Dermorphin, a new peptide from amphibian skin, inhibits the nociceptive thalamic neurons firing rate evoked by noxious stimuli.

Dermorphin is the representative of a new class of potent opioid peptides occurring in amphibian skin and possesses the unique feature of having a D-Ala residue incorporated in the peptide molecule. The effect of dermorphin on the spontaneous and evoked neuronal activity by a nociceptive stimulus was studied in the nucleus lateralis anterior and ventrobasal complex of the rat thalamus. The high firing frequency induced by nociceptive stimuli was blocked when dermorphin was injected intraperitoneally at the dose of 1.5 mg/kg. The action starts about 10 min after injection and lasts on average for 120 min. Naloxone, a specific opioid antagonist, injected i.p. at a dose of 1 mg/kg antagonized the effect of dermorphin. The dermorphin time-course is about twice that of morphine (1.5 mg/kg i.p.) under the same experimental conditions.