Evidence for involvement of glial cell activity in the control of extracellular D-serine contents in the rat brain

The continuous intra-cortical infusion of a glia toxin, fluorocitrate, at the concentration of 1 mM caused a decrease in the cortical extracellular contents of an intrinsic coagonist for the N-methyl-D-aspartate (NMDA) type glutamate receptor, D-serine, by peaking at 40 min by -25% but produced an increase in those of glycine and L-serine. The attenuated glial activity by fluorocitrate was verified by a marked reduction in the extracellular glutamine contents. The present findings suggest that a group of glial cells such as a population of the protoplasmic astrocytes could, at least in part, participate differently in the regulation of the extracellular release of D-serine and another NMDA coagonist glycine in the medial frontal cortex of the rat.

Distribution of anxiogenic-induced c-Fos in the forebrain regions of developing rats

An anxiogenic or a pharmacological stressor, N-methyl-beta-carboline-3-carboxamide (FG-7142), (20 mg/kg, intraperitoneally injected) induced a dense nuclear c-Fos-like immunoreactivity in the pyriform cortex, cingulate and retrosplenial cortex, layers II-VI of the neocortex, lateral habenula, lateral septum, paraventricular nucleus of the thalamus, striatum, central and medial nucleus of the amygdala, but a sparse c-Fos immunostaining in the hippocampus and layer I of the neocortex in the forebrain of 56-day-old rats. Among these regions, the 8-day-old rats expressed much fewer c-Fos-positive cells in the neocortex, lateral habenula, lateral septum and medial nucleus of the amygdala than the young adult rats following the FG-7142 injection. These differences in the regional distribution of a neuronal activity marker, c-Fos, could reflect the postnatal development of neuronal populations or neuron circuits involved in stress and/or emotional response in the forebrain.

An increase in [3H]SCH23390 binding in the cerebral cortex of postmortem brains of chronic schizophrenics

Abnormalities in neural transmission of dopamine play an important role in development of schizophrenia. Dopamine 1 (D1)-like receptors in 16 areas of the cerebral cortex were measured in the postmortem brains of 13 schizophrenics and 10 controls, using [3H]SCH23390 as a ligand for receptor binding. The specific [3H]SCH23390 bindings were statistically significantly increased in the medial and inferior cortex (Brodmann Area (BA) 20 & 21) and superior parietal cortex (BA 7) of schizophrenic patients, compared to those of the controls. The increases were also marked in the cerebral cortices of off-drug cases of patients with schizophrenia, who had not received antipsychotic drugs for more than 40 days before death. These results suggest that there are changes in dopaminergic transmission through the D1 receptors in the parieto-temporal cortex of schizophrenia, and that the altered functions are involved in the pathophysiology of the disease.

Association analysis of the pituitary adenyl cyclase activating peptide gene (PACAP) on chromosome 18p11 with schizophrenia and bipolar disorders

In neurons, pituitary adenyl cyclase activating peptide (PACAP) stimulates signaling cascades, involving cAMP and calcium. PACAP appears to play a role in up-regulation of tyrosine hydroxylase and dopamine beta-hydroxylase via protein kinase C and/or protein kinase A. Furthermore, the PACAP gene (ADCYAP1) is located in chromosome 18p11, where linkage of bipolar disorders and schizophrenia has been reported. In this study, we scanned the coding region of the PACAP gene for mutations in 24 Japanese patients with schizophrenia and 24 Japanese patients with bipolar disorders. No variant in the coding region was found. One polymorphism, INV3-37A/T, in the third intron was detected. Case-control comparisons revealed no significant association between this polymorphism and schizophrenia or bipolar disorders. This study did not provide evidence for the contribution of the PACAP gene to the etiology of schizophrenia or bipolar disorders in the Japanese population.

An association of the polymorphic repeat of tetranucleotide (TCAT) in the first intron of the human tyrosine hydroxylase gene with schizophrenia in a Japanese sample

Tyrosine hydroxylase (TH) is the rate limiting enzyme in the synthesis of dopamine and norepinephrine. A polymorphic repeat of the tetranucleotide (TCAT) in the first intron of the TH gene may behave as a regulatory element for the gene expression. Allelic fragments of the tandem repeat were typed by a PCR-based process with a pair of primers specific for the polymorphic sequence. The association between the polymorphism and schizophrenia was examined in a Japanese sample. There was a statistically significant association between the polymorphism and schizophrenia in females (chi2 = 26.018, p = 0.010), but not in males (chi2 = 15.995, p = 0.305). The genotype heterozygous for the TH9 and TH6 was significantly decreased in female schizophrenics (chi2 = 5.125, p = 0.0236). These results suggest that TH could be considered as a minor gene contributing to the susceptibility of Japanese female schizophrenia.

