Alterations of brain serotonin during experimental tumor growth in mice

Concentrations of serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) were studied in discrete areas of brain and in large intestine of Swiss mice following transplantation of Sarcoma 180 (S 180) ascites tumor. Significant increase in 5-HT levels (2 to 3.5-fold over controls, P < 0.05) was observed in raphe region of the brain throughout the period of tumor growth. Concomitant increase, although of lesser magnitude, was recorded in raphe 5-HIAA content. 5-HT content of hypothalamus, mid brain and caudate putamen, on the other hand, remained relatively unaltered except for an increase at the advanced stage of the disease. While mid brain and hypothalamic 5-HIAA were elevated at the late stage, 5-HIAA values of caudate putamen were normal or slightly reduced during the progression of tumor. Both 5-HT and 5-HIAA levels of the large intestine showed an early decline followed by a modest increase at the late stages. Brain and plasma tryptophan levels were also elevated significantly (P < 0.05) in the tumor hosts. The results suggest a close relationship between increase in serotonin concentrations in the brain, particularly in raphe region, and the progression of S-180 tumor in mice.