Metabolic modulation by amino acid stimulation of the paraventricular nucleus of the hypothalamus.
The role of the paraventricular nucleus of the hypothalamus (PVN) in the regulation of energy expenditure and energy substrate utilization was investigated after the injection of the excitatory amino acid D,L-homocysteic acid (DLH) or its vehicle. Male Wistar rats with chronic PVN cannulae were tested for 1 h with no food available in an open-circuit calorimeter. Whereas low (0.5 nmol), excitatory doses of DLH increased energy expenditure, the thermogenic effect became smaller and then vanished as the DLH dose was increased to inhibitory levels (7 and 50 nmol). None of these doses affected motor activity, indicating a primary thermogenic effect. The highest dose (100 nmol) increased energy expenditure, but this appeared to be secondary to increased locomotor activity. The increased locomotor activity produced by the highest dose of DLH constitutes the first demonstration of an activity effect induced by stimulating the PVN. However, this effect likely reflects the activation of neighboring areas. Only the 50 nmol dose of DLH increased respiratory quotient, indicating a shift toward the preferential utilization of carbohydrates as an energy substrate. These data complement our findings with neuropeptide Y and insulin in showing that different doses of the same substance injected into the PVN may produce qualitatively different effects. Furthermore, the present study demonstrates that exciting PVN neurons activates catabolic forces, whereas inhibiting them activates anabolic forces.
Atrens
D M
DM
Department of Psychology, University of Sydney, NSW, Australia.
Menéndez
J A
JA
D000596:Amino Acids / Q000494:pharmacology*; D000818:Animals; D001831:Body Temperature / Q000187:drug effects; D004734:Energy Metabolism / Q000187:drug effects; D006710:Homocysteine / Q000031:analogs & derivatives / Q000494:pharmacology; D007328:Insulin / Q000494:pharmacology; D008297:Male; D009043:Motor Activity / Q000187:drug effects; D009478:Neuropeptide Y / Q000494:pharmacology; D010101:Oxygen Consumption / Q000187:drug effects; D010286:Paraventricular Hypothalamic Nucleus / Q000033:anatomy & histology / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D015656:Respiratory Mechanics / Q000187:drug effects
D000596:Amino Acids; D007328:Insulin; D009478:Neuropeptide Y; D006710:Homocysteine; C007956:homocysteic acid