Derek Daniels - US grants

The lordosis posture is a sex-specific, hormone-dependant reflex displayed by the female rat in response to flank stimulation by the male rat during copulatory behavior. Because of its dependence on hormonal cues, lordosis has been widely used as an opportunity to study the mechanism of endocrine control of behavior. Although numerous studies have focused on the neural circuitry that transduces hormonal cues to the neural impulses that produce the behavior, technical limitations have prevented a detailed analysis of the information processing that occurs at individual nodes of the pathway. By applying the transneuronal tracer, pseudorabies virus, I intend to identify populations of neurons, particularly in the periaqueductal gray (PAG), which are relevant to the somatic control of lordosis. Specifically, the studies described in this proposal will address questions regarding the exact site(s) of estrogen and GABA interactions within this network.

DESCRIPTION (provided by applicant): The melanocortin system plays a key role in the regulation of food intake and energy homeostasis. Genetic mutations that result in the absence of or aberrant expression of these hormones have an obese phenotype. The mechanism of action of melanocortins and how such signals engage central systems related to food intake remain unclear. Preliminary data in our laboratory indicates that the hypothalamic melanocortin system engages the mitogen activated protein kinase (MAPK) signal transduction pathway. This application proposes to further study this activation and to use it as a tool to investigate the neural pathways that are engaged by melanocortins. Specifically, the experiments within this proposal were designed to 1) examine the activation of MAPK by melanocortins, 2) to determine the source of input to neurons with activated MAPK after melanocortin treatment, 3) to determine the neurochemical phenotype of neurons with activated MAPK after melanocortin treatment, and 4) to examine changes in gene expression that result from melanocortin treatment that may mediate the effects of melanocortins on food intake and energy homeostasis.

[unreadable] DESCRIPTION (provided by applicant): [unreadable] Project summary: candidate, environment, and research. This proposal describes a 5-year training program designed to provide the candidate with the expertise needed to achieve his long-term goal of developing a career as an independent behavioral neuroscientist at an academic research university. The candidate received a Ph.D. in 2001 and has since been conducting research as a postdoctoral fellow in the department of Animal Biology and the Mahoney Institute for Neurological Sciences at the University of Pennsylvania. The Mahoney Institute for Neurological Sciences houses over 180 faculty members from eighteen departments and six schools within the University of Pennsylvania and provides an ideal training environment for the candidate. The proposed mentor, Dr. Steven J. Fluharty, is a well-established researcher in the field of behavioral neuroscience and an expert in the cellular and behavioral responses to the hormone studied in proposed experiments, the potent dipsogen angiotensin II (AngII). The research plan focuses on water, salt, and food intake, key components of body fluid, cardiovascular, and energy homeostasis. Understanding these behaviors as separate, but related forms of ingestive behavior has the potential to reveal novel insights into their control and regulation. The experiments described here are designed to determine the intracellular events associated with the hormonal stimuli for ingestive behavior. AngII receptors produce a diverse array of intracellular responses, yet the connection between any of these responses and the behaviors produced by treatment with AngII remains unclear. The experiments described here take advantage of novel pharmacological approached to determine the behavioral relevance of these divergent intracellular responses to AngII-induced ingestive behaviors and explore commonalities of ingestive behaviors in general. [unreadable] Project summary: Relevance to public health. Ingestion of water, salt, and food is critical for maintenance of homeostasis. Disorders affecting body fluid, cardiovascular, and energy homeostasis include hypertension, heart or kidney disease, diabetes, and obesity. Determining the neural mechanisms through which hormones mediate these behaviors is critical for a complete understanding of the phenomena and may lead to novel therapeutic approaches to combat the relevant disease states. [unreadable] [unreadable]

