Analgesic effects of adrenal chromaffin allografts: contingent on special procedures or due to experimenter bias?

Many articles have reported that adrenal chromaffin cell transplants produce analgesic effects. Surprisingly, studies conducted in our laboratory failed to detect analgesic effects of adrenal chromaffin cell transplants. Although we have attempted to replicate the procedures reported to produce analgesic effects with adrenal chromaffin transplants, many of the different cell preparation procedures we have examined are fairly complex, and it is possible that our transplants were not sufficiently viable because of some subtle difference in our cell preparation procedures. In the present study we attempted to replicate as precisely as possible, and with very large groups to maximize statistical power, the simplest and most straightforward procedures previously reported to produce analgesic effects, adrenal allografts in the formalin test. The first experiment, conducted in our laboratories, failed to detect analgesic effects of intrathecal adrenal allografts in the formalin test. Another study conducted at a different research facility confirmed the absence of analgesic effects in the formalin test but verified that analgesic effects of morphine were detectable under the same blinded conditions. In addition, graft viability was verified histologically, but there was no correlation in either experiment between adrenal chromaffin cell number and pain behaviors. These results demonstrate more clearly than any of our previous reports that the analgesic effects of intrathecal adrenal transplants are not reliable and should not be accepted as valid until they can be produced reliably under rigorously blinded conditions. 2003 by the American Pain Society