Altered sensitivity to footshock after selective serotonin depletion: comparison of electrolytic lesions and neurotoxin injections in the medial forebrain bundle of the rat.

This study compared the changes in an animal's jump threshold with changes in monoamine content of telencephalon after damage to the lateral hypothalamus produced either by electrolytic lesions or by infusions of 6-hydroxydopamine (6-HDA) and 5,7-dihydroxytryptamine (5,7-DHT). Electrolytic lesions produced significant decreases in jump threshold and in telencephalic content of serotonin, norepinephrine, and dopamine. Infusions of 5,7-DHT, with or without pretreatment with desmethylimipramine, always reduced both jump thresholds and serotonin content even when there was no effect on the content of norepinephrine or dopamine. In contrast, 6-HDA had no effect on jump thresholds or serotonin content, even though both norepinephrine and dopamine were greatly reduced. Nonspecific neural damage produced by infusion of neurotoxins was quite small and did not differ in locus or size from that produced by infusion of vehicle. These results suggest that the increased sensitivity to footshock was solely due to the interruption of ascending serotonergic pathways within the lateral hypothalamus and was not a result of damage either to norepinephrine and dopamine pathways or to some other neural system.