POSTED ON November 22, 2022 10:34 pm
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Gta Eflc Offline Activation 14
activation of mglur5 has been reported in a number of seizure models. in the 3-hz stimulation model of prolonged seizures, the activation of mglur5 and ampa receptors has been shown to contribute to the development of epileptiform activity ( yamamoto et al. 1999 ). in the pilocarpine model of epilepsy, the activation of mglur5 has been reported to attenuate spontaneous seizures ( zheng et al. 2007 ). although we report that mglur5 activation attenuates epileptiform bursting induced by 4-ap, it is not yet clear how the mglur5 signaling pathway contributes to the development of epilepsy. however, the role of mglur5 activation has been reported to regulate seizure-induced neuronal changes. increased mglur5 expression in the dentate gyrus and ca1 of the hippocampus has been shown to attenuate seizures induced by kainic acid or electroconvulsive shock ( makino et al. 2004 ).
the glur5 blocker mpep also inhibited bursting, as determined by preincubation for 1 hour and washout of culture medium for 10 min. four-hour treatment of the cultures with bic+4-ap in the presence of mpep completely blocked bursting activity, at bic+4-ap concentrations that completely block bic+4-ap-induced synapse loss ( fig. 5 ) ( n = 9, 5.6 0.8 bursts/min before mpep treatment, 0 bursts/min after mpep treatment; fig. 5d ). these results indicate that blocking mglur5 produces a similar effect as bic+4-ap treatment in our assay. treatment with 2k-1c for 4 h resulted in a massive burst firing ( ma et al. 2004 ) that was abolished by co-treatment with mpep (n = 15; 0.05 0.05 bursts/min before mpep treatment, 0.0 0.1 bursts/min after mpep treatment; fig. 5a, b, and d ). the 4-h-induced bursting was completely blocked by co-treatment with mpep (n = 7; 0.25 0.25 bursts/min before mpep treatment, 0.02 0.03 bursts/min after mpep treatment) ( fig. these results indicate that mglur5 activation by mglur5 agonism is toxic, as determined by the other assay, and by the 4-h-induced synaptic loss assay, which required mglur5 blockade by mpep. blocking mglur5 inhibits the 4-h-induced synaptic loss. the antagonist reduces the effective agonist concentration, since bic+4-ap induces mglur5 activation, pro-epileptiform activity, and synapse loss. thus mglur5-blocking drugs may be effective against the treatment-induced effects. for example, the mpep effect on ap is shown here (anova; p = 0.001). the effect of bic+4-ap on ap is shown here (anova; p = 0.05). similarly, the effect of 2k-1c ap change on ap is shown here (anova; p = 0. in 2k-1c treatment, n = 14 and n = 14 for bic+4-ap and 2k-1c treatment, respectively. #p < 0.05, ***p < 0.001 relative to the control student's t-test; #p < 0.05 relative to the untreated bic+4-ap. anova with the tukey posttest. error bars indicate se.
the relationship between mglur5 and h1a in the context of hippocampal bursting was further explored by electrophysiological approaches. consistent with previous reports, bic+4-ap-induced bursting was reduced by treatment with mpep or by expressing dominant-negative mglur5 ( bottai et al. 2002 ; capogna et al. 2002 ). expression of an mglur5(q/q) mutant form of the receptor that does not generate a current when activated in transfected cells ( capogna et al. 2002 ) was similarly ineffective at attenuating bursting. bic+4-ap-induced bursting was also reduced by expression of a dominant-negative mutant form of h1a in which histidine 4 in the h4 domain was converted to glutamate ( bottai et al. bic+4-ap-induced bursting required both mglur5 and h1a but was not affected by the dominant-negative forms of either, although expression of a non-phosphorylatable form of h1a ( bottai et al. 2002 ) blocked bursting in cells that normally express a phosphorylated form of h1a. therefore, we concluded that mglur5 and h1a form a signaling complex that is required for bic+4-ap-induced bursting in hippocampal neurons. furthermore, it appears that the mechanisms underlying the upregulation of h1a and that of mglur5 operate through distinct mechanisms. the mechanism underlying the expression of bic+4-ap-induced h1a expression involves an erk pathway, while the upregulation of mglur5 was dependent on both activation of erk and a transcriptional mechanism. interestingly, mglur5 activation inhibited bursting, while h1a increased bursting in cultured hippocampal neurons, indicating a complex interaction between mglur5 and h1a with regard to bursting in cultured neurons. although mglur5 is widely distributed throughout the brain ( kawamata et al. 2007 ), there is little known about the role of h1a in adult brain. however, both mglur5 and h1a are expressed in the hippocampus ( bottai et al. 2002 ; avedissian et al. 2007 ), and their functions are likely to be an important part of glutamatergic signaling in this brain region. therefore, the mglur5 and h1a signaling pathway identified here will be of great interest to determine whether they play a similar role in the brain.