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J Zelená

Publications and source records attributed to J Zelená.

At least 19 recordsLinked to original sources
PubMed1999

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.

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PubMed1997

Reinnervation of cat pacinian corpuscles after nerve crush.

The reinnervation pattern of crural pacinian corpuscles was examined by light and electron microscopy in eight adult cats of both sexes 3-18 months after sciatic nerve crush. Normal pacinian corpuscles are each supplied with a single myelinated axon and a single cylindrical axon terminal which may branch in the distal part of the inner core. Reinnervation of these vibroreceptors was very satisfactory after sciatic nerve crush: in a sample of 68 corpuscles examined 3-18 months after the operation, 92.6% were found reinnervated, while only 7.4% remained denervated. At the nerve entry, 84.2% of the reinnervated corpuscles were supplied with a single myelinated axon, while 15.8% received two myelinated axons; some of the axons branched before and after entering the inner core. Near the mid-level of the inner core, 60.3% of 63 reinnervated corpuscles were innervated with a single axon terminal, 22.2% were bilateral, while 17.5% had three or more terminals. Regenerated axon terminals induced the formation of thin lamellar layers in the axial region of the original core and, exceptionally, also at the outer aspect of the original core. In monoterminal corpuscles, the shape and ultrastructure of regenerated endings resembled those of normal controls, whereas in multiterminal corpuscles their shape and profiles were variable. In contrast to previous reports, reinnervated corpuscles did not ultimately become monoterminal. On the contrary, the mean number of 1.3 terminals found in reinnervated crural corpuscles at 3-5 months increased to 1.9 terminals per corpuscle 6-18 months after axotomy.

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PubMed1997

Regeneration of tactile lamellar corpuscles of the rat after postnatal freeze injury.

Tactile lamellar corpuscles were studied after freeze injury of rat toe pads under normal conditions and following permanent denervation in 1- to 65-day-old animals. In the innervated skin, digital corpuscles redifferentiated in all age groups examined during development and maturation. Characteristic of the reinnervated skin was a great diversity in the shape and size of newly formed corpuscles. Small corpuscles with only 1-3 lamellae around their terminals and well-developed corpuscles of about normal size with up to 15 lamellae were sometimes found within the same sample of skin. The regenerated corpuscles were reduced in number; they reappeared in only 50% of dermal papillae in the toe pads after freeze injury in 7-week-old rats, compared with approximately 100% of dermal papillae that contained lamellar corpuscles in normal toe-pad skin. In denervated toes, occasional corpuscular lamellar structures appeared first after freeze injury applied to 34-day-old rats. In the toe pads denervated and injured by freezing in 42- and 49-day-old rats, lamellar structures redifferentiated in about 10% of the papillae, and in 23.5% after freeze injury applied to 2-month-old rats. Unsatisfactory preservation of basal laminae at the former sites of the corpuscles and in the acellular peripheral nerve stumps, and/or insufficient migration of Schwann cells, may be responsible for the absence or abortive regeneration of lamellar structures in denervated skin of food pads after freeze injury in young rats.

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PubMed1997

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.

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PubMed1995

Reinnervation of rat Pacinian corpuscles after nerve crush during the postcritical period of development.

The ultrastructure of crural Pacinian corpuscles was examined after sciatic nerve crush performed in 7- to 20-day-old rats, i.e. during the postcritical period of development when the corpuscles no longer degenerate after axotomy but cease growing. The aim of our study was to assess the innervation pattern and structural changes of the corpuscles following transient denervation and subsequent reinnervation during their maturation and growth. Reinnervated corpuscles were examined by electron microscopy from 2.5 months after nerve crush onwards. After sciatic nerve crush at 7 days of age, the corpuscles are mostly reinnervated with multiple axon terminals, each of them enclosed within a newly formed inner core. The axial multiple cores are in part covered by a layer of concentric inner core lamellae and surrounded by a capsule, both structures having survived from the original corpuscle. After nerve crush at 10 days of age, reinnervated Pacinian corpuscles usually contain, in their axial region, a denervated remainder of the original core together with a few regenerated axon terminals enclosed within new inner cores. These axial structures are surrounded by a layer of concentric lamellae of the original core which may accommodate some regenerated terminals. Additional axon terminals with their small inner cores may be found at the outer aspect of the composite core beneath the capsule. When the nerve is crushed in 15-day-old rats, the inner core which is already well developed remains preserved by the time of reinnervation, and regenerating axons grow in between the original lamellae inducing only moderate neoformation of 2-3 lamellar layers which enclose the terminals. After crushing the sciatic nerve in 20-day-old rats, formation of new inner core lamellae is minimal and regenerated terminals become accommodated between the original lamellar of the core as is the case in adult animals. Regeneration of new inner cores and reinnervation of the preserved lamellar structure thus characterize the recovery of Pacinian corpuscles following reinnervation after nerve crush during the postcritical period of their development.

