Journal of Neuroscience, Vol 10, 2940-2949, Copyright © 1990 by Society for Neuroscience
Effect of acute and daily neurotensin and enkephalin treatments on extracellular dopamine in the nucleus accumbens
PW Kalivas and P Duffy
Department of Veterinary and Comparative Anatomy, Pharmacology and Physiology, Washington State University, Pullman 99164-6520.
The injection of neurotensin or the enkephalin analog Tyr-D-Ala-Gly-
MePhe-Gly(ol) (DAMGO) into the A10 region of rats produces a motor
stimulant effect that is associated with an increase in the postmortem
levels of dopamine metabolites in the nucleus accumbens. These behavioral
and neurochemical effects are augmented following daily administration. In
vivo dialysis in the nucleus accumbens of conscious rats was used to
determine if the acute and augmented behavioral responses following
neurotensin or DAMGO administration are associated with an increase in
extracellular dopamine concentrations. The acute injection of DAMGO
produced a dose-dependent (0.03-3.3 nmol) elevation in extracellular
dopamine and its metabolites in the nucleus accumbens. Neurotensin also
produced a dose-related (0.1-3.3 nmol) increase in dopamine and its
metabolites. The elevation in extracellular dopamine produced by DAMGO, but
not by neurotensin, was positively correlated with the increase in motor
activity. Following daily treatment of either neurotensin (1.0 nmol X 4 d)
or DAMGO (0.03 nmol X 4 d), a significant elevation in extracellular
dopamine levels occurred in the nucleus accumbens compared to an acute
injection. The time course of the change in extracellular dopamine after
daily injections was similar to the time course of the behavioral
stimulation for both compounds. These data demonstrate that enhanced
dopamine release in the nucleus accumbens mediates the acute behavioral
effect of DAMGO but does not entirely explain the motor effects of
neurotensin. However, enhanced dopamine release may mediate the behavioral
sensitization produced by daily injection of both peptides into the A10
region.