| Abstract No.: | B-B2053 |
| Country: | Germany |
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| Title: | THE PRINCIPAL NEURONS OF THE MEDIAL NUCLEUS OF THE TRAPEZOID BODY AND A DISTINCT TYPE OF GLIAL CELL RECEIVE COORDINATED SYNAPTIC INPUT FROM THE CALYX OF HELD |
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| Authors/Affiliations: | 3 Jochen Müller*; 3 Daniel Reyes-Haro; 3 Christiane Nolte; 1 Tatyjana Pivneva; 2 Roland Schaette; 3 Helmut Kettenmann;
1 Bogomoletz Institute of Physiology, Kiev, Ukraine; 2 Institute for Theoretical Biology, Humboldt University zu Berlin, Germany; 3 MDC for Molecular Medicine, department of Cellular Neuroscience, Berlin, Germany
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| Content: | Objectives: The calyx of Held is a giant presynaptic terminal forming an axo-somatic contact to the principal neuron in the medial nucleus of the trapezoid body. It is a glutamatergic synapse playing an important role in sound localization and is designed for rapid signal transmission with high fidelity. In the last few years this preparation has been used to study mechanisms of synaptic transmission and plasticity since both, pre- and postsynaptic elements are accessible to physiological recording and manipulation. However, nothing is known so far about presence and function of glial cells in this brain region. In the present study, we have studied the glial elements associated with the calyx synapse by using acute slices of the brain stem of young (P8-P10) mice.
Materials and Methods: Patch clamp recordings in the whole cell mode were used in parallel with two-photon laser scanning microscopy to describe the physiological and morphological characteristics of the glial cells. Immunohistochemistry and electron microscopy was used to describe the molecular identity and the structural details of the cells investigated.
Results: We found two morphologically distinct types of cells in close association with the calyx synapse, one characterized by passive membrane currents and expression of the astrocytic marker glial fibrillary acidic protein (GFAP, passive cells), the other by voltage gated currents and expression of the proteoglycan NG2 (complex cell). Upon electrical stimulation of the afferent fibres crossing the midline of the brainstem slice, we were able to elicit postsynaptic responses in the complex cell that were sensitive to CNQX, an antagonist of AMPA/kainate type glutamate receptors. We also studied the cell on the ultrastructural level and found synaptic-like structures between the calyx and complex cells. In addition we were able to perform double whole cell recordings of spontaneous activity from principal neurons of the MNTB and closely apposed complex cells. We found that about a third of the glial events were synchronized with the neuron. By determining mEPSCs we could estimate the quantal size of neuronal and glial responses, namely 16 and 12 pA.
Conclusions: Based on the achieved data, we were able to conclude that one glial cell integrates, in average, input from three calyces, but contacts much less release sites than the principal neuron. This might be a way how NG2 positive cells integrate the activity from a small number of synapses.
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