5‐HT1Areceptors couple to activation of Akt, but not extracellular‐regulated kinase (ERK), in cultured hippocampal neurons

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Abstract
5‐HT1A receptors have been hypothesized to mediate some of the neuronal plasticity and behavioral responses stimulated by serotonin selective reuptake inhibitors. Although the cellular signaling pathways required for inducing these actions have not yet been determined, roles for the neuroprotective extracellular‐regulated kinase (ERK) mitogen‐activated protein (MAP) kinase and Akt pathways have been suggested. In the current studies we have utilized primary cultures to directly determine whether hippocampal 5‐HT1A receptors couple to activation of Akt and ERK. We found that E18 hippocampal neurons exhibit a twofold activation of Akt when exposed to nanomolar concentrations of 5‐HT. The 5‐HT1/7 receptor‐selective agonist 5‐carboxamidotryptamine maleate (5‐CT) and the 5‐HT1A/7 receptor‐selective agonist 8‐hydroxy‐N,N‐dipropyl‐aminotetralin (8‐OH‐DPAT) maleate were found to activate Akt with equal efficacy, and similar potency, to 5‐HT. p‐MPPI and WAY‐100635, antagonists selective for 5‐HT1A receptors, completely inhibited 5‐CT‐ stimulated Akt activation. Activation of Akt was also inhibited by pretreatment with pertussis toxin as well as the phosphatidylinositol 3‐kinase inhibitors, wortmannin and LY294002. In contrast, the 5‐HT selective antagonist, SB269970, caused no inhibition. Although the density of 5‐HT1A receptors expressed by cultured neurons was sufficient to activate Akt, no activation of ERK was observed. These findings suggest that Akt, and not ERK, may be relevant to previous reports of hippocampal 5‐HT1A receptors mediating neurotrophic responses.

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