Comprehensive expression analysis of a rat depression model.

Herein we report on a large-scale analysis of gene expression in the 'learned helplessness' (LH) rat model of human depression, using DNA microarrays. We compared gene expression in the frontal cortex (FC) and hippocampus (HPC) of untreated controls, and LH rats treated with saline (LH-S), imipramine or fluoxetine. A total of 34 and 48 transcripts were differentially expressed in the FC and HPC, respectively, between control and LH-S groups. Unexpectedly, only genes for NADH dehydrogenase and zinc transporter were altered in both the FC and HPC, suggesting limited overlap in the molecular processes from specific areas of the brain. Principal component analysis revealed that sets of upregulated metabolic enzyme genes in the FC and downregulated genes for signal transduction in the HPC can distinguish clearly between depressed and control animals, as well as explain the responsiveness to antidepressants. This comprehensive data could help to unravel the complex genetic predispositions involved in human depression.

Nicotine withdrawal induces subsensitivity of hypothalamic-pituitary-adrenal axis to stress in rats: implications for precipitation of depression during smoking cessation.

Epidemiologic studies show that smokers with a past history of depression are more likely to relapse into depression after smoking cessation than those without a history of depression. These studies suggest the existence of a direct biological link between nicotine withdrawal and depression. To investigate the neuronal and hormonal mechanisms of the precipitation of depression during smoking cessation, we used an animal model of nicotine withdrawal and studied the function of the hypothalamic-pituitary-adrenal (HPA) axis, the abnormality of which is implicated in the pathogenesis of depression. Rats were implanted with a minipump delivering nicotine at 6.0 mg/kg/day for 12 days. The minipumps were removed in order to abruptly terminate nicotine infusion. The activity of the HPA axis was determined on day 2 of withdrawal using the stress-induced corticosterone response and the dexamethasone suppression test (DST). At the same time the expressions of glucocorticoid receptor (GR) mRNA in the hippocampus and paraventricular nucleus of hypothalamus (PVN) and corticotropin-releasing hormone (CRH) mRNA in PVN were determined by non-radioactive in situ hybridization. Nicotine withdrawal resulted in lower corticosterone levels during restraint stress, suggesting subsensitivity of the HPA axis to stress. The result of DST, however, did not show a significant difference between nicotine-withdrawal and control rats. These effects of nicotine withdrawal were not accompanied by any changes in the expressions of GR and CRH mRNA in either hippocampus or PVN. These results suggest that subsensitivity of the HPA axis to stress during nicotine withdrawal may be implicated in the precipitation of depression during smoking cessation, although GR and CRH in the HPA axis do not appear to play a significant role.

In vivo binding properties of [carbonyl-11C]WAY-100635: effect of endogenous serotonin.

[Carbonyl-(11)C]WAY-100635 has been reported to be a useful ligand for the investigation of 5-HT(1A) receptor imaging in vivo. However, the cellular distribution and the influence of endogenous serotonin (5-HT) on in vivo binding have not been fully examined. In this study, we investigated the effect of 5,7-dihydroxytryptamine-produced destruction of 5-HT neurons, reserpine-induced 5-HT depletion, and fenfluramine-induced 5-HT increase on [carbonyl-(11)C]WAY-100635 binding in vivo. There was no significant change in the uptake of [carbonyl-(11)C]WAY-100635 in the slice of 5-HT denervated rat brain except in the raphe nucleus, where 5-HT cell bodies exist. There was no obvious effect of enhanced 5-HT release by fenfluramine or decreased release by reserpine on [carbonyl-(11)C]WAY-100635 binding in the dissected brain region. No significant effect was observed in the time course of [carbonyl-(11)C]WAY-100635 in the hippocampus and frontal cortex measured by PET. These results indicated that the in vivo binding of [carbonyl-(11)C]WAY-100635 in the hippocampus and cerebral cortex mainly reflects postsynaptic 5-HT(1A) receptor binding, and that this binding is not sensitive to endogenous 5-HT.

Neonatal phencyclidine treatment selectively attenuates mesolimbic dopamine function in adult rats as revealed by methamphetamine-induced behavior and c-fos mRNA expression in the brain.

