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

Exploration of the anti-insomnia mechanism of Ganoderma by central-peripheral multi-level interaction network analysis

Background

Ganoderma (Lingzhi in Chinese) has shown good clinical outcomes in the treatment of insomnia, restlessness, and palpitation. However, the mechanism by which Ganoderma ameliorates insomnia is unclear. We explored the mechanism of the anti-insomnia effect of Ganoderma using systems pharmacology from the perspective of central-peripheral multi-level interaction network analysis.

Methods

The active components and central active components of Ganoderma were obtained from the TCMIP and TCMSP databases, then screened to determine their pharmacokinetic properties. The potential target genes of these components were identified using the Swiss Target Prediction and TCMSP databases. The results were matched with the insomnia target genes obtained from the GeneCards, OMIM, DisGeNET, and TCMIP databases. Overlapping targets were subjected to multi-level interaction network analysis and enrichment analysis using the STRING, Metascape, and BioGPS databases. The networks analysed were protein-protein interaction (PPI), drug-component-target gene, component-target gene-organ, and target gene-extended disease; we also performed gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses.

Results

In total, 34 sedative-hypnotic components (including 5 central active components) were identified, corresponding to 51 target genes. Multi-level interaction network analysis and enrichment analysis demonstrated that Ganoderma exerted an anti-insomnia effect via multiple central-peripheral mechanisms simultaneously, mainly by regulating cell apoptosis/survival and cytokine expression through core target genes such as TNF, CASP3, JUN, and HSP90αA1; it also affected immune regulation and apoptosis. Therefore, Ganoderma has potential as an adjuvant therapy for insomnia-related complications.

Conclusion

Ganoderma exerts an anti-insomnia effect via complex central-peripheral multi-level interaction networks.

Possible effects of different doses of 2.1 GHz electromagnetic radiation on learning, and hippocampal levels of cholinergic biomarkers in Wistar rats

The present study evaluated whether short-term exposure to different doses of 2.1 GHz radiofrequency electromagnetic radiation (RF-EMR) has different effects on rats' behaviour and hippocampal levels of central cholinergic biomarkers. Animals were divided into three equal groups namely; group 1 was sham-exposed group, group 2-3 were exposed to 45 V/m and 65 V/m doses of 2.1 GHz frequency for 1 week respectively. Numerical dosimetry simulations were carried out. Object location and Y-maze were used as behavioural tasks. The protein and mRNA expression levels of AChE, ChAT, and VAChT, in the hippocampus were tested using Western Blotting and Real-Time PCR. The impairment performance of rats subjected to 65 V/m dose of 2.1 GHz RF-EMR in both object location and Y-maze tasks was observed. The hippocampal levels of AChE, ChAT, and VAChT, were significantly lower in rats exposed to 65 V/m dose of 2.1 GHz RF-EMR than others. The stronger effect of "65 V/m" dose on both rat's hippocampal-dependent behavioural performances and hippocampal levels of cholinergic biomarkers may be due to the stronger effect of "65 V/m" dose where rats' snouts were located at the nearest distance from the monopole antenna. Furthermore, the simulated SAR values were high for 65 V/m electric-field strengths. For the first time, we report the potential dose-dependent effects of short-term exposure to 2.1 GHz radiation on rat's behavioural performances as well as hippocampal levels of cholinergic biomarkers. Further studies are needed to understand the mechanisms by which RF-EMR influences the function of the central cholinergic system in the brain.

G-Protein-Coupled Receptors in CNS: A Potential Therapeutic Target for Intervention in Neurodegenerative Disorders and Associated Cognitive Deficits

Neurodegenerative diseases are a large group of neurological disorders with diverse etiological and pathological phenomena. However, current therapeutics rely mostly on symptomatic relief while failing to target the underlying disease pathobiology. G-protein-coupled receptors (GPCRs) are one of the most frequently targeted receptors for developing novel therapeutics for central nervous system (CNS) disorders. Many currently available antipsychotic therapeutics also act as either antagonists or agonists of different GPCRs. Therefore, GPCR-based drug development is spreading widely to regulate neurodegeneration and associated cognitive deficits through the modulation of canonical and noncanonical signals. Here, GPCRs’ role in the pathophysiology of different neurodegenerative disease progressions and cognitive deficits has been highlighted, and an emphasis has been placed on the current pharmacological developments with GPCRs to provide an insight into a potential therapeutic target in the treatment of neurodegeneration.

