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H Möhler

Publications and source records attributed to H Möhler.

At least 19 recordsLinked to original sources
PubMed2001

Grafts of adenosine-releasing cells suppress seizures in kindling epilepsy.

Adenosine is an inhibitor of neuronal activity in the brain. The local release of adenosine from grafted cells was evaluated as an ex vivo gene therapy approach to suppress synchronous discharges and epileptic seizures. Fibroblasts were engineered to release adenosine by inactivating the adenosine-metabolizing enzymes adenosine kinase and adenosine deaminase. After encapsulation into semipermeable polymers, the cells were grafted into the brain ventricles of electrically kindled rats, a model of partial epilepsy. Grafted rats provided a nearly complete protection from behavioral seizures and a near-complete suppression of afterdischarges in electroencephalogram recordings, whereas the full tonic-clonic convulsions in control rats remained unaltered. Thus, the local release of adenosine resulting in adenosine concentrations <25 nM at the site of action is sufficient to suppress seizure activity and, therefore, provides a potential therapeutic principle for the treatment of drug-resistant partial epilepsies.

Adenosine↗
PubMed2001

GABA(B)-receptor isoforms molecular architecture and distribution.

The slow component of GABAergic inhibition in the brain is mediated by the metabotropic GABA(B)-receptors. Most if not all GABA(B)-receptors are heterodimers of GABA(B)R1 (GBR1) and GABA(B)R2 (GBR2) proteins. Distinctive receptor isoforms are based on the presence of two GBR1 splice variants termed GBR1a and GBR1b. Both were found to be associated with GBR2 suggesting that the isoforms GBR1a/GBR2 and GBR1b/GBR2 represent the vast majority of GABA(B)-receptors in the brain. The two isoforms differed strikingly in their pattern of expression on the regional, cellular and subcellular level. These results point to distinct funcional roles of the two receptor isoforms.

Alternative Splicing↗
PubMed2001

Protein-chemical analysis of Bio-Oss bone substitute and evidence on its carbonate content.

The natural bone substitute Bio-Oss is used in periodontal and maxillofacial surgery to fill bone defects and permit reossification. Recent reports have suggested the presence of TGFbeta and of substantial amounts of protein in Bio-Oss and have questioned its position as a biologically inert material and its safety in clinical applications (Hönig et al., Plast Reconstr Surg 1999;103:1324; Schwartz et al., J Periodontol 2000;71:1258). Bio-Oss was therefore subjected to a detailed biochemical, histochemical and biophysical analysis. In three different types of extracts of Bio-Oss no evidence for the presence of protein based on SDS-PAGE and silver staining was detected. In addition, as shown by Western blotting, there was no immunochemical evidence for the presence of the potential growth-inducing factor TGFbeta. Furthermore, micropolished sections of Bio-Oss failed to be stained with McNeal's Tetrachrome as did microtome sections treated with Goldner's Trichrome. However, Bio-Oss was strongly stained with the protein dye Coomassie blue. This staining was virtually irreversible and is attributed to the carbonate content of Bio-Oss which was detected by thermogravimetry-mass spectrometry. Thus, within the limits of the assay conditions, Bio-Oss does not contain protein material to a measurable extent.

Blotting, Western↗
PubMed2001

GABA(A) receptor subtypes: dissecting their pharmacological functions.

The enhancement of GABA-mediated synaptic transmission underlies the pharmacotherapy of various neurological and psychiatric disorders. GABA(A) receptors are pluripotent drug targets that display an extraordinary structural heterogeneity: they are assembled from a repertoire of at least 18 subunits (alpha1-6, beta1-3, gamma1-3, delta, epsilon, theta, rho1-3). However, differentiating defined GABA(A) receptor subtypes on the basis of function has had to await recent progress in the genetic dissection of receptor subtypes in vivo. Evidence that the various actions of allosteric modulators of GABA(A) receptors, in particular the benzodiazepines, can be attributed to specific GABA(A) receptor subtypes will be discussed. Such discoveries could open up new avenues for drug development.

Animals↗
PubMed2001

Molecular targets for the myorelaxant action of diazepam.