One of the major hypotheses regarding the pathogenesis of schizophrenia is the implication of neurodevelopmental abnormality. However, the mechanism of delayed onset of schizophrenic symptoms, in which increased dopaminergic activity in mesolimbic or mesocortical dopamine systems plays a pathological role, is not known. In this study, we investigated whether the chronic blockade of N-methyl-D-aspartate (NMDA) receptor by phencyclidine (PCP), an NMDA channel blocker, during development could disrupt the dopamine system during later life. Neonatal rats were injected with PCP subcutaneously daily from postnatal day (PD) 1 to PD 14 and their dopaminergic function was evaluated on PD 42 by rating the methamphetamine (MAP)-induced behavior. To illustrate the activated brain regions, the expression of c-fos mRNA in response to a MAP challenge was also studied utilizing in situ hybridization. Chronic neonatal PCP treatment attenuated MAP-induced oral stereotypy (licking and gnawing) and reduced MAP-induced expression of c-fos mRNA in the N. accumbens shell region and VTA but not in the N. accumbens core region, medial striatum, or substantia nigra. These results suggest that neonatal blockade of NMDA receptor, which induces a number of effects in the developing nervous system, may cause long-lasting functional changes of the mesolimbic dopamine system.

Chronic lithium chloride injection increases glucocorticoid receptor but not mineralocorticoid receptor mRNA expression in rat brain.

Lithium has been used clinically for the treatment of bipolar disorders. However, the brain mechanisms, by which lithium acts, are still unclear. An impaired hypothalamic-pituitary-adrenal (HPA) axis has been implicated in the pathogenesis of mood disorders. In this study, we investigated the effects of chronic lithium on the corticosteroid receptors in the brain. Male Wistar rats were injected with LiCl (1.5 mEq/kg) or saline intraperitoneally (i.p.) once a day for 14 days. Twenty-four hours after the last injection, the expressions of mRNA for glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) in the brain were determined by non-radioactive in situ hybridization. Chronic administration of LiCl increased the expression of GR mRNA in the hippocampus and paraventricular nucleus of the hypothalamus (PVN). However, no significant changes were observed in the expression of either MR mRNA in the hippocampus or GR mRNA in the locus ceruleus. Since the hippocampus and PVN mediate negative feedback regulation of the HPA axis, an increased expression of GR mRNA in these regions may normalize HPA axis activity in mood disorders. Thus, the effect of chronic lithium on GR function may be involved in its antimanic and/or prophylactic activity in bipolar disorders.

Neonatal treatment with L-name (NG-nitro-L-arginine methyl ester) attenuates stereotyped behavior induced by acute methamphetamine but not development of behavioral sensitization to methamphetamine.

1. The neurodevelopmental hypothesis of schizophrenia postulates that disturbed nitric oxide (NO) function during neuronal development is one of premorbid factors for schizophrenia in later life. 2. The aim of present study is to investigate behaviorally whether neonatal inhibition of nitric oxide synthase (NOS) affects dopaminergic function, the abnormality of which may be ascribed to a major pathophysiology of schizophrenia. 3. Male rat pups were injected daily with NOS inhibitor, NG-nitro-L-arginine methyl ester (L-NAME), from postnatal day (PD) 1 to 14. 4. When methamphetamine (MAP) was challenged on PD42, MAP-induced stereotypy was significantly attenuated in the L-NAME treated rats. The development of sensitization to the stereotypy-inducing effect of MAP, however, was not prevented with neonatal L-NAME. 5. These results suggest that decreased NO production during neonatal period may disturb normal maturation of dopaminergic system and result in impaired dopaminergic function in adult period.

[Clinical significance of selective serotonin reuptake inhibitor (SSRI) in the treatment of depression].

SSRIs have had a great impact on the diagnosis and treatment of depression, as well as the search for its pathophysiology. Since SSRIs have relatively few adverse effects, it is also effective for treating in a mild forms of depression, which were formerly thought to be treated adequately with only psychotherapy or anti-anxietics. Recent studies on the natural history of depression have revealed the chronicity of this disease. SSRI is now the first-line drug for the continuation and maintenance therapy of depression. Since SSRI primary acts on the serotonergic system, wide use of this drug has questioned the postulated dichotomy of the biological hypothesis of depression, the so-called serotonin depression or norepinephrine depression. A new insight into the monoamine hypothesis of depression has been yielded by SSRI. SSRIs are also effective in the treatment of anxiety disorders such as obsessive-compulsive disorder, panic disorder and social phobia. Thus, SSRIs have also brought new insight into the role of serotonin in the pathophysiology of anxiety.

Differential effects of acute and chronic treatment with typical and atypical neuroleptics on c-fos mRNA expression in rat forebrain regions using non-radioactive in situ hybridization.

