Oral glucose intake inhibits hypothalamic neuronal activity more effectively than glucose infusion

Abstract

Smeets PA, Vidarsdottir S, de Graaf C, Stafleu A, van Osch MJ, Viergever MA, Pijl H, van der Grond J. Oral glucose intake inhibits hypothalamic neuronal activity more effectively than glucose infusion. Am J Physiol Endocrinol Metab 293: E754-E758, 2007. First published June 12, 2007; doi:10.1152/ajpendo.00231.2007.-We previously showed that hypothalamic neuronal activity, as measured by the blood oxygen level-dependent (BOLD) functional MRI signal, declines in response to oral glucose intake. To further explore the mechanism driving changes in hypothalamic neuronal activity in response to an oral glucose load, we here compare hypothalamic BOLD signal changes subsequent to an oral vs. an intravenous (iv) glucose challenge in healthy humans. Seven healthy, normal-weight men received four interventions in random order after an overnight fast: 1) ingestion of glucose solution (75 g in 300 ml) or 2) water (300 ml), and 3) iv infusion of 40% glucose solution (0.5 g/kg body wt, maximum 35 g) or 4) infusion of saline (0.9% NaCl, equal volume). The BOLD signal was recorded as of 8 min prior to intervention (baseline) until 30 min after. Glucose infusion was associated with a modest and transient signal decline in the hypothalamus. In contrast, glucose ingestion was followed by a profound and persistent signal decrease despite the fact that plasma glucose levels were almost threefold lower than in response to iv administration. Accordingly, glucose ingestion tended to suppress hunger more than iv infusion (P Ͻ 0.1). We infer that neural and endocrine signals emanating from the gastrointestinal tract are critical for the hypothalamic response to nutrient ingestion. functional magnetic resonance imaging; glucose homeostasis; insulin; incretins THE BLOOD OXYGEN LEVEL-DEPENDENT (BOLD) signal, produced by functional magnetic resonance imaging (fMRI), is a noninvasive measure of neuronal activity (19, 30,35). We (36, 37) have recently shown that the BOLD signal in the upper part of the hypothalamus of healthy, normal-weight humans consistently declines in response to an oral glucose load, which strongly suggests that glucose ingestion blunts hypothalamic neuronal activity in these subjects. The hypothalamus plays a critical role in the control of energy balance. Neural circuits in hypothalamic nuclei perceive and integrate endocrine and metabolic cues reflecting bodily energy content to coordinate behavior and fuel flux so as to maintain energy homeostasis (28, 34). Thus, adaptations of hypothalamic neuronal activity driven by nutrient ingestion may serve to guard energy equilibrium in the face of an environmental challenge.The mechanism linking glucose intake and changes in hypothalamic neuronal activity in humans is currently unknown. Various metabolic and endocrine cues are worthwhile to consider. Circulating levels of glucose can be sensed by specialized neurons in the arcuate and ventromedial nuclei of the hypothalamus, and these neurons project to other key nuclei (21). Alternatively, insulin inhibits NPY neuronal activit...

Small Decrements in Systemic Glucose Provoke Increases in Hypothalamic Blood Flow Prior to the Release of Counterregulatory Hormones

“…Moreover, the hypothalamus plays a central role in the regulation of appetite and energy expenditureresponses known to be stimulated by hypoglycemia. Our data are consistent with this hypothesis and with prior studies using fMRI-BOLD demonstrating that the hypothalamus is responsive to changes in systemic glucose levels (13)(14)(15)(16)(17). On the other hand, previous studies investigating the effects of hypoglycemia on regional CBF in nondiabetic subjects have not identified an increase in hypothalamic blood flow following insulin-induced hypoglycemia (22,24,25).…”

“…Although most prior studies have relied on animal models to study the neurophysiological response to changes in glucose, newer imaging techniques such as functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) provide an in vivo method to study the effect of changes in peripheral glucose levels on human brain activity. Several fMRI studies in humans have demonstrated that a rise in systemic glucose after glucose ingestion leads to an inhibition of hypothalamic activity (13)(14)(15)(16). In addition, Musen et al (17) recently used fMRI based on the blood oxygenation leveldependent (BOLD) contrast mechanism and found that insulin-induced hypoglycemia leads to hypothalamic activation.…”

Functional MRI of the hypothalamic response to an oral glucose load

“…In contrast, previous studies by Smeets and colleagues [4][5][6] have shown a prolonged decrease in signal in the hypothalamus after oral glucose, continuing for at least 30 min after ingestion. Our data tend to support the results of Smeets and colleagues and contradict the results of Liu and colleagues, in that they show a prolonged rather than shortlived signal decrease after ingestion of glucose.…”

“…Previous experiments using a glucose load have suggested that it is possible in humans to identify changes in the BOLD signal from areas within the hypothalamus [2][3][4][5][6]; however, the results have been contradictory.…”

Altered hypothalamic response to food in smokers

“…Human fMRI studies have shown that brain activity in the hypothalamus is attenuated by feeding (49,50) and the administration of sibutramine, which is a drug used to reduce weight in obese individuals (51). The response to food pictures in the hypothalamus is also positively associated with immediate food intake in a nonsated state (52).…”