Modulatory function of NMDA glutamate receptor on MC3/MC4 receptors agonist-induced hypophagia in neonatal meat-type chicken.

Melanocortin 3 and 4 receptors (MC3R and MC4R) are known as the main receptors for melanocortin-induced hypophagia in mammalian and poultry. Also, central glutamatergic system has mediatory role on function of the melanocortin system in some brain areas. So, the aim of the current study was to determine the role of MC3/MC4 receptors agonist on food intake and its interaction with glutamatergic in 3-h food-deprived (FD3) neonatal broilers. In experiment 1, chickens were intracerebroventricular (ICV) injected with control solution, MTII (MC3/MC4 receptors agonist; 2.45, 4.8 and 9.8 pmol). In experiment 2, control solution, SHU9119 (MC3/MC4 receptors antagonist; 0.5, 1 and 2 nmol) were ICV injected. In experiment 3, birds ICV injected with control solution, SHU9119 (0.5 nmol), MTII (9.8 pmol) and co-injection of the SHU9119 + MTII. Experiments 4-8 were similar to experiment 3, except birds injected with MK-801 (NMDA glutamate receptors antagonist, 15 nmol), CNQX (AMPA glutamate receptors antagonist; 390 nmol), AIDA (mGLUR1 glutamate receptors antagonist; 2 nmol), LY341495 (mGLUR2 glutamate receptors antagonist; 150 nmol) and UBP1112 (mGLUR3 glutamate receptors antagonist; 2 nmol) instead of SHU9119. Then, cumulative food intake was recorded until 120 min after injection. According to the results, dose dependent hypophagia observed after ICV injection of the MTII (p < 0.05). ICV injection of SHU9119 significantly increased food intake in birds (p < 0.05). Co-injection of SHU9119 + MTII significantly inhibited MTII- induced hypophagia in neonatal chicks (p < 0.05). In addition, hypophagia- induced by MTII was significantly attenuated with co-injection of MTII + MK-801(p < 0.05). These results suggested MC3 and MC4 receptors have inhibitory role on food intake and this effect is probably mediated by NMDA glutamate receptors in neonatal chickens.