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PubMed1994

Reinnervation of Pacinian corpuscles by CNS axons after transplantation to the dorsal column: incidence and ultrastructure.

We have investigated the capacity of injured axons in the spinal dorsal columns of young adult rats to reinnervate grafted Pacinian corpuscles. A branch of the hindlimb interosseous nerve with a group of crural Pacinian corpuscles attached to it was autotransplanted to the surface of the spinal cord and the nerve stump was implanted into the dorsal column. Two to three months later 16 grafts were removed for examination by light and electron microscopy. By 3 months after transplantation almost all Schwann cell columns of the grafted nerve branch were occupied by regenerated myelinated and unmyelinated axons. Of 41 corpuscles examined by electron microscopy 24 were reinnervated by 1-3 myelinated fibres which gave rise to multiple terminals in the inner core. The remaining corpuscles appeared to be denervated. Only two of the reinnervated corpuscles contained regenerated endings which reiterated the distinct ultrastructure of normal presynaptic terminals of CNS axons, characterized by clusters of lucent vesicles and paramembranous densities. All other corpuscles were reinnervated by terminals which resembled peripheral mechanosensory endings as they contained mitochondria and very few vesicles. One such corpuscle was coinnervated by small terminals filled with large dense cored vesicles. We assume that the majority of grafted Pacinian corpuscles have been reinnervated by dorsal column axons and that the regenerated terminals with the ultrastructure of peripheral mechanosensory endings derive from central axons of primary sensory neurons, which are apparently capable of constructing mechanosensory-like terminals in response to signals from the Pacinian corpuscles. The vesicle-filled endings are probably formed by second order sensory neurons, corticospinal neurons and small peptidergic neurons unable to adjust their terminals to the new target.

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PubMed1993

Increase in the number of intrafusal muscle fibres in rat muscles after neonatal motor denervation.

Rat muscle spindles disintegrate after total neonatal muscle denervation in which both sensory and motor axons are cut, but develop almost normally during the first three weeks after neonatal de-efferentation, attaining the usual complement of four intrafusal fibres, two bag and two chain fibres. Thereafter additional intrafusal fibres differentiate in most of the de-efferented spindles. We have examined the development of supernumerary fibres in muscle spindles of the rat hind limb muscles one to four months after neonatal de-efferentation using transmission electron microscopy. Additional intrafusal fibres originate both from activated intrafusal myosatellites and by different forms of fibre division. In a sample of 27 muscle spindles examined along the A zone five weeks after de-efferentation, the mean number of intrafusal fibre profiles increased almost two-fold to 7.9 +/- 3.3 (S.D.). Up to 20 intrafusal fibre profiles per spindle cross-section were found in muscles de-efferented for four months. The supernumerary fibres were apparently derived from all three intrafusal fibre types, but predominantly from the chain fibres. It is noteworthy that de-efferentation which causes wasting of extrafusal muscle initiates myogenesis and maintains additional intrafusal fibres within the spindle capsules.

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PubMed1990

Reinnervation of transplanted pacinian corpuscles by ventral root axons: ultrastructure of the regenerated nerve terminals.

