Central Glutaminergic Influences on Viscero-visceral Inhibitory Reflex During Colonal Descending Distension in Ovine Model

Abstract

The aim of presented study was to examine the participation of group I metabotropic glutamate receptors (mGluRs) in development and maintenence reticulo-ruminal motility inhibition caused by visceral pain caused by colonic distension (CD) of different degrees provoked in ovine. Motility inhibition was qualified as a vegetative symptom of the nocifensive effects (viscero-visceral inhibitory reflex). The experiment was carried out on 12 female sheep, Polish merino, in the anoestrus period. A five min CD episode provokes a statistically significant reticulo-ruminal motility inhibition. Intracerebroventriculary (i.c.v.) administration of the group I mGluRs antagonist DL-AP3 10 min prior to CD, prevents the visceral pain development. Practically all pain symptoms were easy to observe and quantify. These symptoms were recurrently appearing in animals suffering colon distension; however, the intensity was smaller than in the case of duodenal distension. It suggests that this model of colic is not only less invasive but also less painful for animals. In conclusion, the development and maintenance of reticulo-ruminal motor inhibition of colonic distension are dependent on group I mGluRs receptor activation in the CNS and that these receptors play a crucial role in modulating the acute colonic pain (experimental colic). This less invasive in vivo method may be useful for testing the efficacy of potentially analgesic xenobiotics in small ruminants.