部門公開セミナー

日 時 2012年04月23日 15:00~16:00
場 所 山手3号館2階大会議室
演 者 Prof. Joachim Luebke(Research Center Juelich, Germany)
演 題 Structural and functional dynamics of input synapses terminating on layer 5 pyramidal neurons in rat somatosensory cortex
要 旨

Synapses are key elements in the induction and maintenance of synaptic transmission and the modulation of synaptic plasticity. Functionally, cortical synapses differ substantially in both synaptic transmission and short-term plasticity. Whether this is reflected in their structural composition remains rather unknown. Realistic values of the number, size and distribution of active zones (AZ) and the organization of the pool of synaptic vesicles are therefore a pre-requisite. Here, synapses terminating on morphologically and functionally identified layer 5 (L5) pyramidal neurons were three-dimensionally reconstructed and quantitatively analysed to correlate structural with functional properties of excitatory L5 pyramidal cell connections that were recorded in acute brain slices. Individual dendrites were densely covered with synapses of various shape and size (4.14 ± 2.75 µm2), ~85% of which were glutamatergic. The majority had only a single, but large AZ (0.21 ± 0.11 µm2) often with perforated pre- and postsynaptic densities. The average size of the total pool of synaptic vesicles was 570 ± 225 vesicles, but varied substantially between individual synapses (200-2000). All synapses had a relatively large readily releasable (10%) and recycling pool (30%). L5 synapses and their target structures were infolded by fine astrocytic processes that could be followed to the synaptic cleft thereby preventing possible glutamate spillover. AMPA- and NMDA-type glutamate receptors were co-localized at these synapses, but varied substantially in densities and distribution. Therefore several structural factors are likely to drive synaptic efficacy, strength and short-term plasticity at L5 synapses: the large AZs, glial processes at the synaptic cleft, the large readily releasable and recycling pool and the distribution pattern of glutamate receptors, in particular in NMDA subunits, at individual AZs.