Interaction of fastigial pressure response and depressor response to nasal perfusion

The fastigial nucleus pressor response (FPR) and the nasal-perfusion diving response were elicited alone and simultaneously to observe the net effect on cardiovascular variables. The fastigial nucleus was electrically stimulated in 14-chloralose-urethane anesthetized dogs and the FPR was characterized by a transient tachycardia with sustained elevations in arterial pressure, left ventricular pressure and maximal dP/dt. The tachycardia was buffered by baroreceptor reflexes during the elevated arterial pressure of the FPR. All variable of the FPR, however, were reduced by superimposition of the diving response upon the FPR. Heart rate was most sensitive to depression by the nasal perfusion which elicited a bradycardia as much as 70 beats/min below the control rate. The nasal-evoked diving response was discussed with respect to the trigeminal depressor response which results from direct stimulation of the spinal trigeminal complex. Algebraic cancellation of the FPR and dive responses is considered along with anatomical and electrophysiological evidence which suggests that these two responses, as well as the baroreceptor reflex, could be integrated at a common site. This site may be the medullary nucleus of the solitary tract which receives projections from trigeminal and glossopharyngeal nerves and from the fastigial nucleus.