Artifacts in routinely immersion fixed nervous tissue

In order to demonstrate the types of artifacts commonly seen in inadequately fixed central nervous system (CNS) tissues, rat brains were fixed by either perfusion or immersion in 10% neutral buffered formalin. Perfused brains were either removed immediately or left in situ for 1 hr prior to removal. Some of the brains destined for immersion fixation were first allowed to sit for either one-half or 1 hr in either room air or in an isotonic saline solution. Other brains were subjected to various handling procedures immediately after removal from the cranial vault in order to simulate the types of trauma which commonly occur during routine removal/dissection. Commonly observed artifacts included the presence of basophilic (dark) neurons, retraction spaces around neurons, vessels, and glial cells, displacement of the neuropil, and neuropil vacuolar change. The results of the fixation and handling procedures utilized in the collection of these brains substantiate the well documented fact that the least degree of artifact will be seen in brains fixed by perfusion and left in situ for a reasonable period of time (several hours) prior to removal.