An association study between two missense variations of the benzodiazepine receptor (peripheral) gene and schizophrenia in a Japanese sample

The benzodiazepine receptor (peripheral) (BZRP) mainly localized on glial cells plays a role in neurosteroid synthesis, and increases with glial proliferation. We have recently reported a significant decrease in the density of BZRP labeled by [3H] PK 11195 in the postmortem brain of chronic schizophrenics, suggesting that dysfunctions of the BZRP are involved in the pathophysiology of schizophrenia. We screened 11 patients with schizophrenia and 10 controls, which were used in a previous postmortem study, for their genomic sequences of the BZRP gene in order to find DNA sequence variations. One novel missense polymorphism (His162Arg) and another previously reported missense mutation (Ala147Thr) were detected. An association study of the identified variations was then performed in an extended Japanese sample of 304 schizophrenic patients and 369 controls. While there was an increased tendency in the frequency of the 162Arg allele of schizophrenics compared to that of the controls (p = 0.0603), no statistically significant association with schizophrenia was observed in the Ala147Thr allele (p = 0.1016). These results do not suggest that the two missense polymorphisms play a major role in the genetic predisposition of schizophrenia in the Japanese sample.

No association of two missense variations of the benzodiazepine receptor (peripheral) gene and mood disorders in a Japanese sample

The benzodiazepine receptor (peripheral) (BZRP) plays an important role in the steroid syntheses of the adrenal glands and brain, which is possibly involved in the pathophysiology of mood disorders. We evaluated an association study between two missense variations of the BZRP gene and mood disorders in a Japanese sample. However, no statistically significant associations with either bipolar disorders or depressive disorders were observed in the allele frequencies, genotype counts, or haplotype distributions for the two variations, although the present sample size had a moderate power (0.46-0.86). These results do not suggest that the BZRP gene plays a role in the genetic predisposition of affective disorders.

Evidence for association of the myo-inositol monophosphatase 2 (IMPA2) gene with schizophrenia in Japanese samples

In our search for candidate genes for affective disorder on the short arm of chromosome 18, we cloned IMPA2, a previously unreported myo-inositol monophosphatase gene, that maps to 18p11.2. We determined its genomic structure and detected three new single nucleotide polymorphisms (SNPs). In the present study, we screened the gene further to search for additional polymorphisms in Japanese samples and identified seven other SNPs, including a novel missense mutation. These polymorphisms clustered into three regions of the gene. Three relatively informative SNPs, 58G>A, IVS1--15G>A and 800C>T from clusters 1, 2 and 3, respectively, were selected for association tests using a case-control design. The Japanese cohort included 302 schizophrenics, 205 patients with affective disorder and 308 controls. Genotyping was done either by melting curve analysis on the LightCycler or by sequencing. All three SNPs showed significant genotypic association (nominal P = 0.031--0.0001) with schizophrenia, but not with affective disorder. These findings increase the relevance of 18p11.2 to schizophrenia susceptibility because GNAL, which has been shown previously to be implicated in schizophrenia in an independent study, is in close physical proximity to IMPA2. Our findings suggest that IMPA2 or a gene nearby may contribute to the overall genetic risk for schizophrenia among Japanese.

An association study between polymorphism of L1CAM gene and schizophrenia in a Japanese sample

L1CAM, a neural cell adhesion molecule, plays an important role in the development of the central nervous system. The human L1CAM gene is located in Xq28. Mutations in the gene are responsible for a wide spectrum of neurological abnormalities and mental retardation. Schizophrenia may result from early neurodevelopmental abnormalities. We screened 30 male and 30 female schizophrenic patients for their genomic sequence of the L1CAM gene in order to determine the DNA sequence variations. Three novel variations located in exon 18 (10564 G > A, GG/AA at codon 758), intron 11 (8575 A > C), and intron 25 (13504 C > T) were detected. An association study of the identified polymorphisms was then performed in a Japanese sample of 152 male and 115 female patients with schizophrenia and 121 male and 114 female control subjects. A statistically significant increase in the count of the 13504 T-allele was observed in the male patients, compared to the male controls, with no differences in the variations of exon 18 or intron 11. There was no statistically significant change in the distribution of allele or genotype of any variations in the female schizophrenics, in comparison with the female controls. These results suggest that the polymorphism in intron 25 plays a role in the genetic predisposition of male schizophrenia in the Japanese sample.

