M. von Düring

Nerve fibres and their terminals of the dura mater encephali of the rat

SummaryThe dura mater encephali of the rat is richly supplied by myelinated (A-axons) and unmyelinated (C-axons) nerve fibres. For the supratentorial part the main nerve supply stems from all three branches of the trigeminal nerve. Finally, 250 myelinated and 800 unmyelinated nerve fibres innervate one side of the supratentorial part. The vascular bed of the dura mater exhibits long postcapillary venules up to 200 μm in length with segments of endothelial fenestration. Lymphatic vessels occur within the dura mater. They leave the cranial cavity through the openings of the cribriform plate, rostral to the bulla tympani together with the transverse sinus, and the middle meningeal artery. The perineural sheath builds up a tube-like net containing the A- and C-axons. It is spacious in the parietal dura mater and dense at the sagittal sinus along its extension from rostral to caudal and at the confluence of sinuses. Terminals of both the A- and C-axons are of the unencapsulated type. Unencapsulated Ruffini-like receptors stemming from A-axons are found in the dural connective tissue at sites where superficial cerebral veins enter the sagittal sinus and at the confluence of sinuses. The terminations of single A-axons together with C-fibre bundles mix up in their final course in one Schwann cell to build up multiaxonal units or terminations (up to 15 axonal profiles). A morphological differentiation is made due to the topography of these terminations; firstly, in different segments of the vascular bed: postcapillary venule, venule, the sinus wall, lymphatic vessel wall, and secondly, within the dura mater: inner periosteal layer, collagenous fibre bundles of the meningeal layer and at the mesothelial cell layer of the subdural space.

Sensory innervation of the Achilles tendon by group III and IV afferent fibers.

SummaryIn sympathectomized cats the innervation of the Achilles tendon by fine afferent nerve fibers was studied with semithin and ultrathin sections. Several different types of sensory endings of group III and group IV nerve fibers were identified.Of the five different types of endings in the group III range (T III endings), two are located within vessel walls. One of them ends in the circumference of the venous vessels (T III/VV). Its lanceolate terminals have characteristic receptor areas at their edges. The second type ends in the adventitia of lymphatic vessels (T III/LV). Its receptive areas are scattered along their terminal course. Two further group III endings ramify within the connective tissue compartments of the vessel-nerve-fascicles of the peritenonium externum and internum. One type is tightly surrounded by collagen fibrils (T III/PTic); the other terminates between the collagen fiber bundles (T III/PTgc). The latter arrangement recalls the ultrastructural relation between nerve terminals and collagen tissue in Golgi tendon organs.The fifth type innervates the endoneural connective tissue of small nerve fiber bundles (T III/EN). At least some of them come into close contact with bundles of collagen fibers which penetrate the perineural sheath to terminate within the endoneurium.The endings of group IV afferents (T IV endings) show a striking topographic relationship to the blood and lymphatic vessels of all connective tissue compartments of the Achilles tendon. They form penicillate endings which may contain granulated vesicles. In any event, they can easily be discriminated from the T III endings in the vessel walls.In close neighborhood to Remak bundles, a cell has been regularly found which fulfilled all ultrastructural criteria for mast cells. But this cell is not a mast cell proper because it is surrounded by a basal lamina (pseudo mast cell).

Epithelial Na+ channels and stomatin are expressed in rat trigeminal mechanosensory neurons

Abstract. Caenorhabditis elegans MEC-4 and MEC-10 are subunits of the degenerin/epithelial Na+ channel (DEG/ENaC) ion channel superfamily thought to be associated with MEC-2 (a stomatin-like protein) in a mechanotransducing molecular complex in specialized touch sensory neurons. A key question is whether analogous molecular complexes in higher organisms transduce mechanical signals. To address this question, we selected mechanoreceptors of the rat vibrissal follicle-sinus complex in the mystacial pad and the trigeminal ganglia for an immunocytochemical and molecular biological study. RT-PCR of poly(A+) mRNA of rat trigeminal ganglia indicated that α-, β-, and γ-ENaC and stomatin mRNA are expressed in rat trigeminal ganglia. Using immunocytochemistry, we found that α-, β-, and γ-ENaC subunits and stomatin are localized in the perikarya of the trigeminal neurons and in a minor fraction of their termination site in the vibrissal follicle-sinus complex, where longitudinal lanceolate endings are immunopositive. We conclude that α-, β-, and γ-ENaC subunits as well as the candidate interacting protein stomatin are coexpressed in a mammalian mechanoreceptor, a location consistent with a possible role in mechanotransduction.

