Alterations in monoamines and GABA in the ventromedial and paraventricular nuclei of the hypothalamus following cold exposure: a reduction in noradrenaline induces hyperphagia.

A microdialysis technique for the in vivo assessment of the monoaminergic and GABAergic levels in the ventromedial (VMN) and paraventricular nuclei (PVN) of the hypothalamus was used in order to examine the activities of neurons that project to the hypothalamic regions and are implicated in the regulation of ingestive behavior and energy balance. Cold exposure increased food intake, as well as the circulating levels of glucose, noradrenaline (NA), 3,5,3'-triiodothyronine, and corticosterone. The dialysate concentrations of NA, dopamine (DA), serotonin (5-HT), and gamma-aminobutyric acid (GABA) in the VMN all decreased after exposure to cold. The changes in extracellular NA, DA, and GABA in the PVN under cold conditions were similar to those in the VMN. NA release in the VMN or PVN was decreased after local electrolytic lesions, which significantly increased food intake. Thus, low activities of noradrenergic axons of neurons terminating in the VMN and PVN may be a good mechanism to induce feeding behavior. Extracellular 5-HT in the PVN was significantly increased, along with a significant decrease in 5-hydroxyindoleacetic acid, in cold-exposed rats, suggesting that serotonergic fibers terminating in the PVM are more closely related to the increases in adrenocortical and thyroid hormone secretion than to food intake. The neuronal activities, indicating that a sympathetic tone is activated on stimulation of the VMN and/or PVN, may be changes in GABAergic and/or serotonergic neurons.