Efficacy of a new neuroprotective agent, Gacyclidine, in a model of rat spinal cord injury

Prevention of the immediate excitotoxic phase occurring in response to spinal cord injury (SCI) is a major issue to reduce the neuronal damage responsible for any ensuing motor deficits. The present study evaluated the neuroprotective efficacy of three noncompetitive NMDA receptor antagonists: Gacyclidine (GK-11), a new compound, Dizocilpine (MK-801), and Cerestat (CNS-1102) in a rat spinal cord contusion model. To mimic human SCI, a standardized model of rat spinal cord closed contusion in which animals spontaneously and progressively recover from the induced paraplegia was employed. Such model, characterized by a slow recovery of hindlimb locomotor function enables easy quantification of the neuroprotection at both the behavioral and cellular level. The animals were treated intravenously with the respective drugs 10 min after the spinal contusion. The dose range study suggested that 1 mg/kg of Gacyclidine was the most effective dose to promote functional recovery in reducing by half the time needed to reach full locomotor recovery. Racemate and enantiomers of Gacyclidine showed similar neuroprotective effects, but treatment with the enantiomers were not as efficacious in promoting full functional recovery. Similarly, a prolonged treatment with the racemate was not as efficious as a single dose, suggesting that a prolonged blockade of the amino-excitatory neurotransmission may be deleterious. Finally, Dizocilpine and Cerestat treatments induced only a partial and delayed neuroprotective effect compared to Gacyclidine. Neuroprotection characterized by a reduction of the cystic cavity and of the astrogliosis was observed with all treatments. As Gacyclidine is already in clinical trials, the present findings suggest the premise that it is a promising agent for limiting the initial neuronal damage induced by CNS trauma leading to better functional recovery.