Cellular, Synaptic and Network Effects of Acetylcholine in the Neocortex

The neocortex is densely innervated by basal forebrain (BF) cholinergic neurons. Long-range axons of cholinergic neurons regulate higher-order cognitive function and dysfunction in the neocortex by releasing acetylcholine (ACh). ACh release dynamically reconfigures neocortical microcircuitry through differential spatiotemporal actions on cell-types and their synaptic connections. At the cellular level, ACh release controls neuronal excitability and firing rate, by hyperpolarizing or depolarizing target neurons. At the synaptic level, ACh impacts transmission dynamics not only by altering the presynaptic probability of release, but also the magnitude of the postsynaptic response. Despite the crucial role of ACh release in physiology and pathophysiology, a comprehensive understanding of the way it regulates the activity of diverse neocortical cell-types and synaptic connections has remained elusive. This review aims to summarize the state-of-the-art anatomical and physiological data to develop a functional map of the cellular, synaptic and microcircuit effects of ACh in the neocortex of rodents and non-human primates, and to serve as a quantitative reference for those intending to build data-driven computational models on the role of ACh in governing brain states.

CHAT gene polymorphism rs3810950 is associated with the risk of Alzheimer's disease in the Czech population

Background

Cholinergic hypothesis of Alzheimer’s disease (AD) is based on the findings that a reduced and/or perturbed cholinergic activity in the central nervous system correlates with cognitive decline in patients with Alzheimer’s disease. The hypothesis resulted in the development of centrally-acting agents potentiating cholinergic neurotransmission; these drugs, however, only slowed down the cognitive decline and could not prevent it. Consequently, the perturbation of the central cholinergic signalling has been accepted as a part of the Alzheimer’s aetiology but not necessarily the primary cause of the disease. In the present study we have focused on the rs3810950 polymorphism of ChAT (choline acetyltransferase) gene that has not been studied in Czech population before.

Methods

We carried out an association study to test for a relationship between the rs3810950 polymorphism and Alzheimer’s disease in a group of 1186 persons; 759 patients with Alzheimer’s disease and 427 control subjects. Furthermore, we performed molecular modelling of the terminal domain (1st-126th amino acid residue) of one of the ChAT isoforms (M) to visualise in silico whether the rs3810950 polymorphism (A120T) can change any features of the tertiary structure of the protein which would have a potential to alter its function.

Results

The AA genotype of CHAT was associated with a 1.25 times higher risk of AD (p <  0.002) thus demonstrating that the rs3810950 polymorphism can have a modest but statistically significant effect on the risk of AD in the Czech population. Furthermore, the molecular modelling indicated that the polymorphism is likely to be associated with significant variations in the tertiary structure of the protein molecule which may impact its enzyme activity.

Conclusions

Our findings are consistent with the results of the meta-analytical studies of the relationship between rs3810950 polymorphism and AD and provide further material evidence for a direct (primary) involvement of cholinergic mechanisms in the etiopathogenesis of AD, particularly as a factor in cognitive decline and perturbed conscious awareness commonly observed in patients with AD.

Cholinergic Modulation of Cortical Microcircuits Is Layer-Specific: Evidence from Rodent, Monkey and Human Brain

Acetylcholine (ACh) signaling shapes neuronal circuit development and underlies specific aspects of cognitive functions and behaviors, including attention, learning, memory and motivation. During behavior, activation of muscarinic and nicotinic acetylcholine receptors (mAChRs and nAChRs) by ACh alters the activation state of neurons, and neuronal circuits most likely process information differently with elevated levels of ACh. In several brain regions, ACh has been shown to alter synaptic strength as well. By changing the rules for synaptic plasticity, ACh can have prolonged effects on and rearrange connectivity between neurons that outlasts its presence. From recent discoveries in the mouse, rat, monkey and human brain, a picture emerges in which the basal forebrain (BF) cholinergic system targets the neocortex with much more spatial and temporal detail than previously considered. Fast cholinergic synapses acting on a millisecond time scale are abundant in the mammalian cerebral cortex, and provide BF cholinergic neurons with the possibility to rapidly alter information flow in cortical microcircuits. Finally, recent studies have outlined novel mechanisms of how cholinergic projections from the BF affect synaptic strength in several brain areas of the rodent brain, with behavioral consequences. This review highlights these exciting developments and discusses how these findings translate to human brain circuitries.

Cholinergic Interneurons Underlie Spontaneous Dopamine Release in Nucleus Accumbens

