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

Summary The Herring bodies in the posterior lobe of the bovine hypophysis are very large (2–600 ) 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.This work was supported by grants 5 RO1 NB 06641 NEUA and 5 R0107492 NEUA from the National Institutes of Health and the Space Sciences Research Center of the University of Missouri. The technical assistance of Mrs. G. Clark and Mr. R. Faup, and the clerical assistance of Mrs. S. Schmidt are gratefully acknowledged.Fellow of the Conséjo National de Investigaciones Científicas y Tecnicas de la República Argentína.     

Ultrastructure of the neurohaemal region of the toad median eminence

Summary According to the internal structure and size of the granules, six types of nerve endings can be distinguished in the toad median eminence: 1. Endings containing mostly dense granules of 600 Å in diameter; 2. Endings containing dense granules of about 800 Å in diameter; 3. Endings which contain dense granules 1,000–2,000 Å in diameter, with the peak at 1,200–1,400 Å; 4. Endings containing granules with a characteristic structure, which differentiate them from the other three types; 5. Scarce endings containing granules 2,000 to 3,800 Å in diameter; and 6. Endings containing only vesicles 400–500 Å in diameter. Types 3 and 4 endings are mainly found in the outer pericapillary zone, and are probably responsible for the strong Gomori-positive reaction observed in this zone. The other four types of endings occur mainly in the inner pericapillary zone, and appear to be Gomori-negative.The probable origins of the different types of endings, and their possible relations with the different releasing factors is discussed.The subendothelial basement membrane has numerous long processes which form a complicated network in contact with all the nerve endings, some nerve fibres and glial cells.Two types of glial cells are described. Pinocytotic vesicles are frequently seen at the points where these cells contact the basement membrane. All the ultrastructural features suggest that these cells are carrying out transport functions.Fellow of the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina.The author is very grateful to Professor H. Heller for his continued encouragement and criticism and to Mr. J. Lane and Mr. P. Heap for their valuable help.     

Ca requirement for aerobic nitrogen fixation by heterocystous blue-green algae

The requirement of Ca²⁺ for growth and nitrogen fixation has been investigated in two strains of heterocystous blue-green algae (Anabaena sp. and Anabaena ATCC 33047). With combined nitrogen (nitrate or ammonium) or with N₂ under microaerobic conditions, Ca²⁺ was not required for growth, at least in concentrations greater than traces. In contrast, Ca²⁺ was required as a macronutrient for growth and nitrogen fixation with air as the nitrogen source. Addition of Ca²⁺ to an aerobic culture without Ca²⁺ promoted, after a lag of several hours, development of nitrogenase activity and cell growth. Provision of air to a microaerobic culture in the absence of Ca²⁺ promoted a drastic drop in nitrogenase activity, which rapidly recovered its initial level upon restoration of microaerobic conditions. Development of nitrogenase activity in response to either Ca²⁺ or low oxygen tension was dependent on de novo protein synthesis. The role of Ca²⁺ seems to be related to protection of nitrogenase from inactivation, by conferring heterocysts resistance to oxygen.     

3-Hydroxypropyl amide formation from 1-aminocyclopropane-1-carboxylic acid by a cell-free ethylene-forming system from olive leaves

The low ethylene yield in a cell-free ethylene-forming system from olive tree leaves ( Olea europaea L. cv. Picual) was investigated. During the incubation, 1-aminocyclopropane-1-carboxylic acid (ACC) was extensively transformed into 3-hydroxypropyl amide (HPA). Enzyme extract, Mn²⁺ and oxygen are responsible for this reaction. Horseradish peroxidase (EC 1.11.1.7) can substitute for the enzyme extract in this reaction. HPA formation could be one reason for the poor in vitro conversion efficiency of ACC to ethylene.