EFFECTS OF BINGE PATTERN COCAINE ADMINISTRATION ON DOPAMINE D-1 AND D-2 RECEPTORS IN THE RAT-BRAIN - AN IN-VIVO STUDY USING POSITRON EMISSION TOMOGRAPHY

The aim of the present study was to determine the effect of ''binge'' pattern cocaine administration on dopamine D-1 and D-2 receptors in th e rat brain. Male Sprague Dawley rats were injected three times at 1 h r intervals with saline or cocaine (15 mg/kg) each day for 2, 7, or 14 d. The in vivo binding of [C-11]SCH23390 (dopamine D-1 receptor antag onist) and [C-11]N-methylspiperone (NMSP; dopamine D-2 receptor antago nist) in the striatal region was measured by a high-resolution positro n emission tomography at 1 and 3.5 hr, respectively, after the last co caine or saline injection. Acute (2 d) binge cocaine administration di d not change the in vivo binding potential of [C-11]SCH23390 or the bi nding of [C-11]NMSP in the striatum. After 7 d of binge cocaine admini stration, a significant decrease in the binding potential of [C-11]SCH 23390 was observed, whereas no change in the binding of [C-11]NMSP was found. After 14 d of binge cocaine administration, the in vivo bindin g was significantly reduced for both [C-11]SCH23390 and [C-11]NMSP. Se parate saturation experiments indicated that the observed alterations of in vivo binding were attributable mainly to apparent alterations in the affinity and not the number of binding sites. These results sugge st that both dopamine D-1 and D-2 receptors may have altered physiolog ically available binding sites after binge pattern cocaine administrat ion.