Sequestration of neuraminidase-treated erythrocytes

SummaryScintigraphic experiments and radioactivity measurements of tissues have shown that the radioactivity of 51Cr-labelled and neuraminidase-treated rabbit erythrocytes is rapidly accumulated in liver and spleen. Sequestration of these erythrocytes by liver and spleen was demonstrated by light and electron microscopy of these tissues after perfusion of the rabbits with solutions for tissue fixation. In liver the phagocytic activity of Kupffer cells was increased after injection of desialylated erythrocytes, while in spleen a significantly enhanced number of erythrocytes was found attached to the sinusoidal walls and in the reticulum of the red pulp.It was shown by scanning electron microscopy that neuraminidasetreatment did not influence the shape of erythrocytes.Desialylated and 51Cr-labelled erythrocytes from the cow are rapidly cleared from the blood-stream with a half-life time of about 3 h.It was shown in an in-vitro test that they adsorb to surviving slices from liver and spleen derived from the same animal. The amount of radioactivity adsorbed is appreciably enhanced in the presence of homologous serum when compared with buffer only.Human neuraminidase-treated erythrocytes are agglutinated in the direct and especially in the indirect Coombs-tests. The involvement of T-antigen in this phenomenon was largely excluded.The in vitro experiments and antibody consumption tests suggest that immunoglobulins (IgG) and complement from serum may be involved in recognition and sequestration of desialylated erythrocytes by macrophages in vivo.

Neuropeptide Y- and substance P-like immunoreactive nerve fibers in the rat dura mater encephali.

SummaryDensity and pattern of nerve fibers with neuropeptide Y-like immunoreactivity (NPY-LI) and substance P-like immunoreactivity (SP-LI) in the rat dura mater encephali were investigated by light and electron microscopy using whole-mount preparations. NPY-LI fibers are observed throughout the encephalic dura mater. A remarkable net of NPY-LI nerve fibers is located in the walls of the sagittal and transverse sinuses. Beyond that NPY-LI network, distinct NPY-LI nerve fibers or plexus occur in the rostral falx, parietal dura mater of the olfactory bulb, supratentorial dura mater, parietal dura mater of the cerebellum, tentorium cerebelli and the ventral dura mater. Electron microscopic studies reveal that NPY-LI is exclusively located in unmyelinated axons of small and large nerve fiber bundles, with or without a perineural sheath. Immunopositive C-fibers are predominantly associated with the vascular bed.SP-LI nerve fibers have a moderate and more uniform distribution in the encephalic dura mater. A distinct plexus of SP-LI fibers follows the branches of the middle meningeal artery and the adjacent dura mater. SP-LI fibers are most prominent in the parietal dura mater of the cerebellum. Fine beaded SP-LI fibers, arising from larger SP-LI fiber bundles, are observed in close association to the capillary bed. SP-LI axons are all unmyelinated. They are found in larger nerve fiber bundles with a perineural sheath or in Schwann cells lacking any perineural sheath.The function of NPY-LI and SP-LI nerve fibers in the rat dura mater is discussed in relation to their topography, density and termination.

Phenomenological diversity of spinal reflexes in brain death.

In brain death, spinal reflexes and automatisms are observed which may cause irritation and even doubt in the diagnosis. In the literature there are no dedicated descriptions of the diversity and of neuroanatomical considerations.

The fine structure of ampullary and tuberous electroreceptors in the South American blind catfish Pseudocetopsis spec.

SummaryTwo types of electroreceptors, the ampullary and the tuberous electroreceptor (silurid knollenorgan) in the epidermis of the catfish, Pseudocetopsis spec., were investigated with semithin and ultrathin serial sections. The ampullary organ contains one or two sensory cells which are embedded in supporting cells at the base of open epithelial canals. They bear some slender microvilli on their apical surface and form several synaptic bars. The afferent myelinated nerve fiber arborizes in the connective tissue papilla and looses its myelin sheath about 30 μm below the supporting cell layer. A second thin myelinated axon occur up to the supporting cell layer. The tuberous electroreceptor organ contains one large receptor cell. Most of the cell body is exposed to the lumen of a specialized proximal canal segment and is closely covered with microvilli. A single myelinated axon looses its myelin sheath within the supporting cell layer about 1 μm before terminating as a flat calyx at the base of the sensory cell. A functional significance of the two types of receptors will be discussed.

