Absence of sparing of spatial navigation, skilled forelimb and tongue use and limb posture in the rat after neonatal dopamine depletion

Abstract

Depletion of caudate-putamen dopamine (DA) was produced by intraventricular injection of 6-hydroxydopamine (6-OHDA) in three day old rats. When adult, the rats were given cognitive and motor tasks sensitive to adult dopamine depletion, including: tests of cue and place spatial navigation in a swimming pool, a test of skilled forelimb use, requiring reaching for small pellets of food, a test of tongue protrusion, requiring tongue extension to lick mash from a spatula, a test of limb posture, sensorimotor tests of orienting to tactile stimulation and catalepsy. Despite apparent normal physical appearance and locomotor behavior, the rats were impaired on all tasks except orienting to tactile stimulation and catalepsy. There was a significant positive correlation between the degree of impairment on the behavioral tasks and the extent of caudate-putamen dopamine depletion. The results show that sparing of function following neonatal dopamine depletion is selective and incomplete. The results are discussed with respect to the questions of sparing of function following neonatal lesions, the heterogeneous nature of the neonatal depletions and the contributions of dopamine to complex spatial and motor behavior in the rat.