Biomedical subjects

R McKernan

Publications and source records attributed to R McKernan.

15 recordsLinked to original sources

PubMed2006

International spinal research trust research strategy. III: A discussion document.

STUDY DESIGN: Discussion document. OBJECTIVES/METHODS: To review the Research Strategy of the International Spinal Research Trust (ISRT), which identifies key areas of basic and clinical research that are likely to be beneficial in developing potential treatments for spinal cord injury for funding. This strategy is intended to both guide the programme of research towards areas of priority and stimulate discussion of the different avenues of research. This latest document has been developed to take into account the scientific progress in the 6 years since publication of the previous Research Strategy. RESULTS/DISCUSSION: The latest scientific developments in research designed to repair the spinal cord and restore function following injury and how they might impact on spinal cord injury research are highlighted.

Biomedical Research↗

PubMed2001

Entropy as the predominant driving force of binding to human recombinant alpha(x)beta(3)gamma(2) GABA(A) receptors.

In order to study the correlation of the thermodynamic driving forces of binding with the efficacies of displacing ligands, the specific binding of [3H]SR 95531 [2-(3-carboxypropyl)3-amino-6-p-methoxyphenylpyridazinium bromide], a GABA(A) receptor antagonist, was studied in cell lines stably expressing human alpha(1)beta(3)gamma(2) and alpha(2)beta(3)gamma(2) GABA(A) receptors. Displacing potencies for the agonists with different efficacies (muscimol, 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP) and piperidine-4-sulfonic acid) and for antagonists (SR 95531 and 5-(4-piperidyl)isothiazol-3-ol) were determined at 0 degrees C, 20 degrees C and 37 degrees C. Displacing potencies were temperature-nearly independent for alpha(1)beta(3)gamma(2) receptors. At alpha(2)beta(3)gamma(2), receptor binding of the antagonists was exothermic, endothermic for the agonists THIP and piperidine-4-sulfonic acid and isothermic for muscimol. The free energy increments of displacement for the binding of the antagonist [3H]SR 95531 versus the agonist [3H]muscimol approach saturation as a function of the efficacies of the displacers only for alpha(1)beta(3)gamma(2) receptors. This suggests that, for binding to alpha(1)beta(3)gamma(2) GABA(A) receptors, displacement is an efficacy-dependent interaction predominantly driven by entropic increases.

Animals↗

PubMed2001

Gamma-aminobutyric acid type B receptors with specific heterodimer composition and postsynaptic actions in hippocampal neurons are targets of anticonvulsant gabapentin action.

Gamma-aminobutyric acid (GABA) activates two qualitatively different inhibitory mechanisms through ionotropic GABA(A) multisubunit chloride channel receptors and metabotropic GABA(B) G protein-coupled receptors. Evidence suggests that pharmacologically distinct GABA(B) receptor subtypes mediate presynaptic inhibition of neurotransmitter release by reducing Ca2+ conductance, and postsynaptic inhibition of neuronal excitability by activating inwardly rectifying K+ (Kir) conductance. However, the cloning of GABA(B) gb1 and gb2 receptor genes and identification of the functional GABA(B) gb1-gb2 receptor heterodimer have so far failed to substantiate the existence of pharmacologically distinct receptor subtypes. The anticonvulsant, antihyperalgesic, and anxiolytic agent gabapentin (Neurontin) is a 3-alkylated GABA analog with an unknown mechanism of action. Here we report that gabapentin is an agonist at the GABA(B) gb1a-gb2 heterodimer coupled to Kir 3.1/3.2 inwardly rectifying K+ channels in Xenopus laevis oocytes. Gabapentin was practically inactive at the human gb1b-gb2 heterodimer, a novel human gb1c-gb2 heterodimer and did not block GABA agonism at these heterodimer subtypes. Gabapentin was not an agonist at recombinant GABA(A) receptors as well. In CA1 pyramidal neurons of rat hippocampal slices, gabapentin activated postsynaptic K+ currents, probably via the gb1a-gb2 heterodimer coupled to inward rectifiers, but did not presynaptically depress monosynaptic GABA(A) inhibitory postsynaptic currents. Gabapentin is the first GABA(B) receptor subtype-selective agonist identified providing proof of pharmacologically and physiologically distinct receptor subtypes. This selective agonism of postsynaptic GABA(B) receptor subtypes by gabapentin in hippocampal neurons may be its key therapeutic advantage as an anticonvulsant.

