Subcortical projections of the pericruciate cortex of cat. An autoradiography study

This communication deals with an autoratiographic analysis of two experiments in which multiple injections of 35S methionine were performed around the cruciate sulcus of cat. One case was studied in coronal sections and the other in sagittal sections. The thalamic projections include: (1) the anterior pole of nucleus reticularis; (2) the rostral pole of the ventral thalamus (VA and VL); (3) parts of the ventrobasal complex (VPLm and (VPM); (4) intralaminary centers, in particular CL; and (5) a region around the ventral end of the fasciculus retroflexus. Instead of a terminal projection, the latter appears to receive a system of collateral fibers which leave the cerebral peduncle at meso-diencephalic levels. An intricate pattern of negatively outlined centers was found. One of them ("nucleus Q") appears as a relatively large, non-labelled field within the ventrobasal thalamus, surrounded by a "halo" of labelled territories from which it is separated by a sharp outline. Other circumscribed negatively outlined fields appear as "islands" interposed between CL and VL. Surprisingly, hardly any target structures were seen beyond the mesencephalon, with the exception of the ipsilateral pontine nuclei and the so called lateral reticular nucleus of the medulla oblongata, contralaterally. The pyramidal tract was well labelled at all levels indicating a large projection to the spinal cord. The reason why no cortico-reticular projections were labelled is not clear.