Principles of Hormone/Behavior Relations

Donald W. Pfaff, Robert T Rubin, Jill E. Schneider, Geoff Head

• Publisher: Academic Press
• Year: 2018
• ISBN:
  9780128026670
• Edition: 2
• Topic: Biological Sciences
• Subtopic: Zoology
• Index: Biological Sciences

Principles of Hormone/Behavior Relations, Second Edition, provides an introduction to the underlying principles of endocrine regulation of behavior, a newly emerging area of research within neurobiology and endocrinology. It addresses the properties of hormone/behavior relations, including the influence of family background, timing issues, neuroanatomical features, cellular mechanisms, and the importance of environmental context and evolution. This new edition incorporates critical advances in the field, also including increased coverage of hormonal influences on food intake, and on the cardiovascular system.

The addition of entirely new principles provides further coverage of epigenetics and appetite. Thoroughly revised and updated, this book is an ideal resource for neuroscientists and researchers engaging in this rapidly expanding field of study.

• Provides a unique structure where each chapter addresses a key principle that is illustrated by numerous basic experimental and clinical examples
• Includes user-friendly features, such as boxed figures with extended captions and references, numerous clinical notes, and a comprehensive list of abbreviations
• Contains numerous illustrations that highlight both the clinical and basic science information

Section I

Characterizing the Phenomena: Hormone Effects on Behavior are Strong and Reliable

Outline

Chapter 1. Hormones Can Facilitate or Suppress Behaviors

Chapter 2. Hormone Combinations Can Be Important for Behavior

Chapter 3. One Hormone Can Have Many Effects

Chapter 4. Hormone Metabolites Can Be the Behaviorally Active Compounds

Chapter 5. There Are Optimal Hormone Concentrations: Too Little or Too Much Can Be Damaging

Chapter 6. Hormones Do Not “Cause” Behavior; They Alter Probabilities of Responses to Given Stimuli in the Appropriate Context

Chapter 7. Hormone-Behavior Relations Are Reciprocal

Chapter 1

Hormones Can Facilitate or Suppress Behaviors

Abstract

This chapter highlights the powerful influences of hormones on behavior. Individual hormones can have facilitating or inhibiting effects on behavior, depending on their concentrations and locations in the central nervous system and, especially, on the overall hormonal milieu in which they exert their actions. Most groups of hormones with related metabolic effects are secreted in an orderly fashion, particularly with respect to their time courses. The principle that hormones are capable of either increasing or decreasing certain behaviors can be extended to the molecular mechanisms in forebrain neurons underlying such behavior. In humans, as in laboratory animals, social tendencies include a wide variety of courtship and reproductive behaviors that further the survival of the species: aggressive behaviors, especially for food acquisition and protection of offspring; communicative responses, which convey emotional and behavioral intent; and pure affiliation, providing emotional support and promoting friendly synergy within a group.

Keywords

Anorexigenic; Castration; Ingestive behavior; Necessary; Orexigenic; Ovariectomy; Remove-and-replace; Sex behavior; Sufficient

The effects of hormones on behavior are powerful. Many behaviors simply do not occur without a requisite level of hormone secretion; therefore, hormones are central to our experience as human beings. For example, without the steroid hormone, testosterone, and its metabolite, estradiol, we would never blossom into full sexual awareness at puberty. Without the facilitatory effects of testosterone and its metabolites, we would live in a “silent spring,” our lives devoid of bird song, the primary behavior whereby male songbirds attract mating partners. In most songbird species, male song is precluded by castration (removal of the testes) and restored by testosterone replacement. In a subset of bird species, the brain mechanisms for courtship song require stimulation by testosterone and/or its metabolite, estradiol. A similar hormonal effect is involved in hormonal control of agonistic behaviors, actions that harm or exclude other animals. Many of our favorite birdsongs, for example, are actually territorial displays used to compete with other males for female mating partners, and these behaviors are also dependent upon testosterone and its metabolites. The neurohormone, oxytocin is critical for the full expression of parental behaviors, actions that promote offspring survival, and affiliative behaviors, actions that bring animals in close contact. Treatments that block oxytocin binding to its receptors will prevent parental care and affiliative behaviors. Hormones have powerful effects on species-specific mating systems, i.e., whether couples practice monogamy, polygyny, and/or polyandry. Monogamy, the tendency to show preference for one mating partner, is facilitated by an array of hormones that includes both oxytocin and vasopressin. Without a fully functional vasopressin receptor, individuals tend toward promiscuous mating preferences, such as polygyny (each male mates with multiple females) and/or polyandry (each female mates with multiple males). The endocannabinoids are a class of endogenous (naturally occurring within the body) hormones essential for the pleasurable experience of eating food. Without the action of the endocannabinoids binding to their receptors in the brain, users of marijuana would not experience “the munchies.” Many other hormones have formidable effects on ingestive behavior (hunger for food, food intake, and foraging), and when we attempt to remove one hormone from the system, many other hormones step in to take its place. These are just a small sampling of behaviors that depend upon hormone action.