Diazepam is used clinically for its myorelaxant, anxiolytic, sedative, and anticonvulsant properties. Although the anxiolytic action is mediated by alpha2 gamma-aminobutyric acid A (GABA(A)) receptors, the sedative action and in part the anticonvulsant action are mediated by alpha1 GABA(A) receptors. To identify the GABA(A) receptor subtypes mediating the action of diazepam on muscle tone, we have assessed the myorelaxant properties of diazepam in alpha2(H101R) and alpha3(H126R) knock-in mice harboring diazepam-insensitive alpha2 or alpha3 GABA(A) receptors, respectively. Whereas in alpha2(H101R) mice the myorelaxant action of diazepam was almost completely abolished at doses up to 10 mg/kg, the same dose induced myorelaxation in both wild-type and alpha3(H126R) mice. It was only at a very high dose (30 mg/kg diazepam) that alpha2(H101R) mice showed partial myorelaxation and alpha3(H126R) mice were partially protected from myorelaxation compared with wild-type mice. Thus, the myorelaxant activity of diazepam seems to be mediated primarily by alpha2 GABA(A) receptors and at high concentrations also by alpha3 GABA(A) receptors.

Animals↗
PubMed2000

Molecular and neuronal substrate for the selective attenuation of anxiety.

Benzodiazepine tranquilizers are used in the treatment of anxiety disorders. To identify the molecular and neuronal target mediating the anxiolytic action of benzodiazepines, we generated and analyzed two mouse lines in which the alpha2 or alpha3 GABAA (gamma-aminobutyric acid type A) receptors, respectively, were rendered insensitive to diazepam by a knock-in point mutation. The anxiolytic action of diazepam was absent in mice with the alpha2(H101R) point mutation but present in mice with the alpha3(H126R) point mutation. These findings indicate that the anxiolytic effect of benzodiazepine drugs is mediated by alpha2 GABAA receptors, which are largely expressed in the limbic system, but not by alpha3 GABAA receptors, which predominate in the reticular activating system.

Animals↗
PubMed2000

Mechanism of action of the hypnotic zolpidem in vivo.

Zolpidem is a widely used hypnotic agent acting at the GABA(A) receptor benzodiazepine site. On recombinant receptors, zolpidem displays a high affinity to alpha 1-GABA(A) receptors, an intermediate affinity to alpha(2)- and alpha(3)-GABA(A) receptors and fails to bind to alpha(5)-GABA(A) receptors. However, it is not known which receptor subtype is essential for mediating the sedative-hypnotic action in vivo. Studying alpha1(H101R) mice, which possess zolpidem-insensitive alpha(1)-GABA(A) receptors, we show that the sedative action of zolpidem is exclusively mediated by alpha(1)-GABA(A) receptors. Similarly, the activity of zolpidem against pentylenetetrazole-induced tonic convulsions is also completely mediated by alpha(1)-GABA(A) receptors. These results establish that the sedative-hypnotic and anticonvulsant activities of zolpidem are due to its action on alpha(1)-GABA(A) receptors and not on alpha(2)- or alpha(3)-GABA(A) receptors.

Animals↗
PubMed1999

Benzodiazepine actions mediated by specific gamma-aminobutyric acid(A) receptor subtypes.

GABA(A) (gamma-aminobutyric acid(A)) receptors are molecular substrates for the regulation of vigilance, anxiety, muscle tension, epileptogenic activity and memory functions, which is evident from the spectrum of actions elicited by clinically effective drugs acting at their modulatory benzodiazepine-binding site. Here we show, by introducing a histidine-to-arginine point mutation at position 101 of the murine alpha1-subunit gene, that alpha1-type GABA(A) receptors, which are mainly expressed in cortical areas and thalamus, are rendered insensitive to allosteric modulation by benzodiazepine-site ligands, whilst regulation by the physiological neurotransmitter gamma-aminobutyric acid is preserved. alpha1(H101R) mice failed to show the sedative, amnesic and partly the anticonvulsant action of diazepam. In contrast, the anxiolytic-like, myorelaxant, motor-impairing and ethanol-potentiating effects were fully retained, and are attributed to the nonmutated GABA(A) receptors found in the limbic system (alpha2, alpha5), in monoaminergic neurons (alpha3) and in motoneurons (alpha2, alpha5). Thus, benzodiazepine-induced behavioural responses are mediated by specific GABA(A) receptor subtypes in distinct neuronal circuits, which is of interest for drug design.

Animals↗
PubMed1999

Genetically modified animals in pharmacological research: future trends.

The recognition of molecular control elements which govern cell and organ function is essential for the development of novel drug therapies and for an understanding of drug actions. Thus, a major interest is focused on methodologies which permit the identification of novel control elements. This is of particular relevance for the identification of drug targets, the distinction of target isoforms, the differentiation of signalling pathways, the generation of disease models and toxicological testing. In this review, we discuss different classes of genetically modified animals and their potential to elucidate biological processes relevant for pharmacological research including functional genomics. Techniques which permit the time- and tissue-specific inducible regulation of gene expression present an important methodological advance.

