The ontogenetic course of dopaminergically mediated gnawing and the potentiation of this behavior by muscimol (a GABA receptor agonist) was explored in developing and young adult mice using a time-sampling (in 5-, 8-, 11-, and 14-day-old pups), or a corrugated paper procedure (in 14-, 17-, 20-, 23-, 26-, 35-, and 53-day-old animals). In experiment 1, the older mice group (14-53 days), displayed a dose-dependent gnawing behavior after methylphenidate, a dopamine indirect agonist (20, 30, 50 mg/kg). Similarly, in 5-, 8-, 11-, and 14-day-old pups, methylphenidate (10, 20, 50 mg/kg) evoked stereotyped gnawing (or indissociable gnawing-licking in 5-day-old pups), with maximal effects after the two lower doses at 8-11 days of age (experiment 2). Muscimol pretreatment (dosages ranging from 0.025 to 1.3 mg/kg) induced a clear-cut potentiation of gnawing elicited by methylphenidate (10 or 20 mg/kg) as early as 8 days of age (experiments 3 and 4). However, muscimol did not potentiate gnawing in 5-day-old pups treated with 10 or 2.5 mg/kg methylphenidate. The effectiveness of methylphenidate in inducing gnawing-licking among 5-day-old pups confirms the early maturation of central dopamine receptors reported in the literature. It is speculated that the absence of potentiating action of muscimol on methylphenidate-induced gnawing-licking at this age may be due to a functional immaturity of the GABAergic striato-nigro-tectal system, which is thought to transmit dopaminergic striatal stereotyped response at the output stations (recent review by Scheel-Krüger 1986).(ABSTRACT TRUNCATED AT 250 WORDS)