Implants of Estradiol Conjugated to Bovine Serum Albumin in the Male Rat Medial Preoptic Area Promote Copulatory Behavior

The expression of mating behavior in male rats is dependent on estrogen-responsive neurons in the medial preoptic area (MPO). Previous reports showed that mating is attenuated if the aromatization of testosterone to estradiol (E<sub>2</sub>) is blocked in the MPO and that mating is maintained by MPO E<sub>2</sub> implants. However, the mechanisms by which E<sub>2</sub> exerts its action are not fully understood. It had been thought that E<sub>2</sub> acted exclusively by binding to nuclear estrogen receptors to exert it effects; however, recent reports suggest that E<sub>2</sub> also binds to membrane-associated receptors activating downstream intracellular cascade responses. In this study, we aimed to determine if an action of E<sub>2</sub> at the cell surface is sufficient to support mating behavior. Therefore, either vehicle, E<sub>2</sub>, or E<sub>2</sub> conjugated to bovine serum albumin (BSA-E<sub>2</sub>: a complex of E<sub>2</sub> and a large protein that will not cross the plasma membrane, thereby restricting the action of E<sub>2</sub> to cell surface signaling) was chronically administered bilaterally to the MPO of castrated, dihydrotestosterone-treated male rats. Mating behavior was supported by MPO BSA-E<sub>2</sub> implants, suggesting that E<sub>2</sub> operates in the MPO via a cell surface mechanism to facilitate male rat mating behavior.

[1]  R. Michael,et al.  Androgen Receptors and Estrogen Receptors Are Colocalized in Male Rat Hypothalamic and Limbic Neurons that Express Fos Immunoreactivity Induced by Mating , 1998, Neuroendocrinology.

[2]  T. Curran,et al.  Expression of c-fos protein in brain: metabolic mapping at the cellular level. , 1988, Science.

[3]  D. Pfaff,et al.  Single unit recording in hypothalamus and preoptic area of estrogen-treated and untreated ovariectomized female rats , 1976, Brain Research.

[4]  G. Greene,et al.  Monoclonal antibodies localize oestrogen receptor in the nuclei of target cells , 1984, Nature.

[5]  M. S. Clarke,et al.  Perimembrane Localization of the Estrogen Receptor α Protein in Neuronal Processes of Cultured Hippocampal Neurons , 2000, Neuroendocrinology.

[6]  C. Wade,et al.  Estrogen Receptor (ER)α and ERβ Exhibit Unique Pharmacologic Properties When Coupled to Activation of the Mitogen-Activated Protein Kinase Pathway. , 2001, Endocrinology.

[7]  P. Davis,et al.  Activation of masculine sexual behavior by intracranial estradiol benzoate implants in male rats. , 1979, Neuroendocrinology.

[8]  Y. Oomura,et al.  17β-Estradiol depolarization of hypothalamic neurons is mediated by cyclic AMP , 1990, Brain Research.

[9]  Y. C. Liu,et al.  Lesions in Medial Preoptic Area and Bed Nucleus of Stria Terminalis: Differential Effects on Copulatory Behavior and Noncontact Erection in Male Rats , 1997, The Journal of Neuroscience.

[10]  R. Michael,et al.  Intracerebral infusion of an aromatase inhibitor, sexual behavior and brain estrogen receptor-like immunoreactivity in intact male rats. , 1995, Neuroendocrinology.

[11]  R. L. Moss,et al.  Differential sensitivity of preoptic-septal neurons to microelectrophoressed estrogen during the estrous cycle , 1976, Brain Research.

[12]  P. Micevych,et al.  A membrane estrogen receptor mediates intracellular calcium release in astrocytes. , 2004, Endocrinology.

[13]  L. Wolin,et al.  The formation of estrogens by central neuroendocrine tissues. , 1975, Recent progress in hormone research.

[14]  R. Bonsall,et al.  Effects of the nonsteroidal aromatase inhibitor, Fadrozole, on sexual behavior in male rats , 1992, Hormones and Behavior.

[15]  C. Roselli,et al.  17β-Estradiol rapidly facilitates chemoinvestigation and mounting in castrated male rats. , 1999, American journal of physiology. Regulatory, integrative and comparative physiology.

[16]  L. Swanson,et al.  The organization of neural inputs to the medial preoptic nucleus of the rat , 1986, The Journal of comparative neurology.

[17]  R. Michael,et al.  Estrogen in the Medial Preoptic Area of Male Rats Facilitates Copulatory Behavior , 2000, Hormones and Behavior.

[18]  C. Ramírez,et al.  Alternative estrogen receptors homologous to classical receptor α in murine neural tissues , 2006, Neuroscience Letters.

