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This Special Issue of Physiology & Behavior contains invited manuscripts based on invited symposia and plenary address presentations made at the 2007 Annual Meeting of the Society for the Study of Ingestive Behavior (SSIB). The meeting was held in Steamboat Springs, Colorado, July 24–28, 2007. The 4-day meeting included plenary addresses, symposia, poster and oral sessions covering a range of topics related to the psychological, physiological and neural controls of various aspects of ingestive behavior. The collection of papers in this Special Issue represents a small proportion of the many excellent presentations included in the invited symposia and plenary addresses.
The first three papers are based on the annual Masterfoods Lecture Series (now called the Mars Lecture Series). The first is by Martin Myers on the molecular and neural mediators of leptin action. Here Myers and colleagues discuss how leptin affects a wide range of physiological processes, from satiety to the incentive salience of food to reproduction and autonomic nervous system activity, via its long form receptor (LepRb) in specific neuronal populations. The molecules that are responsible for mediating leptin’s many actions are now being elucidated and represent an exciting area of future research. This review provides a broad introduction to several leptin-related papers included in this Special Issue.
Caloric restriction (CR) has been demonstrated to prolong lifespan in several species. However, the mechanisms through which CR results in increased longevity are not fully understood. Masterfoods Lecturer Eric Ravussin colleagues review the major physiological, psychological and behavioral changes that result from CR in humans enrolled in the first randomized study of CR, “CALERIE” (Comprehensive Assessment of the Long-term Effect of Reducing Intake of Energy).
The final paper of the Masterfoods Lecture Series was contributed by Michael Tordoff who presents a general overview of gene discovery methods for the non-geneticist. He discusses topics such as phenotype characterization, mouse strain selection, generation of hybrid crosses, interval mapping, congenic strain production, and candidate gene analysis. Using his own studies of calcium consumption as an example, he illustrates the potential for gene discovery methods to uncover novel mechanisms involved in the controls of ingestive behavior.
The 2007 annual meeting marked the debut of the Presidential Symposium aimed at highlighting research of talented new faculty investigators in the field of ingestive behavior. Christopher Morrison reviews data supporting the notion that the leptin signaling system effectively defends against both positive and negative energy balance in order to maintain normal body weight. However, this same system often becomes insufficient in those individuals that become obese. It is unclear why this system fails in obese individuals and is the subject of active investigation. Heike Munzberg presents evidence for differential sensitivity of leptin receptor bearing neurons in various hypothalamic areas suggesting a hierarchical organization within those areas. Data suggest that LepRb expressing neurons in different areas of the hypothalamus access leptin via different mechanisms and that non-arcuate leptin target sites are at least as important compared to the arcuate nucleus in mediating severe phenotypes such as obesity and diabetes in leptin and LepRb deficient mice. In the third article of this series, Darleen Sandoval focuses on the role of glucagon-like peptide-1 (GLP-1) in the regulation of glucose homeostasis and food intake. The role of GLP-1 in the maintenance of glucose homeostasis has been thought to depend completely on peripheral actions of the peptide. However, this review proposes to challenge that idea with recent evidence that links CNS GLP-1 to glucose homeostasis and as such integrates the roles of both CNS and peripheral GLP-1 systems in regulation of glucose. The last paper in this series by Susana Pecina reviews the role of opioid signaling in the nucleus accumbens and the contribution of these mechanisms to food reward guided behaviors. She reviews the “liking” and “wanting” aspect of food rewards and discusses the challenges of studying these two aspects of food reward in animal models. Based on data using “fos plume” technique, ‘liking’ and ‘wanting’, she proposes that the bases of these two attributes of food rewards can be anatomically dissociable in the nucleus accumbens.
In a symposium about Energy Expenditure in Relation to Food Intake and Body Weight Regulation, Dan Bessesen and colleagues describe their work from both rodent and human experiments and demonstrate that the obesity-resistant (OR) rat, as well as the OR human, avoids weight gain by maintaining fat oxidation and decreasing caloric intake when provided with a high fat diet or with overfeeding suggesting a mechanism through which a lean state may be maintained. They propose that ingested nutrients are distributed and redistributed, or ‘trafficked’, among tissues over time. This process in turn may promote or protect against weight gain by altering the reliability of nutrient sensing in a manner that promotes more accurate coupling of dietary fat intake and oxidation.
