Abstract
Domesticated chicks are precocial and therefore have relatively well-developed feeding behavior. The role of hypothalamic neuropeptides in food-intake regulation in chicks has been reported for decades. However, we hypothesized that nutrients and their metabolites in the brain may be involved in food intake in chicks because these animals exhibit a very frequent feeding pattern. Therefore, the purpose of this study was to examine the feeding behavior of chicks as well as the associated changes in free amino acid and monoamine concentrations in the chick brain. The feeding behavior of chicks was recorded continuously for 6 h. The next day, brain and blood samples were collected when the chicks either attempted to have food (hungry group) or turned food down (satiated group), in order to analyze the concentrations of the free amino acids and monoamines. We confirmed that the feeding behavior of neonatal chicks was characterized by short resting periods between very brief times spent on food intake. Several free amino acids in the mesencephalon were significantly lower in the satiated group than in the hungry group, while l-histidine and l-glutamine were significantly higher. Notably, there was no change in the free amino acid concentrations in other brain regions or plasma. As for monoamines, serotonin and norepinephrine were significantly lower in the mesencephalon of the hungry group compared with the satiated group, but 5 hydroxyindolacetic acid (5-HIAA) was higher. In addition, serotonin and norepinephrine levels were significantly higher in the brain stem of the hungry chicks compared with the satiated group, but levels of 5-HIAA and homovanillic acid were lower. Levels of both dopamine and its metabolite, 3,4-dihydroxyphenylacetic acid, were significantly higher in the diencephalon and telencephalon of the chicks in the hungry group. In conclusion, the changes in the free amino acids and monoamines in the brain may have some role in the feeding behavior of neonatal chicks.
Highlights
The appetite biology of birds is generally assumed to have particular similarities with that of mammals (Denbow 1984; Furuse 2002)
While it could be predicted that a certain period of time is needed for the changes of neuropeptides in the brain to occur, it has been reported that 120 min was needed for significant increments to occur of the gonadotropin-inhibitory hormone (GnIH)
It was confirmed that the feeding behavior of neonatal chicks was characterized by frequent food intake, with short resting and sleeping periods in between
Summary
The appetite biology of birds is generally assumed to have particular similarities with that of mammals (Denbow 1984; Furuse 2002). There are many reports concerned with the role of hypothalamic neuropeptides in food-intake regulation (Bungo et al 2000, 2004; Furuse et al 1997a, b, 1999, 2000; Kawakami et al 2000a, b; Kuenzel et al 1987; Tachibana et al 2008, 2009). It is difficult to explain the frequent food intake and resting behavior observed in chicks in terms of the action of neuropeptides; rather, quick changes of metabolites in the brain may contribute to this process. We hypothesized that quick metabolic changes, such as changes in amino acid and monoamine concentrations in the brain, may be associated with the frequent feeding and resting behavior of neonatal chicks. In the present study, we first aimed to clarify feeding behavior of neonatal chicks by measuring the time spent on feeding and resting and further examined the changes in free amino acid and monoamine concentrations in different brain regions that are associated with chicks’ feeding behavior
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