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Biomedical subjects

A N Bateson

Publications and source records attributed to A N Bateson.

At least 37 records · Page 2Linked to original sources
PubMed1996

Chronic treatment with diazepam or abecarnil differently affects the expression of GABAA receptor subunit mRNAs in the rat cortex.

Diazepam and abecarnil produce their overt effects by interaction with the GABAA receptor. Chronic treatment with abecarnil, however, does not induce diazepam-like tolerance. This study investigates the effects of chronic diazepam and abecarnil treatment on expression of GABAA receptor alpha 1-6 beta 1-3 and gamma 1-3 subunit isoform mRNAs in rat cortex. Male Sprague-Dawley rats were injected subcutaneously once daily for 7 or 14 days with 15 mg/kg diazepam or 6 mg/kg abecarnil in sesame-oil vehicle, and steady-state levels of GABAA receptor subunit mRNAs were quantified by solution hybridization. The levels of alpha 4- and alpha-, beta 1- and gamma 3-subunit mRNAs were significantly increased after 7 days of diazepam treatment, and this effect was maintained at 14 days. A significant increase in alpha 3-subunit mRNA was apparent only after 14 days of diazepam treatment and a significant decrease in beta 2-subunit mRNA was seen only after 14 days of abecarnil treatment. Gamma 2-Subunit mRNA was significantly decreased after 14 days of either diazepam or abecarnil exposure. A degree of association between a particular drug treatment and changes in the levels of mRNAs arising from a given gene cluster was noted. Our results are consistent with a model of diazepam dependence based on GABAA receptor subunit isoform switching.

Animals↗
PubMed1996

Chronic administration of antipanic drugs alters rat brainstem GABAA receptor subunit mRNA levels.

Mental illness, such as panic disorder and depression, display comorbidity as well as common therapeutic treatments. These features point toward a common etiology and/or therapeutic pathway. There is evidence to suggest that some antipanic agents may mediate their effects by altering gamma-aminobutyric acid (GABA) levels or by modulating the activity of the GABAA receptor. Chronic stimulation of GABAA receptors by agonists or modulators results in changes in the pharmacological properties of the receptor concomitant with alterations in the expression of specific GABAA receptor subunits. Therefore, we investigated the hypothesis that long-term exposure to three antidepressant/antipanic drugs (imipramine, phenelzine and alprazolam) would produce changes in the steady-state levels of those subunit mRNAs that are believed to encode the major GABAA receptor subtype. Further, these changes in gene expression would be different to those produced by the non-antipanic anxiolytic (buspirone). We report here that, following a 21 day treatment, imipramine, phenelzine, alprazolam and buspirone differentially altered rat brainstem levels of GABAA receptor alpha 1-, beta 2- and gamma 2-subunit RNAs. These results demonstrate novel actions of antidepressant/antipanic drugs on GABAergic neurotransmission.

Animals↗
PubMed1996

Identification of domains in human recombinant GABAA receptors that are photoaffinity labelled by [3H]flunitrazepam and [3H]Ro15-4513.

We have used [3H]flunitrazepam and [3H]Ro15-4513 as photoaffinity labelling agents in combination with a chemical cleavage technique to localize the benzodiazepine recognition sites of specific human recombinant alpha 1 beta 1 gamma 2, alpha 1 beta 3 gamma 2 and alpha 6 beta 3 gamma 2 GABAA receptor subtypes. The chemical agent utilized was hydroxylamine, whose substrate is a relatively rare asparagine-glycine amide bond that occurs only in the alpha subunits of the receptors examined in this study. Cleavage products were resolved using sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). The results of these experiments show that, in the alpha 1 subunit-containing receptors, incorporation of [3H]flunitrazepam occurs within residues 1-103 of the alpha 1 subunit, while incorporation of [3H]Ro15-4513 occurs within the region of the alpha 1 subunit that lies between residue 104 and the C-terminus. Photolabelling of membranes prepared from the alpha 6 beta 3 gamma 2-expressing cell line with [3H]Ro15-4513 resulted in the incorporation of radiolabel into two major protein species of M(r) 56,000 and M(r) 48,000, indicating incorporation into the alpha 6 subunit and possibly also the gamma 2 subunit. Hydroxylamine cleavage of alpha 6-containing receptors labelled with [3H]Ro15-4513 produced a gel profile consistent with the incorporation of the label occurring between residue 125 and the C-terminal. Thus, we have shown that the recognition sites for the agonist [3H]flunitrazepam and the inverse agonist [3H]Ro15-4513 occur within distinct domains of the human GABAA receptor.

