In the central nervous system (CNS), connexin and pannexin gap junctions and hemichannels are an integral component of homeostatic neuronal excitability and synaptic plasticity. Neuronal connexin (Cx) gap junctions form electrical synapses across biochemically similar GABAergic networks, allowing rapid and extensive inhibition in response to principle neuron excitation. Glial Cx gap junctions link astrocytes and oligodendrocytes in the pan-glial network that is responsible for removing excitotoxic ions and metabolites. In addition, Cx gap junctions between glia help constrain excessive excitatory activity in neurons and facilitate astrocyte Ca2+ slow wave propagation. Pannexins (Panxs) do not form gap junctions in vivo, but Panx hemichannels participate in autocrine and paracrine gliotransmission alongside connexin hemichannels. ATP and other gliotransmitters released by Cx and Panx hemichannels maintain physiologic glutamatergic tone by strengthening synapses and mitigating aberrant high frequency bursting. Under pathological depolarizing and inflammatory conditions, gap junctions and hemichannels become dysregulated, resulting in aberrant neuronal firing and seizure. In this review, we present known contributions of Cxs and Panxs to physiologic neuronal excitation and explore how disruption of gap junctions and hemichannels lead to aberrant glutamatergic transmission, purinergic signaling, and seizures.

Inflammation plays a critical role in the pathogenesis of ischemic stroke. This process depends, in part, upon proinflammatory factors released by activated resident central nervous system (CNS) microglia (MG). Previous studies demonstrated that transfer of IL-10+ B-cells reduced infarct volumes in male C57BL/6J recipient mice when given 24 h prior to or therapeutically at 4 h or 24 h after experimental stroke induced by 60 min middle cerebral artery occlusion (MCAO). The present study assesses possible sex differences in immunoregulation by IL-10+ B-cells on primary male vs. female MG cultured from naïve and ischemic stroke-induced mice. Thus, MG cultures were treated with recombinant (r)IL-10, rIL-4 or IL-10+ B-cells after lipopolysaccharide (LPS) activation and evaluated by flow cytometry for production of proinflammatory and anti-inflammatory factors. We found that IL-10+ B-cells significantly reduced MG production of TNF-α, IL-1β and CCL3 post-MCAO and increased their expression of the anti-inflammatory M2 marker, CD206, by cell-cell interactions. Moreover, MG from female vs. male mice had higher expression of IL-4 and IL-10 receptors and increased production of IL-4, especially after treatment with IL-10+ B-cells. These findings indicate that IL-10-producing B-cells play a crucial role in regulating MG activation, proinflammatory cytokine release and M2 phenotype induction, post-MCAO, with heightened sensitivity of female MG to IL-4 and IL-10. This study, coupled with our previous demonstration of increased numbers of transferred IL-10+ B-cells in the ischemic hemisphere, provide a mechanistic basis for local regulation by secreted IL-10 and IL-4 as well as direct B-cell/MG interactions that promote M2+-MG.

Clinical stroke induces inflammatory processes leading to cerebral and splenic injury and profound peripheral immunosuppression. IL-10 expression is elevated during major CNS diseases and limits inflammation in the brain. Recent evidence demonstrated that transfer of IL-10+ B-cells reduced infarct volume in male C57BL/6J (wild-type, WT) recipient mice when given 24 h prior to or 4 h after middle cerebral artery occlusion (MCAO). The purpose of this study was to determine if passively transferred IL-10+ B-cells can exert therapeutic and immunoregulatory effects when injected 24 hours after MCAO induction in B-cell-sufficient male WT mice. The results demonstrated that IL-10+ B-cell treated mice had significantly reduced infarct volumes in the ipsilateral cortex and hemisphere and improved neurological deficits vs. Vehicle-treated control mice after 60 min occlusion and 96 h of reperfusion. The MCAO-protected B-cell recipient mice had less splenic atrophy and reduced numbers of activated, inflammatory T-cells, decreased infiltration of T-cells and a less inflammatory milieu in the ischemic hemispheres compared with Vehicle-treated control mice. These immunoregulatory changes occurred in concert with the predominant appearance of IL-10-secreting CD8+CD122+ Treg cells in both the spleen and the MCAO-affected brain hemisphere. This study for the first time demonstrates a major neuroprotective role for IL-10+ B-cells in treating MCAO in male WT mice at a time point well beyond the ~4 h tPA treatment window, leading to the generation of a dominant IL-10+CD8+CD122+ Treg population associated with spleen preservation and reduced CNS inflammation.