Anorexigenic effects of mesotocin in chicks are genetic background-dependent and are associated with changes in the paraventricular nucleus and lateral hypothalamus.

Mesotocin (MT) decreases food intake and induces hyperthermia in chicks although hypothalamic mechanisms are unknown. The purpose of this study was thus to investigate effects of receptor antagonists and MT on feeding behavior and hypothalamic physiology. Intracerebroventricular injection of 2.5 nmol into broiler chicks was associated with decreased food intake for 180 min and water intake from 60 to 180 min. Cloacal temperatures were elevated in chicks injected with 0.156 and 0.625 nmol at 30 and 60 min, and up to 180 min in those injected with 2.5 nmol. MT also increased temperatures and decreased food and water intake in chicks from lines selected for low (LWS) or high (HWS) body weight with a higher dose threshold but longer food intake response in HWS chicks. An oxytocin receptor antagonist prevented MT-mediated changes in food intake but not water intake or temperature. Yohimbine, an α2-adrenergic receptor antagonist, did not affect food intake, temperature, or MT-mediated effects. MT increased c-Fos immunoreactivity in the paraventricular nucleus (PVN) and lateral hypothalamus (LH). Hypothalamic agouti-related peptide, corticotropin-releasing factor receptor sub-type 1, and melanocortin receptor 3 mRNAs increased in response to MT. There was increased MT mRNA in the LH and L-aromatic amino acid decarboxylase mRNA in the PVN of MT-injected chicks. In conclusion, MT induced anorexia and hyperthermia and reduced water intake. MT was associated with activation of the PVN and LH and differences in the mRNA abundance of some appetite-associated factors, thus implicating these nuclei and several signaling pathways in the effects observed.