RT Journal Article
SR Electronic
T1 Rewarding and Psychomotor Stimulant Effects of Endomorphin-1: Anteroposterior Differences within the Ventral Tegmental Area and Lack of Effect in Nucleus Accumbens
JF The Journal of Neuroscience
JO J. Neurosci.
FD Society for Neuroscience
SP 7225
OP 7233
DO 10.1523/JNEUROSCI.22-16-07225.2002
VO 22
IS 16
A1 Abraham Zangen
A1 Satoshi Ikemoto
A1 James E. Zadina
A1 Roy A. Wise
YR 2002
UL http://www.jneurosci.org/content/22/16/7225.abstract
AB Endomorphin-1 (EM-1) is a recently isolated endogenous peptide having potent analgesic activity and high affinity and selectivity for the μ-opioid receptor. The present study was designed to investigate the rewarding and psychomotor stimulant effects of EM-1 in specific brain regions. We found that rats would learn without priming or response shaping to lever-press for microinjections of EM-1 into the ventral tegmental area (VTA); responding was most vigorous for high-dose injections into the posterior VTA. Rats did not learn to lever-press for microinjections of EM-1 into the nucleus accumbens (NAS) or regions just dorsal to the VTA. Lever-pressing for EM-1 in the VTA was extinguished when vehicle was substituted for the peptide and was reinstated when EM-1 reinforcement was re-established. Conditioned place preference was established by EM-1 injections into the posterior but not the anterior VTA or the NAS. Injection of EM-1 (0.1–1.0 nmol) into the posterior VTA induced robust increases in locomotor activity, whereas injections into the anterior VTA had very weak locomotor-stimulating effects. When injected into the NAS, EM-1 (0.1–10.0 nmol) did not affect locomotor activity. The present findings implicate the posterior VTA as a highly specific and sensitive site for opioid reward and suggest a role for EM-1-containing projections to the posterior VTA in the rewarding effects of other reinforcers.