Objective To observe the effect of inosine on afferent discharge of muscle spindle.Methods The afferent discharge of isolated toad muscle spindle was recorded using air-gap technique.The effects of inosine on the discharge rate of muscle spindle was observed.Results After administration of 0.2mmol/L,0.4mmol/L and 0.8mmol/L inosine,the spontaneous discharge of muscle spindle increased from(0.86?(0.12))Hz,(0.88?(0.12))Hz and(0.85?0.10)Hz to(11.42?2.48)Hz,(21.75?3.03)Hz and(32.25?4.08)Hz,respectively.Conclusion Inosine can increase the afferent discharge rate of muscle spindle,and this effect is dose-dependent.

Objective To investigate changes induced by hindlimb unloading in morphology of nerve endings in soleus muscle spindles.Method Hindlimb unloading model was simulated by tail suspension in female rats.Fast silver-staining was used to observe morphology of nerve endings of single muscle spindle in 7 d,14 d,21 d and 28 d tail-suspended and control rats.Result Nerve endings of muscle spindles in control rats were intact and clear,and there was no obvious abnormality in single soleus muscle spindle of 7 d tail-suspended rats.Slight fragmentation of nerve endings was observed in Equatorial Region of soleus muscle spindle in 14 d tail-suspended rats,while reduction in density and disruption of nerve endings were observed in soleus muscle spindle in 21 d tail-suspended rats.Serious degeneration and distortion of nerve endings were found in soleus muscle spindle in 28 d tail-suspended rats.Conclusion Hindlimb-unloading can induce time-related changes in morphology of nerve endings of muscle spindle in rats soleus muscle.

Objective To observe the changes of diameter of intrafusal fibers and capsule at equatorial region of rat soleus muscle spindle caused by hindlimb-unloading.Method Tail-suspended female rats were used as the model of hindlimb-unloading,all rats were randomly divided into 4 groups according to body weight.The four groups were exposed to tail-suspension for: 7 d,14 d,28 d and 0 d,respectively.The diameter of intrafusal fibers and capsule of single muscle spindle was measured and analyzed.Result The diameter of intrafual fibers,including nuclear-bag fibers and nuclear-chain fibers, were reduced slightly in both 7 d group and 28 d group and obviously reduced in 14 d group.The capsule diameter at equatorial region was obviously reduced in 7 d group.Conclusion Hindlimb-unloading can obviously reduce the diameters of intrafusal fibers and capsule at equatorial region of rat soleus muscle spindle.

Objective To study the effects of choline chloride on activities of myosin adenosine triphosphatase (mATPase) of muscle fibres and muscle atrophy in tail-suspended rats. Method Twenty-four adult female Sprague-dawley rats were averagely divided into 3 groups matched for body mass:control group(CON),tail suspension group(TS) and tail suspension group associated with choline chloride(TS+Cch).Weightlessness was simulated by 14 d tail suspension of rats;gastric lavage with choline chloride was given to 1/2 of the rats during tail suspension (15 mg/kg body weight.i.g.).Activities of myosin adenosine triphosphatase (mATpase) of intrafusal and extrafusal fibres in soleus (SOL) muscle were determined by Ca 2+-ATPase method.Paraffin sections of the soleus muscle were prepared by routine histochemistry method. Result After tail suspension for 14 d it was found: 1) percentage of type Ⅱ fibre in SOL of rats treated with choline chloride decreased distinctly as compared with that in the untreated rats (P

Objective To study the morphological changes of soleus muscle spindle and electrical activity of neurons in Red Nucleus(RN) of the rat after 2 weeks' simulated weightlessness, and to reveal the interaction between proprioceptive inputs of muscle spindles and reciprocal alterations in RN under simulated weightlessness. Methods Twenty female rats were exposed to weightlessness simulated by tail-suspension for 14 days (SW-14d). Body weight(200-220g) matched female rats were control group(Con). The morphological changes in isolated muscle spindle of soleus muscle, the discharges of red nucleus neurons were observed after 14d tail-suspensions by silver staining and extracellular recording respectively. Results Compared with control group ,the nerve ending of muscle spindle in SW-14d was distorted, degenerated and dissolved; the diameters of intrafusal fibers and capsule in equatorial region of soleus muscle spindles were diminished(P＜0.05). The spontaneous cell activity and discharge of RN neurons (spikes/s) induced by afferent firing from muscle spindles after injection of succinylcholine were reduced after 2 weeks' simulated weightlessness respectively (18.44±5.96 vs. 10.19±6.88, 32.50±8.08 vs. 16.86±5.97, P＜0.01). Conclusion The degeneration of muscle spindle induced by simulated weightlessness may be one of the causes that led to alterations in discharges of RN.

Objective To analyse the antinociceptive effect of muscle spindle afferents and the involved mechanism.Methods The single unit of wide dynamic range(WDR) neurons in the spinal cord dorsal horn were recorded extracelluarly.The effects of muscle spindle afferents elicited by intravenous administration of succinylcholine (Sch) on nociceptive responses (C-fibres-evoked responses,C-responses) of WDR neurons were observed before and after bilateral lesions of ventrolateral periaqueduct gray (PAG).And the effects of muscle spindle afferents on the spontaneous discharge of the tail-flick related cell in the rostral ventro medial medulla (RVM) and on the spontaneous discharge of the PAG neurons were observed.Results The C-responses of WDR neurons were significantly inhibited by muscle spindle afferents,and the inhibitory effects were reduced by bilateral lesions of ventrolateral PAG.The spontaneous discharge of the off-cell in the RVM was excited while the on-cell was inhibited by intravenous administration of Sch.The spontaneous discharge of the PAG neurons were excited by muscle spindle afferents.Conclusion Muscle spindle afferents show a distinct effect of antinociception.PAG-RVM descending inhibitory system may play an important role in this nociceptive modulative mechanism.