[Assessment of effects of alpha2-adrenoceptor agonists and antagonists in dorsal hippocampus on muscimol state-dependent memory]

Adrenergic and GABAergic systems of the brain play an important role in memory and learning. According to results of studies, morphine, histamine, and lithium induce state-dependent learning. This study was conducted aiming at assessing the effects of alpha2-adrenergic receptors of CA1 on muscimol state-dependent learning. In this study, Clonidine as agonist and yohimbine as antagonist of alpha2-adrenergic receptor, muscimol as agonist of GABAA receptor and step-through inhibitory avoidance task as a model of learning were used for memory assessment. The data analyzed using one-way analysis of variance, t-test, and Mann-Whitney test. In all statistical assessments, p<0.05 was considered as significance level in the comparison of the groups. Pre-test intra-CA1 injection of muscimol [1.2microg/mice] impaired inhibitory avoidance memory on the test day [p<0.01]. Pre-test injection of muscimol [0.06 and 1.2microg/mice] reversed the memory impaired under pre-training muscimol [1.2microg/mice]; so, muscimol can induce state-dependent learning [p<0.001]. Pre-training injection of Clonidine [0.6 and 1.2microg/mice] also reversed pre-training muscimol [1.2microg/mice, intra-CA1] induced amnesia [p<0.01]. Also pre-test intra-CA1 injection of yohimbine [1.2 and 2.4microg/mice] 2 minutes before administration of effective dose of muscimol inhibited muscimol state-dependent memory [p<0.01]. Overall, It can be conceded that alpha2-adrenergic receptors of dorsal hippocampus have an important role in muscimol state-dependent learning on the test day

[Modulation of muscimol state-dependent learning by alpha 1-adrenergic receptors of the dorsal hippocampus]

Adrenergic and GABAergic systems of the brain play important roles in learning and memory. Previous studies have shown that morphine, histamine and lithium can induce state dependent learning. In the present study we evaluated, the effects of alpha 1-adrenergic receptor of CA1 on muscimol state-dependent learning in mice. Material and In this experimental study adult male NMRI mice were used. The animals were anaesthetized and bilateral implantation of cannula in the CA1 regions of the dorsal hippocampus was performed by using stereotaxic method. Seven days after recovery, we used inhibitory avoidance task for behavioral testing. Data were analyzed by Kruskal-Wallis nonparametric one-way analysis of variance followed by Mann-Whitney test. Pre-training or pre-test intra-CA1 injection of muscimol impaired inhibitory avoidance memory on the test day [P<0.01]. Pre-test injection of muscimol reversed the memory impairment induced by pre-training muscimol injection [P<0.001]. Pre-test intra-CA1 injection of phenylephrine also reversed pre-training muscimol induced amnesia [P<0.01]. Pre-test intra-CA1 injection of prazosin 2 min before administration of the effective dose of muscimol inhibited muscimol state dependent memory [P<0.01]. It can be concluded that the alpha 1-adrenergic receptors of the CA1 may play an important role in the muscimol state dependent learning, on the test day

[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