The release of dopamine from terminals in the NAc is regulated by a number of factors, including voltage-gated ion channels, D2-autoreceptors, and nAChRs. Cholinergic interneurons (CINs) drive dopamine release through activation of nAChRs on dopamine terminals. Using cyclic voltammetry in mouse brain slices, nAChR-dependent spontaneous dopamine transients and the mechanisms underlying the origin were examined in the NAc. Spontaneous events were infrequent (0.3 per minute), but the rate and amplitude were increased after blocking Kv channels with 4-aminopyridine. Although the firing frequency of CINs was increased by blocking glutamate reuptake with TBOA and the Sk blocker apamin, only 4-aminopyridine increased the frequency of dopamine transients. In contrast, inhibition of CIN firing with the μ/δ selective opioid [Met⁵]enkephalin (1 μm) decreased spontaneous dopamine transients. Cocaine increased the rate and amplitude of dopamine transients, suggesting that the activity of the dopamine transporter limits the detection of these events. In the presence of cocaine, the rate of spontaneous dopamine transients was further increased after blocking D2-autoreceptors. Blockade of muscarinic receptors had no effect on evoked dopamine release, suggesting that feedback inhibition of acetylcholine release was not involved. Thus, although spontaneous dopamine transients are reliant on nAChRs, the frequency was not strictly governed by the activity of CINs. The increase in frequency of spontaneous dopamine transients induced by cocaine was not due to an increase in cholinergic tone and is likely a product of an increase in detection resulting from decreased dopamine reuptake.SIGNIFICANCE STATEMENT The actions of dopamine in the NAc are thought to be responsible for endogenous reward and the reinforcing properties of drugs of abuse, such as psychostimulants. The present work examines the mechanisms underlying nAChR-induced spontaneous dopamine release. This study demonstrates that spontaneous dopamine release is (1) dependent of the activation of nicotinic receptors, (2) independent on the spontaneous activity of cholinergic interneurons, and (3) that cocaine increased the detection of dopamine transients by prolonging the presence and increasing the diffusion of dopamine in the extracellular space. The release of acetylcholine is therefore responsible for spontaneous dopamine transients, and cocaine augments dopamine tone without altering activity of cholinergic interneurons.

Cholinergic depletion and basal forebrain volume in primary progressive aphasia

Primary progressive aphasia (PPA) is a heterogeneous syndrome with various neuropathological causes for which no medical treatment with proven efficacy exists. Basal forebrain (BF) volume loss has been reported in PPA but its relation to cholinergic depletion is still unclear. The primary objective of this study was to investigate whether cholinergic alterations occur in PPA variants and how this relates to BF volume loss. An academic memory clinic based consecutive series of 11 PPA patients (five with the semantic variant (SV), four with the logopenic variant (LV) and two with the nonfluent variant (NFV)) participated in this cross-sectional in vivo PET imaging study together with 10 healthy control subjects. Acetylcholinesterase (AChE) activity was quantitatively measured in the neo- and allocortex using N-[¹¹C]-Methylpiperidin-4-yl propionate (PMP)-PET with arterial sampling and metabolite correction. Whole brain and BF volumes were quantified using voxel-based morphometry on high-resolution magnetic resonance imaging (MRI) scans.

In the PPA group, only LV cases showed decreases in AChE activity levels compared to controls. Surprisingly, a substantial number of SV cases showed significant AChE activity increases compared to controls. BF volume did not correlate with AChE activity levels in PPA. To conclude, in our sample of PPA patients, LV but not SV was associated with cholinergic depletion. BF atrophy in PPA does not imply cholinergic depletion.

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Using PET we examined cholinesterase activity in PPA.

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Cholinergic depletion occurred in the logopenic variant.

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Basal forebrain atrophy mainly occurred in the semantic variant.

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Cholinergic depletion did not correlate with basal forebrain atrophy.

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Unexpectedly, semantic variant was associated with cholinergic activity increases.

Nicotinic receptor activation contrasts pathophysiological bursting and neurodegeneration evoked by glutamate uptake block on rat hypoglossal motoneurons

KEY POINTS

Impaired uptake of glutamate builds up the extracellular level of this excitatory transmitter to trigger rhythmic neuronal bursting and delayed cell death in the brainstem motor nucleus hypoglossus. This process is the expression of the excitotoxicity that underlies motoneuron degeneration in diseases such as amyotrophic lateral sclerosis affecting bulbar motoneurons. In a model of motoneuron excitotoxicity produced by pharmacological block of glutamate uptake in vitro, rhythmic bursting is suppressed by activation of neuronal nicotinic receptors with their conventional agonist nicotine. Emergence of bursting is facilitated by nicotinic receptor antagonists. Following excitotoxicity, nicotinic receptor activity decreases mitochondrial energy dysfunction, endoplasmic reticulum stress and production of toxic radicals. Globally, these phenomena synergize to provide motoneuron protection. Nicotinic receptors may represent a novel target to contrast pathological overactivity of brainstem motoneurons and therefore to prevent their metabolic distress and death.