Acetates↗

PubMed2000

Pharmacophore/receptor models for GABA(A)/BzR subtypes (alpha1beta3gamma2, alpha5beta3gamma2, and alpha6beta3gamma2) via a comprehensive ligand-mapping approach.

Pharmacophore/receptor models for three recombinant GABA(A)/BzR subtypes (alpha1beta3gamma2, alpha5beta3gamma2, and alpha6beta3gamma2) have been established via an SAR ligand-mapping approach. This study was based on the affinities of 151 BzR ligands at five distinct (alpha1-3,5,6beta3gamma2) recombinant GABA(A)/BzR receptor subtypes from at least nine different structural families. Examination of the included volumes of the alpha1-, alpha5-, and alpha6-containing subtypes indicated that region L(2) for the alpha5-containing subtype appeared to be larger in size than the analogous region of the other receptor subtypes. Region L(Di), in contrast, appeared to be larger in the alpha1 subtype than in the other two subtypes. Moreover, region L(3) in the alpha6 subtype is either very small or nonexistent in this diazepam-insensitive subtype (see Figure 16 for details) as compared to the other subtypes. Use of the pharmacophore/receptor models for these subtypes has resulted in the design of novel BzR ligands (see 27) selective for the alpha5beta3gamma2 receptor subtype. alpha5-Selective ligand 27 when injected directly into the hippocampus did enhance memory in one paradigm (Bailey et al., unpublished observations); however, systemic administration of either 9 or 27 into animals did not provide an observable enhancement. This result is in complete agreement with the observation of Liu (1996). It has been shown (Liu, 1996; Wisden et al., 1992) that in the central nervous system of the rat (as well as monkeys and pigeons) there are several native subtypes of the GABA(A) receptor which exhibit different functions, regional distributions, and neuronal locations. Although 27 binds more potently at alpha5beta3gamma2 receptor subtypes and is clearly an inverse agonist (Liu et al., 1996; Liu, 1996), it is possible that this ligand acts as an agonist at one or more subtypes. Liu (1996) clearly showed that a number of imidazobenzodiazepines were negative modulators at one subtype and agonists at another. Therefore, selectivity for a particular subtype at this point is not sufficient to rule out some physiological effect at other GABA(A)/BzR subtypes. The inability of 27 to potentiate memory when given systemically is again in support of this hypothesis, especially since alpha1beta2gamma2 subtypes are distributed throughout the brain (Wisden et al., 1992). A drug delivered systemically is far more likely to interact with all subtypes than one delivered to a specific brain region. This observation (systemic vs intrahippocampal) provides further support for the design of more subtype-specific ligands at the BzR to accurately define their pharmacology, one key to the design of new drugs with fewer side effects.

Animals↗

PubMed2000

Subunit composition and pharmacological characterization of gamma-aminobutyric acid type A receptors in frog pituitary melanotrophs.

