Table 2.

Changes in the kynurenine pathway in psychiatric disorders, acute brain and spinal cord disorders, and multiple sclerosis.

Brain (CSF)	SCZ	BD	MDD	TBI	SCI	Stroke	MS
TRP	↓ [70]	↓ [162]	↓ [163]	N [15]	-	↓ [103]	↓ [22]
QUINA	↓ [70]	N [162]	↑ [23]	↑ [15]	↑ [93]	↑ [103]	N or ↑ #
KYNA	↑ [65]	↓ [162]	↓ [163]	↑ [15]	-	↓ [102]	↑ or ↓*
K/T	↑ [65]	N [162]	↑ [163]	↑ [15]	↑ [164]	↑ [165]	↑ [44]
Melatonin	↓ [166]	↓ [167]	↓ [168]	↓ [18]	↓ [169]	↓ [104]	↓ [170]
IDO	↑ [65]	↑ [171]	↑ [172]	↑ [18]	↑ [107]	↑ [102]	↑ [173]
5-HT	↑ [174]	↓ [79]	↑ [88]	↓ [18]	↓ [110]	↓ [175]	↓ [115]
L-KYN	↑ [63]	N [162]	N [163]	↑ [15]	↑ [93]	↑ [176]	↑ [116]
3-HK	↑ [8]	↑ [177]	↑ [82]	↑ [96]	↑ [93]	↑ [178]	↑ [44]
3-HAA	↑ [70]	-	N [179]	N [15]	↑ [93]	↓ [161]	↑ [44]

↑: increase; ↓: decrease; N: nonsignificant difference; - uncertainty ^# There was no difference in the CSF level of QUINA between MS patients and normal subjects, but QUINA was increased in patients with relapsing-remitting MS (RRMS) in the relapse stage [180]. *KYNA increases during acute relapse and decreases during chronic remission [22]. Abbreviations: 3-HAA: 3-hydroxyanthrenillc acid; 3-HK: 3-hydroxykynurenine; 5-HT: 5-hydroxy tryptophan; BD: bipolar disorder; CSF: cerebrospinal fluid; IDO: indoleamine 2,3-dioxygenase; K/T: L-KYN/TRP; KYNA: kynurenic acid; L-KYN: L-kynurenine; MDD: major depressive disorder; MS: multiple sclerosis; QUINA: quinolinic acid; SCI: spinal cord injury; SCZ: schizophrenia; TBI: traumatic brain injury; TRP: L-tryptophan.