UMLS:C0036341 - FACTA Search

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Query: UMLS:C0036341 (schizophrenia)
60,220 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The active moiety of clozapine, the prototypical antipsychotic drug, consists of clozapine and its major metabolite, N-desmethylclozapine (NDMC). Previous studies have suggested that NDMC may be more important than the patent compound itself for the improvement in cognition in patients with schizophrenia treated with clozapine. While the pharmacology of clozapine and NDMC are similar in most respects, NDMC has been shown to be an M1 muscarinic receptor partial agonist whereas clozapine is an M1 antagonist in vitro and in vivo. We hypothesized that NDMC may improve cognition by increasing dopamine (DA) and acetylcholine (ACh) release in medial prefrontal cortex (mPFC) via direct stimulation of M1 receptors, whereas both NDMC and clozapine itself would do so by other mechanisms as well, and that clozapine would inhibit the M1 agonist effect of NDMC. In the present study, using microdialysis in awake, freely moving rats, we found that NDMC at doses of 10 and 20, but not 5 mg/kg, significantly increased DA and ACh release in the mPFC and HIP, but not in the nucleus accumbens (NAC). The M1-preferring antagonist, telenzepine (3 mg/kg), completely blocked NDMC (10 mg/kg)-induced increases in cortical DA and ACh release. Clozapine (1.25 mg/kg), which by itself had no effect on DA or ACh release in the cortex, blocked NDMC (10 mg/kg)-induced ACh, but not DA, release in the mPFC. The 5-HT1A receptor antagonist, WAY100635 (0.2 mg/kg) blocked NDMC (20 mg/kg)-induced cortical DA but not ACh release. These findings suggest that: (1) NDMC is an M1 agonist while clozapine is an M1 antagonist in vivo; (2) M1 agonism of NDMC can contribute to the release of cortical ACh and DA release; (3) NDMC, because of its M1 agonism, may more effectively treat the cognitive impairments observed in schizophrenia than clozapine itself; and (4) M1 receptor agonism may be a valuable target for the development of drugs that can improve cognitive deficit in schizophrenia, and perhaps other neuropsychiatric disorders as well.
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PMID:N-desmethylclozapine, a major metabolite of clozapine, increases cortical acetylcholine and dopamine release in vivo via stimulation of M1 muscarinic receptors. 1590 Mar 18

Muscarinic M1, but not M4, receptors have been shown to be decreased in Brodmann's area (BA) 9 obtained postmortem from subjects with schizophrenia. This study extends that data by measuring levels of muscarinic M2 and M3 receptor protein and mRNAs in BA 9 and BA 40 from the same cohorts of subjects used in the study of M1 and M4 receptors. In addition, the ability of carbachol to stimulate muscarinic receptors that signal through the Gi/o G-proteins was measured in BA 9 from the same cohorts of subjects. There were no changes in levels of muscarinic M2 or M3 protein or M3 mRNA with diagnosis in either CNS region. M2 receptor mRNA could not be detected in BA 9 or BA 40. Finally, carbachol-stimulated GTPgammaS binding did not differ between the diagnostic cohorts in BA 9 (p = 0.64). These data add considerable weight to the argument that the muscarinic M1 receptor is the muscarinic receptor predominantly affected in BA 9 by the pathology of schizophrenia. Given the widespread changes in muscarinic receptors identified in the CNS of subjects of schizophrenia using functional neuroimaging it remains possible that receptors other than the M1 receptor may be altered in different CNS regions.
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PMID:No change in cortical muscarinic M2, M3 receptors or [35S]GTPgammaS binding in schizophrenia. 1621 78