Chapter 14 Comparative anatomy of vertebrate electroreceptors

Publisher Summary This chapter focuses on the comparative anatomy of vertebrate electroreceptors. Electrosensitivity plays an important role in the biological activities of fish and amphibia for prey detection, feeding behaviour and social communication and its significance is reflected in the number of sensory cells and the amount of nerve supply that ranks in the order of other sensory systems. Two types of electroreceptors are characteristic in teleost as well as non-teleost fishes and in some amphibia: the ampullary and the tuberous receptor organs. Three types of ampullae can be distinguished in chondrichthyes with regard to the length of the canal and the size and differentiation of the alveolus: (1) macro-ampullae, (2) micro-ampullae, and (3) mini-ampullae. The macro-ampullae (known as the ampullae of Lorenzini) are macroscopically identified by large pores in the skin surface. Micro-ampullae occur in restricted areas of the maxillary and the mandibular processes of Holocephali and Hexanchidae. The mini-ampullae of freshwater rays, however, exhibit very short canals of about 300–500 μm length.

Degeneration patterns of postganglionic fibers following sympathectomy

SummaryIn cats the time course of degeneration following lumbal sympathectomy was studied in the ramus communicans griseus (reg) and in the nerves to the triceps surae muscle using light and electron microscopic methods.The left lumbar sympathetic trunk including its rami communicantes was removed from L2 to S1 using a lateral approach. The animals were sacrificed between 2 and 48 days after the sympathectomy. Tissue samples were taken (a) one cm proximal to the entrance of the rcg into the spinal nerve, and (b) one cm proximal to the entrance of the nerve into the muscle belly.In the reg signs of degeneration can already be recognized in the myelinated as well as in the unmyelinated axons 48h after sympathectomy. The degenerative processes in the axons reach their peak activity at about 4 days p.o. They end a weck later. Signs of the reactions of the Schwann cells and of the endoneural cells can first be seen 2 days p.o. They are most pronounced around the 8th day p.o., and last at least up to the third week. Thereafter the cicatrization processes settled to a rather steady state (total observation period 7 weeks).In the muscle nerves the first signs of an axonal degeneration of the sympathetic fibers can be recognized 4 days after surgery. The signs of axonal degeneration are most striking about 8 days p.o. They have more or less disappeared another week later. The reactions of the Schwann cells also start on the fourth day but outlast the degenerative processes by some 8 days. Thus the degenerative and reactive processes in the reg precede those in the muscle nerves by 2 days early after surgery and by 6 days 3 weeks later. Seven weeks after surgery, fragments of folded basement lamella and Remak bundles with condensed cytoplasm and numerous flat processes are persisting signs of the degeneration.In addition to the differences in time course between the proximal and the distal site of observation, it was also noted that both the axonal degeneration and the reactions of the Schwann cells are more pronounced in the rcg than in the muscle nerve. For example there was abundant mitotic activity in the central endoneural and Schwann cells whereas we could not detect such activity in the periphery.It is concluded that the time course of degeneration and the intensity of the degenerative and reactive processes is, to a considerable extent, determined by the distance between the site of nerve section and the site from which the specimen is taken. Many of the conflicting data in the literature can be explained by this finding.

Actin, myosin and alpha-actinin containing filament bundles in hyaline cells of the caiman cochlea

Hyaline cells of the auditory organ of the spectacled caiman contain smooth muscle-like filament bundles within their basal cell pole. These bundles were heavily labeled with antibodies to actin, myosin and alpha-actinin (muscular Z-line protein). Since hyaline cells are firmly attached to the basilar membrane these cells may actively modify the stiffness of the basilar membrane. A contractile mechanism in hyaline cells might affect frequency tuning of primary auditory afferents. This frequency tuning has been shown to be a temperature-dependent process in caimans and other submammalian species. The presence of synaptic contacts between efferent nerve fibres and hyaline cells suggests neural control of hyaline cell activity.