Behavioral sensitization to apomorphine in adult rats exposed to cocaine during the preweaning period: A preliminary study

Sixty-day-old rats treated with cocaine (50 mg/kg SC) during postnatal days (PND) 11-20 received daily injections of apomorphine (2.0 mg/kg SC) for 10 consecutive days to examine the development of sensitization to a direct dopamine agonist. Behavior was monitored on days 1, 5, and 10, using a photobeam system, and on day 10 using the videotape assessments as well. Locomotor sensitization to apomorphine developed in the preweaning vehicle-treated males only. Neither the cocaine-treated males nor any females exhibited locomotor sensitization to repeated apomorphine injections at 2 mg/kg. There were no other treatment-related effects except for grooming, which showed an interaction between treatment and gender. Overall, every behavior analyzed showed significant apomorphine effects, except rearing. Margin time (wall hugging), grooming, and quiet were significantly decreased by apomorphine, while locomotion and the duration of sniffing were increased. In summary, these data indicate that with respect to locomotor activity, the development of sensitization to apomorphine at 2.0 mg/kg is prevented by preweaning cocaine administration in males. These data further suggest that developmental cocaine exposure produces long-term alterations in DA D₁ receptor-mediated responses in male rats. Copyright (C) 1999 Elsevier Science Inc.