Conduction velocity in spinal descending pathways of baro- and chemoreceptor reflex.

Activity in the white rami T3 and L2 or 3 has been recorded and averaged with respect to excitation of the carotid sinus baroreceptor afferents produced by the pulsatile blood pressure (baroreceptor reflex) and with respect to brief trains of electrical stimuli exciting low threshold chemoreceptor afferents in the left carotid sinus nerve (chemoreceptor reflex). Experiments were performed on chloralose anaesthetized cats with both vago-depressor nerves cut. From the latency difference between the onset of the responses at the thoracic and their arrival at the lumbar level the spinal conduction velocity for the pathway of each reflex has been calculated. The baroreceptor reflex pathway has slower spinal conduction velocity 3.3 +/- 0.7 m/sec than the chemoreceptor pathway 5.5 +/- 0.9 m/sec. These results indicate that there are separate descending spinal pathways for the two types of reflexes.