A degeneration study of efferent connections of the habenular complex in the opossum.

Abstract

AbstractParts of the medial and lateral habenular nuclei were removed unilaterally in each of thirteen opossums and the brains were studied for fiber degeneration by a modified Nauta method. Degeneration was seen in the ipsilateral, but not the contralateral, habenulopeduncular tract, which at the level of the interpeduncular nucleus underwent a partial decussation over it, whereas there were almost no degenerating fibers in the nucleus itself. Caudal to the nucleus extensive degeneration was present bilaterally among nuclei of the raphé and this extended into the predorsal fasciculus. Many terminals were observed in the nuclei of the raphé and within the deep tegmental nucleus. Although degenerating fibers were seen in the region of the dorsal tegmental nucleus, no terminals could be identified with certainty. Degeneration was also present in the superior colliculus.Bilateral degeneration occurred in the stria medullaris and extended to the preoptic area and the olfactory tubercle. In the dorsal preoptic area a small, but quite definite fiber bundle, separated from the posterior surface of the stria medullaris, traversed the lateral hypothalamus and passed dorsal to the mammillary bodies into the midbrain tegmentum, where it became intermingled with fibers of the habenulopeduncular tract just ventral to the red nucleus.Findings appear to indicate that in the opossum relatively few, if any, fibers of habenular origin terminate in the interpeduncular nucleus. In addition, fairly substantial evidence has been obtained to show that there are a number of efferent fibers within the stria medullaris.