Ascending efferent projections of the gustatory parabrachial nuclei in the rabbit

Neuroanatomical and electrophysiological techniques were used to study efferent projections of the gustatory region of the parabrachial nuclei (PBN) in rabbits. Autoradiographic analysis of [3H]leucine microinjected into electrophysiologically defined gustatory areas of the PBN revealed strong projections to the ventromedial taste component of the ventrobasal complex of the thalamus and also evidence of projections to the lateral hypothalamus, substantia innominata and nucleus centralis amygdala (ACE). Electrical stimulation in the region of ACE was shown to activate antidromically neurons in the PBN responsive to rapid stimuli, confirming gustatory projections to the ventral forebrain. An electrophysiological mapping of units in the amygdala and substantia innominata responsive to electrical stimulation of the gustatory part of the PBN agreed with the autoradiographic data. A proportion of these units were also responsive to gustatory stimuli. However, latencies of evoked response to stimulation of the PBN were unusually long. Outputs from the gustatory PBN to the ventral forebrain may include other modes of polysynaptically integrated information that are largely controlled by interneuronal networks within the PBN.