Fig. 7.   Cholinergic hypoactivity elicited by prenatal nicotine exposure. In the forebrain, the ratio of choline uptake to choline acetyltransferase activity (a biochemical marker of impulse activity) shows a naturally occurring peak at postnatal day 10; nicotine blunts activity before and during the developmental spike (Navarro et al., 1989a). In the hippocampus, [³H]hemicholinium-3 binding to the high-affinity choline transporter, which is regulated by nerve impulse activity, shows both initial postnatal deficits and a later-emerging, permanent deficit in the nicotine group (Zahalka et al., 1992). CON, control; NIC, nicotine; ANOVA, analysis of variance.