Homeostatic responses to palatable food consumption in satiated rats

Abstract

ObjectiveEnergy intake is regulated by overlapping homeostatic and hedonic systems. Consumption of palatable foods has been implicated in weight gain, but this assumes that homeostatic control systems do not accurately detect this hedonically driven energy intake. This study tested this assumption, hypothesizing that satiated rats would reduce their voluntary food intake and maintain a stable body weight after consuming a palatable food.MethodsLean rats or rats previously exposed to an obesogenic diet were schedule‐fed with fixed or varying amounts of palatable sweetened condensed milk (SCM) daily, and their voluntary energy intake and body weight were monitored.ResultsDuring scheduled feeding of SCM, rats voluntarily reduced bland food consumption and maintained a stable body weight. This behavior was also seen in rats with access to an obesogenic diet and was independent of the predictability of SCM access. However, lean rats offered large amounts of SCM showed an increase in total energy intake. To test whether a nutrient deficiency drove this under‐compensatory behavior, SCM was enriched with protein. However, no effect was seen on voluntary energy intake.ConclusionsIn schedule‐fed rats, compensatory reductions in voluntary energy intake were seen, but under‐compensation was observed if large amounts of SCM were consumed.

Neural connectivity between the hypothalamic supramammillary nucleus and appetite‐ and motivation‐related regions of the rat brain

“…In line with our previous observations, there was no divergence in body weight ( P = 0.63, Mann‐Whitney test) or total daily energy intake ( P = 0.11, Mann‐Whitney test) between the SCM group and controls during the SCM scheduled‐feeding period (see Supporting information, Figure S1). In the SuMM, Fos expression was significantly higher in the SCM group compared to controls (control, 34 ± 5 nuclei per section; SCM, 146 ± 15 nuclei per section; P = 0.0007) (Figure A‐E).…”

“…The mechanism underlying these observations is not known, although rats compensate for SCM consumption by reducing their intake of standard diet, suggesting that the difference seen here are not a consequence of a change in body weight or an increase in total daily energy intake. The hypothalamic neurohormone oxytocin has an emerging role in appetite control, and may be involved specifically in an anorexigenic response to carbohydrate intake .…”

“…To confirm the existence of a reciprocal connection between the SuMMandtheDMH,weusedavirallabellingapproachbyinjecting aCre-dependentvirusintotheSuMMorDMHofTH-Crerats.We performedserialinjections(n=12inSuMM,n=12inDMH)withde-creasingvolumeofAAV(1µLto100nL).Weselectedinjectionsthat showed the optimal combination of spatial specificity of the injec- Interestingly, we observed an increase in Fos expression in the SuMM after rats were given access to SCM for the first time Themechanismunderlyingtheseobservationsisnotknown,al-thoughratscompensateforSCMconsumptionbyreducingtheirintakeofstandarddiet, 16 suggesting that the difference seen here are not a consequence of a change in body weight or an increase in total dailyenergyintake.Thehypothalamicneurohormoneoxytocinhas anemergingroleinappetitecontrol,andmaybeinvolvedspecifically inananorexigenicresponsetocarbohydrateintake. 22 Oxytocinmay have a neuromodulatory role in the SuM, 23,24 and we have previously shown that gavage of a high-sugar food increases the electrical activity of oxytocin neurones in the rat supraoptic nucleus, 9…”

A spontaneous binge-like eating model in mice using unpredictable once weekly access to palatable diets

“…For example, in our earlier studies with scheduled daily access, male rats and mice consumed 63% and 86% of their average daily intake from HF diet, and 49% and 45% from Ensure during 2h (Bake et al, 2013). Such substantial caloric intakes markedly reduced energy intake from stock diet during the remainder of the 24h period, although this compensation was incomplete and total caloric intake was generally still elevated in the schedule-fed groups ( Substantial compensation was also observed when male mice were allowed weekly 24h access to a HF diet (Czyzyk et al, 2010), and when male and female rats were given scheduled daily access to sweetened condensed milk (SCM) (Hume, Jachs & Menzies, 2016), although compensation was less efficient when larger amounts of SCM were offered to, and consumed by, male rats (Hume et al, 2016). This ability to compensate at lower SCM intake levels was not affected by irregular presentation times within the daily light/dark cycle (Hume et al, 2016).…”

Nudge, nudge, eat, drink…

“…For most people, their weight generally remains remarkably stable over very long periods of time 3 . A very simple study in rats shows one component of this homeostatic regulation: if rats are given occasional sweet ‘treats’ they do not gain weight 5 – they compensate almost exactly for the additional calorie intake in the sweet food by reducing their intake of bland food (Figure 1). How do they do this?…”