The frog pars intermedia is composed of a single population of endocrine cells directly innervated by gamma-aminobutyric acid (GABA)ergic nerve terminals. We have previously shown that GABA, acting through GABA(A) receptors, modulates both the electrical and secretory activities of frog pituitary melanotrophs. The aim of the present study was to take advantage of the frog melanotroph model to determine the relationship between the subunit composition and the pharmacological properties of native GABA(A) receptors. Immunohistochemical labeling revealed that in situ and in cell culture, frog melanotrophs were intensely stained with alpha2-, alpha3-, gamma2-, and gamma3-subunit antisera and weakly stained with a gamma1-subunit antiserum. Melanotrophs were also immunolabeled with a monoclonal antibody to the beta2/beta3-subunit. In contrast, frog melanotrophs were not immunoreactive for the alpha1-, alpha5-, and alpha6-isoforms. The effects of allosteric modulators of the GABA(A) receptor on GABA-activated chloride current were tested using the patch-clamp technique. Among the ligands acting at the benzodiazepine-binding site, clonazepam (EC50, 5 x 10(-9) M), diazepam (EC50, 10(-8) M), zolpidem (EC50, 3 x 10(-8) M), and beta-carboline-3-carboxylic acid methyl ester (EC50, 10(-6) M) were found to potentiate the whole cell GABA-evoked current in a dose-dependent manner. Methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (IC50, 3 x 10(-5) M) inhibited the current, whereas Ro15-4513 had no effect. Among the ligands acting at other modulatory sites, etomidate (EC50, 2 x 10(-6) M) enhanced the GABA-evoked current, whereas 4'-chlorodiazepam (IC50, 4 x 10(-7) M), ZnCl2 (IC50, >5 x 10(-5) M), and furosemide (IC50, >3 x 10(-4) M) depressed the response to GABA. PK 11195 did not affect the GABA-evoked current or its inhibition by 4'-chlorodiazepam. The results indicate that the native GABA(A) receptors in frog melanotrophs are formed by combinations of alpha2-, alpha3-, beta2/3-, gamma1-, gamma2-, and gamma3-subunits. The data also demonstrate that clonazepam is the most potent, and zolpidem is the most efficient positive modulator of the native receptors. Among the inhibitors, 4'-chlorodiazepam is the most potent, whereas ZnCl2 is the most efficient negative modulator of the GABA(A) receptors. The present study provides the first correlation between subunit composition and the functional properties of native GABA(A) receptors in nontumoral endocrine cells.

Animals↗

PubMed2000

Pharmacophore/receptor models for GABA(A)/BzR alpha2beta3gamma2, alpha3beta3gamma2 and alpha4beta3gamma2 recombinant subtypes. Included volume analysis and comparison to alpha1beta3gamma2, alpha5beta3gamma2, and alpha6beta3gamma2 subtypes.

Pharmacophore/receptor models for 6 recombinant GABA(A)/BzR subtypes (alphax beta3gamma2, x = 1-6) have been established via an SAR ligand mapping approach. This study was based on the affinities of 166 BzR ligands at 6 distinct (alpha1-6beta3gamma2) recombinant GABA(A)/BzR receptor subtypes from at least twelve different structural families. Examination of the included volumes indicated that the shapes of binding pockets for alpha1, alpha2 and alpha3 subtypes are very similar to each other. Region L2 for the alpha5 containing subtype appeared to be larger in size than the analogous region of the other receptor subtypes. Region L(Di), in contrast, appeared to be larger in the alpha1 subtype than in the other subtypes. Moreover, region L3 in the alpha6 subtype is either very small or nonexistent in this diazepam insensitive "DI" subtype as compared to the other subtypes. Preliminary results for the alpha4-containing receptor subtype (DI) indicate that L3 in the alpha4 subtype suffers a similar fate. Use of the pharmacophore/receptor models for these subtypes have resulted in the design of novel BzR ligands selective for the alpha5beta3gamma2, receptor subtype.

Animals↗

PubMed1999

Studies of molecular pharmacophore/receptor models for GABAA/BzR subtypes: binding affinities of symmetrically substituted pyrazolo[4,3-c]quinolin-3-ones at recombinant alpha x beta 3 gamma 2 subtypes and quantitative structure-activity relationship studies via a comparative molecular field analysis.

A series of symmetrically substituted pyrazoloquinolinones was synthesized to probe the BzR binding site of different GABAA/Bz receptor subtypes. The affinities of the ligands for different BzR subtypes have been determined by radioligand binding assays on 5 distinct recombinant GABAA receptor isoforms [alpha x beta 3 gamma 2 (x = 1,2,3,5, or 6)]. Most of the ligands synthesized exhibited potent biological activity in vitro. Among them, 3 ligands exhibited enhanced affinity for the alpha 2 beta 3 gamma 2 subtype in comparison to the other subtypes, six ligands demonstrated higher affinity for the alpha 3 beta 3 gamma 2 subtype, while 2 ligands showed some enhanced affinity for the alpha 5 beta 3 gamma 2 subtype. The remainder of the ligands exhibited relatively higher affinities at the alpha 1 containing subtype. To map out the steric and electronic differences between the benzodiazepine binding subtypes, a QSAR analysis by the method of Comparative Molecular Field Analysis (CoMFA) of each receptor subtypes was carried out.