The case of HM, a man with intractable epilepsy who became amnesic following bilateral medial temporal lobe surgery nearly half a century ago has instigated ongoing research and theoretical speculation on the nature of memory and the role of the hippocampus. Neuropsychological testing showed that although HM had extensive anterograde memory loss he could still acquire motor and cognitive skills implicitly, but could not remember the context of this learning. This has lead to declarative and procedural descriptions of the memory process. Cholinergic and monoaminergic neurotransmitter systems have also been implicated in the memory process and anticholinergic drugs traditionally have been associated with impairment of declarative memory. The cholinergic hypothesis of Alzheimer's disease is a classic example of an application of these neuropharmacological findings. In schizophrenia, preattentive deficits have been amply demonstrated by unconscious priming studies. Memory processes are also impaired in these patients. Dopamine, glutamate and even cholinergic dysfunction has been implicated in the clinical picture of schizophrenia. The present paper will attempt to bring together both the anatomical and pharmacological data from these disparate fields of research under a cohesive theory of cognition and memory. A hypothesis is presented for an inverse relationship between monoaminergic and cholinergic systems in the modulation of implicit (unconscious) and explicit (conscious) cognitive processes. It is postulated that muscarinic cholinergic receptors and monoaminergic systems facilitate unconscious and conscious processes, respectively, and they disfacilitate conscious and unconscious processes, respectively (the purported inverse relationship). In fact, the muscarinic and monoaminergic modulations of a neural network are proposed to be finely balanced such that, if, the activity of one receptor system is modified then this by necessity has effects on the other system. It takes into account receptor subtypes and their effects mediated through excitatory and inhibitory G-protein complexes. For example, m1/D2 and D1/m4 paired receptor subtypes, colocalized on separate neurons would have opposing functional effects. A theory is then presented that the critical underlying pathophysiology of schizophrenia involves a hypofunctional muscarinic cholinergic system, which induces abnormal facilitation of monoaminergic subsystems such as dopamine (e.g., a decrease in m1R function would potentiate D2R function). This extends the idea of an inverted U function for optimal monoaminergic concentrations. Not only would this impair unconscious preattentive processes, but according to the hypothesis, explicit cognition as well including memory deficits and would underlie the mechanism of psychosis. Contrary to current thinking a different view is also presented for the role of the hippocampus in the memory process. It is postulated that long-term explicit memory traces in the neocortex are laid down by phasic coactivation of forebrain projecting monoaminergic systems above some basal firing rate, such as the rostral serotonergic raphe, which projects diffusely to the cortex and according to a modified Hebbian principle. This is the proposed principal function of the hippocampal theta rhythm. The phasic activation of the cholinergic basal forebrain is mediated by projections from a separate cortical structure, possibly the lateral prefrontal cortex. Phasic muscarinic receptor activation is proposed to strengthen implicit memory traces (at a synaptic level) in the neocortex. Thus, the latter are spared by medial temporal surgery explaining the dissociation of explicit from implicit memory.
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PMID:Neuropharmacology of cognition and memory: a unifying theory of neuromodulator imbalance in psychiatry and amnesia. 1630 Sep 5

Clinical studies suggest that adjunct galantamine may improve negative and cognitive symptoms in schizophrenia. These symptoms may be related to impaired dopaminergic function in the prefrontal cortex. Indeed, galantamine has been shown to increase dopamine release in vitro. Galantamine is an allosteric modulator of nicotinic acetylcholine receptors (nAChRs) and, at higher doses, an acetylcholine esterase (AChE) inhibitor. We have previously shown that nicotine, through stimulation of nAChRs in the ventral tegmental area (VTA), activates midbrain dopamine neurons and, hence, potentiation of these receptors could be an additional mechanism by which galantamine can activate dopaminergic pathways. Therefore, the effects of galantamine (0.01-1.0 mg/kg s.c.) on dopamine cell firing were tested in anaesthetized rats. Already at a low dose, unlikely to result in significant AchE inhibition, galantamine increased firing activity of dopaminergic cells in the VTA. The effect of galantamine was prevented by the nAChR antagonist mecamylamine (1.0 mg/kg s.c.), but not the muscarinic receptor antagonist scopolamine (0.1 mg/kg s.c.), and it was not mimicked by the selective AChE inhibitor donepezil (1.0 mg/kg s.c.). Our data thus indicate that galantamine increases dopaminergic activity through allosteric potentiation of nAChRs. Galantamine's effect was also prevented by the alpha7 nAChR antagonist methyllycaconitine (6.0 mg/kg i.p.) as well as the N-methyl-D-aspartate antagonist CGP39551 (2.5 mg/kg s.c.), indicating a mechanism involving presynaptic facilitation of glutamate release. In parallel microdialysis experiments, galantamine was found to increase extracellular levels of dopamine in the medial prefrontal cortex. These results may have bearing on the enhancement of negative and cognitive symptoms in schizophrenia.
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PMID:Galantamine enhances dopaminergic neurotransmission in vivo via allosteric potentiation of nicotinic acetylcholine receptors. 1664 37

