Heterotopic neogenesis of skeletal muscle induced in the adult rat diaphragmatic peritoneum: ultrastructural and transplantation studies.

During the course of a mild chemical peritonitis, new skeletal muscle fibers develop and persist over a twelve-month interval in the diaphragmatic peritoneum. Light and electron microscopic studies revealed that the ectopic fibers developed from myoblasts and myotubes to fully differentiated muscle cells in the same manner as normally situated skeletal muscle. The ectopic fibers were separated from the intrinsic muscle by dense connective tissue and an elastic lamina. Diaphragms taken from normal rats and transplanted to the omentum of isogeneic recipients also developed skeletal muscle neogenesis in the same ectopic location as in the normal diaphragm. Satellite cells, reactive fibroblasts in the peritoneum, mesenchymal stem cells or blood-borne myoblast precursor cells could be the source of these ectopic muscle fibers. The results of the present studies, however, cannot provide conclusive evidence for the origin of the new muscle fibers. Regardless of their source, the methods employed may represent a unique model for the development and prolonged maintenance of skeletal muscle fibers in a heterotopic location in vivo.

Parenteral aluminum compounds produce a local toxic myopathy in rats: importance of the anion.

Aluminum lactate, injected in rats, produced skeletal muscle necrosis of diaphragm and abdominal wall subjacent to peritoneal surfaces. Deeper muscle cells (distal from inoculum) were less severely affected. Ultrastructural studies of diaphragm revealed inoculum coating collagen fibrils, aggregating next to muscle basal lamina and localized within phagocytes. Aluminum lactate penetrated lymphatic vessels and caused reactive changes on the pleural as well as peritoneal surfaces of diaphragm. In contrast, injection of aluminum citrate did not produce myopathy. Also, mixtures of aluminum lactate with aluminum citrate, sodium citrate, or another chelating agent failed to produce myopathy. Therefore, the regional myopathy produced by the lactate salt provides a model for in vivo cytotoxicity of aluminum in which anionic binding is a critical determinant.

Ultrastructural features of the ventromedial region of the laminar nucleus in the red-eared turtle (Chrysemys scripta elegans).

The nuclei of the torus semicircularis, in particular the laminar nucleus, have been functionally implicated in sound localization, vocalization, and mating behavior. In the red-eared turtle the ventromedial region of the laminar nucleus (containing two discrete dense cellular areas and the surrounding neuropil) was examined electron microscopically in the present study. Neuronal cell bodies in the two cellular areas were different in size, shape, cytoplasmic constituents, and their relationship to each other. Cell bodies in the layer beneath the ependymal surface were almost always surrounded by lamellae while cell bodies in the layer above the central nucleus were in close apposition. We are speculating that cell bodies in the superficial layer may be neuroendocrine in nature. This speculation is based on the presence of lipidlike droplets within cell bodies, and previous findings indicating steroid binding and synthesis in this region in reptilian brains. Cell bodies located above the central nucleus were characteristic in that they contained lamellar bodies and extensive well-developed Golgi regions. Closely apposed groups of these cell bodies were frequently surrounded by or in close apposition to large axonal profiles. These profiles were filled with clear core vesicles, numerous mitochondria, and clusters of small dense core particles. Synaptic contacts between large axonal profiles and cell bodies were not observed. The neuropil surrounding cell bodies of the inner layer of this region of the laminar nucleus contained glomeruli composed of a central axon surrounded, and in synaptic contact, with dendrites. Throughout the area of the laminar nucleus studied, synapses appeared to be primarily of the asymmetrical type.

An electrophysiologic and ultrastructural study of the phenylmethanesulfonyl fluoride protection against a delayed organophosphorus neuropathy.

The delayed organophosphorus neuropathy caused by diisopropylfluorophosphate (DFP) can be prevented by pretreatment with phenylmethanesulfonyl fluoride (PMSF). A single injection of DFP (2 mg/kg) into a cat femoral artery produced a delayed neuropathy in the injected leg. Clinical neurotoxic signs in the DFP treated leg were most prominent at 21 to 28 days after DFP administration: a high-step gait with some tip-toe walking. During that time the capacity of the cat soleus alpha-motor nerve terminals to generate a stimulus-evoked repetitive discharge, known as SBR, was greatly attenuated. At that time, the ultrastructure of the motor nerve terminals demonstrated prominent alterations that correlated well with the motor nerve terminal SBR deficit. These alterations included the presence of extensive whorls in nerve terminals and axoplasms, the retraction and disruption of nerve terminals from the synaptic cleft, and a widening of secondary junctional folds. From the sampled population, the incidence of normal terminals in soleus muscles of the DFP-treated leg was only 2%. Cats which received PMSF (30 mg/kg ip) 24 hr before DFP administration did not develop any neurotoxic signs. Motor movements were normal. The SBR function of the soleus alpha-motor nerve terminals was not lost and its incidence approached normal values. Moreover, the ultrastructure was normal in 86% of examined neuromuscular junctions in the PMSF pretreated DFP cats. Thus, in this model, pretreatment with PMSF protected cats against the delayed neurotoxic effects of organophosphorus poisoning.

A morphological study of the effect of glucocorticoid treatment on delayed organophosphorus neuropathy.

The delayed neuropathy caused by the organophosphate diisopropylfluorophosphate (DFP) can be minimized by a high dose glucocorticoid regimen started after exposure to DFP. In cats 21 days after an intraarterial injection (2 mg/kg) of DFP, morphologic alterations of neuromuscular junctions and myelinated intramuscular axons are evident. These alterations include the presence of extensive lamellar whorls in nerve axons and terminals, the disruption and retraction of nerve terminals from the synaptic cleft and a widening of secondary junctional folds with coincident dispersion of the basal lamina. The pathologic changes while more intense in the DFP-treated leg are also evident in the contralateral leg. Only 2% of motor nerve terminals from the soleus of DFP-treated legs were rated as normal in morphologic evaluations. In contrast 90% were rated normal in cats exposed to DFP and subsequently treated with one dose of methyl prednisolone (90 mg/kg, i.v.) and 7 doses (8 mg/kg, i.m.) of triamcinolone over a 20 day period. The mechanism whereby glucocorticoid therapy exerted this effect during the time interval studied remains unresolved. However, this observation may be important in the further definition of both the normal and diseased state.

The effect of glucocorticoid treatment on denervated rat hemidiaphragm.

The degenerative process in phrenic nerve motor nerve terminals following nerve section was analyzed in rats that had previously been subjected to an intensive short term regimen of the steroid preparation triamcinolone. Morphological studies indicated that the onset time of degeneration was similar to that of untreated rats but less severe, and the time for maximal degenerative changes was increased. Concurrent to the preservation of motor nerve terminal structure under conditions of denervation, triamcinolone also induced myopathies in the diaphragm, the white muscle fibers being predominantly affected. Due to the structural aberrations of muscle, the indirect and direct twitch response of hemidiaphragms in triamcinolone treated rats was depressed. Data obtained from indirect post-tetanic potentiation (PTP) responses, however, did express the anatomical preservation of motor nerve terminals. These findings may add support to previous observations for the basis of effectiveness of the glucocorticoids in the treatment of neuromuscular disorders.