Affinity Labels↗
PubMed1996

A novel G protein-coupled P2 purinoceptor (P2Y3) activated preferentially by nucleoside diphosphates.

A partial cDNA was isolated by hybridization screening of an embryonic chick brain library for P2Y purinoceptors. After extension to full length, it revealed an open reading frame that encoded a protein, P2Y3, of 328 amino acids that is nearest in sequence identity to the G protein-coupled P2 purinoceptors obtained by DNA cloning. Expression of P2Y3 in cRNA-injected Xenopus oocytes confirmed that this cDNA encodes a member of the metabotropic purinoceptor family, with a novel order for the relative activities of nucleotides. At 100 microM concentrations, ADP gave the highest activity, and UTP and UDP were also strongly active. When expressed in the human T cell line Jurkat, P2Y3 mediated transient increases in intracellular Ca2+ in response to various nucleotides. Again, an unusual agonist rank order was revealed, with uridine nucleotides being more potent than adenosine nucleotides and UDP being the most potent agonist tested (half-maximal concentration, 0.13 microM) and 10-fold more potent than UTP. 2-Methylthlo-ATP was of relatively low activity in both systems. The receptor transcript is expressed in brain, spinal cord, kidney, and lung and is highly abundant in the spleen but not in other peripheral tissues that we tested. The results indicated that P2Y3 is a previously unknown P2 purinoceptor subtype with a preference for nucleoside diphosphates.

Adenosine Diphosphate↗
PubMed1996

A unitary non-NMDA receptor short subunit from Xenopus: DNA cloning and expression.

A high-affinity homomeric, non-NMDA glutamate receptor was previously purified from the amphibian Xenopus laevis. We have obtained nine peptide sequences from its subunit, applied in cDNA cloning. The cDNA encodes a subunit (XenU1) containing all nine sequences. The 51,600-dalton mature subunit has four hydrophobic domains homologous to the four in the C-terminal half of mammalian non-NMDA receptor subunits. Transient expression in COS cells showed 1:1 binding (at Bmax) of [3H] kainate (KD = 9.1 nM) and of [3H] AMPA (alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid; KD = 62 nM). The competitive binding series domoate > kainate > AMPA > NBQX > glutamate was established (where NBQX is 2,3-dihydroxy-6-nitro-7-sulphamoyl-benzo (f) quinoxaline). Each agonist shows the same KI value against [3H] kainate and [3H] AMPA binding, suggesting a common agonist site, but two conformations thereof are distinguishable by their different affinities for the antagonist NBQX and by the allosteric effect of thiocyanate anion (greatly potentiating AMPA binding, inert with kainate). XenU1 is exceptional among non-NMDA receptor subunits because it lacks most of the large N-terminal domain found in those of mammals and it has high affinity for both kainate and AMPA. It differs from the similarly-short "kainate-binding proteins" (KBPs), in binding AMPA and in forming glutamate receptor channels when the native protein is reconstituted. Moreover, whereas a full-length kainate receptor of mammals, GluR6, is shown here (from a partial cDNA sequence) to exist also in Xenopus, with approximately 97% sequence identity to rat GluR6, XenU1 is much less homologous to any rat kainate or AMPA receptor and also to the KBPs, even from another amphibian, Rana. Another difference is that a potential concensus sequence ("EF hand") for Ca2+ binding is present in the N-terminal domain of XenU1, but not in the chicken (glial) KBP. XenU1 is deduced to be in a new family of non-NMDA receptors.

Amino Acid Sequence↗
PubMed1995

Isolation and sequence analysis of the chicken GABAA receptor alpha 1-subunit gene promoter.

A genomic clone containing the 5'-flanking sequence of the chicken GABAA receptor alpha 1-subunit-encoding gene (GabR alpha 1) was isolated and characterized. An intron was found to interrupt the 5'-untranslated region. The transcription start point (tsp) was determined by primer extension, RNase protection and the amplification of chick brain first-strand cDNA. DNA sequence analysis revealed a number of putative transcriptional regulatory motifs, including a TATA box 30 nucleotides upstream from the tsp, and that this region is a CpG island. While there is conservation between the chicken and human GabR alpha 1 sequences, the chicken GabR alpha 1 promoter has a different structure to those reported for the GABAA receptor beta 3- and delta-subunit-encoding genes.

