NMDA receptors regulate developmental gap junction uncoupling via calcium-dependent signaling pathways
Description
Gap junctions are widespread in the developing mammalian central nervous system (CNS) and are involved in developmental events like neurogenesis, neuronal differentiation, cell migration and neural circuit formation. Neurons are extensively connected by gap junctions during embryonic and early postnatal periods. Between postnatal weeks one to three, neurons become uncoupled in most brain regions and subsequently remain uncoupled under physiological conditions in the adult CNS. In this study, I report that developmental uncoupling of gap junctions in the rat hypothalamus in vivo and in vitro is associated with a decrease in the expression of the neuronal gap junction protein, connexin 36 (Cx36). Assays with dye coupling and western blots showed that the developmental uncoupling and Cx36 down regulation are prevented by blockade of N-methyl-D-aspartate (NMDA) subtype of glutamate receptors, action potentials, calcium/calmodulin protein kinase II/IV (CaMKII/IV) or protein kinase C (PKC). Further, since the transcription factor calcium/CAMP response element binding protein (CREB) is downstream of the above-mentioned kinases, I manipulated the expression of CREB and demonstrated that the phosphorylation of this molecule in essential for uncoupling. Conversely, developmental gap junction uncoupling and Cx36 down-regulation are not affected by blockade of non-NMDA glutamate receptors, protein kinase A (PKA), mitogen activated kinase (MAPK) or L-type voltage-gated calcium channels. Cultured neurons from NMDA Receptor Subunit 1 (NMDAR1) knockout mice showed similar uncoupling properties as those treated with NMDA receptor antagonists. The results demonstrate a causal link among NMDA receptor function, Cx36 down-regulation via CREB signaling, and developmental uncoupling of gap junctions