Comparative distribution of binding of the muscarinic receptor ligands pirenzepine, AF-DX 384, (R,R)-I-QNB and (R,S)-I-QNB to human brain

A growing understanding of the role of muscarinic receptors in the molecular pathology and treatment of schizophrenia

Pre-clinical models, postmortem and neuroimaging studies all support a role for muscarinic receptors in the molecular pathology of schizophrenia. From these data it was proposed that activation of the muscarinic M1 and/or M4 receptor would reduce the severity of the symptoms of schizophrenia. This hypothesis is now supported by results from two clinical trials which indicate that activating central muscarinic M1 and M4 receptors can reduce the severity of positive, negative and cognitive symptoms of the disorder. This review will provide an update on a growing body of evidence that argues the muscarinic M1 and M4 receptors have critical roles in CNS functions that are dysregulated by the pathophysiology of schizophrenia. This realization has been made possible, in part, by the growing ability to visualize and quantify muscarinic M1 and M4 receptors in the human CNS using molecular neuroimaging. We will discuss how these advances have provided evidence to support the notion that there is a sub-group of patients within the syndrome of schizophrenia that have a unique molecular pathology driven by a marked loss of muscarinic M1 receptors. This review is timely, as drugs targeting muscarinic receptors approach clinical use for the treatment of schizophrenia and here we outline the background biology that supported development of such drugs to treat the disorder.

Modulation of Muscarinic Signalling in the Central Nervous System by Steroid Hormones and Neurosteroids

Muscarinic acetylcholine receptors expressed in the central nervous system mediate various functions, including cognition, memory, or reward. Therefore, muscarinic receptors represent potential pharmacological targets for various diseases and conditions, such as Alzheimer's disease, schizophrenia, addiction, epilepsy, or depression. Muscarinic receptors are allosterically modulated by neurosteroids and steroid hormones at physiologically relevant concentrations. In this review, we focus on the modulation of muscarinic receptors by neurosteroids and steroid hormones in the context of diseases and disorders of the central nervous system. Further, we propose the potential use of neuroactive steroids in the development of pharmacotherapeutics for these diseases and conditions.

Aged Brains Express Less Melanocortin Receptors, Which Correlates with Age-Related Decline of Cognitive Functions

Brain G-protein coupled receptors have been hypothesized to be potential targets for maintaining or restoring cognitive function in normal aged individuals or in patients with neurodegenerative disease. A number of recent reports suggest that activation of melanocortin receptors (MCRs) in the brain can significantly improve cognitive functions of normal rodents and of different rodent models of the Alzheimer's disease. However, the potential impact of normative aging on the expression of MCRs and their potential roles for modulating cognitive function remains to be elucidated. In the present study, we first investigated the expression of these receptors in six different brain regions of young (6 months) and aged (23 months) rats following assessment of their cognitive status. Correlation analysis was further performed to reveal potential contributions of MCR subtypes to spatial learning and memory. Our results revealed statistically significant correlations between the expression of several MCR subtypes in the frontal cortex/hypothalamus and the hippocampus regions and the rats' performance in spatial learning and memory only in the aged rats. These findings support the hypothesis that aging has a direct impact on the expression and function of MCRs, establishing MCRs as potential drug targets to alleviate aging-induced decline of cognitive function.

Cholinergic muscarinic M1/M4 receptor networks in dementia with Lewy bodies

Cholinergic dysfunction is central in dementia with Lewy bodies, possibly contributing to the cognitive and psychiatric phenotypes of this condition. We investigated baseline muscarinic M₁/M₄ receptor spatial covariance patterns in dementia with Lewy bodies and their association with changes in cognition and neuropsychiatric symptoms after 12 weeks of treatment with the cholinesterase inhibitor donepezil. Thirty-eight participants (14 cholinesterase inhibitor naive patients, 24 healthy older individuals) underwent ¹²³I-iodo-quinuclidinyl-benzilate (M₁/M₄ receptor assessment) and ^99mTc-exametazime (perfusion) single-photon emission computed tomography scanning. We implemented voxel principal components analysis, producing a series of images representing patterns of inter-correlated voxels across individuals. Linear regression analyses derived specific M₁/M₄ and perfusion spatial covariance patterns associated with patients. A discreet M₁/M₄ pattern that distinguished patients from controls (W_1,19.7 = 16.7, P = 0.001), showed relative decreased binding in right lateral temporal and insula, as well as relative preserved/increased binding in frontal, precuneus, lingual and cuneal regions, implicating nodes within attention and dorsal visual networks. We then derived from patients an M₁/M₄ pattern that correlated with a positive change in mini-mental state examination (r = 0.52, P = 0.05), showing relative preserved/increased uptake in prefrontal, temporal pole and anterior cingulate, elements of attention-related networks. We also generated from patients an M₁/M₄ pattern that correlated with a positive change in neuropsychiatric inventory score (r = 0.77, P = 0.002), revealing relative preserved/increased uptake within a bilateral temporal-precuneal-striatal system. Although in a small sample and therefore tentative, we posit that optimal response of donepezil on cognitive and neuropsychiatric signs in patients with dementia with Lewy bodies were associated with a maintenance of muscarinic M₁/M₄ receptor expression within attentional/executive and ventral visual network hubs, respectively.

Is there a role for antibodies targeting muscarinic acetylcholine receptors in the pathogenesis of schizophrenia?

OBJECTIVE

Muscarinic receptor dysfunction has been suggested to play an important role in the pathophysiology of schizophrenia. Recently, it has also become clear that immune reactivity directed against neurotransmitter receptors may play a pathogenic role in some cases of schizophrenia. The aim of this review is to summarize the case for muscarinic receptor dysfunction in schizophrenia and the evidence supporting the hypothesis that this dysfunction is related to the development of muscarinic receptor-targeting antibodies.

METHOD

The article reviews studies of muscarinic receptors and the presence and potential role(s) of anti-muscarinic acetylcholine receptor antibodies in people with schizophrenia.

RESULTS

There is accumulating evidence that altered or deficient muscarinic signalling underlies some of the key clinical features of schizophrenia. Although the number of studies investigating anti-muscarinic acetylcholine receptor antibodies in schizophrenia is relatively small, they consistently demonstrate that such antibodies are present in a proportion of patients. This evidence suggests that these antibodies could have pathogenic effects or exist as a biomarker to an unknown pathophysiological process in schizophrenia.

