Status epilepticus (StE) in immature rats causes long-term functional impairment. Whether this is associated with structural alterations remains controversial. The present study was designed to test ...the hypothesis that StE at an early age results in neuronal loss. StE was induced with lithium-pilocarpine in 12-d-old rats, and the presence of neuronal damage was investigated in the brain from 12 hr up to 1 week later using silver and Fluoro-Jade B staining techniques. Analysis of the sections indicated consistent neuronal damage in the central and lateral segments of the mediodorsal nucleus of the thalamus, which was confirmed using adjacent cresyl violet-stained preparations. The mechanism of thalamic damage (necrosis vs apoptosis) was investigated further using TUNEL, immunohistochemistry for caspase-3 and cytochrome c, and electron microscopy. Activated microglia were detected using OX-42 immunohistochemistry. The presence of silver and Fluoro-Jade B-positive degenerating neurons in the mediodorsal thalamic nucleus was associated with the appearance of OX-42-immunopositive activated microglia but not with the expression of markers of programmed cell death, caspase-3, or cytochrome c. Electron microscopy revealed necrosis of the ultrastructure of damaged neurons, providing further evidence that the mechanism of StE-induced damage in the mediodorsal thalamic nucleus at postnatal day 12 is necrosis rather than apoptosis. Finally, these data together with previously described functions of the medial and lateral segments of the mediodorsal thalamic nucleus suggest that some functions, such as adaptation to novelty, might become compromised after StE early in development.
The ultrastructure of regenerating intrafusal and extrafusal fibers was studied 18 h to 30 days after heterochronous isotransplantation, in which bupivacaine-treated extensor digitorum longus (EDL) ...or soleus muscles from early postnatal rats were intramuscularly grafted into EDL muscles of adult inbred recipients. As in other models of mammalian muscle regeneration, surviving satellite cells gave rise to presumptive myoblasts, multiplying within the preserved basal lamina tubes at day 4 after grafting. Myoblasts fused to form myotubes with central myonuclei by day 6 after grafting. Extrafusal myotubes differentiated into thin muscle fibers by day 8, which progressively increased in diameter and their nuclei became localized subsarcolemmally from day 13 onwards. The basal laminae of some intrafusal fibers already contained one or more nascent myotubes by day 4 after grafting. Regenerated intrafusal fibers lacked the typical nuclear accumulations and their number varied from one to eight fibers per spindle; additional fibers formed in the periaxial space or between layers of the capsule. Regenerated muscle spindles usually had a thinner outer capsule and a reduced inner capsule and periaxial space. The present study demonstrates that extrafusal and intrafusal muscle fibers degenerate and regenerate after heterochronous isotransplantation in a manner similar to that in standard grafts. However, the time course is slightly different. Degeneration was completed by day 5 after grafting as in free grafts, but the regeneration of extrafusal and intrafusal fibers started 1 or 2 days earlier, apparently because of the rapid and facilitated revascularization from the host muscle compared to that of standard grafts.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Expression of the muscle phenotype is the result of interaction between intrinsic and extrinsic factors, the latter including innervation, mechanical influences and hormonal signals. This minireview ...summarizes some of the current knowledge regarding the regulation of myosin heavy chain (MHC) isoform transitions during muscle development and regeneration. It describes the role of genetic factors, neural and mechanical influences and it focuses on the contribution of thyroid hormones to the differentiation of muscle fiber phenotypes as shown by the regulation of the expression of MHC isoforms and development of myofibrillar ATPase activity. Finally, it shortly summarizes results regarding the differentiation of MHC isoforms in regenerated muscle fibers of the graft after heterochronous isotransplantation in rats with different thyroid status.
Muscle phenotype is determined by combined effects of intrinsic genetic and extrinsic factors like innervation, hormonal levels and mechanical factors or muscle activity. We have been studying the ...effect of altered thyroid hormone levels on the expression of myosin heavy chain (MyHC) isoforms in control and regenerating soleus and extensor digitorum longus muscles of euthyroid, hypothyroid or hyperthyroid female inbred Lewis rats. The fiber type composition has been determined according to the mATPase activity and immunocytochemical staining of MyHC isoforms, the content of MyHC isoforms has been determined by SDS-PAGE, the mRNA levels have been measured by RT-PCR and the ultrastructural transformation has been analyzed by electron-microscopy. Our results indicate that although the innervation plays a decisive role in the determination of muscle phenotype, levels of thyroid hormones contribute to the extent of muscle phenotype transformation.
In the present paper we describe changes of anatomical parameters in inbred Lewis strain rats, namely their body weight, body weight gain per week, absolute and relative heart, thyroid gland and ...skeletal muscle weights, that are assumed to reflect experimentally altered thyroid status. The hyperthyroid state was induced by DL-thyroxine or Na 3,3',5-triiodo-L-thyronine, while methimazole was employed for inducing hypothyroidism. We have found that when compared to euthyroid rats, hypothyroidism resulted in a significantly lower body weight gain, absolute and relative heart weight and, in contrast, in a significant increase of absolute and relative thyroid gland weight. On the other hand, hyperthyroidism led to a significant increase of absolute and relative heart weight and to a significant reduction of absolute and relative thyroid gland weight. However, the body mass was not significantly altered in hyperthyroidism as compared with euthyroid rats. We conclude that our protocol leads to chronic hyper- or hypothyroidism as demonstrated by body, heart and thyroid gland weight changes. These anatomical data can thus be utilized as supplemental criteria for the assessment of the thyroid state of experimental rats.
The ultrastructure of peripheral sensory nerves was investigated in adult Wistar rats suffering from experimental diabetes mellitus 6 and 10 weeks after the injection of streptozotocin. Giant axons ...were seen in sections from the nerves of streptozotocin-treated rats; some contained masses of neurofilaments, others were predominantly filled with ill-defined vesicles. At the swollen axons, the myelin sheath was thinned or absent. In other regions, large intramyelinic vacuoles were observed. A number of nerve fibers broke down completely and underwent Wallerian degeneration. This was accompanied by Schwann cell proliferation and formation of Büngner bands. Concomitantly with axonal degeneration, nerve regeneration started from intact internodes. The pathomorphology of streptozotocin diabetic neuropathy closely resembles that of some toxic distal axonopathies. This points to a common metabolic basis of giant axonopathies of different etiology.
The 2-D stereology can be used advantageously in the case of muscle cross sections stained by routine histochemical and immunocytochemical methods, such as mATPase reaction, when the quality of the ...image is often not sufficient for using image analysis techniques without considerable individual intervention. Other advantages of stereological methods in muscle morphometry are that measurements are made directly on specimens under the microscope and in their simplest arrangement they do not require sophisticated and expensive technical equipment. Furthermore, unbiased results are obtained, no segmentation and edge effect problems arise and the quantity of work invested in stereological estimation is reasonable. Therefore, we have used the stereological methods as our standard technique for assessment of fibre type composition in regenerated soleus muscles grafted from 21- to 28-day-old rats into fast EDL muscles of adult inbred recipients with different plasma levels of thyroid hormones.
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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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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.
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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