? Our working hypothesis is that serotonin (5-HT) receptors are directly responsible for some of the known neuroprotective actions of serotonergic antidepressants in the hippocampus. Our previous studies specifically suggest roles for 5-HT7 and/or 5-HT1A receptors. We have found that 5-HT7 receptors couple to activation of the ERK, Akt, and CREB protective pathways in both cell lines and cultured E18 hippocampal neurons. We have similarly found that 5-HT1 receptors couple to protective pathways in cell lines, though we have not been able to confirm this in E18 hippocampal cultures. The current proposal will further investigate the coupling of 5-HT1A and 5-HTT receptors to ERK, Akt, and CREB in the hippocampus, and directly study neuroprotection. E18 hippocampal neurons will be utilized in Aim 1 to delineate the pathways required for 5-HT receptor-coupling to ERK, Akt, and CREB. The roles of specific cellular components will be identified through the use of selective chemical inhibitors, RNA interference (RNAi), dominant negative constructs, and direct assays of activity. Results from these studies will provide a road map for understanding how alterations in the expression levels or activity of identified pathway components could result in hippocampal pathology.
In Aim 2 we will directly study whether 5- HTT receptor agonists protect hippocampal neurons from apoptosis. E18 hippocampal neurons will be treated with 5-HTT receptor agonists to determine whether they can inhibit the apoptosis induced by two well-studied inducers of apoptosis: 1) nitroprusside (through nitric oxide toxicity) and 2) camptothecin (through DNA damage). Neurons will also be treated with 5-HT7 receptor agonists to determine whether they can inhibit the apoptotic changes induced by agonists for the GR-glucocorticoid receptor. Cultured hippocampal slices from young adult rats will be used in Aim 3 to extend our previous findings in studies designed to determine whether 5-HT_A and 5-HT7 receptors couple to activation of ERK, Akt, and CREB in discrete regions of mature hippocampi. Studies are proposed in Aim 4 to determine the specific roles of 5-HT1A and 5-HT7 receptors in mediating the protective actions of SSRIs observed in animal studies. We propose to perform parallel in vivo and slice culture studies examining the hippocampal effects of 5-HT and selective agonists/antagonists for 5-HT1A and 5-HT7 receptors in stimulating neurogenesis and increasing expression of CREB, BDNF, and TrkB receptors. Slices will be very helpful in interpreting the cause of observed lags in effect since autoreceptors are not present in cultured slices. ? ? ?
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