Intracranial landmarks and other techniques to further improve the precision of stereotaxic tracer injections.

This study is meant to combine traditional aspects of tracer microinjections using bone landmarks like bregma and lambda with novel procedures in which specific parts of the brain can serve as reference points. For telencephalic and diencephalic injections, the brain surface, the interhemispheric groove and the straight sinus can be used as absolute zero points for dorso-ventral, medio-lateral and rostro-caudal coordinates, respectively. In case of brainstem targets, the surface of the rhomboid fossa, the posterior spinal artery and the obex could serve as reference points along the above-mentioned coordinates. The application of high-precision stereotaxic measurements based on intracranial landmarks and sophisticated surgical procedures can yield well-targeted, small and well circumscribed injection sites that make possible the mapping of discrete nuclear subdivisions or delicate nuclei in the brain.