Sensorial, structural and functional response of rats subjected to hind limb immobilization

Responses of cutaneous C-fiber afferents and spinal microglia after hindlimb cast immobilization in rats

Previous studies have shown that persistent limb immobilization using a cast increases nociceptive behavior to somatic stimuli in rats. However, the peripheral neural mechanisms of nociception remain unclear. Using single-fiber electrophysiological recordings in vitro, we examined the general characteristics of cutaneous C-fiber afferents in the saphenous nerve and their responsiveness to mechanical and heat stimuli in a rat model of immobilization-induced pain by subjecting the rats to hindlimb cast immobilization for 4 weeks. The mechanical response of C-fibers appeared to increase in the model; however, statistical analysis revealed that neither the response threshold nor the response magnitude was altered. The general characteristics and heat responses of the C-fibers were not altered. The number of microglia and cell diameters significantly increased in the superficial dorsal horn of the lumbar spinal cord. Thus, activated microglia-mediated spinal mechanisms are associated with the induction of nociceptive hypersensitivity in rats after persistent cast immobilization.

FUNCTIONAL ANALYSIS OF GAIT WITH INSOLE USE IN DIABETIC FEMALE RATS: A CROSS-SECTIONAL STUDY

ABSTRACT Introduction: Diabetes mellitus is a chronic disease that is characterized by causing damage to the peripheral nervous system, generating sensory and motor changes. Objective: This study aims at analyzing the impact of the use of different orthotic insoles on the gait of diabetic female rats. Methods: Twenty-six female Wistar rats were randomly divided into the Control and Diabetic groups. The mechanical sensitivity test was performed manually on the surface of the animals' hind paws using the von Frey test. The functional evaluation was carried out on an adapted platform where the animals were stimulated to walk in order to capture images of the ventral region for measurements of the right and left hind paws. After the images were collected they were processed using Kinovea software version 0.8.27 to assess: stride distance, time, speed and acceleration. Results: There was a reduction in the weight of the animals in the Diabetic Group (p = 0.0018), associated with hyperglycemia (p = <0.0001), and a decrease in mechanical sensitivity as compared to the Control Group (p = 0.0372). Gait analysis showed a reduction in stride speed (p = 0.0482) and acceleration (p = 0.0149), with the silicone orthosis in the Diabetic Group. Conclusions: The silicone orthosis demonstrated a reduction in stride speed and acceleration, without compromising the other variables in the diabetic rats. The other insoles showed no functional difference between groups. Even though the animals showed a change in sensitivity at the end of 28 days of DM induction, this time does not appear to have been able to develop extensive changes in the rats' gait function. Level of evidence II; Therapeutic studies - Investigating the Results of Treatment.

Interplay between hypoactivity, muscle properties and motor command: How to escape the vicious deconditioning circle?

Activity-dependent processes addressing the central nervous system (CNS) and musculoskeletal structures are critical for maintaining motor performance. Chronic reduction in activity, whether due to a sedentary lifestyle or extended bed rest, results in impaired performance in motor tasks and thus decreased quality of life. In the first part of this paper, we give a narrative review of the effects of hypoactivity on the neuromuscular system and behavioral outcomes. Motor impairments arise from a combination of factors including altered muscle properties, impaired afferent input, and plastic changes in neural structure and function throughout the nervous system. There is a reciprocal interplay between the CNS and muscle properties, and these sensorimotor loops are essential for controlling posture and movement. As a result, patients under hypoactivity experience a self-perpetuating cycle, in with sedentarity leading to decreased motor activity and thus a progressive worsening of a situation, and finally deconditioning. Various rehabilitation strategies have been studied to slow down or reverse muscle alteration and altered motor performance. In the second part of the paper, we review representative protocols directed toward the muscle, the sensory input and/or the cerebral cortex. Improving an understanding of the loss of motor function under conditions of disuse (such as extended bed rest) as well as identifying means to slow this decline may lead to therapeutic strategies to preserve quality of life for a range of individuals. The most efficient strategies seem multifactorial, using a combination of approaches targeting different levels of the neuromuscular system.

Combination of hindlimb suspension and immobilization by casting exaggerates sarcopenia by stimulating autophagy but does not worsen osteopenia

