On March 2, 2011, The Journal of Neuroscience published a research article from ION entitled "Post-induction requirement of NMDA receptor activation for late-phase long-term potentiation of developing retinotectal synapses in vivo".  This work was mainly carried out by Ph.D. students Li-qin Gong and Ling-jie He under the supervision of Drs. Xiao-hui Zhang and Mu-ming Poo.

The protein synthesis-dependent form of long-term potentiation (LTP), known as late-phase LTP (L-LTP), has been linked to long-term memory, because specific disruption of L-LTP in transgenic mice or drug-treated mice correlated with defects in long-term memory.  Previous behavioral studies in animals have also indicated that post-training blockade of activation of N-methyl D-aspartate subtype of the glutamate receptor (NMDAR) impaired long-term memory.  However, the synaptic basis for the post-training requirement of NMDARs in memory formation remains unclear, since NMDAR activation is generally known to be required during the induction of LTP.  In the present study, Gong et al. made an important step by demonstrating, at developing Xenopus retinotectal synapses, that establishment of L-LTP in vivo requires NMDAR activation within a critical time window (~30 min) following LTP induction.  Furthermore, they also showed that spontaneous spiking activity immediately after the LTP induction serves a critical role in establishing L-LTP. These findings offer new insights into the synaptic basis for the requirement of post-learning activation of NMDARs, and point to the importance of post-learning spontaneous circuit activity in memory formation.

Figure legend:   Stabilization of L-LTP requires NMDAR activation within 30 min time window after the induction.  

Rec: field potential recording; Sti: electric stimulation; T: tectum;  FB: front brain;  3xTBS (5a€？): 3 episodes of theta burst stimulation spaced by 5 min intervals;  D-AP5: selective NMDAR antagonist; Shadow area: duration of drug application.