Post-injury administration of a combination of memantine and 17β-estradiol is protective in a rat model of traumatic brain injury

Traumatic brain injury (TBI) often leads to substantial adverse cognitive and health outcomes, including permanent disability and death. Preventing these outcomes requires attenuation of the secondary biochemical damage that follows the initial biomechanical insult, but a clinically proven pharmacotherapeutic capable of such has not been identified. In fact, the heterogeneous nature of TBI and the complexity of secondary injury cascades suggest a polytherapeutic approach that targets multiple pathways might be necessary. We and others have reported that 17β-estradiol (E2) is neuroprotective in models of central nervous system injury. Although E2 is neuroprotective and favorably modulates several key components of secondary injury, it does not effectively block the destructive excitotoxic cascade. Thus, administering E2 in combination with a second drug that targets excitotoxicity, such as the FDA-approved uncompetitive NMDA receptor antagonist memantine hydrochloride, may provide additional benefits. Here, we assessed the neuroprotective potential of an acutely administered intravenous bolus dose of a combination of memantine and E2 after induction of experimental TBI in the clinically relevant lateral fluid percussion model. Our results indicate that the combination of these drugs conferred neuroprotection by increasing neuronal survival and decreasing neuronal degeneration in the hippocampus and cortex ipsilateral to injury. Furthermore, administration of this combination improved vestibulomotor deficits and modestly reduced anxiety. We conclude that further investigation of the neuroprotective potential of memantine administered with E2 is warranted.