The ultrastructure of sensory corpuscles in the skin in the hedgehog snout

The ultrastructure of sensory nerve endings was examined in the snout skin in 3 adult hedgehogs (Erinaceus europaeus). The material was taken intravitally under total anaesthesia and processed in a usual way for the electron microscopy. The corpuscles were evaluated in the individual sections and series sections made through the whole corpuscle. In the superficial layers of the dermis simple sensory corpuscles and free endings were found. The simple sensory corpuscles can be divided into three types. a) Corpuscles containing a greater number of lamellae in the inner core, the lamellae are arranged regularly and are separated by two opposite clefts. The capsule is formed by only several lamellae undoubtedly of fibrocytic origin. b) Corpuscles containing a smaller number of wider lamellae in the inner core situated often at random. The clefts are also irregular and are often closed in the superficial layers of the inner core. The capsule is quite simple mostly formed by a single lamella of fibrocyte which often fails to form a continuous coat of the corpuscle. c) The third type is typical of its inner core being formed by few lamellae arranged irregularly. These corpuscles have no connective tissue capsule and are separated from the environments only by the basement membrane of superficial lamellae of the inner core. The corpuscles of the second type resemble considerably the developmental stages of simple sensory corpuscles as described in the literature in the cat. They are the same in size or smaller than the corpuscles of the first type. The free nerve endings occurred in two forms. a) Flattened (lanciform) nerve terminals. The axon is rich in mitochondria. The sides of the flattened terminal is lined with one to three wide lamellae while the axon reaches as far as the surface of the formation which is covered only with the basement membrane. b) Typical free endings rich in mitochondria which are embedded in the cytoplasm of Schwann cells or occasionally are covered only with the basement membrane. The lanciform endings which are not linked up with the hairs here may represent a transition from free endings to simple sensory corpuscles.     

Ultrastructure of Merkel corpuscles in the tongue of the finch,Lonchura striata

Summary Merkel corpuscles in the lingual mucosa of the finch, Lonchura striata, were examined by means of the argyrophilic reaction and electron microscopy. These corpuscles are composed of 12 to 20 flattened Merkel cells and enclosed nerve terminals. The present study demonstrated for the first time argyrophilia in avian subepithelial Merkel cells with the use of Grimelius silver stain. Electron-microscopically, the Merkel cell was characterized by the presence of numerous densecore granules, approximately 80 to 140 nm in diameter, as well as specialized contacts with nerve terminals. The granules showed a tendency to accumulate in the cytoplasm in close association with both nerve terminals and basal lamina. This study also provided unequivocal evidence for exocytotic discharge of Merkel-cell granules at the plasma membrane facing not only the nerve terminals but also the basal lamina. The exocytotic figures toward the nerve terminals can be regarded as synaptic discharge of Merkel-cell granules, but the possibility also exists that the Merkel-cell granules may exert a trophic effect on the nerve terminals. The exocytotic release of Merkel-cell granules toward the basal lamina with no relation to nerve terminals may suggest an endocrine (paracrine) function for the Merkel cell. The avian subepithelial Merkel cells qualify as paraneurons, but their exact nature and function remain enigmatic as is the case of intraepithelial Merkel cells in other vertebrates.     

Ultrastructure of pigeon peripheral blood cells]

The ultrastructural organization of erythrocytes, thrombocytes and white cells (pseudoeosinophils, eosinophils, basophils, lymphocytes, monocytes) of the peripheral blood was studied in the pigeon Columba livia. The specific granules of eosinophils do not contain crystalloid structures characteristic of eosinophilic granules of certain respresentatives of fishes and mammals. Specific basophilic granules are of a large size and have homogeneous osmophilic matrix. The ultrastructure of agranulocytes (lymphocytes and monocytes) have no substantial distinctions from the similar cells of other representatives of vertebrates.     

Ultrastructure of sensory receptors in ascidian tadpoles

Summary An analysis of fine structure and function was conducted on three types of receptors in the cerebral vesicle of two species of ascidian tadpoles (Ciona intestinalis andDistaplia occidentalis). Theocellus is composed of one pigmented, cup-shaped supportive cell, an estimated 15–20 sensory cells, and three lens cells, each with a large body of granules (glycogen ?). The outer segments of the photoreceptoral processes are modified cilia, one per sensory cell, consisting of many lamellae, formed by infoldings of the ciliary membranes, and axonemes of 9 + 0 doublets of microtubules. The lamellae are homologous to retinal disks of vertebrates.Hydrostatic pressure (?)receptors are modified cilia containing tubules which open to the lumen of the cerebral vesicle. These receptors closely resemble the globular, ciliary processes of coronet cells in the saccus vasculosus of fishes. Thestatocyte is a onecell gravity receptor. The part extending into the lumen of the brain contains the nucleus and a large black body which is thought to function as a float. The foot-piece of the cell is firmly anchored in the brain wall; the neck is probably the site of generation of signals. This study was supported by grant 10292 from the USPHS. The senior author held an appointment in the Miller Institute for Basic Research in Science, University of California, during part of the investigation. We appreciate the assistance of Emily Reid, artist; Jean L. Brandenburger, research associate; Professor Gerald Westheimer, consultant; Charles Spowart, collector; and the UCLA Brain Information Service, and the hospitality of Dr. Robert L. Fernald, Director, Friday Harbor Laboratories, University of Washington, U.S.A.