ONTOGENY OF THE BEHAVIORAL-RESPONSE TO DOPAMINE AGONISTS AFTER CHRONIC COCAINE

The behavioral response to separate and combined administration of dop amine D-1 and D-2 receptor agonists was assessed acutely and after chr onic cocaine exposure (30 mg/kg SC b.i.d. for 5 days) in infant (PND11 ) and weanling (PND20) rats. In infants, quinpirole (quin) and SKF-383 93 (SKF) elevated locomotion, mouthing and sniffing acutely. Rearing w as increased and mouthing decreased by combined administration. In wea nlings, quin increased locomotion, mouthing and sniffing in weanlings, while SKF increased only mouthing. SKF inhibited quin-induced rearing and locomotion. Infants treated chronically with cocaine showed sensi tized quin- and quin/SKF-induced locomotion and quin/SKF stimulated re aring and sniffing. In weanlings, locomotion was sensitized with all d rug combinations, and rearing with SKF alone. These results indicate a developmental progression in the psychopharmacological response to do pamine receptor stimulation. While both D-1 and D-2 receptors are acti ve in infants, the full complement of acute responses and complete cap acity for sensitization develop later.