Proprioceptive influences on inferior olivary neurons during phasic reflex movement in the cat

Abstract

The origin of the climbing fiber system from the inferior olive, and its precise synaptic relation with the cerebellar Purkinje cells suggests that the spinoolivocerebellar pathway may contribute to the mechanism of a phasic reflex movement. Intracellular recordings of inferior olivary cells were obtained using glass capillary electrodes in nonanesthesized decerebrate cats during spontaneous clonus of the right gastrocnemius-soleus muscle. Inferior olivary cells were identified as responding to proprioceptive input from the gastrocnemius-soleus muscle by their activation to electrical stimulation and manual stretch of the tendon. Simultaneous records of the inferior olivary cell and the gastrocnemius-soleus myogram and EMG were obtained. Impaled inferior olivary cells were iontophoretically injected with fast green dye and identified histologically by Nissl counterstaining. Impaled inferior olivary cells activated during spontaneous clonus were recorded firing during the contraction phase of the phasic reflex. These results suggest a supraspinal influence on phasic reflex movement via the climbing fiber system based on the established inhibitory output of the Purkinje cells and the spinal inhibitory influence of the Golgi tendon organs during the contraction phase of the phasic reflex. It is suggested that the inhibitory supraspinal influence may combine with the spinal inhibitory influence to assist in inactivating the contraction phase of the phasic reflex.