[Modulation of primary and secondary endings activity of tibialis anterior muscle spindles during contraction induced by caudate nucleus stimulations].

1. Effects of repetitive stimulations of caudate nucleus were studied on static and dynamic sensitivities of contralateral flexor (tibialis anterior) muscle spindle primary and secondary endings in cats anaesthetized with Halothane (Fluothane). Fusimotor effects are interpreted in term of gamma dynamic and gamma static activation. 2. Threshold stimulation induce a gamma dynamic effect on the primary endings sensitivity. Secondary endings activity and muscle tension remainded unaltered. 3. A slight increase of the stimulus strength elicit a gamma dynamic-gamma static effect on the primary endings sensitivity. Simultaneously secondary endings activity was increased and muscle contractions induced. 4. Using graded voltage stimulation permit to increase primary and secondary endings activity without muscle contraction. 5. Two stimulations applied at sufficiently short time interval produce different fusimotor effects. The first stimulation induce the general motor effect previously obtained: gamma dynamic-gamma static modulation of primary endings sensitivity, increase of secondary endings activity, muscular contraction. The second stimulation elicit a gamma dynamic effect on primary endings sensitivity and a depressant effect on secondary endings activity during muscular contractions. 6. Tendon organs discharge during caudate nucleus stimulation was studied comparatively with the primary and secondary endings activity.