Poster Presentation & Flash Talk 46th Annual Meeting of the Fetal and Neonatal Physiological Society 2019

Spatial and temporal profile of microglial and perivascular macrophages in the developing sheep brain (#137)

Isabelle Shearer 1 , Sebastian Quezada Rojas 1 , Shreya Rana 2 , Nadia Hale 2 , David Walker 1 , Mary Tolcos 1 , Bobbi Fleiss 1 3
  1. School of Health and Biomedical Sciences, RMIT University, Bundoora, Victoria, Australia
  2. Hudson Institute of Medical Research, Clayton, Victoria, Australia
  3. INSERM UMR 1141, Neurodiderot, Hopital Robert Debre, Paris, France

Background: Microglia, supported by perivascular macrophage (PVM), play crucial roles in brain development. This knowledge is derived predominantly from studies of the lissencephalic rodent brain. Here we aimed to determine the spatial and temporal profile of microglia and PVM in the fetal sheep brain which, like humans, is large and gyrencephalic.

 

Methods:  Fetal sheep brains were collected at 70 (n=3), 90 (n=3) and 110 (n=3) days gestation (dGA; term ~ 147 days) (i.e. 0.5, 0.6 and 0.75 of term respectively, and during the period of brain growth spurt). Coronal, paraffin sections of the forebrain were then immunostained for Iba1 (pan-microglial marker) and CD163 (PVM marker). Cells were counted in the frontal cortex (FC), somatosensory cortex (SSC), and the CA1 and CA3 regions of the hippocampus. Data was then compared between regions and ages.

 

Results: In all regions of interest there was no difference in numbers of microglia between 70 and 90 dGA. At 70 dGA microglia were present within periventricular white matter tracts. Microglial number increased between 90 and 110 dGA (~ 150%). Across all 3 time points microglial cell counts were greater in the hippocampus compared to the FC and SSC. Across all 3 time points microglial counts were higher in the CA1 region of the hippocampus than the CA3. In contrast, PVMs were not present in the FC or SSC at 70 or 90 dGA, and were then present at a ratio of ~1 PVM to 10 microglia at 110 dGA.

 

Conclusions: In the fetal sheep brain microglia are present from early in cortical development and appear to undergo a significant expansion in number in the cortical mantle and hippocampus during the brain growth spurt; PVMs appear only in the more mature fetal brain. Whether microglia increase in number by proliferation or migration is not yet known.