Animals↗
PubMed1994

Transient expression of the recombinant chick brain P2y1 purinoceptor and localization of the corresponding mRNA.

Extracellular ATP acts at specific cell surface purinoceptors to elicit a wide range of physiological responses. We have recently isolated a cDNA for a G-protein-coupled P2 purinoceptor (P2y1) from chick brain. It has been defined as a P2Y-like purinoceptor by the rank order of potency of P2 purinoceptor ligands, determined electrophysiologically in the Xenopus oocyte expression system. Here, we examine the ligand selectivity of this recombinant receptor, expressed transiently in COS-7 cells. The regional distribution of the P2y1 purinoceptor transcript within the one-day-post-hatch chick brain was also determined. It is widely expressed in the cerebellum and telencephalon and in specific nuclei of the mesencephalon and diencephalon, suggesting a neuronal localization of the P21 purinoceptor.

Adenosine Triphosphate↗
PubMed1993

Cloning and functional expression of a brain G-protein-coupled ATP receptor.

A cDNA encoding a novel member of the G-protein-coupled receptor (GCR) superfamily, an ATP receptor, has been isolated from an embryonic chick whole brain cDNA library by hybridization screening. The encoded protein has a sequence of 362 amino acids (41 kDa) and shares no more than 27% amino acid identity with any known GCR. When expressed as a complementary RNA (cRNA) in Xenopus oocytes a slowly-developing inward current was observed in response to application of ATP. The pharmacology of this expressed protein defines it as a P2Y purinoceptor.

Adenosine Triphosphate↗
PubMed1993

Sequence and novel distribution of the chicken homologue of the mammalian gamma-aminobutyric acidA receptor gamma 1 subunit.

cDNAs have been cloned that encode the chicken (Gallus domesticus) gamma-aminobutyric acidA receptor gamma 1 subunit, the mature sequence of which shares 90, 79, and 69% identity with those of the rat gamma 1, gamma 2, and gamma 3 subunits, respectively. In situ hybridization reveals that there are pronounced differences in the regional and cellular localizations of the corresponding gamma-aminobutyric acidA receptor gamma-subunit mRNA compared with that of the gamma 2-subunit mRNA in 1-day-old chick brain. The absence of the gamma 1-subunit transcript in certain chick brain nuclei of visual and auditory pathways, in which gamma 2-subunit mRNA is present, points to differences in the functional roles of receptors containing one or other of these polypeptides. Certain cells in other brain regions appear to contain both gamma 1- and gamma 2-subunit mRNAs, suggesting that they either have two gamma-aminobutyric acidA receptor subtypes or possess receptors incorporating two different gamma subunits. We have also found contrasts in the distribution patterns, in homologous brain regions, of the chicken gamma 1-subunit mRNA and the rat gamma 1-subunit mRNA. These data may reflect different functional roles of the chicken and rat gamma 1 subunits.

Amino Acid Sequence↗
PubMed1991

Distribution of the GABAA receptor alpha 1- and gamma 2-subunit mRNAs in chick brain.

We have used sequence-specific oligonucleotide probes and in situ hybridisation histochemistry to examine the distribution of the GABAA receptor alpha 1- and gamma 2-subunit mRNAs in serial sections of 1-day-old chick brain. Both transcripts are present together, at high levels, in many brain regions. Differences are found, however, in the relative amounts of these mRNAs in two isthmic nuclei of the optic lobe, the deep cerebellar nuclei, and the dorsal thalamus. We therefore conclude that while the alpha 1 and gamma 2 subunits predominantly occur together in the same receptor complex, they may also be found separately in other GABAA receptor subtypes.

Animals↗
PubMed1991

The chicken GABAA receptor alpha 1 subunit: cDNA sequence and localization of the corresponding mRNA.

We report the sequence of a complementary DNA (cDNA) that encodes the chicken GABAA receptor alpha 1 subunit, which is extremely homologous to mammalian alpha 1 subunits. The distribution of alpha 1 subunit transcripts is shown to correlate mainly, but not completely, with the previously-reported pattern of benzodiazepine type I (BZI) binding sites in the avian brain. These results suggest that the alpha 1 subunit may not necessarily be restricted to receptors having BZI pharmacology.

Amino Acid Sequence↗