Animals↗
PubMed1998

[Pharmacotherapy with benzodiazepines: basic principles and new developments].

Pharmacotherapy of various neurologic and psychiatric disorders is based on amplification of the effects of the inhibitory neurotransmitter GABA in the CNS. Of particular importance is the modulation of GABAA receptors by benzodiazepines. Their effects are activity-dependent and self limiting. With the development of new ligands for the benzodiazepine receptorsite selective activity-profiles with minimal side-effects are sought. Progress is to be expected from partial agonists and in particular from ligands with selectivity for receptor subtypes.

Anti-Anxiety Agents↗
PubMed1998

Immunohistochemical evidence for dysregulation of the GABAergic system ipsilateral to photochemically induced cortical infarcts in rats.

Deficits of GABAergic transmission have been reported to occur in tissue surrounding ischemic cortical lesions between a few days and several weeks after the insult. In the present experiments, we used immunohistochemistry with antibodies against parvalbumin and two major subunits of the GABA(A) receptor (alpha1, alpha2) to characterize the events that underlie these changes at different levels of circuit organization. Neocortical infarcts (2 mm diameter) consistently affecting medial parts of the primary somatosensory cortex were induced photochemically in adult male Wistar rats; animals were allowed to recover for one week before perfusion-fixation. When compared to controls the pattern of immunoreactivity had changed for the al subunit of the GABA(A) receptor seven days after the insult. Ipsilateral to the ischemic lesions, we found a decrease in staining intensity reaching up to 4 mm laterally, resulting in a partial or complete absence of the normal laminar staining pattern. No consistent changes were observed for the alpha2 subunit. Parvalbumin staining revealed pathological alterations in a rim of tissue surrounding the infarct, measuring up to 1 mm from the border of the infarcts. Parvalbumin-positive interneurons in this region showed signs of degeneration; both a reduction of the number of dendrites and, to a lesser extent and only immediately adjacent to the ischemic lesions, a reduction of the number of parvalbumin-positive neurons was readily apparent. The results provide evidence for both a differential regulation of two GABA(A) receptor subunits and degenerative changes of parvalbumin-containing interneurons ipsilateral to cortical infarcts. The relevance of these findings for mechanisms underlying long-term recovery, transient functional deficits and postinfarct seizures warrants further investigation.

Animals↗
PubMed1997

Preclinical and clinical studies of a collagen membrane (Bio-Gide).

Membranes are used to guide the repopulation of defects by preferred cells and to achieve a specific healing effect. The collagen membrane studied, Bio-Gide, was developed particularly for periodontal, peri-implant applications or to improve the ossification of bone defects of any origin. Bio-Gide is a bilayer membrane; one compact and smooth layer is covered by a particularly dense film, designed to prevent the invasion of soft tissue in a membrane-protected bone defect. The other, rough side of Bio-Gide must be placed towards the bone defect in order to make bone ingrowth possible. As a prerequisite for its therapeutic use in humans, the collagen matrix must be devoid of major immunogenicity. The immunological response to the membrane material was analysed in rabbits. Later, a clinical prospective study provided information about the bone regeneration effect under the Bio-Gide membrane inserted in six patients selected at random. The immune response to the collagen membrane Bio-Gide and the bone healing was tested in these patients when undergoing oral surgery.

Animals↗
PubMed1996

Characterization of agonist-induced down-regulation of NMDA receptors in cerebellar granule cell cultures.

Exposure of cerebellar granule cells to NMDA in culture at 5 days in vitro, when cells are not yet vulnerable to NMDA, evoked a pronounced reduction in NMDA receptor activity, measured by NMDA-induced 45Ca2+ influx, and counteracted the normal developmental increase in NMDA receptors. The effect was concentration and time dependent, the half-maximal effect being reached at about 45 microM and by 4-5 h. The decrease in NMDA receptor function was accompanied by a significant reduction in the protein level of the obligatory NMDA receptor subunit (NR) NR1. Both parameters remained at a low level as long as the agonist was present. However, receptor down-regulation was reversible, as receptor protein levels and NMDA responses were restored to control values upon NMDA removal, this process requiring protein synthesis. NMDA treatment also elicited a decrease in NR1, NR2A, and NR2B subunit messenger RNA (mRNA) levels. However, in comparison with NMDA receptor proteins, the decrease was faster, and NMDA receptor mRNA content recovered to control levels within 24 h in spite of the presence of NMDA. Concerning the mechanisms of agonist-induced regulation of NMDA receptor expression, it seems that protein kinase C-mediated protein phosphorylation is not involved, whereas inhibition of Ca2+/calmodulin-dependent kinase II/IV by KN-62 does depress NMDA receptor expression even in the absence of NMDA.

