[3H]vesamicol binding in brain: Autoradiographic distribution, pharmacology, and effects of cholinergic lesions

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Abstract
An autoradiographic analysis of high-affinity binding sites for the vesicular acetylcholine transport blocker [3H]vesamicol (2-(4-phenylpiperidino) cyclohexanol; AH 5183) was conducted in rat brain. [3H]Vesamicol binding was displaced 52–99% by DPPN ([2,3,4,8]-decahydro-3-(4-phenyl-1-piperidinyl)-2-napthalenol) (IC50=14nM) and by ketanserin (500 nM), haloperidol (43 nM), and vesamicol analogs, but not by drugs selective for adenosine, adrenergic, amino acid, calcium channel, monoaminergic, opioid, PCP, sigma, or several other receptor classes. [3H]Vesamicol binding was most concentrated in the interpeduncular nucleus and fifth and seventh cranial nerve nuclei. Moderate binding was found in the lateral caudate-putamen, medial nucleus accumbens, olfactory tubercle, vertical and horizontal diagonal bands of Broca, and basolateral amygdala. The distribution of [3H]vesamicol binding was similar to distributions of acetylcholine (r = 0.88), acetylcholine esterase (r = 0.97), choline acetyltransferase (ChAT) (r = 0.97), and [3H]hemicholinium-3 binding sites (r = 0.95−0.99). Lower correlations were obtained between [3H]vesamicol and muscarinic receptor densities (r = 0.50−0.70). Few exceptions to the match between binding and cholinergic neuronal markers were found, e.g., the molecular layer of the cerebellum and the thalamus. Lesions of cholinergic neuronal projections to the neocortex or hippocampus reduced [3H]vesamicol binding in each of these regions, but to a lesser extent than reductions in ChAT. [3H]Vesamicol binding sites appear to be anatomically associated with brain cholinergic neurons, a locus that is consistent with the control by this site of vesicular acetycholine uptake.