Distal retraction balls in the neurohypophysis after transection of the pituitary stalk

During the first few weeks after transaction of the pituitary stalk retraction balls (Cajal) were found on the fibers of the hypothalamo‐neurohypophyseal nerve tract not only above but also in large numbers below the level at which the nerve tract had been cut. The latter, termed distal retraction balls, are clearly seen in routinely stained sections but are even more conspicuous after impregnation with silver. Distal retraction balls were found in the isolated neurohypophysis of man, monkey, goat and sheep. It is suggested that the development of so many retraction balls distal to the site at which the nerve tract had been severed was due largely to conditions resulting from the peculiar anatomical arrangements of the pituitary gland. Stalk section causes infarction and consequent swelling of pars distalis; this swelling, occurring in the confined space of the pituitary fossa, compresses the neurohypophysis, thereby squeezing out axoplasm from the cut ends of the isolated nerve fibers to form the distal retraction balls. Distal retraction balls were not identified with certainty in the rat, possibly because in this species the pituitary gland is not enclosed in a bony fossa, and the neurohypophysis is therefore not compressed when pars distalis swells.