In:
eLife, eLife Sciences Publications, Ltd, Vol. 4 ( 2015-07-10)
Abstract:
Appetite is controlled in part by the opposing actions of the ‘hunger hormone’ (called ghrelin) and the ‘satiety hormone’ (called leptin). Ghrelin is released by the stomach when empty and stimulates appetite, whereas leptin is released by fat stores and induces feelings of fullness. Both hormones travel via the bloodstream and are detected by a region of the brain called the hypothalamus. Ghrelin and leptin act specifically on a group of cells in the hypothalamus that contains at least two major cell types: AgRP neurons and POMC neurons. Electrode recordings from slices of mouse brain show that AgRP neurons fire more rapidly at night—when mice normally feed—than during the day, whereas POMC neurons do the opposite. This suggests that the activity of AgRP neurons drives food-seeking behavior, whereas POMC firing inhibits it. However, the absence of circulating hormones such as leptin and ghrelin in brain slices makes it difficult to draw firm conclusions about the role of these cells in controlling appetite. Mandelblat-Cerf, Ramesh, Burgess et al. have addressed this issue by performing the first recordings of spiking activity in individual AgRP neurons and other cells that are likely to be POMC neurons in awake mice. Consistent with the results of slice experiments, the firing rate of AgRP neurons increased steadily over the course of the day, suggesting that their activity signals an increasing need for food. Furthermore, as soon as food became available, the firing rate of the AgRP neurons suddenly dropped—even though the animals' energy reserves would still have been low. These results are consistent with the findings of two recent studies reported earlier this year that used different methods to indirectly measure neuronal activity in awake mice. Notably, even after the drop in activity, the firing rates of AgRP neurons remained above those recorded in fully sated mice—which possibly reflects the fact that the animals' energy reserves were still low. The putative POMC neurons generally showed opposite effects to the AgRP neurons. The results of these electrode recordings in awake mice thus suggest that AgRP and POMC neurons together maintain a drive to seek out food sources as energy reserves fall, and to refrain from doing so when energy reserves are plentiful. Moreover, the seemingly paradoxical drop in AgRP firing and increase in POMC firing upon receiving food may act as a signal to temporarily stop searching for food, so that feeding itself can begin. Alternatively, since the release of satiety hormones after eating a meal is slow, these rapid changes in firing may provide more immediate feedback to the neuronal circuits that regulate the drives to seek and consume food.
Type of Medium:
Online Resource
ISSN:
2050-084X
DOI:
10.7554/eLife.07122.001
DOI:
10.7554/eLife.07122.002
DOI:
10.7554/eLife.07122.003
DOI:
10.7554/eLife.07122.004
DOI:
10.7554/eLife.07122.005
DOI:
10.7554/eLife.07122.006
DOI:
10.7554/eLife.07122.007
DOI:
10.7554/eLife.07122.008
DOI:
10.7554/eLife.07122.009
DOI:
10.7554/eLife.07122.010
DOI:
10.7554/eLife.07122.011
DOI:
10.7554/eLife.07122.012
DOI:
10.7554/eLife.07122.013
DOI:
10.7554/eLife.07122.014
DOI:
10.7554/eLife.07122.015
DOI:
10.7554/eLife.07122.016
Language:
English
Publisher:
eLife Sciences Publications, Ltd
Publication Date:
2015
detail.hit.zdb_id:
2687154-3
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