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

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Abstract
The pharmacological properties and functional role of native GABAAreceptors (GABAARs) were investigated in rat hypothalamic neurons expressing the ϵ-subunit with the help of whole-cell patch-clamp recording and single-cell reverse transcription-PCR. Two cell groups were identified: histaminergic tuberomamillary and orexinergic/hypocretinergic neurons. Approximately 25% of histaminergic and 70% of orexinergic neurons contained mRNA encoding for the ϵ-subunit. Double-immunofluorescence staining revealed a somatic localization of this protein in these two neuronal groups. Constitutive activity, diazepam modulation, fast desensitization of maximal currents, and activation by propofol (6-98 μm) of GABAARs did not correlate withϵ-subunit expression. Propofol at 3-12 μmpotentiated GABA-mediated currents similarly in all neurons. However, noise variance analysis of GABA-mediated currents enhanced by propofol revealed a significant difference between ϵ-positive and ϵ-negative neurons. The former displayed no difference between control and potentiated responses, and, in the latter, noise was decreased in the presence of propofol. Spontaneous IPSCs recorded in cultured hypothalamic neurons were prolonged in the presence of propofol in all ϵ-negative neurons, whereas propofol-resistant IPSCs were recorded in ϵ-positive cells. The infrequent expression of the ϵ-subunit may be a key factor in the recently discovered central role of the tuberomamillary nucleus in anesthesia.