Agonist stimulation of the serotonin(1A) receptor causes suppression of anoxia-induced apoptosis via mitogen-activated protein kinase in neuronal HN2-5 cells

Previous studies have indicated that stimulation of neuronal inhibitory rec eptors, such as the serotonin,, receptor (5-HT1A-R), could cause attenuatio n of the activity of both N-type Ca2+ channels and N-methyl-D-aspartic acid receptors, thus resulting in protection of neurons against excitotoxicity. The purpose of this study was to investigate if the 5-HT1A-R is also coupl ed to an alternative pathway that culminates in suppression of apoptosis ev en in cells that are deficient in Ca2+ channels. Using a hippocampal neuron -derived cell line (HN2-5) that is Ca2+ channel-deficient, we demonstrate h ere that an alternative pathway is responsible for 5-HT1A-R-mediated protec tion of these cells from anoxia-triggered apoptosis, assessed by deoxynucle otidyl-transferase-mediated dUTP nick end-labeling (TUNEL). The 5-HT1A-R ag onist-evoked protection was eliminated in the presence of pertussis toxin a nd also required phosphoryfation-mediated activation of mitogen-activated p rotein kinase (MAPK), as evidenced by the elimination of the agonist-elicit ed rescue of neuronal cells by the MAPK kinase inhibitor PD98059 but not by the phosphatidylinositol 3-kinase (PI-3K) inhibitor wortmannin. Furthermor e, agonist stimulation of the 5-HT1A-R caused a 60% inhibition of anoxia-st imulated caspase S-like activity in the HN2-5 cells, and this inhibition wa s abrogated by PD98059 but not by wortmannin. Although agonist stimulation of the 5-HT1A-R caused an activation of PI-3K gamma in HN2-5 cells, our res ults showed that this PI-3K gamma activity was not linked to the 5-HT1A-R-p romoted regulation of caspase activity and suppression of apoptosis. Thus, in the neuronal HN2-5 cells, agonist binding to the 5-HT1A-R results in MAP K-mediated inhibition of a caspase 3-like enzyme and a 60-70% suppression o f anoxia-induced apoptosis through a Ca2+ channel-independent pathway.