Asami Umino

Differential effects of phencyclidine and methamphetamine on dopamine metabolism in rat frontal cortex and striatum as revealed by in vivo dialysis

We have examined the effects of schizophrenomimetic drugs including phencyclidine (PCP) and methamphetamine (MAP) on cortical and striatal dopamine (DA) metabolism using an in vivo dialysis technique in the rat. An acute systemic injection of PCP (2.5–10 mg/kg, intraperitoneally (i.p.)) dramatically increased concentrations of DA, 3,4‐dihydroxy‐phenylacetic acid, and homovanillic acid in the dialysates from the medial frontal cortex in a dose‐dependent fashion. However, PCP (2.5–10 mg/kg, i.p.) caused a much lower augmentation of extracellular DA release, with a significant decrease in dialysate DOPAC levels in the striatum. Moreover, continuous infusion of tetrodotoxin (TTX, 10−5 M) into the prefrontal or striatal region through the microdialysis tube completely blocked the ability of PCP (10 mg/kg, i.p.) to alter the extracellular release of DA and its metabolites in the respective areas. In contrast, MAP (4.8 mg/kg, i.p.) elicited a marked and tetrodotoxin‐resistant increase in DA levels with a significant loss of DOPAC contents in the extracellular space of both the frontal cortex and the striatum. The present results clearly demonstrate the differential effects of PCP on cortical and striatal DA transmission, suggesting that PCP may facilitate DA release in the medial frontal cortex by increasing impulse flow in the DA neurons projecting to the cortical area, whereas PCP‐induced elevation of extracellular DA in the striatum may be caused mainly by reuptake inhibition of DA liberated by basal activity of the striatal DA neurons. The regional variation in PCP‐induced DA release would be due to the combination of NMDA (N‐methyl‐D‐aspartate) receptor blocking and DA reuptake inhibition by the drug. The uniform and TTX‐resistant nature of MAP‐induced changes in brain DA metabolism may result from the direct actions of MAP at DA nerve terminals.

Methamphetamine-induced nuclear c-Fos in rat brain regions

To explore the possible robust changes in neuronal activity in dopamine-poor brain regions after an indirect dopamine agonist, methamphetamine, we have investigated its effects on c-fos expression in rat brain using immunocytochemistry of c-Fos. Intraperitoneal injection of methamphetamine (1.6-4.8 mg/kg), but not of saline, induced a widespread nuclear c-Fos-like immunoreactivity in the pyriform cortex and olfactory tubercle with greatest density followed by the II-VI layers of the neocortex, amygdala, hypothalamus, thalamus, nucleus accumbens and striatum. These expression patterns resemble those elicited by amphetamine and suggest that not only the dopamine-rich subcortical regions but also the cerebral cortex may play a crucial role in behavioral abnormality induced by methamphetamine.

Evidence for involvement of N-methyl-d-aspartate receptor in tonic inhibitory control of dopaminergic transmission in rat medial frontal cortex

Bilateral infusion of DL-2-amino-5-phosphonovalerate (DL-APV) (which is a competitive antagonist for N-methyl-D-aspartate (NMDA) receptor) into the medial frontal cortex of conscious rats increased the amount of 3,4-dihydroxyphenylacetic acid (DOPAC) and the DOPAC/dopamine (DA) ratio in the cortical area. Moreover, intra-prefrontal injection of DL-APV, D-APV, DL-2-amino-7-phosphonoheptanoate and 3-[(+/-])-2-carboxypiperazin-4-yl]-propyl-1-phosphonate (which are selective NMDA receptor antagonists), but not the L-isomer of APV and gamma-glutamyl-aminomethyl sulphonate (a relative antagonist for non-NMDA receptors), facilitated prefrontal DA utilization in a NMDA-reversible manner. These findings suggest that NMDA-type excitatory amino acid receptors may be involved in a tonic inhibitory regulation of dopaminergic transmission in the medial frontal cortex in vivo.

