Regional reward differences within the ventral pallidum are revealed by microinjections of a mu opiate receptor agonist.
The ventral pallidum receives a major projection from the nucleus accumbens, a heavily studied terminus of the mesolimbic dopamine system that is known to be involved in a variety of reward and behavioral functions. Recently, ventral pallidum microinjections of the mu opiate receptor agonist Tyr-D-Ala-Gly-NMe-Phe-Gly-ol-enkephalin (DAMGO) have been shown to increase motor activity while ventral pallidum lesions have been shown to reduce opiate and cocaine self-administration behaviors. These results suggest a possible continuation of the mesolimbic reward/motor circuit from the nucleus accumbens into the ventral pallidum. This study investigated the effects of ventral pallidum DAMGO microinjections on reward and motor/performance through the use of the intracranial self-stimulation rate-frequency curve-shift paradigm. Microinjections of DAMGO (vehicle, 0.03 nmol, and 0.33 nmol) were administered bilaterally in a random dose order with a minimum of 3 days between injections. Rats were tested over three consecutive rate-frequency curves immediately following the opiate microinjections to investigate the time course of drug effects. DAMGO microinjections in the rostral ventral pallidum produced decreases in reward and motor/performance when compared to normal baseline activity or vehicle microinjections. In contrast, DAMGO microinjections into the caudal ventral pallidum produced increases in reward and motor/performance. These data confirm a role for the ventral pallidum in limbic function and extend it to intracranial self-stimulation reward. They also suggest reward modulation in the ventral pallidum is a regionally heterogeneous function and that the rostral ventral pallidum may be a transition area between the nucleus accumbens and the ventral pallidum.
Johnson
P I
PI
Department of Psychology, Northeastern University, Boston, MA 02115.
Stellar
J R
JR
Paul
A D
AD
D000700:Analgesics / Q000494:pharmacology*; D000704:Analysis of Variance; D000818:Animals; D001921:Brain / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D004745:Enkephalins / Q000008:administration & dosage / Q000494:pharmacology*; D005917:Globus Pallidus / Q000187:drug effects / Q000502:physiology*; D008297:Male; D008845:Microinjections; D009043:Motor Activity / Q000187:drug effects; D009928:Organ Specificity; D051381:Rats; D017450:Receptors, Opioid, mu / Q000187:drug effects / Q000502:physiology*; D012054:Reinforcement, Psychology; D012201:Reward; D012653:Self Stimulation
D000700:Analgesics; D004745:Enkephalins; D017450:Receptors, Opioid, mu; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-