A major, long-term interest of our lab is the reproductive neuroendocrine system of the brain In mammals, reproduction is governed by intricate neural and hormonal communication between the brain, pituitary gland and gonads.At the top of this hierarchy are gonadotropin-releasing hormone (GnRH) neurons that are responsible for the pulsatile secretion of luteinizing hormone (LH) from the anterior pituitary gland (Fig. 1). Changes in the frequency of GnRH and LH pulses have a profound effect on the reproductive system, but identification of the “GnRH pulse generator” in the brain has remained a major unanswered question. Similarly, GnRH neurons are under feedback control of gonadal steroid hormones, such as estradiol (E2) and progesterone (P4) secreted by the ovary. However, since GnRH cells lack the type of receptors responsible for feedback control, other neurons that are upstream of GnRH cells must be responsible for this feedback.
Thus, a second unanswered question concerns the pathways by which steroid hormones regulate GnRH secretion, and thereby play a critical role in control of puberty, the estrous/menstrual cycle, and other reproductive events.
Together with Drs. Robert Goodman (West Virginia University) and Lique Coolen (University of Mississippi Medical Center), in 2007 we identified a single subset of neurons in the arcuate nucleus of the hypothalamus that co-expresses three neuropeptides, kisspeptin, neurokinin B and dynorphin, which we later termed “KNDy” neurons. We were among several groups to propose that KNDy neurons comprise a critical component of the GnRH pulse generator, and since that time compelling evidence has accumulated supporting the view that KNDy cells serve as a final common pathway for external and internal regulatory signals that control GnRH secretion in a wide range of mammals. More recently, working with our colleague, Dr. Vasantha Padmanabhan (University of Michigan), we have also focused on the potential role of KNDy cells in reproductive disease. Specifically, we found that the balance of KNDy peptides is altered in an animal model of polycystic ovarian syndrome (PCOS), the most common reproductive disorder among adult women, perhaps leading to the dysfunction of steroid feedback control seen in that disease.
The primary animal model we use for our studies of GnRH and KNDy neurons is the sheep. The sheep has several advantages as an experimental model for neuroendocrine research, most notably the ability to directly measure GnRH from blood collected at the surface of the pituitary gland from unanesthesized animals. This allows us to obtain precise and repeated measurements of GnRH release during pulsatile secretion and other endocrine states. Together with the large size of the sheep brain, this also enables us to perform experiments interrogating structure-function relationships in the brain at a detailed level of analysis. In our work, we employ a wide range of molecular, anatomical, and physiological techniques, including protein and mRNA analyses, confocal immunocytochemistry, electron microscopic immunocytochemistry, in situ hybridization, stereotaxic brain surgery, neuroanatomical tract tracing, intracerebral delivery of pharmacological agents and viral vectors, serial sampling of CSF, portal and peripheral blood, and radioimmunoassay of circulating hormones.
*In last four years