The changes in bax and bcl-2 expression extended into the sub-acute phase in injured male rats, when 17β-estradiol treatment was initiated immediately following injury and continued for 6 weeks (Sribnick et al., 2010). Ventral horn neuron number was higher in cycling and 17β- estradiol-treated OVX rats sustaining SCI, than injured, OVX rats receiving vehicle. This indicates that both endogenous 17β-estradiol and exogenous 17β-estradiol enhance neuronal survival after SCI (Chaovipoch et al., 2006). In the injured spinal cord, the beneficial effects of 17β-estradiol on apoptosis can be mimicked by a GPER agonist and are abolished when GPER expression is knocked down (Hu et al., 2012). Thus, with respect to apoptosis, GPER could be the principal mediator of 17β-estradiol actions in SCI.