Acute amphetamine and/or phencyclidine effects on the dopamine receptor specific binding in the rat brain

Psychotic-like behaviour was induced in rats with a single i.p. injection of AMPH (20 mg/kg b.w.) and/or PCP (10 mg/kg b.w.). The D₁ and D₂ dopamine receptor (DAR) specific binding of [³H]SCH 23390 and [³H]spiperone, respectively, during the 120 min period upon the treatment was examined on cryosections using computerized scanning and image analysis. AMPH, alone or in combination with PCP, induced a transient decrease of the D₁ receptor specific binding in the striatum (30 min; AMPH, −18%; AMPH+PCP, −31%) and nucleus accumbens (30 min; AMPH, −30%; AMPH+PCP, −40%), which was completely abolished at the 120 min point. Only AMPH persistently elevated nigral D₁ receptor specific binding. PCP-induced striatal and accumbal D₁ receptor down-regulation was intensive throughout the 120 min period, while in the s. nigra it was non-significant. A significant increase of the D₂ receptor specific binding was observed only 30 min after the treatment in striatum (AMPH, 15%; PCP, 16%; AMPH+PCP, 13%) and n. accumbens (AMPH, 16%). These alterations of DAR specific binding may reflect a regulation of the DAR and the changes in nigrostriatal and mesolimbic DA-ergic neurotransmission during an intensive drug-induced psychotic-like behavioral expression.