[19]  E. Jensen,et al.  A two-step mechanism for the interaction of estradiol with rat uterus. , 1968, Proceedings of the National Academy of Sciences of the United States of America.

[20]  G. Ball,et al.  Inhibition of Steroid Receptor Coactivator-1 Blocks Estrogen and Androgen Action on Male Sex Behavior and Associated Brain Plasticity , 2005, The Journal of Neuroscience.

[21]  R. Pietras,et al.  Specific binding sites for oestrogen at the outer surfaces of isolated endometrial cells , 1977, Nature.

[22]  L. Swanson,et al.  Projections of the medial preoptic nucleus: A Phaseolus vulgaris leucoagglutinin anterograde tract‐tracing study in the rat , 1988, The Journal of comparative neurology.

[23]  D. Pfaff,et al.  Interconnectedness of Steroid Hormone-Binding Neurons: Existence and Implications , 1986 .

[24]  D. A. Edwards,et al.  Medial preoptic connections with the midbrain tegmentum are essential for male sexual behavior , 1984, Physiology & Behavior.

[25]  J. Davidson.  Activation of the male rat's sexual behavior by intracerebral implantation of androgen. , 1966, Endocrinology.

[26]  Y. Oomura,et al.  17 beta-estradiol depolarization of hypothalamic neurons is mediated by cyclic AMP. , 1990, Brain research.

[27]  Larry W. Swanson,et al.  Brain Maps: Structure of the Rat Brain , 1992 .

[28]  Anne-Marie Brun-Zinkernagel,et al.  Mitochondrial localization of estrogen receptor β , 2004, Proceedings of the National Academy of Sciences of the United States of America.

[29]  J. Rajfer,et al.  Dihydrotestosterone is the active androgen in the maintenance of nitric oxide-mediated penile erection in the rat. , 1995, Endocrinology.

[30]  Estrogen rapidly induces the phosphorylation of the cAMP response element binding protein in rat brain. , 1996, Endocrinology.

[31]  A. Parfitt,et al.  Reversal of bone loss in mice by nongenotropic signaling of sex steroids. , 2003, Science.

[32]  J. Dong,et al.  Identity of an estrogen membrane receptor coupled to a G protein in human breast cancer cells. , 2005, Endocrinology.

[33]  P. Parte,et al.  Temporal changes in the serum levels of gonadotrophins and testosterone in male rats bearing subcutaneous implants of 5 alpha-dihydrotestosterone. , 1992, International journal of andrology.

[34]  Cory C. Funk,et al.  Estrogen dendrimer conjugates that preferentially activate extranuclear, nongenomic versus genomic pathways of estrogen action. , 2006, Molecular endocrinology.

[35]  D. Lubahn,et al.  Masculine Sexual Behavior Is Disrupted in Male and Female Mice Lacking a Functional Estrogen Receptor α Gene , 1997, Hormones and Behavior.

[36]  J. Gustafsson,et al.  Cloning of a novel receptor expressed in rat prostate and ovary. , 1996, Proceedings of the National Academy of Sciences of the United States of America.

[37]  E. Levin,et al.  Requirements for estrogen receptor α membrane localization and function , 2005, Steroids.

[38]  M. Kelly,et al.  Estrogen Modulation of G‐Protein‐Coupled Receptor Activation of Potassium Channels in the Central Nervous System , 2003, Annals of the New York Academy of Sciences.

[39]  Yasuyuki Yamada.  Effects of testosterone on unit activity in rat hypothalamus and septum , 1979, Brain Research.

[40]  M. Welsh,et al.  Effect of subunit composition and Liddle's syndrome mutations on biosynthesis of ENaC. , 1999, The American journal of physiology.

[41]  R. Vadlamudi,et al.  Cloning, expression, and localization of MNAR/PELP1 in rodent brain: colocalization in estrogen receptor-alpha- but not in gonadotropin-releasing hormone-positive neurons. , 2005, Endocrinology.

[42]  M. McGINNIS,et al.  Inhibition of Male Sexual Behavior by Intracranial Implants of the Protein Synthesis Inhibitor Anisomycin into the Medial Preoptic Area of the Rat , 1997, Hormones and Behavior.

[43]  Eric R. Prossnitz,et al.  A Transmembrane Intracellular Estrogen Receptor Mediates Rapid Cell Signaling , 2005, Science.

[44]  G. Greene,et al.  Immunochemical studies of estrogen receptors. , 1984, Journal of steroid biochemistry.

[45]  D. A. Edwards,et al.  Midbrain lesions, dopamine and male sexual behavior , 1986, Behavioural Brain Research.

