G.H. Bourne

Perineural Epithelium: A New Concept of its Role in the Integrity of the Peripheral Nervous System

A multilayered, squamous-celled epithelial cell membrane covering the individual nerve fasciculi of the entire peripheral nervous system ( both voluntary and autonomic) including the sensory and motor end organs has been demonstrated in various species of animals, including man. This membrane is the direct continuation of the pia-arachnoid mater from the central nervous system.Functional significance of this membrane, especially as a diffusion barrier and as a protector of the peripheral nervous system, is briefly discussed.

ULTRASTRUCTURAL STUDIES ON DEVELOPING OOCYTES OF THE SALAMANDER TRITURUS VIRIDESCENS. I. THE RELATIONSHIP BETWEEN FOLLICLE CELLS AND DEVELOPING OOCYTES.

In young oocytes (100–200 μ in diameter) the plasma membrane is smooth and in contact with those of the enveloping follicle cells. As the oocytes develop they become separated from the follicle cells, and the plasma membrane develops microvilli that project into the space between the oocyte and the follicle cells. This space is the zona radiata. Processes from the follicle cells, fewer in number than the microvilli, are also formed and interdigitate with the microvilli. Intrecellular spaces which connect with the zona radiata and theca folliculi are found between the follicle cells. At the same time, an electron dense homogeneous material, in which the microvilli are embedded, is formed between the follicle cells and the oocyte. This material is destined to become the vitelline membrane. The microvilli reach a maximum length of 2.0–2.2 μ at an oocyte diameter of 650–750 μ . Subsequently the microvilli withdraw from the presumptive vitelline membrane and the oocyte plasma membrane is thrown into hillocks and valleys, thus forming a perivitelline space. These observations are discussed with respect to the nutrition of the oocyte and the role of the follicle cells and oocyte in the formation of the vitelline membrane.

Histochemical method for localization of cyclic 3′, 5′-nucleotide phosphodiesterase

SummaryA histochemical method has been described for demonstration of cyclic 3′, 5′-nucleotide phosphodiesterase in tissues. 5′-AMP is formed due to splitting of substrate cyclic 3′, 5′-AMP by cyclic 3′, 5′-AMPase. The 5′-AMP is split into adenosine and phosphate by the 5′-nucleotidase from added snake venom. Endogenous tissue 5′-nucleotidase would contribute to this activity. The phosphate was in turn visualized by conversion to the lead salt in the presence of lead acetate and finally into brownish-black lead sulphide by treatment with yellow ammonia sulphide. Control studies with and without substrate and snake venom, as well as inhibition by theophylline, indicate the test to be specific for cyclic 3′, 5′-AMPase.In the eye the conjunctiva, ciliary process, choroid and retina all showed strongly positive activity. In the kidney the proximal and distal tubules both ascending and descending and the loop of Henle show strongly positive activity — the rest of the elements being negative. The cardiac and skeletal muscle exhibited very little positive activity. The liver showed only mildly positive activity. The villi of the small intestine showed strongly positive activity at the apical part of the cells. Neurons showed very little positive activity in either the cerebral cortex or the cerebellum. On the other hand, the molecular layer in the cerebellum and the plexiform layer of the cerebral cortex showed strongly positive activity. The significance of these findings are briefly discussed.

THE PERINEURAL EPITHELIUM OF SYMPATHETIC NERVES AND GANGLIA AND ITS RELATION TO THE PIA ARACHNOID OF THE CENTRAL NERVOUS SYSTEM AND PERINEURAL EPITHELIUM OF THE PERIPHERAL NERVOUS SYSTEM.

SummaryA multiple layered flat epithelial cell layer covering the sympathetic ganglion chain and its derivatives (e.g. the splanchnic nerves) has been described. This layer is continuous around the grey and white rami communicans and is in turn continuous with the perineural epithelium of peripheral nerves. A capillary plexus and mast cells in this layer have also been demonstrated. This epithelium is shown on the surface of the blood vessel which enters the sympathetic trunk and resembles the leptomeningeal covering of the blood vessels of the central nervous system. The epi- and perineural. and epi- and periganglionic connective tissue layers of the sympathetic system are extremely delicate and minimal in quantity when compared to the epi- and perineurium of peripheral nerves. This paper thus completes the evidence that the whole of the peripheral nervous system and its ganglia (voluntary and autonomic) is isolated from the environment in which it lies and is maintained in an environment similar to or identical with that of the central nervous system.

Ultrastructural studies on developing oocytes of the salamander Triturus viridescens: II. The formation of yolk1

The process of yolk formation in Triturus viridescens is described. Yolk precursor bodies, which have a complex structure of vesicles, granules, and small membranous structures, begin to appear in oocytes with a diameter of 250 μ. Subsequently, in oocytes with a diameter of 500 μ, yolk platelets begin to appear within those bodies. There is no apparent connection between the formation of yolk and mitochondria, dictyosomes, or the endoplasmic reticulum.

