The Effects of Chronic Morphine Administration on Tooth Pulp Thresholds in Dogs and Cats ∗

Summary

The effects of acute and chronically administered morphine on the threshold voltage required to elicit a response to tooth pulp stimulation in the dog and cat were quantitatively compared. A single dose of morphine elevated tooth pulp thresholds to a greater extent in dogs than in cats. After chronic administration, a decrease in the threshold occurred in cats but not in dogs. In the latter, a tolerance to (but not a reversal) of the threshold elevating effect was observed. Tolerance was seen to the overt depressant effects of morphine in dogs but not to the overt excitatory effects in cats. Studies concerned with attempts to delineate the reason (s) for these differences may be useful in advancing our knowledge concerning the mechanisms responsible for the analgesic effect of morphine and the development of tolerance to this drug.