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

The present study examined the effects of local microinjections of the GABA chloride channel blocker Picrotoxin into the superior colliculus (SC) on prepulse inhibition (PPI) of the acoustic startle response (ASR) in rats. PPI is a useful model for the investigation of the neuronal basis of sensorimotor gating which is deficient in some psychiatric disorders, such as schizophrenia. Blockade of GABA activity within the SC by Picrotoxin injections (leading to a moderate stimulation of the SC) significantly enhanced PPI without affecting the ASR baseline amplitude or the spontaneous motor activity. Based on these results we discuss the role of the SC in a hypothetical neuronal circuit mediating PPI of the ASR.
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PMID:Enhancement of prepulse inhibition after blockade of GABA activity within the superior colliculus. 1037 79

Repeated administration of amphetamine or methamphetamine (MA) results in an augmentation of its locomotor-activating effects, which is a phenomenon known as behavioral sensitization. In humans, chronic use of the drug elicits a progressive augmentation in paranoid symptoms that closely resemble schizophrenia. Behavioral sensitization has some common properties with other forms of neural plasticity such as kindling, learning and long-term potentiation (LTP). The author examined in the present study whether behavioral sensitization could be blocked by GABA-benzodiazepine agonists, known to inhibit kindling, learning as well as LTP. Rats (Male Wistar-King rats) treated with MA (1 mg/kg, s.c.) for 10 days displayed significantly enhanced motor activity when tested with MA (1 mg/kg) after a 7-8 day withdrawal period indicating the acquisition of behavioral sensitization. Treatment with clonazepam (CZP) (0.5 and 2.0 mg/kg), a GABA-benzodiazepine agonist, prior to MA administration prevented the acquisition of sensitization. In contrast, treatment with flumazenil (Flu) (10 mg/kg), a GABA-benzodiazepine antagonist, prior to MA administration did not affect the acquisition of sensitization. And treatment with Flu prior to CZP administration suppressed the inhibitory effect of CZP. CZP had no effect on the expression of sensitization in the sensitized rats, when given prior to the MA readministration. These results suggest that stimulation of GABA-benzodiazepine receptors plays a role in the acquisition but not in the expression of behavioral sensitization.
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PMID:The role of gamma-aminobutyric acid (GABA)-benzodiazepine neurotransmission in an animal model of methamphetamine-induced psychosis. 1038 62

The medial septum, diagonal bands, ventral pallidum, substantia innominata, globus pallidus, and internal capsule contain a heterogeneous population of neurons, including cholinergic and noncholinergic (mostly GABA containing), corticopetal projection neurons, and interneurons. This highly complex brain region, which constitutes a significant part of the basal forebrain has been implicated in attention, motivation, learning, as well as in a number of neuropsychiatric disorders, such as Alzheimer's disease, Parkinson's disease, and schizophrenia. Part of the difficulty in understanding the functions of the basal forebrain, as well as the aberrant information-processing characteristics of these disease states lies in the fact that the organizational principles of this brain area remained largely elusive. On the basis of new anatomical data, it is proposed that a large part of the basal forebrain corticopetal system be organized into longitudinal bands. Considering the topographic organization of cortical afferents to different divisions of the prefrontal cortex and a similar topographic projection of these prefrontal areas to basal forebrain regions, it is suggested that several functionally segregated cortico-prefronto-basal forebrain-cortical circuits exist. It is envisaged that such specific "triangular" circuits could amplify selective attentional processing in posterior sensory cortical areas.
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PMID:The basal forebrain corticopetal system revisited. 1041 58

Propagation and prolongation of rapid neuronal discharge underlies the epilepsies. However, episodic focal rapid neuronal discharges limited to discrete nuclei and pathways of the amygdala-hippocampal-septal-hypothalamic networks are the language of physiologic message systems for endocrine regulation and reproductive activities vital to the survival of the organism and the species. To prevent prolongation and propagation of physiologic pulsed excitation to areas outside specific networks and resultant epileptic seizures, these discharges must be limited in extent and time by powerful inhibitory processes. The nucleus accumbens, a unit of the extended amygdala, and the monoamines and GABA are components of the inhibitory networks that restrict physiologic rapid discharge in duration and in location. In parallel to the relationship of excessive neuronal excitation to epilepsy, evidence will be presented that excessive inhibition via one or more components of these inhibitory networks or diminished excitation underlies development of some psychoses, including schizophrenia.
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PMID:Epilepsy, schizophrenia, and the extended amygdala. 1041 70

