Evaluation of Perturbations/Inflammation
The detection of perturbations in the brain is often employed as a key tool in safety assessments. The presence of a perturbation signal is an undesirable finding in safety testing and represents a degree of harm has been caused to the brain. In some approaches, perturbations are used as an indicator to search for signs of permanent damage, serving as a “canary in a coal mine.” In the context of some studies, the detection of a perturbation in itself is enough to warrant a conclusive safety concern. A perturbation represents a stress to the health of the brain, but a perturbation signal alone does not indicate the infliction of permanent damage to the brain. Other endpoints discussed in the next section are able to differentiate an injury/perturbation that resolves versus an injury that leads to permanent damage.
GFAP IHC reveals all astrocytes “resting” or reactive and Nestin IHC reveals only reactive astrocytes.
Iba1 IHC and NSA’s internally developed Reactive Microglia stain are capable of revealing activated microglia. Reactivity in Iba1 stained sections is determined by hypertrophy of the cells. The Reactive Microglia stain shows cells that are in a reactive state due to an acute perturbation. Microglia in a reactive state due to a chronic perturbation are not visible with this method.
NSA’s Reactive Microglia Stain
Resident microglia of the brain become reactive following various forms of insult, including chemical trauma and viral infection (a–c) and physical trauma (d). The NSA protocol stains reactive microglia but not resting microglia. Microglial features visible with our stain are the same as with lectin staining (IsoB4) and antibody staining with CD68 (FA11 clone for mice and ED1 clone for rats). This protocol easily reveals reactive microglia in different species (rat, mice, primate) as opposed to antibodies or lectins that tend to be species dependent.
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