Coadministration of Galanin Antagonist M40 with a Muscarinic M₁Agonist Improves Delayed Nonmatching to Position Choice Accuracy in Rats with Cholinergic Lesions

Abstract

The neuropeptide galanin is overexpressed in the basal forebrain in Alzheimer's disease (AD). In rats, galanin inhibits evoked hippocampal acetylcholine release and impairs performance on several memory tasks, including delayed nonmatching to position (DNMTP). Galanin(1-13)-Pro2-(Ala-Leu)2-Ala-NH2 (M40), a peptidergic galanin receptor ligand, has been shown to block galanin-induced impairment on DNMTP in rats. M40 injected alone, however, does not improve DNMTP choice accuracy deficits in rats with selective cholinergic immunotoxic lesions of the basal forebrain. The present experiments used a strategy of combining M40 with an M1 cholinergic agonist in rats lesioned with the cholinergic immunotoxin 192IgG-saporin. Coadministration of intraventricular M40 with intraperitoneal 3-(3-S-n-pentyl-1,2,5-thiadiazol-4-yl)-1,2,5, 6-tetrahydro-1-methylpyridine (TZTP), an M1 agonist, improved choice accuracy significantly more than a threshold dose of TZTP alone. These results suggest that a galanin antagonist may enhance the efficacy of cholinergic treatments for the cognitive deficits of AD.