Neuropathological Protection after Traumatic Brain Injury in Intact Female Rats Versus Males or Ovariectomized Females

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Abstract
An important consideration in traumatic brain injury (TBI) in females is the influence of hormones on recovery. Recent studies in both cerebral ischemia and TBI have demonstrated an attenuation in both damage and neurologic recovery following hormonal treatment. However, the ability of endogenous hormone levels to provide neuropathological protection after fluid percussion (FP) brain injury has not been studied. The purpose of this experiment was to determine whether endogenous circulating hormones in the female rat could provide neuroprotection compared to males and ovariectomized female animals. Sixty-four Sprague-Dawley rats underwent a moderate (1.7–2.2 atm) right parasagittal FP injury. Intact females (i.e., nonovariectomized) were subjected to injury either during the proestrous (TBI-FP, n = 18) phase of their cycle or nonproestrous (TBI-FNP, n = 19) phase. A separate group of females were ovariectomized (TBI-OVX, n = 10) 10 days prior to FP injury in order to reduce hormone levels. Male animals were also traumatized (TBI-M, n = 17). Appropriate sham controls (Sham-FP, n = 2; Sham-FNP, n = 2; Sham-OVX, n = 2; Sham-M, n = 2) also underwent all aspects of surgery except for the actual FP injury. All groups were sacrificed 3 days following TBI for analysis. Both intact female groups had significantly (p < 0.05) smaller cortical contusions compared to male animals. In addition to this finding, the TBI-FNP group was significantly (p < 0.04) different from the ovariectomized female animals. Ovariectomized rats had larger areas of damage compared to intact females. The TBI-OVX group's cortical contusion volume was similar to male animals. These results provide evidence for endogenous hormonal histopathological protection following parasagittal FP brain injury. The use of hormone therapy after TBI warrants continued exploration.