CONCLUSION

The presence of elevated levels of anti-muscarinic acetylcholine receptor antibodies may identify a subgroup of people with schizophrenia, potentially informing aetiopathogenesis, clinical presentation and treatment. To date, all studies have examined antibodies in participants with chronic schizophrenia, who have likely received antipsychotic medication for many years. As these medications modulate immune functions and regulate receptor densities, it is recommended that future studies screen for the presence of anti-muscarinic antibodies in people experiencing their first episode of psychosis.

Synthesis and Preliminary Evaluation of 11 C-Labeled VU0467485/AZ13713945 and Its Analogues for Imaging Muscarinic Acetylcholine Receptor Subtype 4

Muscarinic acetylcholine receptors (mAChRs) have five distinct subunits (M₁ -M₅ ) and are involved in the action of the neurotransmitter acetylcholine in the central and peripheral nervous system. Attributed to the promising clinical efficacy of xanomeline, an M₁ /M₄ -preferring agonist, in patients of schizophrenia and Alzheimer's disease, M₁ - or M₄ -selective mAChR modulators have been developed that target the topographically distinct allosteric sites. Herein we report the synthesis and preliminary evaluation of ¹¹ C-labeled positron emission tomography (PET) ligands based on a validated M₄ R positive allosteric modulator VU0467485 (AZ13713945) to facilitate drug discovery. [¹¹ C]VU0467485 and two other ligands were prepared in high radiochemical yields (>30 %, decay-corrected) with high radiochemical purity (>99 %) and high molar activity (>74 GBq μmol^-1 ). In vitro autoradiography studies indicated that these three ligands possess moderate-to-high in vitro specific binding to M₄ R. Nevertheless, further physiochemical property optimization is necessary to overcome the challenges associated with limited brain permeability.

Structural insights into the subtype-selective antagonist binding to the M2 muscarinic receptor

Human muscarinic receptor, M₂ is one of the five subtypes of muscarinic receptors belonging to the family of G protein-coupled receptors. Muscarinic receptors are targets for multiple neurodegenerative diseases. The challenge has been designing subtype selective ligands against one of the five muscarinic receptors. We report high resolution structures of a thermostabilized mutant M₂ receptor bound to a subtype selective antagonist AF-DX 384 and a non-selective antagonist NMS. The thermostabilizing mutation S110R in M₂ was predicted using a theoretical strategy previously developed in our group. Comparison of the crystal structures and pharmacological properties of the M₂ receptor shows that the Arg in the S110R mutant mimics the stabilizing role of the sodium cation, that is known to allosterically stabilize inactive state(s) of class A GPCRs. Molecular Dynamics simulations reveal that tightening of the ligand-residue contacts in M₂ receptor compared to M₃ receptor leads to subtype selectivity of AF-DX 384.

Cyto- and receptor architectonic mapping of the human brain

Mapping of the human brain is more than the generation of an atlas-based parcellation of brain regions using histologic or histochemical criteria. It is the attempt to provide a topographically informed model of the structural and functional organization of the brain. To achieve this goal a multimodal atlas of the detailed microscopic and neurochemical structure of the brain must be registered to a stereotaxic reference space or brain, which also serves as reference for topographic assignment of functional data, e.g., functional magnet resonance imaging, electroencephalography, or magnetoencephalography, as well as metabolic imaging, e.g., positron emission tomography. Although classic maps remain pioneering steps, they do not match recent concepts of the functional organization in many regions, and suffer from methodic drawbacks. This chapter provides a summary of the recent status of human brain mapping, which is based on multimodal approaches integrating results of quantitative cyto- and receptor architectonic studies with focus on the cerebral cortex in a widely used reference brain. Descriptions of the methods for observer-independent and statistically testable cytoarchitectonic parcellations, quantitative multireceptor mapping, and registration to the reference brain, including the concept of probability maps and a toolbox for using the maps in functional neuroimaging studies, are provided.

Muscarinic receptor subtype distribution in the central nervous system and relevance to aging and Alzheimer's disease

Muscarinic acetylcholine receptors (mAChRs) are G proteincoupled receptors (GPCRs) that mediate the metabotropic actions of acetylcholine (ACh). There are five subtypes of mAChR, M₁ - M₅, which are expressed throughout the central nervous system (CNS) on numerous cell types and represent promising treatment targets for a number of different diseases, disorders, and conditions of the CNS. Although the present review will focus on Alzheimer's disease (AD) and amnestic mild cognitive impairment (aMCI), a number of conditions such as Parkinson's disease (PD), schizophrenia, and others represent significant unmet medical needs for which selective muscarinic agents could offer therapeutic benefits. Numerous advances have been made regarding mAChR localization through the use of subtype-selective antibodies and radioligand binding studies and these efforts have helped propel a number of mAChR therapeutics into clinical trials. However, much of what we know about mAChR localization in the healthy and diseased brain has come from studies employing radioligand binding with relatively modest selectivity. The development of subtype-selective small molecule radioligands suitable for in vitro and in vivo use, as well as robust, commercially-available antibodies remains a critical need for the field. Additionally, novel genetic tools should be developed and leveraged to help move the field increasingly towards a systems-level understanding of mAChR subtype action. Finally, functional, proteomic, and genetic data from ongoing human studies hold great promise for optimizing the design and interpretation of studies examining receptor levels by enabling patient stratification. This article is part of the Special Issue entitled 'Neuropharmacology on Muscarinic Receptors'.

Alterations of M1 and M4 acetylcholine receptors in the genetically dystonic (dtsz) hamster and moderate antidystonic efficacy of M1 and M4 anticholinergics

Striatal cholinergic dysfunction has been suggested to play a critical role in the pathophysiology of dystonia. In the dt^sz hamster, a phenotypic model of paroxysmal dystonia, M1 antagonists exerted moderate antidystonic efficacy after acute systemic administration. In the present study, we examined the effects of the M4 preferring antagonist tropicamid and whether long-term systemic or acute intrastriatal injections of the M1 preferring antagonist trihexyphenidyl are more effective in mutant hamsters. Furthermore, M1 and M4 receptors were analyzed by autoradiography and immunohistochemistry. Tropicamide retarded the onset of dystonic attacks, as previously observed after acute systemic administration of trihexyphenidyl. Combined systemic administration of trihexyphenidyl (30mg/kg) and tropicamide (15mg/kg) reduced the severity in acute trials and delayed the onset of dystonia during long-term treatment. In contrast, acute striatal microinjections of trihexyphenidyl, tropicamid or the positive allosteric M4 receptor modulator VU0152100 did not exert significant effects. Receptor analyses revealed changes of M1 receptors in the dorsomedial striatum, suggesting that the cholinergic system is involved in abnormal striatal plasticity in dt^sz hamsters, but the pharmacological data argue against a crucial role on the phenotype in this animal model. However, antidystonic effects of tropicamide after systemic administration point to a novel therapeutic potential of M4 preferring anticholinergics for the treatment of dystonia.

