Sensory and secretory potencies and differentiations of the central nervous system

Tomographic reconstruction reveals the morphology of a unique cellular organelle, the aggregated macrotubules (Macrotubuli aggregati) of human retinal horizontal cells

Horizontal cells of the human retina contain unique tubular organelles that have a diameter which is about 10 times larger than that of microtubules (~230 nm). These macrotubuli in most cases form regular aggregates. Therefore we propose to introduce them as Macrotubuli aggregati in the Terminologia histologica. Tomographic investigation of the structures revealed that the walls of the tubules most probably consist of intermediate filaments running nearly parallel to each other and show somewhat regularly attached ribosomes on their inner and also outer surface. About 2% of the organelles exhibit double- to multiple layered walls and less than 1% resemble large scrolls. The tubules may extend 10 to over 20 μm in the cytoplasm and are also encountered in soma-near processes extending into the outer plexiform layer. It remains unclear why these structures are only present in humans and few other species and why almost only in horizontal cells. Speculations on possible functions are discussed.

Sensory innervation of the brain (primary interoceptor neurons of the brain and their asynaptic dendrites)

Published data and our own studies on the sensory innervation of the brain are summarized. Primary interoceptive sensory neurons were analyzed: brain neurons bearing cilia; supraependymal plexuses and intraependymal neurons in contact with the cerebrospinal fluid; Cajal-Retzius neurons in the boundary layer of the cerebral cortex; Dolgo-Saburov paravasal neurons in the brain and spinal cord; Lugaro cells in the cerebellum; and various synaptically NO-positive neurons in the cerebral cortex, whose asynaptic dendrites innervate the precapillary space. Consideration of the lack of pain sensitivity of the brain and the parenchymatous tissues of the internal organs, which contain local primary sensory neurons similar to intramural metasympathetic sensory neurons of Dogel type II, led to the hypothesis that brain and other intraorgan tissue receptors are involved in short "autonomic" reflex arcs controlling only local metabolism but not pain reactions.

H3-thymidine labeled cerebrospinal fluid contacting cells in the regenerating caudal spinal cord of the lizard Lampropholis

Australian scincid lizards (Lampropholis) were injected with a single dose of H3-thymidine during the early stages of tail regeneration in order to study later a possible differentiation of neurons and glial cells within the regenerating spinal cord. After 5 hours post-injection only electrondense or pale ependymal cells took up H3-thymidine. Light and electron microscopic analysis of later stages, 6, 12 and 20 days post-injection, revealed that labeled pale cells were occasionally recognizable 12-20 days post-injection. Many pale unlabeled and a few labeled cells contacted the central canal of the spinal cord and appeared as cerebrospinal fluid contacting cells. The electron microscope showed the presence of stereocilia in the apical cytoplasm of these pale cells, a typical characteristic of cerebrospinal fluid contacting neurons. After 12-20 days post-injection, among ependymal cells rare pale cells containing intermediate filaments were labeled. Other pale cells represented intermediate stages of differentiation between ependymal and neural or glial cells. Differentiated medium-high electrondense ependymal tanicytes were also labeled 6, 12 and 20 days post-injection. This analysis showed that a limited regeneration of cerebrospinal fluid contacting neurons occurs locally in the caudal spinal cord of the scincid lizard Lampropholis.

Astroglial cells in a salamander brain (Salamandra salamandra) as compared to mammals: a glial fibrillary acidic protein immunohistochemistry study

Glial fibrillary acidic protein immunohistochemistry revealed the presence of radial glial cells in the adult salamander brain, forming endfeet on the subpial surface and on blood vessels. In the spinal cord, glial cells are displaced from the ependyma. In mice, antibodies stained astrocytes, and radial glial cells in juveniles.