-Bungarotoxin-sensitive nicotinic responses in rat tuberomammillary neurons

Application of acetylcholine (ACh), nicotine or 1,1-dimethyl-4-phenylpiperazinium elicited an inward current in histaminergic neurons of the tuberomammillary nucleus. These responses were blocked by 25-50 nM α-bungarotoxin. Acutely dissociated neurons from the tuberomammillary nucleus displayed fast, desensitizing responses to ACh. ACh-activated currents exhibited rectification at positive membrane potentials. The Hill coefficient and half-maximally effective concentration (EC₅₀) for ACh were 1.85 and 119 μM, respectively. Desensitization could be fitted by an exponential. Preincubation in low concentrations of ACh diminished subsequent responses to higher concentrations of ACh. The α-bungarotoxin sensitivity in conjunction with the low potency of ACh at this receptor are consistent with its identification as an α7-subunit-containing receptor. These α-bungarotoxin sensitive receptors are ligand-gated cationic channels which are not thought to play a role in synaptic transmission, but they may be an important site for central actions of nicotine.