Somatostatin receptor elevation in rat striatum after diisopropylfluorophosphate administration.

The acute and chronic administration of diisopropylfluorophosphate (DFP), an inhibitor of acetylcholinesterase or of atropine, a blocker of muscarinic cholinergic receptors, did not affect somatostatin-like immunoreactivity (SLI) content in the striatum of rats. Acute and chronic DFP administration increased the number of specific 125I-Tyr11-somatostatin (125I-Tyr11-SS) receptors in cells dissociated from the striatum without changing the affinity constant. Although the increase could be blocked by pretreatment with atropine, it was not due to a direct effect by DFP on somatostatin (SS) receptors, because no rise in 125I-Tyr11-SS binding was produced by high concentrations of DFP (10(-5) M) when added in vitro. The acute administration of atropine alone had no observable effect on the number of SS receptors. However, repeated atropine administration produced a significant decrease in the 125I-Tyr11-SS binding in cells dissociated from the striatum, although the affinity constant was unchanged. The results suggest that interactions between somatostatinergic and cholinergic receptors may be of importance in the rat striatum.