Electrically evoked 5-hydroxytryptamine efflux in rat hypothalamus studied using in vivo amperometry

Changes in 5-hydroxytryptamine (5-HT) efflux have been studied for the first time using differential pulse amperometry (DPA). In vitro observations show that the oxidation potential of 5-HT at 37°C is 160 mV. The amperometric signal corresponding to 5-HT was measured in the lateral hypothalamus after brief electrical stimulation of the dorsal raphe nucleus (10 s, 25 or 50 Hz, 300 μA) every 5 or 10 min. Pargyline (100 mg/kg ip) and d-norfenfluramine (5 mg/kg ip) increased the signal to 194 and 243%, respectively. Tetrodotoxin (1 μl, 100 mM), injected in the proximity of the working electrode, caused the signal to disappear. 8-OH-DPAT (250 μg/kg sc) reduced it to 64% for about 1 h and this effect was completely prevented by the 5HT(1A) antagonist WAY 100635 (1 mg/kg sc). L-Tryptophan (100 mg/kg ip) increased the amperometric signal to 136%. No change was detected when the 5-HT precursor was given to rats pretreated with PCPA (150 mg/kg per day p.o. for 3 days). In conclusion, DPA represents a sensitive-and selective approach for studying 5-hydroxytryptaminergic function, offering a good temporal and anatomical specificity.