Weight-bearing bone is constantly adapting its structure and function to mechanical environments. Loading through routine exercises stimulates bone formation and prevents bone loss, but unloading through bed rest and cast immobilization as well as exposure to weightlessness during spaceflight reduces its mass and strength. In order to elucidate the mechanism underlying unloading-driven bone adaptation, ground-based in vitro and in vivo analyses have been conducted using rotating cell culturing and hindlimb suspension. Focusing on gene expression studies in osteoblasts and hindlimb suspension studies, this minireview introduces our recent understanding on bone homeostasis under weightlessness in space. Most of the existing data indicate that unloading has the opposite effects to loading through common signaling pathways. However, a question remains as to whether any pathway unique to unloading (and not to loading) may exist.
Adaptation, Physiological ; Animals ; Bone and Bones ; cytology ; physiology ; Hindlimb Suspension ; physiology ; Humans ; Osteoblasts ; physiology ; Weightlessness

The aim of the present study was to establish a minimally invasive H reflex model in mice for the benefit of the research of clinical spinal cord injury and related diseases. Minimally invasive surgery was performed in hind limb of Kunming mouse under light anesthesia. The skin was incised at the point of one-third of the distance from greater trochanter to the base of the cauda. A pair of fine copper conductors were inserted into the shallow muscle using a syringe needle. After the needles were withdrawed, the retained conductors were ligated and fixed with the tissues surrounding the sciatic nerve as the first pair of stimulating electrodes. Another pair of conductors were inserted and fixed in medial malleolus close to the tibial nerve as the second stimulating electrodes. Copper conductor was inserted passing the skin above the proximal end of the metatarsal and fixed as the recording electrode. The reference electrode was placed at the walking pad in the base of the big toe using the same method. Electromyography (EMG) was used to record M and H waves in planta pedis muscles. The stimulus was a square wave with a width of 0.2 ms and frequency of 0.3 Hz. The latency time of the M and H waves which were induced from the two pairs of stimulating electrodes was recorded. Nerve conduction velocity (NCV) was then calculated from the distance between the cathodes of the stimulating electrodes and the latency time difference of M or H waves. The result showed the achievement ratios of H reflex induction were 92.73% and 81.82% in sciatic and tibial nerves, respectively. The latency time of H wave was about 7~10 ms. Motor nerve conduction velocity (MNCV) obtained was (25.84 ± 4.70) m/s (n = 35), while sensory nerve conduction velocity (SNCV) was (31.45 ± 7.30) m/s (n = 35). The method established in the present paper is simple to practice, does slight harm to the animal, and can produce waveforms with little interference. With these advantages, the method can be applied for the study of the latency of H reflex, and it is suitable for the researches which demands good physical condition of experimental animal during H reflex study. This model can also be applied to the detection of SNCV and MNCV.
Animals ; Electromyography ; H-Reflex ; physiology ; Hindlimb ; innervation ; Mice ; Neural Conduction ; physiology ; Tibial Nerve ; physiology

Intracortical microstimulation (ICMS) is a technique that was developed to derive movement representation of the motor cortex. Although rats are now commonly used in motor mapping studies, the precise characteristics of rat motor map, including symmetry and consistency across animals, and the possibility of repeated stimulation have not yet been established. We performed bilateral hindlimb mapping of motor cortex in six Sprague-Dawley rats using ICMS. ICMS was applied to the left and the right cerebral hemisphere at 0.3 mm intervals vertically and horizontally from the bregma, and any movement of the hindlimbs was noted. The majority (80%+/-11%) of responses were not restricted to a single joint, which occurred simultaneously at two or three hindlimb joints. The size and shape of hindlimb motor cortex was variable among rats, but existed on the convex side of the cerebral hemisphere in all rats. The results did not show symmetry according to specific joints in each rats. Conclusively, the hindlimb representation in the rat motor cortex was conveniently mapped using ICMS, but the characteristics and inter-individual variability suggest that precise individual mapping is needed to clarify motor distribution in rats.
Animals ; *Brain Mapping ; Electric Stimulation ; Electrodes ; Hindlimb/*physiology ; Male ; Motor Cortex/*physiology ; Rats ; Rats, Sprague-Dawley

