Alpha-Conotoxin MII (CtxMII)

alpha-Conotoxin MII (CtxMII), a peptide toxin from the venom of the predatory cone snail Conus magus, displays an unusual nicotinic pharmacology. Specific binding of a radioiodinated derivative ((125)I-alpha-CtxMII) was identified in brain region homogenates and tissue sections. Quantitative autoradiography indicated that (125)I-alpha-CtxMII binding sites have an unique pharmacological profile and distribution in mouse brain, being largely confined to the superficial layers of the superior colliculus, nigrostriatal pathway, optic tract, olivary pretectal, and mediolateral and dorsolateral geniculate nuclei. Expression of alpha-CtxMII binding sites in the nigrostriatal pathway, combined with evidence for alpha-CtxMII-sensitivity of nicotine-induced [(3)H]dopamine release in rodent striatal preparations indicates that (125)I-alpha-CtxMII binding nicotinic acetylcholine receptors are likely to be physiologically important.