The number of neurons in dorsal root ganglia L4-L6 of the rat

The number of neurons in the dorsal root ganglia L4-L6 of the rat was determined because published data are inconsistent and in general incompatible with the number of afferent axons in the sciatic nerve. Nucleoli were counted in serial sections; epoxy-resin sections 3 microns thick, or paraffin sections 5 microns thick, or unstained 12-microns paraffin sections of osmicated tissue were used. Correction factors for split and multiple nucleoli were obtained by counting nucleolar profiles in consecutive sections of identified cells. Dividing the number of nucleolar profiles into the number of cells gave the factor by which the counts of nucleolar profiles had to be multiplied to obtain the number of neurons. The ganglia L4, L5, and L6 contained about 12,000, 15,000 and 14,000 neurons, respectively, when resin sections were used. The standard deviation for the average of 41,000 neurons in the three ganglia was 8% of the mean value. The results compare well with the number of dorsal root fibers, and with the fact that the sciatic nerve at midthigh, to which less than half of the neurons connect, contains 19,000 afferent axons. The data obtained from the paraffin series were 23% smaller, but still considerably higher and less variable than all previously reported data. The main problem with stained paraffin sections was that most small neurons had multiple nucleoli attached to the membrane of the nuclei, which only measured 10 microns in diameter. The nucleoli often projected into the dark cytoplasm and were difficult to identify.     

Contractile properties, fiber types, and myosin isoforms in fast and slow muscles of hyperactive Japanese waltzing mice

This study focuses on the effects of neuromuscular hyperactivity on the contractile properties, fiber type composition, and myosin heavy chain (MHC) isoform expression of fast-twitch extensor digitorum longus (EDL) and slow-twitch soleus (SOL) muscles in Japanese waltzing mice (JWM) of the C57BL/6J-v2J strain. The same properties were studied in the homologous muscle of control CBA/J mice (CM). In comparison to CM, the JWM exhibited (i) longer activity periods, prolonged bouts of running and a higher food intake, (ii) slower twitch and tetanic contractions of both EDL and SOL muscles, decreased cold and post-tetanic potentiation of the EDL, as well as increased cold and post-tetanic depressions of the SOL. Electrophoretic analyses of MHC isoform revealed a shift toward slower isoforms in both EDL and SOL muscles of JWM as compared to the homologous muscles of CM, namely, a shift from the fastest MHCIIb to the MHCIId/x isoform in the EDL muscle and a shift from MHCIIa to MHCI in the SOL muscle. The latter also contained a higher percentage of type I fibers and displayed a higher capillary density than the SOL muscle of CM. These findings show that the inherently enhanced motor activity of the JWM leads to fiber type transitions in the direction of slower phenotypes. JWM thus represent a suitable model for studying fast-to-slow fiber transitions under the influence of spontaneous motor hyperactivity.     

Early changes in chlorphentermine myopathy of rat studied by freeze fracturing

Chlorphentermine interferes with the metabolism of phospholipids. When administered to the rat in daily doses for 5 days, it causes necrosis of muscle fibers that are rich in mitochondria. Before the onset of necrosis, the following characteristics of freeze-fractured muscle preparations were observed: multilayered lipid globules and single-layered lipid membranes without membrane particles; different stages of exocytosis of lipid through the plasma membrane of the muscle fibers; and areas of plasma membrane that were devoid of particles of intramembranous proteins. These latter areas may arise secondary to exocytosis, to fusion of lipid vesicles with the plasma membrane, or to a direct action of chlorphentermine on the membrane. It is not known whether these areas give rise to membrane defects and fiber necrosis.     

Adenoviral cardiotrophin-1 gene transfer protects pmn mice from progressive motor neuronopathy

Cardiotrophin-1 (CT-1), an IL-6-related cytokine, causes hypertrophy of cardiac myocytes and has pleiotropic effects on various other cell types, including motoneurons. Here, we analyzed systemic CT-1 effects in progressive motor neuronopathy (pmn) mice that suffer from progressive motoneuronal degeneration, muscle paralysis, and premature death. Administration of an adenoviral CT-1 vector to newborn pmn mice leads to sustained CT-1 expression in the injected muscles and bloodstream, prolonged survival of animals, and improved motor functions. CT-1-treated pmn mice showed a significantly reduced degeneration of facial motoneuron cytons and phrenic nerve myelinated axons. The terminal innervation of skeletal muscle, grossly disturbed in untreated pmn mice, was almost completely preserved in CT-1-treated pmn mice. The remarkable neuroprotection conferred by CT-1 might become clinically relevant if CT-1 side effects, including cardiotoxicity, could be circumvented by a more targeted delivery of this cytokine to the nervous system.     

A freeze-fracture study of the plasma membrane of muscle fibres of a patient with chronic creatine kinase elevation suspected for malignant hyperthermia.

