To determine whether repeated exposure of cocaine affects the dopaminergic
innervation of the nucleus accumbens, we employed a typical cocaine-dosing
regimen in adult male Sprague-Dawley rats followed by an immunocytochemical
analysis of tyrosine hydroxylase (TH), Treatment consisted of bi-daily inj
ections of saline or 15 mg/kg cocaine for 5 consecutive days. After 2 or 14
days of withdrawal, sections of the nucleus accumbens (NAc) were processed
for tyrosine hydroxylase and the number of immunoreactive varicosities in
the core and shell were quantified. Two days after treatment, the core demo
nstrated a decrease, while after 14 days of treatment, the shell was found
to contain significantly more TH Immunoreactive varicosities. Additionally,
2 days post-cocaine treatment, core-shell differences were found, however
moderate differences were also found in the saline treatment group, making
the absolute effects of cocaine difficult to separate from injection and ha
ndling effects at this time point. These results suggest that the shell of
the NAc may undergo alterations that could be involved with behavioral sens
itization that typically results from such cocaine treatment regimens. (C)
2000 Elsevier Science Inc.