Abstract
Food anticipatory activity (FAA) refers to a daily rhythm of locomotor activity that emerges under conditions of food restriction, whereby animals develop an intense, predictable period of activity in the few hours leading up to a predictable, daily delivery of food. The neural mechanisms by which FAA is regulated are not yet fully understood. Although a number of brain regions appear to be involved in regulating the development and expression of FAA, there is little evidence to date concerning the role of the anterior agranular insular cortex (AICa). The AICa plays a critical role in integrating the perception of visceral states with motivational behaviour such as feeding. We assessed the effect of bilateral electrolytic or ibotenic acid lesions of the AICa on FAA in male Wistar rats receiving food for varying lengths of time (2 h, 3 h, or 5 h) during the middle of the light phase (starting at either ZT4 or ZT6). Contrary to our initial expectations, we found that both electrolytic and ibotenic acid lesions significantly increased, rather than decreased, the amount of FAA expressed in lesioned rats. Despite increased FAA, lesioned rats did not eat significantly more during restricted feeding (RF) periods than control rats. Similar to controls, AlCa-lesioned rats showed negligible anticipatory activity to a restricted treat suggesting that the increased anticipatory activity in lesioned rats is associated with food restriction, rather than the appetitive value of the meal. Monitoring behaviour in an open field indicated that increased FAA in AlCa-lesioned rats was not explained by a general increase in locomotor activity. Together, these findings suggest that the AICa contributes to the network of brain regions involved in FAA.
Highlights
Feeding schedules that restrict food availability to a fixed time of day induce and entrain food anticipatory rhythms, which are marked by a daily increase in arousal and locomotor activity in the 2-to-4 h period prior to the scheduled meal commonly referred to as food anticipatory activity (FAA)
We expected to find that bilateral lesions of the AICa of Wistar rats would significantly decrease FAA. We found that both electrolytic and ibotenic acid lesions produced a significant increase in FAA, especially before a 2 h meal
In experiment 2 (Fig 1B) we further investigated the effects of bilateral electrolytic lesions of the AICa on FAA in rats under a 2 h (RF1) or 5 h (RF2) schedule starting at ZT6
Summary
Feeding schedules that restrict food availability to a fixed time of day induce and entrain food anticipatory rhythms, which are marked by a daily increase in arousal and locomotor activity in the 2-to-4 h period prior to the scheduled meal (reviewed in [1]) commonly referred to as food anticipatory activity (FAA). Damage in select structures, notably the parabrachial nucleus, dorsomedial hypothalamic nucleus, infralimbic cortex, and cerebellum led to deficits in some measures of FAA, none of these areas alone was found to be necessary for the timing or expression of all food anticipatory circadian rhythms. This suggests that these rhythms are regulated by a distributed brain network of food-entrainable clocks, and not by a central clock structure
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