Orazio Brunetti

The role of capsaicin‐sensitive muscle afferents in fatigue‐induced modulation of the monosynaptic reflex in the rat

1 The role of group III and IV afferent fibres of the lateral gastrocnemious muscle (LG) in modulating the homonymous monosynaptic reflex was investigated during muscle fatigue in spinalized rats. 2 Muscle fatigue was induced by a series of increasing tetanic electrical stimuli (85 Hz, 600 ms) delivered to the LG muscle nerve. Series consisted of increasing train numbers from 1 to 60. 3 Potentials from the spinal cord LG motor pool and from the ventral root were recorded in response to proprioceptive afferent stimulation and analysed before and during tetanic muscle activations. Both the pre‐ and postsynaptic waves showed an initial enhancement and, after a ‘12‐train’ series, an increasing inhibition. 4 The enhancement of the responses to muscle fatiguing stimulation disappeared after L3‐L6 dorsal root section, while a partial reflex inhibition was still present. Conversely, after section of the corresponding ventral root, there was only a reduction in the inhibitory effect. 5 The monosynaptic reflex was also studied in animals in which a large number of group III and IV muscle afferents were eliminated by injecting capsaicin (10 mM) into the LG muscle. As a result of capsaicin treatment, the fatigue‐induced inhibition of the pre‐ and postsynaptic waves disappeared, while the response enhancement remained. 6 We concluded that the monosynaptic reflex inhibition, but not the enhancement, was mediated by those group III and IV muscle afferents that are sensitive to the toxic action of capsaicin. The afferents that are responsible for the response enhancement enter the spinal cord through the dorsal root, while those responsible for the inhibition enter the spinal cord through both the ventral and dorsal roots.

Improvement of Stance Control and Muscle Performance Induced by Focal Muscle Vibration in Young-Elderly Women: A Randomized Controlled Trial

UNLABELLED Filippi GM, Brunetti O, Botti FM, Panichi R, Roscini M, Camerota F, Cesari M, Pettorossi VE. Improvement of stance control and muscle performance induced by focal muscle vibration in young-elderly women: a randomized controlled trial. OBJECTIVE To determine the effect of a particular protocol of mechanical vibration, applied focally and repeatedly (repeated muscle vibration [rMV]) on the quadriceps muscles, on stance and lower-extremity muscle power of young-elderly women. DESIGN Double-blind randomized controlled trial; 3-month follow-up after intervention. SETTING Human Physiology Laboratories, University of Perugia, Italy. PARTICIPANTS Sedentary women volunteers (N=60), randomized in 3 groups (mean age +/- SD, 65.3+/-4.2y; range, 60-72). INTERVENTION rMV (100Hz, 300-500microm, in three 10-minute sessions a day for 3 consecutive days) was applied to voluntary contracted quadriceps (vibrated and contracted group) and relaxed quadriceps (vibrated and relaxed group). A third group received placebo stimulation (nonvibrated group). MAIN OUTCOME MEASURES Area of sway of the center of pressure, vertical jump height, and leg power. RESULTS Twenty-four hours after the end of the complete series of applications, the area of sway of the center of pressure decreased significantly by approximately 20%, vertical jump increased by approximately 55%, and leg power increased by approximately 35%. These effects were maintained for at least 90 days after treatment. CONCLUSIONS rMV is a short-lasting and noninvasive protocol that can significantly and persistently improve muscle performance in sedentary young-elderly women.

Central projections and entries of capsaicin-sensitive muscle afferents.

The entry pathway and central distribution of A delta and C muscle afferents within the central nervous system (CNS) were investigated by combining electron microscopy and electrophysiological analysis after intramuscular injection of capsaicin. The drug was injected into the rat lateral gastrocnemius (LG) and extraocular (EO) muscles. The compound action potentials of LG nerve and the evoked field potentials recorded in semilunar ganglion showed an immediate and permanent reduction in A delta and C components. The morphological data revealed degenerating unmyelinated axons and terminals in the inner sublamina II and in the border of laminae I-II of the dorsal horn at L4-L5 and C1-C2 (subnucleus caudalis trigemini) spinal cord segments. Most degenerating terminals were the central bouton (C) of type I and II synaptic glomeruli. Furthermore, degenerating peripheral axonal endings (V2) presynaptic to normal C were found. Since V2 were previously found degenerated after cutting the oculomotor nerve (ON) or L4 ventral root, we conclude that some A delta and C afferents from LG and EO muscles entering the CNS by ON or ventral roots make axoaxonic synapses on other primary afferents to promote an afferent control of sensory input.

