Effect of parachlorophenylalanine, a brain serotonin depletor, on the prolactin cells of the eel pituitary.

Parachlorophenylalanine (pCPA), an inhibitor of tryptophan hydroxylase depleting brain serotonin in higher vertebrates, was injected into freshwater eels. After 4 or 8 injections (200 mg/kg/day) or 10 injections (100 and 140 mg/kg/day) plasma electrolyte values were not modified. Prolactin (PRL) cells appear less active, with increased granulation after 6 and 10 injections. Their cell height (P less than 0.01) and their nuclear area (P less than 0.001) are reduced. As injections of 5-hydroxytryptophan stimulate PRL cells, these findings suggest that a serotoninergic system may participate in the regulation of PRL cell activity. Brain serotonin depletion probably decreases granule release in PRL cells, a result comparable to the lowering action of pCPA on the plasma PRL level in some mammals.