Systemic administration of 17β-estradiol reduces apoptotic cell death and improves functional recovery following traumatic spinal cord injury in rats

Recent evidence indicates that estrogen exerts neuroprotective effects in both brain injury and neurodegenerative diseases. We examined the protective effect of estrogen on functional recovery after spinal cord injury (SCI) in rats. 17beta-estradiol (3, 100, or 300 mug/kg) was administered intravenously 1-2 h prior to injury (pre-treatment), and animals were then subjected to a mild, weight-drop spinal cord contusion injury. Estradiol treatment significantly improved hind limb motor function as determined by the Basso-Beattie-Bresnahan (BBB) locomotor open field behavioral rating test. Fifteen to 30 days after SCI, BBB scores were significantly higher in estradiol-treated (100 mug/kg) rats when compared to vehicle-treated rats. Morphological analysis showed that lesion sizes increased progressively in either vehicle-treated or 17beta-estradiol-treated spinal cords. However, in response to treatment with 17beta-estradiol, the lesion size was significantly reduced 18-28 days after SCI when compared to vehicle-treated controls. Terminal deoxynucleotidyl transferase-mediated UTP nick-end labeling (TUNEL) staining and DNA gel electrophoresis revealed that apoptotic cell death peaked 24-48 h after injury. Also, SCI induced a marked increase in activated caspase-3 in the spinal cord, evident by 4 h after injury. However, administration of 17beta-estradiol significantly reduced the SCI-induced increase in apoptotic cell death and caspase-3 activity after SCI. Furthermore, 17beta-estradiol significantly increased expression of the anti-apoptotic genes, bcl-2 and bcl-x, after SCI while expression of the pro-apoptotic genes, bad and bax, was not affected by drug treatment. Finally, intravenous administration of 17beta-estradiol (100 mug/kg) immediately after injury (post-treatment) also significantly improved hind limb motor function 19-30 days after SCI compared to vehicle-treated controls. These data suggest that after SCI, 17beta-estradiol treatment improved functional recovery in the injured rat, in part, by reducing apoptotic cell death.