[Evaluation of the interaction between NMDA receptors of nucleus accumbens and muscarinic receptors in memory]

Whereas studies have indicated the interaction between NMDA and cholinergic systems, this study was performed with the aim of determining the role of NMDA receptors in the nucleus accumbens [NAc] in scopolamine-induced amnesia. In this study, at first rats were anesthetized with intra-peritoneal injection of ketamine hydrochloride plus xylazine, and then placed in a stereotaxic apparatus. Two stainless-steel cannulas were placed 2mm above nucleus accumbens shell. All animals were allowed to recover for one week, before beginning the behavioral testing. Then, animals were trained in a step-through type inhibitory avoidance task. The drugs were injected after successful training and before testing. The animals were tested 24h after training, and the step-through latency time was measured as the memory criterion in male Wistar rats. One-way analysis of variance and Tukey's test were used for analysis of the data. p<0.05 was considered statistically significant. Intra-nucleus accumbens [intra-NAc] injection of scopolamine or NMDA caused impairment in memory in rats. Although, co-administration of an ineffective dose of NMDA with an ineffective dose of scopolamine had no significant effect on memory performance, effective doses of NMDA prevented the amnesic effect of scopolamine on inhibitory avoidance memory. On the other hand, intra-NAc injection of NMDA receptor antagonist, i.e., MK-801 caused no change in memory performance by itself, and its co-administration with an effective dose of scopolamine could not prevent the impairing effect of the latter drug. The finding of this study indicated that NMDA receptors in the nucleus accumbens are involved in the modulation of scopolamine-induced amnesia

effects of histaminergic agents in the nucleus accumbens of rats in the elevated plus-maze test of anxiety

The nucleus accumbens [NAc] receive histaminergic neurons from tuberomammillary nuclei. There are reports indicating that central histamine systems are involved in many physiological behavioral processes, including anxiety. The aim of the present study was to assess whether the histaminergic system of the NAc is involved in anxiety-related behaviors. Rats were anesthetized with intra-peritoneal injection of ketamine hydrochloride, plus xylazine and then were placed in a stereotaxic apparatus. In addition, two stainless-steel cannuale were placed 2 mm above the nucleus accumbens shell. Seven days after recovery from surgery, the behavioral testing was started. As a model of anxiety, the elevated plus maze which is a useful test to investigate the effects of anxiogenic or anxiolytic drugs in rodents, was used in male Wistar rats. Intra-NAc administration of histamine [0.01, 0.1 and 1 micro g/rat] increased the percentage of open arm time [%OAT] and open arm entries [%OAE], but not locomotor activity, indicating an anxiolytic response. Furthermore, bilateral microinjections of different doses of the H1 receptor antagonist pyrilamine [0.001, 0.01, 0.1 and 1 micro g/rat] or the H2 receptor antagonist ranitidine [0.001, 0.01, 0.1 and 1 micro g/rat] into the NAc increased%OAT and%OAE, but not locomotor activity. However, both histamine and histamine receptor antagonists showed an anxiolytic-like effect; the antagonists [1 micro g/rat] also decreased the histamine response. The results may indicate a modulatory effect for the H1 and H2 histamine receptors of nucleus accumbens in the anxiety behavior of rats