Antibodies to nicotinic acetylcholine receptors used to probe the structural and functional relationships between brain ?-bungarotoxin binding sites and nicotinic receptors.
Antibodies against peripheral nicotinic acetylcholine receptors (nAChR) were used to determine the proportion of brain ?-bungarotoxin binding sites that are immunologically related to the peripheral nAChR. The ?-bungarotoxin binding component partially purified from rat brain was labelled with [(125)I]?-bungarotoxin and reacted with increasing concentrations of rabbit anti(nAChR) antisera. At least 75% of the brain protein could be immunoprecipitated by rabbit anti(rat muscle junctional nAChR) antiserum (M) whereas an antiserum against Torpedo nAChR (J) was without effect and clearly failed to cross-react with the brain component. Both antisera precipitated 100% of [(125)I]?-bungarotoxin-labelled nAChR from Torpedo marmorata. The lower precipitation of the brain protein was not a consequence of [(125)I]?-bungarotoxin dissociating during the precipitation. We conclude that the majority of ?-bungarotoxin binding sites in brain are clearly recognised by the crossreacting antiserum. Release of [(3)H]dopamine from striatal synaptosomes could be elicited by nicotine in a dose-dependent manner and the response was prevented by the ganglionic blocker mecamylamine, although antagonism by ?-bungarotoxin was less clearcut. Preincubation of the synaptosomes with antiserum M resulted in a statistically significant decrease in the [(3)H]dopamine response to nicotine at all agonist concentrations tested. Antiserum J, however, had no consistent effect on the response. Thus the actions of the antisera parallel their ability to recognise the brain ?-bungarotoxin binding component. We conclude that the cholinergic regulation of dopamine release is in part mediated through a nAChR that is immunologically related to the nAChR of the neuromuscular junction and to the ?-bungarotoxin binding component that can be isolated from rat brain.
Mills
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Department of Biochemistry, University of Bath, Bath BA2 7AY, U.K.
Wonnacott
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