The subcellular and regional distribution of markers for cholinergic activity was studied in goldfish brain. Nicotinic-cholinergic receptor 'activity' was analysed by the binding of [125I]alphabungarotoxin (Kd = 0.5 nm) and muscarinic cholinergic 'activity' by binding of [3H]quinuclidinyl benzilidate (Kd= 0.4 nm). Choline acetyltransferase and acetylcholinesterase activities were also estimated. The subcellular distribution demonstrated an enrichment of the recovered activity in the synaptosomal fractions. In general, the pharmacological studies of receptor binding demonstrated an appropriate specificity for cholinergic receptors. The regional distribution of the markers was compared to data obtained from other species: while choline acetyltransferase in mammals is present in highest specific activity in the telecephalon, in the goldfish the activity is much greater in the hindbrain. Likewise, the binding of quinuclidinyl benzilidate by the diencephalon of the goldfish brain was greater than that by the tetencephalon; but the marked enrichment of choline acetyltransferase in the hindbrain was not accompanied by an enrichment in the material that bound quinuclidinyl benzilidate.
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