Autoradiographic localisation of α-bungarotoxin-binding sites in the central nervous system

SNAKE α-toxins have high specificity and affinity for nicotinic receptors, and have been used widely for the characterisation of peripheral acetylcholine receptors of electric organs and skeletal muscle. In some cases autoradiography has shown the extent and local distribution of bound neurotoxins1–5. Although α-bungarotoxin (α-BTX) does not pass the blood-brain barrier and therefore does not enter the central nervous system (CNS) to a measurable extent6, central nicotinic acetylcholine receptors may bind α-toxins in vitro, and several investigators have used this toxin to characterise brain receptors7–9. Its specificity for central nicotinic receptors has been inferred not only from its peripheral action, but also from cytological and pharmacological observations: binding activity is highest in synaptosomal preparations, and is inhibited by various nicotinic drugs. Studies on the localisation of toxin-binding sites in brains, not so far reported, would be valuable, not only to corroborate neurotoxin specificity, but also to provide information on the regional distribution of nicotinic receptor sites in the CNS.