Table 1.
Feasibility and non-feasibility of obtaining some critical quantitative anatomical data of the minicolumn that is relevant for connectomics and models.
| Light microscopy | Electron microscopy | ||
|---|---|---|---|
| Feasible | Non-feasible | Feasible | Non-feasible |
| Density and spatial distribution of neurons and glia (e.g., cells labeled with NeuN, DAPI) | 1Volume occupied by dendrites, axons and glial processes | Proportion of different types of synapses (e.g., asymmetric and symmetric synapses) | Absolute number and distribution of different types of synapses |
| Density and spatial distribution of different types of neurons and glia (e.g., cells that are immunoreactive for GABA, PV, SOM, Iba1) | Inference of number of synapses established by an axon based on the assumption that one varicosity equals one synapse | 2Identification and characterization of long-range synaptic connections | Complete synaptic connections of the axonal arborization of identified neurons |
| Volume fraction occupied by neurons, glia, neuropil and blood vessels | 3Number of cells projecting to a given brain region (long-range outputs) | General identification of the postsynaptic targets to a given axon terminal (non-characterized postsynaptic dendritic shafts, dendritic spines, somata, axon initial segments) | Full identification and characterization of the postsynaptic targets (i.e., origin and characteristics of all the postsynaptic dendritic shafts, dendritic spines, somata, axon initial segments) |
| Detailed single cell 3D reconstructions of dendritic trees of neurons (cell filling; e.g., intracellular injections of Lucifer Yellow) | 3Number of cells from other brain regions projecting to the minicolumn (long-range inputs) | Complete synaptic input maps on single identified neurons | 4Absolute number of mitochondria in the neuropil |
| Detailed single cell 3D reconstructions of axonal arborization of interneurons (cell filling; e.g., intracellular biocytin labeling) | Spatial relationships of synapses with glial processes | ||
| 2Detailed single cell 3D reconstruction of axonal arborization of projecting neurons (e.g., single neuron-tracing using viral vectors) | |||
| Surface area and volume of dendritic shafts, dendritic spines, somata and axon initial segments of identified cells (e.g., intracellularly injected cells) | |||
| Density of different types of axon terminals (e.g., immunostained for vGlut1, vGAT) | |||
| Complete putative synaptic maps on identified neurons (i.e., characterization of axonal boutons in apposition to neuronal somata, dendrites and axon initial segments of identified neurons | |||
Abbreviations: DAPI, 4′,6-diamidino-2-phenylindole; GABA, γ-Aminobutyric acid; PV, Parvalbumin; NeuN, Neuron-Specific Nuclear Protein; SOM, somatostin; VGlut1, Vesicular glutamate transporter 1; vGAT, Vesicular GABA Transporter. 1This data can be inferred from the total number of neurons, glia and volume fraction of the neuropil coupled with electron microscopy data of the neuropil. 2This data can only be obtained in experimental animals. 3Only a rough estimate can be obtained and only in experimental animals. 4Density and spatial distribution of blood vessels coupled with the density of neurons, glia, mitochondria and synapses are fundamental data to model oxygen delivery and energy consumption of local neural circuits in order to better understand how local synaptic activity is regulated and limited by blood flow (see e.g., Blinder et al., 2013; Magistretti and Allaman, 2015).