Cholinergic System and Post-translational Modifications: An Insight on the Role in Alzheimer's Disease

BACKGROUND

Alzheimer's disease (AD) is the most common form of old age dementia. The formation of amyloid plaques (Aβ), neurofibrillary tangles and loss of basal forebrain cholinergic neurons are the hallmark events in the pathology of AD.

LITERATURE REVIEW

Cholinergic system is one of the most important neurotransmitter system involved in learning and memory which preferentially degenerates in the initial stages of AD. Activation of cholinergic receptors (muscarinic and nicotinic) activates multiple pathways which result in post translational modifications (PTMs) in multiple proteins which bring changes in nervous system. Cholinergic receptors-mediated PTMs "in-part" substantially affect the biosynthesis, proteolysis, degradation and expression of many proteins and in particular, amyloid precursor protein (APP). APP is subjected to several PTMs (proteolytic processing, glycosylation, sulfation, and phosphorylation) during its course of processing, resulting in Aβ deposition, leading to AD. Aβ also alters the PTMs of tau which is a microtubule associated protein. Therefore, post-translationally modified tau and Aβ collectively aggravate the neuronal loss that leads to cholinergic hypofunction.

CONCLUSION

Despite the accumulating evidences, the interaction between cholinergic neurotransmission and the physiological significance of PTM events remain speculative and still needs further exploration. This review focuses on the role of cholinergic system and discusses the significance of PTMs in pathological progression of AD and highlights some important future directions.

Drug Development in Alzheimer's Disease: The Contribution of PET and SPECT

Clinical trials aiming to develop disease-altering drugs for Alzheimer’s disease (AD), a neurodegenerative disorder with devastating consequences, are failing at an alarming rate. Poorly defined inclusion-and outcome criteria, due to a limited amount of objective biomarkers, is one of the major concerns. Non-invasive molecular imaging techniques, positron emission tomography and single photon emission (computed) tomography (PET and SPE(C)T), allow visualization and quantification of a wide variety of (patho)physiological processes and allow early (differential) diagnosis in many disorders. PET and SPECT have the ability to provide biomarkers that permit spatial assessment of pathophysiological molecular changes and therefore objectively evaluate and follow up therapeutic response, especially in the brain. A number of specific PET/SPECT biomarkers used in support of emerging clinical therapies in AD are discussed in this review.

Regional covariance of muscarinic acetylcholine receptors in Alzheimer's disease using (R, R) [(123)I]-QNB SPECT

Alzheimer's disease (AD) is characterised by deficits in cholinergic neurotransmission and subsequent receptor changes. We investigated (123)I-iodo-quinuclidinyl-benzilate (QNB) SPECT images using spatial covariance analysis (SCA), to detect an M1/M4 receptor spatial covariance pattern (SCP) that distinguished AD from controls. Furthermore, a corresponding regional cerebral blood flow (rCBF) SCP was also derived. Thirty-nine subjects (15 AD and 24 healthy elderly controls) underwent (123)I-QNB and (99m)Tc-exametazime SPECT. Voxel SCA was simultaneously applied to the set of smoothed/registered scans, generating a series of eigenimages representing common intercorrelated voxels across subjects. Linear regression identified individual M1/M4 and rCBF SCPs that discriminated AD from controls. The M1/M4 SCP showed concomitant decreased uptake in medial temporal, inferior frontal, basal forebrain and cingulate relative to concomitant increased uptake in frontal poles, occipital, pre-post central and precuneus/superior parietal regions (F1,37 = 85.7, p < 0.001). A largely different perfusion SCP was obtained showing concomitant decreased rCBF in medial and superior temporal, precuneus, inferior parietal and cingulate relative to concomitant increased rCBF in cerebellum, pre-post central, putamen, fusiform and brain stem/midbrain regions (F1,37 = 77.5, p < 0.001). The M1/M4 SCP expression correlated with the duration of cognitive symptoms (r = 0.90, p < 0.001), whereas the rCBF SCP expression negatively correlated with MMSE, CAMCOG and CAMCOGmemory (r ≥ |0.63|, p ≤ 0.006). (123)I-QNB SPECT revealed an M1/M4 basocortical covariance pattern, distinct from rCBF, reflecting the duration of disease rather than current clinical symptoms. This approach could be more sensitive than univariate methods in characterising the cholinergic/rCBF changes that underpin the clinical phenotype of AD.

Muscarinic presynaptic modulation in GABAergic pallidal synapses of the rat

The external globus pallidus (GPe) is central for basal ganglia processing. It expresses muscarinic cholinergic receptors and receives cholinergic afferents from the pedunculopontine nuclei (PPN) and other regions. The role of these receptors and afferents is unknown. Muscarinic M1-type receptors are expressed by synapses from striatal projection neurons (SPNs). Because axons from SPNs project to the GPe, one hypothesis is that striatopallidal GABAergic terminals may be modulated by M1 receptors. Alternatively, some M1 receptors may be postsynaptic in some pallidal neurons. Evidence of muscarinic modulation in any of these elements would suggest that cholinergic afferents from the PPN, or other sources, could modulate the function of the GPe. In this study, we show this evidence using striatopallidal slice preparations: after field stimulation in the striatum, the cholinergic muscarinic receptor agonist muscarine significantly reduced the amplitude of inhibitory postsynaptic currents (IPSCs) from synapses that exhibited short-term synaptic facilitation. This inhibition was associated with significant increases in paired-pulse facilitation, and quantal content was proportional to IPSC amplitude. These actions were blocked by atropine, pirenzepine, and mamba toxin-7, suggesting that receptors involved were M1. In addition, we found that some pallidal neurons have functional postsynaptic M1 receptors. Moreover, some evoked IPSCs exhibited short-term depression and a different kind of modulation: they were indirectly modulated by muscarine via the activation of presynaptic cannabinoid CB1 receptors. Thus pallidal synapses presenting distinct forms of short-term plasticity were modulated differently.