Inhibition of muscle spindle afferent activity during masseter muscle fatigue in the rat

The influence of muscle fatigue on the jaw-closing muscle spindle activity has been investigated by analyzing: (1) the field potentials evoked in the trigeminal motor nucleus (Vmot) by trigeminal mesencephalic nucleus (Vmes) stimulation, (2) the orthodromic and antidromic responses evoked in the Vmes by stimulation of the peripheral and central axons of the muscle proprioceptive afferents, and (3) the extracellular unitary discharge of masseter muscle spindles recorded in the Vmes. The masseter muscle was fatigued by prolonged tetanic masseter nerve electrical stimulation. Pre- and postsynaptic components of the potentials evoked in the Vmot showed a significant reduction in amplitude following muscle fatigue. Orthodromic and antidromic potentials recorded in the Vmes also showed a similar amplitude decrease. Furthermore, muscle fatigue caused a decrease of the discharge frequency of masseter muscle spindle afferents in most of the examined units. The inhibition of the potential amplitude and discharge frequency was strictly correlated with the extent of muscle fatigue and was mediated by the group III and IV afferent muscle fibers activated by fatigue. In fact, the inhibitory effect was abolished by capsaicin injection in the masseter muscle that provokes selective degeneration of small afferent muscle fibers containing neurokinins. We concluded that fatigue signals originating from the muscle and traveling through capsaicin-sensitive fibers are able to diminish the proprioceptive input by a central presynaptic influence. In the second part of the study, we examined the central projection of the masseter small afferents sensitive to capsaicin at the electron-microscopic level. Fiber degeneration was induced by injecting capsaicin into the masseter muscle. Degenerating terminals were found on the soma and stem process in Vmes and on the dendritic tree of neurons in Vmot. This suggests that small muscle afferents may influence the muscle spindle activity through direct synapses on somata in Vmes and on dendrites of neurons in Vmot.

Kv1.1 knock-in ataxic mice exhibit spontaneous myokymic activity exacerbated by fatigue, ischemia and low temperature.

Episodic ataxia type 1 (EA1) is an autosomal dominant neurological disorder characterized by myokymia and attacks of ataxic gait often precipitated by stress. Several genetic mutations have been identified in the Shaker-like K+ channel Kv1.1 (KCNA1) of EA1 individuals, including V408A, which result in remarkable channel dysfunction. By inserting the heterozygous V408A, mutation in one Kv1.1 allele, a mouse model of EA1 has been generated (Kv1.1V408A/+). Here, we investigated the neuromuscular transmission of Kv1.1V408A/+ ataxic mice and their susceptibility to physiologically relevant stressors. By using in vivo preparations of lateral gastrocnemius (LG) nerve–muscle from Kv1.1+/+ and Kv1.1V408A/+ mice, we show that the mutant animals exhibit spontaneous myokymic discharges consisting of repeated singlets, duplets or multiplets, despite motor nerve axotomy. Two-photon laser scanning microscopy from the motor nerve, ex vivo, revealed spontaneous Ca2 + signals that occurred abnormally only in preparations dissected from Kv1.1V408A/+ mice. Spontaneous bursting activity, as well as that evoked by sciatic nerve stimulation, was exacerbated by muscle fatigue, ischemia and low temperatures. These stressors also increased the amplitude of compound muscle action potential. Such abnormal neuromuscular transmission did not alter fiber type composition, neuromuscular junction and vascularization of LG muscle, analyzed by light and electron microscopy. Taken together these findings provide direct evidence that identifies the motor nerve as an important generator of myokymic activity, that dysfunction of Kv1.1 channels alters Ca2 + homeostasis in motor axons, and also strongly suggest that muscle fatigue contributes more than PNS fatigue to exacerbate the myokymia/neuromyotonia phenotype. More broadly, this study points out that juxtaparanodal K+ channels composed of Kv1.1 subunits exert an important role in dampening the excitability of motor nerve axons during fatigue or ischemic insult.

Partial transformation from fast to slow muscle fibers induced by deafferentation of capsaicin-sensitive muscle afferents

Mechanical and histochemical characteristics of the lateral gastrocnemius (LG) muscle of the rat were examined 21 days after capsaicin injection into the LG muscle. The capsaicin caused a decrease in generation rate of twitch and tetanic tension and an increase in fatigue resistance of LG muscle. The histochemical muscle fiber profile evaluated by myosin adenosine triphosphatase and reduced nicotinamide adenine dinucleotide tetrazolium reductase methods showed an increase of type I and IIC fibers and a decrease of the type IIB in whole muscle, and a decrease of the IIA, IIX fibers in the red part accompanied by their increase in the white part. Therefore the capsaicin treatment, which selectively eliminated fibers belonging to the III and IV groups of muscle afferents, induced muscle fiber transformation from fast contracting fatiguing fibers to slowly contracting nonfatiguing ones.

Voluntary Enhanced Cocontraction of Hamstring Muscles During Open Kinetic Chain Leg Extension Exercise Its Potential Unloading Effect on the Anterior Cruciate Ligament