Binding Sites↗

PubMed1998

Predictive models for GABAA/benzodiazepine receptor subtypes: studies of quantitative structure-activity relationships for imidazobenzodiazepines at five recombinant GABAA/benzodiazepine receptor subtypes [alphaxbeta3gamma2 (x = 1-3, 5, and 6)] via comparative molecular field analysis.

Affinities of a series of substituted imidazobenzodiazepines at recombinant alpha1beta3gamma2, alpha2beta3gamma2, alpha3beta3gamma2, alpha5beta3gamma2, and alpha6beta3gamma2 GABAA/benzodiazepine receptor subtypes are reported. Many of these ligands displayed high affinities (low-nanomolar to subnanomolar scale) at all five receptor subtypes. Furthermore, a number of imidazobenzodiazepines exhibited relatively good selectivity at the alpha5-containing receptor isoform. For example, ligand 27 (RY-023) demonstrated a 55-fold higher selectivity at alpha5beta3gamma2 isoforms in comparison to other receptor subtypes. The affinity ratio of alpha1 (the most prevalent subtype in the brain) to alpha5 of this series of ligands ranged from 60- to 75-fold for the most selective ligands. Studies of quantitative structure-activity relationships (QSAR) by means of comparative molecular field analysis (CoMFA) were carried out. As a result, examination of CoMFA models for all five receptor subtypes demonstrated their predictability for affinities of imidazobenzodiazepines at the five receptor subtypes. Regions of molecular fields which would favor or disfavor the binding affinity of a ligand at a specific receptor subtype were examined via CoMFA for alpha1, alpha2, alpha3, alpha5, and alpha6 subtypes. A CoMFA regression analysis was applied to predict the ratio of Ki alpha1/Ki alpha5, an index for the selectivity of a ligand at the alpha5 subtype. All of the CoMFA models offered good cross-validated correlations for the ligands in the test set as well as the ratios of Ki alpha1/Ki alpha5, which demonstrated their potential for prediction.

Animals↗

PubMed1998

Synthesis and evaluation of analogues of the partial agonist 6-(propyloxy)-4-(methoxymethyl)-beta-carboline-3-carboxylic acid ethyl ester (6-PBC) and the full agonist 6-(benzyloxy)-4-(methoxymethyl)-beta-carboline-3-carboxylic acid ethyl ester (Zk 93423) at wild type and recombinant GABAA receptors.

A pharmacophore and an alignment rule have previously been reported for BzR agonist ligands. The design and synthesis of 6-(propyloxy)-4-(methoxymethyl)-beta-carboline-3-carboxylic acid ethyl ester (6-PBC, 24, IC50 = 8.1 nM) was based on this pharmacophore. When evaluated in vivo this ligand exhibited anticonvulsant/anxiolytic activity but was devoid of the muscle relaxant/ataxic effects of "classical" 1,4-benzodiazepines (i.e., diazepam). Significantly, 6-PBC 24 also reversed diazepam-induced muscle relaxation in mice. The 3-substituted analogues 40-46 and 48 of 6-PBC 24 and Zk 93423 27(IC50 = 1 nM) were synthesized and evaluated in vitro to determine what affect these modifications would have on the binding affinity at recombinant BzR subtypes. With the exception of the 3-amino ligands 40 and 41, all the beta-carbolines were found to exhibit high binding affinity at BzR sites. The 3-propyl ether derivative 45 was also evaluated in vivo and found to be devoid of any proconvulsant or anticonvulsant activity at doses up to 40 mg/kg. The 6-(1-naphthylmethyloxy) and 6-octyloxy analogues 25, 26, 28, and 29 of 6-PBC 24 were synthesized to further evaluate the proposed alignment of agonists vs inverse agonists in the pharmacophore of the BzR. In addition, ligands 26 and 29 were designed to probe the dimensions of lipophilic pocket L3 at the agonist site. The activity of 29 was evaluated in vivo; however, this analogue elicited no pharmacological effects at doses up to 80 mg/kg. These and other related beta-carbolines were also examined in five recombinant GABAA receptor subtypes. Ligands 52-61 all exhibited moderate to high affinity at GABAA receptors containing alpha1 subunits. These ligands will be useful in further defining the pharmacophore at alpha1 beta3 gamma2 receptors.

