Keywords: Neuroendocrinology; Vasopressin; Oxytocin; Osmoreception; Gene Regulation
The major focus of my laboratory has been understanding the mechanisms that regulate gene expression and secretion of the hormones, vasopressin (also called antidiuretic hormone) and oxytocin. They are produced by neurons in the hypothalamus, are released from the neurohypophysis into the blood stream, and regulate respectively the two functions that are hallmarks of mammalian physiology: formation of a concentrated urine by the kidneys and mammary gland function.
A unique aspect of this program has been the development and extensive use of an organ-cultured explant preparation of the hypothalamo-neurohypophyseal system that allows study of hormone release and gene expression in an in vitro system. The explant also includes osmoreceptive elements critical for the regulation of vasopressin secretion. Thus, it has significantly advanced our understanding of the mechanisms underlying fluid and electrolyte disturbances observed clinically (e.g. in congestive heart failure, schizophrenia, and aging). These explants are currently being used to evaluate the role of neurotransmitters and steroid hormones in the regulation of vasopressin and oxytocin secretion.
We have recently developed techniques to perform live cell calcium imaging on vasopressin and oxytocin neurons in the same preparation used for the hormone release studies using calcium sensitive fluorescent dyes. This allows us to monitor cellular signals induced by the neurotransmitters and other regulatory molecules that regulate hormone release. The availability of dyes sensitive to a wide range of cell signaling molecules suggests that we will be able to expand this line of research to study the roles of nitric oxide, H+ ions, and other molecules in mediating neurotransmitter regulation of hormone release.
Dispersed primary hypothalamic cultures are also being used to investigate the signals important in regulation of oxytocin and vasopressin gene expression. An example of a neuron from these cultures is shown below. It could either be an oxytocin neuron, as oxytocin is known as the ‘love hormone’ or it could be a vasopressin neuron reflecting the role of vasopressin in regulating cardiovascular function. Other techniques employed in the laboratory include immunohistochemistry, in situ hybridization, image analysis, radioimmunoassay, and mRNA extraction, quantification, and characterization using Northern analysis and RNA protection assays.
Gomes, D.A.*, Z. Song*, W. Stevens, and C.D. Sladek. Switch from desensitizing to non-desensitizing P2X receptors mediates sustained stimulation of vasopressin release. Am J Physiol: Regul Integr Comp Physiology 297(4):R940-9, 2009. *Contributed equally to this work. PMC2763823.
Song, Z. D.A. Gomes, W. Stevens, C.D. Sladek. Multiple 1-Adrenergic Receptor Subtypes Support Synergistic Stimulation of Vasopressin and Oxytocin Release by ATP and Phenylephrine. Am. J. Physiol.: Regul Integr Comp Physiology (Articles in Press, Sept. 2010).
Somponpun, S.J. and C.D. Sladek. Osmotic Regulation of Estrogen Receptor Beta Expression in Vasopressin and Oxytocin Neurons. J. Neuroscience 23 (10):4261-4269, 2003.
Howe, H.E., S.J. Somponpun, and C.D. Sladek. Role of neurokinin 3 receptors in supraoptic vasopressin and oxytocin neurons. J. Neuroscience 24:10103-10110, 2004.
Song, Z., S. Vijayaraghavan, and C.D. Sladek. Simultaneous exposure to ATP and phenylephrine induces a sustained elevation in the intracellular calcium concentration in supraoptic neurons. Am. J. Physiol. Reg. Integrative Physiol. 291:R37-R45, 2006.
Urban, J.H., R. Leitermann, M.R. de Joseph, S.J. Somponpun, M. Woleck, and C. D. Sladek. Influence of dehydration on the expression of neuropeptide Y Y1 receptors in hypothalamic magnocellular neurons. Endocrinology, 147:4122-4131, 2006.
Song, Z., S. Vijayaraghavan, and C.D. Sladek. ATP increases intracellular calcium in supraoptic neurons by activation of both P2X and P2Y purinergic receptors. Am. J. Physiol. Reg. Integrative Comp. Physiol., 292(1):R423-31, 2007.
Sladek, C.D. and W.E. Armstrong. The Neurohypophyseal System. Article in The New Encyclopedia of Neuroscience, a project of the Society for Neuroscience. Available online, 2008.
Sladek, C.D. and S.J. Somponpun. Estrogen Receptors: Their Roles in Regulation of Vasopressin Release for Maintenance of Fluid and Electrolyte Homeostasis. Frontiers in Neuroendocrinology 29(1):114-27, 2008.
Sladek, C.D. and Z. Song. Regulation of vasopressin release by co-released neurotransmitters: Mechanisms of purinergic and adrenergic synergism. Progress in Brain Research (Advances in Vasopressin and Oxytocin – From Gene to Behavior; I.D. Neumann and R. Landgraf, eds) 170:93-107, 2008.