Non-ganglionic cholinergic excitatory pathways in the sympathetic supply to the feline stomach. An efferent system or afferents with excitatory axon collaterals?
Experiments were performed on chloralosed, adrenalectomized cats, paralysed with gallamine and artificially ventilated. Gastric motility was recorded by the balloon method. Efferent stimulation of the cut greater splanchnic nerve, well proximal to the celiac ganglion, could either increase or decrease gastric tone. The excitatory responses called for higher stimulation intensities than the inhibitory ones but were as a rule observed at lower frequencies only (1-4 Hz). They could be abolished by atropine but were not prevented by bilateral vagotomy, hexamethonium nor guanethidine. The latter two drugs rather reversed inhibitory responses to excitatory ones which exhibited a hyperbolic frequency-response relationship with maximal effects already at 2-4 Hz. Heating of a nerve trunk selectively activates thin afferents of the delta group and C-class. Heating of the greater splanchnic nerve caused an increase in gastric motility which, like that caused by electric stimulation, was not prevented by hexamethonium nor guanethidine; nor was it eliminated by cutting the nerve centrally, nor by vagotomy, while it was abolished by atropine. These results suggest that the excitatory gastric responses to efferent splanchnic nerve stimulation are due to antidromic activation of thin afferent fibres. Their functional significance remains obscure but their peripheral arborizations may convey 'axon reflexes' influencing gastrointestinal motility.