Brush / Levine Psychoendocrinology

1. Auflage 2013
ISBN: 978-1-4832-1678-2
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 602 Seiten

Psychoendocrinology covers the advances in the field of biology and the development of highly refined measurement techniques for hormones. The book discusses the partitioning of neuroendocrine steroids and peptides between vascular and cerebral compartments; the mechanisms of the female reproductive behavior; and the sensory, hormonal, and neural determinant of maternal behavior. The text describes the effects of sexual behavior on gonadal function in rodents; the hormonal regulation of learning performance; and the hormonal modulation of memory. The psychobiological perspective on the psychoneuroendocrinology of stress and the behavioral effects of the endogenous opioids are also considered. The book further tackles the hormonal interactions on temperature regulation and temperature regulation under modified physiological states. Endocrinologists, psychobiologists, neurologists, neurobiologists, and students taking related courses will find the book useful.

Autoren/Hrsg.

Brush, F. Robert

Levine, Seymour

Leseproben

CHAPTER TWO

Mechanisms of Female Reproductive Behavior

S. Schwartz-Giblin, B.S. McEwen and D.W. Pfaff

Publisher Summary

This chapter discusses mechanisms of female reproductive behavior. The reproductive behavior of the female rat—the lordosis posture—occurs in the course of natural events during estrus as a reflex response to appropriate somatosensory stimulation by the male rat. The lordosis behavior is the complex product of the stimulation provided by the male partner operating upon a hormone-primed neural substrate. Neural structures from the levels of the hypothalamus and midbrain to the spinal cord and peripheral somatosensory nerves are involved in the circuitry-governing lordosis. A medial and lateral group of axons travel from the ventromedial hypothalamus to the midbrain central gray; the lateral group is more important in the regulation of lordosis. From the time course differences resulted from stimulation and ablation studies in hypothalamus as compared to midbrain, the regulation of feminine sexual behavior can be evaluated. The more rapid effects on lordosis from manipulations of midbrain neurons and the more conventional response of midbrain neurons to both antidromic electrical stimulation from medullary gigantocellular neurons and somatosensory stimulation suggest that the facilitatory effects from central gray are mediated by more classical electrophysiological conduction and synaptic transmission.

I Introduction

The reproductive behavior of the female rat, the lordosis posture, occurs in the course of natural events during estrus as a reflex response to appropriate somatosensory stimulation by the male rat (Fig. 1). Lordosis will only occur in response to the male if the female has been exposed to sufficient levels of estradiol and progesterone for some time previously. In fact, the priming effects of estradiol require 18–24 hours of exposure before progesterone will exert its activational influence over a time delay of at least 1 hour. The lordosis behavior is the complex product of the stimulation provided by the male partner operating upon a hormone-primed neural substrate. Neural structures from the levels of the hypothalamus and midbrain to the spinal cord and peripheral somatosensory nerves are involved in the “circuitry” governing lordosis. We now know a great deal about the hormonal requirements for lordosis and about the receptors and brain sites through which estradiol and progesterone influences are produced. We also are beginning to understand the details of neuroanatomy underlying the lordosis “circuitry” and the specific role of certain neuropeptides and neurotransmitters within this circuitry. This chapter attempts to provide a current picture of these various facets of the problem, beginning with a discussion of the hormone receptors and hormone actions at the hypothalamic level and then describing, in turn, the neural organization and functional interactions at the level of the brainstem and spinal cord.

FIGURE 1 A drawing from a filmed mating encounter showing the lordosis posture of the female rat immediately following the male mount.

II Receptor-Mediated Functions in Hypothalamic and Preoptic Neurons

A Estrogen and Progestin Receptors

Recent progress in understanding how and where steroid hormones alter brain function stems in large part from the detection and localization of receptors for the five major classes1 of steroid hormones in the central nervous system. Estrogen receptors were the first to be identified, characterized, and mapped, whereas receptors for progesterone took much longer before yielding to efforts to study them.

With the introduction of tritiated steroids around 1960, intracellular estrogen receptors were identified and characterized in the uterus and other female reproductive tissues (Jensen and Jacobson, 1962). Studies of the brain soon followed. Like the initial work on the uterus, these studies first established that regions of the brain such as the hypothalamus concentrate and retain systemically administered [3H]estradiol (Eisenfeld and Axelrod, 1965; Kato and Villee, 1967; McEwen and Pfaff, 1970). Subsequently, cytosol receptors and cell nuclear retention of the hormone were demonstrated as the basis of the retention (Eisenfeld, 1970; Zigmond and McEwen, 1970). Furthermore, autoradiographic mapping of the cellular sites of uptake and retention of [3H]estradiol played a major role in establishing the brain as an estrogen target organ (Pfaff, 1968; Stumpf, 1968; Pfaff and Keiner, 1973).