A developmentally regulated and psychostimulant-inducible novel rat gene mrt1 encoding PDZ-PX proteins isolated in the neocortex

Single or repeated exposure to psychostimulants such as amphetamines and cocaine after postnatal week 3 leads to an enduring enhancement in the psychotomimetic responses elicited by a subsequent challenge of a stimulant in rodents. This behavioral sensitization phenomenon has been considered to be the neural consequences of stimulant-induced alterations in gene expression in the brain after a critical period of postnatal development. Using a differential cloning technique, RNA arbitrarily primed PCR, we have now identified from the rat neocortex a novel and developmentally regulated methamphetamine (MAP)-inducible gene mrt1 (MAP responsive transcript 1). mrt1 encodes two major types of PDZ- and PX-domains containing proteins of approximately 62 kDa in size with different carboxy termini, Mrt1a and Mrt1b. The mrt1 mRNAs for Mrt1a, mrt1a, and for Mrt1b, mrt1b, are predominantly expressed in various brain regions and the testes, respectively. Acute MAP injection upregulated mrt1b expression in the neocortex after postnatal week 3 in a D1 receptor antagonist-sensitive manner without affecting mrt1a expression. This upregulation was mimicked by another stimulant, cocaine, whereas pentobarbital and D1 antagonist failed to change the mrt1b transcript levels. Moreover, repeated daily treatment of MAP, but not MAP plus D1 antagonist, for 5 days caused an augmentation of the basal expression of mrt1b 2 and 3 weeks after the drug discontinuation. These late-developing, cocaine-crossreactive, D1 antagonist-sensitive and long-term regulations of mrt1b by MAP are similar to the pharmacological profiles of stimulant-induced behavioral sensitization, and therefore may be associated with the initiation and/or maintenance of the long-term neuronal adaptation.

Phencyclidine increases extracellular dopamine metabolites in rat medial frontal cortex as measured by in vivo dialysis

An acute intraperitoneal injection of phencyclidine (PCP) caused a tetrodotoxin-reversible increase in extracellular release of 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the dialysates from the medial frontal cortex of the rat. Moreover, there was an increase in the tissue content of DOPAC and HVA with acceleration of dopamine (DA), but not noradrenaline, utilization in the cortical area after systemic administration of PCP. These results suggest that PCP facilitates DA metabolism in the medial frontal cortex by increasing impulse flow in the DA neurons projecting to the prefrontal region.

p-Chlorophenylalanine-reversible reduction of σ binding sites by chronic imipramine treatment in rat brain

Repeated treatment with imipramine (10 mg/kg intraperitoneally (i.p.), once daily for 14 days) caused a decrease in the Bmax, without affecting the Kd, of [3H]DTG (1,3-di-o-tolylguanidine) binding to the haloperidol-sensitive sigma sites in the striatum, hippocampus and cerebral cortex of the rat. A similar reduction was observed after chronic administration of a selective serotonin uptake inhibitor, fluoxetine (10 mg/kg i.p., twice daily for 14 days), but not of a selective norepinephrine uptake inhibitor, desipramine (10 mg/kg i.p., once daily for 14 days). Neither a single injection of imipramine (10 mg/kg i.p.) nor addition of imipramine or fluoxetine into the binding assay medium mimicked the changes in the maximal binding of brain sigma sites induced by chronic treatment with these drugs. Finally, depletion of brain serotonin by means of repeated administration of p-chlorophenylalanine, which produces inhibition of the amine synthesis, blocked the ability of repeated imipramine treatment to reduce the maximal number of [3H]DTG binding sites in the striatum and hippocampus. The present results suggest that cerebral serotonergic transmission may play a role in the regulation of cerebral sigma binding sites in the rat.

Developmental changes in distribution patterns of phencyclidine-induced c-Fos in rat forebrain

In the forebrain of 56-day-old rats, histochemical studies revealed that the subcutaneous injection of a psychotomimetic phencyclidine (PCP; 1 and 10 mg/kg) induced a dose-related and dense nuclear c-Fos-like immunoreactivity in the pyriform cortex, layers IV-VI of the neocortex and septum, but a sparse c-Fos immunostaining in the olfactory tubercle and mid-lateral striatum. Infant rats at postnatal day 8 expressed much fewer and more confined c-Fos-positive cells in the neocortex than young adult rats following PCP injection. However, a similar expression pattern of PCP-induced c-Fos was observed in the pyriform cortex, mid-lateral striatum, olfactory tubercle and septum between the infant and adult periods. These developmental changes in the regional distribution of a neuronal activity marker, c-Fos, suggest that neuronal populations involved in PCP-induced abnormal behavior are influenced by postnatal development, at least, in the neocortex.

