Changes in brain tryptophan metabolism elicited by ageing, social environment, and psychological stress in mice

Figures & data

Figure 1 Time schedule of experiments. D: day; W: week.

Figure 2 Changes in the TRP, KYN and serotonin (5-HT) concentrations elicited by ageing, housing condition, and novelty stress. Each bar indicates a group defined by age, stress and housing condition (n = 8). White bar, non-stress; black bar, stress. G, group housing; I, isolation housing. Values are shown as means ± SEM. The results of Tukey–Kramer test for ageing, housing condition, and novelty stress are shown. Between the young adult and adult groups, effects of ageing are shown: #, p < 0.05: ##, p < 0.01. For each age group, effects of housing condition are shown: *, p < 0.05; **, p < 0.01. Effects of novelty stress are shown: +, p < 0.05; ++, p < 0.01. A, prefrontal cortex; B, hippocampus; C, amygdala; D, dorsal raphe nuclei.

Table I.  Changes in the KYN/TRP and 5-HT/TRP ratios elicited by aging, housing condition and novelty stress.

(a) Prefrontal cortex
Young adult		KYN/TRP		5-HT/TRP
Group-housing	Stress ( − )	0.013 ± 0.002		0.254 ± 0.022
	Stress (+)	0.015 ± 0.002		0.339 ± 0.053
Isolation-housing	Stress ( − )	0.023 ± 0.003		0.898 ± 0.108
	Stress (+)	0.015 ± 0.001	^*	0.347 ± 0.037	^*^*
Adult					#
Group-housing	Stress ( − )	0.015 ± 0.002		0.371 ± 0.057
	Stress (+)	0.015 ± 0.001		0.466 ± 0.029
Isolation-housing	Stress ( − )	0.015 ± 0.003		0.927 ± 0.115
	Stress (+)	0.016 ± 0.004		0.580 ± 0.098	^*^* ++
(b) Hippocampus
Young adult		KYN/TRP		5-HT/TRP
Group-housing	Stress ( − )	0.017 ± 0.003		0.200 ± 0.031
	Stress (+)	0.016 ± 0.002		0.131 ± 0.019
Isolation-housing	Stress ( − )	0.024 ± 0.003		0.383 ± 0.039
	Stress (+)	0.017 ± 0.002		0.240 ± 0.028	^*^* ++
Adult					##
Group-housing	Stress ( − )	0.021 ± 0.002		0.364 ± 0.069
	Stress (+)	0.013 ± 0.001		0.313 ± 0.030
Isolation-housing	Stress ( − )	0.021 ± 0.003		0.472 ± 0.055
	Stress (+)	0.017 ± 0.003	+	0.368 ± 0.027
(c) Amygdala
Young adult		KYN/TRP		5-HT/TRP
Group-housing	Stress ( − )	0.014 ± 0.001		0.401 ± 0.045
	Stress (+)	0.015 ± 0.002		0.401 ± 0.042
Isolation-housing	Stress ( − )	0.021 ± 0.003		1.319 ± 0.190
	Stress (+)	0.014 ± 0.002		0.526 ± 0.055	^*^*++
Adult
Group-housing	Stress ( − )	0.015 ± 0.002		0.690 ± 0.105
	Stress (+)	0.013 ± 0.001		0.542 ± 0.054
Isolation-housing	Stress ( − )	0.011 ± 0.001		1.014 ± 0.156
	Stress (+)	0.014 ± 0.004		0.683 ± 0.054	+
(d) Dorsal raphe nuclei
Young adult		KYN/TRP		5-HT/TRP
Group-housing	Stress ( − )	0.017 ± 0.001		0.285 ± 0.036
	Stress (+)	0.015 ± 0.001		0.285 ± 0.028
Isolation-housing	Stress ( − )	0.024 ± 0.004		0.758 ± 0.095
	Stress (+)	0.017 ± 0.004		0.343 ± 0.034	^**++
Adult
Group-housing	Stress ( − )	0.013 ± 0.002		0.378 ± 0.057
	Stress (+)	0.018 ± 0.001		0.312 ± 0.023
Isolation-housing	Stress ( − )	0.017 ± 0.001		0.908 ± 0.242
	Stress (+)	0.016 ± 0.004		0.332 ± 0.033	+

The number of mice used for each group (as defined by age, stress and housing condition) was 8. Values are shown as means ± SEM. The results of Tukey–Kramer test for aging, housing condition, and novelty stress are shown. Between young adult and adult groups, effects of ageing are shown: #, p < 0.05: ##, p < 0.01. For each age group, effects of housing condition are shown: ^*, p < 0.05; ^**, p < 0.01. Effects of novelty stress are shown: +, p < 0.05; ++, p < 0.01. A, prefrontal cortex; B, hippocampus; C, amygdala; D, dorsal raphe nuclei.