Nineteen GABA A receptor (GABA A R) subunits are known in mammals with only a restricted number of functionally identified native combinations. The physiological role of ␤1-subunit-containing GABA A Rs is unknown. Here we report the discovery of a new structural class of GABA A R positive modulators with unique ␤1-subunit selectivity: fragrant dioxane derivatives (FDD). At heterologously expressed ␣1␤x␥2L (x-for 1,2,3) GABA A R FDD were 6 times more potent at ␤1-versus ␤2-and ␤3-containing receptors. Serine at position 265 was essential for the high sensitivity of the ␤1-subunit to FDD and the ␤1N286W mutation nearly abolished modulation; vice versa the mutation ␤3N265S shifted FDD sensitivity toward the ␤1-type. In posterior hypothalamic neurons controlling wakefulness GABA-mediated whole-cell responses and GABAergic synaptic currents were highly sensitive to FDD, in contrast to ␤1-negative cerebellar Purkinje neurons. Immunostaining for the ␤1-subunit and the potency of FDD to modulate GABA responses in cultured hypothalamic neurons was drastically diminished by ␤1-siRNA treatment. In conclusion, with the help of FDDs we reveal a functional expression of ␤1-containing GABA A Rs in the hypothalamus, offering a new tool for studies on the functional diversity of native GABA A Rs. ␥-Aminobutyric acid (GABA),4 the major inhibitory neurotransmitter in the brain, mediates inhibition via GABA A receptors (GABA A R), heteropentameric proteins constructed from subunits derived from several related gene families with six ␣-, three ␤-, three ␥-, one ␦-, one ⑀-, one -, and one -subunit in mammals. In addition 3 rho ()-subunits contribute to what have been called "GABA C receptors" (1). According to the current model of the GABA A R structure the GABA-binding pocket is formed at the ␣/␤-subunit interface, whereas the benzodiazepine (BZ)-binding pocket is located at the ␣/␥ interface (2) with the subunits arranged pseudo-symmetrically around the ion channel in the sequence ␥-␤-␣-␤-␣ anticlockwise when viewed from the synaptic cleft (3).Functional receptor compositions are restricted in their number and delineated on the basis of several criteria such as (i) capability of selected subunits to form a heteropentamer with defined pharmacological properties, (ii) a similar pharmacological fingerprint must be found in native receptors, and (iii) immunohistochemical co-localization of these subunits must be demonstrated at synaptic or extrasynaptic sites (1). Only few subunit combinations are currently accepted as "identified" native GABA A R subtypes with ␤1-containing receptors not among them (1) mainly because subunit-selective pharmacological tools are missing.In total, the GABA A R incorporates more than ten distinct modulatory binding sites targeted by anticonvulsive, antiepileptic, sedative, hypnotic, and anxiolytic compounds belonging to chemically different structural classes (4 -7) with some of them showing receptor type-specific actions. Benzodiazepine (BZ)-site agonists discriminate ␥2-containing GABA A Rs from recombi...

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The histaminergic neurons of the posterior hypothalamus (tuberomamillary nucleus-TMN) control wakefulness, and their silencing through activation of GABA(A) receptors (GABA(A)R) induces sleep and is thought to mediate sedation under propofol anaesthesia. We have previously shown that the β1 subunit preferring fragrant dioxane derivatives (FDD) are highly potent modulators of GABA(A)R in TMN neurons. In recombinant receptors containing the β3N265M subunit, FDD action is abolished and GABA potency is reduced. Using rat, wild-type and β3N265M mice, FDD and propofol, we explored the relative contributions of β1- and β3-containing GABA(A)R to synaptic transmission from the GABAergic sleep-on ventrolateral preoptic area neurons to TMN. In β3N265M mice, GABA potency remained unchanged in TMN neurons, but it was decreased in cultured posterior hypothalamic neurons with impaired modulation of GABA(A)R by propofol. Spontaneous and evoked GABAergic synaptic currents (IPSC) showed β1-type pharmacology, with the same effects achieved by 3 μM propofol and 10 μM PI24513. Propofol and the FDD PI24513 suppressed neuronal firing in the majority of neurons at 5 and 100 μM, and in all cells at 10 and 250 μM, respectively. FDD given systemically in mice induced sedation but not anaesthesia. Propofol-induced currents were abolished (1-6 μM) or significantly reduced (12 μM) in β3N265M mice, whereas gating and modulation of GABA(A)R by PI24513 as well as modulation by propofol were unchanged. In conclusion, β1-containing (FDD-sensitive) GABA(A)R represent the major receptor pool in TMN neurons responding to GABA, while β3-containing (FDD-insensitive) receptors are gated by low micromolar doses of propofol. Thus, sleep and anaesthesia depend on different GABA(A)R types.

Since ancient times ursodeoxycholic acid (UDCA), a constituent of bile, is used against gallstone formation and cholestasis. A neuroprotective action of UDCA was demonstrated recently in models of Alzheimer's disease and retinal degeneration. The mechanisms of UDCA action in the nervous system are poorly understood. We show now that UDCA promotes wakefulness during the active period of the day, lacking this activity in histamine-deficient mice. In cultured hypothalamic neurons UDCA did not affect firing rate but synchronized the firing, an effect abolished by the GABAAR antagonist gabazine. In histaminergic neurons recorded in slices UDCA reduced amplitude and duration of spontaneous and evoked IPSCs. In acutely isolated histaminergic neurons UDCA inhibited GABA-evoked currents and sIPSCs starting at 10 µM (IC50 = 70 µM) and did not affect NMDA- and AMPA-receptor mediated currents at 100 µM. Recombinant GABAA receptors composed of α1, β1–3 and γ2L subunits expressed in HEK293 cells displayed a sensitivity to UDCA similar to that of native GABAA receptors. The mutation α1V256S, known to reduce the inhibitory action of pregnenolone sulphate, reduced the potency of UDCA. The mutation α1Q241L, which abolishes GABAAR potentiation by several neurosteroids, had no effect on GABAAR inhibition by UDCA. In conclusion, UDCA enhances alertness through disinhibition, at least partially of the histaminergic system via GABAA receptors.