Comparative (Q)SAR analysis of benzodiazepine derivatives with different biological activity

211 compounds containing a benzodiazepine moiety (BZD) and belonging to 4 groups of different biological activity (H - inhibitors of reverse transcriptase of HIV-I virus, A - antiarrhythmic agents, G - ligands of benzodiazepine receptor in GABAergic system and C - cholecystokinin receptor antagonists) were subjected to structure-activity relationship (SAR) analysis. SAR investigations of all 211 BZD were based on Discriminant Function Analysis (DFA) of physicochemical data connected with BBB (blood-brain barrier) permeability of studied compounds. DFA was performed with STATISTICA 10.0 software by the stepwise method and resulted in 3 discriminant functions whose quality was assessed by Wilk's lambda parameter. Calculated discriminant functions (roots) were applied to draw the scatter diagram of canonical values that showed all 211 cases divided into 4 groups of different biological activity. The method was successfully validated with a set of 38 BZD derivatives expected to belong to groups H, A, G and C. The reliability of the obtained model was confirmed with a cross-validation test. Classification functions presented in this study may be used as a practical tool for predicting new BZD drugs activity.

Striatal input- and rate-dependent effects of muscarinic receptors on pallidal firing

The globus pallidus (GP) plays a key role in the overall basal ganglia (BG) activity. Despite evidence of cholinergic inputs to GP, their role in the spiking activity of GP neurons has not received attention. We examine the effect of local activation and blockade of muscarinic receptors (MRs) in the spontaneous firing of GP neurons both in normal and ipsilateral striatum-lesioned rats. We found that activation of MRs produces heterogeneous responses in both normal and ipsilateral striatum-lesioned rats: in normal rats the response evoked by MRs depends on the predrug basal firing rate; the inhibition evoked by MRs is higher in normal rats than in striatum-lesioned rats; the number of neurons that undergo inhibition is lower in striatum-lesioned rats than in normal rats. Our data suggest that modulation of MRs in the GP depends on the firing rate before their activation and on the integrity of the striato-pallidal pathway.

Localisation of pre- and postsynaptic cholinergic markers in the human brain

The cholinergic neurotransmission in the central nervous system plays an important role in modulating cognitive processes such as learning, memory, arousal and sleep as well as in modulating locomotor activity. Dysfunction of the central cholinergic system is involved in numerous neuropsychiatric diseases. This review will provide a synopsis on the regional localisation of cholinergic and cholinoceptive structures within the adult human brain. On the cholinergic site data based on the distribution of choline acetyltransferase-immunoreactive structures are in the focus, complemented by data from acetylcholinesterase and vesicular acetylcholine transporter studies. On the cholinoceptive site, the distribution and localisation of receptors that transduce the acetylcholine message, i.e. the muscarinic and the nicotinic acetylcholine receptors is summarized. In addition to these data obtained on post mortem brain an overview of markers which allow for the in vivo monitoring of the cholinergic system in the brain is given. The detailed knowledge on the distribution and localisation of cholinergic markers in human brain will provide further information on the cholinergic circuits of neurotransmission - a prerequisite for the interpretation of in vivo imaging data and the development of selective diagnostic and therapeutic compounds.

Muscarinic receptor changes in the gerbil thalamus during aging

Here we studied muscarinic receptors in the gerbil thalamus at 8 different ages - from 6 to 36 months - using receptor and functional autoradiography. The pharmacological profile inhibiting [(3)H]N-methyl scopolamine ([(3)H]NMS) binding with 50 and 200 nM pirenzepine, 30 nM pFHHSiD and 100 nM AF-DX 116 revealed the predominance of the M(2) muscarinic subtype in the thalamic nuclei studied, mainly in the anteroventral, anteromedial and paraventricular thalamic nuclei. These data correlated with the highest [(35)S]guanylyl-5'-O-(gamma-thio)-triphosphate ([(35)S]GTP gamma S) binding induced in these nuclei by the muscarinic agonist oxotremorine in functional autoradiographic assays. Significant aging-dependent increases in the functional response in these three nuclei were observed, but only the anteroventral and anteromedial thalamic nuclei showed aging-dependent increases in [(3)H]NMS binding. Since these nuclei exert relevant functions, in which cholinergic pathways are involved and acetylcholine release is reported to decrease during aging, we suggest that the anteroventral and anteromedial thalamic nuclei would play critical roles in the cholinergic transmission that require compensatory mechanisms during the aging process and that are not observed in other thalamic nuclei.

SPECT imaging in dementia

Single photon emission computed tomography (SPECT) is a non-invasive functional neuroimaging technique that can be used in the diagnosis of dementia. This review describes some of the SPECT radiotracers available for imaging dementia patients and discusses recommendations for the clinical use of this imaging technique.

Mechanisms of acute cocaine toxicity

Patients with acute cocaine poisoning present with life-threatening symptoms involving several organ systems. While the effects of cocaine are myriad, they are the result of a limited number of cocaine-protein interactions, including monoamine transporters, neurotransmitter receptors and voltage-gated ion channels. These primary interactions trigger a cascade of events that ultimately produce the clinical effects. The purpose of this article is to review the primary interactions of cocaine and the effects that these interactions trigger. We also describe the progression of symptoms observed in cocaine poisoning as they relate to serum cocaine concentrations.

Ethnic stratification of the association of RGS4 variants with antipsychotic treatment response in schizophrenia

BACKGROUND

Genetic association studies, including a large meta-analysis, report association of regulator of G protein signaling 4 (RGS4) with schizophrenia in the context of heterogeneity. The central role of RGS4 in regulating signaling via Gi/o coupled neurotransmitter receptors led us to hypothesize that there may be RGS4 genotypes predictive of specific disease phenotypes and antipsychotic treatment responses.

METHODS

Subjects were 678 individuals with schizophrenia who participated in the Clinical Antipsychotic Trials of Intervention Effectiveness (CATIE). Among the 678 subjects, the inferred ancestries were 198 (29%) "Africa only," 397 (59%) "Europe only," and 83 (12%) "Other." Eight single nucleotide polymorphisms (SNPs) spanning RGS4 were genotyped. Multiple linear regression was used to analyze association of RGS4 markers with Positive and Negative Symptoms Scale (PANSS) scores at baseline and throughout antipsychotic treatment.

RESULTS

Two consecutive markers within RGS4, rs2661319 and rs2842030, were associated with more severe baseline PANSS total score. Treatment with perphenazine was more effective than treatment with quetiapine (p = .010) or ziprasidone (p = .002) in individuals of inferred African ancestry and homozygous for the rs951439 C allele.

