Plasma leptin and hypothalamic neuropeptide Y and galanin levels in Long-Evans rats with marked dietary preferences.

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Abstract
Neuropeptides present in the hypothalamus and new messengers in the periphery such as leptin modulate food intake in mammals. Neuropeptide Y (NPY) and galanin in microdissected brain areas and plasma leptin levels were measured by specific radioimmunoassays during the resting period in rats selected for their strong preference either for carbohydrate or fat, but with identical energy intake. NPY concentrations were 23% lower (p <.02) in carbohydrate-preferring (CP) than in fat-preferring (FP) rats in the parvocellular part of the paraventricular nucleus (PVN), which is one of the main areas involved in the regulation of feeding behavior. On the other hand, galanin was significantly (+25%, p =.03) higher in CP rats than in FP rats in the magnocellular part of the PVN. Plasma leptin was more than 50% higher in FP rats than in CP rats (p <.01) and highly correlated with the fat preference (r=0.57; p =.003) and body weight gain. We conclude that the rats with a spontaneous and marked dietary preference have a characteristic peptidergic profile. Due to their anatomical relationships, neuropeptide Y could act in conjunction with galanin in a peptidergic balance located in the paraventricular nucleus. This model integrates information provided by the energy stores and translated by peripheral messengers such as leptin which could act in a counterregulatory manner in order to limit the overweight induced by the ingestion of unbalanced diets.