Evaluation of neonatal exposure to cocaine on learning, activity, startle,scent marking, immobility, and plasma cocaine concentrations

Prenatal cocaine treatment produces equivocal effects on spatial learning a nd memory; however, no data are available on neonatal treatment as a model of human third-trimester exposure. Sprague-Dawley rats were treated on post natal days (P) 1-10 or 11-20 with cocaine (15 mg/kg x 4 per day at 2-h inte rvals) or saline (P1-P20) and evaluated as adults in the Morris water maze and on tests of activity, startle, scent marking, swimming immobility, and sequential learning. Neonatal cocaine had no effect on mortality; however, early treatment reduced body weight, whereas later treatment did not. Neona tal cocaine had no effects on exploratory activity, swimming ability, seque ntial learning, multiday activity rhythms, scent marking, or swimming immob ility, but augmented acoustic startle amplitude in the early-treated group. Neonatal cocaine also produced an interaction on spatial learning in which the cocaine early-treated males performed slightly more efficiently than c ontrols. Plasma cocaine concentrations were significantly higher in the ear ly-treated group than the later-treated group despite receiving the same we ight-adjusted doses. It was concluded that neonatal cocaine, when administe red during a stage of brain development analogous to human third trimester, induces few behavioral effects based on the assessments used in this study . (C) 2000 Elsevier Science Inc. All rights reserved.