CONCLUSIONS

RGS4 genotypes predicted both the severity of baseline symptoms and relative responsiveness to antipsychotic treatment. Although these analyses are exploratory and replication is required, these data provide support for RGS4 in schizophrenia pathogenesis and suggest a functional role for RGS4 in differential antipsychotic treatment efficacy of schizophrenia.

Muscarinic Receptors in the Thalamus in Progressive Supranuclear Palsy and Other Neurodegenerative Disorders

Progressive supranuclear palsy (PSP) is a neurodegenerative disease with motor, cognitive, and behavioral symptomatology. Cholinergic dysfunction is thought to underpin several key symptoms. There is known pathologic involvement of the corticobasal ganglia-thalamocortical loops in PSP, but little attention has been focused on potential thalamic dysfunction. Using autoradiography, we measured muscarinic M2 and M4 receptors in specific thalamic nuclei involved in the limbic and motor loops in patients with PSP (n = 11) and compared results from brain tissue of subjects with Lewy body dementias (including dementia with Lewy bodies and Parkinson disease with dementia, n = 31), Alzheimer disease (n = 22) and normal elderly control subjects (n = 27). In the thalamus M2 receptors were more abundant than M4 receptors and were most densely concentrated in the anteroprincipal (AP) and mediodorsal (MD) nuclei, which connect to limbic cortices. M2 receptor binding was reduced in the AP nucleus in PSP compared with control subjects and those with Lewy body dementias. M4 receptors were markedly reduced in the MD nucleus in those with PSP compared with control subjects. M4 receptors were also reduced in the subthalamic nucleus in patients with PSP. M4 receptor binding was reduced in the MD nucleus in the Lewy body dementia and Alzheimer disease groups compared with control subjects. There were no significant changes in the ventrolateral nucleus (motor). Cholinergic dysfunction within the AP and MD nuclei of the thalamus may contribute to behavioral and cognitive disturbances associated with PSP.

Muscarinic acetylcholine receptor status in Alzheimer’s disease assessed using (R, R) 123I-QNB SPECT

BACKGROUND

One of the most characteristic changes in Alzheimer's disease (AD) is a deficit in cortical cholinergic neurotransmission and associated receptor changes.

OBJECTIVE

To investigate differences in the distribution of M1/M4 receptors using (R, R) (123)I-iodo-quinuclidinyl-benzilate (QNB) and single photon emission computed tomography (SPECT) in patients with mild/moderate AD and age-matched controls. Also, to compare (123)I-QNB uptake to the corresponding changes in regional cerebral blood flow (rCBF) in the same subjects.

METHODS

Forty two subjects (18 AD and 24 healthy elderly controls) underwent (123)IQNB and perfusion (99m)Tc-exametazime SPECT scanning. Image analysis was performed using statistical parametric mapping (SPM99) following intensity normalisation of each image to its corresponding mean whole brain uptake. Group differences and correlations were assessed using two sample t-tests and linear regression respectively.

RESULTS

Significant reductions in (123)I-QNB uptake were observed in regions of the frontal rectal gyrus, right parahippocampal gyrus, left hippocampus and areas of the left temporal lobe in AD compared to controls (height threshold of p < or = 0.001 uncorrected). Such regions were also associated with marked deficits in rCBF. No significant correlations were identified between imaging data and clinical variables.

CONCLUSION

Functional impairment as measured by rCBF is more widespread than changes in M1/M4 receptor density in mild/moderate AD, where there was little or no selective loss of M1/M4 receptors in these patients that was greater than the general functional deficits shown on rCBF scans.

Alterations of muscarinic and GABA receptor binding in the posterior cingulate cortex in schizophrenia

The posterior cingulate cortex (PCC), a key component of the limbic system, has been implicated in the pathology of schizophrenia because of its sensitivity to NMDA receptor antagonists. Recent studies have shown that the PCC is dysfunctional in schizophrenia, and it is now suspected to be critically involved in the pathogenesis of schizophrenia. Studies also suggest that there are abnormalities in muscarinic and GABAergic neurotransmission in schizophrenia. Therefore, in the present study we used quantitative autoradiography to investigate the binding of [(3)H]pirenzepine, [(3)H]AF-DX 384 and [(3)H]muscimol, which respectively label M1/4 and M2/4 muscarinic and GABA(A) receptors, in the PCC of schizophrenia and control subjects matched for age and post-mortem interval. The present study found that [(3)H]pirenzepine binding was significantly decreased in the superficial (-24%, p=0.002) and deep (-35%, p<0.001) layers of the PCC in the schizophrenia group as compared with the control group. In contrast, a dramatic increase in [(3)H]muscimol binding was observed in the superficial (+112%, p=0.001) and deep layers (+100%, p=0.017) of the PCC in the schizophrenia group. No difference was observed for [(3)H]AF-DX 384 binding between the schizophrenia and control groups. The authors found a significant inverse correlation between [(3)H]pirenzepine binding in the deep cortical layers and [(3)H]muscimol binding in the superficial layers (rho=-0.732, p=0.003). In addition, negative correlations were also found between age and [(3)H]pirenzepine binding in both superficial and deep cortical layers (rho=-0.669 p=0.049 and rho=-0.778, p=0.014), and between age of schizophrenia onset and [(3)H]AF-DX 384 binding (rho=-0.798, p=0.018). These results for the first time demonstrated the status of M1/M4, M2/M4 and GABA(A) receptors in the PCC in schizophrenia. Whilst the exact mechanism causing these alterations is not yet known, a possible increased acetylcholine and down regulated GABA stimulation in the PCC of schizophrenia is suggested.

Association between the CHRM2 gene and intelligence in a sample of 304 Dutch families

The CHRM2 gene is thought to be involved in neuronal excitability, synaptic plasticity and feedback regulation of acetylcholine release and has previously been implicated in higher cognitive processing. In a sample of 667 individuals from 304 families, we genotyped three single-nucleotide polymorphisms (SNPs) in the CHRM2 gene on 7q31-35. From all individuals, standardized intelligence measures were available. Using a test of within-family association, which controls for the possible effects of population stratification, a highly significant association was found between the CHRM2 gene and intelligence. The strongest association was between rs324650 and performance IQ (PIQ), where the T allele was associated with an increase of 4.6 PIQ points. In parallel with a large family-based association, we observed an attenuated - although still significant - population-based association, illustrating that population stratification may decrease our chances of detecting allele-trait associations. Such a mechanism has been predicted earlier, and this article is one of the first to empirically show that family-based association methods are not only needed to guard against false positives, but are also invaluable in guarding against false negatives.

