The Correlation Between The Expression Of StAR And ChAT In Memory-related Brain Regions

Memory is one of the most important advanced brain functions. There are special structures associated with memory in the brain. The cholinergic systems lying in these memory-related brain regions play essential roles in the formation and maintenance of memory. The cholinergic system degenerates in shapes, as well as in functions, during aging. However, the reasons resulting in the degeneration of cholinergic system are still controversial.The effects of cholinergic systems are mediated by acetylcholine (Ach) which is unstable and could be easily broken down by cholinesterase, so the synthetase of Ach-choline acetyltransferase (ChAT) is considered to be one of the specific cholinergic marker proteins for the functional state of cholinergic neurons.Neurosteroids are steroids which could be synthesized in the nervous system de novo, and the rate-limiting step in neurosteroids synthesis is mediated by steroidogenic acute regulatory protein (StAR). As a result, the amount of StAR can indirectly represent the quantity of neurosteroids synthesized. Neurosteroids are proved to play important roles in neurotrophin and neuroprotection, they are also important in the modulation of advanced brain functions. Their effects on cholinergic system are also well investigated. They are proved to play crucial roles in the modulation of both the morphologies and the functions of cholinergic system.Based on these data, we hypothesized that the degeneration of basal forebrain cholinergic system maybe result from the synthesis decline of neurosteroids during aging. Therefore, following experiments were designed to validate this hypothesis. The expression of StAR and ChAT in hippocampus, basal forebrain and prefrontal cortex of female SD rats of 1,6 and 24 month old were measured by means of immunofluorescence (IF) and Western blot methods. And the correlation between the expression of StAR and ChAT was also analyzed. Results showed that both ChAT and StAR were expressed in hippocampus, basal forebrain and prefrontal cortex. StAR was expressed in the cytoplasm of cells of various shapes within all the three regions. Among all the regions researched, both the expression of ChAT and StAR were significantly lower in 1 and 24 month old groups than that of 6 month old group (P<0.05). while their expression in 24 month old group were slightly lower than that of 1 month old group respectively, with no significant difference (P>0.05). Furthermore, the expression of StAR was positively correlated with ChAT in each region researched. These results suggested that neurosteroids could be synthesized in memory-related brain regions, the degeneration of cholinergic system within these regions during aging probably result from the decline of neurosteroids synthesized locally within these regions.