[Identification and study of sympathoactivating neurons of the medulla oblongata]

The neurons with descending axons which activate the lateral horn sympathetic preganglionic (vasomotor) neurons were searched in the lower brain stem of the cat. Localization of these sympathoactivatory neurons in the limit zone of medulla was outlined by means of scanning stimulation. The identification of single bulbar sympathoactivatory neurons was based on the recording of their antidromic discharges elicited by stimulation of descending sympathoactivatory pathways with conduction velocity about 4--8.9 m/s in the dorsolateral funiculi of the cervical spinal cord. The neurons studied have a very low frequency spontaneous discharges (0.1--1.0 imp/s) unrelated with cardiac and respiratory cycles. The alterations of spontaneous discharge frequency were in strict correlation with pressor phases of Maer waves and pressor reflex reactions. The inhibitory effects of the baroreceptor nerve stimulation on spontaneous and elicited discharges of these neurons were never seen. A possible role of the sympathoactivatory neurons identified as an output elements of the bulbar "vasomotor" centre is discussed.