Bulbo-spinal neurons activated by baroreceptor afferents and their possible role in inhibition of preganglionic sympathetic neurons.

In paralyzed cats under chloralose-urethane anaesthesia the medulla oblongata was searched with dye-filled microelectrodes for neurons responding to electrical stimulation of the carotid sinus nerve (CSN) and distension of the isolated carotid sinus (CS). 89 cells localized in the solitary tract nucleus and in the reticular formation ventrally and ventrolaterally to the nucleus exhibited mainly an excitatory input from the CSN. 16 could be also antidromically excited from the cervical spinal cord at C4 level. 11 of these were shown to be excited by a pressure rise in the CS. The latencies of the antidromically driven units ranged from 1.2-2.8 msec and the calculated conduction velocity of the descending fibres was 29 plus or minus 5.2 m/sec. The possibility of involvement of these bulbo-spinal neurons in the inhibition of the preganglionic sympathetic neurons at the spinal cord level is discussed.