Two papers originate from symposia entitled Neurobiology of Anorexia Nervosa, Bulimia Nervosa and Related Behaviors. The first is from Jaquelien Hillebrand who discusses leptin’s potential down-stream mediators responsible for its effect on hyperactivity, a common symptom of anorexia nervosa. The data have implications for understanding mechanisms for activity-based anorexia in an animal model and over the long term may lead to improved treatment for anorexia nervosa. The second paper from Alan Geliebter and colleagues details an experiment examining the gut peptides, ghrelin, PYY and GLP-1, in response to a test meal in obese subjects with and without binge eating disorder (BED). Ghrelin was lower in the pre-meal period and demonstrated a blunted decline in the post meal in BED obese subjects, while PYY and GLP-1 failed to show a difference between the BED and non-BED groups. These findings support the assertion that an alteration in ghrelin signaling is likely to contribute to the overeating aspect of certain eating disorders.
Two contributions come from a symposium on Human Thirst and Sodium Appetite. Richard Mattes and colleagues focus on the relationship between hunger, thirst, eating and drinking in free-living adults. This review draws upon recent data as well as the authors’ own observational studies to examine how shifts in dietary composition or patterns may impact the relationships between hunger and food intake or thirst and drinking ultimately resulting in positive energy balance. Kim Johnson’s group highlights the potential mechanisms underlying excessive sodium intake following sodium depletion or restriction. They propose that hedonic or affective consequences and neural plasticity may follow major fluctuations in sodium balance thus suggesting that reward pathways may be involved in promoting excessive sodium intake.
There are three contributions from the symposium entitled “Social Psychology of Eating: Schachter’s Legacy.” Peter Herman and Janet Polivy revisit Stanley Schachter’s theory on the “external cues” in the control of food intake in humans. In the process of reviewing the beginnings, modifications, and challenges to the Schachter’s original theory of external cues, they provide support for the sensory-normative distinction in the control of eating behavior. This theory proposes that sensory factors (e.g., food palatability) inclined people to maximize their intake, whereas normative factors (e.g., social constraints) restricted what might otherwise be unlimited intake. The next paper in this series by Janet Polivy and colleagues examines the effectiveness of chronic food restriction for extending the lifespan of humans in an environment of abundant external food cues. Laboratory animal studies and preliminary human studies have suggested a healthy benefit from chronic food restriction (60–70% of ad libitum food intake). The authors argue, however, that the persistence of external food cues in line with in a free-living human environment will make it difficult and often unbearable to adhere to severe caloric restriction necessary to achieve the putative health benefits of long-term chronic food restriction. The authors support this position by providing evidence that food cues have a strong effect on the control of food intake, addressing the lack of food cues in a laboratory setting of previous calorie restriction studies, and additional evidence that the presence of food cues under conditions of chronic calorie restriction may be a stressor. Suzanne Higgs outlines the effects cognitive states have on eating behaviors and cites earlier work by Schachter that were relevant to the role of learning and memory. She further details her experiments that have examined the role of manipulating memory of meals on subsequent food intake. In these experiments it was found that enhancing the memory (i.e., by memory recall) of a recent meal, compared with diminishing the memory (i.e., by the use distracters or the passing of time) meal, can reduce food intake during a test meal in healthy subjects. She advances the theory that the hippocampus is involved in meal-based memory by discussing her experiments on food intake in amnesic subjects with hippocampal lesions.
This Special Issue provides an overview of some of the highlights of the research presented at the 2007 SSIB Annual Meeting. SSIB is a multidisciplinary international society aimed at elucidating the varied controls of ingestive behavior. The SSIB extends special appreciation and gratitude to Elsevier and Physiology and Behavior for their continued support. The 2008 annual meeting will be held on July 15–19 in Paris, France. Further information is available on our website: http://www.ssib.org/web/.
The SSIB gratefully acknowledges the support of its corporate benefactors: