The Zucker rat is a strain in which obesity is inherited as an autosomal recessive trait. Both male and female obese offspring display endocrine abnormalities, including several which affect reproductive capability. In other species, the pineal gland has been intimately linked with the reproductive system. The pineal gland in the Zucker rat has not, to date, been examined. The purpose of this project is to initiate a preliminary study of the pineal gland in this species, examining both structural and biochemical aspects. All experiments will be performed on fat/lean pairs of male Zucker rats so that differences in obese animals can be evaluated. Structural examination of the gland will consist of three separate studies: 1) an investigation of the basic morphology of the pineal gland, performed at both light and electron microscopic levels. This study will permit classification of the gland according to the criteria established by Vollrath (1979). 2) an analysis of changes in pineal morphology which result from exposure of the animal to a stimulatory (6:18) light:dark cycle. In this study, three groups of rats will be examined: a control group maintained on a 14:10 light:dark cycle, a second group exposed to a 6:18 light:dark cycle for a period of six weeks, and a third group which will undergo olfactory bulbectomy and then be exposed to the 6:18 light:dark cycle for six weeks. 3) a study of the source of innervation of the pineal gland. This will be determined by severing the superior cervical ganglia with subsequent examination of the pineal tissue for degenerating nerve terminals. The superior cervical ganglia in other species provide significant innervation to the pineal gland. Biochemical examination of the pineal gland will consist of HPLC (high performance liquid chrmatography) analysis of 24-hour changes in the glandular content of serotonin and melatonin. These preliminary studies will provide a basis for additional work on the pineal gland in the Zucker rat.