GABAA receptors, the major synaptic targets for the neurotransmitter GABA, constitute gated chlor... more GABAA receptors, the major synaptic targets for the neurotransmitter GABA, constitute gated chloride channels. By their allosteric, drug- induced modulation, they serve as control elements for the regulation of anxiety, vigilance, and epileptiform activity. The structural requirements of fully functional GABAA receptors in the mammalian brain have remained elusive so far. We report here on the cloning of the gamma 2-subunit cDNA of rat brain and its functional analysis by coexpression with the alpha 1- and beta 1-subunits in Xenopus oocytes, and on the sites of gene expression of the 3 subunits in the rat brain. The recombinant receptor displayed GABA-inducible currents (Imax = 6 microA; Ka = 75 microM) which were allosterically modulated by benzodiazepine receptor ligands (enhancement and inhibition by diazepam and methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate, respectively). In the absence of GABA, pentobarbital elicited a maximal current amplitude similar to that of G...
The involvement of GABA in neuronal differentiation and maturation precedes its role as inhibitor... more The involvement of GABA in neuronal differentiation and maturation precedes its role as inhibitory neurotransmitter in the brain. It was therefore investigated whether GABAA receptors mediating the actions of GABA in neonatal and adult brain can be distinguished by their molecular structure and cellular location. Immunohistochemistry with subunit-specific antibodies was employed to analyze changes in the distribution of GABAA-receptor subunits during postnatal development. In particular, subunit association patterns, as evidenced by colocalization of subunits within individual neurons, were analyzed by confocal laser microscopy. The subunits analyzed include the alpha 1- and alpha 2-subunits, which are associated with pharmacologically distinct GABAA-receptor subtypes, and the beta 2,3-subunits, which are a major constituent of GABAA receptors in both immature and adult rat brain. Each of these subunits exhibited age-dependent changes in their distribution, indicative of a different...
N-methyl-D-aspartate receptor subunit messenger RNAs are widely expressed in the retina and sever... more N-methyl-D-aspartate receptor subunit messenger RNAs are widely expressed in the retina and several types of second and third order neurons are responsive to N-methyl-D-aspartate. Functional N-methyl-D-aspartate receptors are assembled from the NR1 subunit with at least one of the four NR2 subunit variants (NR2A-2D). We have analysed immunohistochemically the cellular distribution of N-methyl-D-aspartate receptors containing the NR2D subunit in the rat and rabbit retina. Using a subunit-specific NR2D antiserum, exclusively bipolar cells with somata localized close to the outer plexiform layer were labelled in both species. The axons were immunoreactive and arborized in the innermost inner plexiform layer. The morphology and localization of these cells, which were much more numerous in rat than in rabbit, suggested that they are rod bipolar cells. This was confirmed in both species by co-localization of the NR2D subunit immunoreactivity with protein kinase C-alpha, a selective marker for rod bipolar cells. At the subcellular level, a distinct polarization in the distribution of NR2D immunoreactivity was demonstrated by confocal laser scanning microscopy: staining was moderate in dendrites arborizing within the outer plexiform layer, intense at that pole of the soma facing the outer plexiform layer, and low in the portion of the soma embedded in the inner nuclear layer. Proximal axonal segments and axonal end-feet in the inner plexiform layer displayed the strongest NR2D subunit immunoreactivity. The axonal staining suggests that neurotransmission of the rod bipolar cells is modulated within the inner plexiform layer by N-methyl-D-aspartate receptors containing the NR2D subunit.
Transmitter-gated ion channels are multisubunit membrane-spanning receptors that serve as rapid s... more Transmitter-gated ion channels are multisubunit membrane-spanning receptors that serve as rapid signal transduction devices regulating the flow of cations or anions through the cell membrane. Cell type—specific flexibility in neurotransmission is accomplished by a multiplicity of channel variants based on the combinatorial assembly of structurally related subunits. The heteromeric subunit structure also permits synaptic plasticity by changes in subunit composition and subunit-specific posttranslational modification. In addition, receptor heterogeneity offers the potential for cell type-specific drug targeting.
