[Computer-assisted screw placement into the posterior pelvic ring: assessment of different navigated procedures in a cadaver trial]. / Computerassistierte Verschraubung des hinteren Beckenrings : Systematischer Vergleich verschiedener Navigationsverfahren am Kadaverpräparat.

OBJECTIVE: Computer-assisted procedures have recently been introduced for navigated iliosacral screw placement. Currently there are only few data available reflecting results and outcome of the different navigated procedures which may be used for this indication. We therefore evaluated the features of a new 3D image intensifier used for navigated iliosacral screw placement compared to 2D fluoroscopic and CT navigation. MATERIALS AND METHODS: Twenty fixed human cadavers were used in this trial. Cannulated cancellous screws were percutaneously implanted in the supine position in four treatment groups. An optoelectronic system was used for the navigated procedures. Screw placement was postoperatively assessed by fluoroscopic 3D scan and CT. The target parameters of this investigation were practicability, precision as well as procedure and fluoroscopic time per screw. RESULTS: All navigated procedures revealed a significant loss of time compared to non-navigated screw placement (2D: p<0.001, 3D: p>0.05, CT: p<0.001). Simultaneously a significant decrease of radiation exposure time was observed in the navigated groups (p<0.001 each). The misplacement rate was 20% in the non-navigated and the 2D fluoroscopic navigated group each. Procedures providing 3D imaging of the posterior pelvis did not produce any screw misplacement (p>0.05). However, the CT procedure was associated with time-consuming registration and high rates of failed matching procedures. CONCLUSION: Our data show a clear benefit of using C-arm navigation for iliosacral screw placement compared with the CT-based procedure. While both fluoroscopy-based navigation procedures decrease intraoperative radiation exposure times, only 3D fluoroscopic navigation seems to improve the precision compared to non-navigated screw placement.

[The Merkel cell: morphology, developmental origin, function]. / Merkelova bunka: morfologie, vývojový puvod, funkce.

Merkel nerve endings are mechanoreceptors in the vertebrate skin. They were named after the person who first described them--F.S. Merkel (1875). They consist of large, pale cells with lobulated nuclei forming synapse-like contacts with enlarged terminal endings of myelinated nerve fibres. Inside the cell are intermediate filaments formed of simple cytokeratins and osmophilic granules containing variety of neuropeptides. In mammals, they can be found in the basal layer of the skin and in those parts of the mucosa, which is derived from ectoderm. In contrast, in birds these cells are located in the dermis. The largest accumulation of Merkel nerve endings was found in whiskers of most mammals apart from man. There has been a controversy concerning the origin of Merkel cells. Results from chick/quail chimeras and most recently also from double transgenic mice have shown that Merkel cells are derived from the neural crest. Merkel cell play a role in the mechano-transduction process. In response to mechanical stimuli calcium ions enter Merkel cell and trigger the release of neurotransmitter probably glutamate. Thus, Merkel cell appears to be essential for characteristic slowly adapting response of these receptors during maintained mechanical stimuli. Cells in the skin of a similar appearance as Merkel cells are probably part of the diffuse neuroendocrine system and they do not function as mechanoreceptors. These cells, rather than those in mechanoreceptors, are most likely the origin of the highly malignant skin cancer called Merkel cell carcinoma.

Topography of muscle spindles and Golgi tendon organs in shoulder muscles of "Monodelphis domestica".

The topography of muscle spindles and Golgi tendon organs in the rotator cuff and surrounding shoulder muscles of a small laboratory marsupial (monodelphis domestica) were studied using light microscopy of serial sections. The shoulder joint of monodelphis has a large degree of freedom of movement allowing this animal to use the upper extremities for a wide range of activities like climbing and manipulating food. Thus, similar to the situation in man the shoulder joint is mainly secured by muscles. Silver stained serial paraffin sections were examined under the light microscope and the distribution of muscle spindles and Golgi tendon organs was reconstructed using three-dimensional image processing. In the two animals examined 113 and 131 muscle spindles respectively were found within the 4 rotator cuff muscles. In addition, 76 and 40 Golgi tendon organs respectively were seen at the musculo-tendinous junctions of these muscles preferentially close to the insertion at the humerus head. Also the surrounding shoulder muscles contain both muscle spindles and Golgi tendon organs in large numbers, but the ratio of Golgi tendon organs per muscle spindle appears to be lower. Number and localization of muscle spindles and Golgi tendon organs suggest, that these receptors are important for both reflex control of shoulder muscle tone as well as monitoring of static position and movement in the shoulder joint.

