Tetrahydronorharmane modulates the depolarisation-induced efflux of 5-hydroxytryptamine and dopamine and is released by high potassium concentration from rat brain slices.

Tetrahydronorharmane (THN), a compound which occurs in man and in rats is supposed to act as a modulator of 5-hydroxytryptaminergic neurones. It is reported here that THN stimulated the potassium-induced release of the neurotransmitter from brain slices. This suggests enhancement of the efflux as a mechanism for the 5-hydroxytryptamine-like action of THN in pharmacological experiments. Furthermore, THN decreased the potassium-evoked efflux of (3H)-dopamine. This is consistent with the inhibition of dopaminergic neurones by THN as seen previously in various in vivo experiments. Finally it is demonstrated that a high concentration of potassium evokes the efflux of (14C)-THN from brain slices. This finding suggests that THN is taken up into neurones and exerts its modulating action on serotonergic neurones either inside or outside the cell.