Activation of fibres in rat sciatic nerve alters phosphorylation state of connexin-43 at astrocytic gap junctions in spinal cord: Evidence for junction regulation by neuronal-glial interactions

Intercellular communication via gap junction channels composed of connexin- 43 is known to be regulated by phosphorylation of this protein. We investig ated whether connexin-43 at astrocytic gap junctions is similarly regulated in response to neural activation. The effect of peripheral nerve stimulati on on connexin-43 phosphorylation state in the spinal cord of rats was exam ined with a monoclonal antibody (designated 13-8300) shown previously to re cognize selectively a dephosphorylated form of connexin-43. Immunolabelling with 13-8300 was absent in the lumbar spinal cord in control animals, but was induced in the dorsal horn ipsilateral to sciatic nerve electrical stim ulation for 15 min or 1 h at a frequency of 1 or 100 Hz. Immunorecognition of connexin-43 by a polyclonal anti-connexin-43 antibody, shown previously to undergo epitope masking under Various conditions, was reduced in the dor sal horn on the stimulated side. These responses were abolished by local an aesthetic or tetrodotoxin application proximal to the site of nerve stimula tion. Selective electrical stimulation of A-fibres or activation of cutaneo us C-fibres by capsaicin evoked labelling with 13-8300 in deep and superfic ial laminae of the dorsal hem, respectively. Nerve stimulation increased th e number of 13-8300-positive astrocytic gap junctions, as well as the level s of dephosphorylated connexin-43 in the dorsal horn on the stimulated side . Sciatic nerve transection produced results similar to those seen after C- fibre activation with capsaicin. Thus, peripheral nerve stimulation evokes astrocytic connexin-43 dephosphor ylation in the spinal cord dorsal hem, suggesting that gap junctional coupl ing between astrocytes in vivo is subject to regulation by neuronal-glial i nteractions following neural activation. (C) 2000 IBRO. Published by Elsevi er Science Ltd.