Food Intake Regulation in Birds: the Role of Neurotransmitters and Hormones

BACKGROUND: Neurotransmitters (NTS) are endogenous chemicals secreted from neural terminals into the synaptic cleft of the chemical neurons in order to affect their receptors. NTS play vital physiological role as stimulatory, inhibitory or modulatory compounds. OBJECTIVES: This review was aimed to summarize the roles of the most important NTS which regulate food intake in the avian species. RESULTS: Over 40 neurotransmitters are known as regulatory agents that control ingestion behavior in mammals and birds. Acetylcholine (Ach), epinephrine (EP), norepinephrine (NEP), histamine, gamma amino butyric acid (GABA), glycine, serotonin and glutamate have been identified as the mediatory agents about regulation of feeding behavior in birds. Based on the molecular weight and the type of efficacy, NTS have been categorized into the two main groups including “the small molecular weight fast-effective NTS and the large molecular wieght slow-effective neuropeptides. Various physiological functions have been presented for NTS and it seems many other unknown effects and even possible interactions among them are still questionable. Appetite control, mediatory role of ingestion behavior and regulation of food intake have recently been highlighted among various roles of NTS in chicken. CONCLUSIONS: Food intake regulation is a complex physiologic process that is under the control of the central and environmental signals. Considering of the involvement of feeding behavior in other major physiological processes such as the growth, immunity and production, it is necessary to realize the role of different mediators which are affecting and modulating food intake in avian species.