Extrasynaptic NMDA receptor dependent long-term potentiation of hippocampal CA1 pyramidal neurons.

In the adult mouse hippocampus, NMDA receptors (NMDARs) of CA1 neurons play an important role in the synaptic plasticity. The location of NMDARs can determine their roles in the induction of long-term potentiation (LTP). However, the extrasynaptic NMDARs (ES-NMDARs) dependent LTP haven't been reported. Here, through the use of a 5-Hz stimulation and MK-801 (an irreversible antagonist of NMDARs) in the CA1 neurons of adult mice hippocampal slices, synaptic NMDARs were selectively inhibited and NMDAR-mediated excitatory postsynaptic currents were not recovered. We found that a robust LTP was induced by 3-train 100-Hz stimulation when the synaptic NMDARs and extrasynaptic NR2B containing NMDARs were blocked, but not in the any of the following conditions: blocking of all NMDARs (synaptic and extrasynaptic), blocking of the synaptic NMDARs, and blocking of the synaptic NMDARs and extrasynaptic NR2A-containing NMDARs. The results indicate that this LTP is ES-NMDARs dependent, and NR2B-containing ES-NMDARs modulates the threshold of LTP induction.

[Effect of acute stress stimulation on the seizure induction in epileptic model rats].

This study was undertaken to observe the effect of acute stress on seizure occurrence in chronic period of epileptic model rats. Lithium-pilocarpine (LiCl-PILO)-induced epileptic rat model was constructed. At the spontaneous recurrent seizure period, acute stress stimulations such as cat's urine and foot electrical shock were applied to observe the behavioral changes and seizure occurrence. The results showed that after the cat's urine stimulation, the self-directed behaviors of the epileptic model rats decreased significantly, while the risk assessment behaviors increased significantly. The seizure occurrence, however, was not observed during the 45 min after the stimulation. Applying electrical foot shocks also did not evoke seizures in epileptic model rats. On the contrast, intra-peritoneal injection of low dose of pentylenetetrazole (PTZ, 30 mg/kg) evoked seizure more efficiently, and the duration of seizure activity was extensively prolonged in epileptic model rats than that of control rats. Taken together, these results indicate that although applying stress stimulations such as cat's urine and electrical foot shock cause several behavioral changes, they are not severe enough to evoke seizure in epileptic model rats.

Functional roles of synaptic and extrasynaptic NMDA receptors in physiological and pathological neuronal activities.

The N-methyl-D-aspartate (NMDA) receptor is a major type of ionotropic glutamate receptor. Many studies have shown that NMDA receptors play a pivotal role in the central nervous system (CNS) under both physiological and pathological conditions. The functional diversity of NMDA receptors can be mainly attributed to their different subunit compositions that perform multiple functions in various situations. Furthermore, recent reports have indicated that synaptic and extrasynaptic NMDA receptors have distinct compositions and couple with different signaling pathways: while synaptic NMDA receptors tend to promote cell survival, extrasynaptic NMDA receptors promote cell death. Currently, intensive efforts are being made to study the pathological role of extrasynaptic NMDA receptors in order to find a more effective approach for the treatment of neurologic disorders. Here we reviewed some recent progress on the participation of synaptic and extrasynaptic NMDA receptors in neurologic diseases including epilepsy, ischemia, schizophrenia, depression and some neurodegenerative diseases.