Hypothalamic differences in expression of genes involved in monoamine synthesis and signaling pathways after insulin injection in chickens from lines selected for high and low body weight.

Long-term selection for juvenile body weight from a common founder population resulted in two divergent chicken lines (low-weight selected line (LWS), high-weight selected line (HWS)) that display distinct food intake and blood glucose responses to exogenous neuropeptides and insulin. The objective of this study was to elucidate putative targets affecting food intake and energy homeostasis by sequencing hypothalamic RNA from LWS and HWS chickens after insulin injection. Ninety-day-old female LWS and HWS chickens were injected with either vehicle or insulin and hypothalamus collected at 1 h postinjection. Through RNA sequencing, a total of 361 differentially expressed genes (DEGs) were identified. There was greater expression of genes, mainly tyrosine hydroxylase (TH), L-aromatic amino acid decarboxylase (DDC), and vesicular monoamine transporter (VMAT), involved in serotonin and dopamine biosynthesis and signaling in LWS than in HWS vehicle-injected chickens. In contrast, after insulin injection, these genes were more highly expressed in HWS than in LWS. We identified 90 single nucleotide polymorphisms (SNPs) existing only in the HWS and 121 SNPs specific to LWS and 5119 SNPs close to fixation (with absolute frequency difference ≥0.9). Four were located in genes encoding enzymes associated with serotonergic and dopaminergic pathways, such as DDC, TH, and solute carrier family 18, member 2 (VMAT). These data implicate differences in biogenic amines such as serotonin and dopamine in hypothalamic physiology between the chicken lines, and these differences might be associated with polymorphisms during long-term selection. Changes in serotonergic and dopaminergic signaling pathways in response to insulin injection suggest a role in whole-body energy homeostasis.

Quantity of glucose transporter and appetite-associated factor mRNA in various tissues after insulin injection in chickens selected for low or high body weight.

Chickens from lines selected for low (LWS) or high (HWS) body weight differ by 10-fold in body weight at 56 days old with differences in food intake, glucose regulation, and body composition. To evaluate if there are differences in appetite-regulatory factor and glucose transporter (GLUT) mRNA that are accentuated by hypoglycemia, blood glucose was measured, and hypothalamus, liver, pectoralis major, and abdominal fat collected at 90 days of age from female HWS and LWS chickens, and reciprocal crosses, HL and LH, at 60 min after intraperitoneal injection of insulin. Neuropeptide Y (NPY) and receptor (NPYR) subtypes 1 and 5 mRNA were greater in LWS compared with HWS hypothalamus (P < 0.05), but greater in HWS than LWS in fat (P < 0.05). Expression of NPYR2 was greater in LWS than HWS in pectoralis major (P < 0.05). There was greater expression in HWS than LWS for GLUT1 in hypothalamus and liver (P < 0.05), GLUT2 in fat and liver (P < 0.05), and GLUT9 in liver (P < 0.05). Insulin was associated with reduced blood glucose in all populations (P < 0.05) and reduced mRNA of insulin receptor (IR) and GLUT 2 and 3 in liver (P < 0.05). There was heterosis for mRNA, most notably NPYR1 (-78%) and NPYR5 (-81%) in fat and GLUT2 (-70%) in liver. Results suggest that NPY and GLUTs are associated with differences in energy homeostasis in LWS and HWS. Reduced GLUT and IR mRNA after insulin injection suggest a compensatory mechanism to prevent further hypoglycemia.