[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. alpha-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.