Animals↗

PubMed1998

Rat and human hippocampal alpha5 subunit-containing gamma-aminobutyric AcidA receptors have alpha5 beta3 gamma2 pharmacological characteristics.

The gamma-aminobutyric acid (GABA)A receptor is a hetero-oligomer consisting of five subunits, the combination of which confers unique pharmacological properties to the receptor. To understand the physiological role of native GABAA receptors, it is critical to determine their subunit compositions. The pharmacological characteristics of human alpha5 beta3 gamma2 and alpha5beta3gamma3 GABAA receptors stably expressed in L(tk-) cells were characterized with the alpha5-selective ligand [3H]L-655,708 and compared with the pharmacological characteristics of [3H]L-655,708 binding sites from rat and human hippocampus. Saturation analyses revealed a 9-fold selective affinity of [3H]L-655,708 for alpha5 beta3 gamma2 receptors (Kd = 1.7 +/- 0.4 nM), compared with alpha5 beta3 gamma3 receptors (Kd = 15 +/- 3 nM). Rat and human hippocampal [3H]L-655,708 binding sites had affinities of 2.2 +/- 0.6 and 1.0 +/- 0.2 nM, respectively, comparable to the affinity of alpha5 beta3 gamma2 receptors. Pharmacological analysis of [3H]L-655,708 binding sites in rat and human hippocampi revealed a strong correlation with the affinities of seven benzodiazepine site ligands for alpha5 beta3 gamma2 but not alpha5 beta3 gamma3 receptors. Immunoprecipitation of [3H]L-655,708 binding sites from rat hippocampus with a gamma2-selective antibody yielded 19 +/- 4% of total benzodiazepine binding sites measured using [3H]Ro15-1788, whereas no specific binding was measured after immunoprecipitation with an anti-gamma3 antibody. Combinatorial immunoprecipitations of [3H]muscimol binding sites with anti-alpha5 and anti-gamma2 or anti-alpha5 and anti-gamma3 antibodies established the preferential expression of alpha5 gamma2 receptors, accounting for 22 +/- 2% of total rat hippocampal GABAA receptors. These observations provide pharmacological and structural evidence for the prevalence of alpha5 beta3 gamma2 GABAA receptors in rat hippocampus, despite the clustering of alpha5 and gamma3 loci on the same chromosome.

Adult↗

PubMed1997

Anticonvulsant activity of azirino[1,2-d][1,4]benzodiazepines and related 1,4-benzodiazepines in mice.

The anticonvulsant properties of several 1,4-benzodiazepine and azirino[1,2-d][1,4]benzodiazepine (ABDZ) derivatives were studied after intraperitoneal (IP) administration in DBA/2 mice (a strain genetically susceptible to sound-induced seizures) and in Swiss mice. The anticonvulsant effects were evaluated on seizures evoked by means of auditory stimulation (109 dB, 12-16 kHz) in animals placed singly under a hemispheric Perspex dome or on seizures induced by administration of pentylenetetrazole. The 1,4-benzodiazepines were generally more potent than the related ABDZ derivatives. The rank order of potency for anticonvulsant activity was flunitrazepam > diazepam > pinazepam > ABDZ5 > ABDZ4 > prazepam > halazepam > ABDZ1 > ABDZ3 > camazepam > ABDZ6 > ABDZ2. The impairment of locomotor performance following IP administration of these derivatives was also evaluated by means of the rotarod test. The rank order of potency for impairment of coordinated motor movements was pinazepam > flunitrazepam > diazepam > ABDZ5 > prazepam > halazepam > ABDZ4 > ABDZ3 > ABDZ1 > camazepam > ABDZ2 = ABDZ6. The potency of various 1,4-benzodiazepines and ABDZs as inhibitors of specific [3H]flumazenil binding to membranes from cerebellum or cortex was evaluated. In general, ABDZs were active as anticonvulsants and inhibited [3H]flumazenil binding in the micromolar range. Radioligand binding studies carried out in stable cell lines demonstrated that none of the ABDZs tested showed a particular subtype specificity. The pharmacological actions of ABDZ4 and ABDZ5, which appeared to be the most potent ABDZs as anticonvulsants, were significantly reduced by treatment with flumazenil (8.24 mumol/kg IP), suggesting a clear involvement of benzodiazepine mechanisms in the anticonvulsant activity of these compounds or their metabolites. The anticonvulsant activity of ABDZ4 and ABDZ5 was also evaluated against seizures induced in DBA/2 mice by two beta-carbolines: methyl-beta-carboline-3-carboxylate (beta-CCM) and methyl-6,6-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM). Both ABDZ4 and ABDZ5 give better protection against seizures induced by beta-CCM than DMCM, suggesting a preferential action on the benzodiazepine receptor subtype BDZ1.

