Somato-sympathetic reflex discharges evoked through supramedullary pathways

Summary

• 1. Sympathetic mass discharges were recorded from lumbar white rami (LWR) in chloralose anaesthetized cats.

• 2. Stimulation of myelinated somatic afferent fibres produced 3 different types of reflex discharges; the previously reported early (spinal) and the late (medullary) reflexes, plus a very late reflex discharge.

• 3. The very late reflex discharge of about 300–350 ms latency was only observed 8–10 h after the initial dose of chloralose (50 mg/kg, i.p.). It disappeared completely after an additional injection of chloralose (5–10 mg/kg, i.v.), although the other two reflexes, the early and late ones, remained throughout.

• 4. After surgical transection of the brain stem at the supra- or mid-pontine level, or after anaemic decerebration, the very late one disappeared completely, although the other two reflexes, the early and late ones, remained.

• 5. The late reflex was followed by the strong depression of discharge activity, but there was no clear relationship between intensity of the depression and appearance of the very late reflex discharge.

• 6. It was concluded that the very late reflex discharge has a suprapontine reflex pathway.