Conversely, hormones can decrease the chances that a specific type of behavior will occur, and in some cases, hormones bring behaviors to an immediate halt. Consider the stress response (Fig. 1.1). When individuals perceive an impending threat to their safety, specific activities are immediately suppressed, including foraging, ingestion, digestion, and copulation. When under attack, survival of a prey animal requires immediate evasive or defensive action and immediate cessation of all other activities. High levels of stress hormones can cause parenting birds to abandon their nests and cause parenting rodents to cannibalize their offspring. In the aftermath of an attack, cessation of energetically expensive behaviors must occur to save energy for healing and recovery. These behavioral priorities are orchestrated by hormones of the stress response, including adrenaline (a.k.a., epinephrine), corticotropin-releasing hormone (CRH), and glucocorticoids, among others.

Figure 1.1 Neurochemical and neuroanatomical systems involved in stress responses. Key are the pathways involving corticotrophin-releasing hormone (CRH) originating in the paraventricular nucleus of the hypothalamus (PVH) and the central nucleus of the amygdala (CnAmy). Notice the two main outputs: endocrine responses and autonomic nervous system responses. Modified from Kaufman, J., et al., 2000. Biol. Psychiatry 48, 778–790. In addition, McEwen and colleagues reported strong glucocorticoid and mineralocorticoid inputs to the hippocampus, which we discuss further in Chapter 13.

Other disruptive hormones or hormone-like substances have their effects during development, and these effects result in deficiencies in adult behavior. For example, synthetic materials that are structurally similar to steroid molecules, such as those that leech from plastics, sewage effluent, pesticides, and herbicides, can interfere with steroids binding to their receptors, thereby disrupting developmental events that are normally controlled by steroids. These endocrine disruptors alter sexual differentiation, the process whereby males are masculinized and females are feminized. Endocrine disruptors have almost wiped out entire species by causing all-male populations of alligators, infertility in bald eagles, and an intersex condition in fish. Endocrine disruptors interfere with hormone action in all vertebrates: fish, amphibians, nonavian reptiles, birds, and mammals (including human beings), as well as in many invertebrate species. Normal, healthy hormone action is linked to reproductive success, whereas endocrine disruption is linked to cessation and alteration of ingestive and reproductive behaviors, obesity, insulin resistance, diabetes, alterations in body fat distribution, and reproductive failure (reviewed by Schneider et al., 2014).

Hormones have both “organizational” and “activational” effects on the brain and behavior. The term activational implies that increases in hormones affect neural circuits that are already developed and ready to be stimulated by hormones. When the circulating hormone levels fall or the hormone is prevented from binding to its receptor, the effects are removed on a relatively rapid time scale. The term was coined to describe the effects of hormones on adult behavior, which decrease or disappear when the hormone is removed from the system. For example, castration decreases aggressive behavior in many different species, and precastration levels of aggressive behavior are restored by treatment with androgens (Fig. 1.2). Activational effects are not permanent: when exogenous hormone treatments end, activational effects also end.

In contrast to activational effects, most organizational effects occur early in development when the foundation of brain structure is being built, and the organizational effects are permanent. After those initial organizational effects of hormones occur, continuous exposure to those hormones is not required to maintain those organizational effects. Hormones that bind to hormone receptors in the fetus, the infant, and in the juvenile set in motion a long series of developmental events that create permanent alterations in neural circuitry. These permanent alterations allow those circuits to be activated by key hormones that rise in adulthood. A main difference between organizational and activational effects is that organizational ones are permanent, whereas activational effects only occur in response to the hormone. Chapter 9 is concerned with organizational effects on behavior, whereas this chapter is concerned with activational effects.

Figure 1.2 A summary of the major hormonal events and their timing in the establishment of androgen- and estrogen-sensitive regulatory pathways for offensive male-typical aggressive behavior in the mouse. Time is marked in days. The development of each pathway depends on exposure to specific testosterone metabolites during a restricted period shortly after birth. From Simon, N., et al., Development and expression of hormonal systems regulating aggression. Ann. NY Acad. Sci. 794, 8–17. © 1996 New York Academy of Science. With permission.

Interim Summary 1.1

• 1. Some hormones have profound stimulatory effects on behavior, and these behaviors only rarely occur in the absence of hormones.
• 2. Some hormones inhibit or decrease the incidence of particular behaviors.
• 3. Hormone effects can be activational and reversible, whereas others are organizational and permanent.

Examples From the History of Behavioral Endocrinology

The following historical account illustrates the fact that experimental behavioral endocrinology originated at the same moment as the field of endocrinology. A related point is that behavior is not only a legitimate topic in experimental neuroendocrinology; it is one of the best end points for any scientific experiment. Behaviors are visible to the naked eye, and quantification can often be accomplished without specialized equipment. For example, long before they could use radioimmunoassay to measure hormone levels, use a thermometer to take body temperature, or use a microscope to examine vaginal epithelial cells, ancient farmers and animal scientists could predict the time of ovulation in their female livestock by the unmistakable change in sex behaviors. Female livestock (e.g., cows) when they are approaching the time of ovulation (the periovulatory period) are said to be in “estrous” because they become increasingly agitated and restless, and the level of agitation increases further in the presence of an adult male of the species. The word estrous comes from a Greek word for gadfly, a biting, irritating insect that evokes frenzy in penned livestock (according to Freeman, 1994). Randy estrous behavior is a reliable marker for hormonal changes that underlie ovulatory cycles. Behaviors are useful in scientific experiments because behaviors are often stereotypical, remarkably robust, and easi...