Serotonin (5HT) expression in rat pups treated with high-tryptophan diet during fetal and early postnatal development

Serotonin (5HT) is a neurotransmitter synthesized in serotonergic neurons of the central nervous system and in the enterochromaffin cells of the gastrointestinal tract. 5HT regulates growth and maturation ofsome cerebral regions in the developing brain as well as the secretion of pituitary growth hormone. Thishormone is necessary for development and growth through the stimulation of insulin-like growth factorsynthesis. The precursor of 5HT, tryptophan (Trp), is an essential amino acid, since the human organismis unable to synthesize it and it is assumed only through diet. The aim of our study was to analyze howa high-tryptophan diet in pregnant rats affects growth and survival of pups until weaning. We moni-tored the number and weight of pups until weaning. Then, we detected serotonin and growth hormonelevels in whole blood by ELISA of surviving pups at the end of the lactation period. We also analyzedby means of immunohistochemistry and Western blot the expression of serotonin in rat gastric tissueand the morphological structure of skeletal muscle tissue of both control and experimental pups. Hyper-serotonemia and very low levels of growth hormone were detected in experimental pups compared tocontrols. Immunohistochemistry demonstrated a strong serotonin expression in stomach samples con-firming that a high intake of tryptophan increases the production of serotonin in enterochromaffin cells,thereby resulting in hyperserotonemia in pups. These data were also strengthened by Western blot anal-ysis. Histological alterations of skeletal muscle fibers in experimental pups were found and showed thatin experimental samples the muscle tissue demonstrated deleterious alterations, being less developedand defined. Our data suggest that a high-tryptophan diet in pregnant rats induces hyperserotonemiain the fetus. Hyperserotonemia results in an excess of serotonin in the brain where it has a negativeinfluence on development of serotonergic neurons and consequently on growth hormone production.