We study the way an important area of the brain, the hypothalamus, regulates the secretion of hormones from the pituitary gland that are involved in reproductiv e processes.

We are particularly interested in the control of secretion of prolactin, the hormone that controls milk synthesis in the mammary gland. The hypothalamus control s prolactin secretion from the anterior pituitary gland in an inhibitory manner. The inhibitory chemical made by nerve cells in the hypothalamus is dopamine. Wh en released into the small blood supply connecting the hypothalamus with the pituitary gland, dopamine inhibits prolactin secretion. Prolactin-releasing stimuli , such as nursing by the hungry infant, inhibit dopamine release from the hypothalamus.

Using approaches such as culture of pituitary cells, radioimmunoassay for measuring prolactin, immunocytochemistry for visualizing dopamine nerve cells and thei r gene activity and high performance liquid chromatography along with electrochemical detection for measuring changes in dopamine in the brain we are pursuing t he following problems:

• It was previously believed that only one population of dopamine nerve cells in the hypothalamus affect prolactin secretion. We have identified two others th at directly affect prolactin secretion and are in the process of characterizing the relative contribution of each

• Prolactin inhibits its own secretion by activating dopamine nerve cells in the hypothalamus. We have identified prolactin receptors on dopamine nerve cells and are in the process of determining how prolactin regulates the activity of these cells.

• We have found that dopamine is not only inhibitory to prolactin secretion, but under certain circumstances it can be stimulatory. We are in the process of d etermining how dopamine can both stimulate and inhibit the same pituitary cell that secretes prolactin.

• We have discovered that a chemical found in the cells lining the blood vessels of all mammals, endothelin, affects the secretion of most of the anterior pit uitary hormones. We are now determining the role endothelin plays in the secretion of each.