What we currently know about the estrogen receptors of the brain is that, from a physicochemical standpoint, they are very similar to those in the pituitary gland and reproductive tract tissues. Moreover, as with the uterus, if [3H]estradiol is applied to estrophilic brain cells, a substantial portion of the radioactivity taken up and retained by the cell can be recovered from the cell nuclei (see Figs. 2A and B). Thus we have every reason to believe that estradiol exerts genomically mediated actions in the brain as well as in the uterus and reproductive tract. Indeed, direct evidence on this point is summarized below.

FIGURE 2A Model of estradiol (E2) interaction with target cells. Diffusion of E2 passively across cell membrane. Formation of E2-receptor complex (E2R) and translocation to cell nucleus. Activation of E2R (E2R) and 4S to 5S transformation.

FIGURE 2B Model of E2R interaction with postulated acceptor and effector sites. From McEwen (1981) by permission.

What is uniquely interesting about estrogen (as well as other steroid receptors) in the brain is its neuroanatomical distribution (Figs. 3 and 4). [Note that the distributions from autoradiographic localization (Fig. 3) and from cytosol receptor assays (Fig. 4) stand in excellent agreement with each other.] The importance of the neuroanatomical distribution of estrogen receptors will be demonstrated repeatedly below in considering estrogen action on feminine sexual behavior, progesterone receptor induction, and neurochemical effects of estrogens in the brain.

FIGURE 3 Distribution of estrogen-concentrating neurons in the brain of the female rat represented schematically in two sagittal sections. Most labeled neurons could be represented in a medial plane (bottom) based primarily on Fig. L740 in the atlas of Konig and Klippel (1963) and Fig. A35 and A36 in the atlas of Zeman and Innes (1963). Estradiol-concentrating neurons in the amygdala and hippocampus are represented in a more lateral plane (top) based on Fig. L2590 in the atlas of Konig and Klippel (1963). Locations of estradiol-concentrating neurons are represented by black dots. From Pfaff and Keiner (1973), by permission.

FIGURE 4 Concentration of E2 receptors in selected nuclei and subregions. Results are expressed as femtomoles per milligram of E2 specifically bound per milligram of protein (fm E2/mg P). The abbreviations used are PVPOA, periventricular preoptic area; MPOA, medial preoptic area; PVAH, periventricular anterior hypothalamus; SCPOA, suprachiasmatic preoptic nucleus; ARC-ME, arcuate nucleus-median eminence; VMN, ventromedial nucleus; MA, medial amygdaloid nucleus; SO, supraoptic nucleus; PVN, paraventricular nucleus; NsT, bed nucleus of the stria terminalis; VPN, ventral premammillary nucleus; DMN, dorsomedial nucleus; DG, dentate gyrus; DB, nucleus of the diagonal band of Broca; OT, olfactory tubercle; LS, lateral septum. From Rainbow (1982a) by permission.

After many unsuccessful attempts using [3H]progesterone, progestin receptors were finally identified using a synthetic progestin, [3H]Ru5020, from Roussel Uclaf in France (McEwen 1982). Like estrogen receptors, neural progestin receptors also appear to be very similar physicochemi-cally to those found in the reproductive tract and pituitary. One important characteristic of these receptors is that in some estrogen-sensitive tissues, such as the uterus, pituitary, and hypothalamus, estrogens induce progestin receptors. Thus, the synergistic interaction between estrogens and progestins on reproductive events including ovulation and sexual behavior may be due in large part to this induction. Figure 5 presents a summary of the areas of the rat brain where progestin receptor induction by estradiol is found. It should be noted that some estrogen-sensitive areas, such as the medial amygdala and bed nucleus, display little if any progestin receptor induction whereas others, such as the ventromedial nucleus and medial preoptic area, display a great deal of induction. Thus progestin receptor induction by estradiol is not a universal feature of estrophilic cells.

FIGURE 5 Concentration of estrogen-inducible and uninduced progestin receptors in selected nuclei and subregions of the female rat brain. Results are expressed as femtomoles of [3H]R5020 specifically bound per mg of total protein (mean ± SEM). The abbreviations used are PVPOA, periventricular preoptic area; MPOA, medial preoptic area; ARC-ME, arcuate-median eminence;...