REGIONAL DIFFERENCES WITHIN THE RAT VENTRAL TEGMENTAL AREA FOR MUSCIMOL SELF-INFUSIONS

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 intracr anial self-administration. Rats were given the opportunity to self-adm inister vehicle alone (artificial CSF) and vehicle containing 25, 50, and 100 mu M muscimol, a GABA(A) agonist, into the anterior or posteri or VTA during four sessions (3 h/session) in standard two-lever operan t chambers. Rats received five times greater infusions of 50 and 100 m u M muscimol than vehicle into the posterior VTA; both doses significa ntly increased responding above vehicle levels on the active and inact ive (control) levers equally. When the response requirement for muscim ol infusions was increased from a fixed-ratio 1 (FR1) to FR3 in a sing le 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 VT A was attenuated by coadministration of picrotoxin. Overall, the resul ts suggest that the activation of GABA(A) receptors in the posterior V TA produces goal-directed behavior. (C) 1998 Elsevier Science Inc.