A Brain Blocker/slicer for the Stereotaxic Plane of the Rat Brain in Stereotaxic Coordinates

satisfying the detail and precision required by researchers in the mid 1960s. However, the requirements for detail and precision have greatly increased in recent decades to the point that, for instance, nearly no researcher targets the general area of the hypothalamus, but instead they target one of the roughly 60 subnuclei in which the hypothalamus has been parcelled. In early 1980 when we commenced the construction of our atlas, we made an in-principle decision that the main feature of our work would be satisfactory slcrcotaxic accuracy. We spent one year and cut 115 brains before we obtained three brains which we thought were cut with sufficient stereotaxic accuracy. Throughout our work we used the Kopf small animal stereotaxic frame. We used fresh tissue to avoid the differential shrinkage and distortion caused by fixation. The atlas coordinates for some central nuclei ((he trochlear and the bed nucleus of the anterior commissure for example) vary by less than 0.2 mm in the coronal, sagittal and horizontal planes. For structures located further from the stereotaxic reference points, the atlas coordinates may differ by as much as 0.5 mm. Even if rats of different strains and sex are used, the coordinates will be substantially accurate if the weight is close to that on which the atlas is based (290g). But this is not the end of the story; the evolution of quality stereotaxic procedure is not complete without a reliable method for ensuring that brain histological preparations are aligned in the same plane as the atlas used. We describe here a blocker for ensuring accurate sectioning of the rat brain so that histological sections can be routinely cut in a plane approximating that of The Rat Brain in Stereotaxic Coordinates.