The intrathecal grafting of adrenal chromaffin cells as a potential analgesic source, to delivery analgesic substances such as catecholamines and opioid peptides, is known to be effective at treating acute and chronic pain in several animal pain models. We tested whether the intrathecal implantation of encapsulated bovine chromaffin cells reduces cold allodynia in a rat model of neuropathic pain induced by chronic constriction injury of the sciatic nerve.

Bovine adrenal medullary chromaffin cells microencapsulated in sodium alginate-poly-l-lysin-alginate (APA) were implanted into the subarachnoid space of rats (n = 10) and foot cold sensitivity was investigated using an acetone test. At the end of the study, histology and capsule catecholamine production were evaluated.

A significant reduction in cold allodynia was observed in animals implanted with chromaffin cells. In addition, the suppression of cold allodynia was reversed by naloxone. Abundant clusters of viable chromaffin cells stained with neutral red, were observed in the retrieved implants and after nicotine stimulation, and catecholamine was quantified. An ultrastructural study showed no fibrotic reaction against capsules, or disorganised capsules.

These results suggest that intrathecal encapsulated chromaffin cells act as "mini pumps", which continuously deliver analgesic substances and produce analgesia in this chronic pain model of nerve injury-without immunosuppressant.