© 1993 by The Society for Integrative and Comparative Biology
Molecular Mechanisms of Signal Integration in Hypothalamic Neurons1
Department of Anatomy and Neurobiology, University of Missouri School of Medicine, Columbia, Missouri 65212
Laboratory of Neuroendocrinology and Behavior, Departments of Biology and Psychology Georgia State University, Atlanta, Georgia 30303
SYNOPSIS. The purpose of this paper is to describe our studies focused on the mechanisms by which hypothalamic neurons process multiple signals and produce an integrated response. We illustrate our research strategy by reviewing our work on two separate neural systems: the hypothalamic paraventricular nucleus (PVN) and the suprachiasmatic nucleus (SCN). We have focused on different peptidergic subpopulations within these nuclei to address two issues. In the PVN, we concentrate on thepopulation of neurons containing thyrotropin-releasing hormone (TRH). These neurons are inhibited by thyroid hormones, but activated by cold exposure. Using a molecular approach, we have demonstrated that theseconflicting signals simultaneously act on the same population of TRH neurons. This system will continue to be a productive model to study the mechanisms by which neurons process multiple signals. In the SCN, we concentrate on the population of neurons containing vasoactive intestinal peptide (VIP), peptide histidine isoleucine (PHI) and gastrin releasingpeptide (GRP). We have demonstrated that injection of all three peptides into the SCN of hamsters mimics the phase-delaying effects of light on circadian wheel running behavior. In addition, the genes encoding these peptides exhibit different 24-hour profiles of changes in neurons of the SCN. These data support the hypothesis that one mechanism by which these neurons produce an integrated response is by changing the concentration ratio of co-released peptides.