Involvement of the orexin ۱ and ۲ receptors in nucleus incertus (NI) on modulation of spatial reference memory in the Morris water maze

The nucleus incertus (NI) is a distinct area within the brainstem near the posterior part of the tegmentum. This part of the brain consists of some heterogeneous neurons that play roles in different functions, including response to stress, arousal, learning, and modulating hippocampal theta rhythm. Orexin neuropeptides also have widespread distributions and overlapping actions within the NI. However, the actions of the orexin receptors in the NI are not well characterized. In the present study, the effect of post-training and pre-probe of trial intra-NI administration of SB-۳۳۴۸۶-A (OX۱R antagonist) (۱۲ μg/۰.۵μl) and TCS-OX۲-۲۹ (OX۲R antagonist) (۱۰ μg/۰.۵ μl) on consolidation and retrieval in Morris Water Maze (MWM) task was examined. In the experiment ۱, rats were trained in MWM and immediately after every training received injections of Dimethyl sulfoxide (DMSO) (control group), SB-۳۳۴۸۶۷-A, and TCS-OX۲-۲۹ into NI. Experiment ۲ was similar to experiment ۱ except rats received DMSO, SB-۳۳۴۸۶-A, and TCS-OX۲-۲۹, ۱۵ minutes before the probe test. In subsequent experiments, probe and visible tests were performed after the last training and distance moved, escape latency, and velocity were recorded. In experiment ۳, rats trained in experiments ۱ and ۲ immediately after the probe test were given trials for visuomotor coordination assessment on the visible platform. The results showed that the spatial reference memory consolidation phase was significantly impaired by SB-۳۳۴۸۶۷-A or TCS-OX۲-۲۹ (P < ۰.۰۵), while the retrieval phase was not affected (P > ۰.۰۵). Therefore, it can be concluded that the orexinergic system in the NI has a key role in consolidation in rats through both OX۱ and OX۲ receptors.

کلیدواژه ها:

Orexin receptors ، Nucleus incertus ، Morris water maze ، Memory