The regional difference in the expression of c-fos mRNA in rat forebrain after either acute or chronic administration of typical (haloperidol and fluphenazine) and atypical neuroleptics (clozapine and (+/-)-sulpiride) was investigated. Rats were injected intraperitoneally with vehicle or neuroleptics daily for 14 days. Twenty-four hours after the last injection, the rats were challenged with vehicle or neuroleptics. C-fos mRNA expression was determined by non-radioactive in situ hybridization. Acute treatment with typical neuroleptics induced a remarkable induction of c-fos mRNA in the dorsolateral striatum, whereas this induction was greatly attenuated by chronic administration. All neuroleptics examined induced c-fos mRNA in the shell region of N. accumbens by acute administration and this expression was still elevated after chronic treatment. Since chronic neuroleptics do not induce tolerance to their antipsychotic activities, our study suggests that the shell region of N. accumbens is an important target site for antipsychotic effects of neuroleptics.

[Glycine therapy of schizophrenia; its rationale and a review of clinical trials].

A major ground of dopamine hypothesis of schizophrenia is that all antipsychotics share dopamine D2 antagonistic activity. However, they are less effective in ameliorating the negative symptoms of schizophrenia. Recently, glutamate hypothesis of schizophrenia has been developed from the observation that phencyclidine, an NMDA receptor antagonist, induces a psychotic state closely resembling schizophrenia in normal individuals. Because glycine potentiates NMDA receptor activity, it has been tried as an adjunct to conventional antipsychotics. Most trials demonstrated a moderate improvement in negative symptoms. In this review we discussed the clinical usefulness of glycine therapy. First we described glutamate hypothesis of schizophrenia as a theoretical basis of glycine therapy. Then we reviewed clinical trials of glycine or other glycinergic agents (glycine receptor partial agonist, D-cycloserine, or the glycine prodrug milacemide). Although long-term side effects of glycine administration have not been fully investigated, glycine therapy could be a potential therapeutic tool for the negative symptoms of schizophrenia.

Regional differences in the effects of glutamate uptake inhibitor L-trans-pyrrolidine-2,4-dicarboxylic acid on extracellular amino acids and dopamine in rat brain: an in vivo microdialysis study.

The effects of the glutamate transporter inhibitor, trans-PDC, on extracellular amino acids, were investigated in the frontal cortex, striatum, hippocampus and cerebellum of rats using in vivo microdialysis. Trans-PDC infusion (0.1, 1, 10 mM) dose-dependently increased Glu and Asp levels, and these increases in the cerebellum were smaller than those in other brain regions. A small but significant dose-dependent increase was observed for Gly and Tau. However, high extracellular Glu induced by trans-PDC was not sufficient to increase extracellular DA in the striatum and frontal cortex.

Antidepressantlike effects of chronic nicotine on learned helplessness paradigm in rats.

BACKGROUND: The association between smoking and depression has been widely investigated. Smoking cessation is known to induce depression to a variable extent, and patients with a history of depression are more likely to experience depressive symptoms. To investigate the hypothesis that nicotine may have an antidepressantlike effect, we used learned helpless rats as an animal model of depression. METHODS: Learned helplessness was produced according to our previous method. Learned helpless rats were implanted with nicotine and escape test was performed at 7 and 14 days after the implantation. RESULTS: The number of escape failure in the rats receiving 1.5 mg/kg/day of nicotine was significantly reduced (p < .05) compared to control at day 14. Furthermore, this effect was blocked when the nicotinic receptor antagonist mecamylamine was coadministered. CONCLUSIONS: These results suggest that chronic nicotine may act as an antidepressant, probably via nicotinic receptors.

Differential expression of c-fos mRNA in rat prefrontal cortex, striatum, N. accumbens and lateral septum after typical and atypical antipsychotics: an in situ hybridization study.

