The Neurosteroids Progesterone and Allopregnanolone Reduce Cell Death, Gliosis, and Functional Deficits after Traumatic Brain Injury in Rats

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Abstract
This report compares the effects of progesterone and its metabolite, allopregnanolone, on the early injury cascade (apoptosis) and long-term functional deficits after TBI. Progesterone (16 mg/kg) or allopregnanolone (4, 8, or 16 mg/kg) were injected at 1 h, 6 h, and then for 5 consecutive days after bilateral contusions of the frontal cortex in adult male rats. Within one day after injury, progesterone and allopregnanolone reduced both the expression of pro-apoptotic proteins caspase-3 and Bax, and apoptotic DNA fragmentation. Progesterone and allopregnanolone also reduced the size of glial fibrillary acid protein (GFAP)–positive astrocytes at the lesion site 24 h after injury. Compared to sham-operated controls at 19 days after injury, injured rats given either progesterone or any of three doses of allopregnanolone had equivalent numbers of ChAT-positive cells in the nucleus basalis magnocellularis. At 19 days post-injury, rats given progesterone or allopregnanolone (8 mg/kg) showed improved performance in a spatial learning task compared to injured rats given only the vehicle. These results provide evidence of the anti-apoptotic and anti-astrogliotic effects of progesterone and allopregnanolone and help to explain why better cognitive performance is observed after injury when animals are given either neurosteroid.