Topography of corpuscular mechanoreceptors in the shoulder joint region of monodelphis domestica.

The topography and structure of corpuscular mechanoreceptors in the shoulder joint capsule and periarticular connective tissue of a small laboratory marsupial (monodelphis domestica) were studied using light and electron microscopy. This animal is known to use its upper extremities for a wide range of activities like climbing and manipulating food. Thus, the shoulder joint of this animal species has a similar wide range of movement as the human shoulder joint, but is small enough for serial sectioning in its entirety. Silver stained serial paraffin sections were examined under the light microscope and the distribution of the different types of mechanoreceptors was reconstructed using three-dimensional image processing. In addition, selected mechanoreceptors were studied electron microscopically. Approximately 100 small lamellated corpuscles were found in the dense connective tissue of the joint capsule close to the insertion on the scapula and in the thickening of the joint capsule close to the glenoid labrum. Ruffini corpuscles were found in much smaller numbers in the moderately dense connective tissue of the axillary region. Only very few Vater-Pacinian corpuscles were seen in the soft periarticular connective tissue. The large number and localization of mechanoreceptor corpuscles in the shoulder joint capsule especially close to the glenoid labrum suggests, that these specialized nerve endings are likely to play an important role in control of joint movement. They can induce protective reflexes during extreme movements in the shoulder joint preventing shoulder luxation by increasing the tone of muscles pressing the humerus head into the glenoid cavity.

Lectin and proteoglycan histochemistry of Merkel cell carcinomas.

Changes in carbohydrate residue expression and in proteoglycan distribution occur during different stages of tumor development and progression. However, few data concerning carbohydrate residue analysis as performed by lectin histochemistry and proteoglycan distribution of Merkel cell carcinoma, a rare malignant tumor of the skin, have been reported. Hence, lectin- and proteoglycan immunohistochemistry was performed on paraffin wax material of 9 cases of Merkel cell carcinomas characterized by cytokeratin and neurofilament immunohistochemistry. The lectin binding pattern of tumor cells varied between lectins with different sugar binding specificities, while within a given nominal sugar specificity intensities were remarkably similar between tumors from different patients. The most intensive reaction was observed using Con A (mannose/glucose-specific) followed by LCA with the same specificity and the N-Acetyl glucosamine-specific lectins (WGA, UDA, CMA), while no fucose binding sites were detected (UEA-I). In addition, N-Acetyl galactosamine residues were only occasionally detected. The lectin binding pattern of Merkel cell carcinoma cells indicated that predominantly N-linked glycans and not O-linked glycans, typical for mucins of most epithelia, were present. Hence these tumor cells were relatively undifferentiated and resembled stem cells more closely than differentiated epithelia. The tumor stroma was especially evaluated in this study and showed a lectin reaction, which was intermediate between the tumor cells and extra-tumoral stroma. For example, the reactions of N-Acetyl galactosamine-specific lectins were intensive in the extra-tumoral stroma but nearly negative in tumor cells, while the lectin reaction of the intra-tumoral stroma was similar to the cellular reaction. These results indicated an influence of tumor cells on the stromal constituents. Antibodies against chondroitin type glycosaminoglycans reacted with the tumor stroma and the pericellular substance around the tumor cells most intensely in - and around the major tumor septae which, in general, were well vascularized. The most intensive immunoreactivity was detected using the chondroitin-6-sulfate antibody. The cellular and membrane-associated reaction for heparan sulfate was less intensive in comparison to epidermal cells. In conclusion the pattern of lectin-binding sites, the high chondroitin(sulfate) specific reactivity and the relatively low intensity of heparan sulfate immunohistochemistry indicate a low degree of differentiation and high malignity of the tumors, which is consistent with the clinical behavior of Merkel cell carcinomas.

Lectin and proteoglycan histochemistry of feline pacinian corpuscles.