The posterior cingulate cortex (PCC) has recently been implicated in the pathophysiology of schizophrenia, through both animal and human studies. We have recently shown abnormal glutamate, GABA, and muscarinic receptor binding in the PCC in schizophrenia. In addition, there is evidence for an abnormal endogenous cannabinoid system in schizophrenia. The endogenous cannabinoid system, including CB1 receptors, is proposed to play a role in modulating neurotransmission via affecting the release of a variety of neurotransmitters, (e.g. GABA). In the present study, we used quantitative autoradiography to investigate the binding of [(3)H]CP-55940 to CB1 receptors in the PCC in schizophrenia subjects compared to controls. A significant 25% increase in CB1 binding was found in the superficial layers (layer I, II) of the PCC of schizophrenia subjects compared to controls, none of whom had recently used cannabis. There was no statistical difference in CB1 binding in the deeper layers (layers III-VI) between the two groups. There were no significant correlations between CB1 binding density and age, PMI, pH, brain weight, freezer storage time, or final recorded antipsychotic drug dose. These results show an increase in CB1 receptor density in the PCC in schizophrenia, and therefore provide support for a role of the endogenous cannabinoid system in schizophrenia.
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PMID:Increased cannabinoid receptor density in the posterior cingulate cortex in schizophrenia. 1671 Jun 82

As part of a continuing effort to design and synthesize highly selective muscarinic agonists for different muscarinic receptor subtypes, several tetra(ethylene glycol)(3-methoxy-1,2,5-thiadiazol-4-yl) [3-(1-methyl-1,2,5,6-tetrahydropyrid-3-yl)-1,2,5-thiadiazol-4-yl] ether (1) analogues were prepared and characterized. Different analogues were synthesized having hydrophilic spacers of di-, tri-, tetra-, penta(ethylene glycol) and tri(propylene glycol) separating the 1,2,5,6-tetrahydropyridine ring from the terminal heterocycle, which was either a 1,2,5-thiadiazole or 1,2,4-thiadiazole ring. Chimeric receptor and molecular modeling studies also were conducted to determine how the ligands interact with muscarinic receptors. The studies revealed that varying the distance of the terminal thiadiazole and the positioning of the methoxy group can increase binding affinity for certain muscarinic receptor subtypes (at M(2) for 13d and M(4) for 1) and enhance functional efficacy at M(4) receptors for 13e and 18b. Moreover, compound 1 exhibited antipsychotic activity as assessed by reversal of apomorphine-induced sensory motor gating deficits, suggesting potential utility in the treatment of schizophrenia.
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PMID:Design and synthesis of novel derivatives of the muscarinic agonist tetra(ethylene glycol)(3-methoxy-1,2,5-thiadiazol-4-yl) [3-(1-methyl-1,2,5,6-tetrahydropyrid-3-yl)-1,2,5-thiadiazol-4-yl] ether (CDD-0304): effects of structural modifications on the binding and activity at muscarinic receptor subtypes and chimeras. 1714 81

Social withdrawal is the first sign and key component of the negative symptoms of schizophrenia. The efficacy of risperidone, an atypical antipsychotic, on the symptom is practically limited by dose-dependent side effects in clinical trials, therefore there is the need for adjuvant treatments. In the present study, we aimed to investigate the synergistic effect and mechanism of risperidone and galantamine, which is a nicotinic acetylcholine receptor (nAChR)-allosteric modulator and a modest cholinesterase inhibitor, on phencyclidine (PCP)-treated mouse model of social withdrawal. At non-effective doses by themselves, co-administration of galantamine (0.05mg/kg) and risperidone (0.05mg/kg) showed synergistic effects on PCP-induced impairments of social interaction and dopamine release in the medial prefrontal cortex (mPFC). The behavioral synergistic effect was abolished by the administration of a dopamine-D(1) receptor antagonist, SCH 23390 (0.02mg/kg, systemic; or 0.02microg/0.5microL/mouse, intra-mPFC), and a nAChR antagonist, mecamylamine (3mg/kg), but not a muscarinic receptor antagonist, scopolamine (0.1mg/kg). Mecamylamine (3mg/kg) also abolished the synergistic effect on dopamine release in the mPFC. We conclude that galantamine may have synergistic effect with risperidone on the negative symptom of social withdrawal in schizophrenia, which is mediated by dopamine-D(1) receptors in the mPFC through nAChR activation-increased dopamine release.
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PMID:Synergistic effect of galantamine with risperidone on impairment of social interaction in phencyclidine-treated mice as a schizophrenic animal model. 1731 62

