SOCIAL-ISOLATION ATTENUATES RAT FOREBRAIN 5-HT RELEASE INDUCED BY KCLSTIMULATION AND EXPOSURE TO A NOVEL ENVIRONMENT

The technique of microdialysis was employed to investigate in vivo 5-h ydroxytryptamine (5-HT) release in isolation-reared rats compared with socially reared rats. Two methods were employed to stimulate 5-HT rel ease: local KCI injection into the frontal cortex of chloral hydrate a naesthetized rats, and the exposure of freely moving rats to a novel e nvironment (the elevated x-maze). Microdialysis probes were implanted into the frontal cortex in the case of KCI stimulation and the ventral hippocampus in the case of exposure to the novel environment, and per fused with artificial CSF (1 mul/min). Dialysis samples were collected every 20 min and analysed for 5-HT and 5-hydroxyindole acetic acid (5 -HIAA) by HPLC with electrochemical detection. Both KCl injection (1 m ul, 100 mM) and a 20 min period on the elevated x-maze produced a sign ificant increase in extracellular 5-HT in the socially reared rats. Ne ither the increase in extracellular 5-HT induced by KCl nor the increa se on exposure to the elevated x-maze were observed in the isolation-r eared rats. Dialysate 5-HIAA was not affected in socially reared or is olation-reared rats, in either protocol. These results suggest that is olation-reared rats have a reduced presynaptic neuronal function to re lease 5-HT.