Separate areas of rat medulla oblongata with populations of serotonin- and adrenaline-containing neurons alter blood pressure after l-glutamate stimulation

Separate populations of serotonin- and adrenaline-containing neurons exist in the ventrolateral medulla oblongata and project to the intermediolateral cell column of the spinal cord. The medullary serotonin nuclei appear to constitute a heterogeneous group with diverse effects on arterial pressure. Microinjections of sodium glutamate (which excites cell bodies but not axons of passage) made in the area of the ventrolateral serotonin cells evokes an increase in arterial pressure which is abolished by prior 5,7-dihydroxytryptamine (5,7-DHT) treatment. In contrast, glutamate microinjection in the area of the serotonin-containing cell bodies in the midline of the medulla evokes falls in arterial pressure and these responses are attenuated by pretreatment with 5,7-DHT. Glutamate microinjection made in the ventrolateral medulla in the area of the adrenaline-containing cells, evokes increases in arterial pressure which are not altered by 5,7-DHT pretreatment. After ablation of the area of the adrenaline-containing cells by electrolytic lesion, the pressor function of the ventrolateral serotonin-containing cells is still observed. These results suggest that although the serotonin-containing neurons of the ventrolateral medulla are closely aligned with the ventrolateral adrenaline area, the serotonin cell groups and the cells of the adrenaline area exert their pressor actions independently.