To clarify the differences among the four main vestibular nuclei in the vestibulo-autonomic reflex, we examined the effects of electrical stimulation of superior, lateral, medial and descending vestibular nuclei (SVN, LVN, MVN and DVN) on posterior hypothalamic area (PHA) neurons in the guinea pig. Ipsi- and contralateral SVN stimulation produced excitation in 30% and 25% of the PHA neurons tested, respectively. Twenty percent of the PHA neurons showed an excitatory response to ipsilateral LVN stimulation while 60% of the neurons tested responded to contralateral LVN stimulation, including excitation of 36% and inhibition of 24%. MVN and DVN stimulation produced little change in PHA neuron activity. These findings suggest that vestibular information processed in the SVN and the LVN is conveyed to the hypothalamus and may then contribute to activation of the vestibulo-autonomic reflex.