Increased DOI-induced head shakings in adult rats neonatally treated with MK-801

We examined the effects of neonatal treatment with MK-801 on 1-(2, 5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI)-induced head shaking as well as [(3)H]ketanserin binding in adult rats. Neonatal rats were injected with MK-801 (0.25 mg/kg, s.c., twice daily) or with saline from postnatal days (PND) 7-18. At PND 60, a statistically significant increase in the frequency of head shaking induced by DOI (1.0 mg/kg, s.c.) was observed in the rats neonatally treated with MK-801, compared to saline-treated rats, without any change in the specific [(3)H]ketanserin binding in the frontal cortex. These results suggest that repeated NMDA receptor blockades during the critical period of brain development produce a long lasting hyper-responsiveness in the 5-HT(2A) receptor-mediated behavior, interfering with the development of neural circuits related to the behavior.

Association study on the DUSP6 gene, an affective disorder candidate gene on 12q23, performed by using fluorescence resonance energy transfer-based melting curve analysis on the LightCycler

We introduced a new genotyping method, fluorescence resonance energy transfer-based melting curve analysis on the LightCycler, for the analysis of the gene, DUSP6 (dual specificity MAP kinase phosphatase 6), in affective disorder patients. The DUSP6 gene is located on chromosome 12q22-23, which overlaps one of the reported bipolar disorder susceptibility loci. Because of its role in intracellular signalling pathways, the gene may be involved in the pathogenesis of affective disorders not only on the basis of its position but also of its function. We performed association analysis using a T>G polymorphism that gives rise to a missense mutation (Leu114Val). No evidence for a significant disease-causing effect was found in Japanese unipolars (n = 132) and bipolars (n = 122), when compared with controls (n = 299). More importantly, this study demonstrates that melting curve analysis on the LightCycler is an accurate, rapid and robust method for discriminating genotypes from biallelic markers. This strategy has the potential for use in high throughput scanning for and genotyping of single nucleotide polymorphisms (SNPs).

Association between polymorphisms in the type 1 sigma receptor gene and schizophrenia

Several antipsychotic agents such as haloperidol and rimcazole are known to bind to sigma receptors with high affinity, and evidence for a potential link between sigma receptors and the etiology of schizophrenia has been reported. The present study was conducted to systematically search for nucleotide variants of the type 1 sigma receptor gene in 48 schizophrenics. Two polymorphisms were found: GC-241-240TT in the 5' flanking region and Gln2Pro. These two polymorphisms were in nearly complete linkage disequilibrium with each other. The Pro2 variant of the Gln2Pro polymorphism changes the endoplasmic reticulum retention signal motif. These polymorphisms were examined in an extended sample of schizophrenics (n = 308) and controls (n = 433) and a significant association between the presence of the TT/Pro2 haplotype and schizophrenia was observed (odds ratio = 1.27, P = 0.04).

An increase in [3H] CGS21680 binding in the striatum of postmortem brains of chronic schizophrenics

We measured adenosine 2a receptors in basal ganglia of 13 schizophrenics and 10 controls, using [3H] CGS21680 as a ligand for the receptor binding assay. There was a significant increase in the specific [3H] CGS21680 binding in the putamen and caudate, but not in the globus pallidus of externa, of the schizophrenic patients, compared to those of controls. These results provide evidence suggesting that adenosine 2a receptors play a role in the pathophysiology of schizophrenia.

Changes in high K+-evoked serotonin release and serotonin 2A/2C receptor binding in the frontal cortex of rats with thioacetamide-induced hepatic encephalopathy

Serotonergic systems were investigated in the frontal cortex of rats with thioacetamide (TAA)-induced acute hepatic encephalopathy (HE). Extracellular basal levels of 5-HT showed no difference between control and HE animals, whereas the levels of 5-HIAA were significantly increased in HE rats. Unlike basal levels, high K+-evoked 5-HT release was significantly higher in HE rats than controls. Bmax of (+/-)-1-(2,5-dimethoxy-4-[125I] iodophenyl)-2-aminopropane ([125I] DOI) binding, mainly labeling postsynaptic 5-HT2A receptors, was significantly decreased without any change in Kd in HE rats. These results suggest that there is no change in basal 5-HT release in the cortex of rats with TAA-induced HE despite the increase in intraneuronal 5-HT metabolism and in the size of releasable 5-HT pool, and that serotonergic neurotransmission via 5-HT2A receptor is altered in the brain area of rats with HE.

