Suppression of Pars Intermedia of Pituitary Body in Hyla regilla by Operations Upon the Gastrula

Abstract

The dual character of the pituitary body and the constant association of its neural and epithelial components throughout the vertebrate sub-phylum, have raised the question of whether or not association of the components is necessary for the development of the gland. Blount (1930), Etkin (1935) and Atwell (1935, 1936) have contributed toward the solution of the problem by means of grafting experiments, performed upon tail-bud stages of early larvae of various amphibian species. This paper is a preliminary account of results obtained by means of a different attack upon the problem.

Smith (1916), Allen (1916) and Atwell (1919) have shown that hypophysectomy in the early anuran larva produces a pigmentary condition which is characterized by aggregation of the melanin granules in the melanophores, dispersion of the pigment granules of the Xantholeucophores and a general reduction of free melanin in the epidermis. Such tadpoles are silvery-white in appearance and have been described as “albino”. This pigmentary condition has been shown to prevail in the absence of the pars intermedia of the pituitary body.

It has been possible to produce the pars intermedia deficiency syndrome in tadpoles of Hyla regilla in 2 different ways, by microsurgical operations made as early as the gastrula stage.

In the first operation a small, rectangular piece of tissue, including the 3 germ layers, is removed from the presumptive medullary region, at a position approximately 95 degrees forward from the dorsal lip of the closing blastopore. This piece of tissue, the width of which is about one-fifth that of the gastrula, is turned end for end and reimplanted. Thus the lateralities of the tissue are reversed, but more important in this connection is the fact that originally anteriorly situated materials are shifted to a more posterior position and vice versa. Tadpoles derived from these gastrulæ are “albino”.

Microscopic sections of these experimental larvæ reveal that the infundibular region of the brain has been shifted to a position posterior to its normal location, and forms from the floor of the myelencephalon instead of from the diencephalon. In the course of development, the pars buccalis arrives at its definitive location, at the anterior end of the notochord, but fails to reach the infundibulum. The pars buccalis remains as a small, darkly staining, comparatively undifferentiated mass of tissue. This microscopic picture has been found in every one of 14 serially sectioned larvæ which had been picked at random from a total of 67 experimental “albinoes”.