Model of spinal cord lateral hemi-excision at the lower thoracic level for the tasks of reconstructive and experimental neurosurgery

Abstract

Purpose. To test the model of spinal cord lateral hemiexcision in young rats.

Materials and methods. Animals ‒ male rats (age about 1 month, body weight about 50 g, inbred derivatives of the Wistar line); the number of experimental groups is: 1) lateral spinal cord hemisection at the level of segments about T12–T13 (Sect; n=11); 2) lateral spinal cord hemiexcision about 1 mm long at the similar level (Exc; n=8). Assessment of motor Function Index (FI) and the Spasticity Index (SI) of the paretic hindlimb was carried out using the Basso–Beattie–Bresnahan (BBB) scale and Ashworth scale, respectively, in our technical modifications. The non-inclusion criteria: the BBB score above 9 points of FI for the ipsilateral hindlimb in a week after injury ‒and / or BBB score less than or equal to 14 points of FI of the contralateral hindlimb during a long follow-up period (in general, 2 animals in the Sect group, 3 animals ‒ in the Exc group). Asymptotic differences in the timing of testing between subgroups and groups were revealed during the first three weeks of follow-up. Interpolation reproduction of individual values of FI and SI was used in exceptional cases. The total follow-up period was 5 months. Statistical analysis was performed using the Mann-Whitney U Test, Wilcoxon Matched Pairs Test, Spearman’s Rank Order Correlation. For pathomorphological study, the method of silver impregnation of the spinal cord longitudinal sections of the Exc group animals obtained in 5 months after the simulation of injury was used.

Results. One week after injury, the FI in the Sect group was 5.9±1.1 according to BBB points, a statistically significant increase in the FI lasted for the first 3 weeks (p<0.05; Wilcoxon Matched Pairs Test), the FI maximum in the group was 10.1±1.1 BBB points, and the FI value at the end of the study was 9.5±1.0 BBB points. In the Exc group, 1 week after injury, the FI was 0.9±0.5 BBB points, during the next week it reached the actual maximum (1.9±0.7 BBB points), by the end of the 5th month it significantly decreased to 0.8±0.3 BBB points (p<0.05; Wilcoxon Matched Pairs Test). One week after injury, the SI value in the Sect group was 0.3±0.1 points according to Ashworth scale, in the Exc group ‒ 0.7±0.1 Ashworth points, a significant increase (p<0.05; Wilcoxon Matched Pairs Test) in SI in the Sect group was noted during the 2nd week and the 2nd month, in the Exc group ‒ during the 2nd and 6th week, as well as the 3rd and 5th month after injury. The SI final and maximal score for the Sect group was 0.8±0.2 Ashworth points, and for the Exc group ‒ 3.6±0.3 Ashworth points. For both groups, there was no correlation between the mean FI value and a significant positive correlation of the mean SI value with the value of the follow-up period (p<0.05; Spearman’s Rank Order Correlation), as well as the absence of correlation between the mean FI and SI values during the total follow-up period. A significant negative correlation (p<0.05; Spearman’s Rank Order Correlation) between individual FI and SI values was found after 1 and 4 weeks, 3 and 5 months after the injury for the Sect group, as well as after 5, 7, 8 weeks and after 3 and 4 months for the Exc group. At all periods of follow-up, the difference in both FI and SI mean values of both groups was significant (p<0.05; the Mann-Whitney U Test).

Conclusions. The studied model of spinal cord injury in young rats is the means of choice for testing solid neural transplantation means for the spinal cord injury restorative treatment. The interpretation of data obtained using the BBB scale on models of lateral half spinal cord injury should be carried out with caution, and the methodology for verifying spasticity requires significant improvement. We recommend that the optimal timing for the FI and SI monitoring after lateral half spinal cord injury is 7 days, 14 days and in 1, 2, 3, 4, 5, 6, and 7 months.