The influence of injection of 5,6-dihydroxytryptamine to the dorsal raphe nucleus on carbachol-induced defensive behavior and regional brain amine content in the cat.

The 5,6-dihydroxytryptamine-induced lesions of serotonergic neurons in the dorsal raphe nucleus of the cat resulted in an increase in the carbachol-induced growling response, a decrease in the concentrations of noradrenaline, serotonin and 5-hydroxyindoleacetic acid in the hypothalamus, midbrain and amygdala, and an increase in the hypothalamic dopamine level. Those changes were observed 6, but not 23, days after the lesion. The results suggest a close correlation between the state of the emotional-defensive arousal and neurochemical changes in the "emotional regions" of the brain. The role of the reduced activity of the serotonergic system in augmenting the emotional-defensive behavior was discussed.