The regional difference in the expression of c-fos mRNA induced by typical and atypical antipsychotics was determined in prefrontal cortex, striatum, N. accumbens and lateral septum in rats by in situ hybridization. Two typical antipsychotics, haloperidol (2 mg/kg) and fluphenazine (2 mg/kg), and three atypical antipsychotics, (-)sulpiride (100 mg/kg), clozapine (20 mg/kg) and OPC-14597 (40 mg/kg), were used. Brains were fixed with 4% paraformaldehyde 45 min after drug administration (i.p.). Brain sections of 30 microns-thickness were made in a cryostat and hybridized with 35S-labelled for c-fos oligonucleotide probe. These sections were apposed to X-ray films and the autoradiograms were semi-quantitatively analysed by computer-assisted densitometry. All antipsychotics used increased c-fos mRNA expression in N. accumbens shell, a region of the forebrain associated with limbic systems. On the other hand, two typical antipsychotics (haloperidol and fluphenazine) that cause a high incidence of acute motor side effects increased the expression of c-fos mRNA in the dorsolateral striatum, an extrapyramidal region primarily involved in motor control. Only clozapine induced c-fos mRNA in the medial prefrontal cortex and lateral septum. These results strongly suggest that the shell region of N. accumbens may be a common site of therapeutic action of antipsychotics.

Nicotine protects against the dexamethasone potentiation of kainic acid-induced neurotoxicity in cultured hippocampal neurons.

To elucidate the neuroprotective effect of nicotine, we investigated whether nicotine may attenuate dexamethasone potentiation of kainic acid-induced neurotoxicity. Primary hippocampal culture was pre-treated with nicotine for 24 h followed by dexamethasone (10(-4) M) for 24 h. Then, cultures were exposed with kainic acid (10(-4) M) and cellular viability was determined by LDH effluxmetry. Nicotine pre-treatment (10(-9)-10(-7) M) dose-dependently attenuated dexamethasone potentiation of kainic acid-induced neurotoxicity. These results may support the epidemiological data suggesting a neuroprotective effect of cigarette smoking on Alzheimer's disease or Parkinson's disease.

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.

Behavioural and neurochemical effects of OPC-14597, a novel antipsychotic drug, on dopaminergic mechanisms in rat brain.

OPC-14597 is a new antipsychotic drug with a unique pharmacological profile. In a behavioural study in rats OPC-14597 did not show cataleptogenic activity even at the highest dose (40 mg/kg, i.p.), whereas it antagonized apomorphine-induced stereotypy dose-dependently (0.5-40 mg/kg). In vivo microdialysis showed that extracellular dopamine (DA) in the striatum was decreased significantly after OPC-14597 administration at higher doses of 10 and 40 mg/kg. Similar results were obtained in extracellular dopamine concentration in the frontal cortex, although the changes in DOPAC and HVA concentrations were smaller than those in the striatum. OPC-14597 also antagonized DA increase induced by the DA autoreceptor antagonist (+)-AJ76. These results that OPC-14597 acts either as an antagonist at postsynaptic dopamine receptors or as an agonist at presynaptic dopamine autoreceptors.

NG-monomethyl-L-arginine, an inhibitor of nitric oxide synthase, increases extracellular GABA in the striatum of the freely moving rat.

We investigated the effect of an NO synthase inhibitor, NG-monomethyl-L-arginine (L-NMMA), on the levels of endogenous GABA in the rat striatum using in vivo microdialysis. Rats were perfused with the artificial CSF containing L-NMMA (0.1, 0.3 and 1.0 mM) or its inactive isomer D-NMMA (1.0 mM) for 1 h. Infusion of L-NMMA, but not its D-isomer, dose-dependently increased GABA concentration. Co-infusion with tetrodotoxin (1 microM) did not antagonize the increase of GABA induced by L-NMMA. These results show that decreased NO activity enhances GABA release even in the absence of depolarization of GABA neurones. We conclude that NO may be directly acting on GABA nerve terminals and tonically inhibiting GABA release or synthesis under basal conditions.

Effect of systemic dexamethasone on extracellular amino acids, GABA and acetylcholine release in rat hippocampus using in vivo microdialysis.

In order to elucidate the mechanism of the cytotoxic effect of glucocorticoid on the rat hippocampus, we studied the effects of dexamethasone, a synthetic glucocorticoid, on neurotransmitter release from the hippocampus by in vivo microdialysis. Dexamethasone (10 mg/kg) was administered i.p. and the extracellular concentrations of the amino acids (glutamate, aspartate, glycine), GABA and acetylcholine were determined in the hippocampus of freely moving rats. Glutamate concentration increased by 20-25% after dexamethasone administration and this effect continued for 1 hour. The extracellular concentration of the other neurotransmitters, however, did not show any significant changes. From these results, we concluded that increased extracellular glutamate may be involved, at least in part, in the cytotoxic effect of glucocorticoid on hippocampal neurons.

Characterisation of extracellular amino acids in striatum of freely moving rats by in vivo microdialysis.

