Psychopharmacological effects of low and high doses of apomorphine during ontogeny

The effects of low (0.05 and 0.1 mg/kg) and high (1.0 and 3.0 mg/kg) doses of apomorphine on locomotor activities and stereotypies of 7, 14, 21, 28 and 35 day old rats were measured using a behavioral time-sampling procedure. High doses of apomorphine induced increases in matrix crossings and locomotor movements at all ages tested. Apomorphine also induced wall climbing behavior in 7 and 14 day olds, but not older animals. A low dose suppression of activity was not seen until beginning at 28 days after birth using matrix crossings as a response measure, or at 35 days after birth using locomotor movements as a response measure. Stereotyped sniffing was not significantly increased by apomorphine until 21 days after birth and thereafter. Results are discussed in terms of differential maturation of dopamine auto- and postsynaptic receptors.