Changes in operation of postural networks in rabbits with postural functions recovered after lateral hemisection of the spinal cord.

KEY POINTS
After lateral hemisection of the spinal cord (LHS), postural functions recover over time. The underlying changes in the operation of postural networks are unknown. We compared the responses of individual spinal neurons and hindlimb muscles to stimulation causing postural limb reflexes (PLR) in recovered LHS-rabbits with those obtained in rabbits with the intact spinal cord and rabbits after acute LHS. We demonstrated that changes underlying the recovery of postural functions take place not only in postural networks that are severely impaired, but also in those that are almost unaffected by acute LHS. PLRs on the LHS side recover mainly due to changes at the brainstem-cerebellum-spinal levels, while the forebrain is substantially involved in the generation of PLRs contralateral to the LHS.


ABSTRACT
Acute lateral hemisection of the spinal cord (LHS) severely impairs postural functions, which recover over time. Here, to reveal changes in the operation of postural networks underlying the recovery, male rabbits with recovered postural functions after LHS at T12 (R-rabbits) were used. After decerebration, we characterized the responses of individual spinal interneurons from L5 along with hindlimb EMG responses to stimulation causing postural limb reflexes (PLRs) which substantially contribute to postural corrections in intact animals. The data were compared with those obtained in our earlier studies of rabbits with the intact spinal cord and rabbits after acute LHS. Although in R-rabbits the EMG responses to postural disturbances both ipsilateral and contralateral to the LHS (ipsi-LHS and co-LHS) were only slightly distorted, PLRs on the co-LHS side (unaffected by acute LHS) were distorted substantially and PLRs on the ipsi-LHS side (abolished by acute LHS) were close to control. Thus, in R-rabbits, plastic changes develop both in postural networks affected and unaffected by acute LHS. PLRs on the ipsi-LHS side recover mainly due to changes at the brainstem-cerebellum-spinal levels, whereas the forebrain is substantially involved in the generation of PLRs on the co-LHS side. We found that in areas of gray matter in which the activity of spinal neurons of the postural network was significantly decreased after acute LHS, it recovered to the control level, while in areas unaffected by acute LHS, it was significantly changed. These changes underlie the recovery and distortion of PLRs on the ipsi-LHS and co-LHS sides, respectively. Abstract figure legend To reveal changes in postural networks underlying recovery of postural functions, in rabbits recovered after the lateral hemisection of the spinal cord, postural corrections caused by lateral tilt of the supporting platform have been evaluated. Then, the rabbits were decerebrated, and activity of individual spinal interneurons of postural networks (F-neurons and E-neurons) located below the lesion were recorded during postural limb reflexes. The results were compared with earlier obtained control data from animals with an intact spinal cord as well as with data obtained after acute lateral hemisection (not shown). We demonstrate that activity of neurons of postural networks does not return to control level in recovered animals. This article is protected by copyright. All rights reserved.