In vivo microdialysis in conscious rats was used to examine the effect of clozapine on serotonin (5-hydroxy tryptamine, 5-HT) efflux in the prefrontal cortex and dorsal raphe nucleus and dopamine efflux in the prefrontal cortex. Both systemic and local administration of clozapine (systemic,10 or 20 mg/kg, i.p.; local, 100 μM) increased 5-HT efflux in the dorsal raphe. However, in the prefrontal cortex, dialysate 5-HT increased when clozapine (100 μM) was administered through the probe, while no effect was observed when it was administered systemically. By pretreatment with the selective 5-HT1A receptor antagonist p-MPPI (3 mg/kg, i.p.), systemic treatment of clozapine (10 mg/kg, i.p.) significantly increased 5-HT efflux in the prefrontal cortex. This result suggests that the ability of clozapine to enhance the extracellular concentrations of 5-HT in the dorsal raphe attenuates this drug's effect in the frontal cortex, probably through the stimulation of 5-HT1A somatodendritic autoreceptors in the dorsal raphe. We also found that pretreatment with p-MPPI (3 mg/kg, i.p.) attenuated by 45% the rise in cortical dopamine levels induced by clozapine (10 mg/kg, i.p.). These findings imply that the reduction in serotonergic input from the dorsal raphe nucleus induced by clozapine could lead to an increase in dopamine release in the prefrontal cortex. Key words: 5-HT1A receptor, clozapine, microdialysis, 5-HT, dopamine.
The role of lateral habenula–dorsal raphe nucleus circuits in higher brain functions and psychiatric illness
