Fat pad-specific effects of lipectomy on foraging, food hoarding, and food intake

Abstract

Unlike most species, after food deprivation, Siberian hamsters increase foraging and food hoarding, two appetitive ingestive behaviors, but not food intake, a consummatory ingestive behavior. We previously demonstrated (Wood AD, Bartness TJ, Am J Physiol Regul Integr Comp Physiol 272: R783-R792, 1997) that increases in food hoarding are triggered by directly decreasing body fat levels through partial surgical lipectomy; however, we did not test if lipectomy affected foraging, nor if the magnitude of the lipid deficit affected food hoard size. Therefore, we tested whether varying the size of the lipectomy-induced lipid deficit and/or foraging effort affected foraging, food hoarding, or food intake. This was accomplished by housing adult male Siberian hamsters in a foraging/hoarding system and removing (x) both epididymal white adipose tissue (EWATx) pads, both inguinal white adipose tissue (IWATx) pads, or both EWAT and IWAT pads (EWATx + IWATx) and measuring foraging, food hoarding, and food intake for 12 wk. The lipectomy-induced lipid deficit triggered different patterns of white adipose tissue mass compensation that varied with foraging effort. Foraging for food (10 wheel revolutions to earn a food pellet) abolished the EWATx-induced compensation in IWAT pad mass. The magnitude of the lipid deficit did not engender a proportional change in any of the appetitive or consummatory ingestive behaviors. EWATx caused the greatest increase in food hoarding compared with IWATx or EWATx + IWATx, when animals were required to forage for their food. Collectively, it appears that the magnitude of a lipid deficit does not affect appetitive or consummatory behaviors; rather, when energy (foraging) demands are increased, loss of specific (gonadal) fat pads can preferentially stimulate increases in food hoarding.

Physiological mechanisms for food-hoarding motivation in animals

“…Therefore, an alternative view, as noted above, is the notion that energy flux may be a key controlling factor affecting food hoarding. This view supports most of the existing data on food hoarding, not only the increased food-hoarding-associated decreases in body fat (pregnancy and lactation (Bartness 1997); food restriction (Mauer & Bartness 1994;Wood & Bartness 1996b;Day et al 1999) and lipectomy (Wood & Bartness 1997;Dailey & Bartness 2008a)), but also the increases in food hoarding not associated with reductions in total body fat such as seen with small increases in foraging effort (Day & Bartness 2001), the nearly immediate effects of changes in the caloric density of the diet, either dilution or enhancement (Wood & Bartness 1996a), and the acute peripheral or central administration of appetite-stimulating peptides as discussed below. Therefore, it may be that there are common underlying processes for the metabolic control of food hoarding that are shared with those controlling food intake (Friedman & Stricker 1976) and fertility (Wade & Schneider 1992) as we have postulated previously (Day & Bartness 2001).…”

“…We predicted that the greater the surgically induced lipid deficit, the greater the magnitude of the hoarding response; however, this was not found. Specifically, EWATx caused the greatest increase in food hoarding even though IWATx produced approximately twice and EWATx þ IWATx three times the lipid deficit of EWATx in Siberian hamsters required to forage for their food (Dailey & Bartness 2008b). Food intake was not affected by lipectomy in this experiment (Dailey & Bartness 2008b) or in all lipectomy experiments across a wide range of animal species (for a review, see Mauer et al 2001).…”

“…Specifically, EWATx caused the greatest increase in food hoarding even though IWATx produced approximately twice and EWATx þ IWATx three times the lipid deficit of EWATx in Siberian hamsters required to forage for their food (Dailey & Bartness 2008b). Food intake was not affected by lipectomy in this experiment (Dailey & Bartness 2008b) or in all lipectomy experiments across a wide range of animal species (for a review, see Mauer et al 2001). Collectively, it appears that the magnitude of a lipid deficit does not affect appetitive or consummatory behaviours; rather the loss of specific fat pads (EWAT) can preferentially stimulate increases in food hoarding.…”

“…B (2010) In a study examining the effects of foraging effort on food hoarding as well as on body fat levels (Day & Bartness 2001), we noticed that the epididymal white adipose tissue (EWAT) pad that surrounds the testes was decreased across all the foraging efforts even though total body fat only decreased at the highest foraging effort (Day & Bartness 2001). Therefore, we methodically and explicitly manipulated lipid levels by excising varying amounts of WAT by removing both EWAT pads (EWAT lipectomy; EWATx), both inguinal WAT pads (IWATx; each IWAT pad is approximately twice the size of an EWAT pad) or both EWAT and IWAT pads (EWATx þ IWATx; Dailey & Bartness 2008b). We predicted that the greater the surgically induced lipid deficit, the greater the magnitude of the hoarding response; however, this was not found.…”

“…Outside of these lipectomy studies on food hoarding by Siberian hamsters (Wood & Bartness 1997;Dailey & Bartness 2008a), there are several studies in support of a potential relation between body mass/fat and food hoarding. Food deprivation and restriction studies of normal laboratory rats, as well as dietary obese ('supermarket diet'-fed; Winn & Herberg 1985) and genetically obese (Zucker fa/fa) rats (Herberg & Winn 1982), demonstrate increases in food hoarding/carrying with increases in food deprivation/restriction.…”