The innervation of the vas deferens of the guinea-pig.

1. The compound action potential of the hypogastric nerve of the guinea-pig contained two main elevations. The low-threshold fibres had a range of conduction velocities from 1.5 to 10 m/sec. The high threshold fibres conducted action potentials at less than 1 m/sec. The hypogastric nerve contained small myelinated fibres and non-myelinated fibres.2. In the preparation in vitro, junctional potentials and contractions were elicited by stimulation of the rapidly conducting fibres alone. Trains of C fibre volleys were ineffective.3. In the preparation in vivo, conduction from the hypogastric nerve to the vas deferens nerve was unidirectional and abolished by hexamethonium. After the administration of hexamethonium, the contraction produced by stimulation of the vas deferens nerve was unaffected.4. The close arterial injection of acetylcholine (ACh) into the pelvic viscera caused centrifugal activity in the motor fibres of the vas deferens nerve, but no impulses were detected in the hypogastric nerve.5. Ganglion cells are present in the last 2 cm of the hypogastric nerve.6. It is concluded that there is a ganglionic relay between the hypogastric and vas deferens nerves.