ABSTRACT

Excitotoxicity is thought to be one of the early processes in the onset of amyotrophic lateral sclerosis (ALS) because high levels of glutamate have been detected in the cerebrospinal fluid of such patients due to dysfunctional uptake of this transmitter that gradually damages brainstem and spinal motoneurons. To explore potential mechanisms to arrest ALS onset, we used an established in vitro model of rat brainstem slice preparation in which excitotoxicity is induced by the glutamate uptake blocker dl-threo-β-benzyloxyaspartate (TBOA). Because certain brain neurons may be neuroprotected via activation of nicotinic acetylcholine receptors (nAChRs) by nicotine, we investigated if nicotine could arrest excitotoxic damage to highly ALS-vulnerable hypoglossal motoneurons (HMs). On 50% of patch-clamped HMs, TBOA induced intense network bursts that were inhibited by 1-10 μm nicotine, whereas nAChR antagonists facilitated burst emergence in non-burster cells. Furthermore, nicotine inhibited excitatory transmission and enhanced synaptic inhibition. Strong neuroprotection by nicotine prevented the HM loss observed after 4 h of TBOA exposure. This neuroprotective action was due to suppression of downstream effectors of neurotoxicity such as increased intracellular levels of reactive oxygen species, impaired energy metabolism and upregulated genes involved in endoplasmic reticulum (ER) stress. In addition, HMs surviving TBOA toxicity often expressed UDP-glucose glycoprotein glucosyltransferase, a key element in repair of misfolded proteins: this phenomenon was absent after nicotine application, indicative of ER stress prevention. Our results suggest nAChRs to be potential targets for inhibiting excitotoxic damage of motoneurons at an early stage of the neurodegenerative process.

PET tracers for imaging brain α7 nicotinic receptors: an update

Positron emission tomography (PET) molecular imaging of brain targets is a powerful tool to diagnose, follow up, and develop treatments and personalized medicine for a number of acute and chronic brain disorders. The availability of β+ emitter tracers labelled with [(11)C] or [(18)F] having optimal characteristics of affinity and selectivity for alpha-7 nicotinic receptors (α7R) has received considerable attention, due to the major implication of these receptors in brain functions. The aim of this review is to identify the interest and need for the in vivo exploration of α7R by PET molecular imaging, which tools are currently available for this and how to progress.

Cholinergic interneurons in the dorsal and ventral striatum: anatomical and functional considerations in normal and diseased conditions

Striatal cholinergic interneurons (ChIs) are central for the processing and reinforcement of reward-related behaviors that are negatively affected in states of altered dopamine transmission, such as in Parkinson's disease or drug addiction. Nevertheless, the development of therapeutic interventions directed at ChIs has been hampered by our limited knowledge of the diverse anatomical and functional characteristics of these neurons in the dorsal and ventral striatum, combined with the lack of pharmacological tools to modulate specific cholinergic receptor subtypes. This review highlights some of the key morphological, synaptic, and functional differences between ChIs of different striatal regions and across species. It also provides an overview of our current knowledge of the cellular localization and function of cholinergic receptor subtypes. The future use of high-resolution anatomical and functional tools to study the synaptic microcircuitry of brain networks, along with the development of specific cholinergic receptor drugs, should help further elucidate the role of striatal ChIs and permit efficient targeting of cholinergic systems in various brain disorders, including Parkinson's disease and addiction.

Scopolamine provocation-based pharmacological MRI model for testing procognitive agents

There is a huge unmet need to understand and treat pathological cognitive impairment. The development of disease modifying cognitive enhancers is hindered by the lack of correct pathomechanism and suitable animal models. Most animal models to study cognition and pathology do not fulfil either the predictive validity, face validity or construct validity criteria, and also outcome measures greatly differ from those of human trials. Fortunately, some pharmacological agents such as scopolamine evoke similar effects on cognition and cerebral circulation in rodents and humans and functional MRI enables us to compare cognitive agents directly in different species. In this paper we report the validation of a scopolamine based rodent pharmacological MRI provocation model. The effects of deemed procognitive agents (donepezil, vinpocetine, piracetam, alpha 7 selective cholinergic compounds EVP-6124, PNU-120596) were compared on the blood-oxygen-level dependent responses and also linked to rodent cognitive models. These drugs revealed significant effect on scopolamine induced blood-oxygen-level dependent change except for piracetam. In the water labyrinth test only PNU-120596 did not show a significant effect. This provocational model is suitable for testing procognitive compounds. These functional MR imaging experiments can be paralleled with human studies, which may help reduce the number of false cognitive clinical trials.