Animals↗

PubMed1997

Differences in agonist/antagonist binding affinity and receptor transduction using recombinant human gamma-aminobutyric acid type A receptors.

Using human gamma-aminobutyric acid type A (GABAA) receptor subunit combinations, expressed in cell lines and Xenopus laevis oocytes, the pharmacology of a number of ligands interacting directly with the GABA recognition site has been studied in [3H]muscimol binding and electrophysiologically. The binding affinity of GABAA agonist and antagonist ligands showed small but statistically significant dependence on the subunit composition of receptors that include gamma 2 and different alpha and beta subunits. The potency of antagonist ligands was largely independent of receptor subunit composition, whereas the composition of receptors expressed in oocytes strongly influenced the EC50 value of agonists. An apparent reciprocal correlation between subunits favoring agonist binding and antagonist binding, respectively, was observed. Whereas antagonists showed comparable potencies in binding and functional studies, the potency of agonists in binding studies was generally two to three orders of magnitude higher than the agonist potencies measured electrophysiologically. 5-(4-Piperidyl)isothiazol-3-ol, which behaves as a low efficacy partial agonist at GABAA receptors in cultured cortical neurons, showed no efficacy in oocytes, but produced pure antagonist effects with a binding/functional affinity ratio between those observed for the agonists and antagonists. It is concluded that the GABAA receptor mechanisms transducing binding into physiological response, but not the binding per se, is dependent on the receptor subunit composition.

Animals↗

PubMed1995

Subcellular localization of the GABAA receptor gamma 2 subunit in the rat spinal cord.

The fine subcellular organization of the GABAA receptor complex in the adult rat spinal ventral horn was analysed by immunocytochemistry using a specific polyclonal antiserum raised against the gamma 2 subunit. This subunit confers benzodiazepine sensitivity on the chloride channel of the GABAA receptor. With both fluorescent and peroxidase staining, the immunoreactivity was mainly observed in the grey matter and more specifically in the dorsal and ventral horns on medium and large neurons. A high number of immunostained somata were clustered in regions corresponding to motor nuclei. On the neuronal surface, labelling appeared as fluorescent dots over the more diffuse staining that was present on the soma and proximal part of dendrites. At the ultrastructural level, peroxidase end product was in most cases associated with the internal side of postsynaptic differentiations facing terminal boutons enriched with pleiomorphic small clear vesicles. The positively stained synapses were encountered on proximal dendrites of neurons and throughout the neuropil of the ventral horn (layers VII-IX). An immunoreactivity on the postsynaptic membrane was occasionally found to decorate large pieces of membrane not directly apposed to presynaptic active zones. In addition, presynaptic labelling was observed at axoaxonic contacts and at extrasynaptic sites on membranes within boutons, sometimes themselves apposed to gamma 2 immunoreactivity. Finally, we also observed gamma 2 immunoreactivity at the cytosolic face of the plasma membrane of some glial elements. These results give morphological evidence for the involvement of GABAA receptors in both post- and presynaptic inhibition in the rat spinal ventral horn. The presence of gamma 2 subunit immunoreactivity at these different synaptic contacts suggests that the two types of inhibition can be modulated by benzodiazepine drugs. The findings also provide anatomical evidence for the possible regulation of GABA release through an autoreceptor, and for GABAergic communication between neuronal and glial components.

