Kynurenic acid and 5,7-dichlorokynurenic acids improve social and object recognition in male rats

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Abstract
The present study describes the effect of kynurenic (KYNA) and 5,7-dichlorokynurenic (DCKA) acids, acting as selective antagonists at the glycine site on the NMDA receptor complex, upon short-term memory of male rats. Oxiracetam (OXIR) or pramiracetam (PRAM) were used as reference compounds. In the social recognition test, adult animals were injected SC with a drug or vehicle immediately after the first exposure to a juvenile male, 21–24 days old, and reexposed to the same or a novel juvenile 120 min later. Time spent by adults in social investigation of juveniles was measured. Animals treated with KYNA or DCKA (0.3, 3 and 30 mg/kg in both cases) and OXIR (30 and 60 mg/kg) had significantly reduced investigation time when reexposed to the same juvenile as compared to controls. No reduction of investigation time was found in those drugged animals reexposed to a novel juvenile. The findings suggest that KYNA and DCKA improved retention of memory for olfactory stimuli in adult male rats. In the object recognition test, the duration of exploration of two identical objects during the sample trial and the familiar and a new object during the choice trial, performed 60 min later, was evaluated. Drugs or vehicles were administered SC 30 min prior to the sample trial. On choice one, animals treated with KYNA or DCKA (0.6 and 30 mg/kg in both cases) and PRAM (30 mg/kg) spent more time in exploring a new object than the familiar one as compared to controls. This suggests that the drugged animals were able to remember the familiar object. It may be concluded that KYNA and DCKA participate in mechanisms underlying recognition/memory processes in rats.