Evidence for respiratory neuromodulator interdependence after cholinergic disruption in the ventral respiratory column

Reverse dialysis of the muscarinic receptor antagonist, atropine (ATR, 50 mM), into the pre-Bötzinger Complex region of the ventral respiratory column (VRC) of awake and sleeping goats increases breathing frequency and serotonin (5-HT), substance P (SP), glycine, and GABA concentrations in the effluent dialysate. Herein, we report data from goats in which we reverse dialyzed 5 mM ATR or specific antagonists of M2 or M3 muscarinic receptors into the VRC. The effects on frequency of all three antagonists were not significantly different from time control studies. 5 mM ATR and the M3 antagonist increased SP sevenfold less than 50 mM ATR. The antagonists had no effect on 5-HT, glycine, and/or GABA, suggesting that the increases in glycine and GABA with 50 mM ATR were secondary to the larger increases in 5-HT and/or SP. These data are suggestive of neuromodulator interdependence, whereby attenuation of one neuromodulator is compensated for by local changes in other neuromodulators to stabilize breathing.

The role of alpha-7 nicotinic receptors in food intake behaviors

Nicotine alters appetite and energy expenditure, leading to changes in body weight. While the exact mechanisms underlying these effects are not fully established, both central and peripheral involvement of the alpha-7 nicotinic acetylcholine receptor (α7nAChR) has been suggested. Centrally, the α7nAChR modulates activity of hypothalamic neurons involved in food intake regulation, including proopiomelanocortin and neuropeptide Y. α7nAChRs also modulate glutamatergic and dopaminergic systems controlling reward processes that affect food intake. Additionally, α7nAChRs are important peripheral mediators of chronic inflammation, a key contributor to health problems in obesity. This review focuses on nicotinic cholinergic effects on eating behaviors, specifically those involving the α7nAChR, with the hypothesis that α7nAChR agonism leads to appetite suppression. Recent studies are highlighted that identify links between α7nAChR expression and obesity, insulin resistance, and diabetes and describe early findings showing an α7nAChR agonist to be associated with reduced weight gain in a mouse model of diabetes. Given these effects, the α7nAChR may be a useful therapeutic target for strategies to treat and manage obesity.

Regional brain imaging of vesicular acetylcholine transporter using o-[125 I]iodo-trans-decalinvesamicol as a new potential imaging probe

In this study, the regional rat brain distribution of radioiodinated o-iodo-trans-decalinvesamicol ([(125) I]OIDV) was determined in vivo to evaluate its potential as a single-photon emission computed tomography (SPECT) imaging probe for vesicular acetylcholine transporter (VAChT). Following intravenous injection, [(125) I]OIDV passed freely across the blood-brain barrier and accumulated in rat brain. The accumulation of [(125) I]OIDV in rat brain was significantly reduced by coadministration of (+/-)-vesamicol (0.125 µmol). In contrast, the coadministration of σ-receptor ligands, such as (+)-pentazocine (0.125 µmol) as a σ-1 receptor ligand and (+)-3-(3-hydroxyphenyl)-N-propylpiperidine (0.125 µmol) as a σ-1 and σ-2 receptor ligands, barely affected the accumulation of [(125) I]OIDV in rat brain. These findings in vivo were corroborated by autoradiographic analysis ex vivo. The authors found that the tracer binds with pharmacological selectivity to VAChT in rat brain and predicted that it may likewise serve in translational SPECT imaging studies of this marker in the integrity of cholinergic innervations.

Spatial reference memory deficits precede motor dysfunction in an experimental autoimmune encephalomyelitis model: the role of kallikrein-kinin system

Multiple sclerosis (MS) is a progressive T cell-mediated autoimmune demyelinating inflammatory disease of the central nervous system (CNS). Although it is recognized that cognitive deficits represent a manifestation of the disease, the underlying pathogenic mechanisms remain unknown. Here we provide evidence of spatial reference memory impairments during the pre-motor phase of experimental autoimmune encephalomyelitis (EAE) in mice. Specifically, these cognitive deficits were accompanied by down-regulation of choline acetyltransferase (ChAT) mRNA expression on day 5 and 11 post-immunization, and up-regulation of inflammatory cytokines in the hippocampus and prefrontal cortex. Moreover, a marked increase in B1R mRNA expression occurred selectively in the hippocampus, whereas protein level was up-regulated in both brain areas. Genetic deletion of kinin B1R attenuated cognitive deficits and cholinergic dysfunction, and blocked mRNA expression of both IL-17 and IFN-γ in the prefrontal cortex, lymph node and spleen of mice subjected to EAE. The discovery of kinin receptors, mainly B1R, as a target for controlling neuroinflammatory response, as well as the cognitive deficits induced by EAE may foster the therapeutic exploitation of the kallikrein-kinin system (KKS), in particular for the treatment of autoimmune disorders, such as MS, mainly during pre-symptomatic phase.

[(123)I]-IBVM SPECT imaging of cholinergic systems in multiple system atrophy: A specific alteration of the ponto-thalamic cholinergic pathways (Ch5-Ch6)

We evaluated in vivo the integrity of brain cholinergic pathways in Multiple System Atrophy (MSA) and the relationship between cholinergic dysfunction and motor disturbances, by measuring the vesicular acetylcholine transporter (VAChT) expression using Single Photon Emission Computed Tomography (SPECT) and [(123)I]-iodobenzovesamicol ([(123)I]-IBVM).

