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Structural and functional characterisation of M/T cells using Ca2+ Imaging and Activity Correlation Imaging in dendritic networks of the developing Xenopus brain

dc.contributor.advisorSchild, Detlev Prof. Dr. Dr.
dc.contributor.authorOkom, Camille Inès Alexandra
dc.titleStructural and functional characterisation of M/T cells using Ca2+ Imaging and Activity Correlation Imaging in dendritic networks of the developing Xenopus brainde
dc.contributor.refereeSchild, Detlev Prof. Dr. Dr.
dc.description.abstractengOlfactory information collected in the nose is conveyed from the axon terminals of olfactory receptor neurons to the dendritic tufts of mitral/tufted (M/T) cells across glutamatergic synapses. These synaptic interactions occur within glomeruli, the spherical neuropil structures where presynaptic and postsynaptic fibres intermingle. The second-order projection neurons, the M/T cells carry out sensory processing and integration of the olfactory signals. In Xenopus laevis larvae, sensitivity to temperature drops is encoded by a group of receptor neurons terminating a particular glomerulus, called the γ-glomerulus. Interestingly, several studies brought evidence that some M/T cells receive their input from more than one glomerulus. Yet, the implications of such a connectivity in terms of multi-processing and encoding of olfactory information have not yet been investigated. We hypothesised that the multiple glomerular innervation by M/T cells would enable them to collect and integrate both chemical and thermic information. Consequently, Ca2+ imaging experiments performed in olfactory bulb slices revealed that most temperature-sensitive M/T cells also responded to chemical odourants, indicating that the dual-sensitivity of these cells is a function of their one-to-many glomerular connectivity. Furthermore, Xenopus M/T cells display upon odourant stimulation three types of temporal activity patterns: activated, inhibited, unresponsive, which corroborate previous research showing that reciprocal and lateral M/T cell inhibition affects odour representations in the rodent bulb. Inhibitory periglomerular and granule cells establish contact with M/T cells through dendrodendritic synapses and constitute a scalable inhibitory lever on M/T cell outputs. In order to test the effect of GABA-mediated inhibition on Xenopus M/T cells, the Ca2+ dynamics of M/T ensembles were compared in the presence or absence of gabazine, a GABA-A receptor antagonist. The blockade of inhibition drastically altered the patterns of odour responses in M/T cells. Moreover, gabazine did not desynchronise correlated patterns of spontaneous activity across these neurons, but enhanced them. These results demonstrate that GABAergic inhibition of M/T cells drives odour discrimination and contrast enhancement of overlapping odour signals in these neurons. In contrast, it plays a minor role, if any, in the coupling of M/T cells’ baseline activities. Finally, simultaneous patch-clamp recordings and Ca2+ imaging proved that action potentials (APs) and AP-related Ca2+ signals backpropagate in the dendrites of Xenopus M/T cells. Spontaneous and somatically evoked APs activated Ca2+ channels generating Ca2+ spikes were observed in dendritic branches and glomerular endings. Besides, the cross-correlation analysis of Ca2+ fluctuations along M/T cell dendrites exposed differential activities of dendritic sub-compartments. Early evidence suggests that gabazine enhances the uniformity of backpropagating spikes along
dc.contributor.coRefereeFiala, André Prof. Dr.
dc.subject.engolfaction, Xenopus, mitral cells, thermosensitivity, inhibition, dendrite, calcium imagingde
dc.affiliation.instituteGöttinger Graduiertenschule für Neurowissenschaften, Biophysik und molekulare Biowissenschaften (GGNB)de
dc.subject.gokfullBiologie (PPN619462639)de

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