Any method that deforms the skin of the extremities may increase lymphatic flow rate, and may be applied to treat peripheral lymphedema. This study was undertaken to investigate whether or not elastic adhesive tape with passive exercise can increase lymph flow in the rabbit hind leg by effective and periodic skin deformation. Cannulation into a pre-popliteal afferent lymphatic vessel in the lower left leg of 22 male New Zealand White rabbits was performed under a stereomicroscope. After stabilization, lymph was collected at rest or during passive exercise with an electric motor at 60 r.p.m. for 15 minutes and was then measured. Lymph flow rate was calculated and expressed as g/hour. Increase of lymph flow rate due to taping was significant only for passive exercise (p=0.0317). The lymph flow rate increased linearly as the area of tape was increased (p=0.0011), and lymph flow rates were significantly different according to site (p=0.0017). Tape on the anterior aspect of the ankle caused salient deformation and tended to increase the lymph flow rate more so than tape on the dorsum of the foot (p=0.0831). Taping with elastic adhesive tape in passive exercise increased the lymph flow rate in the rabbit hind leg by deforming the skin, which suggests a novel therapeutic method in cases of peripheral lymphedema.
Animals ; *Bandages ; Elasticity ; Hindlimb/*physiology ; Lymph/*physiology ; Male ; Motion ; Rabbits ; Support, Non-U.S. Gov't

We studied the effects of simulated microgravity on mouse oocytes maturation, and analyzed whether the tail-suspended model can be applied to investigate simulated microgravity effects on reproductive processes in female mice. Mouse oocytes were cultured in vitro with microgravity simulated by a rotating wall vessel bioreactor and by tail-suspended model, and the maturation rate of the mouse oocytes in the two models were examined in vivo. The maturation rate of mouse oocytes cultured in simulated microgravity was 8.93%, and that was 72.33% in 1g gravity. In ratio, oocyte maturation rate had no significant difference between the rotational group and control group. Microgravity simulated by the tail-suspended model inhibited mouse oocytes maturation and increased the rate of oocytes abnormity. The maturation rate of tail-suspended mouse oocytes was 14.54%, which was significantly lower than that of control group. Tail-suspended model should be an ideal model to investigate simulated microgravity effects on reproductive processes of female mice.
Animals ; Cells, Cultured ; Female ; Hindlimb Suspension ; Mice ; Oocytes ; cytology ; physiology ; Oogenesis ; physiology ; Weightlessness Simulation

OBJECTIVETo study the effects on rats' bone mineral density and bone biomechanics by suspensory simulated weightlessness and removing suspension.

METHODSTwenty Wistar rats were divided into two groups randomly as control group and model group. Suspend the model group rats for 14 days, then remove suspension and continue to feed for another 14 days. Feed control group rats for 28 days. Detect the bone mineral density (BMD) in vivo of cranial bone, second thoracic vertebra, fourth lumbar vertebra, pelvis, right radioulna and right femoral bone of each group at the 14th day. At the 28th day,execute all the rats and take out of right femoral bone and fourth lumbar vertebra for detecting BMD and the intensity of biomechanics.

RESULTSAt the 14th day in experiment, being compared with control group,the BMD of femoral bone, pelvis and lumbar vertebra in model group decreased significantly (P < 0.001, P < 0.001, P < 0.01) and the change of BMD of cranial bone, thoracic vertebra and radioulna in model group was not remarkable (P > 0.05). At the 28th day in experiment, the BMD of femoral bone and lumbar vertebra, the maximal load of femoral bone decreased significantly in model group as compared with control group (P < 0.01, P < 0.001, P < 0.01).

CONCLUSIONBMD in vive body showed that suspensory simulated weightlessness for 14 days could cause disorder of bone metabolism and remarkable mineral loss of weight bearing bone, even BMD and biomechanical intensity of weight bearing bone decrease obviously when removing suspension for 14 days. The results suggest that the disorder of bone metabolism could not be recovered in short time.

Animals ; Biomechanical Phenomena ; Bone Density ; Bone and Bones ; physiology ; Hindlimb Suspension ; Male ; Rats ; Rats, Wistar ; Weightlessness Simulation

OBJECTIVETo investigate the effects of 100 Hz sinusoidal vibration on H reflex and M wave in rat soleus muscle following immobilization.

METHODSThe immobilization of rat soleus muscle was induced as a disuse muscle model, and 100 Hz sinusoidal vibration was generated by a vibrator and applied to the immobilized soleus muscle, then the changes of H reflex and M wave in muscle were observed after 14 d.

RESULTSCompared to control, after 14 d of immobilization M(max) in soleus muscle decreased (P<0.01), stimulus threshold and S(max) increased (P<0.01); Hmax and H(max)/M(max) decreased (P<0.05, S(max) increased (P<0.05). Compared to immobilized soleus muscle, after 14 d of immobilization with 100 Hz sinusoidal vibration, the M(max) increased(P<0.01), stimulus threshold and S(Mmax) decreased (P<0.05), H(max) (P<0.01) increased and H(max)/M(max) increased (P<0.05).

CONCLUSION100 Hz sinusoidal vibration plays a significant antagonist role against the changes in H reflex and M wave in rat soleus muscle following immobilization.

