Summary Statement. Paraspinal muscle contain higher proportion of slow-twich fibers. The fixation of the rat tail induced transition of muscle fiber types in the paravertebral muscles characterised by the decrease in the proportion of the slow type myosin heavy chain. Introduction. Lumbar degenerative kyphosis often accompanies back pain, easy fatigability, fatty degeneration and atrophy of back muscles. There are two types of skeletal muscle fibers according to oxidative activities: slow-twich (Type 1) and fast-twitch (Type 2) fibers. Type 2 fibers were subdivided into three types: Type 2A, 2B and 2D/X. Each fiber type primarily expresses a specific isoform of myosin heavy chain (MHC). It has been known that back muscles contain higher proportion of MHC type 1. However, the impact of kyphosis on the proportion of fiber types in the paravertebral muscles has not been fully understood. The aim of this study is to analyze the transition of muscle fiber types after kyophotic or straight fixation using a rat tail model. Methods. A rat tail was fixed in straight or kyphotic position (straight or kyphosis group) by a custom-made external fixator and wires. A group of animals which underwent only pierced wounds in their tails served as control. The gene expression profiles of isoforms of MHCs in dorsal coccygeal muscles were analyzed by quantitative RT-PCR. The fiber types of muscles were assessed using SDS-PAGE. Band densities of silver-stained gel were quantified. Results. At first, the gene expression profiles of MHCs and protein expression in the dorsal coccygeal muscles were compared with tibilis anterior and gastrocunemius muscles. Higher proportion of MHC type 1 gene and protein expression were confirmed in the dorsal coccygeal muscles than tibialis anterior and gastrocuneimus muscles. MHC type 2B protein expression was not detected in dorsal coccygeal muscles. Next, coccygeal muscles after straight or kyphotic fixation were analyzed and compared with control. Gene expression of MHC type 1 was decreased at 7 and 28 days after fixation in straight and kyphosis group. The significant difference was seen at 28 days in kyphosis group. The band densities of MHC protein type 1 and 2A plus 2D/X were decreased in both straight and kyophosis groups at 28 days after fixation while sample volume was adjusted by wet wight of dissected coccygeal muscles. The mean proportion of MHC protein type 1 separated by SDS-PAGE were decreased in straight and kyphosis group. The difference was significant in straight group. Discussion. Our results demonstrated that the fixation of the rat tail induced transition of muscle fiber types in the paravertebral muscles characterized by the decrease in the proportion of the MHC type 1. Back muscles are required to contract continuously to keep posture. Slow-twitch fibers in back muscle contribute for continuous contraction. Slow-twitch fibers utilise energy efficiently by oxidative process while fast-twitch fibers mainly consume glucose through glycolysis producing lactate acid. Not only decreased amount of MHC but also decreased proportion of MHC type 1 might be the reason of easy fatigability in lumbar degenerative kyphosis. The limitations of this study is the difference between human paravertebral and rat coccygeal muscles and short duration of observation

Summary Statement. Patients with adolescent idiopathic scoliosis show clear signs of abnormal motor coordination between the long superficial paraspinal muscles and the deep rotators. These findings suggest an abnormal behavior of the deep rotator muscles at the concave side. Introduction. An imbalance between the myoelectric activity of the muscles of the convexity and the concavity has been described in patients with adolescent idiopathic scoliosis (AIS). These findings are based on EMG patterns recorded with surface electrodes that do not distinguish between deep and superficial muscles. This work was aimed at analyzing the coupled behavior of the superficial and deep paraspinal muscles in subjects with AIS at both sides of the curve. Material. A total of 16 females (mean age, 16.2±4.3 years) with AIS between 20 and 35° Cobb (mean, 32.8±11.9°) underwent electromyography of the paraspinal muscles by direct intramuscular disposable concentric electrodes (Dantec DCN. TM. ) of 25mm and 37mm in length, and 0.46 mm. in diameter. A total of 4 electrodes were inserted at the apex on both sides of the curve (2 in deep rotator muscle and 2 in the long paraspinal superficial muscles). Myoelectrical activity was recorded simultaneously in the four muscle groups in different positions: standing, flexion, extension, right and left lateralizations, and rotations toward the side of the concavity and convexity. A 4-channel Keypoint® electromyography device (Medtronic, Denmark) was used. The recorded signals were analyzed in a laptop with Windows. ®. 7 Intel Core i3 64bit with Matlab. ®. R2012a. The following parameters were analyzed: Signal power, Mean and Median frecuency, and the Dimitrov spectral index, a marker of muscle fatigue. In addition, the signal power in each task was normalised by the signal power in standing position. The records were compared with those obtained in 4 healthy subjects, matched in age, without spinal deformity. Results. The signal amplitude in different subjects and tests ranged from tens of microvolts up to two milivolts. Most of the energy of the EMG signal was concentrated below 500 Hz in power spectrum density chart. In standing position, the activity of the deep muscle was greater than that of the long superficial paraspinal muscles, with higher activation in the convex side (63% of cases). Increased activity of the deep muscles as compared to the surperficial layers was also evident during flexion of the spine, with a higher activity of the deep muscles of the concavity. The 4 muscle groups showed low activity during spine extension movements, though the deep rotator activity was always greater than the superficial paraspinal muscles. In rotation exercises, the most active muscles were found the contralateral with a clear inhibition of the deep muscles of the concavity in the rotation to that side. This did not apply for rotation through the convex side. It was also noticeable that in the case of deep muscles, both sides of the spine require high activation when performing left flexion. Conclusions. Patients with AIS show clear signs of abnormal motor coordination between the superficial paraspinal muscles and the deep rotators. These findings do not clearly define whether this mismatch is primary or secondary to the presence of the deformity although they suggest an abnormal behavior of deep rotator muscles that could have etiopathogenic relevance

A rat model of lumbar root constriction with an additional sympathectomy in some animals was used to assess whether the sympathetic nerves influenced radicular pain. Behavioural tests were undertaken before and after the operation.

On the 28th post-operative day, both dorsal root ganglia and the spinal roots of L4 and L5 were removed, frozen and sectioned on a cryostat (8 μm to 10 μm). Immunostaining was then performed with antibodies to tyrosine hydroxylase (TH) according to the Avidin Biotin Complex method. In order to quantify the presence of sympathetic nerve fibres, we counted TH-immunoreactive fibres in the dorsal root ganglia using a light microscope equipped with a micrometer graticule (10 x 10 squares, 500 mm x 500 mm). We counted the squares of the graticule which contained TH-immunoreactive fibres for each of five randomly-selected sections of the dorsal root ganglia.

The root constriction group showed mechanical allodynia and thermal hyperalgesia. In this group, TH-immunoreactive fibres were abundant in the ipsilateral dorsal root ganglia at L5 and L4 compared with the opposite side. In the sympathectomy group, mechanical hypersensitivity was attenuated significantly.

We consider that the sympathetic nervous system plays an important role in the generation of radicular pain.