LASTING INCREASE IN D1 DOPAMINE-RECEPTORS IN THE LATERAL PART OF THE SUBSTANTIA-NIGRA PARS RETICULATA AFTER SUBCHRONIC METHAMPHETAMINE ADMINISTRATION

To examine the possible involvement of D1 dopamine receptors in behavioral sensitization induced by subchronic methamphetamine (MAP) administration, regional D1 receptors labeled with [H-3]SCH 23390 were examined using binding assay and quantitative autoradiography. Rats received 4 mg/kg/day MAP (i.p.) for 14 days, and were decapitated after an abstinence period of 24 h, 7 days or 21 days. In MAP-treated rats, a significant decrease in K(d) in the mesolimbic area was observed 24 h but not 7 days after the last injection. Neither K(d) nor B(max) changed in the striatum or medial prefrontal cortex of MAP-treated rats after any period of abstinence. Autoradiography revealed a significant increase in specific [H-3]SCH 22390 binding in the lateral part of the substantia nigra pars reticulata (SNr) of MAP-treated rats. Since this increase lasted up to 21 days after cessation of subchronic MAP administration, it is suggested that lasting increase in the nigral D1 receptors may be associated with the biological changes underlying MAP-induced behavioral sensitization.