Sex differences in basal hypothalamic anorectic and orexigenic gene expression and the effect of quantitative and qualitative food restriction

Abstract

BackgroundResearch into energy balance and growth has infrequently considered genetic sex, yet there is sexual dimorphism for growth across the animal kingdom. We test the hypothesis that in the chicken, there is a sex difference in arcuate nucleus neuropeptide gene expression, since previous research indicates hypothalamic AGRP expression is correlated with growth potential and that males grow faster than females. Because growth has been heavily selected in some chicken lines, food restriction is necessary to improve reproductive performance and welfare, but this increases hunger. Dietary dilution has been proposed to ameliorate this undesirable effect. We aimed to distinguish the effects of gut fullness from nutritional feedback on hypothalamic gene expression and its interaction with sex.MethodsTwelve-week-old male and female fast-growing chickens were either released from restriction and fed ad libitum or a restricted diet plus 15% w/w ispaghula husk, a non-nutritive bulking agent, for 2 days. A control group remained on quantitative restriction. Hypothalamic arcuate nucleus neuropeptides were measured using real-time PCR. To confirm observed sex differences, the experiment was repeated using only ad libitum and restricted fed fast-growing chickens and in a genetically distinct breed of ad libitum fed male and female chickens. Linear mixed models (Genstat 18) were used for statistical analysis with transformation where appropriate.ResultsThere were pronounced sex differences: expression of the orexigenic genes AGRP (P < 0.001) and NPY (P < 0.002) was higher in males of the fast-growing strain. In genetically distinct chickens, males had higher AGRP mRNA (P = 0.002) expression than females, suggesting sex difference was not restricted to a fast-growing strain. AGRP (P < 0.001) expression was significantly decreased in ad libitum fed birds but was high and indistinguishable between birds on a quantitative versus qualitative restricted diet. Inversely, gene expression of the anorectic genes POMC and CART was significantly higher in ad libitum fed birds but no consistent sex differences were observed.ConclusionExpression of orexigenic peptides in the avian hypothalamus are significantly different between sexes. This could be useful starting point of investigating further if AGRP is an indicator of growth potential. Results also demonstrate that gut fill alone does not reduce orexigenic gene expression.Electronic supplementary materialThe online version of this article (10.1186/s13293-018-0178-6) contains supplementary material, which is available to authorized users.

Risk factors for poor health and performance in European broiler production systems

“…Male broiler birds are approximately 20% heavier than female broilers of the same age when fed ad libitum [54,55]. Male broilers have an higher expression of agouti-related protein in the hypothalamus, which is suggested to be good indicator for the growth potential of a bird due to its modulating role in the central melanocortin system [56]. Farms that had recurrent problems of dysbacteriosis were found to have lower EPI.…”

Regulation of Agouti-Related Protein and Pro-Opiomelanocortin Gene Expression in the Avian Arcuate Nucleus

“…We have further evidence for this at the genetic level. When we compared AGRP gene expression between males and females in 12-week-old broiler breeder chickens that had been re-fed for 2 days after food restriction, expression was significantly higher in males and this difference was replicated in ad libitum -fed fully mature chickens of another genetic strain ( 64 ). The higher AGRP expression in males is consistent with the fact that they grow faster and attain a higher mature body mass.…”

“…This could potentially mitigate some of the undesirable effects of constant hunger by providing more total food and therefore more opportunity for the expression of natural foraging and ingestive behaviors. However, it is uncertain whether birds fed on such diets still experience a “metabolic hunger.” To address this, we provided restricted-fed 12-week-old broiler breeder birds with ad libitum access to food for 2 days compared to birds re-fed a diet over the same time period that was diluted with the non-nutritive bulking agent ispaghula husk, and to birds that remained on a restricted diet ( 64 ). We measured significantly increased AGRP expression and decreased POMC expression compared to fully fed controls in both food-restricted birds and in those receiving the dietary bulking agent.…”

Concurrent changes in photoperiod-induced seasonal phenotypes and hypothalamic CART peptide-containing systems in night-migratory redheaded buntings

“…For example, in ad libitum fed broiler chickens, hypothalamic CART mRNA levels were higher in males than the females (Caughey et al 2018 ). Similarly, both acute and chronic fasting enhanced AgRP/NPY, but not POMC/CART, mRNA levels in the mediobasal hypothalamus of Japanese quails and chicks (Boswell et al 2002 ; Higgins et al 2010 ; Phillips-Singh et al 2003 ; Song et al 2012 ; Higgins et al 2010 ; Caughey et al 2018 ). Hence, our data showing the co-expression of CART and α-MSH peptides in the IN and IH neurons of redheaded buntings is a novel observation.…”