1, M2, and M4 receptor knockout mice

Muscarinic M1/M4 receptor stimulation can reduce abuse-related effects of cocaine and may represent avenues for treating cocaine addiction. Muscarinic antagonists can mimic and enhance effects of cocaine, including discriminative stimulus (SD) effects, but the receptor subtypes mediating those effects are not known. A better understanding of the complex cocaine/muscarinic interactions is needed to evaluate and develop potential muscarinic-based medications. Here, knockout mice lacking M1, M2, or M4 receptors (M1−/−, M2−/−, M4−/−), as well as control wild-type mice and outbred Swiss-Webster mice, were trained to discriminate 10mg/kg cocaine from saline. Muscarinic receptor antagonists with no subtype selectivity (scopolamine), or preferential affinity at the M1, M2, or M4 subtype (telenzepine, trihexyphenidyl; methoctramine, AQ-RA 741; tropicamide) were tested alone and in combination with cocaine. In intact animals, antagonists with high affinity at M1/M4 receptors partially substituted for cocaine and increased the SD effect of cocaine, while M2-preferring antagonists did not substitute, and reduced the SD effect of cocaine. The cocaine-like effects of scopolamine were absent in M1−/− mice. The cocaine SD attenuating effects of methoctramine were absent in M2−/− mice and almost absent in M1−/− mice. The findings indicate that the cocaine-like SD effects of muscarinic antagonists are primarily mediated through M1 receptors, with a minor contribution of M4 receptors. The data also support our previous findings that stimulation of M1 receptors and M4 receptors can each attenuate the SD effect of cocaine, and show that this can also be achieved by blocking M2 autoreceptors, likely via increased acetylcholine release.