COMPUTER-ASSISTED 3-DIMENSIONAL RECONSTRUCTION OF BRAIN-REGIONS FROM SERIAL SECTION DIGITIZED IMAGES - APPLICATION TO THE ORGANIZATION OF STRIATONIGRAL RELATIONSHIPS IN THE RAT

We have developed a software which allows the three-dimensional recons truction of brain regions from serial section digitized images. This s oftware, which generates wire-frame three dimensional models, requires at least a 486 PC microcomputer running Microsoft Windows(R) (3.x or 95). Mosaics of high resolution images, covering large brain areas, di gitized by means of a camera fitted on a microscope equipped with a mo torized stage, are handled by our software as single high resolution i mages. Serial sets of such images may be segmented and manually aligne d. We have utilized this software to study the organization of striata l efferences within the substantia nigra pars reticulata, as well as t he distribution of neuronal cell bodies within the substantia nigra pa rs compacta after micro-ionophoretic application of wheat germ aggluti nin conjugated to horseradish peroxidase into the orofacial sensorimot or region of the striatum. The three dimensional representation of ant erogradely labeled striatal efferences confirmed and determined the la mellar organization previously postulated from serial plane section mi crographs. The distribution in the rat brain of retrogradely labeled n igro-striatal cell bodies, which had not yet been studied after inject ion of tracer into functionally identified regions of the striatum, re vealed two subpopulations: a first one rather dense, located in the an terior half of the substantia nigra pars compacta, which was in close register with the striatal efferences, and a second one, much more sca ttered and less numerous, located in the posterior part of the structu re which extended far from the substantia nigra along the medio-latera l axis. Our three dimensional reconstruction software will now be used to study the neuronal connectivity within the basal ganglia and other brain regions.