Amphetamine Locomotor Sensitization and Conditioned Place Preference in Adolescent Male and Female Rats Neonatally Treated with Quinpirole

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Neonatal quinpirole treatment has been shown to produce an increase in dopamine D2-like receptor sensitivity that persists throughout the subject's lifetime. The objective was to analyze the effects of neonatal quinpirole treatment on effects of amphetamine in adolescent rats using locomotor sensitization and conditioned place preference procedures. Sprague-Dawley rats were treated with quinpirole (1 mg/kg) or saline from postnatal days (P)1 to P11 and raised to adolescence. For locomotor sensitization, subjects were given amphetamine (1 mg/kg) or saline every second day from P35 to P47 and were placed into a locomotor arena. In female rats, neonatal quinpirole treatment enhanced amphetamine locomotor sensitization compared with quinpirole-free controls sensitized to amphetamine. Male rats demonstrated sensitization to amphetamine, although this was muted compared with female rats, and were unaffected by neonatal quinpirole. For conditioned place preference, subjects were conditioned for 8 consecutive days (P32-39) with amphetamine (1 mg/kg) or saline and a drug-free preference test was conducted at P40. Rats treated with neonatal quinpirole enhanced time spent in the amphetamine-paired context compared with quinpirole-free controls conditioned with amphetamine, but only female controls conditioned with amphetamine spent more time in the drug-paired context compared with saline-treated controls. Increased D₂-like receptor sensitivity appears to have enhanced the behavioral effects of amphetamine, but these effects were more prevalent in adolescent female rats compared with male rats.