Alteration of nicotinic cholinergic agonist binding sites in hippocampus after fimbria transection.

Nicotinic cholinergic agonist binding sites were studied in rat hippocampus by the binding of [3H]acetylcholine in the presence of 1.5 microM atropine sulfate. Following transection of the fimbria/fornix there was a 49% increase in the binding of [3H]acetylcholine reflecting an increase in the affinity of the receptor binding site from Kd = 18.82 +/- 3.6 nM in control animals to Kd = 9.06 +/- 1.2 nM in experimental tissue. Chronic administration of the agonist nicotine (4 mg/kg/day) by osmotic minipumps produced an increase in the binding of 10 nM [3H]acetylcholine after 14 days (49% increase over control) and after 28 days (141% increase over controls). These data are consistent with the suggestion that [3H]acetylcholine labels a nicotinic cholinergic receptor in rat brain. Further they support the notion that some of the termination sites of the septal-cholinergic projection to the hippocampus are nicotinic.