Animals ; Electromyography ; Female ; H-Reflex ; physiology ; Hindlimb Suspension ; Muscle Contraction ; physiology ; Muscle Spindles ; physiology ; Muscle, Skeletal ; physiology ; Rats ; Rats, Sprague-Dawley ; Vibration

OBJECTIVETo observe the change of nitric oxide (NO) levels in the blood and the morphological change of the muscles in the limbs of rats during the (IR) injury and after being intervened by L-arginine (L-Arg) and L-nitroarginine (L-NNA).

METHODSSixty-six male Sprague-Dawley (SD) rats were used an d grouped into the normal controls, the sham injury controls, the IR injury group and the intervention groups (L-Arg group and L-NNA group). After 6 hours of ischemia, followed by reperfusion for 3, 12 or 24 hours, the samples in the IR injury group were obtained. The rats in the intervention groups were given L-Ar g (100 mmol/L) and L-NNA (10 mmol/L), respectively, through the abdominal cavity. Then the anterior tibial muscle in the right limb was obtained for histological examination, the anterior tibial muscle in the left limb for ultrastructure observation and the blood for assay of NO in all the rats. NO was assayed by indirect measurement of NO(2)(-)/NO(3)(-) with Griess method.

RESULTSThere was no significant difference of NO between the normal controls and the sham injury controls (P>0.05). But NO significantly decreased in the IR injury group (P<0.01), and further decreased with reperfusion (P<0.01) and reached the lowest point at 12 hours after reperfusion. The level of NO in the L-Arg group was significantly higher than that in the IR injury group ( P<0.01), but was not significantly different from that in the controls (P>0.05). In the L-NNA group, NO decreased to the undetectable level (P<0.01). Histological examination and ultrastructure observation showed the muscles were normal in the control groups. After 6 hours of ischemia, the skeletal muscles displayed injuries, and they were most severely injure d after 12 hours of reperfusion. In the L-Arg group, the skeletal muscles were less injured, while in the L-NNA group, the injury was similar to that in the I R injury group.

CONCLUSIONSWhen the limbs of the rats sustain IR, NO in the blood decreases. Meanwhile, the muscles in the limbs are injured. When L-Arg is given, NO in the blood is restored and the muscles are protected. When L-NNA completely inhibits NO, no protection of the muscles is shown.

Animals ; Arginine ; pharmacology ; Hindlimb ; Male ; Muscle, Skeletal ; blood supply ; ultrastructure ; Nitric Oxide ; physiology ; Rats ; Rats, Sprague-Dawley ; Reperfusion Injury ; physiopathology

Amnion ; cytology ; Animals ; Brain Injuries ; therapy ; Cell Transplantation ; Cells, Cultured ; Female ; Hindlimb ; physiology ; Humans ; Rats ; Rats, Sprague-Dawley ; Transplantation, Heterologous

This study was aimed to investigate the changes of muscle protein synthesis and degradation under different movement conditions, so as to provide theoretical basis for muscle atrophy mechanism. Sprague Dawley (SD) rats were randomly divided into control, endurance training (treadmill training), hind limb overhanging and eccentric training (treadmill training, angle -16º) groups. The gastrocnemius muscles of rats were taken and weighed. The muscle was sectioned, and HE staining was employed to determine the cell's cross-sectional area. Protein expression of p-Akt was measured by immunohistochemistry; and the expressions of MuRF1 and FoxO1 were determined by Western blot. The results showed that, compared with control group, hind limb overhanging and eccentric training groups exhibited decreased muscle weight and cross-sectional area, but endurance training group did not show any changes. The expressions of p-Akt in endurance and eccentric training groups, not in hind limb overhanging group, were significantly higher than that in control group. Compared with that of control, MuRF1 protein remained unchanged in endurance training groups, but was increased in eccentric training and hind limb overhanging groups; FoxO1 protein was decreased in endurance training group, but was increased in eccentric training and hind limb overhanging groups. These results indicate that movement (endurance and eccentric training) can activate Akt expression, but does not increase muscle weight, whereas eccentric training and hind limb overhanging can increase the expressions of MuRF1 and FoxO1, and induce amyotrophy, suggesting MuRF1 and FoxO1 are major determinant factors in muscle atrophy.
Animals ; Forkhead Transcription Factors ; physiology ; Hindlimb Suspension ; Muscle Proteins ; physiology ; Muscle, Skeletal ; physiology ; Muscular Atrophy ; physiopathology ; Nerve Tissue Proteins ; physiology ; Physical Conditioning, Animal ; Proto-Oncogene Proteins c-akt ; physiology ; Rats ; Rats, Sprague-Dawley ; Tripartite Motif Proteins ; Ubiquitin-Protein Ligases ; physiology