Article

Touch Organs in the Hairy and Glabrous Skin of Some Mammals (an Ultrastructural Comparison)

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Abstract

Touch organs of the skin in mammals consist of a mechanical transducting component and a sensory component. In the hairy skin, examples of these mechanical transducting components can be seen in the epithelium of hair follicles, and in the hairless skin in the epidermal papillae of the cone skin or the epidermal ridges of the ridges skin. In hairy skin all sinus and guards hairs and most of the vellus hairs are touch organs. The sinus and guard hairs are equiped with Merkel endings, free nerve endings, palisades of lanceolate nerve endings and pilo-Ruffini complexes. The total number of nerve endings varies in guard hairs between 50-200 and between 500-2000 in sinus hairs depending on the size of the follicle. The skin surrounding the body orifices, glabrous skin of the tip of the nose and skin of the finger tips is rich in touch organs. Touch organs of the cone skin known as Eimer organs consist of free nerve endings and of Merkel endings innervating the epidermal cone. Below these cones, the papillary layer shows small lamellated corpuscles and also free nerve endings. In the ridge skin epithelial ridges and crypts, the corresponding dermal papillae, their blood vessels and nervous elements together form the touch organs. In the basal layer of the glandular ridge up to 10 Merkel nerve endings are visible. In young individuals the connective tissue papilla of each crypt shows one Meissner corpuscle and several free nerve endings.

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... Reticular endings. Dense concentrations of nerve fibers had been seen at the upper level of the cavernous sinus in previous EM studies (Andres, 1966;Halata, 1975;Halata and Munger, 1980a;Halata, 1990;Loo and Halata, 1991). However, because the arbors do not label with silver stains, the full intricacy of their ramifications was first revealed in an anti-PGP9.5 ...
... In this study, we demonstrated comparable PGP9.5-immunopositive ramifications of the endings in the cat FSCs as well as informative three-dimensional aspects in both rat and cat for the first time. The highly ramifying appearance of the endings in both species may be equivalent to endings interpreted by others as the Ruffini-like endings (Andres, 1966;Halata, 1975Halata, , 19901980a,b). The reticular endings have major differences in morphology and distribution in the cat and rat FSCs. ...
Article
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Our confocal three-dimensional analyses revealed substantial differences in the innervation to vibrissal follicle-sinus complexes (FSCs) in the rat and cat. This is the first study using anti-protein gene product 9.5 (PGP9.5) immunolabeling and confocal microscopy on thick sections to examine systematically the terminal arborizations of the various FSC endings and to compare them between two species, the rat and the cat, that have similar-appearing FSCs but different exploratory behaviors, such as existence or absence of whisking. At least eight distinct endings were clearly discriminated three dimensionally in this study: 1) Merkel endings at the rete ridge collar, 2) circumferentially oriented lanceolate endings, 3) Merkel endings at the level of the ring sinus, 4) longitudinally oriented lanceolate endings, 5) club-like ringwulst endings, 6) reticular endings, 7) spiny endings, and 8) encapsulated endings. Of particular contrast, each nerve fiber that innervates Merkel cells at the level of the ring sinus in the rat usually terminates as a single, relatively small cluster of endings, whereas in the cat they terminate en passant as several large clusters of endings. Also, individual arbors of reticular endings in the rat ramify parallel to the vibrissae and distribute over wide, overlapping territories, whereas those in the cat ramify perpendicular and terminate in tightly circumscribed territories. Otherwise, the inner conical body of rat FSCs contains en passant, circumferentially oriented lanceolate endings that are lacking in the cat, whereas the cavernous sinus of the cat has en passant corpuscular endings that are lacking in the rat. Surprisingly, the one type of innervation that is the most similar in both species is a major set of simple, club-like endings, located at the attachment of the ringwulst, that had not previously been recognized as a morphologically unique type of innervation. Although the basic structure of the FSCs is similar in the rat and cat, the numerous differences in innervation suggest that these species would have different tactile capabilities and perceptions possibly related to their different vibrissa-related exploratory behaviors.
... Long hair would be superfluous in this respect. In regard to C. hottentotus, which has no well developed sinus hairs or even lacks them, it is important to note that every type of hair is a tactilc device (Halata 1990Halata , 1993 ). The stiff carpal vibrissae of N. ehrenbergi should be more resistant against bending under submersed conditions . ...