The muscle biopsy from a 12-year-old boy with chronic creatine kinase elevation was studied by electron microscopy. At the age of 7 years the patient had a possible abortive attack of malignant hyperthermia. The biopsy specimen contained many fibres with segmental contracture and necrosis; thin sections showed defects of the plasma membrane with loss of glycogen granules into the interstitium. Freeze-fracturing of the plasma membrane showed clustering of intramembranous particles and some membrane areas were devoid of particles and of pinocytotic caveolae. The E-face showed irregular elevations and the P-face corresponding defects. These deviations of the fracture-plane were due to manifest membrane openings, to abnormalities of the structure of the lipid bilayer, to clustering of membrane particles or to the fact that intracellular membranes often were abnormally close to the plasma membrane. The findings suggest that a disintegration of the lipid-protein system of the membrane precedes the formation of manifest defects. The manifest defects resembled those in Duchenne muscular dystrophy. It is unknown whether the changes seen by freeze-fracturing were specific for a myogenic disorder and whether they were due to a basic membrane abnormality or to defects in other systems of the muscle cell.     

Axonal branching following crush lesions of peripheral nerves of rat

Branching of myelinated and unmyelinated nerve fibers in normal and regenerating personal and soleus nerves was studied by light and electron microscopy. There were at most 2% more myelinated and 13% more unmyelinated axons in the distal as compared with the proximal nerve segments. Two to four weeks after a crush lesion the distal axons became 2-3 times more numerous; thereafter their number decreased. The number of axons in the proximal nerve segment did not change. The number of myelinated sprouts in most regenerated nerves equalled the number of myelinated fibers in the proximal nerve, while the number of unmyelinated axons after 12-19 weeks was 18-60% higher than normal. Branching was not restricted to the crush region. The results indicate that following a crush lesion all axons branch but only branches of unmyelinated fibers persist for a prolonged period of time. It is tentatively suggested that regenerating axons branch when searching for a target and that when contact is made with the target this prevents additional branching and eliminates redundant branches. Myelinated axons are guided by existing Schwann cells, whereas unmyelinated axons do not follow predetermined pathways; this may explain their greater tendency to form permanent branches.     

The Kety–Schmidt technique for repeated measurements of global cerebral blood flow and metabolism in the conscious rat

Cerebral activation will increase cerebral blood flow (CBF) and cerebral glucose uptake (CMR_glc) more than it increases cerebral uptake of oxygen (CMR_O2). To study this phenomenon, we present an application of the Kety–Schmidt technique that enables repetitive simultaneous determination of CBF, CMR_O2, CMR_glc and CMR_lac on awake, non-stressed animals. After constant intravenous infusion with ¹³³Xenon, tracer infusion is terminated, and systemic arterial blood and cerebral venous blood are continuously withdrawn for 9 min. In this paper, we evaluate if the assumptions applied with the Kety–Schmidt technique are fulfilled with our application of the method. When measured twice in the same animal, the intra-individual variation for CBF, CMR_O2, and CMR_glc were 10% (SD: 25%), 8% (SD: 25%), and 9% (SD: 28%), respectively. In the awake rat the values obtained for CBF, CMR_O2 and CMR_glc were 106 mL [100 g]^?1 min^?1, 374 μmole [100 g]^?1 min^?1 and 66 μmole [100 g]^?1 min^?1, respectively. The glucose taken up by the brain during wakefulness was fully accounted for by oxidation and cerebral lactate efflux. Anaesthesia with pentobarbital induced a uniform reduction of cerebral blood flow and metabolism by ≈40%. During halothane anaesthesia CBF and CMR_glc increased by ≈50%, while CMR_O2 was unchanged.     

The effect of peripheral nerve injury on immature motor and sensory neurons and on muscle fibres. Possible relation to the histogenesis of Werdnig-Hoffmann disease

Sciatic nerve section in newborn rats causes loss of almost all motoneurons and of two thirds of the sensory neurons. Single motor axons may regenerate but they innervate only few muscle fibres. The nonreinnervated fibres vanish and are replaced by fat cells. The reinnervated muscle fibres are overloaded, hypertrophy, and eventually necrotize. Their satellite cells regenerate new fibres; most of them develop aneurally and then disappear. The muscles, if reinnervated at all, after 1 year consist of a mixture of hypertrophic fibres, non-innervated regenerates, and fat cells, and resemble muscle from patients with infantile spinal muscular atrophy Werdnig-Hoffmann. In immature rat muscles, restricted reinnervation and functional overload of the few innervated fibres maintain a self-enhancing process which eventually leads to the replacement of the entire muscle by fat tissue. It is suggested that Werdnig-Hoffmann disease starts during fetal life and that similar mechanisms are operative. The clinical progression would then depend on the extent of degeneration due to overload and on regeneration and reinnervation in the muscles rather than on the rate of continuous loss of anterior horn cells. Immature motoneurons in rat die when they loose contact with their target; one might therefore speculate that the primary lesion in Werdnig-Hoffmann disease is peripheral rather than central, and that lack of neuronotorophic influences causes the loss of anterior horn cells.