Lipopolysaccharide-induced inflammation does not alter muscle spindle afferent mechanosensation or sensory integration in the spinal cord of adult mice.

Inflammation is known to alter nervous system function, but its effect on muscle spindle afferent mechanosensation and sensory integration in the spinal cord has not been well studied. We tested the hypothesis that systemic inflammation induced by an intraperitoneal injection of the endotoxin lipopolysaccharide (LPS; 7.5 × 105 endotoxin units/kg 18 h before experiment) would alter muscle spindle afferent mechanosensation and spinal cord excitability to Group Ia input in male and female adult C57Bl/6 mice. LPS injection caused a systemic immune response, evidenced by decreased white blood cell, monocyte, and lymphocyte concentrations in the blood, increased blood granulocyte concentration, and body weight loss. The immune response in both sexes was qualitatively similar. We used an in vitro muscle-nerve preparation to assay muscle spindle afferent response to stretch and vibration. LPS injection did not significantly change the response to stretch or vibration, with the exception of small decreases in the ability to entrain to high-frequency vibration in male mice. Similarly, LPS injection did not alter spinal cord excitability to Group Ia muscle spindle afferent input as measured by the Hoffman's reflex test in anesthetized mice (100 mg/kg ketamine, 10 mg/kg xylazine). Specifically, there were no changes in M or H wave latencies nor in the percentage of motor neurons excited by electrical afferent stimulation (Hmax /Mmax ). Overall, we found no major alterations in muscle proprioceptor function or sensory integration following exposure to LPS at a dose and time course that causes changes in nociceptor function and central processing.

Ataxic Guillain-Barré syndrome and acute sensory ataxic neuropathy form a continuous spectrum.

BACKGROUND: Ataxic Guillain-Barré syndrome is characterised by profound ataxia with negative Romberg sign and no ophthalmoplegia. Its nosological relationship to acute sensory ataxic neuropathy has yet to be discussed. METHODS: Medical records were reviewed of patients suffering acute ataxia and reduced muscle stretch reflexes but without external ophthalmoplegia. Clinical features and laboratory findings were analysed. Rat muscle spindles were immunostained by anti-GQ1b and -GD1b antibodies. RESULTS: The Romberg sign was negative in 37 (69%) of 54 patients with acute ataxic neuropathy without ophthalmoplegia, but positive in the other 17 (31%). The negative and positive subgroups had similar features; preceding infectious symptoms (86% vs 83%), distal paraesthesias (70% vs 88%), superficial sense impairment (27% vs 24%), IgG antibodies to GQ1b (65% vs 18%) and GD1b (46% vs 47%) and cerebrospinal fluid albuminocytological dissociation (30% vs 39%). Findings did not differ between the subgroups of 466 patients with Fisher syndrome with and without sensory ataxia. Acute ataxic neuropathy patients more often had anti-GD1b (46% vs 26%) and less often anti-GQ1b (50% vs 83%) antibodies than Fisher syndrome. Anti-GQ1b and -GD1b antibodies strongly stained parvalbumin-positive nerves in rat muscle spindles, indicative that proprioceptive nerves highly express GQ1b and GD1b. CONCLUSION: Clinical and laboratory features suggest that ataxic Guillain-Barré syndrome and acute sensory ataxic neuropathy form a continuous spectrum. The two conditions could be comprehensively referred to as 'acute ataxic neuropathy (without ophthalmoplegia)' to avoid nosological confusion because Fisher syndrome is not classified by the absence or presence of sensory ataxia. That is, acute ataxic neuropathy can be positioned as an incomplete form of Fisher syndrome.

Determination of slow-tonic MyHC immunoreactivity is an important step in the evaluation of muscle spindles in porcine extraocular muscles.

We have tested our hypothesis suggesting (i) that for the reliable determination and counting of muscle spindles (Msp) at the light microscopy level in extraocular muscles (EOM), analysis of the spindle specific myosin heavy chain (MyHC) immunoreactivity of intrafusal fibers, especially after staining with anti-slow-tonic MyHC antibodies, is the most convenient tool, (ii) that the number of Msp determined by the slow-tonic MyHC immunoreactivity of intrafusal fibers in EOM is much lower than that based on histological examination and (iii) that the previously reported numbers of Msp based on histological examination of EOM could be overestimated. In order to determine the number and distribution of Msp and to analyze the MyHC isoform immunoreactivity of intrafusal fibers in porcine EOM, paraffin sections of three 9-month-old pig medial (MR) and lateral rectus (LR), levator palpebrae (LP) and retractor bulbi (RB) muscles were stained histologically or using specific monoclonal antibodies (mAbs) against MyHC isoforms. Msp in recti and LP muscles studied by immunocytochemistry contained nuclear bag (NB) fiber(s) reacting with mAbs against slow-tonic, slow-twitch, alpha-cardiac and neonatal MyHCs, but not with the mAb against fast-twitch MyHC, which, on the contrary, stained nuclear chain (NC) fibers. Based on determination of spindle specific slow-tonic MyHC isoform immunoreactivity we have found 72 Msp in the MR and 68 Msp in the LR and 12 Msp in LP muscles, which was only 62, 55 and 32% of the Msp total counts according to histological examination, respectively. In the RB muscle, we have even found only 15 spindle-like-structures composed of encapsulated thin muscle fibers, which possessed only a reaction with anti-fast-twitch MyHC mAb, but lacked slow-tonic, slow-twitch or alpha-cardiac MyHCs immunoreactivity. Our analysis of porcine EOM confirmed the above suggestions, demonstrating, for the first time in the pig, the presence of "false Msp" mimicking encapsulated muscle fibers on histological sections that lack spindle specific MyHC immunoreactivity. In analogy with other muscles we suggest that "false Msp" are not innervated by sensory axons and therefore do not contribute to the physiological sensation of the muscle length changes. Our results thus show that the reliable identification of functionally effective Msp in EOM must involve immunohistochemical analysis of spindle specific MyHC isoforms of intrafusal fibers, as "false" spindles appearing on histologically stained sections as encapsulated muscle fibers could be regarded as "true" Msp and thus increase the spindle number counts in earlier studies.