This study addresses two questions. Can mature, denervated and transplanted Pacinian corpuscles accept innervation from motor axons? If so, does the alien target influence the structural characteristics of the regenerated motor axon terminals? Pacinian corpuscles from the hind leg of young rats, together with a segment of the nerve branch through which they receive their sensory innervation, were autotransplanted to the surface of the spinal cord and the nerve stump anastomosed to the central stump of a transected lumbar ventral root. Between 4 and 5 months later the grafts were studied by electron microscopy. Ventral root axons regenerated through the endoneurial tubes of the grafted nerve to reach the corpuscles, most of which became reinnervated by one to three myelinated fibres. The fibres lost their myelin sheaths before entering the inner core, branched, and gave rise to multiple terminals in the inner core. The regenerated terminals were packed with spherical synaptic vesicles and closely resembled normal motor nerve terminals. Thus motor axons are able to reinnervate Pacinian corpuscles but the structural characteristics of the terminals are apparently not modified by the alien target tissue. This finding contrasts with previous studies, in which it was found that terminals of the central axons of large dorsal root ganglion cells, induced to reinnervate Pacinian corpuscles, displayed the structural characteristics of peripheral sensory endings rather than those of dorsal root terminals in the spinal cord.

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PubMed1990

Effacement and regeneration of tactile lamellar corpuscles of rat after postnatal nerve crush.

The development of Meissner-like lamellar corpuscles was studied in rat toe pads under normal conditions and after crushing the sciatic nerve in 1- to 15-day-old animals. During normal development, rat lamellar corpuscles begin to differentiate first by postnatal day 8. By this time, sensory axons have grown up to the apex of dermal papillae and form axon terminals beneath epidermis. The terminals are ensheathed by lamellar cells derived from Schwann cells. First thin lamellae are formed around the terminals 8-12 days after birth, and the number of lamellar layers increases until the corpuscles become structurally mature by 20 days after birth. A mature corpuscle consists of two or more terminals, each surrounded by approximately 10 lamellae, all components being enclosed by an incomplete capsule. No lamellar corpuscles develop in toe pads after crushing the sciatic nerve in newborn rats, and only occasional corpuscles regenerate after nerve crush at 5 days of age. The corpuscles fail to develop because dermal papillae remain permanently denervated after crushing the nerve early postnatally. After nerve crush in 10-day-old rats, lamellar corpuscles regenerate by 1 month after the operation, but they remain underdeveloped: their number and size are smaller than normal even 1 year after injury, and their terminals are encircled only by 1-3 lamellar layers. After nerve crush in 15-day-old rats, the corpuscles recover upon reinnervation and their size and lamellation become almost normal.

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PubMed1988

Grafts of pacinian corpuscles reinnervated by dorsal root axons.

In adult rats, a piece of the crural interosseous nerve with several Pacinian corpuscles attached was removed from the crural region, autotransplanted onto the surface of the lumbar spinal cord and connected with the peripheral stump of a transected dorsal root. From 10 days up to 6 months after the operation, the grafts were investigated by light and electron microscopy. The regenerating dorsal root axons grew along the grafted nerves into the attached Pacinian corpuscles. By 1-2 months after the operation, the nerves and their branches became almost completely reinnervated by myelinated and unmyelinated dorsal root axons. In a sample of corpuscles examined 2-6 months after grafting, 75% of corpuscles were found reinnervated; each of them was supplied by 1-5 large myelinated axons that formed multiple axon terminals in the inner core. The maximal number of axonal profiles found in a transverse section through different levels of the inner core varied, in individual corpuscles, from 3 to 17 axons and terminals. The dorsal root terminals formed in the grafted corpuscles were mainly filled with mitochondria and resembled peripheral sensory endings. In some instances, the newly formed endings developed lateral processes and membrane specializations characteristic for peripheral Pacinian terminals. Thus regenerating dorsal root axons recognize a grafted peripheral mechanoreceptor as their target and reinnervate it with axon terminals, most of them structurally transformed into peripheral sensory endings.

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PubMed1986

Transplantation of pacinian corpuscles of the rat into the brain.

