[3H](-)nicotine binding sites in fetal human brain.

The development of putative nicotinic binding sites in brains from human fetuses of 12-19 weeks gestation was studied. The binding of 3Hnicotine to fetal human brain membranes, using a rapid filtration method, was saturable and stereospecific. Scatchard analysis revealed a single class of high affinity sites with a Kd of 1.5 +/- 0.5 nM and a Bmax of 4.5 +/- 1.9 fmol/mg protein (n = 11). 3Hnicotine binding increased between the ages of 12 and 19 weeks in human fetal brain (r = 0.63, n = 20, P less than 0.01). In competition studies nicotinic agonists were the most effective in inhibiting 3Hnicotine binding whereas antagonists were relatively ineffective. Ki values for displacing ligands in the presence of 3Hnicotine were: cytisine, 1.6 nM; (-)nicotine, 16 nM; (+) nicotine, 510 nM; dihydro-beta-erythroidine, 1.9 microM; dimethyl-4-phenylpiperazinium, 6.5 microM; choline chloride, 25 microM. Atropine and alpha-bungarotoxin failed to inhibit binding up to 50 microM. Comparison of dissected brain regions revealed regional variations in the density of nicotinic binding sites: specific binding of 3Hnicotine was greatest in the nucleus basalis of Meynert, globus pallidus, caudate-putamen and thalamus, and lowest in the medulla. These results are interpreted in relation to the development of functional cholinergic transmission in human fetal brain, and the potential vulnerability of this system to maternal tobacco usage.