Antagonistic properties of quipazine at presynaptic serotonin receptors and alpha-adrenoceptors in rat brain cortex slices.

Rat brain cortex slices preincubated with 3H-serotonin or 3H-noradrenaline were superfused with physiological salt solution, and the effect of quipazine on the 3H overflow evoked by electrical field stimulation was examined. 1. The electrically evoked tritium overflow from brain slices preloaded with 3H-serotonin was increased by quipazine in a concentration-dependent manner. The concentration-response curves of unlabelled serotonin and noradrenaline for their inhibitory effects on impulse-evoked 3H overflow were shifted to the right by quipazine. 2. In brain slices preincubated with tritiated noradrenaline, quipazine caused an increase in electrically stimulated 3H overflow which was less marked than the effect on brain slices preloaded with 3H-serotonin. The concentration-response curve of unlabelled noradrenaline for its decreasing effect on stimulation-evoked 3H overflow was shifted to the right by quipazine. We conclude that quipazine blocks presynaptic inhibitory serotonin receptors and alpha-adrenoceptors on monoaminergic neurones of the rat brain cortex.