DESCRIPTION (provided by applicant): Maintaining cardiovascular health relies on a number of physiological and behavioral mechanisms that monitor, respond to, and alleviate perturbations in body fluid homeostasis. Angiotensin II (AngII), the bioactive product of the renin-angiotensin system, is an important component of these actions, especially in the response to hypovolemia. AngII affects numerous systems including the kidney, adrenal gland, gastrointestinal tract, vascular smooth muscle, and brain. The central effects of AngII include increases in water and NaCl intake, critical behaviors for the maintenance of body fluid and cardiovascular homeostasis. These behavioral effects are mediated largely through AngII type 1 (AT1) receptors, which stimulate several intracellular signaling pathways including one that leads to increased inositol trisphosphate (IP3) formation and protein kinase C (PKC) activation, and another that increases phosphorylation of mitogen activated protein (MAP) kinase. Recent experiments suggest different relative contributions of these pathways to the water and NaCl intake induced by AngII. The experiments in the present proposal use behavioral, pharmacological, electrophysiological, molecular, and neuroanatomical approaches to explore the role of these intracellular signaling pathways in the control of AngII- induced water and NaCl. Specifically, the experiments will (1) determine the roles of the Gq/IP3/PKC and MAP kinase signaling pathways in AngII-induced water and NaCl intake; (2) determine the role of individual signaling pathways on neural activity at primary and downstream sites of AngII action in the brain; and (3) test the role of these signaling pathways and receptor phosphorylation on desensitization of the intracellular and behavioral responses after multiple treatments with AngII. These experiments use a multifaceted approach and a variety of techniques to answer these questions from behavioral, anatomical, electrophysiological, and neurochemical perspectives. PUBLIC HEALTH RELEVANCE: Ingestion of water, salt, and food is critical for proper function of numerous body systems. Disorders related to energy and fluid imbalance include hypertension, obesity, heart disease, and diabetes. Understanding the neural mechanisms through which hormones mediate the ingestion of water, salt, and food may lead to novel therapeutic approaches to combat these relevant disease states.

Project Summary: Diabetes is a growing epidemic in the United States. Drugs that target glucagon- like peptide-1 (GLP-1) or its receptor (GLP-1R) are used to treat type 2 diabetes mellitus. In addition to the demonstrated therapeutic efficacy for diabetes, GLP-1 analogs decrease food intake. The effect on food intake is promising because of the clear association between diabetes and obesity. More recent studies, however, show that GLP-1R agonists also decrease water intake. This is particularly relevant for certain patient populations that are at high risk for both diabetes and dehydration. In older adults, for example, the incidence of diabetes is more than two times greater than it is in younger adults and dehydration is common and particularly problematic in the elderly. As such, knowing how GLP-1 affects fluid intake is essential to inform treatment decisions and help lead to future therapies that treat diabetes and reduce body weight, while preventing any complications related to decreased fluid intake. Studies from our laboratory suggest that GLP-1 can act in the brain to suppress fluid intake, but it remains unknown if endogenous GLP-1 is normally involved in the regulation of fluid intake. The studies in this proposal are designed to test the working model that GLP-1 does, indeed, play a role in the control of fluid intake and, more specifically, does so by acting as a satiety signal. The proposal describes experiments that test the following Specific Aims: 1) Does knockdown of GLP-1 or GLP-1R increase drinking behavior and is this effect the same in male and female rats? 2) What effect do challenges to body fluid homeostasis have on GLP-1-expressing cells in the CNS, particularly in the nucleus of the solitary tract (NTS)? 3) What is the effect of challenges to body fluid homeostasis on targets of NTS projections? These experiments use multiple approaches including viral-mediated knockdown, measures of gene expression, in vivo microdialysis, optogenetics, and refined analysis of behavior to test for changes in fluid intake, neural activity, gene expression, and release of GLP-1. These studies will improve our understanding of the control of fluid intake and could have a broader impact by improving our understanding of peptides that have divergent actions (e.g., used as hormone and neuromodulator). From a translational perspective, the experiments will provide greater insight regarding treatment options for patients with diabetes and could reveal information about the link between co-morbid disorders related to energy balance (e.g., obesity) and disorders related to fluid balance (e.g., hypertension).