RETARDED ACQUISITION AND REDUCED EXPRESSION OF CONDITIONED LOCOMOTOR-ACTIVITY IN ADULT-RATS FOLLOWING REPEATED EARLY MATERNAL SEPARATION - EFFECTS OF PREFEEDING, D-AMPHETAMINE, DOPAMINE ANTAGONISTS AND CLONIDINE

Adult hooded rats exposed to a repeated maternal separation procedure during the neonatal period showed a blunted expression of locomotor hy peractivity conditioned to the presentation of the daily food ration, We have demonstrated that the expression of food-conditioned anticipat ory hyperactivity is sensitive to the response-enhancing effects of sy stemic d-amphetamine (0.5; 1.0 mg/kg) and to the response-attenuating effects of the selective dopamine D-2 antagonist sulpiride (8; 20 mg/k g), the selective dopamine D-1 antagonist SCH 23390 (0.01; 0.022 mg/kg ) and the mixed alpha(1)/alpha(2) adrenoceptor agonist clonidine (5; 1 5 mu g/kg) in a dose dependent manner. Animals from the early separati on groups showed a reduced enhancement of activity in response to 0.5 mg/kg d-amphetamine and a greater attenuation of activity in response to 8 mg/kg sulpiride and 5 mu g/kg clonidine. Female separated rats al so exhibited an attenuated locomotor response to the unconditioned sti mulant effects of 0.5 mg/kg systemic d-amphetamine. The experiments co nfirm that early maternal separation attenuates the response to condit ioned appetitive cues in adult rats and implicate altered dopaminergic and noradrenergic function in the changes. It is possible that early maternal separation in the rat may offer a useful preparation for inve stigation of the neural substrates mediating affective development and affective psychopathology.