| Abstrakt: |
The ultrastructure of normal neural lobes of adult rabbits is described. The major part consists of non-myelinated fibres containing neural swellings at intervals. These enclose the neurosecretory granules, mitochondria and a few microtubules. The swellings are connected by narrow nerve fibres with parallel neurotubules but no granules. The Herring bodies resemble large neural swellings and may contain many neurotubules. They are sometimes enclosed by multilamellate sheaths. True myelinated nerve fibres full of granules also occur. The relationship between the neural swellings and pituicytes is discussed. The pituicyte cytoplasm contains many delicate fibrils but it does not resemble an active secretory cell. The blood vessels are characterised by an unusually wide perivascular space containing two condensed layers of basement membrane. These layers can be traced into channels which extend from the perivascular spaces and break up the tissue into lobules. It is suggested that these channels form a mucopolysaccharide spongework that may be important in relation to the release of hormones. The common feature of ether-treated, dehydrated and immature animals is the absence of electron-dense cores from the neurosecretory granules. Such glands are not completely depleted of hormones and much of the hormonal activity is still associated with a sedimentable fraction. Loss of electron density may be due to diffusion of the neurophysin carrier or to a change in configuration of the neurophysin molecules resulting in inaccessibility of both osmiophilic and hormone binding sites. The unbound hormone may be stored in the mucopolysaccharide sponge-work and released gradually into the blood stream. [ABSTRACT FROM AUTHOR] |
