Hippocampal Expression of Connexin36 and Connexin43 during Epileptogenesis in Pilocarpine Model of Epilepsy

Abstract

Background:Gap junctions (GJs) provide direct intercellular communications that are formed by hexameric protein subunits, called connexin (Cx). The role of Cxs in epileptogenesis has not received sufficient attention. Hippocampus with a critical function in epileptogenesis has a wide network of GJs. We examined the protein expression levels of hippocampal Cx36 (the prominent Cx present between GABAergic interneurons) and Cx43 (the main Cx expressed by astrocytes) during epileptogenesis in the pilocarpine model of epilepsy.Methods:Male Wistar rats received scopolamine (1 mg/kg, s.c.). Pilocarpine (380 mg/kg, i.p.) was administered 30 min thereafter to induce status epilepticus (SE). SE was stopped 2 h later by diazepam (10 mg/kg, i.p.). Cx36 and Cx43 protein expression was assessed by Western blot analysis in the hippocampus of SE-experienced rats, after injection of diazepam (F0 subgroup), after acquisition of focal seizures (F3 subgroup), and after development of generalized seizures (F5 subgroup). The control subgroups, C0, C3, and C5, were aged-matched rats, which received saline (1 ml/kg, i.p.) instead of pilocarpine. Injection of scopolamine and diazepam, and dissection of hippocampi were carried out at the same time interval as the test subgroups.Results:SE emerged in 67.1% of pilocarpine-treated animals. Focal and generalized seizures developed 3.8±0.4 and 7.0±0.5 days after SE, respectively. Cx36 protein abundance was not significantly different between test and control groups in the three time points. However, Cx43 protein level showed 40% increase in F3 subgroup (P<0.05 compared to C3, P<0.01 compared to F0 and F5).Conclusion:Hippocampal Cx43 is overexpressed in pilocarpine model of epileptogenesis after acquisition of focal seizures.

Effects of Constitutive and Acute Connexin 36 Deficiency on Brain-Wide Susceptibility to PTZ-Induced Neuronal Hyperactivity

“…To further understand the relationship between Cx36 and hyperactivity, we asked the reciprocal question: how does hyperactivity affect Cx36? Similar to the seizure susceptibility studies, work to identify this relationship has remained conflicting (Söhl et al, 2000 ; Laura et al, 2015 ; Motaghi et al, 2017 ; Wu et al, 2017 ). Previous approaches used to address this question (e.g., qPCR, western blot) lacked the necessary spatial resolution to determine if the effects of hyperactivity on Cx36 vary based on the brain region.…”

“…In rodent seizure models and epilepsy patient post-mortem samples, some groups have found that Cx36 expression was increased (Collignon et al, 2006 ; Laura et al, 2015 ; Wu et al, 2017 ), while others found decreased Cx36 expression (Söhl et al, 2000 ; Condorelli et al, 2003 ) or no change (Motaghi et al, 2017 ). Furthermore, even though seizures result in brain-wide changes in neuronal connectivity (Morgan et al, 2010 ), seizure-induced changes in Cx36 expression had only been examined in the dorsal telencephalon (cortex and hippocampus) (Condorelli et al, 2003 ; Laura et al, 2015 ; Motaghi et al, 2017 ; Wu et al, 2018 ). Potential changes to Cx36 expression in other brain areas following neuronal hyperactivity remain unknown.…”

Effects of constitutive and acute Connexin 36 deficiency on brain-wide susceptibility to PTZ-induced neuronal hyperactivity

“…To further understand the relationship between Cx36 and hyperactivity, we asked the reciprocal question: how does hyperactivity affect Cx36? Similar to the seizure susceptibility studies, work to identify this relationship has remained conflicting (Laura et al, 2015;Motaghi et al, 2017;Söhl et al, 2000;X. Wu et al, 2017).…”

“…In rodent seizure models and epilepsy patient post-mortem samples, some groups have found that Cx36 expression was increased (Collignon et al, 2006;Laura, Xóchitl, Anne, & Alberto, 2015;X. Wu, Wang, Hao, & Feng, 2017), while others found decreased Cx36 expression (Condorelli, Trovato-Salinaro, Mudo, Mirone, & Belluardo, 2003;Söhl et al, 2000) or no change (Motaghi, Sayyah, Babapour, & Mahdian, 2017). Furthermore, even though seizures result in brain-wide changes in neuronal connectivity (Morgan, Gore, & Abou-Khalil, 2010), seizure-induced changes in Cx36 expression had only been examined in the dorsal telencephalon (cortex and hippocampus) (Condorelli et al, 2003;Laura et al, 2015;Motaghi et al, 2017;X.…”

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“…In rodent seizure models and epilepsy patient post-mortem samples, some groups have found that Cx36 expression was increased (Collignon et al, 2006;Laura et al, 2015;Wu et al, 2017), while others found decreased Cx36 expression (Söhl et al, 2000;Condorelli et al, 2003) or no change (Motaghi et al, 2017). Furthermore, even though seizures result in brain-wide changes in neuronal connectivity (Morgan et al, 2010), seizure-induced changes in Cx36 expression had only been examined in the dorsal telencephalon (cortex and hippocampus) (Condorelli et al, 2003;Laura et al, 2015;Motaghi et al, 2017;Wu et al, 2018). Potential changes to Cx36 expression in other brain areas following neuronal hyperactivity remain unknown.…”