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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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