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To investigate the effects on evoked thalamic neuronal activity of application of notochordal cells and chondrocyte-like cells derived from nucleus pulposus (NP) onto a dorsal root ganglion (DRG) and to compare these effects with a previously reported increased thalamic activity induced by NP.Nucleus pulposus was harvested from tail discs of adult rats and the disc cells were separated into two cell populations, notochordal cells and chondrocyte-like cells. The two cell populations were applied separately, or in combination, to the L4 DRG of anaesthetised female Sprague-Dawley rats during acute electrophysiological experiments. In control experiments, cell suspension medium was applied on the DRG. Recordings from the contralateral thalamus were sampled for 40 min while electrically stimulating the ipsilateral sciatic nerve at above Aδ-fibre thresholds.Application of notochordal cells resulted in a decrease in evoked thalamic activity within 10 min while chondrocyte-like cells did not induce any changes during the 40 min of recording. The difference in evoked thalamic activity 40 min after notochordal and chondrocyte-like cell application, respectively, was statistically significant. Neither an increased concentration of chondrocyte-like cells alone nor a combination of the two cell populations induced any changes in thalamic activity.Separate exposure of the DRG to the two NP-derived cell populations induced different effects on evoked thalamic activity, but none of the tested cell samples induced an increase in neuronal activity similar to that previously observed with NP. This indicates a high complexity of the interaction between NP and nervous tissue.

It is known that 24 h or more after epidural application of autologous nucleus pulposus, functional and structural changes are established in adjacent nerve roots. It is, however, not known how soon after the application these changes appear. The aim of this study was to reduce the exposure duration to 3 h and to evaluate nerve function and histological changes in the nerve tissue during this time period. A total of 12 pigs was used. In ten pigs, autologous nucleus pulposus (NP) was applied epidurally on the cauda equina. Nerve function was then monitored for 3 h by measurements of muscle action potentials (MAP) in the tail muscles, following nerve root stimulation cranial to the exposed zone. In five of the ten pigs with NP application, nerve root compression to 50 mm Hg was added by means of an inflatable balloon. In two control animals, neither NP nor compression was applied. At the end point, nerve root specimens were harvested for histological assessment. No reduction of MAP amplitude was detected in any of the series. However, there was an epidural accumulation of leucocytes and mast cells, as well as minor axonal and Schwann cell changes in both the NP and NP+ compression series, as compared to the control series. Morphological changes in terms of an epidural inflammatory reaction and minor axonal and Schwann cell damage may thus be demonstrated within 3 h of NP application, with or without compression. However, there is no functional deterioration of the nerve roots detectable within this time period.

In an attempt to evaluate whether experimental disc herniation can result in changes in walking pattern, presumably indicating pain, four groups of rats – sham (n = 5), disc puncture (NP, n = 5), displacement of nerve root and ganglion (DIS, n = 5), and the combination of disc puncture and displacement (NP + DIS, n = 6) – were assessed when walking in a Plexiglas corridor at day 2–14 after surgery. All surgical procedures were performed at the L4–5 level on the left side. Step length analysis showed that rats in the NP and DIS series had no difference between the legs initially, but a tendency towards slightly shorter left steps at day 8–12, whereas the animals in the NP + DIS series had slightly shorter right steps day 2–10. However, no statistically significant differences compared with the sham series could be detected for any of the groups. Nerve dysfunction on the operated side was only observed on one occasion in two rats and on 2 days in one rat, all from the NP + DIS series. Apparent limping was seen in three of the animals in the NP + DIS series and in one in the DIS series. Limping and nerve dysfunction only co-incided on one occasion out of a total of 13 observations of limping, suggesting that the limping was induced by pain and not neurologic deficit. In conclusion, the combination of epidural nucleus pulposus and displacement induced a limping whereas nucleus pulposus or displacment alone did not. Assessment of limping thus seemed to provide adequate information of presence of pain, but step length measurement did not provide any useful data. Although walking analysis may be a valuable assessment of sciatic pain, better modalities must be developed to analyze experimentally induced nerve root pain.

Bone cement is sometimes used for vertebral body reconstruction following tumor removal. During such procedures, the polymerization of the methyl-metacrylate in the bone cement generates heat. Such temperature increase might cause damage to the nerve roots within the spinal canal. In the present study, pig cauda equina nerve roots were subjected to controlled temperature increases by means of a heat-generating probe. A temperature of 40°C applied for 5 min did not cause any changes in nerve root function. However, 70°C resulted in a complete block of nerve root function within 5 min. Histological nerve fiber damage was seen after exposure to 60°C and 70°C. The present study provides basic knowledge of heat-resistance properties of spinal nerve roots that might be directly applicable as guidelines for safety margins during surgical spine reconstruction procedures using bone cement.