Voltammetric detection of the release of 5-hydroxyindole compounds throughout the sleep-waking cycle of the rat

Abstract

In the present work, differential pulse voltammetry (DPV) measurements of the extracellular fraction of 5-hydroxyindole compounds were performed in rats under long-term chronic conditions. In the nucleus Raphe Dorsalis (n.RD), the voltammetric signal measured at +300 mv (peak 3) disappeared completely 70 to 90 min after injection of Clorgyline (10 mg/kg), a monoamine oxidase inhibitor type A (MAOI-A); the signal measured in such conditions is thus dependent upon extracellular 5-hydroxyindoleacetic acid (5-HIAA peak 3). Deprenyl, an MAOI type B, at the same dose, induced only a slight increase in peak 3 height; according to the fact that MAO-B is selectively located in the 5-HT neurons and since their inhibition does not decrease 5-HIAA peak 3 nor the endogenous 5-HIAA content as measured with High Performance Liquid Chromatography (HPLC), 5-HIAA measured with DPV in the extracellular fluid of untreated animals might come from 5-HT released and metabolized by MAO-A outside the 5-HT neurons. In animals implanted for measurements of both voltammetric and polygraphic parameters, the 5-HIAA peak 3 measured mainly in the anterior and ventral part of the n.RD exhibited large increases in its height during slow-wave sleep (SWS: +39%) and paradoxical sleep (PS = +71%) as compared to the waking state (W = 100%); these variations could reflect the dendritic release of 5-HT. In the Caudate nucleus (n.Cd) the same voltammetric signal presented reverse fluctuations, i.e. an increase during W and a decrease during SWS and PS.(ABSTRACT TRUNCATED AT 250 WORDS)