F. Stutinsky

A comparative ultrastructural study of the pars tuberalis of various mammals, the chicken and the newt

SummaryThe pars tuberalis of the rat, mouse, garden door mouse, European hamster, cat, cattle, chicken and newt is composed of two main cell types: specific secretory cells and follicular cells. The specific cells are characterized by comparable morphologic features in the investigated species, despite differences in the diameter of the secretory granulated vesicles; the ultrastructural morphology of these cells is different from that of any of the known cell types of the adenohypophysis. The follicular cells are devoid of secretory granules, they do not only line the numerous follicular cavities of the pars tuberalis but may also be found in the periphery of the cell cords (border cells). In addition, gonadotrophic cells are found; they predominate in the distal portion of the pars tuberalis and are definitely activated by castration or hypophysectomy. Experimental interventions on most of the major endocrine systems did not cause any noticeable ultrastructural changes in the specific cells. It appears certain that the pars tuberalis secretes a specific hormone whose function remains to be determined.

Colchicine effects on neurosecretory neurons and other hypothalamic and hypophysial cells, with special reference to changes in the cytoplasmic membranes

SummaryThe morphological effects of colchicine on the entire neurosecretory (NS) tract and on various hypothalamic nuclei have been studied. The perturbation in axonal flow, indicated by the accumulation of NS material, coincide with fragmentation of the cytoplasmic membranes, i. e. the Golgi apparatus and the endoplasmic reticulum, whereas the neurotubules remain relatively well preserved. Autophagic destruction of NS material is observed along the entire length of the NS fibres. The rapid and systematic changes in the axoplasmic reticulum, known to store calcium, lead us to envisage a role for this system — similar to that of the sarcoplasmic reticulum — in controlling the transport of NS vesicles. The junctional zone between the stalk and the neural lobe seems to play a particular rôle in the transport of NS material to the posthypophysial terminals of the NS axons. Colchicine provokes an increase in dense-cored vesicles in most of the neurons of the other hypothalamic nuclei studied: arcuate, suprachiasmatic, periventricular and ventromedial. Membranous alterations are also observed in these sites. Colchicine administered to animals which were hypothyroid, castrated or adrenalectomized, reveals stimulated neurons, identified by their excessive content of dense-cored vesicles. These neurons display no specific localization, for they occur in all hypothalamic nuclei, irrespective of the stimulation. The frequency of stimulation of neurons of the periventricular nucleus is striking.

Corticotrophic cells in the rostral zone of the pars intermedia and in the adjacent neurohypophysis of the rat and mouse

SummaryIn the mouse, the rostral zone of the pars intermedia is almost exclusively composed of typical corticotrophic cells. They are located around and even within the neural stalk, at the level of transition between stalk and neural lobe. In the rat, the corticotrophic cells of the rostral zone are found in scattered islets among the MSH producing cells, and also in the neural lobe. In both the rat and mouse, these cells are in direct contact with various types of nerve terminals. Synaptoid contacts with aminergic and neurosecretory nerve fibers are observed. Furthermore they are also closely related to the hypophysial portal vessels. Following adrenalectomy, the cells located in the neurohypophysis always react more intensely than tose in the rostral zone. The functional significance of these corticotrophic cells which are subject to both humoral and neural regulation remains as yet hypothetical. Their participation in neurogenic stress response seems probable.

Herring Bodies Reexamined: An Ultrastructural Experimental Investigation of the Rat Neural Lobe1,2

In 1970 (a), DELLMANN/RODRIGUEZ gave a detailed account of the ultrastructure of mammalian Herring bodies and subdivided them into three main types. Type I Herring bodies are characterized by the presence of numerous neurosecretory granulated vesicles and a few mitochondria, Type I1 Herring bodies contain many dense lamellar bodies, a very extensive axoplasmic reticulum and only a few neurosecretory granulated vesicles, and Type I11 Herring bodies possess a still more extensive axoplasmic reticulum together with numerous mitochondria and a varying number of neurosecretory granulated vesicles. Based upon these morphologic characteristics it was hypothesized that Type I Herring bodies are nothing else but an accumulation of neurosecretory granulated vesicles, the excess of which is being disposed of through a process of involution in the Type I1 Herring bodies, (in 1970 the term degeneration was used to characterize localized catabolic events which usually do not entail interruption of the axonal continuity: see conclusions) followed by restitutional events in the Type I11 Herring bodies. As the first part of this hypothesis was based upon the observed similarity between the morphologic pictures of degenerating amphibian neurosecretory axons (DELLMANN/RODRIGUEZ, 1970 b) and Type I1 Herring bodies, i t was felt that an investigation of degenerating mammalian neurosecretory axons might