The Journal of Neuroscience, December 15, 2002, 22(24):10856-10863
Elevated Expression of 5-HT1B Receptors in Nucleus
Accumbens Efferents Sensitizes Animals to Cocaine
John F.
Neumaier1,
Evelyn S.
Vincow1,
Andreas
Arvanitogiannis2,
Roy A.
Wise3, and
William A.
Carlezon Jr2
1 Department of Psychiatry and Behavioral Sciences and
Harborview Medical Center, University of Washington, Seattle,
Washington 98195, 2 Department of Psychiatry, Harvard
Medical School and McLean Hospital, Belmont, Massachusetts 02478, and
3 Intramural Research Program, National Institute on Drug
Abuse, Baltimore, Maryland 21224
Although the effects of psychostimulants on brain dopamine systems
are well recognized, the direct actions of cocaine on serotonin systems
also appear to be important to its addictive properties. For example,
serotonin actions at 5-HT1B receptors in the ventral tegmental area (VTA) modulate cocaine-induced dopamine release in the
nucleus accumbens (NAcc) and alter the rewarding and stimulant properties of cocaine. However, the mechanisms of these effects have
been unclear, because several neuron types in VTA express 5-HT1B receptors. One possibility is that
5-HT1B receptors on the terminals of GABAergic projections
from NAcc to VTA inhibit local GABA release, thereby disinhibiting VTA
neurons. We tested this hypothesis directly by using viral-mediated
gene transfer to overexpress 5-HT1B receptors in NAcc
projections to VTA. A viral vector containing either epitope
hemagglutinin-tagged 5-HT1B and green fluorescent protein
(HA1B-GFP) cassettes or green fluorescent protein cassette
alone (GFP-only) was injected into the NAcc shell, which sends
projections to the VTA. HA1B-GFP injection induced elevated expression
of 5-HT1B receptors in neuronal fibers in VTA and increased
cocaine-induced locomotor hyperactivity without affecting baseline
locomotion. Overexpression of 5-HT1B receptors also shifted
the dose-response curve for cocaine-conditioned place preference to
the left, indicating alterations in the rewarding effects of cocaine.
Thus, increased expression of 5-HT1B receptors in NAcc
efferents, probably in the terminals of medium spiny neurons projecting
to the VTA, may contribute to psychomotor sensitization and offer an
important target for regulating the addictive effects of cocaine.
Key words:
herpes simplex virus; gene transfer; ventral
tegmental area; conditioned place preference; locomotor; hyperactivity
Copyright © 2002 Society for Neuroscience 0270-6474/02/222410856-08$05.00/0