GABA mimetics decrease extracellular concentrations of 5-HIAA (as measured by in vivo voltammetry) in the dorsal raphe of the rat.

The effect of gamma-aminobutyric acid (GABA) mimetics on extracellular concentrations of 5-hydroxyindoleacetic acid (5-HIAA) (as measured by differential pulse voltammetry with carbon fiber electrodes) in the dorsal raphé has been investigated in the rat. Systemic administration of dipropylacetamide decreased extracellular 5-HIAA to a similar extent, and within a comparable time course, in the dorsal raphé and striatum. Similar results were obtained after intradorsal raphé infusion of muscimol (100 ng). In contrast, local infusion of tetrodotoxin into the dorsal raphé failed to alter serotonin metabolism in this area. It is concluded that GABA depresses serotonin metabolism not only in nerve endings, but also in dendrites (and/or cell bodies) of serotonergic neurons.