Regulation of extracellular concentrations of 5-hydroxytryptamine (5- HT)in mouse striatum by 5-HT(1A) and 5-HT(1B) receptors

The ability of selective serotonin (5-HT) receptor agonists to reduce the extracellular concentration of 5-HT was examined in the striatum of awake, unrestrained mice by in vivo microdialysis. Systemic administration of either 8-OH-PIPAT {R-(+)-trans-8-hydroxy-2-[N-n-propyl-N-(3'-iodo-2'- propenyl)] aminotetralin}, a novel 5-HT(1A) receptor agonist, or CP 94,253, a selective 5-HT(1B) receptor agonist, resulted in significant dose-related reductions of striatal 5-HT. The effect of 8-OH-PIPAT (1.0 mg/kg) was blocked by pretreatment with WAY 100635 (0.1 mg/kg), a selective 5-HT(1A) receptor antagonist, but it was not blocked by pretreatment with GR 127935 (0.056 mg/kg), a selective 5-HT(1B/1D) receptor antagonist. The effect of CP 94,253 (1.0 mg/kg) was blocked by pretreatment with GR 127935 (0.056 mg/kg) but was not blocked by pretreatment with WAY 100635 (0.1 mg/kg). Neither WAY 100635 nor GR 127935 altered extracellular 5-HT levels at the doses that were able to completely block the effects of either 8-OH-PIPAT or CP 94,253. The present findings suggest that, on systemic administration, both 8-OH-PIPAT and CP 94,253 are potent and selective agonists at the somatodendritic 5- HT(1A) autoreceptor and terminal 5-HT(1B/1D) autoreceptor, respectively, and are each able to cause decreases in extracellular levels of 5-HT in the mouse striatum by activating a distinct set of receptors.