Effects of intrahippocampal GABAB receptor antagonist treatment on the behavioral long-term potentiation and Y-maze learning performance.

GABAB receptor is present at pre- and post-synaptic sites and participates in many brain functions including cognition, reward and anxiety. Although a lot of research has shown that activation or blockade of GABAB receptor may produce different even opposing effects on long-term potentiation (LTP) and cognitive function, there is little information available concerning the effect of GABAB receptor on behavioral LTP, a learning-induced LTP model. Herein, we firstly examined the effects of 2-OH saclofen, a GABAB receptor antagonist, on the induction of behavioral LTP and Y-maze learning performance. In addition, GABAB receptor has been reported to be present on cholinergic terminals and to regulate the ACh release. Therefore, we also investigated the effect of 2-OH saclofen on the impairments in behavioral LTP and cognitive function induced by scopolamine, an acetylcholine receptor antagonist. We found that intrahippocampal application of 2-OH saclofen could significantly enhance the population spike (PS) amplitude with a dose-response relationship, and 20 µM 2-OH saclofen evidently facilitated the formation of behavioral LTP in the perforant pathway to the dentate gyrus (PP-DG) and led to an obvious improvement in maze learning performance. Furthermore, intrahippocampal 20 µM 2-OH saclofen administration could markedly reverse the scopolamine-induced impairments in behavioral LTP and maze performance. Our data demonstrate that blockade of GABAB receptor displays a facilitatory role in the induction of behavioral LTP and maze learning task, and the antagonist of GABAB receptor seems to exert the potentially therapeutic value in the cognitive defect induced by cholinergic dysfunction.

Neuroprotection of cordycepin in NMDA-induced excitotoxicity by modulating adenosine A1 receptors.

Cerebral ischemia impairs physiological form of synaptic plasticity such as long-term potentiation (LTP). Clinical symptoms of cognitive dysfunction resulting from cerebral ischemia are associated with neuron loss and synaptic function impairment in hippocampus. It has been widely reported that cordycepin displays neuroprotective effect on ameliorating cognitive dysfunction induced by cerebral ischemia. Therefore, it is necessary to study whether cordycepin recovers cognitive function after brain ischemia through improving LTP induction. However, there has been very little discussion about the effects of cordycepin on LTP of cerebral ischemia so far. In the present study, we investigated the effects of cordycepin on LTP impairment and neuron loss induced by cerebral ischemia and excitotoxicity, using electrophysiological recording and Nissl staining techniques. The models were obtained by bilateral common carotid artery occlusion (BCCAO) and intrahippocampal NMDA microinjection. We also explored whether adenosine A1 receptors involve in the neuroprotection of cordycepin by using western blot. We found that cordycepin remarkably alleviated LTP impairment and protected pyramidal cell of hippocampal CA1 region against cerebral ischemia and excitotoxicity. Meanwhile, cordycepin prevented the reduction on adenosine A1 receptor level caused by ischemia but did not alter the adenosine A2A receptor level in hippocampal CA1 area. The improvement of LTP in the excitotoxic rats after cordycepin treatment could be blocked by DPCPX, a selective antagonist of adenosine A1 receptor. In summary, our findings provided new insights into the mechanisms of cordycepin neuroprotection in excitotoxic diseases, which is through regulating adenosine A1 receptor to improve LTP formation and neuronal survival.