Adrenal medullary chromaffin cells are ideal candidates for the transplantation studies, because they contain and release several neuroactive substances, which are known to influence pain sensitivity in the central nervous system (CNS). This chapter demonstrates that pain sensitivity can be altered following implantation of adrenal chromaffin cells into some of the CNS regions involved in pain modulation, such as the mid-brain periaqueductal gray (PAG) and the dorsal horn of the spinal cord of adult rats. The results show that morphological findings correlate well with the behavioral studies, whereby pain sensitivity is greatly altered following implantation of chromaffin cells. This implies that reduction in pain sensitivity can be brought about by the implantation of chromaffin cells containing neuroactive substances into appropriate regions of the neuraxis and opens up the possibility for a potentially new approach to pain therapy. An important aspect in this regard is the ability for adrenal chromaffin cells to survive for long periods. Thus, the preliminary studies on rats suggest that these grafts can survive and retain the potential to induce alterations in pain sensitivity for at least twelve months.
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