Effects of Binge Pattern Cocaine Administration on Dopamine D1and D2Receptors in the Rat Brain: AnIn VivoStudy Using Positron Emission Tomography

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Abstract
The aim of the present study was to determine the effect of “binge” pattern cocaine administration on dopamine D1and D2receptors in the rat brain. Male Sprague Dawley rats were injected three times at 1 hr intervals with saline or cocaine (15 mg/kg) each day for 2, 7, or 14 d. Thein vivobinding of [11C]SCH23390 (dopamine D1receptor antagonist) and [11C]N-methylspiperone (NMSP; dopamine D2receptor antagonist) in the striatal region was measured by a high-resolution positron emission tomography at 1 and 3.5 hr, respectively, after the last cocaine or saline injection. Acute (2 d) binge cocaine administration did not change thein vivobinding potential of [11C]SCH23390 or the binding of [11C]NMSP in the striatum. After 7 d of binge cocaine administration, a significant decrease in the binding potential of [11C]SCH23390 was observed, whereas no change in the binding of [11C]NMSP was found. After 14 d of binge cocaine administration, thein vivobinding was significantly reduced for both [11C]SCH23390 and [11C]NMSP. Separate saturation experiments indicated that the observed alterations ofin vivobinding were attributable mainly to apparent alterations in the affinity and not the number of binding sites. These results suggest that both dopamine D1and D2receptors may have altered physiologically available binding sites after binge pattern cocaine administration.