Role of Paraventricular Nucleus in Acquisition and Retrieval of Memory and Learning in a Passive Avoidance Learning Task in Rats

Many neurotransmitters such as arginine, vasopressin and oxytocin are involved in learning and memory processes. These neurotransmitters are synthesized by paraventricular and supraoptic nuclei (PVN and SON) of hypothalamus. The present study was conducted with the purpose of investigating the effects of PVN on memory acquisition and retrieval in a passive avoidance task. In the present experimental study, adult male Wistar rats weighing 200-250 g were randomly divided into sham (without any treatment), control saline and lidocaine groups of seven. Cannulation was performed by stereotaxic method. To inactivate the PVN, 0.5 µl of 2% lidocaine was microinjected into the nucleus through the cannula using the Hamilton syringe. Behavioral studies were done to assess the acquisition and retrieval memory using shuttle box, and the step through latency (STL) was recorded. Data analysis showed that no significant differences were found in STL (P>0.05) between the group receiving lidocaine and the other two (the sham group and the saline group) during the acquisition phase, but retention test results showed significant reduction in STL in the group receiving lidocaine (18.14±3.8) compared to the sham group (31.14±11.7) and the saline group (33.7±12.1) (p=0.03 and p<0.01, respectively). The results of the study indicated that the PVN may be involved in the retrieval of learning, whereas the given nucleus seems to have no important role in the acquisition of learning and memory.