Sulforhodamine 101 (SR101)

Overview

Sulforhodamine 101 (SR101) is a red fluorescent dye which is water-soluble and non-fixable.

It is a preferential astrocyte marker both in vitro and in vivo and is frequently used in neurophysiological experiments. It also labels oligodendrocytes.

The exact uptake mechanism of SR101 is unclear. It is thought that SR-101 is taken up by astrocytes and diffuses through the astrocyte syncytium via gap junctions.

Uses and applications

The dye is commonly used for in vivo brain imaging and allows in vivo imaging of oligodendrocytes. It may be applied topically to the exposed cortex or administered via injection.

The dye has a wide range of applications. For example, it is often used to identify astrocytes, to counterstain astrocytes and has been extensively used with calcium-sensitive dyes to distinguish calcium signals derived from neurons and astrocytes.

Caution and care

Care should be taken when using the dye as it is not as specific for astrocytes as initially reported and as the dye labels oligodendrocytes, it cannot be assumed that all SR101 labelled cells are astrocytes.

The dye also differs in staining intensity depending on the brain region being investigated (it does not label astrocytes in brainstem slices as strongly or specifically as in the hippocampus or cortex).

SR101 also has effects on excitatory neuronal activity and can induce cortical seizure-like activity.

Hülsmann et al (2017) recommend that to minimize excitatory side effects, SR101 concentrations should be kept as low as possible or the labelling procedure could be carried out after the experiment.

If possible, researchers should carry out additional measures to confirm specificity of SR101 staining in their experiments (e.g. electrophysiological whole-cell recordings of SR101-labeled cells and post hoc IHC).