The Role Of NMDA Receptor NR2B Subunit In The Induction Of LTP In Auditory Cortex Of C57BL/6 Mice Slices During Postnatal Development

Previous studies indicated that the developmental changes in NR2B expression paralleled with the developmental changes of synaptic plasticity, and early experience that affected developmental plasticity also delayed the developmental decline in NR2B expression and NMDAR physiology. So it was supposed that NR2B subunit played an important role in experience-dependent developmental plasticity and changes in NR2B expression would affect developmental plasticity. Because of the close relationship between Long-term potentiation and NMDA receptor, we decided to study the role of NMDA receptor NR2B subunit in the induction of LTP in Auditory cortex of C57BL/6 mice during postnatal development.1. The Properties of LTP in Auditory cortex of C57BL/6 miceIn the auditory cortex of C57BL/6 mice, Long-term potentiation of FP slope was studied by extracellular recording technique from population neurons. Tetanic stimulation of the white matter produced LTP in layer II/III. 100 Hz high frequency stimulation (HFS) could elicit LTP more effectively than theta burst stimulation (TBS) can, which mimices natural spike bursting.2. The impact of NR2B in the induction of LTP in Auditory cortex of C57BL/6 mice2.1 The effect of blocking NR2B before critical period on LTP in Auditory cortexMice were implanted small pieces of Elvax containing NR2B subunit-selective antagonist ifenprodil on the surface of auditory cortex (AC) on postnatal days 14 (P14, before critical period). By extracellular recording LTP in the auditory cortex of C57BL/6, we studied the effects of chronically releasing ifenprodil on introdution of LTP and auditory learning and memory.The animal implanted with ifenprodil-Elvax before critical period had decreased LTP, which is extremely significant different from that of normal animals, while there is no difference between sham control animals and normal anmals, and animals implanted with ifenprodil-Elvas after critical period and normal animals. Moreover, the distinctness beteen TBS-induced LTP and HFS-induced LTP became larger in animals implanted ifenprodil-Elvax before critical period. The results suggest that NMDA receptor NR2B subunit do play a crucial role in the induction of LTP in Auditory cortex of C57BL/6 mice during postnatal development. It is also implicated that the LTP induced by the stimulation mimicing natural rhyme would be more easily influenced by NMDA receptor.2.2 The effect of activating NMDA receptor on LTP in Auditory cortexMice were implanted small pieces of Elvax containing NR2B subunit-selective antagonist ifenprodil on the surface of auditory cortex (AC) on postnatal days 14 (P14, before critical period). Before recording, using NMDA in the ACSF, we studied if NMDA could reverse the effect of ifenprodil blocking on indution of LTP and auditory learning and memory.The slices bathed with NMDA had increased LTP. No matter normal .animals or animals implanted with ifenprodil-Elvax, the ACSF including NMDA could impove LTP amplitudes. Moreover, the LTP amplitudes in slices of animals implanted with ifenprodil-Elvax even could be greater than that of normal animals by activating NMDA receptor. Furhermore, NMDA changed the difference originally between TBS-induced LTP and HFS-induced LTP. After bathing of NMDA, the amplitude ofIBS-induced LTP was higher than that of HFS-mduced LTP in both active animal slices. These data implicated that NMDA was crucial to LTP induction of C57BL/6 mice auditory cortex, and the LTP induced by theta burst stimulation would depend more on NMDA receptor.In summary, after implanting Elvax containing NR2B subunit-selective antagonist ifenprodil on the surface of auditory cortex of C57BL/6 mice during critical period, we observed decreased LTP in mature mice. The results suggested that after ifenprodil blocked NR2B subunits of NMDA receptor in auditory cortex, the induction of LTP, experience-dependent plasticity and auditory memory of adult animals had been influeced. On the contrary, by activating NMDA receptor during bathing period bef...