Decreases in peripheral-type benzodiazepine receptors in postmortem brains of chronic schizophrenics

We measured the peripheral-type benzodiazepine receptors (PBRs), a marker of gliosis, in 26 brain areas (cerebral cortex, thalamus and extrapyramidal system) of the postmortem brains of 13 chronic schizophrenics and 10 controls, using [3H] PK 11195 as a ligand for the receptor assay. The specific [3H] PK 11195 binding was significantly decreased in three brain areas (superior parietal cortex, primary visual area and putamen) of schizophrenics, although there were no changes in the binding in the other brain areas. Scatchard analysis revealed that there were decreases in both the Bmax and Kd of [3H] PK 11195 binding in the brain areas. These results were almost in accordance with a number of neuropathological studies reporting that there was no change or reduction in glial cells in the brain regions of schizophrenics and suggested that the decreased density of PBRs in the brain may be involved in the pathophysiology of schizophrenia, associated with reduced production of neurosteroids coupled to PBRs.

Postnatal development of peripheral-type benzodiazepine receptors in rat brain and peripheral tissues

We examined the postnatal development of peripheral-type benzodiazepine receptors (PBRs), labelled with [3H]PK 11195, in rat brain and peripheral tissues. Specific [3H]PK 11195 binding exhibited a heterogeneous patterns of postnatal development in the rat: three patterns of increase, decrease and no change. Hence, the density of the PBRs can be independently regulated in each tissue during postnatal development, and the postnatal alterations in the density might be parallel with the functional activities coupled to the receptors.

A postmortem study of glycine and its potential precursors in chronic schizophrenics

We have measured the concentrations of glycine and its potential precursors, serine and threonine, in 20 areas of the postmortem brains of chronic schizophrenics and controls using high-performance liquid chromatography by pre-column derivatization with dimethyl-amino-azobenzene sulphonyl chloride. The regional distribution pattern of glycine in the postmortem brains with and without the disease was more similar to that of serine (r = 0.874, P < 0.0001) than to that of threonine (r = 0.476, P < 0.01). A multiple regression analysis with regressor variables including diagnosis, age at death and interval between death and freezing revealed that there is a significant difference between schizophrenics and controls in the contents of these amino acids in a number of brain areas. The level of glycine in the orbitofrontal cortex of schizophrenics was found to be significantly increased in schizophrenics, with a tendency to an increase in that of serine. The increase in glycine was also significantly high in the off-drug group of schizophrenics who had not taken antipsychotics more than 40 days before death. Prominent decreases in both glycine and serine were observed in the somesthetic cortex of the on-drug schizophrenics. Serine was found to be significantly decreased in the putamen of the off-drug schizophrenics. A marked decrease in threonine was also observed in the supramarginal cortex and posterior portion of the lateral occipitotemporal cortex of the off-drug group of schizophrenics and in the putamen of all schizophrenics. The highly similar distribution pattern of glycine and serine in the postmortem brains supports the close coupling of synthesis and metabolism between these chemicals in human brains. The increased content of glycine in the orbitofrontal cortex, the reduced level of serine in the putamen and the decrease in threonine in the cerebral cortices, which were prominent in the off-drug schizophrenics, may be involved in the pathophysiology of schizophrenia.

Effects of chronic treatment with haloperidol on [3H]PK 11195 binding in the rat brain and peripheral tissues

The effects of chronic treatment with haloperidol on [3H]PK 11195 binding and labelling of the peripheral-type benzodiazepine receptor (PBR) in the rat brain and peripheral tissues were investigated using an in vitro receptor binding technique. The intraperitoneal injection with haloperidol (0.3 or 1.0 mg/kg) for 21 days produced a significant increase in the specific [3H]PK 11195 binding only in the olfactory bulb, but not in the other brain areas or peripheral tissues, while single or subchronic (4 days or 7 days) administration with the drug (0.3 mg/kg, i.p.) failed to increase the binding in the olfactory bulb. Scatchard analysis revealed a significant increase in the maximum number of [3H]PK 11195 binding sites in the olfactory bulb after chronic treatment with haloperidol, showing no change in the affinity of the binding. These results suggest that there is an interaction between PBR and the pharmacological actions of haloperidol in the brain area, and that some compensatory mechanism may be involved in the PBR changes.

