Circulatory depression following low frequency stimulation of the sciatic nerve in anesthetized rats

Earlier experiments have shown that afferent electrical stimulation of the sciatic nerve for 30 min induces a long-lasting post-stimulatory endorphin-dependent decrease in blood pressure in awake spontaneously hypertensive rats (SHR). In the present study we have examined whether this depressor response can be observed also in anesthetized SHR. The sciatic nerve was stimulated for 30 min with low-frequent (3 Hz) trains of impulses and the changes in blood pressure, heart rate and renal nerve activity were observed during the stimulation and in the post-stimulatory period. Animals anesthetized with Nembutal, Althesin and N2O did not show any post-stimulatory depression. In contrast, during chloralose anesthesia combined with muscle paralysis with Flaxedil, sciatic nerve stimulation induced a long-lasting post-stimulatory decrease in blood pressure due to central inhibition of sympathetic activity. The decrease in blood pressure could be prevented by naloxone and was therefore likely to be mediated via activation of central endorphin systems.