A comparison of palm morphology of the fossorial rodents Nannospalax ehrenbergi (Nehring, 1898) and Cryptomys hottentotus (Lesson, 1826) with Rattus rattus (Linneaus, 1758), which digs to a much lesser degree, and in relevant structures represents the rodent morphotype, reveals conspicuous differences. Among these, the presence of an irregularly folded, less prominent interdigital pad region without distinct pads is an apomorphic rodent character of C. hottentotus and N. ehrenbergi. The apomorphic lack of long vibrissae carpales in C. hottentotus and N. ehrenbergi, in respect to the rodent morphotype, indicates a limited capability of agile motion of the forelimbs during movements not involved with digging. The broad palms, ventrally closed claws and a strongly developed flexion crease are interpreted as adaptations for digging in C. hottentotus and N. ehrenbergi. The broad palms serve as shovel-like devices to move the substratum. The flexion crease and reduced distal pads indicate that the digits are bent towards the proximal pad region forming a kind of scraper or hoe during digging. For this action the ventrally closed claws resist bending stresses better. The long claws of C. hottentotus indicate that they are more extensively used for penetrating the substratum than it is the case in N, ehrenbergi.
... In the upper cervical spine of monodelphis domestica, two classes of morphologically and functionally different joint receptors have been described: free nerve endings and small lamellated corpuscles. Three types (the above two and Ruffini corpuscles) were previously found in the joints of other mammals (Boyd 1954;Clark and Burgess 1975;Grigg 1975;Halata 1977) as well as in other tissues e. g. in the skin (Halata 1975(Halata , 1990. These receptors can be clearly identified by their characteristic structure. ...
Article
In order to investigate the sensory innervation, the upper cervical spine of a small laboratory marsupial (monodelphis domestica) was examined with serial section light microscopy and re-embedding of selected sections for electron microscopy. Large numbers of free nerve endings supplied by A delta- and C-fibres were found in the longitudinal ligaments and facet joint capsules. Electron microscopically, areas of direct contact between axon and collagen fibres of the surrounding connective tissue separated only by the basal lamina were observed. Such structural adaptations suggest mechanoreceptive or polymodal nociceptive functions. In addition, about 100 small lamellated corpuscles were found in the longitudinal ligaments mainly concentrated around the first intervertebral disk. Electron microscopy shows finger-like processes extending from the axon terminal into the inner core lamellae. These are the likely sites of the mechanoelectric transduction process. Smaller numbers of lamellated corpuscles were seen in the lower intervertebral disks and facet joint capsules. Lamellated corpuscles are known to function as rapidly adapting mechanoreceptors supplementing information supplied by muscle spindles to the CNS about position and movement of the cervical spine.
Article
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Article
The classical observations of the skin as a target for melanotropins have been complemented by the discovery of their actual production at the local level. In fact, all of the elements controlling the activity of the hypothalamus-pituitary-adrenal axis are expressed in the skin including CRH, urocortin, and POMC, with its products ACTH, α-MSH, and β-endorphin. Demonstration of the corresponding receptors in the same cells suggests para- or autocrine mechanisms of action. These findings, together with the demonstration of cutaneous production of numerous other hormones including vitamin D3, PTH-related protein (PTHrP), catecholamines, and acetylcholine that share regulation by environmental stressors such as UV light, underlie a role for these agents in the skin response to stress. The endocrine mediators with their receptors are organized into dermal and epidermal units that allow precise control of their activity in a field-restricted manner. The skin neuroendocrine system communicates with itself and with the systemic level through humoral and neural pathways to induce vascular, immune, or pigmentary changes, to directly buffer noxious agents or neutralize the elicited local reactions. Therefore, we suggest that the skin neuroendocrine system acts by preserving and maintaining the skin structural and functional integrity and, by inference, systemic homeostasis.
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Article
SummaryFor the first time the cartilaginous nasal skeleton of the rostrum of adult soricids has been reconstructed on the basis of histological serial sections. The length of the cartilaginous nasal skeleton of Neomys fodiens is 8.4 mm, i.e. about 35% of the total head length, while that of Sorex araneus is 4 mm, i.e., about 20% of the head length. However, both specimens were preserved in different functional states: The nasal skeleton of the Neomys-specimen is extended, whereas that of the Sorex-specimen is retracted by about 25% of its maximum length of 5.4 mm which would represent about 27% of the total head length. In both taxa, the caudalmost part of the rostral cartilage is subdivided into three elements, which can telescope into one another. Consequently, the proximal portion of the nasal septum, which forms a central axis with a rounded cross-section, is more or less straight in the Neomys-specimen, whereas in the Sorex-specimen the posterior elements are pushed into one another and the proximal portion of the nasal septum is bent in a S-like shape. The cartilaginous rostral skeleton can be retracted by a strong facial muscle, the newly defined M. retractor proboscidis, which originates on each side from the alveolar processes of the premaxillaries and inserts on the nasal roof cartilage. A number of additional structural details of the nasal skeleton are described and interpreted functionally, but an evaluation of their phylogenetic-systematic significance is postponed until additional soricid taxa have been studied.
