Development of microglia in fetal and postnatal neocortex of the pig, the European wild boar (Sus scrofa)

Abstract

Knowledge on cortical development is based mainly on rodents besides primates and carnivores, all being altricial. Here, we analyzed a precocial animal, the pig, looking at dorsoparietal cortex from E45 to P90. At E45, most ionized calcium‐binding adapter molecule 1‐positive (Iba1+) cells had a macrophage‐like morphology and resided in meninges and choroid plexus. Only a few cells were scattered in the ventricular and subventricular zone (VZ and SVZ). At E60/E70, all laminar compartments displayed microglia cells at a low‐to‐moderate density, being highest in VZ and SVZ followed by intermediate zone/white matter (IZ/WM). The cortical plate and marginal zone displayed only a few Iba1+ cells. Cells were intensely labeled, but still had poorly arborized somata and many resembled ameboid, macrophage‐like microglia. Concurrent with a massive increase in cortical volume, microglia cell density increased until E85, and further until E100/E110 (birth at E114) to densities that resemble those seen postnatally. A fraction of microglia colabeled with Ki67 suggesting proliferation in all laminar compartments. Cell‐to‐cell distance decreased substantially during this time, and the fraction of microglia to all nuclei and to neurons increases in the laminar compartments. Eventually, of all cortical DAPI+ nuclei 7–12% were Iba1+ microglia. From E70 onwards, more and more cells with ramified processes were present in MZ down to IZ/WM, showing, for instance, a close association with NeuN+, NPY+, and GAD65/67+ somata and axon initial segments. These results suggested that the development of microglia cell density and morphology proceeds rapidly from mid‐gestation onwards reaching near‐adult status already before birth.

Development of myelin in fetal and postnatal neocortex of the pig, the European wild boar Sus scrofa

“…The material for the immunohistochemical staining is from our fetal pig brain collection (Ernst et al 2018 ; Sobierajski et al 2022 ). Material has been obtained from the Üfter Mark area managed by the Regionalverband Ruhr Grün.…”

“…After cryoprotection, tissue slabs were stored frozen in TissueTek at − 80 °C until cutting. Coronal 25 µm cryostat sections of dorsolateral parietal and occipital neocortex mounted on silanized slides were submitted to antigen retrieval (40 min citrate buffer pH 5–6 at 80 °C and cooling down slowly for about 1 h) followed by immunohistochemistry as described (Sobierajski et al 2022 ). Antibodies are listed in Table 2 .…”

“…Quantification of PDFGFRα + cells and nearest neighborhood analysis was done as described for the assessment of microglia (Sobierajski et al 2022 ). Regions of interest were placed over the selected cortical compartments of the confocal images.…”

Neocortical pyramidal neurons with axons emerging from dendrites are frequent in non-primates, but rare in monkey and human

“…The 5-month pig material was obtained from the Institutes of Physiology and Anatomy, Medical Faculty, University Mannheim (donated by Prof. Martin Schmelz). The P90 European wild boar material was from current studies ( Ernst et al, 2018 ; Sobierajski et al, 2022 ; Table 2 ). Adult macaque and P60 infant macaque material not used for immediate histological assessment had been stored after fixation and glycerol infiltration in isopentane at –80°C.…”

Neocortical pyramidal neurons with axons emerging from dendrites are frequent in non-primates, but rare in monkey and human

“…Cryoprotected slabs of these brains had been stored since then embedded in TissueTek at -80 o C. The 5 month pig material was obtained from the Institutes of Physiology and Anatomy, Medical Faculty, University Mannheim (donated by Prof. Martin Schmelz). The P90 European wild boar material has been from current studies (Ernst et al, 2018;Sobierajski et al, 2021). Sections were pretreated with 3% H 2 O 2 in TBS for 30 min, rinsed, incubated for 1 h in 0.5% Triton in TBS, blocked in 5% horse serum in TBS for 2 h followed by incubation in mouse anti-SMI-32 to stain somata and dendrites of subsets of pyramidal cells, and rabbit anti-βIV-spectrin (Höfflin et al, 2017) to stain the AIS.…”