Abstract Benzodiazepines, a group of minor tranquillizers, bind in a selective, stereo-specific f... more Abstract Benzodiazepines, a group of minor tranquillizers, bind in a selective, stereo-specific fashion to a receptor site in human brain. Diazepam, their main representative, is bound with an apparent dissociation constant of 7 nM. The potency of various benzodiazepines in displacing diazepam parallels closely their therapeutic and pharmacological potencies. The density of the receptor site varies 24 fold in human brain, with the highest level in cerebral cortex and cerebellum. The apparent affinity of the receptor site, however, is remarkably similar in twenty different brain regions. The characteristics of the benzodiazepine receptor site suggest that it represents the site of therapeutic action of the benzodiazepines in human brain.
The highest structural diversity of GABAA-receptor subunits is observed among members of the alph... more The highest structural diversity of GABAA-receptor subunits is observed among members of the alpha-subunit class. Using subunit-specific antisera, the receptors containing the alpha 2-subunit were characterized. Western blots revealed an apparent molecular size of 52 kDa for the alpha 2-subunit. Immunohistochemically, the alpha 2-subunit was most preponderant in areas which lack the alpha 1-subunit, e.g. striatum and olfactory bulb granule cell layer, suggesting that these two subunits represent largely distinct receptor subtypes. Pharmacologically, the receptor population which was immunoprecipitated by the alpha 2-subunit-specific antisera displayed a drug binding profile characterized by a low affinity for CL 218872, beta CCM and zolpidem. This is in striking contrast to the high affinities of these ligands displayed by receptors immunoprecipitated by the alpha 1-subunit-specific antiserum. Thus, the alpha 1- and the alpha 2-subunit characterize two GABAA-receptor populations which greatly differ in brain distribution and pharmacological profile.
GABAA receptors, the major synaptic targets for the neurotransmitter GABA, constitute gated chlor... more GABAA receptors, the major synaptic targets for the neurotransmitter GABA, constitute gated chloride channels. By their allosteric, drug- induced modulation, they serve as control elements for the regulation of anxiety, vigilance, and epileptiform activity. The structural requirements of fully functional GABAA receptors in the mammalian brain have remained elusive so far. We report here on the cloning of the gamma 2-subunit cDNA of rat brain and its functional analysis by coexpression with the alpha 1- and beta 1-subunits in Xenopus oocytes, and on the sites of gene expression of the 3 subunits in the rat brain. The recombinant receptor displayed GABA-inducible currents (Imax = 6 microA; Ka = 75 microM) which were allosterically modulated by benzodiazepine receptor ligands (enhancement and inhibition by diazepam and methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate, respectively). In the absence of GABA, pentobarbital elicited a maximal current amplitude similar to that of G...
The involvement of GABA in neuronal differentiation and maturation precedes its role as inhibitor... more The involvement of GABA in neuronal differentiation and maturation precedes its role as inhibitory neurotransmitter in the brain. It was therefore investigated whether GABAA receptors mediating the actions of GABA in neonatal and adult brain can be distinguished by their molecular structure and cellular location. Immunohistochemistry with subunit-specific antibodies was employed to analyze changes in the distribution of GABAA-receptor subunits during postnatal development. In particular, subunit association patterns, as evidenced by colocalization of subunits within individual neurons, were analyzed by confocal laser microscopy. The subunits analyzed include the alpha 1- and alpha 2-subunits, which are associated with pharmacologically distinct GABAA-receptor subtypes, and the beta 2,3-subunits, which are a major constituent of GABAA receptors in both immature and adult rat brain. Each of these subunits exhibited age-dependent changes in their distribution, indicative of a different...