Bacterial artificial chromosome transgenic analysis of dynamic expression patterns of regulator of G-protein signaling 4 during development. I. Cerebral cortex

Signaling through G-protein-coupled receptors is modulated by a family of regulator of G protein signaling (RGS) proteins that have been implicated in several neurological and psychiatric disorders. Defining the detailed expression patterns and developmental regulation of RGS proteins has been hampered by an absence of antibodies useful for mapping. We have utilized bacterial artificial chromosome (BAC) methods to create transgenic mice that express GFP under the control of endogenous regulator of G-protein signaling 4 (RGS4) enhancer elements. This report focuses on expression patterns in the developing and mature cerebral cortex. Based on reporter distribution, RGS4 is expressed by birth in neurons across all cortical domains, but in different patterns that suggest region- and layer-specific regulation. Peak expression typically occurs before puberty, with complex down-regulation by adulthood. Deep and superficial neurons, in particular, vary in their patterns across developmental age and region and, in primary sensory cortices, layer IV neurons exhibit low or no expression of the GFP reporter. These data suggest that altering RGS4 function will produce a complex neuronal phenotype with cell- and subdomain-specificity in the cerebral cortex.

In vivo SPECT imaging of muscarinic acetylcholine receptors using (R,R) 123I-QNB in dementia with Lewy bodies and Parkinson's disease dementia

INTRODUCTION

Alterations in cholinergic function have been reported to be associated with dementia. The aim of this study was to investigate differences in the distribution of muscarinic acetylcholine receptors (mAChRs) using (R,R) 123I-iodo-quinuclidinyl-benzilate (QNB) and single photon emission computed tomography (SPECT) in dementia with Lewy bodies (DLB), Parkinson's disease dementia (PDD) and age-matched controls. 123I-QNB binding was also compared to the corresponding cerebral perfusion changes in the same subjects.

METHODS

63 subjects (24 controls, 14 DLB, 25 PDD) underwent 123I-QNB and perfusion 99mTc-exametazine SPECT scanning. Image analysis, using statistical parametric mapping (SPM99), involved spatial normalisation of each image to a customised template, followed by smoothing and intensity normalisation of each image to its corresponding mean whole brain uptake. Group effects and correlations were assessed using two sample t tests and linear regression respectively.

RESULTS

Relative to controls, significant elevation of 123I-QNB binding was apparent in the right occipital lobe in DLB and right and left occipital lobes in PDD (height threshold p<or=0.001 uncorrected). PDD also showed significant loss in uptake in frontal regions and temporal lobes bilaterally that was not present in DLB. These patterns appeared to be independent of any corresponding rCBF changes.

CONCLUSION

Significant elevation of mAChRs in the occipital lobe was associated with DLB and PDD. This may relate to the visual disturbances that are prevalent in these disorders. Further studies are required in order to establish the role of mAChRs in visual function.

Differential effects on [35S]GTPgammaS binding using muscarinic agonists and antagonists in the gerbil brain

In this work, we studied the in vitro G-protein activation induced by muscarinic agonists using [(35)S]guanylyl-5'-O-(gamma-thio)-triphosphate ([(35)S]GTPgammaS) autoradiographic methods to characterize the M(2) and M(4) muscarinic subtypes response. Thus, we describe a detailed characterization of the increases in [(35)S]GTPgammaS binding elicited by carbachol (Cch) and oxotremorine (OXO) (binding in the presence minus binding in the absence of agonist) throughout the gerbil brain (Meriones unguiculatus). For both agonists, the strongest stimulations were found in the superficial gray layer of the superior colliculus, the anteroventral and anteromedial thalamic nuclei, the anterior paraventricular thalamic nucleus, and the caudate-putamen. The comparative study using OXO and Cch suggested that OXO is able to detect differences in the response of structures enriched in M(4) muscarinic receptors, showing a lower potency to stimulate these brain areas. Furthermore, using increasing concentrations of selective M(2) (AF-DX 116) and M(1)/M(4) (pirenzepine) antagonists to inhibit specific Cch- or OXO-induced [(35)S]GTPgammaS binding, significant differences were observed in M(2)-enriched structures but not in M(4)-enriched ones such as the caudate-putamen. These data indicate that appropriate muscarinic agonist stimulation, together with selective inhibition of this effect using functional autoradiography, can be used as a tool to unravel the M(2)- and M(4)-muscarinic subtype-mediated response.

Effects of rivastigmine on sustained attention in schizophrenia: an FMRI study

This study assessed the neural correlates of the effects of rivastigmine, a CNS-selective cholinesterase inhibitor, given as an add-on therapy to antipsychotics-treated patients with schizophrenia who displayed moderate cognitive impairments, using functional magnetic resonance imaging (fMRI) during a sustained attention task. The study used a placebo-controlled, randomized, double-blind longitudinal design. Twenty patients stable on antipsychotics, 11 assigned to receive rivastigmine and 9 to receive placebo, underwent fMRI and clinical assessments at baseline and after 12 weeks. The fMRI task used a periodic block design and involved 3 conditions: rest, detecting a nonzero number ("nonzero" condition), and detecting a specific number ("specific number" condition) among a series of 6-digit numbers. Online data (via button presses) were acquired on both occasions. Behavioral results showed a trend (P = 0.075) for the rivastigmine-treated patients to have more correct responses and the placebo group to have fewer correct responses at 12 weeks compared with baseline in the "nonzero" condition. There was also an increase in regional brain activity in the cerebellum in the rivastigmine group at 12 weeks in both conditions, which was only partially explained by change in behavioral measures; no change was observed in the placebo group. Our results showed that rivastigmine treatment increased cerebellar activity and influenced attentional processes.

Membrane phospholipid composition, alterations in neurotransmitter systems and schizophrenia

This review addresses the relationship between modifications in membrane phospholipid composition (MPC) and alterations in dopaminergic, serotonergic and cholinergic neurotransmitter systems in schizophrenia. The main evidence in support of the MPC hypothesis of schizophrenia comes from post-mortem and platelet studies, which show that in schizophrenia, certain omega-3 and omega-6 polyunsaturated fatty acid (PUFA) levels are reduced. Furthermore, examination of several biochemical markers suggests abnormal fatty acid metabolism may be present in schizophrenia. Dietary manipulation of MPC with polyunsaturated fatty acid diets has been shown to affect densities of dopamine, serotonin and muscarinic receptors in rats. Also, supplementation with omega-3 fatty acids has been shown to improve mental health rating scores, and there is evidence that the mechanism behind this involves the serotonin receptor complex. This suggests that a tight relationship exists between essential fatty acid status and normal neurotransmission, and that altered PUFA levels may contribute to the abnormalities in neurotransmission seen in schizophrenia.