The hypothesis that the pathophysiology of schizophrenia may be associated with a dysfunction in GABA transmission in the human prefrontal cortex was investigated. Human post mortem brain tissue from 10 control cases and six cases of schizophrenia were processed for amino acid analysis and for radioactive in situ hybridization. Laminae III and V of three prefrontal cortical areas were examined in detail, namely Brodmann areas 9, 10 and 11. Of these three areas significant changes in GABAergic markers were found only in areas 9 and 10. Of note, a significant decrease in the tissue content of GABA was observed and this was accompanied by a marked increase in the cellular expression of the GABA(A) receptor alpha-1 subunit messenger RNA and a marked decrease in the expression of human GABA transporter-1, the messenger RNA encoding the neuronal GABA transporter protein. The amino acid analysis data provided in this study coupled with the detailed cellular study of several GABAergic markers in the human prefrontal cortex provide direct evidence in support of a disturbance in GABA transmission in the prefrontal cortex, which may be loosely termed "hypofrontality".
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PMID:Measurement of GABAergic parameters in the prefrontal cortex in schizophrenia: focus on GABA content, GABA(A) receptor alpha-1 subunit messenger RNA and human GABA transporter-1 (HGAT-1) messenger RNA expression. 1046 26

Recent postmortem studies have demonstrated subtle alterations in the hippocampal formation (HIPP) of patients with schizophrenia (SZ). These changes include a decreased density of nonpyramidal neurons (NPs), an increase of the GABAA, but not benzodiazepine receptors and a neuroleptic-dose-related increase of GAD65-IR terminals, particularly in sectors CA3 and CA2. High resolution studies of the GABAA receptor have further suggested that a decrease of disinhibitory GABAergic activity (i.e., GABA-to-GABA) in stratum pyramidale of CA3 may coexist with reduced inhibitory modulation (i.e., GABA-to-excitatory pyramidal neuron) in the stratum oriens of this same sector. These changes could potentially involve excitotoxic damage to interneurons in CA2; but, the precise time frame for the induction of such an injury during pre- versus postnatal life cannot as yet be inferred from the available data. These findings are consistent with reports of abnormal oscillatory rhythms and increased basal metabolic activity in the HIPP of patients with SZ. The fact that patients with manic depression also show a decrease of NPs in CA2 suggests that changes in the GABA system may not be related to a susceptibility gene for SZ. Rather, these alterations could be associated with a nonspecific factor, such as stress, experienced either early in life or much later during adolescence or adulthood. Presumably, there are also changes associated in other transmitter systems that may play a more specific role in establishing the SZ phenotype.
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PMID:Evidence for altered trisynaptic circuitry in schizophrenic hippocampus. 1047 13

This paper presents an overview of recent microscopic studies that have sought to define how limbic circuitry may be altered in postmortem schizophrenic brain. The discussion is organized around several basic questions regarding the manner in which interconnections within and between the anterior cingulate cortex and hippocampal formation and involving the glutamate, GABA and dopamine systems may contribute to the pathophysiology of this disorder. The answers to these questions are used to derive several conclusions regarding circuitry changes in schizophrenia: 1) Schizophrenia is not a 'typical' degenerative disorder, but rather it is one in which excitotoxicity may contribute to neuronal pathology, whether or not cell death occurs; 2) Three or more neurotransmitter systems may be simultaneously altered within a single microcircuit; 3) Each transmitter system may show circuitry changes in more than one region, but such changes may vary on a region-by-region basis; 4) The pathophysiology of schizophrenia may involve 'mis-wirings' in intrinsic circuits (microcircuitry) within a given region, but significant changes are probably also present at the level of interconnections between two or more regions within a network (macrocircuitry); 5) While some microscopic findings appear to be selectively present in schizophrenia and be related to a susceptibility gene for this disorder, others may also be present in patients with bipolar disorder; 6) Although some of the circuitry changes seen in schizophrenia and bipolar disorder seem to be associated with neuroleptic exposure, most are not and may reflect the influence of non-specific environmental factors such as pre- and/or postnatal stress; 7) Normal postnatal changes at the level of both macro- and microcircuitry within the limbic system may serve as 'triggers' for the onset of schizophrenia during adolescence. Taken together, these emerging principles can provide a framework for future postmortem studies of schizophrenic brain.
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PMID:Emerging principles of altered neural circuitry in schizophrenia. 1071 52

