In order to analyse the reflex mechanisms of sympathetic nervous activities, reflex potentials were recorded from the lumbar sympathetic trunk of 56 chloralose anesthetized cats with single pulse stimulation of the contralateral sciatic nerve.
1. Two kinds of reflex potentials were identified: the late reflex potential (LRP) with low threshold and long latency (80-120 msec), and the less marked early one (ERP) with higher threshold and shorter latency (25-50 sec).
2. The LRP disappeared whereas the ERP was still observed following spinal transection at the Cl or Th8 level.
3. Following brain stem transection made starting at the upper midbrain level downwards to the lowest level of the pons, the LRP as well as ERP showed no significant reduction of amplitude. However with transections of the medulla oblongata from its highest level to downwards, the LRP decreased gradually in amplitude until it disappeared completely at the lowest level of the medulla oblongata, although the ERP was still observed.
4. Following administration of Nembutal of graded doses, the LRP diminished rapidly and disappeared before the ERP did.
5. No clear cut result about the time of disappearance of the two reflex potentials was obtained in the case of asphyxiation owing to markedly increased random sympathetic discharges following asphyxiation.
6. On the basis of these experimental results, it was suggested that the reflex center of the LRP is located in the medulla oblongata and that of the ERP is in the spinal cord.