20 research outputs found
Inhibition of astroglial connexin43 hemichannels with TAT-Gap19 exerts anticonvulsant effects in rodents
Accumulating evidence shows a key function for astrocytic connexin43 (Cx43) signaling in epilepsy. However, the lack of experimental distinction between Cx43 gap junction channels (GJCs) and hemichannels (HCs) has impeded the identification of the exact contribution of either channel configurations to epilepsy. We therefore investigated whether TAT-Gap19, a Cx mimetic peptide that inhibits Cx43 HCs but not the corresponding Cx43 GJCs, influences experimentally induced seizures in rodents. Dye uptake experiments in acute hippocampal slices of mice demonstrated that astroglial Cx43 HCs open in response to the chemoconvulsant pilocarpine and this was inhibited by TAT-Gap19. In vivo, pilocarpine-induced seizures as well as the accompanying increase in D-serine microdialysate levels were suppressed by Cx43 HC inhibition. Moreover, the anticonvulsant action of TAT-Gap19 was reversed by exogenous D-serine administration, suggesting that Cx43 HC inhibition protects against seizures by lowering extracellular D-serine levels. The anticonvulsive properties of Cx43 HC inhibition were further confirmed in electrical seizure mouse models, i.e. an acute 6 Hertz (Hz) model of refractory seizures and a chronic 6 Hz corneal kindling model. Collectively, these results indicate that Cx43 HCs play a role in seizures and underscore their potential as a novel and druggable target in epilepsy treatment
Identification of GSK-3 as a potential therapeutic entry point for epilepsy
In view of the clinical need for new antiseizure drugs (ASDs) with novel modes of action, we used a zebrafish seizure model to screen the anticonvulsant activity of medicinal plants used by traditional healers in the Congo for the treatment of epilepsy, and identified a crude plant extract that inhibited pentylenetetrazol (PTZ)-induced seizures in zebrafish larvae. Zebrafish bioassay-guided fractionation of this anticonvulsant Fabaceae species, Indigofera arrecta, identified indirubin, a compound with known inhibitory activity of glycogen synthase kinase (GSK)-3, as the bioactive component. Indirubin, as well as the more potent and selective GSK-3 inhibitor 6-bromoindirubin-3'-oxime (BIO-acetoxime) were tested in zebrafish and rodent seizure assays. Both compounds revealed anticonvulsant activity in PTZ-treated zebrafish larvae, with electroencephalographic recordings revealing reduction of epileptiform discharges. Both indirubin and BIO-acetoxime also showed anticonvulsant activity in the pilocarpine rat model for limbic seizures and in the 6-Hz refractory seizure mouse model. Most interestingly, BIO-acetoxime also exhibited anticonvulsant actions in 6-Hz fully kindled mice. Our findings thus provide the first evidence for anticonvulsant activity of GSK-3 inhibition, thereby implicating GSK-3 as a potential therapeutic entry point for epilepsy. Our results also support the use of zebrafish bioassay-guided fractionation of antiepileptic medicinal plant extracts as an effective strategy for the discovery of new ASDs with novel mechanisms of action
Intrastrain differences in seizure susceptibility, pharmacological response and basal neurochemistry of Wistar rats
The sexual behavior induced-inhibition of aromatase activity in the preoptic nucleus is mediated by glutamate release.
Anticonvulsant effect of a ghrelin receptor agonist in 6Hz corneally kindled mice
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Glutamate controls brain estrogen synthesis during sexual interactions
Besides their long-lasting effects mediated by a modulation of gene transcription, brain-derived estrogens can rapidly regulate (within minutes) reproductive behaviors. In vitro, the activity of aromatase (AA), the enzyme responsible for the conversion of androgens into estrogens, is also regulated on a similar short time-scale, via phosphorylation of the enzyme resulting from changes in neuronal activity or glutamate release. Acute changes in AA have been documented ex vivo in specific brain regions following exposure to social or stressful stimuli but the mechanism underlying these regulations is not known. To investigate whether glutamate is implicated in these rapid changes in AA, male quail received a unilateral injection of kainate in the medial preoptic nucleus (POM). The left and right preoptic areas were collected 20 min later and assayed separately by the tritiated water technique for AA. As shown previously in preoptic explants maintained in vitro, AA was downregulated in the kainate-injected hemisphere as compared to the non-injected side. To determine whether the decline in AA detected in the POM after a sexual interaction could be mediated by an increased release of glutamate in this region, extracellular glutamate concentration was measured by in vivo microdialysis with a probe implanted in the POM of sexually mature males. Dialysate was collected every 3 minutes over three periods of 15 min when the male was (1) alone, (2) allowed to freely copulate with a female and (3) alone again. A transient rise in extracellular glutamate concentration was observed specifically and immediately after the expression of cloacal contact movements, when semen is transferred to the female. Glutamate returned to a basal level after the female was removed. Together, these results indicate that the mechanism of acute regulation of aromatase activity by glutamate identified in vitro is potentially responsible for the acute regulation of the enzyme observed in vivo following copulation. As rapid changes in brain estrogen synthesis and its actions are apparently related to the control of sexual motivation rather than sexual performance, follow up experiments should now determine whether the release of glutamate in the POM occurs in parallel with an increase in motivation or follows the termination of the copulatory sequence
Higher susceptibility to 6 Hz corneal kindling and lower responsiveness to antiseizure drugs in mouse models of Alzheimer's disease
The intracerebral injection of A\u3b2<sub>1-42</sub> oligomers does not invariably alter seizure susceptibility in mice
Preoptic glutamate and estradiol release during male sexual behavior
Beside its long-term control by steroids, male sexual behavior is also modulated by
neuroestrogens in a dynamic way (within minutes) in a number of species ranging
from fishes to mammals. Studies in male Japanese quail have also identified following
exposure to a receptive female a rapid decrease in the activity of brain aromatase
(AA) the enzyme responsible for the conversion of androgens into estrogens. These
effects occur mainly within the medial preoptic nucleus (POM), a sexually dimorphic
structure of the preoptic area that plays a key role in the activation of male sexual
behavior and contains the highest AA in the brain. In vitro studies demonstrated that
AA can be rapidly inhibited by calcium-dependent phosphorylations of the enzyme
triggered by the activation of AMPA and kainate receptors. We confirmed here this
rapid effect of glutamate on AA by injecting kainate in the POM of anesthetized
males and measuring AA in the tissue after brain collection. AA in POM was inhibited
in the kainate-injected hemisphere compared to the control hemisphere injected with
vehicle. In a second experiment, we showed by in vivo microdialysis that glutamate is
released in POM during copulation. These results thus suggest that glutamate
controls dynamic changes of AA that occur in the brain during sexual interactions. To
confirm that the decrease in AA leads to an actual reduction of local estradiol
concentration, we quantified via microdialysis and radioimmunoassay changes in
estradiol concentration in the male POM during sexual interactions with a female.
Surprisingly, a dramatic elevation of estradiol was observed during copulation.
Estradiol has been shown to enhance acutely male sexual motivation, therefore the function of its increase in the POM could be to maintain motivation during the entire
sexual encounter. The decrease of AA observed ex vivo after copulation would then
reflect a compensatory mechanism to restore baseline pre-copulatory conditions.
Importantly, these results highlight that although long-term changes in AA are often
used as a proxy for local estradiol concentrations, these two measures can show
major short-term discrepancies possibly reflecting variations in estrogen turnover