We studied carbohydrate residues of glycoproteins and proteoglycans (PGs) in peritoneal Pacinian corpuscles of five adult cats. Terminal monosaccharides of glycoproteins and related polysaccharides were identified by lectin histochemistry and the PGs and glycosaminoglycans (GAGs) by specific antibodies. The most intensive lectin staining reactions indicated an abundance of glycoconjugates with terminal mannose (Man) or sialic acid residues, but no complex-type oligosaccharides were detected within the corpuscles. Terminal fucose (Fuc) and galactose (Gal) residues typical for O-linked mucin-type glycoproteins generally associated with high water binding capacity were also absent. Antibodies against unsulfated chondroitin (C-0-S), chondroitin-4-sulfate (C-4-S), and decorin showed positive reactions in the interfibrillar spaces between the lamellae, around collagen fibers, and around the lamellae of the perineural capsule, especially in the outer parts known to contain Type II collagen. Biglycan showed a preference for the innermost part of the perineural capsule (intermediate layer), known to contain Type V collagen. Collagen V and biglycan are both linked to growth processes. Hyaluronic acid (HA), chondroitin-6-sulfate (C-6-S) chains, and a chondroitin sulfate proteoglycan (CSPG) were co-localized in the terminal glia. The study of carbohydrates with high water binding capacity may contribute to our understanding of the high viscoelasticity of Pacinian corpuscles.

Lectin histochemistry of microvascular endothelium in chick and quail musculature.

The lectin binding pattern of muscular microvessels in chick, quail and chick/quail chimeras was analysed. Paraffin wax sections of muscles from embryonic and adult animals were used. The biotin-labelled lectins were detected by avidin-alkaline phosphatase complex. The following lectins bound to muscular microvessels including arterioles, capillaries and venules of both species: SNA-I (Sambucus nigra agglutinin), MAA (Maackia amurensis agglutinin), AIA (Artocarpus integrifolia agglutinin), VAA-I, VAA-II and VAA-III (Viscum album agglutinin I-III), WGA (wheat germ agglutinin), LEA (Lycopersicon esculentum agglutinin). Endomysium and basement membranes of muscle fibres were also stained to a variable extent and intensity. Only SNA-I stained almost exclusively the endothelium of blood vessels. WFA (Wisteria floribunda agglutinin) bound to the quail endothelium only. MPA (Maclura pomifera agglutinin) marked vessels in adult muscles of chick and quail, but embryonic vessels were stained in quail only. Our results show that lectin histochemistry is a useful tool for visualisation of microvasculature in avian species. In particular, WFA and MPA can be used to determine the origin of endothelia in chick/quail chimeras.

Developmental origin of avian Merkel cells.

We have investigated the developmental origin and ultrastructure of avian Merkel cells by electron microscopy and chick/quail transplantation experiments. On embryonic day 3, chick leg primordia were homotopically grafted onto Japanese quail host embryo. Fourteen days later, quail cells that had migrated into grafted chick legs were identified according to the masses of heterochromatin associated with the nucleolus that are characteristic for quail. Both in chick and quail, Merkel cells are usually located in the dermis just below the epidermis. They are placed between nerve terminals either individually or in small groups wrapped in sheaths that are formed by glial cell processes. Occasionally, some Merkel cells appear in nerve fascicles and within Herbst corpuscles. Merkel cells, as well as glial cells, in grafted chicken legs were of quail origin. This finding provides evidence against the epidermal origin of avian Merkel cells and indicates that Merkel cells are derived from neural crest cells that colonise, together with glial cells and melanocytes, the developing limb primordium.

Sensory nerve endings in the hard palate and papilla incisiva of the goat.

The sensory innervation of the papilla incisiva in the hard palate of the domestic goat was studied with light and electron microscopy, supplemented by electrophysiological studies of free nerve endings. The goat lacks incisor teeth. Grass and leaves are not bitten, but pulled off by pressing them between the tongue and papilla incisiva. Thus, the masticatory mucosa is subject to particularly heavy mechanical loads requiring functional specialization of the horny epithelium in the form of thickening, i.e., the papilla incisiva and 12-14 pairs of rugae palatinae. A thin layer of firm connective tissue (lamina propria) attaches the mucosa to the periost of the hard palate. Sensory nerve fibers were found most abundantly in the papilla incisiva. Their number decreased drastically in aboral direction. A section through the first four rugae palatinae contains only about 10% of the number of free nerve endings found in the same area of mucosa from the papilla incisiva. Four types of sensory nerve endings were found. Free nerve endings were seen ubiquitously in the epithelium and superficial layer of the lamina propria. Merkel nerve endings were found in the bases of the epithelial thickenings in the papilla incisiva and rugae palatinae. Few Ruffini corpuscles were found in the deeper layer of the lamina propria, while lamellated corpuscles were seen just below the basement membrane of the epithelial pegs. Thus, a variety of sensory nerve endings were found in the hard palate, especially in those areas that are in close contact with the tongue during chewing of food. This rich innervation suggests an important role in monitoring the mechanical properties of food. Recordings were made from cell bodies supplying these terminals. Classic low-threshold, slowly adapting responses were observed in Ass afferent populations. This activity was probably mediated by Merkel type endings. Alternately, high-threshold and suprathreshold responses obtained from Adelta category afferents were likely to be nociceptive. In support of this, threshold and suprathreshold sensitization was observed following injection of serotonin into the receptive field of Adelta populations. This activity was likely to be derived from the aforementioned free nerve endings.