Background: A number of research studies provide evidence that hamstring cocontraction during open kinetic chain knee extension exercises enhances tibiofemoral (TF) stability and reduces the strain on the anterior cruciate ligament. Purpose: To determine the possible increase in hamstring muscle coactivation caused by a voluntary cocontraction effort during open kinetic chain leg-extension exercises, and to assess whether an intentional hamstring cocontraction can completely suppress the anterior TF shear force during these exercises. Study Design: Descriptive laboratory study. Methods: Knee kinematics as well as electromyographic activity in the semitendinosus (ST), semimembranosus (SM), biceps femoris (BF), and quadriceps femoris muscles were measured in 20 healthy men during isotonic leg extension exercises with resistance (R) ranging from 10% to 80% of the 1-repetition maximum (1RM). The same exercises were also performed while the participants attempted to enhance hamstring coactivation through a voluntary cocontraction effort. The data served as input parameters for a model to calculate the shear and compressive TF forces in leg extension exercises for any set of coactivation patterns of the different hamstring muscles. Results: For R≤ 40% 1RM, the peak coactivation levels obtained with intentional cocontraction (l) were significantly higher (P < 10–3) than those obtained without intentional cocontraction (l0). For each hamstring muscle, maximum level l was reached at R = 30% 1RM, corresponding to 9.2%, 10.5%, and 24.5% maximum voluntary isometric contraction (MVIC) for the BF, ST, and SM, respectively, whereas the ratio l/l0 reached its maximum at R = 20% 1RM and was approximately 2, 3, and 4 for the BF, SM, and ST, respectively. The voluntary enhanced coactivation level l obtained for R≤ 30% 1RM completely suppressed the anterior TF shear force developed by the quadriceps during the exercise. Conclusion: In leg extension exercises with resistance R≤ 40% 1RM, coactivation of the BF, SM, and ST can be significantly enhanced (up to 2, 3, and 4 times, respectively) by a voluntary hamstring cocontraction effort. The enhanced coactivation levels obtained for R≤ 30% 1RM can completely suppress the anterior TF shear force developed by the quadriceps during the exercise. Clinical Relevance: This laboratory study suggests that leg extension exercise with intentional hamstring cocontraction may have the potential to be a safe and effective quadriceps-strengthening intervention in the early stages of rehabilitation programs for anterior cruciate ligament injury or reconstruction recovery. Further studies, including clinical trials, are needed to investigate the relevance of this therapeutic exercise in clinical practice.

Effects of focal vibration in subject with shoulder impingement

SISMES VI NATIONAL CONGRESS Naples, 26–28 September 2014 The Marcello Faina Lecture Fitness and health effects of recreational football for untrained individuals across the life span

Balance and cyclic rapidity adaptations in children aged from 6 to 11 after proprioceptive or coordinative training

Female skin conductance and regional differences in thermal sudomotor activity at rest and during exercise in different environmentsIntroduction: The motor activities contribute to the child’s educational process1 , promote the prevention of many diseases2 and promote the development of self-efficacy perceived 3. In the Apulia region to 39,2% of children of 8 years has excess weight (2010) 4; targeted interventions are needed to counteract the sedentary habits5 ; reduce body weight and increase the self-perception, through a wide repertoire of motor activities. Methods: It has been carried out an intervention of extracurricular physical activities for 6 months. Motor test have been proposed (T0 vs T1)6: standing long jump; 20-m speed; 1 Kg medicine ball throw; the self-report: Perceived Physical Ability Scale for Children (PPAS_C)7 to 28 children divided into overweight and obese according to cutt off of Cole8, attending primary school (F = 12; age: M ± ds = 9.76 ± 0.84; BMI: M ± ds = 24,28 ±2,13; M = 16; age: M ± ds = 9.20 ± 1.54; BMI M±ds 27,60±4.07). Results: Apart from the descriptive statistics, it was carried out the ANOVA 2 analysis of the variance (test: T0 vs T1) x 2 (sex) repeating the measurements for the last factor, in order to highlight the significant differences related to the dependent variables taken into consideration. The significativity index was set to p< 0,05. Some differences emerged with respect to the test-retest within the tests: standing long jump (Female: p = 0,003; Male, p = 0,001); 1 Kg medicine-ball throw (Female: p = 0,02; Male: p =0,003); in the scale of PPAS_C (Female: p = 0,000; Male: p = 0.04). We highlight gender differences in the standing long jump: females have higher performance than males (p = 0,02); in the scale of PPAS_C not show differences. Males and females show a reduction in BMI (T0 vs T1 ): F: M ± ds = 24,28 ±2,13 vs 23,39± 2,03; M: 27,60±4,07 vs 27,38 ± 4,18. Conclusion: The study found positive effects on levels of motor performance and physical self-perception after the program extracurricular. The experiences of success, measured in terms of increased motor abilities of real and perceived, are essential to prevent childhood overweight. Recent studies have shown that physical activity interventions, combined with healthy eating habits, at school and in extracurricular, can reduce children’s BMI9. References 1. Bailey R (2006), JSH,76, 397-401 2. Brambilla P et al. (2010), Int J Obes , 35,16-28 3. Feltz DL et al (2008), Champaign, IL: HK 4. http://www.epicentro.iss.it/territorio/puglia.asp 5. Biddle SJH et al. (2011), Br J Sports Med, 45, 937-942 6. Morrow JR et al. (2005), Champaign, IL: HK 7. Colella D et al. (2008), SBP, 36,841-8 8. Cole TJ et al. (2000), BMJ, 320,1240-3 9. Lavelle HV et al.(2012), J Public Health, 20,1-10 The psychobiosocial state inventory: preliminary evidence of factorial validity