Regional Differences Within the Rat Ventral Tegmental Area for Muscimol Self-Infusions

Abstract

The present study examined the effects of activating GABA A receptors in the anterior and posterior regions of the ventral tegmental area (VTA) on operant reinforcement behavior, using the technique of intracranial self-administration. Rats were given the opportunity to self-administer vehicle alone (artificial CSF) and vehicle containing 25, 50, and 100 μM muscimol, a GABA A agonist, into the anterior or posterior VTA during four sessions (3 h/session) in standard two-lever operant chambers. Rats received five times greater infusions of 50 and 100 μM muscimol than vehicle into the posterior VTA; both doses significantly increased responding above vehicle levels on the active and inactive (control) levers equally. When the response requirement for muscimol infusions was increased from a fixed-ratio 1 (FR1) to FR3 in a single-lever chamber, the total session responses increased approximately twofold. Muscimol was not self-infused when cannula placements were in the anterior VTA. The self-infusion of muscimol into the posterior VTA was attenuated by coadministration of picrotoxin. Overall, the results suggest that the activation of GABA A receptors in the posterior VTA produces goal-directed behavior.