AtT-20 cells, which produce ß-endorphin,
and AtT-20/hENK cells, which are AtT-20 cells
transfected with a proenkephalin gene, were
implanted in the rat spinal subarachnoid space
in an effort to produce an antinociceptive effect.
Host rats were tested for antinociceptive activity
by standard nociceptive tests, tail flick and hot
plate. Although cell implants had minimal effect
on the basal response to thermal nociceptive
stimuli, administration of the ß2-adrenergic
agonist isoproterenol produced antinociception
in the cell-implanted group but not in the
control group. The antinociceptive effect of
isoproterenol was dose-related and could be
blocked by the opioid antagonist naloxone.
Immunohistochemical analysis of spinal cords
revealed the presence of enkephalin-negative
cells surrounding the spinal cord of rats
receiving AtT-20 cell implants, and enkephalinpositive
cells surrounding the spinal cord of rats.
receiving AtT-20/hENK cell implants. These
results suggest that opioid-releasing cells
implanted around rat spinal cord can produce
antinociception and may provide an alternative
therapy for chronic pain.