Effects of neonatal dopamine depletion on spatial ability during ontogeny

Evidence suggests that dopaminergic systems are critical for the learning and memory of spatial discriminations in the adult rat. However, the effect that early dopaminergic lesions have on spatial discriminations throughout development has not been examined. Thus the present experiments investigated the effects of neonatal dopamine (DA) depletion on spatial discrimination tasks. Subjects were lesioned at 3 and 6 days of age with intraventricular 6-hydroxydopamine preceded by desipramine. In Experiment 1 subjects were tested before weaning for the ability to spontaneously alternate in a T-maze both in the presence of their home cage shavings and with a screen covering the shavings. Lesioned animals were significantly impaired in their ability to spontaneously alternate. Control and lesioned animals both showed a decrease in performance when the screen prevented full access to the shavings, and the magnitude of the impairment was significantly greater for the lesioned animals. In Experiment 2, subjects were tested after weaning in an appetitively motivated task in T-maze. The task required both a functional working and a reference memory. Lesioned animals were impaired on both the working and the reference component of the task; however, the magnitude of the impairment was greater in the working memory task. These results suggest that early lesions of general DA systems produce deficits in tasks requiring spatial alternation behavior. These deficits can be exaggerated by certain environmental stimuli and are not reversed by food reward.