23 February 1990
Vol 247, Issue 4945

About The Cover

Dark-field photomicrograph of the anterior hypothalamus of a hamster immunostained with antibodies to vasopressin, showing the paired suprachiasmatic nuclei (SCN) between the third ventricle and optic chiasm (top) and the magnocellular vasopressin cells (yellow fireworks) of the paraventricular nucleus, above which is the SCN. The SCN, the locus of the mammalian biological clock, can be identified as two oval structures at the base of the brain (toward title). See page 975. [Photographic image by Russell Foster]