Distribution of sensory receptors in joints of the upper cervical column in the laboratory marsupial monodelphis domestica.

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.

Sensory nerve endings in the hard palate and papilla incisiva of the rhesus monkey.

The sensory innervation of the hard palate of the rhesus monkey was studied by light and electron microscopy. The mucosa of the hard palate is subject to a particularly heavy mechanical load requiring functional specialisation of the horny epithelium in the form of thickenings - the papilla incisiva and eight pairs of rugae palatinae. A thin layer of firm connective tissue (lamina propria) attaches the mucosa to the periost of the hard palate. Sensory nerve fibres were found most abundantly in the papilla incisiva and first rugae palatinae. Their number decreases in an aboral direction. Five types of sensory nerve endings were found. Free nerve endings were ubiquitous in the epithelium and lamina propria. Merkel nerve endings were found in the basal layer of the epithelium of the papilla incisiva and rugae palatinae. Meissner corpuscles were located in the connective tissue between epithelial pegs, while lamellated corpuscles were seen below the epithelial pegs. Ruffini corpuscles were found in the deeper layer of the lamina propria. Thus, a variety of sensory nerve endings were found in the hard palate, especially in those areas that are in close contact with the tongue during chewing of food. This rich innervation suggests an important role in monitoring the mechanical properties of food and the position of the tongue.

Development of mechanoreceptor numbers in embryonic chick-quail chimeras.

Our experiments addressed the problem of the regulation of the number of mechanoreceptors by sensory axons and/or their peripheral target tissues. According to a previous study (Zelená et al. 1997) white leghorn chickens have more muscle spindles in the plantaris muscle (45.4+/-7.8; mean+/-SD) than the Japanese quail (35.3+/-4.8) and significantly more Herbst corpuscles in the crural region (380.0+/-85.0) than the quail (124.9+/-32.8). Embryonic chick-quail chimeras were therefore used as a model with distinct recombinations of the nerve supply and peripheral tissue for studying the developmental control of these mechanoreceptors. The chick host leg bud was replaced with a quail leg bud of equal age and vice versa on embryonic day 3, prior to the onset of innervation of the periphery. Shortly before hatching the chimeras were sacrificed and muscle spindles and Herbst corpuscles counted. Recombinations of chicken nerves with quail limb buds have shown that the richer nerve supply by chick Ia axons induced a significant increase in the number of muscle spindles in the plantaris muscles (55.5+/-13.4) of the grafted quail limb. In some instances, a similar increase in spindle numbers was also found in control legs grafted onto hosts of the same species. In the reverse type of chimera where chick embryo legs were grafted onto quail hosts, spindles developed in lower numbers (27.3+/-3.2). In that case the lower number of Ia axons in quail nerves induced a lower number of spindles in the chicken muscle. The numbers of Herbst corpuscles were, however, low in both types of chimera. Quail legs grafted onto host chick embryos contained 126.8+/-26.4 corpuscles, presumably due to a restrictive influence of the smaller crural area in the quail. Chick legs grafted onto quail hosts had only 99.6+/-34.1 crural corpuscles; the target area in chick embryo legs failed to attract more quail axons and/or to induce axonal sprouting. The developmental regulation of the number of the two types of mechanoreceptors examined in our study thus differ. While sensory axons appear to play the dominant role in the development of muscle spindles, their role seems to be restricted by hitherto unknown peripheral factors during the development of Herbst corpuscles.

Sensory nerve endings in the anterior cruciate ligament (Lig. cruciatum anterius) of sheep.

