Synaptic transmission in the superior cervical ganglion of the cat after reinnervation by vagus fibres.

1. A vagus-sympathetic anastomosis was performed in the cat by connecting end to end the cranial trunk of the vagus to the cranial end of the cervical sympathetic trunk, both severed under the ganglia.2. Forty to sixty days after the anastomosis, the ocular signs of sympathetic paralysis (such as myosis and prolapse of the nictitating membrane) which had developed shortly after the operation, had completely disappeared, thus suggesting the recovery of synaptic transmission in the ganglion. In case of plain preganglionic denervation after the same period the ocular signs of cervical sympathetic paralysis were still present.3. Contraction of the nictitating membrane could be induced by electrical stimulation of both the vagus preanastomotic and the sympathetic postanastomotic-preganglionic trunks. Ganglionic blocking agents induced the blockade of the ;new' ganglionic synaptic function, while nicotine and pilocarpine provoked a marked contraction of the nictitating membrane.4. Electron microscopy showed that the preganglionic regeneration of vagus fibers resulted in the formation of new synapses, mainly of axodendritic type, identical to normal ganglionic synapses. Moreover, after cutting the preanastomotic trunk of the vagus, these new ganglionic presynaptic profiles degenerated, thus proving their vagal origin.5. During restoration of the synaptic contacts readjustment of dendritic tips occurred.