Histaminergic neurons of the tuberomamillary nucleus display pacemaker properties; their firing rate is regulated according to behavioural state by gabaergic inhibition. Whole-cell recordings and single-cell RT-PCR from acutely isolated rat tuberomamillary neurons were used to characterize GABA -evoked currents and to correlate them with the expression pattern of 12 GABAA receptor subunits. We report differences in sensitivity to GABA and zinc as well as in the modulation of IPSC-decay times by zolpidem in histaminergic neurons expressing gamma-subunits at different levels. Immunocytochemistry and pharmacological analysis of whole-cell GABA-currents in these neurons revealed that all carry the gamma2-subunit protein and that all receptors contain at least one gamma-subunit. Neurons with different expression levels of gamma-subunits displayed a difference in cooperativity of GABA and zolpidem binding which we explain by the presence of one vs. two gamma-subunits in one receptor. Thus, we describe here native GABAA receptor function in relation to its stoichiometry.