Journal of Neuroscience, Vol 12, 4372-4380, Copyright © 1992 by Society for Neuroscience
Increases in extracellular dopamine in the nucleus accumbens by cocaine are inversely related to basal levels: effects of acute and repeated administration
F Weiss, MP Paulus, MT Lorang and GF Koob
Department of Neuropharmacology, Scripps Research Institute, La Jolla, California 92037.
Repeated administration of cocaine enhances several of the behavioral and
neurochemical responses to subsequent cocaine injections, an effect that
has been attributed, in part, to decreased somatodendritic autoreceptor
sensitivity of mesocorticolimbic dopamine (DA) neurons. Such changes in
autoregulation may not only modify the direct effects of cocaine on
extracellular DA levels but also result in tonically increased basal DA
release in the terminal areas of the mesocorticolimbic DA system. The
present study was therefore designed to investigate the effects of repeated
cocaine administration on basal extracellular DA concentrations in the
nucleus accumbens (NAC) using in vivo microdialysis procedures in
halothane-anesthetized rats. We subsequently examined the relationship
between basal DA levels and the increase in extracellular DA produced by an
acute injection of cocaine, and determined whether this relationship was
altered by prior, repeated exposure to cocaine. Rats received one daily
intraperitoneal injection of cocaine (30 mg/kg) or its vehicle (saline) for
10 consecutive days. On days 1, 3, or 7 after termination of the repeated
cocaine treatment, extracellular DA levels in the NAC were determined under
basal conditions and following a single intraperitoneal cocaine challenge
injection (10 mg/kg) in separate groups of rats. Repeated cocaine
administration produced a substantial increase in basal DA release in the
NAC that was most prominent on day 1 post-cocaine (mean +/- SEM: 10.7 +/-
2.55 nM vs 3.55 +/- 0.56 nM) but was no longer apparent on day 7
post-cocaine. Higher extracellular DA levels were also observed after
cocaine challenge in rats that received repeated cocaine treatments.
Similar to the increase in basal release, this effect was most pronounced
on day 1 post-cocaine (23.6 +/- 4.36 nM vs 12.61 +/- 1.76 nM) but did not
persist through day 7 post-cocaine.(ABSTRACT TRUNCATED AT 250 WORDS)