[1251]2α-BUNGAROTOXIN AND [3H]QUINUCLIDINYLBENZILATE BINDING IN CENTRAL NERVOUS SYSTEMS OF DIFFERENT SPECIES

Abstract— ¹²⁵I]Diiodo α-bungarotoxin (¹²⁵I]₂BuTx) and ³H]quinuclidinylbenzilate (³H]QNB) binding sites were measured in post-nuclear membrane fractions prepared from whole brains or brain regions of several species. Species studied included Drosophila melanogaster (fruit fly), Torpedo californiea (electric ray), Carassius auratus (goldfish), Ram pipiens (grass frog), Kana cutesheiana (bullfrog), Rattus norvegicus (rat, Sprague-Dawley), Mus muscalus (mouse, Swiss random, C58/J, LG/J), Oryctolagus cuniculus (rabbit, New Zealand Whitc), and Bos (cow). Acetyl-CoA: choline O -acetyltransferase (EC 2.3.1.6) levels were also determined in the post nuclear supernatants and correlated with the number of binding sites.
All species and regions except Drosophila had 16–150 fold more ³H]QNB binding sites than ¹²⁵I]₂BuTx binding sites. Brain regions with the highest levels of ¹²⁵I]₂BuTx binding were Drosophila heads (300 fmol/mg), goldfish optic tectum (80fmol/mg), and rat and mouse hippocampus (3040 fmol/mg). The highest levels of ³H]QNB binding were seen in rat and mouse caudate (1.3–1.6 pmol/mg). Lowest levels of ³H]QNB and ¹²⁵I]₂BuTx binding were seen in cerebellum. The utility of ¹²⁵I]₂BuTx and ³H]QNB binding as quantitative measures of nicotinic and muscarinic acetylcholine receptors in CNS is discussed.