Trauma‐induced golgi‐like staining of neurons: A new approach to neuronal organization and response to injury

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Abstract
A new esterification‐silver approach to the directed staining of the dendritic trees of traumatized neurons is described. Stained neurons compare favorably to those labeled with silver chromate Golgi impregnations in the visualization of dendritic arbors. Cells in all parts of the brain, including the hypothalamus, hippocampus, cerebral cortex, cerebellum, striatum, spinal cord, thalamus, and olfactory bulb, can be detected after focal trauma to that region. Selection of neurons to be stained is made by increasing their affinity for silver with many different types of directed neuronal trauma, including micropipette wounds, pressure, surgical incision, chemical cytotoxicity, and impact trauma. Trauma to one area of the brain results in dendritic arbors staining only in the injured area; other areas of the brain are free of dendritic staining. Injury can be produced either in vivo or in vitro. In vitro injury to neurons allows a high degree of localization and facilitates the analysis of neuronal response to trauma in the absence of complicating factors such as blood flow and secondary injury. The selective affinity for silver staining in this approach is increased very rapidly, allowing detection of traumatized cells fixed minutes after injury. Brains of all mammals used appear to stain similarly, including the rat, mouse, pig, and human. Axons, although labeled less frequently than dendritic arbors, are induced to stain just as rapidly as dendrites. The ability to visualize a large part of the dendritic tree after trauma allows the segregation of neuronal subtypes on the basis of their differential response to injury. Subpopulations of cells in the same area of the brain appear to respond differently to trauma. Differential response of neurons to trauma can easily be detected. For instance, slight variations in trauma can be used to label selectively the major subpopulations of neurons in the hippocampus, including pyramidal cells, interneurons near the pyramidal cell layer, or granule cells. Similarly, neurons of the hypothalamic paraventricular and arcuate nuclei respond to compression trauma much more dramatically than other cell types in the same region of the hypothalamus. Hypothalamic neurons were studied extensively, particularly in regions that are difficult to routinely stain with Golgi impregnations, including the arcuate, paraventricular, supraoptic, and suprachiasmatic nuclei. Trauma to these areas was made in vitro after removal of the brain from the skull, allowing easy access to the ventral surface of the brain. The approach described here is useful for studying dendritic arbors throughout the nervous system, for addressing a number of questions relating to early cell injury and for detecting which neurons have been damaged in different models of neuronal function on the basis of selective cellular damage. The cellular basis for the specific labeling is common to a wide variety of neuronal insults, suggesting a commonality of mechanism for neuronal response to injury. We postulate that cytoskeletal changes induced by injury may be a cellular substrate for the esterification‐related silver labeling.