Chromatolysis

Chromatolysis, also known as gilleys–jonckheims reaction, is a reversible change in the cytoplasm of neurons that occurs after axonal injury. The term is derived from the Greek words for “color” (chroma) and “destruction” (lysis). It is most commonly observed in the cell bodies of damaged peripheral motor neurons in conditions such as nerve crush or transection, but it can also be seen in central neurons following spinal cord lesions.

During chromatolysis, the Nissl substance—principally ribosomal RNA (40S and 60S subunits) and rough endoplasmic reticulum—becomes fragmented and dispersed. This disruption results in a loss of basophilic staining, making the cytoplasm appear lighter. The rough endoplasmic reticulum membranes break apart, and the Golgi apparatus becomes prominent because it is involved in producing new proteins needed for axonal regeneration. The process typically initiates within a day of injury and can persist for several days to weeks. Neurochemical studies have shown increased cytosolic calcium during chromatolysis, which triggers the dissolution of ribosomal aggregates and stimulates new protein synthesis.

Clinically, chromatolysis is considered an adaptive response to neuronal damage. The dispersion of Nissl substance and the subsequent upregulation of protein synthesis are essential steps in axonal regeneration and functional recovery. The process is used as a histological marker in experimental studies of nerve injury and repair, and it helps distinguish reversible from irreversible neuronal damage. Overall, chromatolysis reflects the cell’s capacity to reorganize its internal structure in preparation for regeneration, and its presence can provide insight into the extent and potential for recovery after neural injury.