Astronauts in space experience a unique environment that causes the concomitant loss of bone and muscle. However, the interaction between these tissues and how osteopenia and sarcopenia affect each other is unclear. We explored this relationship by exaggerating unloading-induced muscle loss using a unilateral casting model in conjunction with hindlimb suspension (HLS). Five-month-old, male C57Bl/6J mice subjected to HLS for 2 weeks displayed a significant decrease in gastrocnemius and quadriceps weight (-9-10%), with a two-fold greater decrease in muscle mass observed in the HLS + casted limb. However, muscle from casted limbs had a higher rate of protein synthesis (+16%), compared to HLS alone, with coordinated increases in S6K1 (+50%) and 4E-BP1 (+110%) phosphorylation. Increased protein content for surrogate markers of autophagy, including LC3-II (+75%), Atg7 (+10%), and Atg5-12 complex (+20%) was only detected in muscle from the casted limb. In proximal tibias, HLS resulted in significant decreases in bone volume fraction (-24% vs -8%), trabecular number (-6% vs +0.3%), trabecular thickness (-10% vs -2%), and trabecular spacing (+8.4% vs +2%) compared to ground controls. There was no further bone loss in casted limbs compared to HLS alone. In tibia midshafts, HLS resulted in decreased total area (-2% vs +1%) and increased bone mineral density (+1% vs -0.3%) compared to ground controls. Cortical bone from casted limbs showed an increase in cortical thickness (+9% vs +2%) and cortical area/total area (+1% vs -0.6%) compared to HLS alone. Our results suggest that casting exacerbates unloading-induced muscle loss via activation of autophagy. Casting did not exacerbate bone loss suggesting that the unloading-induced loss of muscle and bone can be temporally dissociated and the effect of reduced muscle activity plays a relatively minor role compared to reduced load bearing on trabecular bone structure.

Análise da função pulmonar e estrutura micromecânica após 14 dias de restrição de movimento em ratas

RESUMO A imobilização é uma condição que compromete diversos segmentos e sistemas orgânicos, inclusive o sistema respiratório, levando a alterações estruturais e funcionais. O objetivo deste estudo foi analisar a função pulmonar e estrutura micromecânica após 14 dias de restrição de movimento de ratas. Foram utilizados catorze ratas Wistar com massa corporal entre 210 g±50 g, distribuídas em dois grupos, compostos por (n=7) cada grupo: Controle (C) e Imobilizado (I). O procedimento de imobilização envolveu abdômen (e últimas costelas), pelve, quadril e joelho em extensão, além de tornozelo em flexão plantar, por duas semanas. Após esse período de imobilização, foi realizada a análise da função pulmonar por ventilador mecânico para pequenos animais (flexiVent) e manobras de recrutamento alveolar (MR). E, posteriormente, foram retiradas tiras do pulmão de cada animal para analisar a micromecânica pulmonar. Para a análise estatística, utilizou-se o teste t não pareado com significância estatística (p<0,05), expresso como média±erro padrão da média. O grupo I apresentou mudanças significantes nos parâmetros da resistência das vias aéreas (RN) pré-MR(C=0,067±0,003 cmH2O.s/mL, I=0,095±0,004 cmH2O.s/mL, p<0,05) e histerisividade (η) pré-MR(C=0,203±0,004 cmH2O.s/mL, I=0,248±0,013 cmH2O.s/mL, p<0,05), que retornaram a seus valores de normalidade pós-MR, considerando-se RN pós-MR (C=0,064±0,003 cmH2O.s/mL, I=0,065±0,004 cmH2O.s/mL, p<0,05) e η (C=0,209±0,005 cmH2O.s/mL, I=0,214±0,007 cmH2O.s/mL, p<0,05). Conclui-se que a imobilização acarreta alterações funcionais reversíveis no sistema respiratório após 14 dias de restrição de movimento, o que é evidenciado pela redução de RN e η pós-MR.

A dramatic blood plasticity in hibernating and 14-day hindlimb unloading Daurian ground squirrels (Spermophilus dauricus)

We compared the effects of hibernation inactivity and 14-day hindlimb unloading in non-hibernating period on biochemical, rheological, and hematological parameters of blood in Daurian ground squirrels (Spermophilus dauricus). Twenty-four squirrels were randomly divided into four groups: control (CON), hibernation (HIB), post-hibernation (POST), and 14-day hindlimb unloading (HU). The results showed that serum enzymes (L-lactate dehydrogenase, alanine aminotransferase, and aspartate aminotransferase) activities decreased in HIB, POST, and HU squirrels compared with CON. Total protein (including albumin and globulin) maintained in HIB but decreased in HU compared with CON. Total cholesterol and high-density lipoprotein-cholesterol increased in HIB but maintained in HU and POST compared with CON. Meanwhile, serum creatinine decreased and urea increased in HU compared with CON. All blood ions concentrations were unchanged in HIB, POST, and HU squirrels compared with CON except calcium which increased in HIB compared with CON, and phosphorus which increased in HIB and POST compared with CON. Most of detected serum biochemical analytes in POST recovered to the CON level. Blood viscosity, which was unchanged in all shear rates in HU, increased in HIB and recovered in POST in lower shear rates compared with CON. Erythrocyte and corpuscular volume decreased in HIB and HU but maintained in POST compared with CON. All the routine hematological parameters recovered in POST as compared with CON except platelet, which decreased in HIB and POST but maintained in HU compared with CON. In conclusion, our results suggested a remarkable ability to maintain blood homeostasis in hibernating squirrels.