Assessment of tyrosine hydroxylase immunoreactive innervation in five subregions of the nucleus accumbens shell in rats treated with repeated cocaine

To explore the effects of behavioral sensitization on the anatomy of the nu cleus accumbens shell, we employed a typical cocaine dosing paradigm and as sessed tyrosine hydroxylase immunoreactive varicosities in five different a reas of the shell, as well as the core of the nucleus accumbens. Rats were given bidaily injections of either saline (1 ml/kg i.p.) or cocaine (15 mg/ kg i.p.) for 5 consecutive days, and sacrificed either 2 or 14 days from th e last injection. Sections of the nucleus accumbens were processed for tyro sine hydroxylase immunoreactivity and the number of immunoreactive varicosi ties in contact with neuronal cell bodies was quantified in each of the sub regions of the shell, as well as the core of the nucleus accumbens. Compare d to saline controls, the cocaine-treated animals showed a significant augm entation in tyrosine hydroxylase immunoreactivity in two of the five subreg ions after 2 days of withdrawal in the shell, but not in the core. No diffe rences were found in any region tested after 14 days of withdrawal. These d ata are the first to suggest that increases in nucleus accumbens presynapti c tyrosine hydroxylase may play a role in the development of behavioral sen sitization, but not in the long-term expression of this phenomenon. (C) 200 0 Wiley-Liss, Inc.