Effects of commonly used analgesics and Antiinflammatory drugs, in acute and chronic Pain in the naked mole-rat (heterocephalus Glaber) using the formalin test

Abstract

The aim of the present study was to investigate the effect of commonly used analgesic and anti-inflammatory drugs in the naked mole-rat. Two centrally acting narcotic analgesics (pethidine hydrochloride and codeine phosphate). two non-steroidal antiinflammatory drugs (acetylsalicylic acid and naproxen) and two steroidal antiinflammatory drugs (hydrocortisone sodium succinate and dexamethasone phosphate) were used. The animals were kept under controlled laboratory conditions. The formalin test was performed by injecting a dilute solution of formalin (20 ul of 10% formalin) subcutaneously in the right hind paw of both control and test animals. Two parameters, the number of licks and the time spent licking the paw (sec) were monitored in blocks of 5 min for either 1 h or 2 h. The vehicle or drug were inj ected 30 min prior to the formalin test. The injection of dilute formalin produced two periods of pain behaviour characterized by licking and biting of the injected paw, the early (0-5 min) and the late (25-60 min) phase. Pethidine (20 or 30 mg/kg) and codeine (10, 25 or 50 mg/kg) significantly reduced licking activity in a dose-dependent manner, in both the early and late phase. In addition, pethidine and codeine administration also induced agonistic, hypersensitive, hyperactive behaviour and motor impairment that was naloxone (2 mg/kg) reversible. Acetylsalicylic acid (400 or 600 mg/kg), naproxen (200 mg/kg). hydrocortisone (75 or 150 mg/kg) and dexamethasone (30 mg/kg) significantly reduced licking and pain related activity in a dose-dependent manner but in the late phase only. It is concluded that the naked mole-rat has anti-nociceptive systems that can be activated by administration of the narcotic and non-narcotic drugs used. It appears that the opioid system. in the naked mole-rat is more involved in the regulation of agonistic and motor behaviour. than anti-nociception.