Effects of simulated weightlessness on Calbindin D-28K-immunoreactivity in rat soleus muscle spindle.

Objective. To analyze the mechanism involved in muscle spindle deterioration during simulated weightlessness. Method. Using the immunoperoxidase reaction utilizing the ABC (avidin-biotin-complex) method, Calbindin D28K-like immunoreactivity (CaBP-LI) of intrafusal fibres in soleus muscle were detected in 7 d, 14 d tail-suspended rats and compared with control rats. Result. The extrafusal muscle fibres and nerve fibres did not exhibit immunoreactivity to CaBP. CaBP-LI was found in some of the intrafusal muscle fibres in all the muscle spindles. After 14 d suspension, the immunoreactivity to CaBP of the intrafusal fibres decreased markedly. Conclusion. Simulated weightlessness could induce changes in the immunoreactivity of rat soleus muscle spindle to CaBP, which may contribute to the deterioration of muscle spindle.

Effects of simulated microgravity on immunoreactivity of conjugated-ubiquitin of muscle spindles of soleus in rats.

It is well known that the muscle spindle is a receptor of muscle's tension and length, it plays an important role in maintaining the muscle's tension. The aim of the present study is to compare the cross-section area (CSA) and the immunoreactivity of conjugated-ubiquitin in soleus extrafusal and intrafusal fibers after simulated-microgravity in order to demonstrate the role of muscle spindle in muscle atrophy induced by simulated microgravity.

Postnatal expression of myosin heavy chains in muscle spindles of the rat.

The immunocytochemical expression of two myosin isoforms in intrafusal muscle fibers was examined in soleus muscles of neonatal (zero to six days postpartum) and adult rats. Monoclonal antibodies specific for myosin heavy chains of the slow-tonic anterior latissimus dorsi (ALD58) and fast-twitch pectoralis (MF30) muscles of the chicken were used. In adults ALD58 bound to the intracapsular regions of bag1 and bag2 fibers and MF30 bound to the intracapsular regions of bag2 and chain fibers. The extracapsular regions of intrafusal fibers and all extrafusal fibers did not react to ALD58 or MF30. Bag1 and bag2 fibers of neonatal rats expressed immature myosin patterns but chain fibers did not. The adult pattern of immunoreactivity of intrafusal fibers developed by the fourth postnatal day, when the patterns of motor but not sensory innervation in the spindle are still immature. Data suggest that the expression and maintenance of the specific anti-myosin immunoreactivity of intrafusal fibers during postnatal development of rat spindles is dependent upon sensory but not motor innervation. Moreover, afferents might regulate the gene expression responsible for synthesis of myosins isoforms specific to intrafusal fibers only in those myonuclei located within the capsule, but not in the myonuclei in extracapsular regions of intrafusal fibers.

Development of immunohistochemical characteristics of intrafusal fibres in normal and de-efferented rat muscle spindles.

Intrafusal muscle fibres in adult muscle spindles differ in their myosin composition. After selective motor denervation intrafusal muscle fibres develop mature ultrastructural characteristics. In order to evaluate the role of fusimotor innervation on the maturation of the myosin composition of intrafusal muscle fibres we have examined with immunohistochemical techniques i) the postnatal development of muscle spindles in new-born rats and in 7-21 day old rats; ii) muscle spindles in the EDL of 21-day-old rats de-efferented at birth. For the characterization of myosins in intrafusal fibres we used three myosin antisera: antipectoral myosin, antiheart myosin and antiheart myosin adsorbed with muscle powder from the soleus muscle of guinea pig. We show in this study that during development intrafusal fibres change immunoreactivity and that in the absence of motor innervation bag fibres do not fully develop the myosin characteristics of control spindles. We conclude that the maturation of bag1 and bag2 fibres apparently requires next to the inductive influence of sensory axon terminals the presence and activity of fusimotor axons.

The affinity of concanavalin A and wheat germ agglutinin for components of the muscle spindle.

Sections through the soleus muscle of the rat were incubated with concanavalin A (Con A) or wheat germ agglutinin (WGA) conjugated to fluorescein isothiocyanate. Binding of these lectins to structures which comprise the muscle spindle was studied by fluorescence microscopy. The distribution of the lectins was heaviest in the outer capsule of the spindle and at the surface of intrafusal muscle fibres. The periaxial space in the equatorial region of spindles was unlabelled except in the immediate vicinity of the axial bundle. Binding by Con A was more extensive than by WGA, suggesting that more glucopyranoside units are accessible within the muscle spindle than are those of N-acetylglucosamine.

Early street rabies virus infection in striated muscle and later progression to the central nervous system.

Twelve isolates of street rabies virus were inoculated intramuscularly into young hamsters and the course of infection was followed by frozen section immunofluorescence. Animals infected with 10 of the 12 viruses had antigen in striated muscle at day 3, but involvement of other tissues was absent or extremely sparse. Muscle infection was still most pronounced at day 6, but neuromuscular spindle, nerve, and brain infections were also detected in a majority of animals. Progression of infection was continuous, with striking terminal accumulations of antigen. The early myotropism of rabies virus may yield the virus which invades the peripheral nervous system, and may represent a phase of infection vulnerable to postexposure intervention.