INTRA-VTA INJECTIONS OF THE MU-OPIOID ANTAGONIST CTOP ENHANCE LOCOMOTOR-ACTIVITY

In this paper we report on the effects of microinjections of the mu-op ioid antagonist CTOP (D-Pen-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2) into th e ventral tegmental area (VTA) on activity and ingestive behavior in t he rat. Intra-VTA CTOP (0.015, 0.15, and 1.5 nmol per side) dose-depen dently increased activity, whereas it had no effect on feeding and dri nking behavior. These results are consistent with previous reports tha t intra-VTA injections of CTOP enhance extracellular dopamine levels i n the nucleus accumbens. Furthermore, we propose a model of VTA mu-opi oid mechanisms that might account for these surprising effects of intr a-VTA CTOP.