Dizocilpine (MK-801) elicits a tetrodotoxin-sensitive increase in extracellular release of dopamine in rat medial frontal cortex

We have examined in the rat the effects of a selective non-competitive antagonist for the N-methyl-D-aspartate (NMDA) type excitatory amino acid receptor, dizocilpine (MK-801), on cortical dopamine (DA) metabolism using an in vivo dialysis technique. An acute intraperitoneal injection of MK-801 (0.4-1.25 mg/kg) dramatically increased the concentrations of dopamine, 3,4-dihydroxy-phenylacetic acid and homovanillic acid in the dialysates from the medial frontal cortex in a dose-dependent fashion. Moreover, MK-801 caused a delayed and small augmentation of the cortical extracellular release of 5-hydroxyindoleacetic acid. Continuous infusion of tetrodotoxin into the prefrontal region via the microdialysis tube completely blocked the ability of MK-801 (1.25 mg/kg, intraperitoneally) to augment the extracellular release of DA, its metabolites and the serotonin metabolite in the frontal cortex. The present results suggest that MK-801 facilitates DA release in the medial frontal cortex by increasing impulse flow in the DA neurons projecting to the cortical area adding further support to the view that the NMDA receptor may be involved in the tonic inhibition of frontal cortical DA neurons. It is also proposed that frontal serotonin neurons might be under regulation by excitatory amino acidergic transmission via the NMDA receptor.

Characterization of the phencyclidine-induced increase in prefrontal cortical dopamine metabolism in the rat

We have investigated the effects of a schizophrenomimetic drug phencyclidine (PCP) and N‐methyl‐D‐aspartate (NMDA)‐related agents alone or in combination on dopamine metabolism in the medial prefrontal cortex and striatum of the rats by measuring the tissue concentrations of dopamine and its metabolite, 3,4‐dihyroxyphenylacetic acid (DOPAC), and the rate of dopamine disappearance (dopamine utilization) after its synthesis inhibition. Systemic injection of PCP and selective, non‐competitive, NMDA antagonists caused an increase of both tissue concentrations of DOPAC and dopamine utilization in the prefrontal cortex but not in the striatum. The PCP‐induced augmentation of cortical dopamine metabolism was not influenced by selective lesion of ascending noradrenergic neurones. Intra‐prefrontal cortical infusion of PCP or selective competitive or non‐competitive antagonists of the NMDA receptor mimicked the ability of systemic PCP injection to enhance DOPAC levels and dopamine utilization in the prefrontal cortex. However, an NMDA antagonist injected into the cell body area of the mesocortical dopaminergic neurones failed to affect dopamine metabolism in the prefrontal cortex. The increasing effects of PCP and selective NMDA antagonists on cortical dopamine utilization were not additive, although a dopamine receptor antagonist, haloperidol, still accelerated the disappearance of dopamine, even in the presence of PCP. Intra‐cortical or intra‐ventricular infusion of NMDA or D‐alanine but not L‐alanine, attenuated the ability of systemic PCP administration to facilitate prefrontal dopamine utilization. These data suggest that PCP might activate prefrontal cortical dopaminergic neurones, at least in part, by blocking the NMDA receptor in the prefrontal cortex which participates in a tonic inhibitory control of the mesoprefrontal dopaminergic projections.

Selective serotonin reuptake inhibitors, fluoxetine and paroxetine, attenuate the expression of the established behavioral sensitization induced by methamphetamine

To obtain an insight into the development of a new pharmacotherapy that prevents the treatment-resistant relapse of psychostimulant-induced psychosis and schizophrenia, we have investigated in the mouse the effects of selective serotonin reuptake inhibitors (SSRI), fluoxetine (FLX) and paroxetine (PRX), on the established sensitization induced by methamphetamine (MAP), a model of the relapse of these psychoses, because the modifications of the brain serotonergic transmission have been reported to antagonize the sensitization phenomenon. In agreement with previous reports, repeated MAP treatment (1.0 mg/kg a day, subcutaneously (s.c.)) for 10 days induced a long-lasting enhancement of the increasing effects of a challenge dose of MAP (0.24 mg/kg, s.c.) on motor activity on day 12 or 29 of withdrawal. The daily injection of FLX (10 mg/kg, s.c.) or PRX (8 mg/kg, s.c.) from 12 to 16 days of withdrawal of repeated MAP administration markedly attenuated the ability of the MAP pretreatment to augment the motor responses to the challenge dose of the stimulant 13 days after the SSRI injection. The repeated treatment with FLX or PRX alone failed to affect the motor stimulation following the challenge of saline and MAP 13 days later. These results suggest that the intermittent and repetitive elevation of serotonergic tone may inhibit the expression of the motor sensitization induced by pretreatment with MAP. It is proposed that clinically available serotonin reuptake inhibitors could be useful for preventing the recurrence of hallucinatory-paranoid state in drug-induced psychosis and schizophrenia.