Physiology, Endocrinology, and Reproduction

Fifty-five generations of chickens selected for low (LWS) and high (HWS) body weight at 8 weeks of age has resulted in a 10-fold differ­ ence in body weight at selection age. Some of the LWS are anorexic, while HWS are hyperphagic and obese. We hypothesized that differ­ ences in appetite regulatory factor mRNA between the lines would be accentuated by food withdrawal and measured mRNA abundance of appetite-associated factors in the hypothalamus of fed and fasted LWS and HWS. Five-day old male LWS and HWS chicks (n = 24) were randomly divided into 2 treatments; 1) continuous access to a starter diet or 2) 3 h feed withdrawal, after which hypothalamus and abdominal fat were collected (no fat was present in LWS). The mRNA abundance of agouti-related peptide (AGRP), neuropeptide Y (NPY), NPY recep­ tor 1 (NPYR1), melanocortin receptor 1 (MC4), glucose transporter 1 (GLUT1) and forkhead box protein O1 (FOXO1) was measured by real time PCR. Expression values were calculated by the ΔΔCT method with β-actin as the internal control. Data were analyzed by ANOVA using the Glimmix procedure (SAS 9.3), with effects of line, treatment and tissue as the repeated measurement, and Tukey’s test was used for pairwise comparisons. For AGRP, NPY and NPYR1, there was greater (P < 0.05) abundance in LWS than HWS, whereas for FOXO1 and MC4 there was greater (P < 0.05) expression in HWS. There was an interaction of line x treatment (P = 0.01) where NPY mRNA was greater in fed LWS chicks than fed HWS (P = 0.0005) and fasted LWS (P = 0.02) chicks. All of the mRNA were more abundant in hypothalamus than abdominal fat (P < 0.02) except FOXO1 which was almost 2 fold greater (P < 0.0001) in fat than in hypothalamus. In conclusion, there was greater expression of food intake-stimulation factors in LWS and greater abundance of satiety-inducing factors in HWS. These results suggest that differences in food intake between LWS and HWS are associated with differences in the appetite circuitry of the hypothalamus and that these differences are accentuated under certain feeding conditions.