AFFERENT NERVE GROUPS AND SYMPATHETIC REFLEX PATHWAYS

In chloralose-anesthetized cats, two reflex sympathetic discharges were recorded from lumbar white rami after single shock stimulation of peripheral afferent nerves: an early discharge associated with a spinal reflex pathway, and a late discharge associated with a supraspinal pathway. The following relationship between afferent fibers and reflex pathways were noted: 1. (1) Excitation of only Group I hindlimb muscle fibers did not evoke reflex sympathetic discharges. 2. (2) Excitation of hindlimb Group II plus fibers, or of Group Aα or Aβ hind- or forelimb cutaneous, or visceral fibers evoked only the supraspinal reflex. Beyond its threshold the late response increased with stimulus strength. 3. (3) Stimulus strengths greater than threshold for Group III hindlimb muscle, or Group Aδ hind- or forelimb cutaneous, or visceral fibers evoked the spinal sympathetic reflex. The discharge increased with stimulus strength. 4. (4) Supraspinal sympathetic reflexes were present in all fore- and hindlimb studies. Spinal reflexes were consistently found in hindlimb nerve studies but in only one out of four forelimb nerve studies. 5. (5) Stimuli strong enough to excite C fibers often caused increases in the late reflex sympathetic discharge. Such increases might be due to a C-fiber activated spinal pathway reflex. 6. (6) Strychnine or tetanic stimulation of the peripheral nerves led to increased amplitudes of both early and late sympathetic responses to succeeding single shocks. 7. (7) Stimulation of Aα or Aβ cutaneous afferent evoked an early sympathetic reflex in chronic spinal cats. Excitation of smaller fibers increased the amplitude of this reflex but did not evoke a late reflex. © 1969.