EFFECTS OF ACCUMBENS DALA MICROINJECTIONS ON BRAIN-STIMULATION REWARD AND BEHAVIORAL ACTIVATION IN INTACT AND 6-OHDA TREATED RATS

The effects of bilateral nucleus accumbens microinjections of d-ala-met-enkephalinamide (DALA) were assessed in behavioral activation and lateral hypothalamic self-stimulation (LHSS) rate-frequency curveshift paradigms in normal and accumbens 6-OHDA (4.0 mu g) treated rats. Microinjections of DALA (2.5 mu g/mu l) in the behavioral activation paradigm had little effect on normal activity; however, DALA administered to 6-OHDA treated rats produced a significant overall increase in locomotion. The 6-OHDA DALA-induced locomotion effect peaked at 2 weeks after 6-OHDA treatment and then returned to baseline levels by week 5 posttreatment. Using LHSS, DALA tested over a range of doses (2.5, 5, 10, 20 mu g/mu l) displayed a weak biphasic reward effect only at the highest dose, which was characterized by an initial suppression followed by an elevation. DALA significantly depressed initial operant motor/performance in LHSS in a dose dependent fashion. Microinjections of the normally ineffective low dose of DALA (2.5 mu g/mu l) following accumbens 6-OHDA treatment produced a significant LHSS reward decrease 2 weeks posttreatment, while LHSS motor/performance was relatively unaffected. Results are discussed in terms of opiate-dopamine and limbic-motor interactions.