[³H]Nicotine binding sites in developing fetal brains in rats

[³H]Nicotine binding sites were examined in developing fetal brains in rats. The fetal brain membranes bound [³H]nicotine with a similar affinity to that of adult brain membranes. This binding was displaced by unlabelled nicotine or carbamylcholine, the inhibition concentrations being approximately the same for fetal and adult brain preparations. α-Bungarotoxin had no effect on [³H]nicotine binding to fetal brain membranes as well as to adult brain preparations. The specific [³H]nicotine binding was first detectable on day 16 of gestation and it increased several folds until birth.