Article
Hair is actively pigmented only when it grows: the melanogenic activity of follicular melanocytes (MC) is strictly coupled to the anagen stage of the hair cycle. In catagen, melanin formation is switched off and is absent throughout telogen. The appearance of pigmentation is preceded, and further accompanied by, a time-frame - restricted, differential pattern of tyrosinase transcription, translation, and enzyme activities during the development of anagen follicles. In this speculative review, we argue that signals required for melanin synthesis and pigment transfer to bulb keratinocytes (KC) are intrinsic to the skin, rather than coming from the serum. First, the proopiomelanocortin (POMC) gene is expressed and translated during anagen, but is below the level of detectability in telogen; POMC is a precursor protein for adrenocorticotropin and melanotropins, which are potent regulators of MC proliferation and differentiation. Second, fibroblasts and KC produce factors that affect MC proliferation and differentiation. We suggest that signals regulating follicular MC activity partially derive from cutaneous cells expressing POMC. Vice versa, MC transfer to surrounding KC pigment granules with potent bioregulatory properties. MC also produce and secrete various signal molecules that can regulate mesenchymal and epithelial cell functions. Anagen-associated melanogenesis and the cyclic production of a pigmented hair shaft result from programmed and tightly coordinated epithelial-mesenchymal-neuroectodermal interactions, in which MC may act not only as pigmentary, but also as hair growth-regulatory cells.
Article
The location and structure of sensory nerve endings was examined in the mucosa and in the gingiva propria adjacent to the third premolar of Monodelphis domestica by light and electron microscopy. The mucous membrane of the gingiva propria is covered with a stratified keratinized squamous epithelium. The mucous membrane of the adjacent inner aspect of the lip and of the vestibulum oris were covered with a nonkeratinized squamous epithelium. Free nerve endings, Merkel nerve endings and lamellated corpuscles were found in all the examined areas. Free nerve endings were located in the connective tissue papillae between the epithelial cones, in the basal layer of the epithelium and directly under the epithelium of the cones. They were innervated by myelinated A-delta- and nonmyelinated C-fibers. The basal layer of the first three to four epithelial cones of the gingiva propria contained single or groups of Merkel nerve endings. The epithelial cones of the oral mucous membrane contained five times more Merkel nerve endings than those of the vestibular mucous membrane. Lamellated corpuscles were mainly found in the plica sublingualis. In the connective tissue below the epithelial cones of the mucous membranes they usually occur with a perineural capsule, in the connective tissue papillae between the cones they occur without a perineural capsule. In the latter position they resemble the Meissner corpuscles of glabrous skin.(ABSTRACT TRUNCATED AT 250 WORDS)
Article
Sinus hairs were isolated from rats and examined in an isolated organ bath while superfused with oxygenated synthetic interstitial fluid. The distal end of the deep vibrissal nerve was teased for single unit recordings of responses from slowly adapting mechanoreceptors to standard bending of the hair. Sinus hair type I and type II receptors could be clearly identified by their respective characteristic firing pattern. Their responses were stable for at least 5 h even if the sinus hair had been stored at 4 degrees C for 24 h beforehand. Electron microscopic examination of these hairs at the end of experiments showed well preserved ultrastructure without abnormalities. The short diffusion distances in this preparation make it well suited for studying drug effects with the aim of investigating the mechanoelectric transduction process in these receptors.
Article
The function of Merkel cells in mechanotransduction has remained controversial Single unit recordings were made from Merkel cell receptors (sinus hair type I, St I) and another slowly adapting mechanoreceptor (sinus hair type II, St II) in isolated rat sinus hairs by applying controlled mechanical displacements to the hair shaft. Chloroquine (50-300 microM) caused a concentration dependent inhibition of Merkel cell receptor responses to mechanical stimulation. In contrast, both stimulated and spontaneous spike activity of St II receptors was increased by the same concentrations of chloroquine. Ultrastructural examination of chloroquine treated sinus hairs revealed swollen Merkel cells with multiple vacuoles and randomly distributed granules while other neural and surrounding structures showed no striking morphological changes. These results suggest that the Merkel cell plays a mechanotransducer role in Merkel cell receptors.
Article
The classical observations of the skin as a target for melanotropins have been complemented by the discovery of their actual production at the local level. In fact, all of the elements controlling the activity of the hypothalamus-pituitary-adrenal axis are expressed in the skin including CRH, urocortin, and POMC, with its products ACTH, alpha-MSH, and beta-endorphin. Demonstration of the corresponding receptors in the same cells suggests para- or autocrine mechanisms of action. These findings, together with the demonstration of cutaneous production of numerous other hormones including vitamin D3, PTH-related protein (PTHrP), catecholamines, and acetylcholine that share regulation by environmental stressors such as UV light, underlie a role for these agents in the skin response to stress. The endocrine mediators with their receptors are organized into dermal and epidermal units that allow precise control of their activity in a field-restricted manner. The skin neuroendocrine system communicates with itself and with the systemic level through humoral and neural pathways to induce vascular, immune, or pigmentary changes, to directly buffer noxious agents or neutralize the elicited local reactions. Therefore, we suggest that the skin neuroendocrine system acts by preserving and maintaining the skin structural and functional integrity and, by inference, systemic homeostasis.
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