Animals↗
PubMed1995

Agonist-induced down-regulation of NMDA receptors in cerebellar granule cells in culture.

In contrast to the acute toxic effect of NMDA on mature cerebellar granule cells, chronic treatment with NMDA (140 microM from 1 to 9 days in vitro) did not compromise cell survival. Such treatment markedly suppressed NMDA receptor activity: at 8 days in vitro NMDA-induced 45Ca2+ influx was reduced by approximately 60% and acute exposure to NMDA (highest concentration tested, 1 mM) at 9 days in vitro did not cause detectable toxicity. The reduction in NMDA receptor activity was accompanied by a significant decrease (approximately 80% at 9 days in vitro) in the level of the NR1 and the NR2A NMDA receptor subunit protein, detected using the selective photoaffinity ligand [125I]CGP55802A. It seems, therefore, that the agonist-induced decrease in NMDA receptor activity is due to receptor down-regulation. In contrast to the marked influence of chronic NMDA exposure on the cellular content of the NMDA receptor subunit proteins, mRNA levels of the different subunits (NR1, NR2A, NR2B and NR2C) were not significantly affected. It seems, therefore, that agonist-induced down-regulation of the NMDA receptor involves critically mRNA translation and/or post-translational regulation.

Animals↗
PubMed1995

Colocalization of gephyrin and GABAA-receptor subunits in the rat retina.

Gephyrin is a protein that copurifies with the glycine receptor (GlyR) and is required for the clustering of GlyRs at postsynaptic sites. Previously, it was thought that antibody mAb 7a, directed against gephyrin, was a specific marker for GlyR. However, there is evidence that gephyrin can also be found at nonglycinergic synapses. Here, immunocytochemistry was applied to show this directly for the rat retina. Both gephyrin and different subunits of the gamma-aminobutyric acid (GABA)A receptor were localized to discrete puncta in the inner plexiform layer, and these puncta were shown by electron microscopy to represent synaptic sites. Double immunocytochemistry revealed that GABAA receptors and GlyRs are not colocalized. However, gephyrin and different subunits of GABAA receptors were found to occur at the same synapses. The amount of colocalization varied with the GABAA receptor subunit composition and was most extensive for the alpha 2 subunit, less for the alpha 3 subunit, and minimal for the alpha 1 subunit. The gephyrin present at GABAergic synapses of the retina might also be involved with clustering of receptors at the postsynaptic sites. Hence, localization of gephyrin can no longer be considered as a unique marker of glycinergic synapses.

Animals↗
PubMed1995

GABAA receptor subunits have differential distributions in the rat retina: in situ hybridization and immunohistochemistry.

The distributions of nine different subunits of the gamma-aminobutyric acidA (GABAA) receptor (alpha 1, alpha 2, alpha 3, alpha 5; beta 1, beta 2, beta 3; gamma 2; delta) were investigated in the rat retina using immunocytochemistry and in situ hybridization. With the exception of the alpha 5 subunit, all subunits could be localized. Each subunit was expressed in characteristic strata within the inner plexiform layer (IPL). Some subunits (e.g., gamma 2) showed a ubiquitous distribution, while others (e.g., delta) were restricted to narrow sublayers. Double labeling experiments using different combinations of the subunit-specific antibodies revealed colocalizations of subunits within individual neurons. Additionally, GABAA receptor subunits were mapped to distinct populations of retinal neurons by coapplication of defined immunocytochemical markers and subunit-specific antibodies. Cholinergic amacrine cells were found to express the alpha 2, beta 1, beta 2/3 and delta subunits, while dopaminergic amacrine cells express the alpha 2, alpha 3 and gamma 2 subunits. Dissociated rod bipolar cells express the alpha 1 and gamma 2 subunits. In summary, this study provides evidence for the existence of multiple GABAA receptor subtypes in the retina. The distinct stratification pattern of the subunits in the IPL suggests that different functional circuits involve specific subtypes of GABAA receptors.

Animals↗