Allopregnanolone and Progesterone Decrease Cell Death and Cognitive Deficits After a Contusion of the Rat Pre-frontal Cortex

We compared the effects of three different doses of allopregnanolone (4, 8 or 16 mg/kg), a metabolite of progesterone, to progesterone (16 mg/kg) in adult rats with controlled cortical impact to the pre-frontal cortex. Injections were given 1 h, 6 h and every day for 5 consecutive days after the injury. One day after injury, both progesterone-treated (16 mg/kg) and allopregnanolone (8 or 16 mg/kg)-treated rats showed less caspase-3 activity, and rats treated with allopregnanolone (16 mg/kg) showed less DNA fragmentation in the lesion area, indicating reduced apoptosis. Nineteen days after the injury, rats treated with progesterone and allopregnanolone (8 or 16 mg/kg) showed no difference in necrotic cavity size but had less cell loss in the medio-dorsal nucleus of the thalamus and less learning and memory impairments compared with the injured vehicle-treated rats. On that same day the injured rats treated with progesterone showed more weight gain compared with the injured rats treated with the vehicle. These results can be taken to show that progesterone and allopregnanolone have similar neuroprotective effects after traumatic brain injury, but allopregnanolone appears to be more potent than progesterone in facilitating CNS repair.