Involvement of nicotinic and muscarinic receptors in synaptic transmission in cat superior cervical ganglions reinnervated by vagal primary afferent axons.

Artificial synapses were established in the superior cervical ganglion reinnervated by vagal afferent fibers by heterologous cross-anastomosis between the cranial end of nodose ganglion and the caudal end of superior cervical ganglion in cats. Formation of functional synapses was evidenced by unilateral mydriasis and contraction of the nictitating membrane in response to inflation of the stomach with a balloon or to electrical stimulation of the afferent vagus. Electron microscopic findings indicated that the vagal afferent fibers terminated in the superior cervical ganglion after cross-anastomosis. In the superior cervical ganglion reinnervated by the afferent vagus, activities of choline acetyltransferase and cholinesterase were higher than those in the preganglionically denervated ganglion, but lower than those in the sympathetic preganglionically reinnervated ganglion. Contractions of the nictitating membrane and postganglionic action potentials evoked by electrical stimulation of the vagal artificial preganglionic trunk in the cross-anastomosed ganglion were blocked by treatment with tetraethylammonium and also with atropine. Atropine did not affect these responses in the normal and the preganglionically reinnervated ganglion, except at an early stage after operation. Comparisons of pharmacological properties in normal, anastomosed, preganglionically denervated and reinnervated ganglia indicated that activation of muscarinic receptors in the anastomosed ganglia is probably not secondary to an incomplete nerve supply, but may be dependent on the nature of the nonmyelinated vagal afferent fibers. The possibility that the transmitter involved may be acetylcholine is discussed.