Animals↗

PubMed1995

GABAA receptor-like immunoreactivity in the goldfish brainstem with emphasis on the Mauthner cell.

The distribution of the GABAA receptor in the goldfish brainstem and on the Mauthner cell membrane was investigated with both optical and electron microscopy using a polyclonal antibody raised against the intracellular loop of the rat gamma 2 subunit. At the optical level, immunofluorescent dots were detected on small and large neurons belonging to vestibular and reticular nuclei. On the Mauthner cell plasmalemma, a gamma 2-like immunoreactivity was observed predominantly on the tip of the lateral dendrite. Fluorescent parches were intermingled with a more diffuse staining. Immunoreactive spots of weaker intensity were also present on the soma and some were also observed inside and within the periphery of the axon-cap as well. Observations at the electron microscopic level revealed that the peroxidase end-product predominates postsynaptically in front of release sites in the studied nuclei and on the Mauthner cell. On the lateral dendrite of the neuron, numerous immunopositive postsynaptic differentiations were encountered on spines. Stained glial elements were encountered in the different areas studied. These results demonstrate that the GABAA receptor gamma 2 subunit has a precise distribution on neuronal membranes and suggest that it could be involved in the remote dendritic inhibition of the Mauthner cell and in the control of input-output properties of both vestibular and reticular nuclei.

Animals↗

PubMed1994

Effects of L-690,488, a prodrug of the bisphosphonate inositol monophosphatase inhibitor L-690,330, on phosphatidylinositol cycle markers.

In order to enhance the entry into cells of L-690,330, a bisphosphonate inhibitor of inositol monophosphatase (IMPase; a key, enzyme in the phosphatidylinositol (Pl) cell signaling pathway), the tetrapivaloyloxymethyl ester prodrug, L-690,488 [tetrapivaloyloxymethyl 1-(4-hydroxyphenoxy)ethane-1,1-bisphosphonate], was synthesized. The effects of L-690,488 were studied in cholinergically (carbachol)-stimulated rat cortical slices and Chinese hamster ovary cells stably transfected with the human muscarinic m1 receptor (m1 CHO cells). The accumulation of [3H]inositol monophosphates or [3H]cytidine monophosphorylphosphatidate ([3H]CMP-PA) after [3H]inositol or [3H]cytidine prelabeling, respectively, and inositol 1,4,5-trisphosphate and inositol 1,3,4,5-tetrakisphosphate mass were measured. In rat cortical slices and m1 CHO cells, the maximum response and time course of accumulation of [3H]inositol monophosphates for L-690,488 and lithium were similar. However, the concentrations of L-690,488 required to produce these effects (EC50 values of 3.7 +/- 0.9 and 1.0 +/- 0.2 microM in cortical slices and m1 CHO cells, respectively) were much lower than with lithium (0.3-1.5 mM). Likewise, the time course and maximum accumulation of [3H] CMP-PA in L-690,488-treated m1 CHO cells was similar to lithium but L-690,488 was again much more potent (EC50 values = 3.5 +/- 0.3 microM and 0.52 +/- 0.03 mM for L-690,488 and lithium, respectively). In addition, L-690,488 attenuated the carbachol-induced elevation of inositol 1,4,5-trisphosphate and inositol 1,3,4,5-tetrakisphosphate in m1 CHO cells, an effect reported previously with lithium. These results are all consistent with L-690,488 and lithium both depleting intracellular inositol as a consequence of inhibition of IMPase. That these effects of L-690,488 on the PI cycle are indeed due to inositol depletion is shown by the observation that the effects of L-690,488 on CMP-PA accumulation could be overcome by addition of exogenous myo-inositol (EC50 = 1.7 +/- 0.5 mM). These data show that inhibition of IMPase produces effects on the PI cycle comparable to lithium. As a corollary, the effects of lithium on the PI cycle are therefore consistent with its major mechanism of action being inhibition of IMPase.

Animals↗