Nicotine sensitization increases dendritic length and spine density in the nucleus accumbens and cingulate cortex.

This study investigated the effects of repeated administrations of nicotine (0.7 mg/kg) on dendritic morphology in the nucleus accumbens (NAcc), prefrontal cortex (Cg 3), and parietal cortex (Par 1). Animals were habituated for 3 days to a locomotor box, and after habituation, every second day for 5 weeks rats were placed into the locomotor chamber immediately after a subcutaneous injection of nicotine or saline. Rats demonstrated tolerance to an initial hypoactive response after each nicotine injection, and this was followed by an increase in activity after each injection (behavioral sensitization). This increase in activity was still present on a nicotine challenge after a 2-week abstinence period. One week after the nicotine challenge day, all rats were perfused and brains were removed. These brains we stained using Golgi-Cox procedures, and dendrites from the nucleus accumbens (N Acc), medial frontal cortex (Cg 3) and parietal cortex (Par 1) were analyzed using the camera lucida procedure. Results showed that rats receiving nicotine demonstrated an increase in dendritic length and spine density relative to controls in the NAcc and Cg3 brain areas, but not Par 1. The increase observed in the NAcc was significantly greater than what has been found with amphetamine or cocaine, and possible underlying mechanisms were discussed.