Central muscarinic receptor subtypes (M1 and M3) involved in carbacol-induced hypophagia in neonatal broiler chicken.

Aim: Food intake regulated by a complex of physiologic mechanisms in the nervous system. Muscarinergic system has an important role in the central regulation of appetite in mammals, but there is no information for Muscarinic receptors in avian. The purpose of this study was to examine the effects of intracerebroventricular injection of carbachol (cholinergic agonist), Telenzepine (M ₁ receptor antagonist), AF-DX116 (M ₂ receptor antagonist), 4-DAMP (M ₃ receptor antagonist), and PD102807 (M ₄ receptor antagonist) on feeding behavior in 3-h food-deprived (FD ₃ ) neonatal broiler chicken. Materials and Methods: In experiment 1, chicken intracerebroventricular injected with carbachol (125, 250, and 500 nmol). In experiment 2, birds intracerebroventricular injected with telenzepine (125, 250, and 500 nmol). In experiments 3-5, birds intracerebroventricular injected with AF-DX 116 (125, 250, and 500 nmol), 4-DAMP (125, 250, and 500 nmol), and PD102807 (125, 250, and 500 nmol), respectively. In experiment 6, broilers intracerebroventricular injected with carbacol (500 nmol), co-injection of telenzepine (125 nmol)+carbacol (500 nmol), and 4-DAMP (125 nmol)+carbacol (500 nmol). In experiment 7, injection procedure was carbacol (500 nmol), co-injection of AF-DX116 (125 nmol)+carbacol (500 nmol), and PD102807 (125 nmol)+carbacol (500 nmol). Then, food intake measured until 120 min after injection. Results: According to the data, carbachol (250 and 500 nmol) significantly decreased food intake in comparison with control group ( P  < 0.05). Intracerebroventricular injection of telenzepine (250 and 500 nmol) and 4-DAMP (250 and 500 nmol) significantly increased food intake ( P  < 0.05). In addition, carbacol-induced hypophagia was significantly attenuated by co-injection of telenzepine + carbacol ( P  < 0.05). Also, co-injection of 4-DAMP + carbacol decreased the effect of carbacol on food intake ( P  < 0.05). However, AF-DX116 and PD102807 had no effect on hypophagia induced by carbacol ( P  > 0.05). Conclusion: These results suggest, hypophagic effect of muscarinergic system is mediated via M ₁ and M ₃ receptors in neonatal chicken.