Pain Sensitivity of Trout and Analgesia Induced by Intranasal Administration of Dermorphine

Pain is the major sense in vertebrates that performs signaling and protective functions in the case of potential damage to the body. The problem of pain, which is of prime importance for humans, is extensively investigated in higher vertebrates [1], However, only a few works have attempted to study the sense of pain in fish. Verheijen [2] regarded a kind of "cough" observed in carps on damaging their mouth with a sharp hook as a manifestation of pain. Other authors showed that morphine, an exogenous analgesic compound, rose the threshold of pain induced in goldfishes by electrical stimulation [3]. In lampreys, the spinal cord and trigeminal ganglion contain the cells that respond by discharges on pressure applied with a strength that could damage the skin [4]. These studies suggest that fishes, like higher vertebrates, have a system of pain reception.