Evaluation of the commonly used analgesics in the naked mole-rat (heterocephalus glaber) and the root-rat mole-rat (tachyoryctes splendens) using the hot-plate test

Abstract

The aims of the experiments were to study pain mechanisms and behaviour in two species of mole-rats, the naked mole-rat (Heterocepha/us g/aber) and the root-rat mole-rat (Tachyoryctes sp/endens). Two opioids (pethidine and codeine), three. non-steroidal anti-inflammatory drugs (paracetamol, acetylsalicylic acid (ASA) and indomethacin) and two steroid anti-inflammatory drugs (dexamethasone and hydrocortisone) were used in this study. The hot-plate test used in this study was set at a temperature of 600 C. The two species of mole-rats were kept under controlled laboratory conditions. In both species of mole-rats the opiates used (pethidine: 10, 20 or 30 mg/kg, codeine: 15, 25, 35 or 50 mg/kg) had no antinociceptive effect but instead induced a dose-dependent reduction in response latency. Administration of pethidine or codeine also induced aggressive behaviour and sensorimotor effects in the naked mole-rat. The change in behaviour was not observed in the root-rat mole-rat after pethidine administration. Paracetamol (400 mg/kg) and indomethacin (40 or 50 mg/kg) caused a significant increase in stepping latency in the naked mole-rat. Lower doses of these drugs had no antinociceptive effect. No anti nociceptive effect of either acetylsalicylic acid (200, 400 or 600 mg/kg), hydrocortisone (75, 150 or 225 mg/kg) or dexamethasone (10, 20 or 30 mg/kg) was demonstrated in the study. It is concluded that the opioid system of the mole-rat plays no role in the regulation of thermal nociception. In the naked mole-rat however, the opioid system seems to play an important role in the regulation of aggressive and motor behaviour.