The Neural Mechanism of Rectal Motility Response Induced by the Epicardial Application of Lactic Acid

The epicardial application of lactic acid induced a biphasic rectal motility response in lightly anaesthetised, open-chested and artificially ventilated cats. This rectal biphasic response is reflexogenic in nature as epicardial lignocaine abolished such response. This rectal biphasic response is abolished by cardiac sympathectomy and reprecipitated by left inferior cardiac afferent nerve stimulation. Such response is also abolished by sacral ventral rhizotomy and reproduced by stimulation of the peripheral cut end of split sacral ventral roots. This indicates that the afferent and efferent pathways for such reflex are lying in the cardiac sympathetic and sacral pelvic nerves, respectively. The higher centers involved for such reflex are lying above the mid-collicular level of the brain as decerebration at the mid-collicular level completely abolished such type of rectal response. Furthermore, the relaxation phase and contraction phase of such rectal response are mediated through nitric oxide release and cholinergic neurones, respectively, as NG-nitro-L-arginine and atropine abolished relaxation and contraction phase of the rectal response, respectively.