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Kynurenergic manipulations influence excitatory synaptic function and excitotoxic vulnerability in the rat hippocampus in vivo.
- Source :
-
Neuroscience [Neuroscience] 2000; Vol. 97 (2), pp. 243-51. - Publication Year :
- 2000
-
Abstract
- Competing enzymatic mechanisms degrade the tryptophan metabolite L-kynurenine to kynurenate, an inhibitory and neuroprotective compound, and to the neurotoxins 3-hydroxykynurenine and quinolinate. Kynurenine 3-hydroxylase inhibitors such as PNU 156561 shift metabolism towards enhanced kynurenate production, and this effect may underlie the recently discovered anticonvulsant and neuroprotective efficacy of these drugs. Using electrophysiological and neurotoxicological endpoints, we now used PNU 156561 as a tool to examine the functional interplay of kynurenate, 3-hydroxykynurenine and quinolinate in the rat hippocampus in vivo. First, population spike amplitude in area CA1 and the extent of quinolinate-induced excitotoxic neurodegeneration were studied in animals receiving acute or prolonged intravenous infusions of L-kynurenine, PNU 156561, (L-kynurenine+PNU 156561) or kynurenate. Only the latter two treatments, but not L-kynurenine or PNU 156561 alone, caused substantial inhibition of evoked responses in area CA1, and only prolonged (3h) infusion of (L-kynurenine+PNU 156561) or kynurenate was neuroprotective. Biochemical analyses in separate animals revealed that the levels of kynurenate attained in both blood and brain (hippocampus) were essentially identical in rats receiving extended infusions of L-kynurenine alone or (L-kynurenine+PNU 156561) (4 and 7microM, respectively, after an infusion of 90 or 180min). However, addition of the kynurenine 3-hydroxylase inhibitor resulted in a significant decrement in the formation of 3-hydroxykynurenine and quinolinate in both blood and brain. These data suggest that the ratio between kynurenate and 3-hydroxykynurenine and/or quinolinate in the brain is a critical determinant of neuronal excitability and viability. The anticonvulsant and neuroprotective potency of kynurenine 3-hydroxylase inhibitors may therefore be due to the drugs' dual action on both branches of the kynurenine pathway of tryptophan degradation.
- Subjects :
- 3-Hydroxyanthranilic Acid metabolism
Animals
Blood-Brain Barrier
Enzyme Inhibitors pharmacology
Hippocampus drug effects
Kynurenic Acid pharmacology
Kynurenine analogs & derivatives
Kynurenine pharmacology
Kynurenine 3-Monooxygenase
Male
Mixed Function Oxygenases antagonists & inhibitors
Neurotoxins pharmacology
Pyramidal Cells drug effects
Pyramidal Cells physiology
Quinolinic Acid pharmacology
Rats
Rats, Sprague-Dawley
Butyrates pharmacology
Hippocampus physiology
Kynurenic Acid metabolism
Kynurenine metabolism
Neuroprotective Agents pharmacology
Subjects
Details
- Language :
- English
- ISSN :
- 0306-4522
- Volume :
- 97
- Issue :
- 2
- Database :
- MEDLINE
- Journal :
- Neuroscience
- Publication Type :
- Academic Journal
- Accession number :
- 10799756
- Full Text :
- https://doi.org/10.1016/s0306-4522(00)00030-0