Down-regulation of the sodium channel Nav1.1 α-subunit following focal ischemic brain injury in rats: In situ hybridization and immunohistochemical analysis

Change in sodium channel (NaCh) activity can play a role in reorganization, recovery, or possibly excitotoxic damage after CNS injury. Alteration of sodium channel function has been reported to occur in a variety of neuropathological states including epilepsy and brain injury. Previously we reported that out of five NaCh alpha subunit genes that were down-regulated, Nav1.1 exhibited the most dramatic and sustained alterations following focal cerebral ischemia in the rat. In the present study, we evaluated the acute spatial and temporal time course distribution of Nav1.1 mRNA (in situ hybridization) and protein (immunohistochemistry) following ischemic brain injury. Male rats were subjected to 2 h of middle cerebral artery occlusion (MCAo) followed by reperfusion and brain tissue was collected at 2, 6, 24, and 48 h post-MCAo. Analysis of brain tissue revealed a qualitative drop in both mRNA and protein levels of Nav1.1 throughout ischemic regions, beginning at the early stage of injury (6h) with dramatic losses at later stages (24 and 48 h). Quantitative cell counts and optical density measurements indicated significant decreases in the percent of brain cells immunoreactive for Nav1.1 as well as a loss of signal in those cells positive for Nav1.1 in the injured cortex and striatum as compared to the contralateral hemisphere. Double labeling with NeuN and Nav1.1 immunoflouresence confirmed that the predominate loss of Nav1.1 immunoreactivity was in neurons. In conclusion, these data map the time-dependent loss of Nav1.1 mRNA and protein following focal ischemic brain injury in the rat out to 48 h post-injury.