Properties of transmission at a giant glutamatergic synapse in cerebellum: the mossy fiber-unipolar brush cell synapse
D. J. Rossi, S. Alford, E. Mugnaini and N. T. Slater Department of Physiology, Northwestern University Medical School, Chicago, Illinois 60611, USA. 1. The synaptic activation by mossy fibers (MFs) of unipolar brush cells (UBCs) in the vestibular cerebellum (nodulus and uvula) was examined using pat...
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Veröffentlicht in: | Journal of neurophysiology 1995-07, Vol.74 (1), p.24-42 |
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Zusammenfassung: | D. J. Rossi, S. Alford, E. Mugnaini and N. T. Slater
Department of Physiology, Northwestern University Medical School, Chicago, Illinois 60611, USA.
1. The synaptic activation by mossy fibers (MFs) of unipolar brush cells
(UBCs) in the vestibular cerebellum (nodulus and uvula) was examined using
patch-clamp recording methods in thin, rat cerebellar slices with Lucifer
yellow-filled pipettes for subsequent fluorescence microscopic verification
of the cell morphology. 2. UBCs were distinguished from adjacent granule
cells in thin cerebellar slices in the uvula and nodulus regions by their
larger soma diameters and short dendritic brush, greater whole-cell
capacitance, and a prolonged, biphasic excitatory postsynaptic current
(EPSC) to stimulation of MFs. 3. Thin-section transmission electron
micrographs of the MF-UBC synapse displayed an unusually extensive area of
synaptic apposition estimated to measure 12-40 microns2. The majority of
UBCs was innervated by a single MF. At high magnification, individual
clusters of presynaptic vesicles could be discerned, separated by regions
of presynaptic membrane lacking vesicles, but apposed to continuous regions
of postsynaptic density. Thus, after release, transmitter diffusion from
the synaptic cleft must traverse considerable stretches of postsynaptic
membrane before escape into extracellular space. In contrast, MF-granule
cell synapses in these cerebellar regions resembled glutamate synapses in
other brain regions in that the total synaptic area measured < or = 4
microns2. These synaptic junctions were flanked by short stretches of
unspecialized plasma membrane, providing a short (0.5 micron) diffusional
path from the site of neurotransmitter release to a branch point of the
extracellular space. 4. The MF-evoked EPSC in UBCs was composed of a fast
(10-90% rise time: 0.70 ms) and slow (10-90% rise time: 395 ms; 10-90%
decay time: 3.1 s) component. The fast component was blocked by the
alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid/kainate (AMPA/KA)
antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (10 microM) and displayed
linear current-voltage (I-V) relations in the presence or absence of
external magnesium. 5. The slow EPSC was also mediated by glutamate
receptors, but in most neurons both AMPA/KA and N-methyl-D-aspartate (NMDA)
receptors contributed to the slow EPSC, with the contribution of NMDA
receptors predominating in the majority of cells. Consequently, although
all cells displayed linear I-V rela |
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ISSN: | 0022-3077 1522-1598 |
DOI: | 10.1152/jn.1995.74.1.24 |