The localization of substance P in brain regions that coordinate stress responses and receive convergent monoaminergic innervation suggested that substance P antagonists might have psychotherapeutic properties. Like clinically used antidepressant and anxiolytic drugs, substance P antagonists suppressed isolation-induced vocalizations in guinea pigs. In a placebo-controlled trial in patients with moderate to severe major depression, robust antidepressant effects of the substance P antagonist MK-869 were consistently observed. In preclinical studies, substance P antagonists did not interact with monoamine systems in the manner seen with established antidepressant drugs. These findings suggest that substance P may play an important role in psychiatric disorders.

Fast inhibitory neurotransmission in the mammalian CNS is mediated primarily by the neurotransmitter gamma-aminobutyric acid (GABA), which, upon binding to its receptor, leads to opening of the intrinsic ion channel, allowing chloride to enter the cell. Over the past 10 years it has become clear that a family of GABA-A receptor subtypes exists, generated through the coassembly of polypeptides selected from alpha 1-alpha 6, beta 1-beta 3, gamma 1-gamma 3, delta, epsilon, and pie to form what is most likely a pentomeric macromolecule. The gene transcripts, and indeed the polypeptides, show distinct patterns of temporal and spatial expression, such that the GABA-A receptor subtypes have a defined localization that presumably reflects their physiological role. A picture is beginning to emerge of the properties conferred to receptor subtypes by the different subunits; these include different functional properties, differential modulation by protein kinases, and the targeting to different membrane compartments. These properties presumably underlie the different physiological roles of the various receptor subtypes. Recently we have identified a further member of the GABA-A receptor gene family, which we have termed theta, which appears to be most closely related to the beta subunits. The structure, function, and distribution of theta-containing receptors, and receptors containing the recently reported epsilon subunit, are described.

We report the isolation and characterization of a cDNA encoding a novel member of the GABA receptor gene family, ⑀. This polypeptide is 506 amino acids in length and exhibits its greatest amino acid sequence identity with the GABA A receptor ␥3 subunit (47%), although this degree of homology is not sufficient for it to be classified as a fourth ␥ subunit. The ⑀ subunit coassembles with GABA A receptor ␣ and ␤ subunits in Xenopus laevis oocytes and transfected mammalian cells to form functional GABA-gated channels. ␣1␤1⑀ GABA A receptors, like ␣1␤1␥2s receptors, are modulated by pentobarbital and the steroid 5␣-pregnan-3␣-ol-20-one but, unlike ␣1␤1␥2s receptors, are insensitive to flunitrazepam. Additionally, ␣1␤1⑀ receptors exhibit rapid desensitization kinetics, as compared with ␣1␤1 or ␣1␤1␥2s. Northern analysis demonstrates widespread expression of a large ⑀ subunit transcript in a variety of nonneuronal tissues and expression of a smaller transcript in brain and spinal cord. Sequence analysis demonstrated that the large transcript contained an unspliced intron, whereas the small transcript represents the mature mRNA, suggesting regulation of expression of the ⑀ subunit via neuronally restricted RNA splicing. In situ hybridization and immunocytochemistry reveal a pattern of expression in the brain restricted primarily to the hypothalamus, suggesting a role in neuroendocrine regulation, and also to subfields of the hippocampus, suggesting a role in the modulation of long term potentiation and memory.

ABSTRACT␥-Aminobutyric acid type A (GABA-A) receptors are a major mediator of inhibitory neurotransmission in the mammalian central nervous system, and the site of action of a number of clinically important drugs. These receptors exist as a family of subtypes with distinct temporal and spatial patterns of expression and distinct properties that presumably underlie a precise role for each subtype. The newest member of this gene family is the subunit. The deduced polypeptide sequence is 627 amino acids long and has highest sequence identity (50.5%) with the ␤1 subunit. Within the rat striatum, this subunit coassembles with ␣2, ␤1, and ␥1, suggesting that ␥-aminobutyric acid type A receptors consisting of arrangements other than ␣␤ ؉ ␥, ␦, or do exist. Expression of ␣2␤1␥1 in transfected mammalian cells leads to the formation of receptors with a 4-fold decrease in the affinity for ␥-aminobutyric acid compared with ␣2␤1␥1. This subunit has a unique distribution, with studies so far suggesting significant expression within monoaminergic neurons of both human and monkey brain.In the mammalian central nervous system, inhibitory neurotransmission is mediated primarily by the ␥-aminobutyric acid (GABA), which acts on GABA type A (GABA-A) receptors, ligand-gated ion channels acting over a rapid time frame. Over the past 10 years, it has become clear that a family of GABA-A receptor subtypes exists, generated through the coassembly of polypeptides selected from ␣1-␣6, ␤1-␤3, ␥1-␥3, ␦, , and to form what is most likely a pentameric macromolecule (1-6). The subunits show distinct patterns of temporal and spatial expression, so that GABA-A receptor subtypes have a defined localization presumably reflecting their physiological role (7)(8)(9)(10)(11).In this article, we report the identification and characterization of a further member of the GABA-A receptor gene family that we have termed theta (). MATERIALS AND METHODSCloning of Subunit cDNA. Full-length cDNA was cloned starting from sequence information in GenBank entry U47334. PCR was performed under standard conditions, on human whole-brain cDNA (CLONTECH) with oligonucleotide primers specific to the 5Ј and 3Ј ends of the U47334 sequence. A single PCR product of approximately 1,600 bp was obtained. The 5Ј and 3Ј ends of the coding region corresponding to full-length U47334 sequence were obtained by 5Ј and 3Ј anchored PCR using human brain Marathon cDNA (CLON-TECH). Full-length cDNA (GenBank accession no. AF144648) was generated by PCR using a primer derived from sequences surrounding the initiating methionine incorporating a consensus Kozak sequence (12), and a primer based on the 3Ј untranslated region of the anchored PCR product. The PCR product (1,958 bp) was sequenced completely on both strands by primer walking by using dye terminator chemistry and an Applied Biosystems model 373A sequencer.Epitope-tagged subunit was constructed that contained nucleotides Ϫ224 to ϩ99 (i.e., the 5Ј untranslated region, the signal peptide, 6 amino acids of the mature protein) of bovine ...

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