tokens: In spontaneously hypertensive , stroke - prone rats , microinjection of methyldopa into the area of the midline B3 serotonin cell group in the ventral medulla caused a potent hypotension of 30 - 40 mm Hg , which was maximal 2 - 3 h after administration and was abolished by the serotonin neurotoxin 5,7-dihydroxytryptamine ( 5,7-DHT ) injected intracerebroventricularly .