Increases in strychnine-insensitive glycine binding sites in cerebral cortex of chronic schizophrenics: evidence for glutamate hypothesis

Strychnine-insensitive glycine binding sites, an absolute requirement of the responses mediated by N-methyl-D-aspartate (NMDA) receptors, were measured in the postmortem brains of 13 chronic schizophrenics and 10 controls, using a radiolabeled receptor assay. Specific [3H]glycine binding was significantly increased in six of the 16 areas of the cerebral cortex that were investigated. Scatchard analysis performed in these areas showed a significant increase in the maximum number of binding sites, with no change in the affinity of binding. Multiple regression analysis confirmed that the increase was not due to age at death or interval from death to freezing. The increase was also observed in the off-drug cases of schizophrenics who had not taken antipsychotics for more than 40 days before death. These results suggest that the increases in NMDA-associated glycine binding sites, possibly ascribed to the postsynaptic compensation for impaired glutamatergic neurotransmission, might be implicated in the pathophysiology of schizophrenia.

Excitatory amino acids: implications for psychiatric disorders research

The hyperdopaminergic theory of schizophrenia may account for some types of schizophrenia, but schizophrenia with negative symptoms or resulting in a chronic state of deterioration after repeated relapses cannot be explained by this theory. This minireview first discusses the interactions between dopamine and excitatory amino acid (EAA) neurons to produce abnormal behavior. Secondly, it deals with the influence of the psychotropic drugs on EAA, such as the relationship between phencyclidine and the hypoglutamate theory, the involvement of EAA in behavioral sensitization induced by amphetamines, the interactions between antipsychotic, antidepressant and antianxiety drugs and EAA, considering the possibility of developing newer psychotropic drugs related with EAA. Finally, glutamate receptors measured in postmortem schizophrenic brains are tabulated and the bases of the hypoglutamate hypothesis are discussed.

Measurement of glutamate, aspartate and glycine and its potential precursors in human brain using high-performance liquid chromatography by pre-column derivatization with diethylaminoazobenzene sulphonyl chloride

This paper describes a high-performance liquid chromatographic technique, with dimethylaminoazobenzene sulphonyl chloride derivatization, for the measurement of glutamate, aspartate and glycine and its potential precursors in human brain tissue. The derivatization procedure is simple, sensitive and highly reproducible. The derivatized amino acids are stable and can be analysed by reversed-phase chromatography with visible detection at an absorption wavelength of 436 nm. A preliminary application to the determination of the concentrations of several amino acids in several regions of the human brain is described.

Alpha-[3H]amino-3-hydroxy-5-methylisoxazole-4-propionic acid binding to human cerebral cortical membranes: minimal changes in postmortem brains of chronic schizophrenics

The binding of alpha-[3H]amino-3-hydroxy-5-methylisoxazole-4-propionic acid ([3H]AMPA), a selective ligand for the ion channel-linked quisqualate receptor, was evaluated in Triton X-100-treated membranes of human cerebral cortex. The presence of chaotropic ions produced divergent effects on specific [3H]AMPA binding: A twofold increase in the binding was observed with thiocyanide at 100 mM, although iodide (100 mM) and perchlorate (100 mM) reduced the binding. Chemical modifications of the sulfhydryl group with p-chloromercuriphenylsulfonic acid (PCMBS) produced threefold increases in specific [3H]-AMPA binding in the absence of KSCN as well as in the presence of KSCN. Treatment with dithiothreitol restored the enhanced specific [3H]AMPA binding by PCMBS to the basal level. Although specific [3H]AMPA binding in the absence of KSCN showed a single site (KD = 220 nM, Bmax = 235 fmol/mg of protein), curvilinear Scatchard plots of specific [3H]AMPA binding in the presence of 100 mM KSCN can be resolved into two binding sites with the following parameters: KD1 = 5.82 nM, Bmax1 = 247 fmol/mg of protein; KD2 = 214 nM, Bmax2 = 424 fmol/mg of protein. Quisqualate and AMPA were the most potent inhibitors of the [3H]AMPA binding in the presence of KSCN. Potent inhibitors of the binding included beta-N-oxalylamino-L-alanine (L-BOAA), cysteine-S-sulfate, L-glutamate, 6-cyano-7-nitroquinoxaline-2,3-dione, and 6,7-dinitroquinoxaline-2,3-dione. Kainate, L-homocysteine sulfinic acid, and L-homocysteic acid were active with an IC50 value of a micromolar concentration, whereas L-cysteic acid and L-cysteine sulfinic acid were weakly active.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of chronic administration of MK-801 upon local cerebral glucose utilisation and ligand binding to the NMDA receptor complex

