NEUROPHARMACOLOGICAL EVIDENCE FOR THE ROLE OF DOPAMINE IN VENTRAL PALLIDUM SELF-STIMULATION

The present study examines the role of dopaminergic neurotransmission in modulating the reinforcing effect of ventral pallidum (VP) intracra nial self-stimulation (ICSS). Fifty four adult rats were implanted wit h a monopolar moveable stimulating electrode in the VP. Rate-frequency functions were determined by logarithmically decreasing the number of pulses in a stimulation train from a value that sustained maximal res ponding to one that did not sustain responding. After the ICSS thresho lds stabilized, the animals received treatments with several doses of cocaine and of various selective drugs acting at the level of DA recep tor subtypes. Their effects on threshold and asymptotic rate were anal yzed. Cocaine produced a significant decrease in ICSS threshold but ha d no significant effect on the asymptotic rate. A significant decrease in ICSS threshold was also seen with the D-3 agonist 7-OH-DPAT This w as associated with a decrease rather than an increase in performance. D-1 and D-2 DA receptor blockers (haloperidol, SCH-23390, raclopride a nd sulpiride) produced a dose dependent increase in ICSS threshold and a decrease in the maximal rate. The results suggest that DA plays a m odulatory role in VP intracranial self-stimulation, and that D-1, D-2 and D-3 receptors are involved in the mediation of this effect, althou gh to different extents.