抄録
The synaptic effects of glutamate are mainly mediated by ionotropic glutamate receptors accumulated at postsynaptic plasma membrane. Induction and maintenance of the long-term potentiation (LTP) and depression (LTD) of synaptic efficacy have been reported to be mediated by several distinct mechanisms such as modulations of channel property and quantity of AMPA-type glutamate receptors (AMPAR) in synapses with distinct time windows after the induction. Therefore, in order to understand cellular and molecular mechanisms underlying learning and memory, it is important to know precise localization of ionotropic glutamate receptors and these dynamics on the neuronal membrane before and after the LTP and LTD induction in vivo. Here, we employed the unilateral dentate gyrus (DG) -LTP in the hippocampus and parallel fiber-Purkinje cell synapse LTD in the cerebellum to analyze distributions of ionotropic glutamate receptors in single synapses by quantitative SDS-digested freeze-fracture replica immunolabelling. Analysis was carried out at middle molecular layer of DG 45 min, 6 and 24 hours after the LTP induction and at middle molecular layer of the flocculus and paraflocculus after 10 min and 60 min training of horizontal optkinetic response. Results indicate that AMPARs but not NMDARs nor delta2 receptors underwent changes in numbers of receptors in synapses upon LTP or LTD induction in vivo. Additionally, AMPARs at synapses on the dendritic spine are regulated more dynamically than those on the dendritic shafts after the induction. [J Physiol Sci. 2007;57 Suppl:S59]
