Bulbospinal tryptaminergic neurones. A search for the role of bulbospinal tryptaminergic neurones in the control of sympathetic activity.

1. The possible role of bulbospinal tryptaminergic neurones in the control of sympathetic activity has been investigated in anaesthetised cats. 2. Depletion of spinal cord stores of 5-hydroxytryptamine was achieved by systemic administration of p-chlorophenylalanine or by intraspinal microinjections of 5,6-dihydroxytryptamine. 3. Blood pressure was little changed by these treatments, neither was the pattern of ongoing activity in sympathetic nerves (arterial pulse rhythmicity and respiratory modulation), the influence of pulmonary afferent nerves on this activity (determined by an airway occlusion technique), the sympatho-inhibitory influence of the carotid sinus baroreceptors, nor the sympatho-inhibitory or -excitatory influences of somatic afferent nerves. 4. Since both p-chlorophenylalanine and 5,6-dihydroxytryptamine treatment caused extensive disruption of the bulbospinal tryptaminergic neurones, it was concluded that these play no significant role in the mediation of the responses tested in anaesthetised cats in the present study.