Crossed actions of group I muscle afferents in the cat.

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Abstract
Reflex actions evoked by electrical stimulation of contralateral quadriceps, hamstring and gastrocnemius-soleus muscle afferents were investigated using intracellular recording from motoneurons, in chloralose-anesthetized, acute, low spinal cats. Contralateral group I afferents evoked excitatory post-synaptic potentials only occasionally. Contralateral group II afferents evoked post-synaptic potentials (excitatory to extensor motoneurons and inhibitory to flexor motoneurons) from the quadriceps nerve; contralateral group III afferents evoked post-synaptic potentials (with the same pattern as quadriceps group II) from all muscles tested. Contralateral group I afferents facilitated Ia reciprocal inhibition, and both the excitatory and inhibitory reflex actions from Ib afferents. This is taken to indicate an action of these afferents on interneurons interposed in ipsilateral reflex pathways.