H. D. Dellmann

Degeneration and Regeneration of Neurosecretory Systems

Publisher Summary Degenerative and regenerative phenomena have substantially contributed to the knowledge of neurosecretory systems. The general structural organization, the degeneration, and regeneration of neurosecretory neurons, and the process of neurosecretion are identical throughout the animal kingdom. In the first phase after interruption of a neurosecretory axon, the proximal and distal stumps react identically with the development of a dense system of tubular formations and with an increase in other axoplasmic organelles conveyed to the stumps from more proximal or more distal portions of the axon. During the second phase growth, cones containing numerous tubular formations and vesicles start to sprout from the axon in the proximal stump as an initiation of regeneration. The third phase in the proximal stump leads to the progressive establishment of new axon terminals in contact with a newly developed vascular plexus; these terminals are identical to those observed in the normal neural lobe.

Herring bodies; an electron microscopic study of local degeneration and regeneration of neurosecretory axons

SummaryThe Herring bodies in the posterior lobe of the bovine hypophysis are very large (2–600 μ) and can be classified into three types. The type I Herring body contains an accumulation of neurosecretory granules. These Herring bodies are very scarce and should not be confused with the numerous, but small, axonal swellings which also contain neurosecretory granules.The type II Herring body is characterized by the presence of a varying number of normal, moderately electron dense and “empty” vesicles, autophagic vacuoles, multilamellate bodies and occasional mitochondria. These Herring bodies are frequently observed.The type III Herring body is typified by the presence of dense vesicles connected to tubular formations which contain material of variable electron density, of filaments, and of long slender and very numerous mitochondria.The presence of multilamellate bodies and autophagic vacuoles suggests that the type II Herring body is in a degenerating phase. This concept is further substantiated by the similarity between this type of Herring body and transected neurosecretory axons in which degeneration is occurring.A similar comparison suggests that the type III Herring body is undergoing a regenerative process. Our current concept of the structure and function of Herring bodies is revised in the discussion.

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.

The rostral zone of the intermediate lobe of the mouse hypophysis, a zone of particular concentration of corticotrophic cells. A light and electron microscopic study.

SummaryThe rostral zone of the intermediate lobe of the mouse hypophysis can clearly be distinguished from the other lobes of the adenohypophysis, especially from the pars tuberalis and the remainder of the intermediate lobe. It consists almost exclusively of corticotrophic cells which show reactive changes after adrenalectomy. The hypophysial stalk is entirely surrounded by this zone; laterally it forms large cell aggregations which extend dorsally as thin cell strands. The corticotrophs are also found within the hypophysial stalk which they invade along the blood vessels; frequently they are dispersed among the typical cells of the intermediate lobe, especially along the neural lobe and the hypophysial cleft.

Nematosomes or nucleolus-like bodies in hypothalamic neurons, the subfornical organ and adenohypophysial cells of the rat

SummaryFibrillar intracytoplasmic bodies, generally referred to as nematosomes or nucleolar like bodies (NLBs), are not only observed in various types of neurons in the hypothalamus and subfornical organ but also in the glandular cells of the pars tuberalis and the pars intermedia hypophyses. According to their cytochemical properties the NLBs are probably of ribonucleoprotein nature. Within the neurons NLBs occur within perikarya and processes. Their presence within the neurosecretory nerve fibers of the neural lobe proves their ability to migrate within the axon. Morphologic modifications of NLBs are observed in stimulated neurons and after colchicine treatment. Colchicine causes a characteristic dense texture of NLBs and a peripheral agglomeration of mitochondria very similar to the rosette arrangement observed in oocytes. Our findings suggest a structural and functional similarity of NLBs in neurons and oocytes, in which their nucleolar origin appears obvious and where they seem to represent preribosomal material. It is very likely that the axonal migration of the NLBs reflects transport of ribosomal RNA for delayed utilization (as in oocytes).

