Pharmacological evidence supporting a role for IL-1, IL-2 and serotonin in the inflammation induced by Schistosoma mansoni soluble egg antigen (SEA) in rat paws

Ketamine-xylazine anaesthesia and orofacial administration of substance P: A lethal combination in rats

BACKGROUND AND AIMS

Ketamine+xylazine mixture is a widely used anaesthetic in animal experiments. In rats anaesthetized with this mixture, we have shown that injection of carrageenan, a standard proinflammatory stimulus, into the cheek (intra-oral injection) induced oedema. A likely mediator of this oedema is substance P (SP), a major transmitter of sensory nerves in orofacial tissue. We have assessed the effects of intra-oral injection of SP in rats.

EXPERIMENTAL APPROACH

SP (50-1μg per rat) was injected intra-orally in male adult Holtzman or Wistar rats, anaesthetized with ketamine+xylazine. For comparison, histamine (50μg) and 5-HT (5μg) were similarly injected. Antagonists of SP (SR140333, 2mg/kg), of histamine (pyrilamine, 2mg/kg) or of 5-HT (pizotifen, 2mg/kg) were subcutaneously (s.c.) injected, 30min before the corresponding agonist. Oedema in the cheek was assessed by measuring tissue thickness with calipers.

RESULTS

Intra-oral injection of SP (1-50μg per rat) in Holtzman or Wistar rats anaesthetized with ketamine+xylazine induced, dose-dependently, death within 15min, accompanied by signs of excessive salivation. Rats pretreated with SR140333 were protected against SP-induced lethality and the excessive salivation. However, intra-oral injection of either histamine or 5-HT did not induce death, only a characteristic cheek oedema. These doses of SP injected into the hindpaws of conscious Holtzman and Wistar rats only induced oedema with no deaths. In rats anaesthetized with inhaled isoflurane, intra-oral SP (50μg) induced only cheek oedema, with no deaths or excessive salivation. This oedema was prevented by pre-treating rats with SR140333, pyrilamine and pizotifen.

CONCLUSION

It is likely that the deaths were due to excessive salivation induced by the particular combination of ketamine and SP. Our results are presented as a warning to other experimenters who might use these two otherwise non-toxic conditions and the consequent unexpected and needless loss of experimental animals.

Tissue-selective inflammation in the oral cavity of the rat

In the current study, carrageenan (CG; 100-1000 μg/site) was injected intraorally in the cheeks of Holtzman or Wistar rats to evaluate the consequences of administration of a non-immunogenic stimulus in the orofacial region. Subsequent inflammation was measured as oedema (increased thickness of the cheek wall using digital calipers), relative to the other cheek injected with saline. Oedema formation and tissue collection for histopathological studies were assessed at 0.5, 1, 2, 3, 4, 6, 24, 48, 72, 96, 120 and 144 h after injection. In parallel, other groups of rats were injected with CG in the hind paw, to provide a reference response. The inhibitor of prostaglandin biosynthesis, indomethacin, and antagonists of histamine, serotonin and NK1 receptors were injected s.c., 0.5 h before CG. CG induced a dose-related oedema more rapidly from 0 to 2 h which lasted for at least 72 h, showing a biphasic profile (peak at 2 and 24 h), compared with the monophasic oedema induced in rat paws (maximal duration of 24 h). Histopathological analysis of the CG-injected cheek revealed oedema formation with little leukocyte recruitment at 1-3 h, mast cell degranulation at 6 h, and a mixed polymorphonuclear and mononuclear cell infiltrate by 24 h. Histamine and serotonin antagonists and indomethacin, but not the NK1 antagonist, decreased cheek oedema in the first 4 h following carrageenan. Taken together, our data indicated important differences in the pattern of inflammation between the oral cavity and the paw which will determine the therapeutic approach to the treatment of inflammatory conditions in the oral cavity.