A single evoked afterdischarge produces rapid time-dependent changes in connexin36 protein expression in adult rat dorsal hippocampus

Gap junctions between neurons contribute to synchronous neuronal firing and may play a role in the pathophysiology of epilepsy. We examined the expression of a number of gapjunction subunits, including the neuronal gapjunction forming protein connexin36 (Cx36), in the hippocampus at various time points following an electrically stimulated afterdischarge (AD) in freely-moving animals. Once recovered from electrode implantation, animals were tested with an escalating series of stimulations until an AD was evoked. Suprathreshold stimulation produced a brief AD with no convulsion. Groups. of animals were sacrificed at 3, 12, and 24 h post- stimulation, and connexin expression was assessed via semiquantitative immunoblotting. Compared to implanted non-stimulated controls, a significant decrease in Cx36 expression was observed in the stimulated dorsal hippocampus at 3 It post- stimulation, which returned to control levels by 24 It. No changes were seen in the ventral hippocampus. As well, no changes were seen in other selected connexin proteins including Cx26, Cx32, and Cx43, thought to be expressed primarily in glia, in either dorsal or ventral hippocampus. These data suggest that a relatively brief hypersynchronous neuronal discharge can produce rapid and specific changes in Cx36 expression, which may have implications for both normal brain function and the pathophysiology of epilepsy. (c) 2006 Elsevier Ireland Ltd. All rights reserved.