Developmental Relationship Between Pars Intermedia of Pituitary and Brain in Tadpoles

Abstract

An inhibitory control of the growth and functional activity of the pars intermedia of the hypophysis of the tadpole through the in-fundibulum has been suggested by the author to account for the finding of overgrowth and excess activity of this gland in grafts, and after infundibular lesion. In his careful work with pituitary grafts in the salamander, however, Blount reported an intensity of pigmentation only in proportion to the number of grafts and no overgrowth in the grafts. Since in Blount's work successful grafts were secured only when brain was transplanted with the gland, whereas in this author's work with tadpoles the graft took successfully independently of the presence of brain it was thought that the circumstance of the presence of brain with the primordial graft might account for the difference in the characteristic growth picture of the graft in these two cases. This theory would be consistent with the first mentioned hypothesis of inhibitory control of the p. intermedia through the infundibulum. To test this, a series of grafts of the pituitary was made with and without brain. The experiment was performed on Rana pipiens tadpoles. The hosts were tadpoles which had been hypophysectomized in the tail-bud stage and used when about 12 mm total length. Only silver (successfully hypophysectomized) animals were used. The site for the implant was prepared by removing the eyeball through a slit in the dorsal skin, thus leaving a relatively large pocket for the reception of the graft. The grafts were taken from tail-bud embryos. In one series the pituitary primordium with as little adherent tissue as possible was used, and in the second series a variable amount of adjacent brain material was included with each graft.