Sectioning of brain tissues

INTRODUCTIONA fixed brain, although harder than the brain in its natural state, is still not hard enough to cut into very thin slices. To make uniform, thin sections, the brain must be frozen. A wide variety of sectioning devices are available, each with their own requirements. With a microtome, for example, a very sharp knife is drawn manually across a brain that has been frozen to a chilled platform using dry ice. After each cut, the knife is lowered mechanically by a preset amount, giving consistent sections of a required thickness. A drawback of this instrument is that the temperature of the platform can fluctuate, thus causing changes in the quality of the sections. Other instruments, such as a cryostat, maintain the platform-mounted brain and the knife inside an enclosed refrigerated compartment. The temperature is kept at -20°C, and electronics are used to control the speed of the knife and the thickness of the sections. Some models can be set up to make a series of sections automatically.