Investigations on the hypothalamo-neurohypophysial neurosecretory system of the grass frog (Rana pipiens) after transection of the proximal neurohypophysis

SummaryWith the onset of degeneration of the neurosecretory nerve fibers following transection of the proximal neurohypophysis, the pituicytes phagocytize these nerve fibers. Concomitant with a considerable increase in the size of the pituicytes, which reaches a peak between 8 and 10 days after the transection, the following sequence of events can be observed: reduction of the amount of intergranular axoplasm, increase in the size of some granules, partial or total loss of the electron density of the neurosecretory granules, loss of granule membranes, fusion of some granules, polymorphous axonal content in digestion vacuoles, formation of multilamellate bodies, digestion vacuoles with moderately electron dense peripheral material, empty digestion vacuoles. At about 12 days after the transection many vacuoles appear which subsequently disappear as the pituicytes shrink. Free neurosecretory granules resulting from the disappearance of the axolemma remain intact in the intercellular and perivascular connective tissue spaces and are eventually phagocytized by pituicytes and pericytes.Phagocytosis is considered to be a basic function of pituicytes. The problems related to this function as well as the possible implications for the interpretation of Herring bodies are discussed.

A light and electron microscopic study of the pre- and postnatal development and secretory differentiation of the pars tuberalis of the rat hypophysis

SummaryThe development of the pars tuberalis was studied in the rat fetus from 13 days of gestation to 6 weeks after birth. After the closure of Rathkes pouch, the pars tuberalis anlage is clearly distinguishable from the anlagen of the partes intermedia and distalis. It comprises the entire basal portion of the adenohypophysial anlage; the limit between the anlagen of the pars tuberalis and the pars distalis is defined by Atwells recess, i.e. the pathway taken by the hypophysial vessels coming from the vascular plexus of the median eminence.At 14 days the pars tuberalis cells are characterized by the presence of glycogen which persists in the adult. Their secretory differentiation (elaboration of granules with a diameter of 100–120 nm) is obvious at 15 days of gestation. It therefore, clearly precedes that of the other hypophysial cell types. Its functional differentiation takes place well before its adhesion to the primary vascular plexus of the portal system. Cystic formations appear just before birth in the pars tuberalis, much later than those of the pars distalis.These observations on the development of the pars tuberalis, together with previous observations on the adult PT in various species, showing that the specific glandular cells of the pars tuberalis are cytologically different from all known adenohypophysial cell types, seem to indicate a specific endocrine function of this lobe.

Ultrastructure and hormonal content of the proximal stump of the transected hypothalamo-hypophysial tract of the frog (Rana pipiens)

SummarySeveral types of neurosecretory fibers were observed in the normal infundibulum of the frog. After transection of the median eminence, these neurosecretory fibers of the proximal stump reacted asynchronously, but followed approximately the same pattern: a “passive accumulation” of granules observed early after the transection was followed by an “active axonal reaction” with the appearance of numerous tubular formations which are thought to be related to the Golgi apparatus. They filled the axon almost completely, and then became dilated and filled with an electron dense material. Subsequently these dilatations pinched off and gave origin to new neurosecretory granules. These locally packed granules plus others which were probably formed in more proximal parts of the axon, and the perikaryon and then transported distally, accumulated in the proximal axonal stumps and started to fill the fibers retrogradely.There was a parallelism between the increase of tubular formations and neurosecretory granules larger then 1,500 Å in diameter, on one side, and the vasopressor activity of the proximal stump, on the other. The latter increased at an approximate rate of 1 mU/stump/day.The regeneration of the fibers of the hypothalamo-median eminence system is suggested by the presence in the proximal stump of fibers filled with granules smaller than 1,000 Å in diameter (normally seen in the median eminence) and the fact that 40% of the vasopressor activity of the extracts was not abolished by the thioglycollate treatment, which could be due to the presence of vasopressor amines other than adrenaline. The appearance towards the end of the observation period of a few “nerve endings” of several types contacting the perivascular basement membrane of vessels of the proximal stump would indicate that the neural lobe and median eminence functions were being reestablished, at least partially.

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