Genetic and ontogenetic variations in locomotor activity following treatment with scopolamine or d-amphetamine.

Highly inbred mice of 3 strains (A/J, DBA/2J, and C57BL/6J) were tested in an open field at 14, 21, or 28 days of age. Ten minutes prior to testing, mice received treatment of saline, scopolamine (.5 or 1.0 mg/kg of body weight), or d-amphetamine (.5, 1.0, or 5.0 mg/kg). The d-amphetamine (5.0 mg/kg) increased activity in all strains at 14 days and 28 days of age, and at 21 days significantly increased activity in all except the C5BL/6. In contrast, increased activity with the scopolamine treatment was seen in DBA/2 at 21 days, but not in A and C57BL/6 until 28 days postnatally. The data support a caudal-rostral gradient of brain development with the inhibitory cholinergic system developing more slowly than the excitatory catecholamine system. In addition, strain-specific differences in activity levels are discussed in relation to the differential rates of chloinergic maturation.