GABA_A receptor heterogeneity in histaminergic neurons

Abstract

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.

Pharmacological Properties of GABAAReceptors in Rat Hypothalamic Neurons Expressing the ϵ-Subunit

“…Cells were separated by gentle pipetting and placed in the recording chamber. Whole-cell patch-clamp recordings in voltage-clamp mode, fast drug application, and single-cell reverse transcription (RT)-PCR procedures were performed as described previously (Sergeeva et al, 2002). Briefly, patch electrodes were sterilized by autoclaving and filled with the following solution (in mM): 140 CsCl, 2 MgCl 2 , 0.5 CaCl 2 , 5 EGTA, and 10 HEPES/CsOH, adjusted to pH 7.2.…”

“…All solutions flowed continuously, gravity driven, at the same speed and lateral movements of the capillaries exposed a cell to either control or test solutions. Hypothalamic neurons display a high cell-to-cell variability in sensitivity to GABA (Sergeeva et al, 2002). Therefore, solutions containing propofol or diazepam plus four different GABA concentrations (2.5, 5, 10, and 20 M) were prepared.…”

“…We showed (Sergeeva et al, 2002) that a fraction of histaminergic neurons from the tuberomamillary (TM) nucleus of the hypothalamus express the ⑀-subunit; however, functional features of this expression and the exact location of the ⑀-subunit protein in this region are unknown. The low percentage of ⑀-positive cells in the TM nucleus has prompted our investigation of another neuronal group in the posterior hypothalamus, the orexin neurons, in which the ⑀-subunit mRNA is found in all neurons with in situ hybridization (Moragues et al, 2003).…”

Histamine neuronal system as a therapeutic target for the treatment of cognitive disorders

“…GABA A -R activation directly inhibits histaminergic cell firing rate [120,121], whereas GABA A -R inhibition increases TMN histamine release significantly [122]. Depending on GABA A -R-subunit expressions, histaminergic neurons displayed different sensitivities to GABA [123,124]. This may account for the functional heterogeneity of GABAergic responses displayed by histaminergic neurons following stimulation of the diagonal band of Broca, the antero-lateral hypothalamus, or the lateral preoptic area [120].…”

Histamine in the brain: Beyond sleep and memory

“…Tracing studies failed to reveal any topographical organization of the histaminergic projections arising from the TMN, however, two recent studies suggest that histamine neurons are functionally heterogeneous, based on differential activation by acute stress [87], and on the expression of different g-subunits that confer different sensitivity to exogenous GABA [88]. As reported previously [44], infusions of the CB1 receptor agonist methanandamide (mAEA) in the posterior hypothalamus in the proximity of the histaminergic cell bodies, increase histamine release from histaminergic projection areas such as the NBM and striatum ( Fig.…”