This study examines the structure of sensory nerve endings in the sheep anterior cruciate ligament (ACL). Three types of nerve endings are found: free nerve endings (FNE), Ruffini corpuscles, and lamellated corpuscles. The FNE (more than 100) are found subsynovially. The afferent nerve fibres are either thin myelinated axons (Adelta) or C fibres with diameters of 1-2 microm. FNE have been reported to function as thermoreceptors and polymodal nociceptors. In addition, FNE are also seen between fascicles of collagen fibres, often close to blood vessels. Part of this group may be efferent autonomic fibres controlling local blood flow. The corpuscles are seen subsynovially and between fascicles of connective tissue close to the attachment points of the ACL. A ligament contains about 20 Ruffini corpuscles, which are mainly located in the subsynovial connective tissue. They consist of cylinders formed from perineural cells surrounding the afferent myelinated axons (diameters 4-5 microm) with enlarged nerve terminals anchored between collagen fibres. These enter in bundles from the surrounding connective tissue at one open pole, pass through the length of the cylinder, and leave at the other pole. Functionally, Ruffini corpuscles have been described as slowly adapting stretch receptors. Lamellated corpuscles (usually between 5 and 15) are found in the subsynovial connective tissue. The afferent myelinated axon has a diameter of 4-6 microm, and the nerve terminal is located in the centre of numerous layers formed by lamellated terminal glial cells and by a perineural capsule. They are known to function as rapidly adapting pressure receptors. The most important function of the ACL is its mechanical function, but additional sensory functions must be considered triggering reflex mechanisms in case of extreme positioning or overload.

Crural Herbst corpuscles in chicken and quail: numbers and structure.

Herbst corpuscles were studied in the crural region of perinatal and adult chicken and quail in order to find out their number and dimensions and to learn more about their structure, especially in relation to size. Crural corpuscles are arrayed in an encapsulated string between tibia and fibula. They are closely packed together; a small number of corpuscles is found apart from the string, often attached to the periost. The strings of corpuscles are approximately 40 mm long in adult chicken and 20 mm long in the quail. The crural region of the chicken contains 382.8 +/- 90.9 (mean +/- SD) corpuscles, the numbers ranging from 301 to 582; in the quail, the mean number is 119.2 +/- 27.9, with a range from 83 to 167 corpuscles. In the chicken, one axon supplies an average of 1.60 corpuscles; in the quail, the relation of axons to corpuscles is approximately 0.92. In both species, final numbers of crural corpuscles are already attained before hatching and no difference is found in the mean number and range of corpuscles between perinatal and adult birds. In both chicken and quail, individual strings contain corpuscles of various sizes, from large to very small. The chicken corpuscles are generally twice as large in diameter and often longer than those of the quail. The corpuscles are composed of an axon terminal that projects two rows of axonal spines into the clefts of the inner core and ends with an ultraterminal bulb; the terminal is surrounded with a bilaterally symmetrical inner core, amorphous inner space containing collagen fibrils of various thickness, and a capsule. Large chicken corpuscles contain inner cores composed of up to 100 lamellae, while quail inner cores have half that number at the most. The capsules are usually composed of 8 to 10 lamellar layers in both species, but they are thicker in the chicken than in the quail. The possible functional significance of individual structural components of Herbst corpuscles is discussed.

Topography of mechanoreceptors in the shoulder joint region--a computer-aided 3D reconstruction in the laboratory mouse.

BACKGROUND: We investigated the pattern of distribution of corpuscular sensory nerve endings in the shoulder region of the laboratory mouse in relation to their functional properties. METHODS: Twelve adult female white NMRI-F2-mice were used. The topography of sensory nerve endings in the shoulder joint region was reconstructed by three-dimensional image processing by using serial silver-stained sections of paraffin-embedded samples. Semithin sections obtained from additional samples were used for light microscopy. RESULTS: Within the fibrous layer of the joint capsule, three types of mechanoreceptors were identified: small lamellated corpuscles of the Pacini type, Ruffini corpuscles, and Golgi tendon organs. Intracapsular small lamellated corpuscles of the Pacini type (in an average number of 29/joint) were found mainly in three areas: in the predominantly flaccid tissue of the axillary region, in the denser ventromedial parts of the capsule, close to the scapula, and in the tight texture of the fiber bundles near the glenoid labrum. Ruffini corpuscles were identified only in small numbers (2/joint) in the ventral aspect of the articular capsule of two animals. Golgi tendon organs (14 or 15 receptors/joint) were discovered predominantly in close vicinity to the joint capsule at the muscle tendon junction of the inserting rotator cuff muscles and in the biceps brachii and triceps brachii muscles. CONCLUSIONS: In view of their location in the shoulder joint capsule and the glenoid labrum, corpuscular mechanoreceptors evidently play an important role in joint control by inducing protective reflex actions in phases of extreme or abnormal movement. The density of sensory receptors in distinct areas of the shoulder joint capsule appears to be related to zones that are subjected to increased biomechanical stress during physical activity.

