Correlation of changes in brain indoleamine metabolism with onset of anorexia in rats.

The association of elevated brain serotonergic activity with cancer anorexia was investigated in three experiments. Significant increases in whole brain tryptophan, serotonin and 5-hydroxyindoleacetic acid in anorectic rats bearing methylcholanthrene sarcomas demonstrated the general nature of this phenomenon. In the Walker 256 sarcoma model, significant increases in whole brain serotonin and 5-hydroxyindoleacetic acid immediately preceded the onset of anorexia, suggesting that these changes in serotonin activity were not caused by decreased food intake. Investigations of regional brain changes in serotonin activity of rats bearing Walker 256 tumors revealed widespread increases in tryptophan, while serotonin was increased in the diencephalon and cerebellum and 5-hydroxyindoleacetic acid was increased in the cortex, hippocampus, diencephalon, pons-medulla and cerebellum. Therefore, these experiments demonstrate that increased brain serotonin activity is a general phenomenon, being observed in two lines of anorexia-producing tumors, that it precedes the onset of anorexia and that selective increases in serotonin activity occur within different regions of the brain.