LACK OF EFFECT OF HALOPERIDOL OR METHAMPHETAMINE TREATMENT ON THE MESSENGER-RNA LEVELS OF 2 DOPAMINE D(2)-RECEPTOR ISOFORMS IN RAT-BRAIN

In order to investigate whether changes of the two mRNAs encoding the D2 receptor isoforms were induced by chronic haloperidol or methamphetamine treatment in rats, we measured the brain mRNA levels using in situ hybridization histochemistry (ISHH). We used two oligonucleotide probes, an ''insert'' probe to hybridize with the longer D2 receptor, D2(444), mRNA, and a ''spanning'' probe to hybridize with the shorter D2 receptor, D2(415), mRNA. Both D2 mRNAs were detected by ISHH in the caudate putamen, nucleus accumbens, substantia nigra, pars compacta and ventral tegmental area. The distributions and the amounts of the mRNAs for the two D2 isoforms did not change after chronic administration of haloperidol (1 mg/kg/day for 14 days, ip) or methamphetamine (4 mg/kg/day for 14 days, ip). These results suggest that the changes of D2 receptor density induced by chronic neuroleptic and psychostimulant treatment are not due primarily to receptor expression.