• Jun He, Stuart W Hoffman, and Donald G Stein.
• Department of Psychology, Emory University, Atlanta, GA 30322, USA.
• Restor Neurol Neuros. 2004 Jan 1;22(1):19-31.

PurposeIn the current study we investigated whether allopregnanolone, a metabolite of progesterone, could replicate progesterone's beneficial effects in promoting spatial learning ability after bilateral medial prefrontal cortex contusions in rats. Allopregnanolone has been shown to enhance GABA neurotransmission, whereas its isomer epiallopregnanolone does not have this property. Thus, epiallopregnanolone was chosen as a control substance to examine further the role of GABA transmission in post-trauma neuroprotection.MethodsAfter the contusion, rats were given 4 mg/kg treatment of either allopregnanolone or epiallopregnanolone for five consecutive days beginning 1 hr post-injury. Control groups only received vehicle treatment at the same time points. A spatial learning task (Morris Water Maze, MWM) was performed at 7 days post-injury for 10 days. Subsequent histological analyses of brain tissue were conducted to determine quantitatively the neuronal losses in both the mediodorsal nucleus of the thalamus (MDN) and the nucleus basalis magnocellularis (NBM).ResultsAllopregnanolone-treated rats showed better performance in the MWM compared to the vehicle-treated injury group. The histological analyses also revealed that the allopregnanolone-treated injury group had less neuronal loss in both the MDN and the NBM compared to the vehicle-treated injury group. In contrast, epiallopregnanolone did not facilitate MWM performance or reduce neuronal loss in the MDN and the NBM after TBI.ConclusionBased on our findings, we suggest that allopregnanolone may mediate the effects of progesterone in promoting cognitive and morphological recovery from TBI through, among others, its direct or indirect effects on GABA-modulated neurons in the MDN and the NBM.

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