N-methyl-D-aspartate receptor subunit messenger RNAs are widely expressed in the retina and sever... more N-methyl-D-aspartate receptor subunit messenger RNAs are widely expressed in the retina and several types of second and third order neurons are responsive to N-methyl-D-aspartate. Functional N-methyl-D-aspartate receptors are assembled from the NR1 subunit with at least one of the four NR2 subunit variants (NR2A-2D). We have analysed immunohistochemically the cellular distribution of N-methyl-D-aspartate receptors containing the NR2D subunit in the rat and rabbit retina. Using a subunit-specific NR2D antiserum, exclusively bipolar cells with somata localized close to the outer plexiform layer were labelled in both species. The axons were immunoreactive and arborized in the innermost inner plexiform layer. The morphology and localization of these cells, which were much more numerous in rat than in rabbit, suggested that they are rod bipolar cells. This was confirmed in both species by co-localization of the NR2D subunit immunoreactivity with protein kinase C-alpha, a selective marker for rod bipolar cells. At the subcellular level, a distinct polarization in the distribution of NR2D immunoreactivity was demonstrated by confocal laser scanning microscopy: staining was moderate in dendrites arborizing within the outer plexiform layer, intense at that pole of the soma facing the outer plexiform layer, and low in the portion of the soma embedded in the inner nuclear layer. Proximal axonal segments and axonal end-feet in the inner plexiform layer displayed the strongest NR2D subunit immunoreactivity. The axonal staining suggests that neurotransmission of the rod bipolar cells is modulated within the inner plexiform layer by N-methyl-D-aspartate receptors containing the NR2D subunit.
Transmitter-gated ion channels are multisubunit membrane-spanning receptors that serve as rapid s... more Transmitter-gated ion channels are multisubunit membrane-spanning receptors that serve as rapid signal transduction devices regulating the flow of cations or anions through the cell membrane. Cell type—specific flexibility in neurotransmission is accomplished by a multiplicity of channel variants based on the combinatorial assembly of structurally related subunits. The heteromeric subunit structure also permits synaptic plasticity by changes in subunit composition and subunit-specific posttranslational modification. In addition, receptor heterogeneity offers the potential for cell type-specific drug targeting.
Abstract Benzodiazepines, a group of minor tranquillizers, bind in a selective, stereo-specific f... more Abstract Benzodiazepines, a group of minor tranquillizers, bind in a selective, stereo-specific fashion to a receptor site in human brain. Diazepam, their main representative, is bound with an apparent dissociation constant of 7 nM. The potency of various benzodiazepines in displacing diazepam parallels closely their therapeutic and pharmacological potencies. The density of the receptor site varies 24 fold in human brain, with the highest level in cerebral cortex and cerebellum. The apparent affinity of the receptor site, however, is remarkably similar in twenty different brain regions. The characteristics of the benzodiazepine receptor site suggest that it represents the site of therapeutic action of the benzodiazepines in human brain.
The highest structural diversity of GABAA-receptor subunits is observed among members of the alph... more The highest structural diversity of GABAA-receptor subunits is observed among members of the alpha-subunit class. Using subunit-specific antisera, the receptors containing the alpha 2-subunit were characterized. Western blots revealed an apparent molecular size of 52 kDa for the alpha 2-subunit. Immunohistochemically, the alpha 2-subunit was most preponderant in areas which lack the alpha 1-subunit, e.g. striatum and olfactory bulb granule cell layer, suggesting that these two subunits represent largely distinct receptor subtypes. Pharmacologically, the receptor population which was immunoprecipitated by the alpha 2-subunit-specific antisera displayed a drug binding profile characterized by a low affinity for CL 218872, beta CCM and zolpidem. This is in striking contrast to the high affinities of these ligands displayed by receptors immunoprecipitated by the alpha 1-subunit-specific antiserum. Thus, the alpha 1- and the alpha 2-subunit characterize two GABAA-receptor populations which greatly differ in brain distribution and pharmacological profile.
Uploads
Papers by H. Mohler