Abstract
Differential fixation of rat brain has been described using formaldehyde, glutaraldehyde and hydroxyadipaldehyde by perfusion or prolonged immersion. Fixation by prolonged immersion appears preferable since it produces a similar result with greater simplicity. Distribution of reaction product resulting from adenosine triphosphate hydrolysis in these fixed brains appears different and characteristic for each of these fixatives when they are used in this manner. More adenosine triphosphatase activity in rat brain was observed following formalin fixation than after fixation with either glutaraldehyde on hydroxyadipaldehyde; in this respect formalin fixation is recommended for over-all study of adenosine triphosphatase activity in the brain. The use of glutaraldehyde and hydroxyadipaldehyde seems indicated when study of enzymes surviving these fixatives is desired. Beside varying inactivation by different aldehyde fixatives, adenosine triphosphatase activity of rat brain has been characterized by distinct substrate preference and by chemical inhibition.
Specificity of adenosine triphosphatase localization in rat cerebrum by electron microscopy seems enhanced by such differential fixation since differences in enzymatic activity not previously apparent can he recognized in closely related structures such as components of the blood-brain barrier. Since adenosine triphosphatase activity of astroglia in corpus callosum as well as in subpial and subependymal glial networks is glutaraldehyde resistant, an enzymatic similarity perhaps related to their physiological activity is indicated in these cells. Astroglia of cortex evince enzyme activity that survives only formalin fixation, suggesting a different function for cortical astrocytes. The enzymatic activity of oligodendrocytes appears to be a diphosphatase inactivated by glutaraldehyde and hydroxyadipaldehyde, and in this is strikingly similar to diphosphatase of Golgi apparatus.