Although clinical use of N-methyl-D-aspartate (NMDA) receptor antagonists will involve prolonged drug administration, knowledge of the functional consequences of chronic NMDA receptor blockade is limited. Local cerebral glucose utilisation was measured in conscious rats in 74 discrete brain regions after chronic administration of (+)-5-methyl-10,11-dihydro-5H-dibenzo [a,d] cyclohepten-5,10-imine (MK-801) (0.5 mg/kg i.p.). Chronic treatment with MK-801 caused small, significant changes in glucose use in 4 of the 74 brain areas; parietal cortex (-13%), frontal cortex (-10%), subthalamic nucleus (-14%) and nucleus accumbens (-17%). These focal alterations in glucose use were not associated with changes in ligand binding to various sites within the NMDA receptor complex (i.e. agonist recognition site, glycine site, ion channel site) which were assessed autoradiographically. The acute effects of MK-801 on glucose utilisation were significantly enhanced after chronic MK-801 in 7 brain regions (e.g. frontal and parietal cortices) and attenuated in 6 brain regions (e.g. nucleus accumbens, hippocampus, posterior cingulate cortex). Neither local enhancement nor attenuation of the acute response to MK-801 was due to alterations in ligand binding to sites within the NMDA receptor complex. The data clearly indicate that the functional consequences of NMDA blockade are altered after chronic MK-801 treatment in an anatomically organised, though complex manner. These adaptive functional changes after chronic MK-801 treatment cannot be attributed readily to alterations in the NMDA receptor complex in affected regions.

Effects of MK-801 upon local cerebral glucose utilisation in conscious rats following unilateral lesion of caudal entorhinal cortex

Local cerebral glucose utilisation was examined in 62 discrete regions of conscious rats following unilateral ibotenic acid lesion of the caudal entorhinal cortex, and subsequent pharmacological challenge with (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (MK-801), a non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist. Fourteen days after unilateral lesion of the entorhinal cortex, there were no significant alterations in local cerebral glucose use except within the lesioned entorhinal cortex (reduced by 31% compared to sham-operated control animals). In sham-operated animals, systemic administration of MK-801 (0.5 mg/kg, i.v.) induced anatomically organised alterations in glucose use with increases in olfactory areas, subicular complex and some limbic areas (posterior cingulate cortex, mammillary body and anteroventral thalamic nucleus), and decreases in the inferior colliculus and neocortex (auditory, sensory-motor, somatosensory and frontal cortices). In animals with unilateral entorhinal cortex lesions, the metabolic response to MK-801 differed significantly from the response to the drug in sham-lesioned animals in a number of regions, viz. hippocampus, molecular layer (ipsilateral to lesion), entorhinal cortex (ipsilateral), dentate gyrus (ipsilateral), presubiculum (bilateral), parasubiculum (bilateral) and nucleus accumbens (bilateral). The ability of MK-801 to reduce glucose use in the neocortex was not altered by entorhinal cortex lesion. These data suggest that the functional consequences of non-competitive NMDA receptor blockade are dependent in some areas upon the integrity of the perforant pathway from the entorhinal cortex to the hippocampus.

Effects of unilateral intrahippocampal injection of MK-801 upon local cerebral glucose utilisation in conscious rats

The effects of unilateral intrahippocampal injections of the non-competitive NMDA receptor antagonist, MK-801, on local cerebral glucose utilisation have been examined in conscious rats using [14C]2-deoxyglucose autoradiography. The intrahippocampal injection of MK-801 (10 nmol) induced significant marked increases in glucose use in the ipsilateral hippocampus molecular layer and dentate gyrus (by 31 and 44%, respectively). Function-related glucose use in brain regions with known neuronal connections with the site of drug administration (e.g. entorhinal cortex, septal nucleus, mamillary body) was minimally altered after intrahippocampal MK-801 administration. Blockade of hippocampal NMDA receptors does not appear to modify activity, as reflected in local glucose utilisation, in hippocampal afferent and efferent circuits in conscious rats.

Effects of MK-801 upon local cerebral glucose utilisation in conscious rats and in rats anaesthetised with halothane

The effects of MK-801 (0.5 mg/kg i.v.), a non-competitive N-methyl-D-aspartate (NMDA) antagonist, upon local cerebral glucose utilisation were examined in conscious, lightly restrained rats and in rats anaesthetised with halothane in nitrous oxide by means of the quantitative autoradiographic [14C]-2-deoxyglucose technique. In the conscious rats, MK-801 produced a heterogenous pattern of altered cerebral glucose utilisation with significant increases being observed in 12 of the 28 regions of gray matter examined and significant decreases in 6 of the 28 regions. Pronounced increases in glucose use were observed after MK-801 in the olfactory areas and in a number of brain areas in the limbic system (e.g., hippocampus molecular layer, dentate gyrus, subicular complex, posterior cingulate cortex, and mammillary body). In the cerebral cortices, large reductions in glucose use were observed after administration of MK-801, whereas in the extrapyramidal and sensory-motor areas, glucose use remained unchanged after MK-801 administration in conscious rats. In the halothane-anaesthetised rats, the pattern of altered glucose use after MK-801 differed qualitatively and quantitatively from that observed in conscious rats. In anaesthetised rats, significant reductions in glucose use were noted after MK-801 in 10 of the 28 regions examined, with no area displaying significantly increased glucose use after administration of the drug. In halothane-anaesthetised rats, MK-801 failed to change the rates of glucose use in the olfactory areas, the hippocampus molecular layer, and the dentate gyrus.(ABSTRACT TRUNCATED AT 250 WORDS)