M2/M4 muscarinic receptor binding in the anterior cingulate cortex in schizophrenia and mood disorders

We have previously shown a decrease in [(3)H]pirenzepine binding to M1/M4 muscarinic receptors in the anterior cingulate cortex in schizophrenia but not in major depression or bipolar disorder. The present study aimed to extend these findings by examining the binding of [(3)H]AF-DX 384 to M2/M4 receptors in the same cohort of subjects. Using quantitative autoradiography we measured [(3)H]AF-DX 384 binding in the anterior cingulate cortex of 15 schizophrenia, 15 bipolar, 15 major depression and 15 control cases. Post-mortem tissue was obtained from the Stanley Foundation Brain Bank. [(3)H]AF-DX 384 binding had a homogenous distribution amongst the layers of the anterior cingulate cortex, was higher in males than in females and declined with prolonged storage of tissue. An inverse correlation between [(3)H]AF-DX384 binding and age of onset of the disease was observed in the schizophrenia group suggesting that the earlier the age at onset the higher the binding was. In the depression group, there was a significant effect of gender on [(3)H]AF-DX 384 binding with females having lower binding in comparison to males. In the bipolar group, there was a significant inverse correlation between antipsychotic medication and [(3)H]AF-DX 384 binding, suggesting that the higher the dose of medication the lower the binding was. No differences in [(3)H]AF-DX 384 binding were seen between the four groups. The present results provide no evidence of M2/M4 receptor alterations in the anterior cingulate cortex in schizophrenia and affective disorders and extend the body of evidence implicating cortical M1 but not M2 involvement in the pathology and pharmacotherapy of schizophrenia.

A high n-6 polyunsaturated fatty acid diet reduces muscarinic M2/M4 receptor binding in the rat brain

The aim of this study was to examine the influence of different fat diets on muscarinic acetylcholine receptor binding. Nineteen male Sprague-Dawley rats were divided into four groups and fed a diet of either high saturated fat, n-6 polyunsaturated fatty acid (PUFA), n-3 PUFA or low fat (control) for 8 weeks. Using quantitative autoradiography, [(3)H]pirenzepine binding to muscarinic M1/M4 receptors and [(3)H]AF-DX384 binding to M2/M4 receptors were measured throughout the brain in all four groups. The main findings were that compared to the low fat control group, M2/M4 receptor binding was significantly reduced in the dorsolateral, dorsomedial and ventromedial parts of the caudate putamen (61-64%, p < 0.05), anterior cingulate cortex (59%, p < 0.01), dentate gyrus and CA1-3 fields of the hippocampus (32-43%, p < 0.01) of rats on a high n-6 PUFA diet; however, no differences in M1/M4 receptor binding densities between the four groups were observed. These results suggest that a diet high in n-6 PUFA, but not of n-3 PUFAs or saturated fat, may selectively alter M2/M4 receptor-mediated signal transduction in the rat brain.

Smoking during early pregnancy affects the expression pattern of both nicotinic and muscarinic acetylcholine receptors in human first trimester brainstem and cerebellum

Prenatal nicotine exposure is associated with an increased risk of complications during pregnancy and childhood. In this study the expression of nicotinic and muscarinic acetylcholine receptors in first trimester pons, medulla oblongata and cerebellum from abortus (5-12 weeks of gestation) of smoking and nonsmoking women was compared. A significant age-related increase in binding of nicotinic receptor subtype alpha4 was found in both pons and cerebellum only in fetal tissue from non-smoking women, while a similar increase was observed in medulla oblongata from fetuses exposed to smoking. A significant age-related increase in binding of muscarinic receptor subtype m2 was observed in pons from abortus of smoking compared with non-smoking women. The gene expression pattern of both alpha4 and alpha7 nicotinic receptor subunits was changed after smoking in all three regions investigated. Smoking also changed the expression of m1 and 2 muscarinic receptor mRNA in pons, m1 mRNA in cerebellum and the m3 mRNA in medulla oblongata. The findings indicate that early prenatal nicotine exposure affects the normal developmental pattern of the cholinergic system in human fetal brain.

SPET imaging of central muscarinic receptors with (R,R)[123I]-I-QNB: methodological considerations

Investigations on the effect of normal healthy ageing on the muscarinic system have shown conflicting results. Also, in vivo determination of muscarinic receptor binding has been hampered by a lack of subtype selective ligands and differences in methods used for quantification of receptor densities. Recent in vitro and in vivo work with the muscarinic antagonist (R,R)-I-QNB indicates this ligand has selectivity for m(1) and m(4) muscarinic receptor subtypes. Therefore, we used (R,R)[(123)I]-I-QNB and single photon emission tomography to study brain m(1) and m(4) muscarinic receptors in 25 healthy female subjects (11 younger subjects, age range 26-32 years and 14 older subjects, age range 57-82 years). Our aims were to ascertain the viability of tracer administration and imaging within the same day, and to evaluate whether normalization to whole brain, compared to normalization to cerebellum, could alter the clinical interpretation of results. Images were analyzed using the simplified reference tissue model and by two ratio methods: normalization to whole brain and normalization to cerebellum. Significant correlations were observed between kinetic analysis and normalization to cerebellum, but not to whole brain. Both the kinetic analysis and normalization to cerebellum showed age-related reductions in muscarinic binding in frontal, orbitofrontal, and parietal regions. Normalization to whole brain, however, failed to detect age-related changes in any region. Here we show that, for this radiotracer, normalizing to a region of negligible specific binding (cerebellum) significantly improves sensitivity when compared to global normalization.

