DR. MIARON JACOB O OLE

Data available on the role of the opioid systems of the naked mole-rat in nociception is scanty and unique compared to that of other rodents. In the current study, the effect of DAMGO, DPDPE and U-50488 and U-69593 on formalin-induced (20 μl,10%) nociception were investigated. Nociceptive-like behaviors were quantified by scoring in blocks of 5 min the total amount of time (s) the animal spent scratching/biting the injected pawin the early (0–5 min) and in the late (25–60 min) phase of the test. In both the early and late phases, administration of 1 or 5 mg/kg of DAMGO or DPDPE caused a naloxone-attenuated decrease in the mean scratching/biting time. U-50488 and U-69593 at all the doses tested did not significantly change the mean scratching/biting time in the early phase. However, in the late phase U-50488 or U-69593 at the highest doses tested (1 or 5 mg/kg or 0.025 or 0.05 mg/kg, respectively) caused a statistically significant and naloxone-attenuated decrease in the mean scratching/biting time. The data showed that mu, delta or kappa-selective opioids causes antinociception in the formalin test in this rodent, adding novel information on the role of opioid systems of the animal on pain regulation.

Propranolol, a nonselective β-blocker and selective β-blockers (metoprolol a β1-blocker and ICI 118551 a β2-blocker) were used to investigate the β-adrenoceptor-mediated adrenaline-induced increase in whole-body and organ VO2 in five whether sheep. Transit time blood flow probes were chronically implanted on the portal vein and the external iliac artery and sampling catheters were placed in the mesenteric artery, iliac vein and portal vein. Oxygen consumption by the whole body was measured by open circuit calorimetry, and oxygen consumption by the portal-drained viscera and the hindquarter was determined from A-VO2 differences and organ blood flow. Absolute pre-infusion VO2 values for the whole body, portal-drained viscera and hindquarters were 236 ± 7.4, 61 ± 6.0 and 13 ± 3.1 mL min−1 respectively. The mean changes in VO2 in response to infusion were 74 vs. 11, 26, 10 and 12 mL min−1 (SE = 9.1) for whole body; 31 vs. −2, −15, 13 and −4 mL min−1 (SE = 7.3) for portal-drained viscera and 8 vs. −0.4, 2.1, 1.0 and −2.7 mL min−1; SE = 4.3) for hindquarters during adrenaline, control, propranolol, metoprolol and ICI 118551 treatments, respectively. Adrenaline increased VO2 (P < 0.05) in the whole body and portal-drained viscera, but not hindquarters relative to controls. All β-blockers suppressed (P < 0.05) the adrenaline-induced increase in VO2 except for the portal-drained viscera where metoprolol was less effective and the hindquarters where β-blockers had no effect. The blood flow pattern was similar to VO2 responses for the portal-drained viscera. The nonselective β1 and β2 blockers were effective in reducing the adrenaline-induced increases in blood flow from the portal-drained viscera and to the hindquarters, with more pronounced β-adrenoceptor-mediated haemodynamic effects. The results indicate that the β-adrenoceptor system modulates whole body VO2, clearly establishes that adrenaline induces an increased VO2 in portal-drained viscera which can be reversed by a β2 or nonselective β blocker and implicates β adrenoceptors as an influencing factor in the maintenance energy requirements of ruminants.

Three tests of nociception were adapted for the use in crocodiles (47.0-65.2cm long). In the capsaicin instillation test, capsaicin in concentrations of 10^<-9> to 10^<-3> g/ml instilled in the eye induced concentration related protective reactions which were counted. In the formalin test, 150 μl of 5% formalin was injected subcutaneously in the fore paw, and the time spent "lifting the foot" and "not using the foot" was recorded. In the hot plate test, the plate temperature was set at 55℃ and the latency until the following behavioural categories occurred was recorded: "lifting toes", "lifting foot", and "attempt to escape". This test could be repeated with similar results after an interval of 60 min. It was concluded that the crocodile has a well developed nociceptive system, and it may be possible to study the function of this system using these modifications of well known tests of nociception.