Histological and histochemical observations on the capsule of the muscle spindle in normal and denervated muscle

Histological and histochemical studies of dephosphorylating enzyme distribution in muscle spindle capsule of guinea pig thigh muscles and cat calf muscles

Ultrastructural studies on developing oocytes of the salamander Triturus viridescens: III. Early cytoplasmic changes and the formation of pigment

The early cytoplasmic changes in the developing oocyte of Triturus viridescens are described. The pigment granules are shown to develop within membrane-limited vesicles, and it is suggested that these vesicles may originate in the dictyosomes. The endoplasmic reticulum is shown to take a vesicular form in Triturus viridescens.

Histochemical detection of l-gulonolactone: phenazine methosulfate oxidoreductase activity in several mammals with special reference to synthesis of vitamin C in primates

SummaryAn improved detection of activity of l-gulonolactone oxidase, which is responsible for the final oxidative step in the synthetic process of l-ascorbate from glucose in animals, was achieved using phenazine methosulfate and cyanide. Cold acetone fixation eliminated non-specific deposition of formazan on lipid droplets. The specificity of the method was tested and proven by a biological control, histochemical controls, inhibitors and activators. By application of the method, strong reactivity was found in the cytoplasm of centrilobular parenchymal cells of livers of the opossum, rat, ground squirrel and flying squirrel. Staining of dog liver was moderate and centrilobular. Prosimians were strongly positive: The centrilobular localization was found in the tree shrew and galago; slow lorises and some pottos showed strong reactivity in centrilobular cells and some peripheral cells as well. These prosimians seem to be able to synthesize l-ascorbate as many lower mammals are. On the contrary, true simians (i.e. the squirrel monkey, spider monkey, rhesus monkey and chimpanzee) were negative as guinea pigs were, suggesting their probable inability for l-ascorbate synthesis.

Enzyme-histochemical studies on the hypothalamus with special reference to the supraoptic and paraventricular nuclei of squirrel monkey (Saimiri sciureus)

SummaryDetailed histochemical studies have been made on the distribution of various enzymes such as phosphatases, cholinesterases, glycolytic enzymes and respiratory enzymes in various components of the hypothalamus with special reference to the supraoptic and paraventricular nuclei of the Squirrel Monkey. Cytological studies have also been made by the McManus, Einarson, Gomori and Bargmann methods.A few neurons of these nuclei showed scanty Gomori-positive material in the cytoplasm for the Gomori and Bargmann methods. Nissl granules were located in the peripheral cytoplasm of most neurons. No glycogen granules were observed in these neurons. For these reasons, the Squirrel Monkey, like the rat, may not be a suitable species for the study of neurosecretory phenomena.The axons of these neurons were negative for the specific cholinesterase test, though the perikaryon and some parts of the processes gave a moderately positive reaction. These neurons may be non-cholinergic and the cholinergic fibers from an unknown nucleus may end in synapses on their cell bodies. Blood vessels and glial cells in the neurosecretory nuclei showed non-specific cholinesterase activity. This enzyme may hydrolyze the acetylcholine which has escaped splitting by specific cholinesterase. Alkaline phosphatase and acid phosphatase in these neurons may be involved in the metabolism concerned with the production of neurosecretory material. The neurons may be physicochemical receptors and may get enough energy and raw material to synthesize the neurosecretory material from the rich blood supply. Neurons of the supraoptic and paraventricular nuclei as well as other hypothalamic neurons, like neurons of other regions of the brain, are well equipped with the enzymes of the glycolytic pathways and the tricarboxylic acid cycle. Since the glial cells of these nuclei have amylophosphorylase activity and glycolytic pathways, they may work as energy donators to the neurons of the neurosecretory nuclei.

Histochemical mapping of the distribution of monoamine oxidase in the diencephalon and basal telencephalic centers of the brain of squirrel monkey (Saimiri sciureus)

The activity of monoamine oxidase (MAO) was mapped at the macroscopic level using 50 μ thick fresh frozen sections arranged in a caudo-cranial series of sections through the diencephalon and basal telencephalic centers of the squirrel monkey brain. The various thalamic nuclei show a mild MAO reaction except the nuclei periventricularis and para- and subfascicularis, which show moderate MAO reaction. The hypothalamus, in general, shows a stronger MAO reaction than the thalamus, because of its involvement in various autonomic functions. The nuclei paraventricularis, supraopticus and ventromedialis hypothalami are particularly prominent because of the stronger MAO activity they show in contrast to other hypothalamic areas. The nucleus caudatus, putamen and globus pallidus show mild to moderate MAO activity. The fiber bundles of fimbria hippocampi, fornix, anterior commissure and internal capsule show a moderate to moderately strong MAO reaction. The nuclei of the amygdaloid complex differ little from one another and show negligible to mild MAO activity. The nuclei dorsalis, medialis and lateralis septi show a mild MAO reaction compared to the moderate activity in the nuclei fasciculi diagonalis Brocae and triangularis septi.