Differences in catecholamine metabolism and behaviour in neonatal broiler and layer chicks.

1. To clarify the difference in behavioural activities and catecholamine metabolism between layer and broiler-type chicks two experiments were conducted. 2. In experiment 1, 1-d-old male layer and broiler chicks were placed in an open-field area and their responses were investigated for 10 min. The responses of the two strains were remarkably different, with broilers being less active than layers. Vocalisations rapidly decreased in broilers whereas those of layers remained elevated during the 10 min. 3. In experiment 2, 1-d-old chicks of both strains were killed and brain catecholamine concentrations were determined in three parts of the brain: telencephalon, optic lobe and brain stem. 4. In the whole brain, dopamine (DA) and dihydroxyphenylacetic acid (DOPAC) were significantly higher in broilers. However, the values for norepinephrine (NE), epinephrine (E) and 4-hydroxy-3-methoxyphenylacetic acid (HVA) were similar between strains. The ratios of metabolite/precursor were also calculated: HVA/DOPAC was higher in layers, while NE/DA, E/NE and DOPAC/DA were not significantly different between strains. 5. These results suggest that behavioural activities differ greatly, while there are some differences in catecholamine metabolism between the two strains.

Intracerebroventricular administration of GABA-A and GABA-B receptor antagonists attenuate feeding and sleeping-like behavior induced by L-pipecolic acid in neonatal chicks.

It has been demonstrated that L-pipecolic acid (L-PA), a major metabolic intermediate of L-lysine (L-Lys) in the mammalian and chicken brain, is involved in the functioning of the GABAergic system. A previous study has shown that intracerebroventricular (i.c.v.) injection of L-PA suppressed feeding and induced sleep-like behavior in neonatal chicks; however, the precise relationship between the GABAergic system and L-PA has not been clarified. In the present study, the role of the GABA-A or GABA-B receptors in the suppression of food intake and induction of sleeping-like behavior by L-PA was investigated. Chicks were injected i.c.v. with the GABA-A antagonist picrotoxin or GABA-B antagonist CGP54626 along with L-PA. Although suppression of food intake by L-PA was restored partially by co-injection with CGP54626, but not picrotoxin, sleep-like behavior induced by L-PA was suppressed significantly by both antagonists. These results suggested that L-PA activated both GABA-A and GABA-B receptors, and GABA-B receptors alone contributed to food intake whereas both receptors contributed to sleep-like behavior.