Final answer:
Red neurons appear within 12 to 24 hours after neuronal injury, and changes in the Nissl substance become visible within 1 to 2 days. These markers of damage are identifiable using immunohistochemistry and fluorescent microscopy techniques.
Step-by-step explanation:
Neuronal damage can be visualized through certain morphological changes that occur in the cells, and two well-known markers of neuronal injury are red neurons and changes to the Nissl substance. Red neurons refer to the appearance of eosinophilic (red-staining) neuronal cell bodies that typically manifest within 12 to 24 hours following a damaging event, such as a lack of oxygen (ischemia) or other types of injury. Nissl Substance, which comprises the rough endoplasmic reticulum and ribosomes involved in protein synthesis, typically dissipates or disappears after neuronal injury, a process termed chromatolysis, and this typically begins to be visible within 1 to 2 days post-injury.
Scientists can identify and visualize such changes in neurons by using various imaging techniques. For example, immunohistochemistry can be used to attach fluorescent labels to molecules indicative of cell damage or regeneration. As described in the provided information, fluorescent microscopy can be employed to visualize newly generated neurons in brain tissue by detecting the incorporation of bromodeoxyuridine (BrdU) into the DNA of cells in the S phase of cell division. This technique, among others, helps researchers understand the complex processes of cell damage and regeneration in the nervous system.