Interaction of diet and drugs in the regulation of brain 5-hydroxyindoles and the response to painful electric shock

Abstract

The long-term consumption of a tryptophan-poor, corn diet by rats decreases electroshock response thresholds. This hyperalgesia appears to be related directly to diet-induced reductions in the brain concentrations of the putative neurotransmitter, serotinin. Rehabilitating corn-fed animals by feeding them the corn diets supplemented with tryptophan restores brain serotonin and pain thresholds to normal; similarly, injecting the tryptophan-deficient, corn-fed animals with fluoxetine, a drug that blocks the uptake of serotonin into brain neurons, also restores the electroshock response thresholds to control levels. The tryptophan hydroxylase inhibitor, p -chlorophenylalanine, increases the hyperalgesia to electroshock in corn-fed rats and further reduces brain serotonin concentrations. Injection of the amino acid valine, on the other hand, produces hyperalgesia and decreases brain serotonin in casein-fed rats but not in animals fed the corn diet. These data lend support to the hypothesis that serotonin neurons may mediate the sensitivity or reactivity to painful stimuli.