Abstract
The pharmacological profile and the anatomical localisation of muscarinic cholinergic receptor subtypes were studied in the pigeon bursa of Fabricius, using radioligand binding and autoradiographic techniques with [ 3H]quinuclidinyl benzilate (QNB) as a ligand. [ 3H]QNB was specifically bound to sections of bursa of Fabricius. The binding was time-, temperature- and concentration-dependent. The dissociation constant was 0.31 ± 0.02 nM, and the maximum density of binding sites averaged 38 ± 2.5 fmol/mg protein. The pharmacological profile of [ 3H]QNB binding to sections of pigeon bursa of Fabricius was consistent with the labelling of M 2, M 3 and M 4 muscarinic receptor subtypes. Light microscope autoradiography showed the localisation of [ 3H]QNB binding sites in the medulla, in follicular septa, in the cortico-medullary border and in lesser amounts in the cortical layer. The functional significance of these receptors should be clarified in future studies.
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