Modulation by drugs of the release of total tritium and 3H-5-HT from rat hypothalamic slices.

The release of total tritium and 3H-5-hydroxytryptamine (5-HT) evoked by electrical stimulation from prelabelled rat hypothalamic slices was studied. Lysergic acid diethylamide (LSD) decreased white methiothepin increased both total tritium and 3H-5-HT overflow. The proportion of total tritium present as 3H-5-HT was equivalent under control conditions and in the presence of methiothepin and slightly increased in the presence of LSD. Whereas the addition of the 5-HT uptake blocker, citalopram, did not modify the evoked release of total tritium, the monoamine oxidase inhibitor, pargyline, decreased it. In the presence of either of these drugs the proportion of 3H-5-HT was increased. In the presence of citalopram, the inhibition by LSD was reduced on both the release of total tritium and of 3H-5-HT. It thus appears that changes in electrically evoked total tritium overflow in general reflect changes in 3H-5-HT release. When uptake inhibitors or monoamine oxidase inhibitors are present in the medium, the situation is, however, more complex and results from experiments measuring only the release of total tritium should be interpreted with caution.