Investigations were also performed on young (pre-menopausal) and old (post-menopausal) female ovariectomized (OVX) rats that were implanted with Silastic capsules containing either 180 μg/ml 17β-estradiol or vehicle, prior to a crush injury at the mid-thoracic level. 17β-Estradiol-treated, young OVX rats had significantly better BBB scores compared to vehicle-treated OVX or normally cycling rats (Chaovipoch et al., 2006). However, there were no significant differences between the BBB scores of vehicle-treated OVX rats and normally cycling rats. This indicates that endogenous estrogen does not influence recovery of locomotor function and exogenous 17β-estradiol is necessary to observe amelioration ofmotor deficits. Accordingly, significantly morewhitematterwas sparedwhen OVX rats received exogenous 17β- estradiol, whereas endogenous estrogen did not alter the extent of white matter sparing. Using a similar paradigm, favorable but less pronounced effects of 17β-estradiol were also observed in older rats.