[Brain stem and very late reflex response of the vasoconstrictor neurons to impulses of somatic A-afferents].

In decerebrated unanesthetized cats single stimuli to the tibial nerve A-afferents apart from the late response, a discharge with a latency of 60--140 ms, elicited another discharge, a "very late" response (VLR) with a latency of about 0.35 s. This response was easily detectable, in almost all experiments in "mesencephalic" animals, but in different pontine sections including the ponto-bulbar junction and most rostral parts of the medulla oblongata, it was seen only in one out of 18 animals. At slightly more caudal sections of the brain stem (in "bolfar" animals) VLR was seen in 10 out of 11 animals. Thus, in the region of the ponto-bulbar junction there exist structures that tonically suppress the activity of the VLR generating system. It was shown that the activity of this system is augmented by summation processes of two types, developing in long (seconds) and short (milliseconds) time periods.