Scanning and transmission electron microscopy of the subfornical organ of the grass frog (Rana pipiens)

Summary The ventricular surface of the subfornical organ of the frog is made up of ependymal cells with numerous apical microvilli, occasional cytoplasmic protrusions and many vacuoles projecting into the lumen of the third ventricle. Between these cells dendrites of cerebrospinal fluid-contacting neurons reach the ventricle to terminate in bulbous enlargements. In addition, flask-shaped encephalo-chromaffin cells, containing granulated vesicles and aggregates of filaments in their cytoplasm, project into the cerebrospinal fluid. Surrounding the centrally located capillaries are enlarged dendrites and axons of heterogeneous morphology, some of which appear to originate within the subfornical organ, intermingled with dendrites and axons of normal structure. The glial cells in this region, especially the microglial cells, often contain large lipofuscin inclusions, suggestive of degeneration and subsequent phagocytosis of some of the enlarged dendrites and axons. The normally scarce neurosecretory peptidergic axons become more evident and form typical Herring bodies in stalk-transected animals. Neuronal perikarya of varying morphology are predominantly located peripheral to the region of enlarged dendrites and axons. Supraependymal macrophages are particularly numerous on the subfornical organ.Abbreviations used CSF cerebrospinal fluid - SEM scanning electron microscope, scanning electron microscopy - SFO subfornical organ - TEM transmission electron microscope, transmission electron microscopy Supported, in part, by NIH grant NB 07492The skillful technical assistance of J.G. Linner and the secretarial assistance of Ann Gerdom are gratefully acknowledged. The SEM studies were made possible through a grant from the Graduate College of Iowa State University and the use of the SEM facility in the Department of Botany     

Plasma immunoreactive calcitonin in the frog (Rana pipiens)

1. Plasma immunoreactive calcitonin (iCT) and ionic calcium [( Ca]i) were measured in intact frogs (Rana pipiens) within complete 24 hr light-dark cycles over an 18 month period. 2. Plasma iCT exhibits an annual periodicity about the annual mean of 10.0 ng/ml, with an amplitude of 5.4 ng/ml that peaks in October. 3. Within an annual cycle, a significant inverse association exists between the basal monthly levels of plasma iCT and [Ca]i for animals maintained in freshwater control conditions. 4. When subjected to a high calcium environment during the latter half of the year, plasma [Ca]i and iCT were elevated above control levels but exhibited independent cyclic patterns. 5. A distinct seasonal response of increased iCT in a high calcium environment may be related to the secretory activity of the ultimobranchial glands and physiological responsiveness to other calcemic hormones; e.g. parathyroid hormone and vitamin D.     

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

Summary Several 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.This investigation was supported by grants 5RO1 NB 06641 NEUA and 5RO1 NB 07492 NEUA from the National Institute of Health and by the Space Sciences Research Center of the University of Missouri. The authors wish to thank Mrs. G. Clark, Mr. G. Ribas and Mr. R. Faup for their valuable technical help.Fellow of the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina.     

Ultrastructure of the developing thymus of the leopard frog (Rana pipiens)

Summary A study of the ultrastructure of the developing thymus of the leopard frog (Rana pipiens) revealed that the thymus had undergone all of the major changes which would persist through larval life and metamorphosis by the time that the animals had reached larval stage IV of Taylor and Kollros (1946). These changes included development of an outer, lymphoid cortical region and an inner, essentially nonlymphoid medulla; mitotic activity among lymphoid cell precursors and the formation of the first small lymphocytes; development of complex cysts containing PAS-positive material and the appearance of other signs of secretory activity among epithelial cells of the medulla; and differentiation of large myoid cells containing bundles of striated muscle fibrils. The changes are particularly noteworthy because they first appear during a period in which the animals are known to be developing the capacity to respond immunologically to allografts.Supported by a grant from the National Institutes of Health number GM-11782 to E.P.V.     

A light and electron microscopic study of the preoptic nucleus of the grass frog (Rana pipiens), under normal conditions and following transection of the preoptico-neurohypophysial tract

Degenerative and regenerative processes occur in the preoptic neurons following transection of the preoptico-neurohypophysial tract. Three types of responses after transection were observed: affected, recovered, and degenerated neurons. However, transection of the tract did not stop the synthesis of neurosecretory granulated vesicles. The affected neurosecretory neurons showed nuclear changes, increased number of Golgi complexes, and dilated cisternae of rER, as well as, an increased number of dense bodies. The recovered neurosecretory neurons contained long non-dilated cisternae of rER which were organized in a concentric manner. Also seen were large nuclei with evenly distributed chromatin, less active Golgi complexes, and vesicles. The degenerated neurosecretory neurons exhibit pyknotic nuclei, a net of dilated cisternae of rER, dense bodies, and electron dense cytoplasm.     

NAG infection of grass frog (Rana temporaria) tadpoles]

Rana temporaria tadpoles (2250) were contaminated with three types of NAG vibrio cultures. Clinical, bacteriological and morphological examinations showed the larvae to be suffering from an acute infection during the first 2 days after the contamination. Then the vibrios persisted in the tadpole organism for a long time and were excreted in the feces.     

The germfree leopard frog (Rana pipiens): preliminary report.

Eggs and sperm were aseptically collected from leopard frogs (Rana pipiens) and passed into sterilized flexible film isolators. Egg fertilization was accomplished, and germfree tadpoles were produced. The germfree tadpoles were active and free-swimming for 3 weeks, but only 6.2% survived to 4 weeks of age. None survived after the 4th week.     

Ontogeny of B cells expressing IgM in embryonic and larval tissues of the American grass frog, Rana pipiens

Affinity-purified, fluorochrome-tagged F(ab')(2) antibody fragments specific for heavy (mu) chains of Rana pipiens IgM were prepared from hyperimmune rabbit sera. By using two-color immunofluorescent procedures we observed that (1) the first cells expressing IgM, termed pre-B cells, lack detectable quantities of membrane or surface IgM but contain detectable quantities of cytoplasmic IgM (smu(-)/cmu(+)), (2) sIgM(+) B cells were the second type of IgM containing cell to appear in development, and (3) plasma cells, which contain copious quantities of cIgM, were the final phenotype to appear in the development of B cells expressing IgM. These cells were first observed in the pronephros of the developing urogenital system. Shortly after their appearance in the pronephros, cells in B lineages were observed in the liver. These observations (1) are consistent with recent studies of B lymphopoiesis in the aorta-gonad-mesonephros (AGM) region in endothermic vertebrates, including mice, (2) suggest that there are fundamental ontogenetic and phylogenetic similarities between cells and tissues of developing vertebrate immune systems, and (3) evoke questions concerning the possible function(s) of lymphocytes in developing anurans up to metamorphosis and beyond.