Molecular biology of serotonergic systems in avian brains

Abstract

Serotonin (5-hydroxytryptamine, 5-HT) is a phylogenetically conserved neurotransmitter and modulator. Neurons utilizing serotonin have been identified in the central nervous systems of all vertebrates. In the central serotonergic system of vertebrate species examined so far, serotonergic neurons have been confirmed to exist in clusters in the brainstem. Although many serotonin-regulated cognitive, behavioral, and emotional functions have been elucidated in mammals, equivalents remain poorly understood in non-mammalian vertebrates. The purpose of this review is to summarize current knowledge of the anatomical organization and molecular features of the avian central serotonergic system. In addition, selected key functions of serotonin are briefly reviewed. Gene association studies between serotonergic system related genes and behaviors in birds have elucidated that the serotonergic system is involved in the regulation of behavior in birds similar to that observed in mammals. The widespread distribution of serotonergic modulation in the central nervous system and the evolutionary conservation of the serotonergic system provide a strong foundation for understanding and comparing the evolutionary continuity of neural circuits controlling corresponding brain functions within vertebrates. The main focus of this review is the chicken brain, with this type of poultry used as a model bird. The chicken is widely used not only as a model for answering questions in developmental biology and as a model for agriculturally useful breeding, but also in research relating to cognitive, behavioral, and emotional processes. In addition to a wealth of prior research on the projection relationships of avian brain regions, detailed subdivision similarities between avian and mammalian brains have recently been identified. Therefore, identifying the neural circuits modulated by the serotonergic system in avian brains may provide an interesting opportunity for detailed comparative studies of the function of serotonergic systems in mammals.

The Influence of Dietary Synbiotic on Agonistic Behavior, Stress, and Brain Monoamines via Modulation of the Microbiota–Gut–Brain Axis in Laying Hens

“…The avian hippocampus may also assist with emotional and cognitive processing like the mammalian hippocampus, where serotonin assists in this regulation [55,56]. Serotonin is synthesized in the brainstem-specifically the raphe nuclei-and then projected out into many regions of the brain including the hippocampus [57]. One study also found similar serotonin genes and receptors in the hippocampus to those of mammals that are related to fear-related behaviors [56,58].…”

Reduced Nitric Oxide Synthase Involvement in Aigamo Duck Basilar Arterial Relaxation

“…All reagents were used in accordance with the relevant manufacturer's instructions. Each of the selected agonists had previously been validated in vertebrate species (including avian species) [17][18][19][20]. Their reported effects on cerebral arteries in a range of species as demonstrated in vitro studies are shown in Table 1.…”