Investigation of m1/m4 muscarinic receptors in the anterior cingulate cortex in schizophrenia, bipolar disorder, and major depression disorder

Abnormal cholinergic neurotransmission has been suggested to occur in psychiatric illness. Therefore, this study investigated cholinergic muscarinic receptors in the anterior cingulate cortex (ACC) of schizophrenia, bipolar disorder and major depression disorder (n=15 per group). We used quantitative autoradiography to measure [(3)H]pirenzepine binding to M1 and M4 receptors. Brain tissue was obtained from the Stanley Foundation Neuropathology Consortium. [(3)H]pirenzepine binding was higher in superficial laminae (I-II) than in deep laminae (III-VI) of the ACC. There was a significant 24% reduction in the density of [(3)H]pirenzepine in the deep laminae and a significant 19% reduction in the upper laminae of the ACC in the schizophrenia group compared to the control group. There were no differences in [(3)H]pirenzepine binding in any laminae of the ACC in the bipolar or major depression groups compared with the control group, except for a trend towards decreased [(3)H]pirenzepine binding in subjects with major depression relative to control subjects. We also detected a significant effect of suicide on [(3)H]pirenzepine binding in the ACC in subjects who died as a result of suicide relative to those who did not, which was more evident in patients with schizophrenia. A significant effect of the onset of the disease was also observed that was more evident in patients with bipolar disorder. The study provides evidence of decreased muscarinic receptor density in the ACC in schizophrenia but no evidence for significant changes in these receptors in the bipolar and major depression groups. The changes observed in schizophrenia may contribute to dysfunctional ACC neural circuits.

The neurobiology and control of anxious states

Fear is an adaptive component of the acute "stress" response to potentially-dangerous (external and internal) stimuli which threaten to perturb homeostasis. However, when disproportional in intensity, chronic and/or irreversible, or not associated with any genuine risk, it may be symptomatic of a debilitating anxious state: for example, social phobia, panic attacks or generalized anxiety disorder. In view of the importance of guaranteeing an appropriate emotional response to aversive events, it is not surprising that a diversity of mechanisms are involved in the induction and inhibition of anxious states. Apart from conventional neurotransmitters, such as monoamines, gamma-amino-butyric acid (GABA) and glutamate, many other modulators have been implicated, including: adenosine, cannabinoids, numerous neuropeptides, hormones, neurotrophins, cytokines and several cellular mediators. Accordingly, though benzodiazepines (which reinforce transmission at GABA(A) receptors), serotonin (5-HT)(1A) receptor agonists and 5-HT reuptake inhibitors are currently the principle drugs employed in the management of anxiety disorders, there is considerable scope for the development of alternative therapies. In addition to cellular, anatomical and neurochemical strategies, behavioral models are indispensable for the characterization of anxious states and their modulation. Amongst diverse paradigms, conflict procedures--in which subjects experience opposing impulses of desire and fear--are of especial conceptual and therapeutic pertinence. For example, in the Vogel Conflict Test (VCT), the ability of drugs to release punishment-suppressed drinking behavior is evaluated. In reviewing the neurobiology of anxious states, the present article focuses in particular upon: the multifarious and complex roles of individual modulators, often as a function of the specific receptor type and neuronal substrate involved in their actions; novel targets for the management of anxiety disorders; the influence of neurotransmitters and other agents upon performance in the VCT; data acquired from complementary pharmacological and genetic strategies and, finally, several open questions likely to orientate future experimental- and clinical-research. In view of the recent proliferation of mechanisms implicated in the pathogenesis, modulation and, potentially, treatment of anxiety disorders, this is an opportune moment to survey their functional and pathophysiological significance, and to assess their influence upon performance in the VCT and other models of potential anxiolytic properties.

Muscarinic receptors in basal ganglia in dementia with Lewy bodies, Parkinson's disease and Alzheimer's disease

Derivatives of the muscarinic antagonist 3-quinuclidinyl-4-iodobenzilate (QNB), particularly [123I]-(R,R)-I-QNB, are currently being assessed as in vivo ligands to monitor muscarinic receptors in Alzheimer's disease (AD) and dementia with Lewy bodies (DLB), relating changes to disease symptoms and to treatment response with cholinergic medication. To assist in the evaluation of in vivo binding, muscarinic receptor density in post-mortem human brain was measured by autoradiography with [125I]-(R,R)-I-QNB and [125I]-(R,S)-I-QNB and compared to M1 ([3H]pirenzepine) and M2 and M4 ([3H]AF-DX 384) receptor binding. Binding was calculated in tissue containing striatum, globus pallidus (GPe), claustrum, and cingulate and insula cortex, in cases of AD, DLB, Parkinson's disease (PD) and normal elderly controls. Pirenzepine, AF-DX 384 and (R,S)-I-QNB binding in the striatum correlated positively with increased Alzheimer-type pathology, and AF-DX 384 and (R,R)-I-QNB cortical binding correlated positively with increased Lewy body (LB) pathology; however, striatal pirenzepine binding correlated negatively with cortical LB pathology. M1 receptors were significantly reduced in striatum in DLB compared to AD, PD, and controls and there was a significant correlation between M1 and dopamine D2 receptor densities. [3H]AF-DX 384 binding was higher in the striatum and GPe in AD. Binding of [125I]-(R,R)-I-QNB, which may reflect increased muscarinic M4 receptors, was higher in cortex and claustrum in DLB and AD. [125I]-(R,S)-I-QNB binding was higher in the GPe in AD. Low M1 and D2 receptors in DLB imply altered regulation of the striatal projection neurons which express these receptors. Low density of striatal M1 receptors may relate to the extent of movement disorder in DLB, and to a reduced risk of parkinsonism with acetylcholinesterase inhibition.

The role of cortical cholinergic pre- and post-synaptic receptors in taste memory formation

A number of studies have implicated cholinergic activity in the mediation of learning and memory processes. However, the specific role of muscarinic receptors in memory formation mechanisms is less known. The aim of the present study is to evaluate the effects of muscarinic antagonist M2 presynaptic receptor, AFDX-116 (0.5mM) and M1 and M3 post-synaptic receptor pirenzepine (100mM), as well as a non-selective muscarinic antagonist, scopolamine (136mM), in the insular cortex (IC) during acquisition and retrieval of conditioned taste aversion (CTA). In addition, we evaluate the effects of those antagonists in cortical ACh release by in vivo microdialysis and the effects on the induction of in vivo LTP in the BLA-IC projection. The results showed that the cortical microinjections of scopolamine and pirenzepine, but not AFDX-116, produced significant disruption in the acquisition of CTA, without effects during retrieval. Microinjections of scopolamine and AFDX-116 produced significant cortical ACh release, while infusions of pirenzepine did not produce any release. Application of scopolamine and pirenzepine diminished induction of LTP in the BLA-IC projection, but not AFDX-116, as compared with vehicle. The induction of BLA-CI LTP seems to be modulated by post-synaptic muscarinic acetylcholine receptors and not by pre-synaptic muscarinic receptors. These results suggest a differential involvement of cholinergic receptors during acquisition and retrieval of aversive memory formation, as well as a differential role of muscarinic receptors in the biochemical and electrophysiological processes that may underlay aversive memory.