Recovery of hindlimb motor functions after spinal cord transection is enhanced by grafts of the embryonic raphe nuclei.

In this study, a piece of embryonic tissue from the raphe nucleus was transplanted into the spinal cord below the lesion 1 month after transection. Two months later the recovery of hindlimb motor function in rats which had received a transplant of neural tissue (ST rats) was much better than in spinal control animals without the graft (SC rats). Analysis of the electromyographic (EMG) activity showed that the timing of muscle activity during locomotor-like movement of hindlimbs in ST rats was more regular than in SC rats. In SC rats the relationships between EMG burst duration (soleus, tibialis anterior) and step cycle duration were significantly altered. The restoration of hindlimb motor function of ST rats was also reflected in the better interlimb coordination during locomotor-like hindlimb movements. The results of several behavioural tests demonstrated that the responses to stimulation of various receptors, such as tactile or proprioceptive, in ST rats were more complex than in SC rats. Additionally, unlike in SC animals, in ST rats long-lasting spontaneous episodes of air stepping movement of hindlimbs accompanied by a relatively high amplitude of EMG activity were obtained. These results confirm that grafted embryonic raphe nuclei which contain serotoninergic cells are likely to increase the excitability of neuronal circuitry in the injured spinal cord. Moreover, transplantation of embryonic raphe nuclei encourages the recovery of hindlimb motor function in adult rats even when the grafting is carried out several weeks after spinal cord injury.