Long-Term Plasticity at the Mitral and Tufted Cell to Granule Cell Synapse of the Olfactory Bulb Investigated with a Custom Multielectrode in Acute Brain Slice Preparations

Abstract

Single extracellular stimulation electrodes are a widespread means to locally activate synaptic inputs in acute brain slices. Here we describe the fabrication and application of a multielectrode stimulator that was developed for conditions under which independent stimulation of several nearby sites is desirable. For the construction of the multielectrode we have developed a method by which electrode wires can be spaced at minimal distances of 100 μm. This configuration increases the efficiency of stimulation paradigms, such as the comparison of proximal induced and control inputs for studies of synaptic plasticity.In our case the multielectrode was used for acute olfactory bulb slices to independently excite individual nearby glomeruli; the technique allowed us to demonstrate homosynaptic bidirectional long-term plasticity at the mitral/tufted cell to granule cell synapse. We also describe the determinants for successful recordings of long-term plasticity at this synapse, with mechanical and electrophysiological recording stability being tantamount. Finally, we briefly discuss data analysis procedures.

Anatomical and Functional Connectivity at the Dendrodendritic Reciprocal Mitral Cell–Granule Cell Synapse: Impact on Recurrent and Lateral Inhibition

“…Assumption 4: The Granule Cells-Mediated Anatomical Connectivity Between Individual Glomerular Ensembles Is Spatially Isotropic While detailed anatomical data on this issue are not available as of yet (since their quantification would require large-scale electron microscopy and reconstruction), currently available evidence indicates that dedicated dendrodendritic connections between certain glomeruli seem unlikely to play a major role in MC-GC connectivity: MCs and yet more so glomerular MC ensembles have radially symmetric dendritic fields as described above, probably to maximize the spatial range of the glomerular input/output. Using a multi-electrode stimulation device, we also consistently observed that a given GC can be excited (and even fired) from several adjacent glomeruli both in rats and mice (Stroh et al, 2012;Chatterjee et al, 2016;Lukas et al, 2018), in line with results based on optogenetic activation (Burton and Urban, 2015). Thus, a given GC is likely to belong to more than one glomerular column, again arguing against specific connectivities.…”