A Simple Device to Orientate Rat Brain for Cutting According to De Groot's Atlas. ∗

Most experimental work involving microscopic examination of the rat brain is done with the help of De Groot's Stereotaxic Atlas ( 1 ). In the stereotaxic apparatus the upper jaw of the rat is placed on the upper incisor bar at a height of 5 mm above the level of the interaural line. The horizontal zero plane is tangent to the upper surface of the incisor bar, and passes intracerebrally through the anterior and posterior commissures. The vertical zero plane is taken perpendicularly to the horizontal plane. The atlas is composed of tracings taken from transverse sections parallel to the chosen vertical plane. De Groot states that he has chosen this plane because it effects a somewhat equal distribution of important centers on either side in the regions of the diencephalon and telencephalon.

Duplication for brain cutting of the angle found in the atlas is the keynote to easy and rapid comparison of histological sections with the tracings. This angle can easily be achieved in every rat brain that is serially cut if the simple device shown in Fig. 1 is used to cut the anterior tip of the brains which have been fixed for 24 hours in formalin. The angle at which the brain is positioned in the stereotaxic apparatus can be duplicated after the brain has been removed from the skull by placing it on a wooden block which has an angle of 28°. A sharp blade can then be lowered perpendicularly to the base of the inlstrument. This produces a transverse section which slants posteriorly and forms an angle of approximately 118° with the ventral surface of the blrain (Fig. 2). Embedding, after trhe fixation has been completed, is done by placing this anterior cut surface on the bottom of the embedding dish. When the block is later set up on the microtome, almost no adjustment is necessary to obtain the exact orientation described in the atlas. Thus no long experience is needed by the technician, and the rapid adjustment will increase his efficiency. If a great deal of work is involved the utility of this device is evident.