ISOLATION REARING ENHANCES THE LOCOMOTOR STIMULANT PROPERTIES OF INTRA-PERIFORNICAL SULPIRIDE, BUT IMPAIRS THE ACQUISITION OF A CONDITIONEDPLACE PREFERENCE

Previous data indicated that infusions of the D-2/D-3 dopamine recepto r antagonist sulpiride within the perifornical region of the lateral h ypothalamus may engage neural circuitry relevant to activation of the mesoaccumbens dopamine projection. The present work examined this prop osition further. Experiment 1 examined the ability of intra-perifornic al sulpiride to induce a conditioned place preference, using an unbias ed conditioning procedure. Thus, bilateral guide cannulae were implant ed to gain access to the perifornical region of the lateral hypothalam us. Following recovery, animals were subjected to an initial exposure to the place preference apparatus, The apparatus consisted of three di stinctive compartments, the central compartment allowing access to the two outermost compartments. Initial exposure indicated equal preferen ce for each. Then, in alternating sessions, animals received infusions of sulpiride (5, 10 or 20 mu g) before being placed in one of the two outermost compartments, and infusions of vehicle before being placed in the alternate compartment. Compartment-drug pairings were counterba lanced across animals. Four drug, and four saline sessions were comple ted, each being separated by at least 2 full days. On the final test d ay, animals were allowed Free access to compartments, and the time spe nt in each was compared with that of initial exposure. Results showed that intra-perifornical sulpiride increased activity during drug-condi tioning sessions in an incremental Fashion, and supported dose-depende ntly the acquisition of a conditioned place preference. Experiment 2 e xamined the effects of isolation rearing upon the locomotor stimulant properties of intra-perifornical sulpiride, and the acquisition of a c onditioned place preference. Rats were raised from weaning either alon e (isolation-reared) or in groups of five (socially-reared controls) u ntil 4 months of age. Consistent with previous reports of the effects of isolation rearing upon psychomotor stimulant responsivity, here iso lates were found to be more responsive to the locomotor stimulant prop el tics of intra-perifornical sulpiride, but were less responsive to t he ability of intra-perifornical sulpiride to support the acquisition of a conditioned place preference. These data were suggested to provid e further support for the proposition that blockade of dopamine recept ors of the D-2 family within the perifornical region of the lateral hy pothalamus results in the activation of the mesoaccumbens dopamine pro jection, via the ventral tegmental area.