The GABA-A agonist muscimol facilitates muscular twitches and locomotor movements in the neonatal mouse.

The effects of nonsedative doses of muscimol, a postsynaptic GABA-A agonist, on neurobehavioral activities in 5- and 11-day-old newborn mice were assessed using an observational point sampling procedure. Muscimol activated the emission of muscular twitches after injections of 0.025 or 0.050 mg/kg in 5-day-old pups, and 0.075 mg/kg in 11-day-old pups. At 0.075 mg/kg, the GABA agonist also produced an increase of locomotor movement levels in the younger age group. Given that muscimol at low dosages typically produces an increase of locomotion in mature mice, it is suggested that the GABAergic activity involved in locomotor behaviors is functional very early in life. Furthermore, since twitching behavior exhibited while lying presumably indicates paradoxical sleep early in life, it is speculated that muscimol may have activated this form of sleep in our newborn mice.