Arcuate nucleus homeostatic systems reflect blood leptin concentration but not feeding behaviour during scheduled feeding on a high-fat diet in mice

Abstract

Hypothalamic homeostatic and forebrain reward-related genes were examined in the context of scheduled meal feeding without caloric restriction in C57BL/6 mice. Mice fed ad libitum but allowed access to a palatable high-fat (HF) diet for 2 hours a day rapidly adapted their feeding behaviour and consumed approximately 80% of their daily caloric intake during this 2-hour scheduled feed. Gene expression levels were examined during either the first or second hour of scheduled feeding vs 24 hours ad libitum feeding on the same HF diet. Gene expression of neuropeptide Y, agouti-related peptide, cocaine- and amphetamine-regulated transcript, pro-opiomelanocortin, long-form leptin receptor and suppressor of cytokine signalling-3 in the hypothalamic arcuate nucleus (ARC), as well as enkephalin, dynorphin, dopamine-2-receptor and dopamine-3-receptor in the nucleus accumbens (NAcc) in the forebrain, were measured by in situ hybridisation. Mice fed ad libitum on a HF diet had the highest total caloric intake, body weight gain, fat mass and serum leptin, whereas schedule-fed mice had a mild obese phenotype with intermediate total caloric intake, body weight gain, fat mass and serum leptin. The effects of feeding regime on ARC gene expression were emphasised by significant positive or negative correlations with body weight gain, fat mass and blood leptin, although they did not appear to be related to feeding behaviour in the schedule-fed groups (ie, the large, binge-type meals) and did not reveal any potential candidates for the regulation of these meals. Mechanisms underlying large meal/binge-type eating may be regulated by nonhomeostatic hedonic processes. However, assessment of opioid and dopamine receptor gene expression in the NAcc did not reveal evidence of involvement of these genes in regulating large meals. This complements our previous characterisation of ARC and NAcc genes in schedule-fed mice and rats, although it still leaves open the fundamental question about the underlying mechanisms of meal feeding.

Keywords: binge-type eating; energy balance gene expression; mice; palatable diet; scheduled feeding.

Figure 1

Caloric intake of C57BL/6 mice fed on a high‐fat diet with ad libitum or scheduled access. (A) Caloric intake during scheduled feeding time for all groups. (B) Total daily caloric intake during days 8 to 17 of the dietary manipulation showing calories consumed from standard diet and a high‐fat diet. Percentages above bars refer to calories consumed from high‐fat diet during scheduled feeding time relative to total 24‐hour intake. Pale grey bars, calories derived from control diet (CON); black bars, calories derived from a high‐fat (HF) diet. Different letters indicate P<.05 by one‐way ANOVA and Student‐Newman‐Keul post‐hoc test for total caloric intake. (C) Caloric intake during the scheduled feeding period on the day of sacrifice. Pale grey bars, intake during first hour of scheduled feeding; black bars, cumulative intake during the first and second hours of scheduled feeding. Data are presented as the mean±SEM

Figure 2

Body composition parameters of C57BL/6 mice fed on a high‐fat diet with ad libitum or scheduled access: (A) body weight gain (g), (B) body fat mass (g) and (C) body lean mass (g). Different letters indicate P<.05 by one‐way ANOVA and Student‐Newman‐Keul post‐hoc test. Data are presented as the mean±SEM. CON, standard pellet diet; HF, high‐fat

Figure 3

Quantification of mRNA gene expression in the arcuate nucleus of C57BL/6 mice fed on a high‐fat diet with ad libitum or scheduled access. (A) Serum leptin levels. (B‐G) Quantification of autoradiograph signals of (B) neuropeptide Y (NPY), (C) agouti‐related peptide (AgRP), (D) cocaine‐ and amphetamine‐regulated transcript (CART), (E) pro‐opiomelanocortin (POMC), (F) long‐form leptin receptor (OB‐Rb) and (G) suppressor of cytokine signalling‐3 (SOCS3), showing representative images used for quantification. Expression was normalised to the control group for each probe. Different letters indicate P<.05 by one‐way ANOVA and Student‐Newman‐Keul post‐hoc test. Data are presented as the mean±SEM. CON, standard pellet diet; HF, high‐fat

Figure 4

Quantification of mRNA gene expression in the nucleus accumbens of C57BL/6 mice fed on a high‐fat diet with ad libitum or scheduled access. (A‐D) Quantification of autoradiograph signals of endogenous opioids (A) dynorphin (DYN) and (B) enkephalin (ENK), and dopamine receptors (C) dopamine‐2‐receptor (D2‐R) and (D) dopamine‐3‐receptor (D3)‐R, showing representative images used for quantification. Expression was normalised to the control group for each probe. Data are presented as the mean±SEM. CON, standard pellet diet; HF, high‐fat