The location of spinal neurons with long descending axons (long descending propriospinal tract neurons) in the cat: a study with the horseradish peroxidase technique

The distribution spinal neurons with long descending axons was studied in the cat by means of retrograde transport of horseradish peroxidase. Labeled neurons appeared bilaterally in the cervical and the thoracic cord following injections in the lumbosacral cord. In some cases hemisections were made rostrally and contralaterally to the injections in an attempt to determine whether or not the axons crossed. Neurons with uncrossed descending axons were located in laminae I, V, VII and VIII. Lamina I neurons were present in all the spinal segments. In lamina V labeled neurons were distributed mainly laterally in the cervical cord but medially and laterally in the thoracic cord. In the upper cervical and the thoracic cord laminae VII and VIII neurons were distributed very densely along the lateral cord, accounting for 30 and 40 of the total labeled neurons, respectively. In the cervical enlargement they were located in the middle part of lamina VII and in lamina VIII, accounting for about 25% of the total labeled neurons. Neurons with crossed descending axons were found in laminae V, VII and VIII, in the medial part of lamina VII including the intermediomedial nucleus of the thoracic levels and close to the central canal. Lamina V neurons were very small in number. The largest collections of labeled neurons were present in the medial part of laminae VII and VIII. They accounted for about 45% to 55% and 37% of the total in the cervical and the thoracic cord. These neurons may function as the long spinal reflex paths for forelimb-hindlimb synergies and the intercalated paths between the supraspinal descending tracts and the spinal motor centers.

The rhombencephalic recess in the rat. A light and electron microscopic study

The rhombencephalic recess, an ependymal organ, has been studied for the first time by light- and electron microscopy. It is situated mediosagitally on the floor of the rhomboid fossa at the level of the colliculus facialis. The recess and the superimposed tissue are built up by tanycytes, their apices being connected by tight junctions. HRP, injected into the c.s.f., does not penetrate into the intercellular clefts of the recess area. The recess area reveals a certain autonomy regarding its supply with arteries and capillaries. A blood-brain barrier exists, but shows slight leakage in circumscribed areas as a result of intense transendothelial vesicular transport. The organization of the recess area is compared with that of other ependymal organs, especially circumventricular organs.

Ventricular surface of rabbit hippocampus: a scanning electron microscope study

Portions of the ependyma were obtained from the hippocampus of adult rabbits and processed for scanning electron microscopy. The major part of the ependymal surface was covered with a dense layer of cilia, some of these cilia showed bulbous preterminal enlargements. Irregularly arranged pits of variable diameter were also seen. Pes hippocampi showed fewer cilia and deeper furrows than did the remainder of the hippocampus.

The structure of the rhombencephalic roof in the frog

The structure of the rhombencephalic roof has been studied by serial section histology in 12 adult frogs, 3 recently metamorphosed frogs and 8 tadpoles of the species Rana temporaria. The roof of the rhombencephalon caudal to the choroid plexus consists of a delicate layer of ependyma which appears to be intact from the time of its development in the tadpole until the stage of metamorphosis. In the adult frog it is an attenuated structure displaying variable deficiencies with an apparent communication between the rhombencephalic ventricle and the surrounding subarachnoid space. The significance of this acquired communication between internal and external cerebrospinal fluid compartments in the adult frog is discussed in relationship to the classical concepts of bulk flow of the CSF in humans. Some of the limitations of these classical concepts are also discussed, and the approach to these problems by studying the comparative morphology of the CSF system in vertebrate animals is justified.

Inverse prominence of ependyma and capillaries in the spinal cord of vertebrates: a comparative histochemical study

Spinal cords of 15 species representing six classes of vertebrates and the protochordate amphioxus were examined with histochemical methods for esterase, ATPase, LDH, PAS, and PAS-phosphorylase. Ependymal and glial cell processes were demonstrated and resembled heavy metal impregnations. Capillaries also were shown. The prominence of glycogen-rich ependymal structures in the spinal cord of nonmammalian vertebrates, and the increase in intramedullary blood vessels in placental mammals, suggest an inverse relationship between the relative development of the ependyma and of the blood supply. The marsupial opossum has sparseness of both ependyma and capillaries, but exhibits an extensive pattern of branched glial processes in both white and gray matter.

[Changes in the subcommissural organ of white rats with age]

Histological and histochemical methods were applied to the study of 82 male rats of different age (newborn, 1-, 2-, 5-, and 17-month-old). Microstructure of the subcomissural organ (SCO) was investigated; the height of its ependyma was measured. In rats at all the age groups studied ependymocytes secreted substances of glucoproteid nature; a moderate content of RNA persisted in the cells, and also a high activity of non-specific esterases. Secretory activity of ependymocytes increased with the growth of the animals, remaining high in adult rats; it fell in the old animals. Age changes of the SCO consisted in the reduction of the height of the ependyma, of the number of cell layers in it and atrophy of the villi.

Histological and histochemical study on the ependyma of Bradypus tridactylus

Histological and histochemical aspects of the whole encephalic ventricular system of eight specimens of Bradypus tridactylus were studied. After anesthesia and perfusion, the encephalons were obtained by craniotomy. Transverse serial sections of the encephalon, stained according to Azan (Heidenhain's method) or Kluver-Barrera for nerve cells and myelinated nerve fibers; silver impregnation was carried out according to Cajal-De Castro's or Palmgren's methods. The following histochemical reactions were used: PAS (McManus), metachromasia, acid phosphatase (Gomori), Brachet's and Gomori's trichromic reaction (modified by Bargmann for neurosecretion). Histologically, different characteristics of the ependymal cells in different areas were observed, which would be related to functional peculiarities of each area of the encephalic ventricles. The ependymal cells showed discrete apical basophilia due to the presence of RNA which disappears after treatment with crystalline ribonuclease. The PAS reaction indicated the presence of a small quantity of PAS-positive substances in the apical zone of the ependymal cells and the subependymal tissue. These substances disappeared after the salivary amylase test, indicating the presence of glycogen. The acid phosphatase reaction was negative.

Proliferative characteristics of the ependymal layer during the early development of the mouse neocortex: a pilot study based on recording the number, location and plane of cleavage of mitotic figures

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On the Recessus mesocoelicus in some primates

The recessus mesocoelicus was studied in Cebus, Macaca fascicularis and in Pan troglodytes. The shape of this recessus is variable within and across species (funnel-shaped, simple tube, a tube ending with 2 smaller diverticula). The ependyma of the oral wall of the recessus is of the same kind as the ependyma of the subcommissural organ, whereas the ependymal of the caudal wall has changed in Macaca and Pan in the sense, that it has obviously lost its secretory activity. No Reissner’s fibre was found in the recessus in the specimen studied.