Ependym und Circumventriculäre Organe

Publisher Summary Of the whole nervous system, the peripheral nerves are normally by far the richest in mast cells. Mast cells are also present in other parts of the nervous system containing connective tissue, e.g., meninges, choroid plexus, and area postrema, while other parts-except the pineal body, hypophysis, and the thalamus-are practically void of such cells. There is abundant evidence that the mast cells in the nervous system, like those in other parts of the organism, contain heparin and that they are able to synthesize, store, and, under certain conditions, release biogenic amines. This chapter focuses on the distribution and the properties of mast cells in peripheral nerves and their reaction, and also on possible pathophysiological significance in peripheral nerve lesions. In certain lesions of the peripheral nerves the mast cells are degranulated with consequent release of their products, which may in turn affect the development of other accompanying tissue changes. Thus, it is likely that biogenic amines released from mast cells can influence the permeability of the vasa nervorum and thereby contribute to the development of edema accompanying certain injuries to peripheral nerves. Products released from mast cells in injured peripheral nerves may also be involved in other processes characteristic of degenerating nerves. The heparin component of the mast cells may play a role in the enzymic breakdown of lipids in the myelin sheaths.

Mast cells in the nervous system.

The study of the pineal organ now excites various scientific communities, among them endocrinologists, neuropharmacologists, and neurochemists. The very high concentrations of biogenic amines in the mammalian pineal, as well as its extensive and easily accessible autonomic innervation, make this organ a useful experimental model for studying monoamine biochemistry, the actions of various pharmacological agents, and the endogenous and exogenous controls on the sympathetic nervous system. In addition, after decades of contradictory results, experimental paradigms have finally been developed which provide compelling evidence that secretions of the mammalian pineal organ physiologically control several neuroendocrine functions, principally involving the anterior pituitary gland and its peripheral “target organs.”

The Pineal Organ

This survey is based on selected data from the large literature as well as on own observations and discusses aspects of pineal phylogenetic and ontogenetic development, the fine structure of the mammalian pineal, its biochemistry and physiology. The author has been trying to integrate data, to stress the structural, biochemical and functional specificity of the organ, and to point to problems which should be further investigated. He has not been shy of one or two, perhaps fruitful, speculations.

The Mammalian Pineal Organ

Publisher Summary This chapter gives general introduction surveying the essentials of mammalian pineal structure, innervation, biochemistry, and function. On morphological grounds, the mammalian pineal can be considered an endocrine organ. From a functional standpoint, however, the chapter hesitates to consider the mammalian pineal to be an endocrine organ in the classical sense, because till now, there is not a single pineal compound fulfilling all of the criteria of a pineal hormone, for example, a pineal substance being produced in the gland and having a specific functional influence on a specific target organ. The mammalian pineal is composed of strings of cells, often showing a pseudofollicular arrangement between these strings, connective tissue strands are present containing arterioles and venules. The parenchymal cell cords consist of pineal-specific cell elements, the pinealocytes. Most of their perikarya show, for example, a nucleus which is often lobulated, many mitochondria, rough and smooth endoplasmic reticulum and a well-developed Golgi apparatus producing dense-core and lucent vesicles.

The mammalian pineal gland and its control of hypothalamic activity

The number and distribution of mast cells were studied in pineal bodies of 16 mammalian species. In cattle, goat, monkey and guinea-pig the cells occurred in large numbers; in man, sheep, marmoset and mouse there was a moderate amount, and they were almost absent in pineal bodies of horse, rat, pig, dog, hamster, fox, cat and rabbit. In 17 human pineal bodies, 11 of which were obtained from normal individuals, the mast cell population was 3 ± 0.5 mast cells per microscopical field (0.32 mm in diameter). The histamine content in pineal bodies of several mammals was also determined. The substance occurred in high amount in the pineal body of cattle, in moderate amount in that of goat, man and sheep, and could not be detected in horse, pig, rabbit and rat. In human and cattle pineal bodies the histamine content could be correlated to the mast cell population; in other species the same correlation was only suggested. In in vitro experiments octylamine released histamine from the pineal body of cattle, while compound 48/80 was ineffective. It is suggested that the hypotensive action of pineal extract reported by several authors might be due to the histamine content of this gland.

Luiz Carlos M. Faleiro

Papers

Study of mast cell and histamine contents of the pineal body.