Acta Med. 1998, 41: 3-11
Ventromedial Nucleus of Hypothalamus is Related to the Development of Cancer-Induced Anorexia: In Vivo Microdialysis Study
Based on reports that increased hypothalamic ventromedial nucleus (VMN) - serotonin (5-HT) is associated with cancer anorexia and recent findings in our laboratory that low levels of dopamine (DA) in the VMN are associated with prolonged inter meal intervals thus decreased food intake, and reports that setting up satiation is concomitant with descending levels of DA in the rostromedial hypothalamus, we hypothesized that an elevated 5-HT to low DA ratio in the VMN modulates food intake in cancer anorexia. Methods: In Expt 1: A microdialysis cannula guide was placed stereotactically into the VMN of methylcholanthrene (MCA) sarcoma tumor-bearing (TB) Fischer rats and in non-tumor-bearing (NTB) and pair-fed (PF) controls. When TB rats manifested anorexia by a decrease in food intake, VMN-5-HT, its metabolite 5-hydroxyindolacetic acid (5-HIAA), and DA with its metabolite 3,4,-dihydroxyphenylacetic acid (DOPAC) were measured by in vivo microdialysis using HPLC during baseline, in response to food, and after feeding. In Expt 2: TB rats had tumor removed and VMN microdialysis performed 7 days later. Results: Increased 5-HT release and turnover, and significantly reduced DA release with increased DOPAC occured in TB vs NTB or PF rats. When food was offered, intake in TB rats was significantly lower than in NTB control rats. During eating, VMN-5-HT rose and peaked significantly earlier in TB vs NTB rats, while DA release was significantly reduced. With eating, the 5-HT and DA metabolism became reduced in all rats. Seven days after surgical removal of the tumor, 24h food intake had increased to the level of controls; and when food was offered during microdialysis, intake in TB rats increased (ns relative to control), but was not yet normal. VMN microdialysis showed that 5-HT was normal at baseline, as well as during and after eating, while DA remained depressed. The metabolic turnover of 5-HT and DA was significantly lower in TB-r and PF vs NTB rats. We conclude that increased 5-HT/DA ratio is related to the development of cancer-induced anorexia.
Keywords
Food intake, Ventromedial nucleus of hypothalamus (VMN), Neurotransmitters, Serotonin (5-HT), Dopamine (DA), 5-hydroxyindolacetic acid (5-HIAA), 3,4-dihydroxyphenylacetic acid (DOPAC), Cancer anorexia.
Funding
Work was supported in part by grant DK43796 from the National Institutes of Diabetes and Digestive and Kidney Diseases, NIH; by grant 85A95 from the American Institute for Cancer Research; and by grant IGA MZ ČR 4095-3.
References
Copyright
Published by the Karolinum Press. For permission to use please write to actamedica@lfhk.cuni.cz.
