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

Abstract— [ 125 I]Diiodo α‐bungarotoxin ([ 125 I] 2 BuTx) and [ 3 H]quinuclidinylbenzilate ([ 3 H]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 [ 3 H]QNB binding sites than [ 125 I] 2 BuTx binding sites. Brain regions with the highest levels of [ 125 I] 2 BuTx binding were Drosophila heads (300 fmol/mg), goldfish optic tectum (80fmol/mg), and rat and mouse hippocampus (3040 fmol/mg). The highest levels of [ 3 H]QNB binding were seen in rat and mouse caudate (1.3–1.6 pmol/mg). Lowest levels of [ 3 H]QNB and [ 125 I] 2 BuTx binding were seen in cerebellum. The utility of [ 125 I] 2 BuTx and [ 3 H]QNB binding as quantitative measures of nicotinic and muscarinic acetylcholine receptors in CNS is discussed.