Extending our cell culture findings to experimental SCI in rats, we observed protection of the injured cord in acute phase.[9, 10]
Supraphysiological levels of estrogen attenuated inflammation, reduced or restricted the lesion volume, prevented axonal degeneration, and preserved myelin in acute experimental SCI. Moreover, the profound proteolytic events of the Ca2+
-activated proteinase calpain were reduced which prevented the apoptosis of neurons largely present in caudal penumbra by estrogen treatment when administered immediately after SCI in rats.[9, 10]
In addition, similar high dose estrogen could mitigate the damage and restore functionality in chronic SCI in rats.[21
] Such neuroprotective studies paved the path for further investigation of the clinical relevance on the efficacy of lower physiological doses of estrogen, applied immediately and at different times in the acute SCI paradigm. Subsequently, results from these studies helped to explore low dose estrogen efficacy in chronic SCI in rats. Indeed, estrogen mediated neuroprotection in SCI in rats was attained at much lower doses in subsequent studies in our laboratory.
Other protective effects of estrogen administration following SCI thus far include prevention of astrogliosis and microgliosis, reduction of proteolytic and apoptotic markers, and preservation of the axon-myelin structural unit. The estrogen-mediated attenuation of all these parameters is essential and important for recovery of neurological function following SCI. Functional recovery may be enhanced further by promoting microvessel growth and restoring blood supply, needed for cell survival as cells may die due to ischemia caused by disruption of blood vessels following the primary injury to SC. Since estrogen is known to promote angiogenesis and microvessel growth, its administration may help protect cells from ischemic damage following SCI. One of our goals is also to explore the angiogenic mechanism in both acute and chronic SCI.
Apart from our findings there are a few studies from other laboratories that have addressed the estrogen efficacy in SCI. An increase in expression of the estrogen receptors ER-α and ER-β mRNA in lumbar SC motoneurons has been reported after axomotomy following sciatic nerve crush injury in bilaterally ovariectomized mice where exogenously supplied estrogen capsules (24 μg) rendered a sustained supraphysiological level of serum estrogen for the first three weeks.
Estrogen treatment induced gene expression resulting in acceleration of the growth and maturation of the axons. Furthermore, estrogen receptors were transported from the perikaryon into regenerating neurites, where they promoted local regeneration through the non-genomic ERK-activated signaling pathway.
Such protective effects of estrogen on motoneurons reflected well in experimental SCI in which it improved functional recovery in the injured rat, in part, by reducing apoptotic cell death with estrogen pretreatment (3-300 μg).
Furthermore, in a post-treatment paradigm in the same study, male rats were given a single injection of estrogen (100 μg/kg) immediately post-injury, which also showed significant recovery in locomotor activity coupled with decreased morphologic outcome. Subsequently adopting a 1 h post-SCI treatment regimen, the same group of researchers confirmed the steroid’s neuroprotective mechanism being partly mediated by induction of Bcl-2 through PI3K/Akt-dependent CREB activation.
Estrogen also reduced the severity of autonomic dysfunction in SCI in male mice with administration of physiological dosage of estrogen in mice, wherein involvement of non-central/non-spinal mechanisms has been suggested.
Protection by estrogen was further confirmed in SCI induced by complete crush injury. Estrogen effects in such severe SCI were assessed by comparing non-ovariectomized, ovariectomized control, and ovariectomized with low physiological level estrogen supplementation (corresponding to 20 pg/ml in blood) in premenopausal and postmenopausal female rats. The study reported improved BBB scores, white matter sparing, and lower motor neuron survival by 21-day post injury.
Another group reported that pretreatment with estrogen reduced the development of inflammation, tissue injury, neutrophil infiltration, expression of iNOS, COX-2 activity and several apoptotic markers associated with SC trauma
whereas we observed similar effects in a more preclinical post-treatment approach.[9, 10], 
The estrogen receptor antagonist ICI 182,780 has been used to confirm the estrogen-receptor involvement in neuroprotective action of estrogen following SCI.
A separate study by another group, who adopted our previously reported estrogen dosing regimen (a higher 4 mg/kg and a lower 100 μg/kg), highlighted a transient neuroprotective window through which estrogen protected SC by stimulating early cytokines release and astroglial responses.
These investigators suggested that such stimulations might prevent the spread of lesion and retard inflammatory cells to migrate into the surrounding tissue during the critical first week following SCI. The study reported improved locomotor-recovery over 4 weeks after injury and inferred them as probably the consequence of the transient hike in astroglial reactivity due to estrogen.
As opposed to all the affirmative reports on estrogen efficacy following SCI, a solitary report suggests that gender differences in SCI are not estrogen-dependent and hence estrogen may not provide a viable therapy following SCI.
On the contrary, estrogen-related gender differences on the survival of rats following traumatic brain injury has been reported.
However, multiple reports on estrogen efficacy in experimental SCI conducted in diverse animal models spanning from acute through chronic models with various dosage regimens and confirming different aspects of neuroprotection certainly are in favor of the multi-active estrogen as a therapeutic agent. The results further validate its use as a promising candidate for the treatment of SCI.
A major challenge is establishment of the minimal effective dose taking into account the gender bias of the SCI victims and discerning the post-injury temporal window in which it will provide beneficial effect. To this end, our studies on post-injury treatment with estrogen, progressively lowering the dose from supraphysiological to physiological and with post-injury time-point of application, add greatly to the clinical relevance of estrogen as a promising agent in the treatment of SCI.