Mapreg is developing pregnenolone methyl ether (MAP4343), an injectable neurosteroid stimulator of the tubulin polymerisation and neurite growth stimulator. The synthetic pregnenolone-derivative MAP4343 (3β-methoxy-preg-nenolone) binds in vitro to microtubule-associated-protein 2 (MAP2), stimulates the polymerization of tubulin, enhances the extension of neurites and protects neurons against neurotoxic agents. MAP4343 has been selected after screening of a large library ofnatural and synthetic steroids. MAP4343 has similar in vitro activity as pregnenolone; it cannot be converted into metabolites with hormonal activities, and has been shown to have in vivo beneficial effects in rat models of spinal cord injury. MAP4343 has an interesting pharmacological profile because no in vitro affinity for any CNS neurotransmitter receptor was found. MAP4343 has been shown to have antidepressant efficacy in rats. In the rat isolation-rearing model of depression, administration of MAP4343 showed persistent efficacy in recovering recognition memory deficit, stronger and more rapid anxiolytic activity, and more rapid rescue of passive coping behavior compared with FLX. The behavioral effects of MAP4343 correlated with changes in α-tubulin isoforms in the hippocampus, amygdala, and pre-frontal cortex (PFC). Its efficacy was also assessed in vivo with the most commonly used thoracic spinal cord compression/contusion models in rats. In the three models used, the post-traumatic subcutaneous injection of MAP4343 significantly improved the recovery of locomotor function after spinal cord injury, as shown by an earlier and more complete recovery compared to vehicle-treated rats. The results obtained in three different rat models of spinal cord injury demonstrate the beneficial effects of this therapeutic strategy and identify MAP4343 as a potential treatment for acute spinal cord injury. MAP4343 received EU Orphan Drug designation for spinal cord injury. MAP4343 is in phase II clinical trials by Mapreg for the treatment of depression and in phase I clinical trials for the treatment of spinal cord injury and traumatic brain injury.