METHODS

Nine patients with probable MSA and 12 healthy volunteers underwent a dynamic [(123)I]-IBVM SPECT-CT scan and a magnetic resonance imaging (MRI) scan. All patients were examined with the Unified MSA Rating Scale (UMSARS; subscale I = activities of daily living (ADL), II = motor and IV = disability). CT and MRI images were used to register the dynamic SPECT image to the Montreal Neurological Institute brain template, which includes the regions of interest (ROI) of striatum and Ch1 (medial septum nucleus-hippocampus), Ch4 (nucleus basalis of Meynert-cortex) and Ch5-Ch6 (pedunculopontine and laterodorsal tegmental nuclei-thalamus) cholinergic pathways. For each ROI, pharmacokinetic modeling of regional time activity curves led to the calculation of [(123)I]-IBVM to VAChT binding potential (BPND) value, proportional to VAChT expression.

RESULTS

When compared to controls, BPND values for MSA in Ch5-Ch6 were significantly decreased in both the pedunculopontine-laterodorsal nuclei and the thalamus (p = 0.004 and p = 0.006, respectively). Additionally, thalamus BPND values were correlated with UMSARS ADL (p = 0.006), motor (p = 0.002) and disability (p = 0.02) sub-scores. UMSARS motor subscale items 13 (postural instability) and 14 (gait) were also correlated with thalamus BPND values (p = 0.04).

CONCLUSION

Ch5-Ch6 are the most affected cholinergic pathways in MSA at both cell bodies and thalamic cholinergic terminals. These results underscore the relevant role of [(123)I]-IBVM SPECT for improving our understanding of the pathophysiology in MSA.

Muscarinic acetylcholine receptor activation blocks long-term potentiation at cerebellar parallel fiber-Purkinje cell synapses via cannabinoid signaling

Muscarinic acetylcholine receptors (mAChRs) are known to modulate synaptic plasticity in various brain areas. A signaling pathway triggered by mAChR activation is the production and release of endocannabinoids that bind to type 1 cannabinoid receptors (CB1R) located on synaptic terminals. Using whole-cell patch-clamp recordings from rat cerebellar slices, we have demonstrated that the muscarinic agonist oxotremorine-m (oxo-m) blocks the induction of presynaptic long-term potentiation (LTP) at parallel fiber (PF)-Purkinje cell synapses in a CB1R-dependent manner. Under control conditions, LTP was induced by delivering 120 PF stimuli at 8 Hz. In contrast, no LTP was observed when oxo-m was present during tetanization. PF-LTP was restored when the CB1R antagonist N-1-(2,4-dichlorophenyl)-5-(4-iodophenyl)-4-methyl-N-1-piperidinyl-1H-pyrazole-3-carboxamide (AM251) was coapplied with oxo-m. Furthermore, the suppressive effect of oxo-m on PF-LTP was abrogated by the GDP analog GDP-β-S (applied intracellularly), the phospholipase C inhibitor U-73122, and the diacylglycerol lipase inhibitor tetrahydrolipstatin (THL), suggesting that cannabinoid synthesis results from the activation of Gq-coupled mAChRs present on Purkinje cells. The oxo-m-mediated suppression of LTP was also prevented in the presence of the M3 receptor antagonist DAU 5884, and was absent in M1/M3 receptor double-KO mice, identifying M3 receptors as primary oxo-m targets. Our findings allow for the possibility that cholinergic signaling in the cerebellum--which may result from long-term depression (LTD)-related disinhibition of cholinergic neurons in the vestibular nuclei--suppresses presynaptic LTP to prevent an up-regulation of transmitter release that opposes the reduction of postsynaptic responsiveness. This modulatory capacity of mAChR signaling could promote the functional penetrance of LTD.

High density of nicotinic receptors in the cingulo-insular network

The nicotinic system plays an important role in ordinary cognition, particularly in attention. The main nicotinic receptor in the human brain is the heteromeric α4β2 neuronal nicotinic acetylcholine receptor (nAChR), which is distributed throughout the brain, with an especially high density in the thalamus and brainstem. Despite the important role of α4β2 nAChRs in various physiological functions and pathological conditions, their distribution in the human cortex remains poorly characterized. We assessed the in vivo distribution of α4β2 nAChRs in the human cortex in a group of seven non-smoking healthy subjects, using 2-[(18)F]F-A-85380 PET and a volume-of-interest-based analysis. We showed that cortical nAChR density was highest in the insular and anterior cingulate cortices. In functional magnetic resonance imaging studies, these two cortical regions and the thalamus have been shown to be highly correlated during the resting state and various tasks. Here, we also directly assessed nAChR density in this cingulo-insular network as defined in an independent dataset using resting-state functional connectivity, and compared it to other control-related networks, to the default mode network as well as to sensory and motor networks. Receptor density was significantly higher in the cingulo-insular network. This network has been suggested to maintain a variety of foundational capacities fundamental to cognitive function. The demonstration of a high nAChR density in the insular and anterior cingulate cortices reflects a particular neurochemical organization of the cingulo-insular network, and suggests an important role of the nicotinic receptors in its functions.

