Activation of the androgen receptor alters the intracellular calcium response 155 to glutamate in primary hippocampal neurons and modulates sarco/endoplasmic reticulum calcium ATPase 2 transcription

Androgens have been shown to have a number of effects on hippocampal function. Although androgen receptors (AR) are found at high levels in hippocampal neurons, the intracellular mechanisms responsible for androgen's actions are unknown. If androgens were capable of altering internal calcium concentration ([Ca2+](i)), they could influence a variety of intracellular signaling pathways, maintain neuronal homeostasis and Ca2+ induced excitotoxicity. In the present study, calcium imaging was used to measure the [Ca2+](i) in rat primary hippocampal neurons treated with either the AR agonist dihydrotestosterone (DHT), DHT+flutamide (AR antagonist), flutamide alone, or vehicle for 24 h and subsequently presented with an excitatory glutamate stimulus. In the absence of glutamate stimulation, DHT treatment caused a significant upward shift in baseline [Ca2+](i) when compared with neurons from all other groups. Glutamate had a greater effect on [Ca2+](i) in DHT-treated neurons and DHT-treated neurons returned to baseline levels significantly faster than all other groups. Cycloplazonic acid, an inhibitor of sarco/encloplasmic reticulum calcium ATPase (SERCA) had a larger response in DHT-treated neurons compared with controls, suggesting increased Ca2+ stores in DHT-treated neurons. In all cases the effects of DHT were blocked by treatment with flutamide indicating an AR-mediated mechanism. To determine a possible mechanism by which AR activation could be influencing [Ca2+](i), SERCA2 mRNA levels were measured in primary hippocampal neurons. SERCA2 is inserted into the encloplasmic reticulum (ER) membrane and functions to rapidly pump [Ca2+](i) into the ER. Following treatment of primary hippocampal neurons with DHT, SERCA2 mRNA was increased, an effect that was blocked in the presence of flutamide. Taken together these results indicate that DHT, working through AR, causes an up-regulation of SERCA2, which increases the sequestering of [Ca2+](i) in the endoplasmic reticulum of hippocampal neurons. Such changes may allow the neurons to respond more robustly to a stimulus and recover more quickly following a highly stimulatory challenge. (c) 2007 IBRO. Published by Elsevier Ltd. All rights reserved.