Dopamine-GABAergic mechanisms of rearing and locomotion in infant and weanling mice

Abstract

This ontogenetic study examined the modulatory effects of the GABA-A agonist muscimol on supported rearing and locomotion induced by the indirect dopamine agonist D-amphetamine. Infant 14-day-old, weanling 20-day-old, and adult 53-day-old outbred mice were tested. In the adult mice, muscimol at 1.3 mg/kg attenuated 2 mg/kg D-amphetamine-induced locomotion but not rearing, whereas 1.9 mg/kg muscimol blocked both behaviors. While 0.025 mg/kg muscimol reduced 2 mg/kg D-amphetamine-induced rearing without altering locomotion in infants, it affected neither rearing nor locomotion in weanlings. At this age, 0.075 mg/kg muscimol blocked both behaviors well. In the infant mice, however, this dose of muscimol engendered gnawing and self-biting, a typical effect of dopamine-GABAergic pharmacological activation. A smaller dose of 1.25 mg/kg D-amphetamine was necessary to avoid this effect and to obtain a direct attenuation of locomotion and rearing. Given that we have previously obtained an attenuation of D-amphetamine-induced locomotion and wall climbing (which is mostly displayed by preweanling murines) with muscimol in 8- and 11-day-old neonatal mice pups (Tirelli, 1989a), it is concluded that maturation of dopamine-GABAergic behavioral functions follows a near-monotonic continuity starting a few days after birth. © 1990, Psychonomic Society, Inc.. All rights reserved.