THE RETINOHYPOTHALAMIC PROJECTION AND OXIDATIVE-METABOLISM IN THE SUPRACHIASMATIC NUCLEUS OF PRIMATES AND TREE SHREWS

This study compared the patterns of retinal projections and oxidative metabolism in the hypothalamus of squirrel monkeys, Bonnet macaques, and tree shrews. Intraocular injections of horseradish peroxidase in primates demonstrated that retinal terminals were present from the anterior to posterior poles of the suprachiasmatic nucleus (SCN). The terminals were primarily located in the ventral and ventrolateral regions of the SCN. In addition, there was a relatively even density and distribution of retinal terminals between the ipsila- teral and contralateral projections. The pattern of oxidative metabolism in the hypothalamus of the primates examined demonstrated that the SCN is highly metabolic relative to the surrounding area, and distinct regions of the SCN exhibit clear differences in metabolism. These distinct metabolic regions may reflect functional subdivisions within the SCN. In addition, elevated metabolism is foundalong the hypothalamo-optic chiasm border. The retinal projection to the hypothalamus in tree shrews was very different from that of the primates examined. The contralateral retinal projection was very dense, but the ipsilateral retinalprojection was very sparse. Retinal terminals were primarily distributed along the lateral border of the SCN. Both theSCN and the region lateral to the SCN exhibited elevated oxidative metabolism relative to the surrounding hypothalamus. © 1990 S. Karger AG, Basel.