In adult inbred rats of the AVN strain, branches of the crural interosseous nerve were dissected out from donors and transplanted into the brain of recipients, together with a cluster of Pacinian corpuscles, (either into a suction cavity or the cerebral cortex) into a slit 1-2 mm deep. The grafts were fixed and processed for electron microscopy 10 days to 6 months after the operation, and their ultrastructure was examined. Sporadic axons of small diameter grew into the nerve branches of some of the grafts from 11 days onward, and became myelinated during the 2nd month after the operation, but none of the transplanted Pacinian corpuscles became reinnervated. The corpuscles, however, survived denervation and grafting. Most of them retained a well-preserved inner core and an intact capsule, consisting of a normal complement of 29.2 +/- 1.0 (mean +/- SE) capsular layers (n = 8), as did the corpuscles previously examined after denervation in situ. Some of the corpuscles underwent degenerative changes, presumably due to a delayed or restricted revascularization. In this group of corpuscles, the inner core underwent disintegration and was gradually replaced by collagen fibrils, whereas the capsule remained preserved but the number of its layers eventually reduced by 40%. It is assumed that the lack of reinnervation of the grafted Pacinian corpuscles was due to the paucity of regenerating axons, and their failure to form correct projections along those Schwann cell columns connected with the corpuscles.

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PubMed1985

Structure of tendon organs of the rat after neonatal de-efferentation.

The number, size and structure of tendon organs were examined in leg muscles of the rat 3-19 weeks after de-efferentation performed in newborn animals by removal of the lumbosacral spinal cord. After this operation, tendon organs differentiated and grew in disused muscles and were innervated by primary sensory neurons, the dorsal roots of which had been disrupted. Three weeks after de-efferentation extensor digitorum longus muscles contained 14.1 +/- 1.0 (mean +/- standard error) and soleus muscles had 14.2 +/- 1.6 tendon organs, which corresponds to the mean number of tendon organs in the respective control muscles. The mean size of tendon organs was, however, changed. Tendon organs became on the average by 53% longer and by 35% thinner in de-efferented extensor digitorum longus muscles that were prolonged due to immobilization, as compared with shorter and wider tendon organs in de-efferented soleus muscle that remained in the shortened position. The ultrastructural differentiation of tendon organs was completed after the operation as under normal conditions. Thus it can be concluded that elimination of muscle function during the period of postnatal development indirectly affects the mean size of these receptors, but does not otherwise interfere with their morphogenesis.

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PubMed1985

The differentiation of muscle stretch receptors in the rat after neonatal de-efferentation.

It has been established previously that muscle stretch receptors of the rat fail to develop after neonatal denervation, but differentiate in full number per muscle after de-efferentation, when sensory innervation remains preserved. Recent immunocytochemical and morphometric studies have revealed, however, that some properties of stretch receptors are altered after motor denervation. In de-efferented muscle spindles, the maturation of myosin of the nuclear bag fibres becomes arrested. In de-efferented tendon organs, the mean length becomes increased and mean width decreased in in extensor digitorum longus muscles which become prolonged after de-efferentation, whereas the opposite changes occur in de-efferentation soleus muscles which become shortened. In spite of these alterations, however, neonatal de-efferentation does not impede the differentiation of ultrastructural characteristics and functional properties of stretch receptors. Thus motor innervation and muscle function are dispensable, whereas sensory innervation is absolutely essential for the development of stretch receptors.

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PubMed1984

The effect of long-term denervation on the ultrastructure of Pacinian corpuscles in the cat.

The ultrastructure of Pacinian corpuscles of the cat located in the crural region and innervated by the interosseous nerve was studied 1 to 14 months after denervation. Both the Pacinian inner core and capsule remained well preserved one month after denervation. However, the denervated inner cores underwent progressive atrophy and wasting, which resulted in a gradual reduction of the amount of inner-core cells and lamellae, widening of interlamellar clefts, formation of empty spaces in the axial region and a considerable increase in the number of collagen fibrils. In spite of the wasting, the inner core still survived 14 months after denervation, but at least half of its volume became occupied by collagen fibrils which surrounded the remaining inner-core cells and lamellae. Collagen fibrils assembled in the denervated core were markedly thinner than those found in the capsule, as is also the case in normal Pacinian corpuscles. In the capsule, discrete focal degeneration, occasional pyknosis of the innermost capsular cells and macrophage infiltration were observed from the first month after nerve section onward, but the number of capsular layers remained within the normal range (30-40) up to 14 months after denervation.

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PubMed1984

Multiple axon terminals in reinnervated Pacinian corpuscles of adult rat.

