Latent learning in a radial arm maze following neonatal dopamine depletion

Animals neonatally depleted of dopamine show decreases in exploratory behaviour. As latent learning may depend on exploratory behaviour the present study was undertaken to examine the effects of neonatal dopamine depletion on latent learning. In two experiments dopamine was depleted neonatally, using 6-hydroxydopamine injected intracisternally on day 1 after birth. In both experiments, exploratory behaviour, measured as rearing and head-dip responses in a modified openfield/holeboard, was reduced in the dopamine depleted rats whereas ambulatory behaviour was elevated. In a modified radial arm maze also, rearing responses were decreased while ambulation was increased for the 6-hydroxydopamine treated rats. Latent learning was tested in each experiment following preexposure to the maze for either a single trial or four trials. 6-Hydroxydopamine treated rats demonstrated a comparable latent learning effect to vehicle treated rats after four maze exposures but showed a greatly attenuated latent learning effect following only a single exposure. It is suggested that the effects of neonatal dopamine upon maze and latent learning are secondary to the effects on hyperactivity, reduced exploration and/or increased neophobia shown by these rats.