Magnocellular neurons of the rat supraoptic nucleus are endowed with functional nicotinic acetylcholine receptors

Acetylcholine can stimulate the release of vasopressin.(25) In organ-cultur ed hypothalamo-neurohypophyseal systems, acetylcholine enhanced vasopressin release by acting in or near the supraoptic nucleus.(28) Extracellular rec ordings(3,9,13) suggested that acetylcholine can increase supraoptic neuron excitability, These effects could be mimicked, in part, by nicotine or blo cked by nicotinic antagonists, suggesting that they might be mediated by ni cotinic acetylcholine receptors, Autoradiography indicated that alpha-bunga rotoxin binding sites are present in the supraoptic nucleus;(8,14,19,27) ho wever, neither acetylcholine nor nicotine binding sites could be detected.( 8,14,27) Thus, the existence, let alone the nature, of nicotinic receptors in the supraoptic nucleus has so far remained elusive. The present work att empts to determine: (i) whether functional nicotinic receptors are present in this nucleus; (ii) whether they are located on neurosecretory magnocellu lar cells or at presynaptic sites; (iii) what their pharmacological and bio physical properties are; (iv) whether they influence the activity of all or only part of supraoptic neurons. Whole-cell recordings were performed in h ypothalamic slices or in acutely dissociated supraoptic neurons and the eff ect of nicotinic agonists was tested under voltage-clamp conditions. Autora diography was done in coronal hypothalamic sections, using [H-3]epibatidine and [I-125]alpha-bungarotoxin as ligands, Our results indicate that suprao ptic neurons possess functional nicotinic receptors containing the alpha 7 subunit, (C) 1999 IBRO, Published by Elsevier Science Ltd.