2004A0005 - Photoperiodic Changes in Nociception (nerve pathways concerned with the condition of pain)

Pain Code = 3D

As with many of the animal experiments conducted by Dr. Nelson this one is again exploring how seasonal changes impact animals. In this case he is looking at pain sensation and perception.

ILACUC approved the protocol to use 80 Siberian hamsters. The animals are housed in cages that provide two different light & dark parameters. One set of hamsters will be LD 16hrs:8hrs, the other 8:16. The P.I. notes that, "Laboratory strains of mice and rats do not respond to day length."

After 10 weeks the hamsters begin their testing.

"Each animal will be placed on a hot plate surface held at a constant temperature of 52 degrees celcius (126 degree Fahrenheit). Locomotion of the hamster will be limited by a plexiglass barrier. Latency to produce a nociceptive (pain) response to the heat stimulus by either licking the hindpaw, shaking the hindpaw, or vocalization will be measured to the nearest second. A time limit of 45 sec will be imposed after which the animal will be removed from the hot plate to prevent possible tissue damage. ... Testing will take place during a single trial per 24 hr period for each animal, given that the literature demonstrates that repeated hot plate testing results in profound latency changes within subjects. (the animals don't want to put their paw down and feel pain again - surprise - surprise)"

"At the conclusion of the experiment, all animals will be euthanized."

Well this animal experiment appeared to have design problems because in June 2004 an amendment was submitted to ILACUC stating that due to the "substantial covering of fur on the bottom of these hamsters' paws the experiments were not producing the results expected by the PI. An additional 40 Siberian hamsters were also requested.

After a meeting with Dr. Noe Tirado-Muniz, it was decided that "a temperature of 60 C (140 F) and a time limit of 5 minutes would be the most appropriate for hot plate testing of these animals."

"Second, we would like to repeat the originally proposed experiments on Siberian hamsters that have had hair removed from their feet prior to testing with depilatory cream."

"In addition, we would like to add an experiment that would follow all the hot plate procedures ... but in which animals would receive a single injection of naloxone, a non-selective competitive opioid antagonist, one hour before hot plate testing. The purpose of this experiment is to determine whether any changes in pain sensitivity resulting from the photoperiod manipulation are mediated by opioid mechanisms."

ILACUC approved the amendment with no comment. Not even to comment where the PI appears to indicate that mice will now be involved in the experiment. No mice are approved but the PI writes, "the previous hot plate temperature and time limits will remain as in the original protocol for all experiments conducted on mice."

Well, well things are still not going exactly as planned so in August 2004 an amendment was submitted to ILACUC stating:

the hamsters that had the hair removed from the bottom of their paws were still not responding as expected. "...none of the hamsters in either photoperiod treatment (LD) displayed a nociceptive (pain) response to the hot plate stimulus during the 45 sec time limit. We currently request an extension of the time limit ... from 45 sec to 2 min, while keeping the hot plate temperature identical to that previously approved, 56 C(133 F). We believe that this time extension will allow us to detect photoperiodic differences in pain sensitivity in these hamsters."

Without comment ILACUC approved the amendment.