Effects of dexamethasone and acetylsalicylic acid on inflammation caused by Complete Freund's adjuvant in the naked mole rat (Heterocephalus glaber).

The naked mole rat (NMR) is a fossorial rodent that has been observed to have a unique nociceptive system in comparison to others. In this study, we explored on characterization of chronic inflammation in the NMR using Complete Freund's adjuvant (CFA) and investigated the effects of dexamethasone and acetylsalicylic acid on the resulting inflammation. The NMRs were injected with 0.1 ml of CFA subcutaneously in the right hind paw, and an equivalent volume of normal saline was injected to the control group. Swelling of the injected right hind limb was observed within 24 h of injection, which involved the tibiotarsal joint, palmar surface and the digits of the injected paw. Swelling persisted for 6 weeks of experimentation and peaked between day 14 and 21. The resulting inflammation affected the mobility, stance and joint rigidity of CFA treated NMRs in comparison to the control group. Treatment of the chronic phase of the inflammation from the 11th day with dexamethasone and acetylsalicylic acid showed no statistical significance in paw circumference compared to the control group, other than on a few, negligible occasions. The present data showed that CFA was able to induce chronic inflammation in the NMR, and the NMR could thus be established as a model for chronic inflammation. There is, however, need for more sensitive parameters to evaluate the effects of anti-inflammatory drugs.

Modulation of formalin-induced pain-related behaviour by clonidine and yohimbine in the Speke's hinged tortoise (Kiniskys spekii).

The study was designed to investigate the involvement of noradrenergic and serotonergic receptor systems in the modulation of formalin-induced pain-related behaviour in the Speke's hinged tortoise. Intradermal injection of 100 µL of formalin at a dilution of 12.5% caused pain-related behaviour (hindlimb withdrawal) that lasted for a mean time of 19.28 min (monophasic response). Intrathecal administration of clonidine (α2 -adrenergic receptor agonist) and yohimbine (α2 -adrenergic receptor antagonist) at a dose of 40 µg/kg and 37.5 µg/kg or 50 µg/kg, respectively, caused a highly significant reduction in the duration of the formalin-induced pain-related behaviour. The effect of clonidine was reversed by intrathecal administration of yohimbine at a dose of 26.7 µg/kg. The effect of yohimbine at a dose of 50 µg/kg was reversed by intrathecal injection of 20 µg/kg of the serotonergic receptor antagonist methysergide maleate. When performing antagonistic reactions, the administration of the antagonist was followed immediately by that of the agonist. The study indicates that for experimental purposes, intrathecal route of drug administration through the atlanto-occipital joint is effective in tortoises. The data also suggest that testudines have noradrenergic and serotonergic systems that appear to play a role in the modulation of pain in this species.

Effects of opioids in the formalin test in the Speke's hinged tortoise (Kinixy's spekii).

Little is known about analgesia in lower vertebrates such as the Speke's hinged tortoise (Kinixy's spekii), yet of late they are increasingly being adopted as pets. The effects of morphine (5, 7.5, 10 and 20 mg/kg), pethidine (10, 20, and 50 mg/kg) and naloxone (5 mg/kg) on nociception induced by the formalin test (12.5%, 100 microL) were studied in the Speke's hinged tortoise. Formalin induced a monophasic limb retraction behavioural response and its duration was recorded. The behaviour lasted for 16.4 +/- 0.8 min. Morphine (7.5, 10 and 20 mg/kg) and pethidine (20 and 50 mg/kg) induced significant decrease in the duration of limb retraction in the formalin test. The anti-nociceptive effects were naloxone (5 mg/kg) reversible. The data suggest that the formalin test is a good test for studying nociception and anti-nociception in tortoises and that the opioidergic system plays a role in the control of nociception in these animals.

Effects of dehydration and heat stress on food intake and dry matter digestibility in East African ruminants.

Comparative investigations were made between wild and domestic ruminants from arid and semi-arid regions and those species from non-arid areas in an attempt to evaluate the adaptations of these ruminants in terms of the effects of heat stress and dehydration on food intake and digestibility. The effect of (a) an intermittent heat load (a daily light cycle of 12 h at 22 degrees C and 12 h at 40 degrees C) compared to 22 degrees C throughout the day and (b) dehydration level of 15% weight loss, with and without the heat load, on the intake and digestibility of a poor quality hay was investigated in the Grant's gazelle, Oryx, the domestic Turkana goats, fat-tailed sheep, zebu cattle, Thomson's gazelle and wildebeest. The intermittent heat load with water available ad libitum depressed the food intake of zebu cattle and Turkana goats by more than 40%. It had no significant effect on the food intake of the other species. The Thomson's and Grants gazelle, oryx, wildebeest and fat-tailed sheep appear well adapted to withstanding a periodic heat load. Dehydration at 22 degrees C caused a marked depression on food intake of all the species investigated. Dehydration together with a heat load caused no further reduction in the food intake by the Grants's gazelle, oryx, and goats but it did cause a further reduction in the intake in the other species. The small non-domestic ruminants (i.e. Grant's and Thomson's gazelle) appear much more digestive efficient than any of their domestic counterpart.

Effects of pethidine, acetylsalicylic acid, and indomethacin on pain and behavior in the mole-rat.

The antinociceptive and behavioral effects of pethidine (10, 20, or 30 mg/kg), acetylsalicylic acid (200, 400, or 600 mg/kg) and indomethacin (20, 40, or 50 mg/kg) in the naked mole-rat was studied in the hot-plate test. Instead of inducing analgesia, pethidine caused a dose-dependent reduction in response latency. Sensorimotor impairment and aggressive behavior were also observed following administration of pethidine (20 or 30 mg/kg). All animals receiving pethidine (30 mg/kg) died following fighting when kept in colony cages. Aggressive behavior and death was prevented by naloxone or by keeping animals in single cages. Acetylsalicylic acid (600 mg/kg) and indomethacin (40 or 50 mg/kg) caused a significant increase in response latency. It is concluded that in the mole-rat pethidine elicits aggression, sensorimotor impairment, and apparent hyperalgesia.

The formalin test in the naked mole-rat (Heterocephalus glaber): analgesic effects of morphine, nefopam and paracetamol.

The present experiments were initiated to study the effects of morphine, nefopam and paracetamol in the naked mole-rat, a hairless rodent that lives in subterranean colonies of up to 300, following the inability to demonstrate morphine analgesia in the hot-plate test in the rodent. The formalin test was used. Injection of 20 microliters 10% formalin produced two periods of high licking and pain behaviour, the early (0-5 min) and the late phase (15-60 min). Morphine (10 or 20 mg/kg), nefopam (10 or 20 mg/kg) and paracetamol (200 mg/kg) significantly inhibited the two phases. Paracetamol (400 mg/kg) produced significant analgesia only during the late phase. It is concluded that, unlike in the hot-plate test, it is possible to demonstrate the analgesic effects of morphine in the naked mole-rat, in the formalin test.