Evaluation of 5 Intermediate Structural Variations of Microglia Within an Organotypic Hippocampal Slice Model After Regionalized Toxic Injury

The dendritic cell of the CNS, the microglia (MG), is an initiation point of the immunological response within the post-blood-brain barrier (BBB) compartment. Microglia drastically changes in response to cell stress to a much different non-dendritic morphologies. This investigation postulates that if the first MG responses to toxic injury are isolated and studied in greater morphological detail, there is much to be learned about microglia's metamorphosis from and M2 to an M1 state. The organotypic hippocampal slice was the experimental setting used to investigate microglial response to toxic injury; this isolates dendritic cell to post-BBB cells dynamics from the impact of nonspecific of in vivo blood-derived signaling. Within the context of biochemically verified precise toxic cell injury/death (induced with mercury or cyanide in combination with 2-deoxy-glucose) to a specific region within the hippocampal slice, MG's morphological response was evaluated. There was up to 35% increase in microglia activation proximally to injury (CA3 region) and no changes distally (DG region) when compared to control slices treated with PBS. Maximum microglia activation consisted of a 3 plus-fold increase in the distance between the nucleus membrane and the cell membrane, which underscores an extensive and quantifiable amount of membrane rearrangement. This quantification can be applied to contemporaneous AI image analysis algorithms to demarcate and quantify relative MG activation in and around a site of injury. In between baseline and activated MG morphologies, 5 intermediate morphologies (or structural variations) are described as it relates to its cell body, nucleus, and dendrites. The result from this study reconciles details of MG's structure to its holistic characteristics in relation to parenchymal cell stress.