The ultrastructure of Pacinian corpuscles localized beneath the crural interosseous membrane was examined two weeks to 18 months after crushing the sciatic nerve in adult rats. The Pacinian inner core and capsule remained preserved during the transient period of denervation. Regenerating axons reached Pacinian corpuscles approximately three weeks after nerve crush. Up to 15 axonal sprouts entered a single corpuscle at the initial stage of reinnervation, but only 1-3 axons increased in size, myelinated and formed axon terminals in the inner core, the excess sprouts being eliminated. Most corpuscles of the crural group were reinnervated by the end of the first month. Three to 19 months after nerve crush, 10% of corpuscles examined were found to be monoaxonal and monoterminal as before the operation; 74% contained multiple terminals; 16% remained denervated. Over half the multiterminal corpuscles were supplied with a single myelinated axon that branched inside the corpuscles; the rest received two or three myelinated axons which formed several terminals. The terminals were distributed at random, usually in the axial region between the lamellae of the inner core. They were cylindrical, with an oval profile; the larger terminals were filled with mitochondria and microtubules at their circumference and contained a core of neurofilaments. Lateral processes of the terminals were filled with vesicles and had membrane specializations as in normal corpuscles. The mean number of terminals in reinnervated corpuscles was 4.07 +/- 0.37 (S.E.M.) at three months, and 3.26 +/- 0.49 (S.E.M.) 6-18 months after nerve crush. This small decrease was apparently the result of degeneration occasionally observed in some axon terminals at later stages of reinnervation. These experiments thus demonstrate that most rat Pacinian corpuscles become reinnervated with multiple terminals after nerve injury and maintain multiterminal innervation permanently.

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PubMed1983

The in-series and in-parallel components in rat hindlimb tendon organs.

The structure of the tendon organs was studied in the shank muscles of adult rats both under the light- and electron-microscope. The rat tendon organs measure on the average about 500 microns in length and 60 microns in diameter. Most tendon organs are surrounded by muscle fibres and their short individual tendons, and insert into the aponeuroses or intramuscular tendons. Each tendon organ consists of a neurotendinous core composed of collagen bundles that represent tendons of 5-10 muscle fibres; it is innervated by a Ib sensory fibre that branches and terminates among the loose collagen fascicles of the core. Sensory terminals are oriented both transversely and longitudinally. Their position and relation to collagen bundles indicate that, during tendon organ activation, the terminals are probably depolarized both by lateral compression and elongation. The core is enclosed in a capsule that consists of about 5 lamellar layers of capsular cells and closely resembles the perineurium. The majority of the tendon organs also comprise a purely tendinous compartment in the lumen or within the capsular wall. These tendinous components remain separated from the neurotendinous core and do not come into contact with axon terminals. The collagen fibrils of the tendinous compartments are densely packed and larger in diameter than those of the neurotendinous core. The sensory terminals of the tendon organ lie in series with those muscle fibres and collagen bundles that constitute the neurotendinous core, but they are in parallel with the purely tendinous tendon organ components and their respective muscle fibres. Thus, one tendon organ may comprise both in series and in parallel components, which is apparently reflected in its function. It is suggested that the purely tendinous tendon organ compartments account for the in-parallel effects upon the function of tendon organs described in some recent electrophysiological studies.

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PubMed1982

Survival of Pacinian corpuscles after denervation in adult rats.

The ultrastructure of Pacinian corpuscles located on the crural interosseous membrane was studied in adult rats 6h to 10 months after transection of the right sciatic nerve. Axon terminals degenerated one day after transection and were engulfed and resorbed by cells of the inner core within one week. The axial space left after removal of the axonal debris was closed by the lamellae of the inner core. The main structural features of the inner core and capsule remained preserved after denervation throughout the period of study. The denervated inner cores, however, became atrophic 10 months after neurotomy, their mean diameter being reduced by 17.5% compared with that of contralateral control corpuscles. The number of capsular lamellae was unaltered, and perineurial pathways of the peripheral nerve stump remained preserved. Schwann cells proliferated and formed Büngner bands during the first month after denervation, but retracted their processes and became atrophic at later stages after neurotomy. Survival of Pacinian corpuscles after long-term denervation in adult rats is in contrast to their rapid degeneration within several days after nerve section in neonates.

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