Perturbations/Inflammation
NSA’s FDA Neurotoxicity Presentation 2015
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.
Astrocyte Perturbations:
GFAP IHC reveals all astrocytes “resting” or reactive and Nestin IHC reveals only reactive astrocytes.
GFAP
Nestin-Reactive Astrocytes
Microglia Perturbations
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.
Iba1 IHC
Iba1 hypertrophied microglia
Iba1 normal microglia
Iba1 vs CD68
Not all hypertyrophied microglia stain positive with CD68
Iba1-hypertrophied microglia in rat cortex
CD68 clone ED-1 (rat)
Iba1-hypertrophied microglia in mouse cortex
CD68 clone FA-11 (mouse)
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