Pregnancy Following Bilateral Section of the Cervical Sympathetic Trunks in the Rabbit. ∗

The ovulation which follows coitus is known to depend upon the activity of the anterior lobe of the hypophysis. This activity must depend upon the central nervous system. However, at the nresent time the efferent pathway to the anterior lobe of the hvooohysis is only a matter of conjecture as to whether it is direct or indirect. The tractus supraoptico-hypophyseus passes from the nucleus supraopticus to the posterior lobe (Greving 1 ). The only innervation which is known for the anterior lobe is from the carotid plexus. If the pathway from the central nervous system to the anterior lobe of the hypophysis is a direct one, it is conceivable that it may pass to it by way of the carotid plexus. Cannon and his coworkers 2 showed in one cat that conception and delivery could take place following complete removal of the thoracolumbar sympathetic outflow from the central nervous system.

In a series of 8 adult rabbits which had been isolated for 3 weeks, the cervical sympathetic trunk was sectioned bilaterally below the superior cervical sympathetic ganglion. In one of the animals, the superior cervical sympathetic ganglion was removed bilaterally. The animals were bred about one week after the operation. Each of them became pregnant and delivered an average litter of 7 plus young. Autopsies were done to control the operations. The observations show that the pathway through the superior cervical sympathetic ganglion is not essential for ovulation in the rabbit. While the possibility must be recognized that there may be some slight contribution to the carotid plexus from the other cervical sympathetic ganglia, by far the greatest portion of this plexus is derived from the superior ganglion.

When this evidence in the rabbit is combined with that of Cannon in the cat, it seems that there are only 2 other possibilities for efferent pathways to the anterior lobe of the hypophysis: either there are contributions to the carotid plexus from cranial nerves such as Cobb and Finesinger 3 and Chorobski and Penfield 4 have described from the greater superficial petrosal nerve or the pathways from the hypothalamus must activate the posterior lobe of the hypophysis which in turn may exert an influence on the anterior lobe by hormonal transmission.