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Research into the role of tryptophan (TRP) breakdown away from the serotonergic to
the kynurenine (KYN) pathway by stimulating the brain-endocrine-immune axis system
interaction has brought new insight into potential etiologies of certain human behavioral
and mental disorders. TRP is involved in inappropriate social interactions, such as
feather-destructive pecking behavior (FP) in birds selected for egg laying. Therefore, our
goal was to determine the effect of social disruption stress on FP and the metabolism
of the amino acids TRP, phenylalanine (PHE), tyrosine (TYR), their relevant ratios, and on
large neutral amino acids which are competitors with regard to their transport across the
blood-brain barriers, at least in the human system, in adolescent birds selected for and
against FP behavior. We used 160 laying hens selected for high (HFP) or low (LFP) FP
activity and an unselected control line (UC). Ten pens with 16 individuals each (4 HFP
birds; 3 LFP birds; 9 UC birds) were used. At 16 weeks of age, we disrupted the groups
twice in 5 pens by mixing individuals with unfamiliar birds to induce social stress. Blood
plasma was collected before and after social disruption treatments, to measure amino
acid concentrations. Birds FP behavior was recorded before and after social disruption
treatments. HFP birds performed significantly more FP and had lower KYN/TRP ratios.
We detected significantly higher FP activity and significantly lower plasma PHE/TYR ratios
and a trend to lower KYN/TRP ratios in socially disrupted compared to control pens. This
might indicate that activating insults for TRP catabolism along the KYN axis in laying hens
differs compared to humans and points toward the need for a more detailed analysis of
regulatory mechanisms to understand the role of TRP metabolism for laying hen immune
system and brain function. |
