ALPHA-BUNGAROTOXIN-SENSITIVE NICOTINIC RESPONSES IN RAT TUBEROMAMMILLARY NEURONS

Application of acetylcholine (ACh), nicotine or 1,1-dimethyl-4-phenylp iperazinium elicited an inward current in histaminergic neurons of the tuberomammillary nucleus. These responses were blocked by 25-50 nM al pha-bungarotoxin. Acutely dissociated neurons from the tuberomammillar y nucleus displayed fast, desensitizing responses to ACh. ACh-activate d currents exhibited rectification at positive membrane potentials. Th e Hill coefficient and half-maximally effective concentration (EC(50)) for ACh were 1.85 and 119 mu M, respectively. Desensitization could b e fitted by an exponential. Preincubation in low concentrations of ACh diminished subsequent responses to higher concentrations of ACh. The alpha-bungarotoxin sensitivity in conjunction with the low potency of ACh at this receptor are consistent with its identification as an alph a 7-subunit-containing receptor. These alpha-bungarotoxinsensitive rec eptors are ligand-gated cationic channels which are not thought to pla y a role in synaptic transmission, but they may be an important site f or central actions of nicotine.