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Central pipecolic acid increases food intake under ad libitum feeding conditions in the neonatal chick
Tomo Takagi1, Tetsuya Tachibana, Ei-Suke Saito
1Laboratory of Advanced Animal and Marine Bioresources, Graduate School of Bioresource and Bioenvironmental Sciences, Kyushu University, 812-8581 Fukuoka-shi, Japan.
Insights
L-pipecolic acid (L-PA) increases food intake in neonatal chicks under ad libitum feeding, unlike its previously observed suppressive effect in fasted birds. This hyperphagic effect involves both GABA-A and GABA-B receptors.
Area of Science:
- Neuroscience
- Metabolic Biochemistry
- Animal Physiology
Background:
- L-pipecolic acid (L-PA) is a key L-lysine metabolite in the brain.
- Previous research indicated L-PA suppresses feeding in neonatal chicks via GABA-B receptors.
- Endogenous L-PA levels vary with feeding status.
Purpose of the Study:
- To investigate the effect of L-PA on food intake in neonatal chicks under ad libitum feeding.
- To determine the receptor mechanisms underlying L-PA's influence on feeding behavior.
Main Methods:
- Intracerebroventricular (i.c.v.) injection of L-PA into neonatal chicks.
- Administration of GABA-A and GABA-B receptor antagonists (picrotoxin and CGP54626, respectively).
- Measurement of food intake following L-PA and antagonist treatments.
Main Results:
- L-PA (0.5 or 1.0 mg) significantly increased food intake in chicks fed ad libitum.
- The hyperphagic response to L-PA was reduced by both picrotoxin (GABA-A antagonist) and CGP54626 (GABA-B antagonist).
Conclusions:
- L-pipecolic acid induces hyperphagia in neonatal chicks under ad libitum feeding conditions.
- This hyperphagic effect is mediated by the activation of both GABA-A and GABA-B receptors.
- L-PA exhibits differential effects on food intake depending on the bird's feeding state.
Abstract:
It has been demonstrated that L-pipecolic acid (L-PA) is a major metabolic intermediate of L-lysine in the mammalian and chicken brain. A previous study showed that intracerebroventricular (i.c.v.) injection of L-PA suppressed feeding in neonatal chicks, and the actions were associated with gamma-aminobutyric acid (GABA)-B receptor activation. It has been reported that endogenous L-PA in the brain fluctuated under different feeding conditions. In the present study, we investigated the effect of i.c.v. injection of L-PA on food intake in the neonatal chick under ad libitum feeding conditions. The food intake was increased by 0.5 or 1.0 mg L-PA under ad libitum feeding conditions contrary to previous studies using fasted birds. A hyperphagic effect of L-PA (0.5 mg) was attenuated by both GABA-A receptor antagonist (picrotoxin, 0.5 microg) and GABA-B receptor antagonist (CGP54626, 21.0 ng). These results indicate that a hyperphagic effect of L-PA is mediated by both GABA-A and GABA-B receptors and L-PA differentially affects food intake under different feeding conditions in the neonatal chick.
