Objective: To investigate the impact of different drugs and different volumes injected intraspinally on the nerve function and find out the safe intraspinally injection volume.
Methods: Ninety-six adult Sprague-Dawley rats were randomly divided into 12 equal groups to be injected intraspinally with normal saline (NS) 2 microl, 4 microl, 6 microl, or 10 microl, viral buffer 2 microl, 4 microl, 6 microl, or 10 microl, or Ad-LacZ (1 x 10(9) pfu/ml) 2 microl, 4 microl, 6 microl, or 10 microl at the level of T13 respectively immediately after the laminectomy was performed. Another 6 adult SD rats only underwent T13 luminal decompression and used as controls. Basso-Beattie-Bresnahan locomotor rating scale was used to evaluate the motor function of their hind limbs after 1, 2, 3, 4, 5, and 6 days, and 1, 2, 3, and 4 weeks. One and 2 weeks after the injection 2 rats from each group were killed and the remaining 4 rats in each group were killed 4 weeks after the injection. Histological examination was done with HE staining and toluidine blue staining. X-gal staining was used to observe the expression of adenovirus in the spinal cord.
Results: The extent of motor deficits and tissue damage increased following the increase of intraspinal injection volume (P = 0.000). The severity of damage of the Ad-LacZ was significantly greater than those of the NS and virus buffer groups (P = 0.044), however, there were no significant differences in the severity of damage among NS groups and virus buffer groups (P = 1.000). X-Gal staining showed that the reporter gene LacZ was expressed in all Ad-LacZ groups. The great the dose the more severe the damage. Four weeks later the effective residual rates f the grey and white matters of the Ad-LacZ groups were all significantly lower than those of the other 2 groups, however, there were no significant differences in the effective residual rates f the grey and white matters among the NS and virus buffer groups.
Conclusion: Intraspinal injection results in functional deficit and tissue damage in the spinal cord. The extent of tissue damage increases following the increase of intraspinal injection volume. Different drugs cause different tissue damage. The intraspinal injection of Ad-LacZ results in more tissue damage. The volume of 4 microl is the safe volume for injection, 6 microl is a critical volume.