Expression changes of somatostatin receptor subtypes sst2A, sst2B, sst3 and sst4 after a cortical contusion trauma in rats.

The neuropeptide somatostatin acts as a neuromodulator in the CNS in a predominantly inhibitory manner. In this study, an ipsilateral cortical and hippocampal damage in the brain of adult rats was induced by a cortical contusion trauma in order to examine subsequent changes of expression of different somatostatin receptor subtypes (sst). By using subtype specific antibodies we found a clear decline of expression level for sst2A, sst2B, sst3 and sst4 subtypes in the pyramidal cell layer of the ipsilateral hippocampus. Nissl staining revealed that this decline of expression level is due to cell death of sst expressing neurons within the first 48 h after trauma. Additionally we found a progressive infiltration of sst4 positive cells into regions of cortical and hippocampal damage. The number of these cells increases strikingly within the first 3 days after trauma and it seems that their morphology changes from a round to an astrocyte-like shape. Moreover, sst4 and sst2A positive cells accumulate in the ipsilateral ependym and pyramidal-like cells expressing sst4 were found beneath the damaged CA3 pyramidal layer. Taken together, after trauma we found deterioration of sst positive neurons and an additional activation of sst4 and sst2A expressing cells the final fate of which has to be elucidated further.