Abstract
In the nervous system synaptic input arrives chiefly on dendrites and their type and distribution have been assumed pivotal in signal integration. We have developed an immunohistochemistry (IH)-correlated electron microscopy (EM) method – the “mirror” technique – by which synaptic input to entire dendrites of neurochemically identified interneurons (INs) can be mapped due preserving high-fidelity tissue ultrastructure. Hence, this approach allows quantitative assessment of morphometric parameters of synaptic inputs along the whole length of dendrites originating from the parent soma. The method exploits the fact that adjoining sections have truncated or cut cell bodies which appear on the common surfaces in a mirror fashion. In one of the sections the histochemical marker of the GABAergic subtype, calbindin was revealed in cell bodies whereas in the other section the remaining part of the very same cell bodies were subjected to serial section EM to trace and reconstruct the synaptology of entire dendrites. Here, we provide exemplary data on the synaptic coverage of two dendrites belonging to the same calbindin-D28K immunopositive IN and determine the spatial distribution of asymmetric and symmetric synapses, surface area and volume of the presynaptic boutons, morphometric parameters of synaptic vesicles, and area extent of the active zones.
Highlights
Neurons typically receive synaptic input on their dendrites from presynaptic boutons, about hundred times more than on the cell body
Despite the wealth of theoretical and modeling efforts which emphasize the computational power along the soma-dendrite domain the precise distribution of synapses and their interaction which result in changes in the membrane potential according to the input
Serial section electron microscopy (EM) was carried out Serial Section Electron Microscopy of CB + Dendrites
Summary
Neurons typically receive synaptic input on their dendrites from presynaptic boutons, about hundred times more than on the cell body. It has been conjectured that in the cerebral cortex each neuron type is implicated in specific circuit functions, i.e., the input components along the dendrites are characteristic for the particular neuron type (Karimi et al, 2020). This basic tenet has not been validated experimentally due largely to technical difficulties. They used confocal microscopy (Sohn et al, 2016), which returned positional information about the synapses along the dendrites, without morphometric parameters which are accessible only by using electron microscopy (EM) (Domínguez-Álvaro et al, 2020; Montero-Crespo et al, 2020)
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