Stereotaxic Approach of a Target Structure

This chapter covers the use of a stereotaxic atlas and cranial landmarks to determine the spatial coordinates of a brain structure and the handling of a stereotaxic apparatus. From a short definition of stereotaxy, the reader, already familiar with the three-dimensional reference system described in Chap. 2, is first guided through a presentation of the main atlases available for rats and mice and a detailed description of a conventional stereotaxic apparatus. A short section notably addresses the issue of stereotaxic precision and describes the principle of a vernier and its use for the measurement of the distances and positions of stereotaxic holders and micropositioners. The main part of this chapter then covers the methodology for a correct determination of the anteroposterior, mediolateral, and dorso-ventral coordinates of a brain structure from the cranial landmarks bregma and lambda. Importantly, this section also addresses the topographical organization of blood vessels that may prevent or constrain the insertion of foreign material such as cannulae at a given set of coordinates. Examples are given with two brain structures, the substantia nigra pars reticulata (SNr), approached vertically, and the vertical limb of the diagonal band of Broca, approached with a 10° mediolateral angle. Illustrated with figures this chapter is aimed to help users in performing accurate determination and measurements of stereotaxic coordinates.