Immunoisolating encapsulation of intrathecally implanted bovine chromaffin cells prolongs their survival and produces anti‐allodynic effect in spinally injured rats

We have previously reported that intrathecal (i.t.) implantation of bovine chromaffin cells has an anti-allodynic effect in a rat model of mechanical and cold allodynia-like neuropathic pain after spinal cord injury. The technique of encapsulation of the cells by a semipermeable membrane has been developed recently. The present study was undertaken to investigate the effects of encapsulated bovine chromaffin cells on the allodynia-like pain in the same model. Capsules with bovine chromaffin cells or control capsules were implanted in the spinal subarachnoidal space in rats. Their response in behavioural tests were recorded for 2 months. At termination, the capsules were explanted and examined morphologically with tyrosine hydroxylase immunohistochemistry. The mechanical allodynia was totally abolished from week 2 after implantation of the cells and throughout the 8-week test period. The abnormal cold response was also attenuated in about half of the animals. The threshold to acute nociceptive stimulation was not affected. Eight weeks after implantation, 60–80% of the encapsulated chromaffin cells were still tyrosine hydroxylase positive. No effects were observed with control capsules. The results indicate that spinal implantation of encapsulated xenogeneic chromaffin cells may be useful in treating some refractory painful states associated with spinal cord injury. Immunoisolation of chromaffin cells by a semipermeable membrane may inhibit immunorejection, prolong the survival of the cells and enhance their anti-allodynic effect.