Projections to areas of the nucleus tractus solitarii related to circulatory and respiratory responses in cats.

Using chloralose-anesthetized cats, afferent projections to the nucleus tractus solitarii (NTS) were studied in relation to circulatory and respiratory responses. Horseradish peroxidase (HRP) was injected into 3 distinct regions of the NTS: the rostral regions from which electrical stimulation elicited pressor and apneustic responses: the intermediate regions from which stimulation elicited depressor and apneic responses; the commissure regions from which stimulation elicited depressor and hypopneic responses. HRP-labeled cells were sought throughout the medulla oblongata upward including the telencephalon. The results indicate that: many neurons of the frontal cortex (sigmoid gyrus, anterior ectosylvian gyrus, anterior sylvian gyrus, and anterior suprasylvian gyrus) project bilaterally to the 3 regions, predominantly to the rostral regions; a few neurons of the bed nucleus of the stria terminalis project almost ipsilaterally to the 3 regions; a few neurons of the nucleus amygdalae centralis project almost ipsilaterally to the 3 regions; many neurons of the paraventricular nucleus project bilaterally to the 3 regions, predominantly to the ipsilateral commissure regions; a moderate number of neurons of the fastigial nucleus project contralaterally to the rostral regions. These findings suggest that there are some specific projections to each region of the NTS from various supramedullary nuclei, which may be involved in modulation of the cardiovascular and respiratory systems.