Functional maturation of the GABAergic inhibition on dopamine-mediated behaviours during the neonatal period in the mouse.

Previous works have indicated that systemic injection of GABA-agonists depress motoric behaviours in neonatal murids, suggesting an early maturation of GABAergic inhibitory processes. In this paper, the inhibitory effects of muscimol, a postsynaptic GABAA-agonist, on D-amphetamine-induced enhancement of locomotion, wall-climbing and head-raising were examined in neonatal 5-, 8- and 11-day-old mouse pups, using a direct observational procedure. The results show that muscimol can selectively attenuate high levels of locomotion, wall-climbing and head-raising produced by the indirect dopamine agonist in 8- as well as 11-day-old pups. However, while muscimol is able to moderate amphetamine-induced wall-climbing and head-rising in 5-day-old pups, no GABAergic inhibition was seen for locomotion at this age. Licking episodes elicited by amphetamine in 11-day-old pups can be magnified by muscimol if the dosage of the former is relatively too potent. It is suggested that the GABAergic inhibitory processes on dopaminergic functioning have reached good levels of functional maturation in the neonatal murid.