Widespread decreases in cortical muscarinic receptors in a subset of people with schizophrenia

These studies were undertaken to investigate the selectivity of cortical muscarinic receptor radioligand binding in muscarinic M(1) and M(4) receptor knockout mice and to determine whether a marked decrease in [(3)H]pirenzepine binding in Brodmann's area (BA) 9 from a subset of people with schizophrenia was predictive of decreased muscarinic receptors in other central nervous system (CNS) regions. Our data show that, under the conditions used, [(3)H]pirenzepine binding was highly selective for the muscarinic M(1) receptor whereas both [(3)H]AF-DX 386 and [(3)H]4DAMP had less discriminatory power. In addition, the data suggest that a marked decrease in [(3)H]pirenzepine binding in BA 9 from a subset of people with schizophrenia is predictive of decreases in muscarinic receptors in other CNS regions. However, there were some region-specific decreases in muscarinic receptors in tissue from people with schizophrenia who were outside this subset. These data add to a growing body of evidence suggesting there are widespread decreases in muscarinic receptors in the CNS of some subjects with schizophrenia, as demonstrated by neuroimaging. Our data have implications for understanding the potential clinical utility of drugs directed at the orthosteric and allosteric sites of muscarinic receptors to treat schizophrenia.

Molecular Neurobiology of Depression: PET Findings on the Elusive Correlation with Symptom Severity

Molecular mechanisms in the brain are assumed to cause the symptoms and severity of neuropsychiatric disorders. This review concerns the elusive nature of relationships between the severity of depressive disorders and neuromolecular processes studied by positron emission tomography (PET). Recent PET studies of human depression have focused on serotonergic, dopaminergic, muscarinic, nicotinic, and GABAergic receptors, as well as central processes dependent on monoamine oxidase, phosphodiesterase type 4, amyloid plaques, neurofibrillar tangles, and P-glycoprotein. We find that reliable causal links between neuromolecular mechanisms and relief from depressive disorders have yet to be convincingly demonstrated. This situation may contribute to the currently limited use of PET for exploring the neuropathways that are currently viewed as being responsible for beneficial effects of antidepressant treatment regimes.

Progressive supranuclear palsy: in vivo SPECT imaging of presynaptic vesicular acetylcholine transporter with [123I]-iodobenzovesamicol

PURPOSE

To evaluate the integrity of brain cholinergic pathways in vivo in patients with progressive supranuclear palsy (PSP) by measuring the vesicular acetylcholine transporter expression at single photon emission computed tomography (SPECT) with [123I]-iodobenzovesamicol.

MATERIALS AND METHODS

All participants provided informed written consent according to institutional human ethics committee guidelines. Ten patients with PSP and 12 healthy volunteers underwent dynamic [123I]-iodobenzovesamicol SPECT and magnetic resonance (MR) imaging. CT and MR images were used to register the dynamic SPECT image to the Montreal Neurologic Institute brain template, which includes the regions of interest of the striatum and the septo-hippocampal, innominato-cortical, and ponto-thalamic cholinergic pathways. For each region of interest, pharmacokinetic modeling of regional time activity curves was used to calculate [123I]-iodobenzovesamicol to vesicular acetylcholine transporter binding potential value, proportional to vesicular acetylcholine transporter expression.

RESULTS

When compared with control participants, patients with PSP had binding potential values that were unchanged in the striatum and septohippocampal pathway, significantly lower in the anterior cingulate cortex (P=.017) in the innominatocortical pathway, and significantly decreased in the thalamus (P=.014) in the pontothalamic cholinergic pathway. In addition, binding potential values in the thalamus were positively correlated with those in the pedunculopontine nucleus (ρ=0.81, P<.004) and binding potential values in both the thalamus (ρ=-0.88, P<.001) and pedunculopontine nucleus (ρ=-0.80, P<.010) were inversely correlated with disease duration.

CONCLUSION

Cholinergic pathways were differentially affected in the PSP group, with a significant alteration of pontothalamic pathways that increased with disease progression at both cell body and terminal levels, while the innominatocortical pathway was only mildly affected, and the septohippocampal pathway and the striatum were both preserved.

