Contribution of estrogen receptors alpha and beta in the brain response to traumatic brain injury

Although there is evidence that estradiol has neuroprotective effects after traumatic brain injury (TBI)
in female rats, it is unclear which estrogen receptor (ER) subtype, ERa or ERb, mediates this effect. The authors
therefore examined the roles of the different ERs in this effect. Here the authors used the ERa selective agonist propyl
pyrazole triol (PPT) and the ERb selective agonist diarylpropionitrile (DPN) alone and in combination in female rats
to investigate this question.
Methods. Before the ovariectomized animals were injured using the Marmarou TBI technique, they were randomly
divided into the following 9 groups: control, sham, TBI, vehicle, E1 (physiological dose of 17-b estradiol), E2
(pharmacological dose of 17-b estradiol), PPT, DPN, and PPT+DPN. Levels of blood-brain barrier (BBB) disruption
(5 hours) and water content (24 hours) were evaluated after TBI. In groups receiving drugs or vehicle, treatment was
administered as a single dose intraperitoneally 30 minutes after induction of TBI.
Results. Results showed that brain edema or brain water content after TBI was lower (p < 0.001) in the E2, PPT,
DPN, and PPT+DPN groups than it was in the vehicle group. After trauma, the Evans blue dye content or BBB permeability
was significantly higher in the TBI and vehicle groups (p < 0.001) than in the E2, PPT, DPN, and PPT+DPN
groups. The inhibitory effects of PPT+DPN on brain water content, neurological scores, and Evans blue dye content
were the highest for all groups. Although both PPT and DPN increased neurological scores after TBI, PPT appears to
be more effective in increasing neurological scores.
Conclusions. Neuroprotective effects of estradiol on brain edema, BBB permeability, and neurological scores
are mediated through both ERa and ERb. This may suggest a therapeutic potential in the brain trauma for ER-specific
agonists.