To investigate the characteristics of extracellular amino acids released from the striatum, we performed in vivo microdialysis in non-anaesthetised, freely moving rats. Amino acids were determined after precolumn derivatisation with o-phthalaldehyde by high-performance liquid chromatography and fluorescence detection. The omission of Ca2+ in the perfusion medium partially decreased the basal concentration of aspartate and glutamate. This shows that a small fraction of basal concentration of aspartate and glutamate is of neuronal origin. The effect of high K+ and veratrine stimulation was evaluated in the presence or absence of Ca2+ or tetrodotoxin (1 microM). High K+ and veratrine caused a remarkable increase in the aspartate and glutamate efflux. The omission of Ca2+ only partially decreased K(+)-stimulated aspartate and glutamate efflux. Tetrodotoxin completely antagonised veratrine-stimulated aspartate and glutamate efflux. Although glycine and taurine releases were stimulated by high K+ and veratrine, their release was not always antagonised with Ca2+ omission or tetrodotoxin inclusion. Thus, the neuronal origin of stimulated release of glycine and taurine is unclear. Although tetrodotoxin sensitivity and Ca2(+)-dependency are regarded as a basic criterion for classical neurotransmitters in microdialysis experiments, they should not be adapted to the physiological characteristics of the release of amino acids.

Antiepileptic drug pharmacokinetics and neuropharmacokinetics in individual rats by repetitive withdrawal of blood and cerebrospinal fluid: milacemide.

1. The kinetics and metabolism of milacemide have been studied in an animal model which allows the simultaneous investigation of the temporal inter-relationships of drugs and metabolites in blood (pharmacokinetics) and cerebrospinal fluid (CSF, neuropharmacokinetics) in individual freely moving rats. 2. Milacemide dose-dependently increased CSF glycine and glycinamide (intermediary metabolite) concentrations. This confirms that milacemide is a CNS glycine prodrug. 3. Pretreatment with L-deprenyl (2 mg kg-1), a specific inhibitor of monoamine oxidase type B (MAO-B), almost completely prevented the formation of glycinamide and increased milacemide accumulation in CSF. Tmax and t1/2 were significantly increased and Cmax and AUC values were decreased for glycinamide compared to controls. Pretreatment with clorgyline (5 mg kg-1), a specific inhibitor of MAO-type A, only moderately decreased glycinamide Cmax and AUC values. 4. After milacemide administration (100, 200 and 400 mg kg-1, i.p.) serum and CSF milacemide concentrations rose linearly and dose-dependently. Serum glycinamide concentrations exhibited small dose-dependent rises but these were not linearly related. In contrast, CSF glycinamide concentrations rose linearly and dose-dependently with Cmax values 2.5, 3.2 and 4.1 times greater than the corresponding values for serum glycinamide after giving 100, 200 and 400 mg kg-1 respectively of milacemide. 5. Serum glycine concentrations were unaffected but CSF concentrations increased dose-dependently and these were significant at the higher milacemide doses (200 and 400 mg kg-1). Animals given 400 mg kg-1 milacemide had glycine values which were still significantly elevated 7 h later. 6. In conclusion, serum milacemide rapidly enters and equilibrates with the CNS compartment where it is metabolised primarily by MAO-B to glycinamide and finally to glycine. Metabolism in the peripheral compartment is negligible.

Milacemide effects on the temporal inter-relationship of amino acids and monoamine metabolites in rat cerebrospinal fluid.

The temporal inter-relationship of various amino acids and monoamine metabolites in rat cerebrospinal fluid was examined after acute administration of milacemide (100, 200 or 400 mg/kg i.p.), a glycine prodrug. Glycine concentrations rose linearly and dose dependently (20-190%) but were only significantly elevated at the higher milacemide dose (200 and 400 mg/kg). In animals given 400 mg/kg, glycine values were still significantly elevated 8 h later. A concomitant increase (20-25%) in serine and taurine and a decrease in alanine cerebrospinal fluid values were observed at the highest milacemide dose. Other amino acids were unaffected. While cerebrospinal fluid 5-hydroxyindoleacetic acid concentrations were unaffected, the dopamine metabolites, 3,4-dihydroxyphenylacetic acid and homovanillic acid, exhibited a linear dose-dependent reduction. However, only homovanillic acid values were significantly decreased after 400 mg/kg milacemide. Cerebrospinal fluid analysis may be useful as a first screen in ascertaining putative neurochemical changes associated with drug administration.