DIURNAL CHANGES IN SEROTONIN CONTENT OF FRONTAL POLE AND PAIN SENSITIVITY IN RAT

This study examined the relationship between diurnal variations in pain sensitivity, and serotonin content of frontal pole, hippocampus and amygdala in the rat. Rats demonstrated significantly longer paw-lick latencies in response to a painful thermal stimulus during light hours as compared with dark hours. Similarly, all three brain regions demonstrated a significantly higher serotonin content during light as compared with dark hours. There was a significant correlation (0.66) between paw-lick latencies and serotonin content of frontal pole but not with serotonin content of hippocampus or amygdala. The occurrence, in a normal animal, of a heightened sensitivity to a painful stimulus during dark hours when serotonin content of brain is also lowest is consistent with studies demonstrating that lowering of serotonin content by means of lesions, drugs or tryptophan deficient diets also produces an increased sensitivity to painful stimuli. © 1978.