Fig. 14.   Regional selectivity and persistence of effect of a single injection of nicotine (Nic) or cocaine (Coc) on DNA synthesis in neonatal rat brain (Anderson-Brown et al., 1990; McFarland et al., 1991). Both drugs inhibit DNA synthesis within the first 30 min after injection, but only the effect of nicotine is regionally selective, favoring regions that have high nicotinic receptor concentrations. Cocaine elicits uniform inhibition across all regions. The effect of nicotine persists for 4 hr after drug administration, whereas the effect of cocaine does not.