Adrenergic pathways in glycine-mediated feeding behavior: Evidence from layer chickens

Glycinergic and adrenergic systems are integral to the regulation of meal consumption in avian species; however, the interactions between these systems have not been previously documented. This investigation was conducted to explore the interplay between the central glycinergic and adrenergic systems in regulating feed consumption among egg-type chickens. To this end, six separate experiments were performed. The first experiment involved intracerebroventricular (ICV) infusion of normal saline and glycine at different doses (50, 100, and 200 nmol) to determine its effective dose. In experiments 2-6, sub-effective doses of various adrenergic receptor antagonists—prazosin (an antagonist of α1 receptor), yohimbine (an antagonist of α2 receptor), metoprolol (an antagonist of β1 receptor), ICI 118.551 (an antagonist of β2 receptor), and SR 59230R (an antagonist of β3 receptor)—were co-administered with an effective dose of glycine to assess the potential involvement of adrenergic receptors in glycine-mediated feed intake. The cumulative feed consumption was subsequently measured at intervals of 30, 60, and 120 minutes post-administration. The findings indicated that glycine infusion at doses of 100 and 200 nmol significantly reduced meal consumption in layer chickens compared to the saline-treated control group (P < 0.05). Additionally, co-infusion of a β2 receptor antagonist attenuated the hypophagic effects typically induced by glycine (P < 0.05). However, co-administration of α1, α2, β1, and β3 receptor antagonists did not alter glycine-induced hypophagia (P ≥ 0.05). These findings suggest that the role of glycine in decreasing feed consumption in layer chickens could be facilitated by β2 adrenergic receptors.