[Effects of caudate nucleus stimulations on the primary and secondary endings activity of soleus muscle spindle].

Effects of repetitive stimulation of the contralateral caudate nucleus on the static discharge and dynamic sensitivity of soleus muscle spindle primary and secondary endings were studied in cats anaesthetized with Halothane (Fluothane). By progressive increasing the depth of anaesthesia two different fusimotor effects could be observed. 1. A static facilitatory effect; under light anaesthesia the static discharge of primary and secondary endings were strongly increased. The response of the primary endings to phasic stretch of the muscle was generaly decreased. 2. A depressant effect; under deep anaesthesia the static discharge of primary and secondary endings were decreased. The dynamic sensitivity of the primary endings was lightly increased or remained unaltered. The ventro-lateral part of the caudate nucleus is mainly responsible for these effects; Caudate nucleus fusimotor effects were compared with those induced by gamma dynamic and gamma static fibers stimulations.