Abstract
Chronic exposure to drugs of abuse is known to modulate tyrosine hydroxylase (TH) levels in the mesolimbic dopamine system. In this study, 12 d of cocaine self-administration in rats (4 hr/d) reduced TH immunoreactivity by 29% in the nucleus accumbens (NAc) shell, but not core, after a 1 week withdrawal period. In contrast, TH immunoreactivity in the NAc was completely restored in animals that experienced extinction training (4 hr/d) during the same withdrawal period. Extinction training also increased TH levels in the ventral tegmental area (VTA) by 45%, whereas TH was not altered in the VTA by cocaine withdrawal alone. Thus, extinction-induced normalization of NAc TH levels could involve increased TH synthesis, stability, and/or transport from the VTA to the NAc. A similar extinction training regimen failed to alter TH levels in the NAc or VTA of rats trained to self-administer sucrose pellets, indicating that TH regulation in cocaine-trained animals is not a generalized effect of extinction learning per se. Rather, these data suggest that neuroadaptative responses during cocaine withdrawal ultimately are determined by a complex interaction between chronic drug exposure and drug-seeking experience. The ability of extinction training to restore NAc TH levels is hypothesized to accelerate recovery from dopamine depletion and anhedonia during cocaine withdrawal.
Highlights
Chronic exposure to drugs of abuse is known to modulate tyrosine hydroxylase (TH) levels in the mesolimbic dopamine system
This study examined the effects of chronic cocaine selfadministration, withdrawal, and extinction training on regulation of TH immunoreactivity in nucleus accumbens (NAc) and ventral tegmental area (VTA) tissue
We found that 12 d of 4 hr daily access to cocaine self-administration decreases TH immunoreactivity in NAc shell, but not core, and this reduction persists and intensifies for at least 1 week into withdrawal
Summary
Chronic exposure to drugs of abuse is known to modulate tyrosine hydroxylase (TH) levels in the mesolimbic dopamine system. Extinction-induced normalization of NAc TH levels could involve increased TH synthesis, stability, and/or transport from the VTA to the NAc. A similar extinction training regimen failed to alter TH levels in the NAc or VTA of rats trained to self-administer sucrose pellets, indicating that TH regulation in cocaine-trained animals is not a generalized effect of extinction learning per se. A similar extinction training regimen failed to alter TH levels in the NAc or VTA of rats trained to self-administer sucrose pellets, indicating that TH regulation in cocaine-trained animals is not a generalized effect of extinction learning per se Rather, these data suggest that neuroadaptative responses during cocaine withdrawal are determined by a complex interaction between chronic drug exposure and drug-seeking experience. Rapid Communications are posted online approximately one month earlier than they would appear if printed They are listed in the Table of Contents of the open issue of JNeurosci. The publication date is the date of posting online at www.jneurosci.org
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