Brain microsomal metabolism of phencyclidine in male and female rats

Thiophene is Toxic to Cerebellar Granule Cells in Culture After Bioactivation by Rat Liver Enzymes

Several compounds that are not neurotoxic by themselves can cause toxic effects in vivo after enzymatic bioactivation. Thiophene is an industrial solvent known to produce degeneration primarily of the granule cells in the cerebellum when administered to animals in vivo. The mechanism for thiophene toxicity is not known, although it has been suggested that thiophene metabolism may lead to formation of oxidative intermediates that could function as the ultimate toxicants. In the present work we have used rat cerebellar granule cells (CGCs) in culture combined with rat liver postmitochondrial (S9) fraction as a source of biotransformation enzymes to test the toxicity of thiophene in vitro. The results demonstrate that thiophene is toxic to rat cerebellar granule cells in culture only after biotransformation. Furthermore, the toxic effects were reduced by cytochrome P450 (CYP) inhibitors and by scavengers of reactive molecules (alpha-tocopherol, reduced glutathione, and phenyl-N-tert-butylnitrone). These findings support the hypothesis that thiophene requires metabolism to produce the ultimate toxicant, and that the cytochrome P450 enzyme system is involved in the metabolism.

Hyperactivity of Endoplasmic Reticulum Associated Exocytosis Mechanism Contributes to Acute Phencyclidine Intoxication

Phencyclidine (PCP) produces schizophrenia-like psychosis and acute PCP-intoxications; however, whether glutamate/NMDA-receptor blockade by PCP modulates or not these mechanisms has remained to be clarified. To clarify this mechanism, we determined interaction among voltage-gated Na(+)-channel inhibitor, tetrodotoxin (TTX), Golgi-disturbing-agent, brefeldin-A (BFA), and PCP on releases of glutamate, GABA, and monoamine in prefrontal-cortex (pFC), using microdialysis. PCP increased basal monoamine release, whereas it decreased basal GABA release, without affecting glutamate release. PCP increased K(+)-evoked monoamine release, whereas it decreased K(+)-evoked glutamate and GABA releases. TTX reduced basal monoamine and GABA releases without affecting glutamate release, whereas BFA did not affect them. Interestingly, BFA and TTX inhibited PCP-associated basal monoamine release and abolished PCP-induced reduction of basal GABA release without affecting glutamate release. BFA and TTX reduced K(+)-evoked releases of all neurotransmitters. BFA inhibited PCP-associated K(+)-evoked monoamine release, but TTX did not affect them. PCP-induced reduction of K(+)-evoked GABA and glutamate releases was abolished by TTX and BFA. These results indicate that PCP reduces GABAergic transmission via NMDA-receptor blockade and activates intracellular endoplasmic-reticulum-associated signal-transduction, resulting in enhancement of monoaminergic transmission in pFC. Thus, these PCP properties support the hypothesis that mechanisms of the neurological symptoms of acute PCP-intoxication, convulsion, and rhabdomyolysis may be involved in both reduction of GABAergic-transmission and activation of endoplasmic-reticulum-associated signal-transduction induced by PCP.

Motor effects of amphetamine in rats pretreated with either dizocilpine or phencyclidine

The aim of the present study was to examine motor effects of amphetamine (AMPH) in rats pretreated with either dizocilpine (MK-801) or phencyclidine (PCP), and to estimate possible differences in these effects. Our results showed that AMPH increases the duration of motor effects of PCP, while it does not change motor effects of MK-801. These findings may reflect different mechanisms of action of MK-801 and PCP, as well as selective influence of AMPH on metabolism of these drugs.

Regional and cellular distribution of CYP2D subfamily members in rat brain

1. Human CYP2D6 is present in brain, metabolizes many drugs and has been implicated in Parkinson's and Alzheimer's diseases and some cancers. It is still unclear which of the six known rat CYP2D subfamily members is/are homologous to human CYP2D6. 2. In this study, RT-PCR, Southern and Western blotting and immunohistochemical techniques were used to study the distribution of CYP2D subfamily member mRNA and proteins across 10 rat brain regions. CYP2D subfamily mRNA and protein levels were correlated with brain dextromethorphan O-demethylation (DOD), a measure of human CYP2D6 and rat CYP2D1 activities. 3. The data showed a strong relationship between CYP2D1 and CYP2D1-18 with brain DOD activity. In addition, it was shown that CYP2D proteins are present in brain mitochondrial as well as microsomal membranes. CYP2D subfamily member mRNA and proteins varied across brain regions and were highly concentrated in specific cell types. 4. These data strongly suggest that CYP2D1 and not CYP2D5 mediates DOD activity in rat brain, and may be the rat homologue of human CYP2D6. The highly localized nature of CYP2D indicates that in specific neurones enzyme levels may approach hepatic levels and, hence, contribute to local alterations in brain drug metabolism.

Metabolism of drugs of abuse by cytochromes P450

Studies of most drugs of abuse utilize in vivo animal experimentation so that the responses measured reflect the pharmacokinetics of the administered drug as well as its pharmacodynamics. These drugs are generally lipid soluble chemicals and their elimination is dependent on metabolism, so an understanding of this process is critical to the interpretation of responses. This review summarizes the interaction between drugs of abuse and cytochromes P450, the oxidative enzymes that catalyze the first step of the metabolic process. Although they process their substrates by a common chemical mechanism, these enzymes differ markedly in their regulation, i.e. induction and inhibition, their substrate selectivities, the metabolites they generate and their relative concentration in different species. The activity of an enzyme catalyzing a specific metabolic reaction can be altered by prior xenobiotic exposure, by its genetics and by a co-administered drug, so that the pharmacokinetics of the drug under study can vary with the history of the individual subject. These issues are obviously important in human studies so, when possible, the relevant human enzymes involved in the processes described have been identified.

Phencyclidine in the social interaction test: an animal model of schizophrenia with face and predictive validity

Phencyclidine (PCP) is a hallucinogenic drug that can mimic several aspects of the schizophrenic symptomatology in healthy volunteers. In a series of studies PCP was administered to rats to determine whether it was possible to develop an animal model of the positive and negative symptoms of schizophrenia. The rats were tested in the social interaction test and it was found that PCP dose-dependently induces stereotyped behaviour and social withdrawal, which may correspond to certain aspects of the positive and negative symptoms, respectively. The effects of PCP could be reduced selectively by antipsychotic drug treatment, whereas drugs lacking antipsychotic effects did not alleviate the PCP-induced behaviours. Together these findings indicate that PCP effects in the rat social interaction test may be a model of the positive and negative symptoms of schizophrenia with face and predictive validity and that it may be useful for the evaluation of novel antipsychotic compounds.