Central pathways relaying cardiovascular afferent information to amygdala

It has been suggested that cardiovascular information to the amygdala is relayed through the paraventricular nucleus of the hypothalamus (PVH) and the parabrachial nucleus (PB;7). To test this possibility spontaneously firing units in the amygdala of 12 chloralose-anesthetized cats were monitored for changes in firing frequency during electrical stimulation of PVH and PB and for their responsiveness to baroreceptor (BA) and chemoreceptor (CA) activation. In the ipsilateral amygdala 27 of 140 units responded to PVH stimulation, 9 of which also responded to CA and none to BA, whereas 46 of 150 units responded to PB stimulation, 11 of which also responded to CA and 2 to BA. To demonstrate the relative contribution of the PVH and PB in relaying cardiovascular information to the amygdala, in an additional six cats, the effect of neuronal block and lesions of these two nuclei on potentials evoked in the amygdala by stimulation of the buffer nerves was tested. Reversible neuronal block with injections of procaine in the PB significantly attenuated these evoked potentials. Electrolytic and chemical (kainic acid) lesions in the same PB sites also were effective in attenuating the responses. The potentials were unaltered by injection of procaine in the PVH. These results indicate that the PB is a site of relay of chemoreceptor and of some baroreceptor information from the medulla to the amygdala.