The pathophysiology of schizophrenia involves dysfunction of the dorsolateral prefrontal cortex, and this dysfunction may be related to alterations in GABA neurotransmission. Determining the causes and consequences of altered GABA neurotransmission in schizophrenia requires knowledge of which subpopulations of cortical GABA neurons are affected. The chandelier class of GABA neurons are of interest in this regard because their axon terminals form distinctive vertical arrays (termed 'cartridges') which synapse exclusively with the axon initial segments of pyramidal neurons, the principal class of cortical excitatory neurons. We evaluated the integrity of chandelier neuron cell bodies and axon cartridges in PFC areas 9 and 46 of schizophrenic subjects using immunocytochemical techniques and antibodies against parvalbumin and the GABA membrane transporter GAT-1. Schizophrenic subjects did not differ from matched control subjects in the relative density, laminar distribution or size of parvalbumin-containing neurons. In contrast, the density of GAT-1-immunoreactive chandelier neuron axon cartridges was decreased by 40% in schizophrenic subjects compared to both normal controls and subjects with other psychiatric disorders. The axon terminals of other subclasses of GABA neurons did not appear to be similarly affected. These findings suggest that disturbed GABA neurotransmission in the PFC of schizophrenic subjects may be due to a selective alteration of GAT-1 protein in the axon terminals of chandelier neurons.
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PMID:GABAergic local circuit neurons and prefrontal cortical dysfunction in schizophrenia. 1071 53

Schizophrenia is considered to be associated with a hyperfunction of the dopaminergic system and with abnormalities in hippocampal information processing. To clarify whether an enhanced dopaminergic activity alters the hippocampal output, the effect of dopamine (DA) on inhibitory postsynaptic responses (IPSPs) in subicular neurons was examined. DA (200 microM) induced a small and inconsistent hyperpolarization that was accompanied by a reduction of membrane resistance. DA decreased polysynaptic IPSPs which was paralleled by a depression of isolated AMPA/kainate and NMDA receptor-mediated excitatory postsynaptic responses (EPSPs). In contrast, DA had no effect on isolated monosynaptic GABA(A) and GABA(B) receptor-mediated IPSP/Cs. We conclude that in addition to membrane effects, DA decreases polysynaptic IPSPs by attenuating the glutamatergic drive onto subicular interneurons.
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PMID:Dopamine depresses polysynaptic inhibition in rat subicular neurons. 1075 76

Experimental and clinical data suggest that GABA-ergic drugs such as valproate may have a potential role in the treatment of schizophrenia. The authors designed a 21-day prospective, double-blind, randomized, placebo-controlled pilot study of divalproex sodium as add-on treatment to haloperidol in 12 hospitalized patients with acute exacerbations of chronic schizophrenia. All patients received haloperidol 10 mg/day for 3 days and 15 mg/day for the remaining 18 days. In addition, five patients were randomly assigned to receive divalproex augmentation and seven to receive placebo. The divalproex dose was adjusted to a target serum concentration of 75 microg/mL for 2 weeks; placebo replaced divalproex during the third and last weeks to determine any carryover effect. Psychiatric rating scales were administered at baseline and on days 7, 14, and 21. Although the placebo group improved with haloperidol treatment, the divalproex group demonstrated greater improvement. On day 21, the divalproex group had greater improvement from baseline on the Clinical Global Impression Scale (p < or = 0.04), Brief Psychiatric Rating Scale (p < or = 0.13), and Schedule for Assessment of Negative Symptoms scores (p < or = 0.007). After divalproex withdrawal on day 15, a carryover effect was observed during week 3. The authors concluded that the addition of divalproex sodium to standard antipsychotic drugs may prove effective in relieving the symptoms of acute schizophrenia. Future studies may benefit from the design of this pilot study. However, it is premature to apply this augmentation strategy in the clinical setting just yet because of the small sample size and the likely heterogeneity of the disorder.
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PMID:Randomized, placebo-controlled pilot study of divalproex sodium in the treatment of acute exacerbations of chronic schizophrenia. 1083 Oct 24


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