The brain stem and the very late reflex response of vasoconstrictor neurons to impulses of somatic A-afferents

Abstract

Single stimulation of A-fibers of the tibial nerve evoked not only a late response — a discharge of the latent period 60–140 msec — in the renal nerve of unanesthetized decrebrate cats, but also a very late response (VLR), with a latent period of about 0.35 sec. This response was easily elicited in nearly all experiments on “mesencephalic” animals, but after division of the brain stem at different levels of the pons, including the region of the pontobulbar junction and the most rostral portions of the medulla, it was discovered in only 1 of 18 animals. After division of the brain stem rather more caudally (in “bulbar” animals) VLR was found in 10 of 11 animals. In the region of the pontobulbar junction there are thus structures which tonically inhibit the activity of the system generating the VLR. It is shown that the activity of this system is potentiated by two types of summation processes: Some taking place during long (seconds) and others taking place during short (milliseconds) time intervals.