In vivo voltammetry in the B3 group of serotonin neurons of the rat medulla oblongata after drug-induced modifications of arterial pressure

Differential normal pulse voltammetry (DNPV) using an electrochemically treated carbon fiber electrode was applied to the investigation of the in vivo changes in extracellular 5-hydroxyindoleacetic acid (5HIAA) in the B3 group of serotonin neurons during experimental manipulations of arterial pressure. Drug-induced hypertension (phenylephrine infusion) caused, during the infusion, an increase in extracellular 5HIAA concentration which continued to rise, reaching +100% 2 hours after stopping the infusion. In contrast, drug-induced hypotension (sodium nitroprusside infusion) was not associated with any change in extracellular 5HIAA during the infusion while the return to the initial arterial pressure caused a progressive increase in the electrochemical signal, reaching +50% one hour after stopping the infusion. These data show that the extracellular 5HIAA concentration is increased when the arterial pressure increases, a result which suggests that B3 serotonin neurons could have a vasodepressor role in the central regulation of arterial pressure.