Chapter 10
Non-Homeostatic Intake of Snack Foods: Molecular Triggers and Effects on Brain Activity Pattern Tobias Hoch,*,1 Andreas Hess,2 and Monika Pischetsrieder1 1Department of Chemistry and Pharmacy, Food Chemistry Division, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Schuhstr. 19, 91052 Erlangen, Germany 2Institute of Experimental and Clinical Pharmacology and Toxicology, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Fahrstr. 17, 91054 Erlangen, Germany *E-mail:
[email protected].
Craving for special types of food like snack food can tremendously influence our energy balance. The result: obesity due to a non-homeostatic, hedonic food intake, i.e. an intake of energy independent of hunger and satiety. The intake of potato chips – an often craved highly palatable snack food – has a great influence on whole brain activity pattern. Especially the reward system as well as circuits regulating food intake, sleep and locomotor activity are affected. Furthermore, we could show that the fat and carbohydrate content is a main contributor to the palatability of potato chips. These first steps of the identification of the molecular triggers and the corresponding effects on brain activity pattern of the non-homeostatic intake of highly palatable snack food are reviewed in this chapter.
Introduction Hedonic food intake, eating for pleasure without a physiological need, can overrule the homeostatic energy balance and therefore, in the long run, lead to hyperphagia, i.e. an energy intake beyond satiety (1). Besides chocolate © 2015 American Chemical Society
and sweets, savory snacks like potato chips are very attractive to many people and largely contribute to energy intake (2, 3). Hedonic hyperphagia can be influenced by the emotional state, mental health conditions or sleep deprivation (4). Furthermore, molecular food composition and energy density are decisive factors for the induction of hedonic hyperphagia (5, 6). Many physiological systems are involved in the regulation of food intake, like distinct brain systems, hormones, dopamine, melanocortins, opioids or endocannabinoids (7–12). In our work, we investigated the influence of the intake of potato chips on whole brain activity pattern of ad libitum fed rats. Furthermore, we analyzed the main contributors to the palatability of potato chips by using a two choice preference test with rats.
Influence of Snack Food on Feeding Related Behavior and Whole Brain Activity Pattern of Rats We could show that the intake of the snack food potato chips has a decisive influence on feeding related behavior and whole brain activity pattern of ad libitum fed rats (13). To investigate the links between food intake and behavior or brain activity we developed a protocol using manganese-enhanced magnetic resonance imaging (MEMRI) (14, 15). As displayed in Figure 1, we conducted our study on a 4-week based schedule with male Wistar rats (Charles River, Sulzfeld, Germany, n=16 per group) which had access to standard chow pellets and tap water ad libitum over the whole course of the study. The schedule started with a one week habituation phase (HP) in which the animals were familiarized with the study conditions. In the following one week training phase (TP), the rats got in contact with the respective test food potato chips or powdered standard chow presented additionally to the standard feed. The test food was provided throughout the whole TP 24 hours a day for 7 days. In the following intermediate phase (IP, one week), the test food was removed to simulate withdrawal. For the upcoming manganese phase (MnP), rats were implanted with osmotic pumps, filled with the contrast agent manganese chloride. Activation of cells/neurons is accompanied by an influx of Ca2+, particularly at the synapse. Manganese is transported using Ca2+ transport systems like voltage gated Ca2+ channels. Therefore, also Mn2+ is transported into the neuropil of activated neurons. In contrast to Ca2+, Mn2+ accumulates in the cells with only a slow release over weeks and acts as MRI contrast agent due to its paramagnetic character. Therefore, the integral activity of distinct brain areas can be measured by MEMRI (15). Application of manganese chloride has a toxicological drawback. Single injections of the required dose led to a suppressed food intake and activity in general. Eschenko et al. (2010) (16) suggested the use of implanted osmotic pumps, which release the contrast agent continuously at a rate of 1 µL/h over 7 days. This application method had no toxic or behavioral side effects and enabled an integral measurement of structure specific whole brain activity pattern during the intake of potato chips over 7 days. 120
Figure 1. Study design for the investigation of the influence of snack food intake on whole brain activity pattern by manganese-enhanced magnetic resonance imaging (MEMRI). Crushed potato chips and powdered standard chow were used as test food. Reproduced with permission from reference (13).
During the study, we evaluated behavioral data of 16 rats in 4 cages per group. Test food intake was measured on a daily basis and locomotor activity was recorded continuously over the 7 days of TP and MnP in one-hour-bins.
Figure 2. Test food (A) and energy (B) intake of the animals of the snack food group (SF, snack food crushed potato chips) and the standard chow group (STD, powdered standard chow). Both parameters are shown separately during the 12 hours light and 12 hours dark cycle as well as during training phase (TP) and manganese phase (MnP). The mean ± standard deviation of 16 animals in each group as an average over 7 days of the respective period is shown. *** p