The structure of sensory nerve endings in the knee joint capsule of the dog.

The ultrastructure and distribution patterns of sensory nerve endings in the dorsal knee joint capsules of the beagle dog (Canis familiaris) have been investigated using light and electron microscopy. Each dorsal knee joint capsule was divided into four quadrants, cut into small pieces and then processed for electron microscopy. Free nerve endings and corpuscular nerve endings (Ruffini and lamellated corpuscles) were found. They were most frequently observed in the medial-proximal quadrant of the dorsal joint capsule. All nerve endings were found to be situated within or adjacent to the fibrous layer of the capsule. No nerve endings were found within the synovial layer. Free nerve endings were usually situated at the border between the fibrous layer and the synovial layer near blood vessels. Their associated afferent axon was myelinated (1.5-2.5 microns in diameter) or non-myelinated (0.3-1.5 microns in diameter). Ruffini corpuscles were found in the fibrous layer and within the dorsal ligamentous apparatus. Each Ruffini corpuscle was surrounded by a multilayered perineural capsule which was usually incompletely developed. The perineural capsule is the continuation of the perineurium of the afferent axon and gives a cylindrical form to the corpuscles. Ruffini corpuscles were present as single, cylindrical structures (small corpuscles) or as aggregates of these cylinders (large corpuscles). Both varieties consist of terminal nerve endings surrounded by collagen fibres which pass through the opened ends of the cylinders. The diameter and length of the small Ruffini corpuscles were 80 microns and 400 microns, as compared to 200 microns and 800 microns for the large aggregated forms. The supplying afferent axons of both types were 4-5 microns in diameter. Two types of small lamellated corpuscles could be observed in the fibrous layer: very small corpuscles, 55 microns long, 25 microns wide and medium corpuscles, 100 microns long, 40 microns wide. Each consists of an inner core of terminal Schwann cells, a nerve terminal and a perineural capsule. Some lamellated corpuscles had two inner cores and two nerve terminals. The diameter of the afferent axon was approximately 6 microns. Vater-Pacini corpuscles were not found in the dorsal knee joint capsule of the dog.

Selective phototoxic destruction of quinacrine-loaded Merkel cells is neither selective nor complete.

Experiments were performed on slowly adapting type I mechanoreceptors in an isolated rat skin-nerve preparation (SA I receptors) and in an isolated rat sinus hair preparation (St I receptors). Merkel cells were stained in vitro with the fluorescent dye quinacrine and irradiated with ultraviolet (UV) light (2 mW for up to 1 h) while recording receptor responses to standard mechanical stimuli every 30 s. In addition, thresholds for electrically evoked action potentials were tested by applying electrical stimuli to the skin through the same stylus used for mechanical stimulation. UV irradiation resulted in abrupt failure to respond to mechanical stimuli in 73% of the SA I receptors examined (n = 37) within less than 1 h. This confirms previous reports of phototoxic destruction of Merkel cells. However, several minutes after the receptors failed to respond to mechanical stimulation, thresholds for electrical stimuli applied to the receptive field increased sharply. About 40% of the St I receptors (n = 13) irradiated with UV light following quinacrine staining stopped responding to bending of the hair within 1 h. In contrast, none of the seven St II receptors treated in the same way showed significant changes in the responses. Electron microscopic examination of sinus hairs after quinacrine staining alone showed slight changes in the appearance of Merkel cells, and in particular enlargement of the perinuclear space. These changes did not affect receptor responses. Electron microscopic studies of sinus hairs with receptors that had maintained normal responses to mechanical stimuli after quinacrine staining and 1 h of UV irradiation revealed that a substantial number of Merkel cells still had a normal ultrastructure while adjacent nerve terminals were severely swollen and partially compressing the Merkel cells. No changes were observed in lanceolate nerve terminals forming the morphological substrate of St II receptors. These results demonstrate that sensitivity to phototoxic destruction following quinacrine staining varies greatly among Merkel cells, with some maintaining normal function and ultrastructural appearance even after 1 h of UV irradiation. On the other hand there is clear evidence that the phototoxic damage affects the nerve terminals as well. Such experiments can therefore not provide conclusive proof about the role of Merkel cells in these mechanoreceptors.

Chloroquine specifically impairs Merkel cell mechanoreceptor function in isolated rat sinus hairs.

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.

An isolated rat vibrissal preparation with stable responses of slowly adapting mechanoreceptors.

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.