Extracellular 5-hydroxytryptamine inhibits 5-hydroxytryptamine release from rat brain cortex slices

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Abstract
Rat brain cortex slices preincubated with 3H-5-hydroxytryptamine were superfused with physiological salt solution and stimulated electrically, or they were superfused with Ca2+-free solution containing 25 mM K+ and stimulated by introduction of 1.3 mM CaCl2 for 2 min. After blockade of neuronal 5-hydroxytryptamine (5-HT) uptake with clomipramine or paroxetine, the 3H overflow evoked by both methods of stimulation was decreased by unlabelled 5-HT and increased by methiothepin. The inhibition caused by 5-HT was antagonized by simultaneous administration of methiothepin. The inhibition by 5-HT of Ca2+-induced overflow was also observed in the presence of tetrodotoxin. These results suggest than 5-HT regulates its own release from central serotoninergic neurones by activating presynaptic 5-HT autoreceptors, thus decreasing the availability of Ca2+ for stimulus-release coupling.