Cholinergic deficit and response to donepezil therapy in Parkinson's disease with dementia

BACKGROUND

Although donepezil, an acetylcholinesterase inhibitor, has been proved to be effective in ameliorating cognitive impairment in Parkinson's disease with dementia (PDD), the responsiveness of patients to donepezil therapy varies. [5-(11)C-methoxy]donepezil, the radiolabeled form of donepezil, is a ligand for positron emission tomography (PET), which can be exploited for the quantitative analysis of donepezil binding to acetylcholinesterase and for cholinergic imaging.

OBJECTIVES

To investigate the deficits of the cholinergic system in the brain in PDD and its association with response to donepezil therapy.

METHODS

Twelve patients with PDD and 13 normal control subjects underwent [5-(11)C-methoxy]donepezil-PET imaging. For patients with PDD, daily administration of donepezil was started after [5-(11)C-methoxy]donepezil-PET imaging and continued for 3 months.

RESULTS

In the PDD group, the mean total distribution volume of the cerebral cortices was 22.7% lower than that of the normal control group. The mean total distribution volume of the patients with PDD was significantly correlated with improvement of visuoperceptual function after 3 months of donepezil therapy.

CONCLUSION

The results suggest that donepezil therapy is more effective in patients with less decrease in acetylcholinesterase, a binding site of donepezil, at least in the specific cognitive domain.

Synaptic localization of acylpeptide hydrolase in adult rat telencephalon

Acylpeptide hydrolase (ACPH), a serine protease present in the central nervous system (CNS), is believed to have a function in modulating synaptic plasticity, cleavage of beta amyloid peptide and degradation of aggregated oxidized proteins. In this report, we demonstrate for the first time the presence of ACPH in the synapse and its preferential localization at the pre-synaptic side. We isolated subcellular fractions from the rat telencephalon enriched in pre- versus post-synaptic components by using differential centrifugation steps to evaluate ACPH catalytic activity and expression level. Relative ACPH levels were determined by Western blot techniques while antibodies against synaptophysin and PSD-95 were used as positive pre- and post-synaptic markers, respectively. Our results show that ACPH protein levels are significantly increased at the synapse, which correlates with a 56% increase in ACPH activity. Furthermore, Western blot experiments show that ACPH is preferentially located at the pre-synaptic side and this is consistent with the increase of its enzymatic activity in fractions enriched in pre-synaptic components. These results give new insights regarding the localization and a putative role of ACPH in the CNS.

Involvement of the cholinergic system in conditioning and perceptual memory

The cholinergic systems play a pivotal role in learning and memory, and have been the centre of attention when it comes to diseases containing cognitive deficits. It is therefore not surprising, that the cholinergic transmitter system has experienced detailed examination of its role in numerous behavioural situations not least with the perspective that cognition may be rescued with appropriate cholinergic 'boosters'. Here we reviewed the literature on (i) cholinergic lesions, (ii) pharmacological intervention of muscarinic or nicotinic system, or (iii) genetic deletion of selective receptor subtypes with respect to sensory discrimination and conditioning procedures. We consider visual, auditory, olfactory and somatosensory processing first before discussing more complex tasks such as startle responses, latent inhibition, negative patterning, eye blink and fear conditioning, and passive avoidance paradigms. An overarching reoccurring theme is that lesions of the cholinergic projection neurones of the basal forebrain impact negatively on acquisition learning in these paradigms and blockade of muscarinic (and to a lesser extent nicotinic) receptors in the target structures produce similar behavioural deficits. While these pertain mainly to impairments in acquisition learning, some rare cases extend to memory consolidation. Such single case observations warranted replication and more in-depth studies. Intriguingly, receptor blockade or receptor gene knockout repeatedly produced contradictory results (for example in fear conditioning) and combined studies, in which genetically altered mice are pharmacological manipulated, are so far missing. However, they are desperately needed to clarify underlying reasons for these contradictions. Consistently, stimulation of either muscarinic (mainly M(1)) or nicotinic (predominantly α7) receptors was beneficial for learning and memory formation across all paradigms supporting the notion that research into the development and mechanisms of novel and better cholinomimetics may prove useful in the treatment of neurodegenerative or psychiatric disorders with cognitive endophenotypes.

Acetylcholine: future research and perspectives

Ever since the initial description of chemical transmission in the early part of the 20th century and the identification of acetylcholine (ACh) as the first such transmitter, interests grew to define the multiple facets of its functions. This multitude is only partially covered here, but even in the areas preselected for this special issue, research on the cholinergic system is still thriving. Notwithstanding an impressive amount of knowledge that has been accumulated, partly triggered by the cholinergic hypothesis of Alzheimer's disease (AD [1]), the different reviews in this issue not only summarise our current state of the art, they also highlight that this field has still large potential for future development. Taken from these reviews, we here pinpoint several topics fit for future attention.