Effect of repeated electroconvulsive shocks on serotonergic neurons

Abstract

The hypothermia induced by the serotonin (5-HT) 1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) was attenuated in rats that had received a cource of six electroconvulsive shocks (ECS) over a two-week period. The firing activity of dorsal raphe 5-HT neurons, as well as their responsiveness to microintophoretic applications of 5-HT and 8-OH-DPAT, was unaltered in ECS-treated rats. The electrically evoked overflow of [ 3H]5-HT from preloaded slices of guinea pig hypothalamus was unchanged after the same ECS treatment. The concentration-effect curves of the 5-HT autoreceptor agonist 5-carboxyamindotryptamine (0.1–100 nM) were similar in slices prepared from control and ECS-treated guinea pigs. In addition, the reduction in the evoked [ 3H]5-HT overflow obtained by increasing the stimulation frequency from 1 to 5 Hz, which is due to a greater activation of terminal 5-HT autoreceptors at the higher frequency, was not altered by the ECS treatment. The enhancing effects of the 5-HT autoreceptor antagonist methiothepin (0.1–1 μM) and of the 5-HT 3 (0.1–1 μM) on the evoked [ 3H]5-HT overflow were unaltered by the ECS treatment. These results thus indicate that repeated ECS attenuates the 8-OH-DPAT- induced hypothermia in rats, as previously reported, but does not affect the firing activity of 5-HT neurons and the sensitivity of their somatodendritic 5-HT 1A autoreceptors in the dorsal raphe. The function of 5-HT terminals in the guinea pig hypothalamus was also unaffected by repeated ECS. In conclusion, repeated ECS does not affect the function of 5-HT neurons at the cell body and nerve terminal.