Cholinergic dysfunction has been implicated as a putative contributing factor in the pathogenesis of schizophrenia. Recently, we showed that cholinergic denervation of the neocortex in adult rats leads to a marked increase in the behavioral response to amphetamine. The main objective of this study was to investigate if the enhanced locomotor response to amphetamine seen after cortical cholinergic denervation was paralleled by an increased amphetamine-induced release of dopamine in the nucleus accumbens and/or striatum. The corticopetal cholinergic projections were lesioned by intraparenchymal infusion of 192 IgG-saporin into the nucleus basalis magnocellularis of adult rats. Amphetamine-induced dopamine release in the nucleus accumbens or striatum was monitored by in vivo microdialysis 2 to 3 weeks after lesioning. We found that cholinergic denervation of the rat neocortex leads to a significantly increased amphetamine-induced dopamine release in the nucleus accumbens. Interestingly, the cholinergic lesion did not affect amphetamine-induced release of dopamine in the striatum. The enhanced amphetamine-induced dopamine release in the nucleus accumbens in the cholinergically denervated rats could be reversed by administration of the muscarinic agonist oxotremorine, but not nicotine, prior to the amphetamine challenge, suggesting that loss of muscarinic receptor stimulation is likely to have caused the observed effect. The results suggest that abnormal responsiveness of dopamine neurons can be secondary to cortical cholinergic deficiency. This, in turn, might be of relevance for the pathophysiology of schizophrenia and provides a possible link between cholinergic disturbances and alteration of dopamine transmission.
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PMID:Cortical cholinergic deficiency enhances amphetamine-induced dopamine release in the accumbens but not striatum. 1771 6

Schizophrenia is widely acknowledged as being a syndrome, consisting of an undefined number of diseases probably with differing pathologies. Although studying a syndrome makes the identification of an underlying pathology more difficult; neuroimaging, neuropsychopharmacological and post-mortem brain studies all implicate muscarinic acetylcholine receptors (CHRM) in the pathology of the disorder. We have established that the CHRM1 is selectively decreased in the dorsolateral prefrontal cortex of subjects with schizophrenia. To expand this finding, we wanted to ascertain whether decreased cortical CHRMs might (1) define a subgroup of schizophrenia and/or (2) be related to CHRM1 genotype. We assessed cortical [(3)H]pirenzepine binding and sequenced the CHRM1 in 80 subjects with schizophrenia and 74 age sex-matched control subjects. Kernel density estimation showed that [(3)H]pirenzepine binding in BA9 divided the schizophrenia, but not control, cohort into two distinct populations. One of the schizophrenia cohorts, comprising 26% of all subjects with the disorder, had a 74% reduction in mean cortical [(3)H]pirenzepine binding compared to controls. We suggest that these individuals make up 'muscarinic receptor-deficit schizophrenia' (MRDS). The MRDS could not be separated from other subjects with schizophrenia by CHRM1 sequence, gender, age, suicide, duration of illness or any particular drug treatment. Being able to define a subgroup within schizophrenia using a central biological parameter is a pivotal step towards understanding the biochemistry underlying at least one form of the disorder and may represent a biomarker that can be used in neuroimaging.
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PMID:Decreased cortical muscarinic receptors define a subgroup of subjects with schizophrenia. 1831 61

Pharmacological evidence has implicated cholinergic dysfunction in the manifestation of psychotic symptoms. The purpose of the present study was to clarify the roles of muscarinic and nicotinic receptors in several animal models of schizophrenia. A muscarinic receptor agonist, oxotremorine (0.03-0.3 mg/kg), reversed hyperlocomotion in mice and disruption of prepulse inhibition (PPI) caused by methamphetamine in rats, similar to a typical antipsychotic drug, haloperidol (0.1-0.3 mg/kg). In addition to modulating hyperdopaminergic function, oxotremorine as well as clozapine (3-10 mg/kg) reversed the disruption of PPI caused by ketamine, an N-methyl-D-aspartate antagonist in rats, which mimics the clinical symptoms of schizophrenia. One of the spontaneous mouse models, DBA/2J exhibited lower PPI than C57BL/6J. Oxotremorine (0.03-0.06 mg/kg) increased PPI in DBA/2J but not C57BL/6J. On the other hand, a nicotinic receptor agonist, nicotine (0.06-0.6 mg/kg), exhibited no effects on the four animal models of symptoms of schizophrenia we tested. These findings suggest that muscarinic receptors play important roles in animal models to examine sensory gating which is known to be disrupted in schizophrenic patients, and hence activation of muscarinic receptors may provide an alternative approach for the treatment of psychotic symptoms in addition to classical antipsychotics.
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PMID:Antipsychotic property of a muscarinic receptor agonist in animal models for schizophrenia. 1865 95

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