Difference in the norepinephrine levels of experimental and non-experimental rats with age in the object recognition task.

In the present study, we investigated the performance of adult and juvenile rats in the Object Recognition Task (ORT). While it is well known that the performance of rat in ORT differs with age, the reason for the difference as well as the underlying neurotransmitter that may have led to these differences were investigated. In the present study, juvenile rats of postnatal day 40-45 (PND 40-45) and adult rats of postnatal day 60+ (PND 60+) were subjected to a two trial ORT. The juvenile rats did not discriminate between the novel object and the familiar object, while the adult rats discriminated the novel from the familiar object. On estimating brain concentrations of norepinephrine (NE), it was observed that the NE level in MTL (medial temporal lobe) of adult experimental rats was significantly higher than the adult non-experimental rats. In juvenile rats, no significant difference was observed in the NE levels of experimental rats in comparison to its non-experimental counterparts. Administration of yohimbine (α(2A) adrenergic receptor antagonist) enhanced the level of NE in juvenile rats and reversed the difference seen with age. From the present study, we conclude that the deficit in memory seen is likely due to the difference in NE levels with task and this can be reversed by yohimbine which enhance NE levels.