L-kynurenine (Kyn) is a key element of tryptophan metabolism; it is enzymatically converted by kynurenine aminotransferase II (KAT II) to kynurenic acid (KYNA), which acts as an antagonist to the NMDA receptor-glycine site. Kyn is also an endogenous ligand of the aryl hydrocarbon receptor (AhR), a transcription factor that regulates the expression of a diverse set of genes. KYNA levels are reduced in several regions of the brain of Huntington's disease (HD) patients. The present work uses an AhR-null mouse and age-matched wild-type mice to determine the effect of the absence of AhR on KYNA availability. We found that, in AhR-null mice, there is an increase of KYNA levels in specific brain areas associated with higher expression of KAT II. Moreover, we induced an excitotoxic insult by intrastriatal administration of quinolinic acid, a biochemical model of HD, in both AhR-null and wild-type mice to evaluate the neurological damage as well as the oxidative stress caused by the lesion. The present work demonstrates that, in specific brain regions of AhR-null mice, the levels of KYNA are increased and that this induces a neuroprotective effect against neurotoxic insults. Moreover, AhR-null mice also show improved motor performance in the rotarod test, indicating a constitutive protection of striatal tissue.

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Huntington’s disease (HD) is a hereditary neurodegenerative disorder of the central nervous system that mainly affects the basal ganglia and has no cure. The mutation is located at an abnormal expansion of the CAG triplet in the Huntingtin gene. Humans show psychiatric, behavioural and motor disorders. Transgenic animal models are essential to the study of HD since the disease only affects humans. Therefore, the aim of this article was to describe the formation and maintenance of and to validate the progressive neurological phenotype of an R6/1 transgenic mouse colony. To achieve our objective, the colony founder was imported from Jackson Laboratories, and the mice were kept under controlled environmental conditions. The animals were bred at the vivarium of the Instituto Nacional de Neurología y Neurocirugía Man­uel Velasco Suárez. The R6/1 transgenic mice were successfully bred and showed genetic and phenotypic characteristics similar to the ones previously reported. Our colony is currently established and validated with the condi­tions of our vivarium and has produced more than four generations of R6/1 mice. The establishment of the R6/1 colony and its maintenance through generation is an advantage since it allows us to follow the authenticity of the transgenic mice regarding their phenotypic and motor behaviours. Fur­thermore, these animals can be compared with other transgenic mice that reproduce some of the main characteristics of the disease manifested in hu­mans, making these transgenic R6/1 mice a useful tool for the study of HD.