Arch Ital Biol
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The early component of the postural responses which accompany the limb flexion during unilateral stimulation of the motor cortex in the cat is not of reflex origin, but results from a central command. These postural adjustments are characterized by a decreased force under the limb diagonally opposite to the moving one and an increased force under the other two. Since the lateral vestibular nucleus (LVN) exerts an excitatory influence on ipsilateral limb extensor motoneurons, experiments were performed in cats to establish whether the cortical-induced postural changes were mediated through the LVN. ⋯ Moreover, histological controls indicated that the structure responsible for these postural changes corresponded to the middle part of the LVN. The specificity of the results was shown by the fact that unilateral microinjection of 0.25 microliters of the GABA-A antagonist bicuculline or the GABA-B antagonist phaclofen (at 5-8 micrograms/microliter saline) into the LVN produced a postural asymmetry opposite in sign to that elicited in the same experiments by the corresponding agonists. These injections did not modify the amplitude of the cortical-induced limb flexion, but rather enhanced the amplitude of the early component of the postural responses in the other three limbs.(ABSTRACT TRUNCATED AT 400 WORDS)