Tetrodotoxin elevates arterial pressure but not plasma vasopressin when injected into the caudal ventrolateral medulla of the rabbit.

When tetrodotoxin (TTS) is microinjected into the caudal ventrolateral medulla it elevates arterial pressure. This is consistent with previous microinjection experiments which show that the injected region contains neurons whose activity inhibits peripheral sympathetic vasomotor tone. However, TTX does not alter plasma vasopressin and this suggests that increases in plasma vasopressin which follow electrolytic lesions may result from excitatory effects of the lesions.