Regional reward differences within the ventral pallidum are revealed by microinjections of a mu opiate receptor agonist |
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Authors: | Patricia I. Johnson J.R. Stellar A.David Paul |
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Affiliation: | Department of Psychology, Northeastern University, 125 Nightingale Hall, Boston, MA 02115, U.S.A. |
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Abstract: | 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 μ opiate receptor agonist Tyr--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. |
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Keywords: | ventral pallidum intracranial self-stimulation reward μ opiate receptors DAMGO |
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