Alterations in the N-methyl-D-aspartate receptor complex following focal cerebral ischemia

The functional integrity of the N-methyl-D-aspartate receptor complex following focal cerebral ischemia in the rat has been examined at a time when brain tissue is irreversibly damaged. Twelve hours after unilateral permanent middle cerebral artery occlusion, [3H]-MK-801 binding was not significantly altered in the ischemic cerebral cortex compared to sham-operated animals. Moreover, the enhancement of [3H]MK-801 binding by exogenous glutamate was preserved in an area of the brain that was permanently damaged by the ischemic insult.

Effects of NMDA antagonists, MK-801 and CPP, upon local cerebral glucose use

The effects upon cerebral glucose utilisation of (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine (MK-801, a non-competitive N-methyl-D-aspartate (NMDA, receptor antagonist) and 3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP, a competitive NMDA receptor antagonist) were examined in conscious, lightly restrained rats. Cerebral glucose utilisation was assessed quantitatively in 74 brain regions with [14C]2-deoxyglucose autoradiography. The intravenous (i.v.) administration of MK-801 (0.05-5 mg/kg) induced heterogeneous patterns of altered cerebral glucose utilisation with statistically significant increases being observed in 21 brain areas and statistically significant decrease in 8 brain regions. Pronounced dose-related increases in glucose use were observed after MK-801 in the subicular complex, hippocampus molecular layer, dentate gyrus, limbic system (posterior cingulate cortex; mamillary body; anteroventral thalamic nucleus), olfactory areas and substantia nigra (pars reticulata). Glucose use in the neocortex and inferior colliculus was particularly sensitive to reduction by MK-801 administration. The pattern of altered glucose use after administration of CPP (3-30 mg/kg, i.v.) differed markedly from that observed after MK-801 treatment. Statistically significant increases in glucose use after CPP were noted in 11 brain areas and statistically significant decreases in 5 of the regions examined. Regions in which increases were noted after CPP included hippocampus molecular layer, olfactory areas, cochlear nucleus, vestibular nucleus, cerebellar nucleus, superior olives and substantia nigra (pars reticulata). These data indicate that widespread, anatomically organised alterations in cerebral function are associated with the administration of NMDA receptor antagonists despite the minor role normally ascribed to these receptors in conventional fast synaptic transmission. The distinct patterns of response to competitive and non-competitive antagonists may be a reflection of the differential responses of the two modes of receptor blockade to increased glutaminergic transmission.

Differential effects of competitive and non-competitive N-methyl-D-aspartate antagonists on glucose use in the limbic system

The effects on cerebral glucose utilisation of 3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP, a competitive N-methyl-D-aspartate (NMDA) receptor antagonist), and (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine (MK-801, a non-competitive NMDA receptor antagonist) have been examined in conscious rats. Cerebral glucose utilisation was assessed quantitatively with 14C-2-deoxyglucose autoradiography. MK-801 (0.05-5 mg/kg, i.v.) markedly increased glucose use in a number of limbic brain areas such as the mamillary body, anterior thalamic nucleus, posterior cingulate cortex and hippocampus. CPP (3-30 mg/kg, i.v.), in contrast, effected minimal alterations in glucose use in the limbic system. The functional consequences in vivo, as reflected in local cerebral glucose use, of competitive blockade of the NMDA receptor differ markedly from blockade with non-competitive antagonists.

Neurotransmitters, receptors and neuropeptides in post-mortem brains of chronic schizophrenic patients

In the analysis of post-mortem brains of 14 chronic schizophrenic patients and 10 controls, biochemical evidence of a hyperdopaminergic state was found in the basal ganglia of schizophrenics; tyrosine hydroxylase activity was increased with a concomitant increase of homovanillic acid. Unusually high tyrosine hydroxylase activity was noted in 2 schizophrenic cases. The Bmax value of 3H-spiperone binding for schizophrenics was higher than the controls. We also found increased specific binding of 3H-kainic acid to the prefrontal cortex in schizophrenics. A negative correlation existed between 3H-kainic acid binding in the medial frontal cortex, and glutamic acid content in various brain areas. Increased immunoreactivity of substance P was found in more than ten brain areas. Methionine-enkephalin was also increased in three areas of the prefrontal cortex of schizophrenics. These results suggest that the hyperdopaminergic state co-existed with glutamatergic hypofunction and increased neuropeptides in various brain areas of chronic schizophrenic patients.

