Activation of α 1 -adrenoceptors in rat hypothalamic ventromedial nucleus can excite neurons and facilitate female sexual behavior. To identify the α 1 -adrenoceptor subtype(s) involved, the α 1 B -adrenoceptor-specific antagonist chloroethylclonidine (100 μM) and/or the α 1 A -adrenoceptor-selective antagonist 5-methyl urapidil (1 or 2.5 μM) or WB-4101 (0.1-10 μM) were applied to a recording chamber bathing the hypothalamic slice containing the ventromedial nucleus. In all the neurons tested, both types of antagonists blocked, often completely, excitatory responses to nonselective α 1 -adrenoceptor agonists. Since the doses used were unlikely to make these antagonists nonselective, the results suggest that activation of both α 1 A - and α 1 B -adrenoceptor subtypes was necessary for α 1 -adrenoceptor agonists to evoke an excitation, or that with the present application method - injection into the continuously perfused chamber - chloroethylclonidine did not act specifically. In preincubation (at 37°C for 90 min) where it was reported to act by specific alkylation, chloroethylclonidine (100 μM) but not the vehicle abolished the excitation evoked by an α 1 -adrenoceptor agonist, but not that by carbachol or other excitants. Also, either in bath application or incubation, chloroethylclonidine worked equally efficiently on slices from ovariectomized rats, that reportedly contain few α 1 B -adrenoceptors, and from those treated with estrogen which induces α 1 B -adrenoceptors selectively, suggesting that α 1 B -adrenoceptor was necessary even when in low abundance. Thus, it is likely that the activation of both α 1 A - and α 1 B -adrenoceptor subtypes and also thereby, their respective couplings to second messengers are necessary to mediate the actions of α 1 -adrenoceptor agonists in exciting hypothalamic neurons.