An increase in striatal Met-enkephalin-like immunoreactivity in neonatally dopamine-depleted rats

A pronounced decrease in dopamine content in both the striatum and the mesolimbic area was observed up to 120 days of age after treatment with 6-hydroxydopamine (100 micrograms, intracisternally) following desipramine pretreatment (20 mg/kg, i.p.) at the 5th postnatal day. In the 6-hydroxydopamine-treated rats, Met-enkephalin-like immunoreactivity in the striatum was found to have increased at 35 and 70 days old, although it remained unchanged at 25 days old. The neonatal administration of 6-hydroxydopamine, however, did not affect the peptide content in the mesolimbic area at any age. These results indicate that the neonatal dopamine reduction changes the Met-enkephalinergic neuronal activity in the striatum at the adult age.

Circadian fluctuations in pain responsiveness and brain Met-enkephalin-like immunoreactivity in the rat

The 24-hour patterns of pain responsiveness and brain Met-enkephalin-like immunoreactivity (MLI) were determined in male Wistar rats housed under a 12-hour light and dark cycle (lights on from 0700 hr to 1900 hr). A circadian rhythm was observed in latencies to hot plate test (55 degrees C), showing the peak level near the onset of the dark phase (2000 hr). Pretreatment with naloxone (5 mg/kg, subcutaneously) decreased the highest latency (2000 hr), but did not change the lowest latency (1100 hr). In the mesolimbic area and the striatum, MLI had a negative correlation with the circadian fluctuation in pain sensitivity. MLI at 2000 hr was reduced significantly compared to that at 1100 hr in the basal ganglia, the frontal cortex and the substantia nigra. These results suggest that the circadian variation in hot plate latencies follows a circadian change in the activity of the endogenous opioid peptides system, and that Met-enkephalin may participate in the enhancement of the opioid system in the brain.

Chronic dietary treatment with antidepressants decrease brain Met-enkephalin-like immunoreactivity in the rat

This report describes the effect of chronic dietary treatment with antidepressants or antimanic drugs on brain Met-enkephalin-like immunoreactivity in the rat. The chronic treatment was administered through food containing 250-1000 mg desipramine, imipramine or clomipramine, 200-800 mg amoxapine or mianserin, 750-1500 mg lithium chloride, or 50 mg haloperidol per 1 kg food for 40 days. In the striatum, each antidepressant decreased the enkephalin content, while lithium or haloperidol, having an antimanic effect, increased the enkephalin content. Following the chronic administration of each antidepressant tested, the concentration of the peptide was reduced in the nucleus accumbens, hypothalamus and thalamus. We further examined the acute effect of the antidepressant (10 or 20 mg/kg) on the striatal enkephalin content at 60 min after a single intraperitoneal injection. The striatal content was decreased after the acute treatment with each antidepressant tested. These results indicate that the antidepressants had an effect on the neuronal activity of Met-enkephalin not only after chronic treatment, but also after acute treatment. The reduction in Met-enkephalin-like immunoreactivity after prolonged treatment with the antidepressant may possible contribute to the mechanism of antidepressive action.

Cold and immobilization stress-induced changes in pain responsiveness and brain Met-enkephalin-like immunoreactivity in the rat

Pain responsiveness and Met-enkephalin-like immunoreactivity (MLI) were studied in the rat after cold (25 degrees C) and immobilization stress for different lengths of time (30 min, 90 min and 180 min). The 30-min stress-induced analgesia (as measured by the tail-flick method), which was partially antagonized by pretreatment with naloxone (5 mg/kg, SC), and the magnitude of this analgesia was less than that of the 90-min stress or 180-min stress. The 30-min stress resulted in a significant decrease in MLI in the mesolimbic area, striatum, hypothalamus and thalamus. After the 90-min stress, MLI was found to be significantly decreased in the prefrontal cortex, amygdaloid nuclei and piriform cortex, thalamus and hippocampus, while the 180-min stress failed to induce a significant change in any brain area tested. As such a change in MLI content was thought to be related to an increase in the activity of the endogenous Met-enkephalin neuronal system, the activation of this system by the stress, especially in the hypothalamus and thalamus, seemed to be associated with analgesia.