[46]  O. Rønnekleiv,et al.  Modulation of G protein-coupled receptors by an estrogen receptor that activates protein kinase A. , 1997, Molecular pharmacology.

[47]  R. Michael,et al.  Effects of testosterone and aromatase inhibition on estrogen receptor-like immunoreactivity in male rat brain. , 1994, Neuroendocrinology.

[48]  R. Santen,et al.  Estrogen rapid action via protein complex formation involving ERα and Src , 2005, Trends in Endocrinology & Metabolism.

[49]  Preoptic and subthalamic connections with the caudal brainstem are important for copulation in the male rat. , 1994 .

[50]  A. Araque,et al.  Estradiol Regulates the Slow Ca2+-Activated K+ Current in Hippocampal Pyramidal Neurons , 2003, The Journal of Neuroscience.

[51]  C. Pfaffmann,et al.  Olfactory and hormonal influences on the basal forebrain of the male rat. , 1969, Brain research.

[52]  D. Pfaff.  Drive: Neurobiological and Molecular Mechanisms of Sexual Motivation , 1999 .

[53]  P. Mermelstein,et al.  Evidence for a non-genomic action of progestins on sexual receptivity in hamster ventral tegmental area but not hypothalamus , 1992, Brain Research.

[54]  R. Kirk.  Experimental Design: Procedures for the Behavioral Sciences , 1970 .

[55]  C. Lange,et al.  Steadying the boat: integrating mechanisms of membrane and nuclear‐steroid‐receptor signalling , 2005, EMBO reports.

[56]  N. Lorenzon,et al.  Differential expression of estrogen receptor beta splice variants in rat brain: identification and characterization of a novel variant missing exon 4. , 2000, Brain research. Molecular brain research.

[57]  D. Nance,et al.  Effects of hypothalamic and preoptic lesions on reproductive behavior in male rats , 1977, Brain Research Bulletin.

[58]  G. W. Williams,et al.  Inhibition of male sex behavior by androgen receptor blockade in preoptic area or hypothalamus, but not amygdala or septum , 1996, Physiology & Behavior.

[59]  K. Ley,et al.  Interaction of oestrogen receptor with the regulatory subunit of phosphatidylinositol-3-OH kinase , 2000, Nature.

[60]  M. Vagell,et al.  The Role of Aromatization in the Restoration of Male Rat Reproductive Behavior , 1997, Journal of neuroendocrinology.

[61]  F. Leeuwen,et al.  Differential Localization of Estrogen Receptors in Various Vasopressin Synthesizing Nuclei of the Rat Brain , 1990, Journal of neuroendocrinology.

[62]  J. Ham,et al.  Structural organization and expression of the mouse estrogen receptor. , 1987, Molecular endocrinology.

[63]  Richard G. W. Anderson,et al.  ERβ Has Nongenomic Action in Caveolae , 2002 .

[64]  T. Pappas,et al.  Membrane estrogen receptors identified by multiple antibody labeling and impeded‐ligand binding , 1995, FASEB journal : official publication of the Federation of American Societies for Experimental Biology.

[65]  V. Krishnan,et al.  Estrogen activates mitogen-activated protein kinase in native, nontransfected CHO-K1, COS-7, and RAT2 fibroblast cell lines. , 2005, Endocrinology.

[66]  E. Krebs,et al.  Rapid membrane effects of steroids in neuroblastoma cells: effects of estrogen on mitogen activated protein kinase signalling cascade and c-fos immediate early gene transcription. , 1997, Endocrinology.

[67]  M. Goldstein,et al.  Effects of ibotenic acid-induced neuronal degeneration in the medial preoptic area and the lateral hypothalamic area on sexual behavior in the male rat , 1982, Brain Research.

[68]  L. Heimer,et al.  Mating Behaviour of Male Rats after Lesions in the Preoptic Area , 1964, Nature.

[69]  Few things in life are "free": cellular uptake of steroid hormones by an active transport mechanism. , 2005, Molecular interventions.

[70]  Qing Lu,et al.  Striatin assembles a membrane signaling complex necessary for rapid, nongenomic activation of endothelial NO synthase by estrogen receptor alpha. , 2004, Proceedings of the National Academy of Sciences of the United States of America.

[71]  H. Carrer,et al.  Effects of estrogen on neuronal growth and differentiation , 2005, The Journal of Steroid Biochemistry and Molecular Biology.

[72]  L. Martini,et al.  The transformation of testosterone into dihydrotestosterone by the brain and the anterior pituitary. , 1972, Journal of steroid biochemistry.

[73]  Doris Zumpe,et al.  Estradiol in the male rat amygdala facilitates mounting but not ejaculation , 2003, Physiology & Behavior.

[74]  A. Clancy,et al.  Effects of Estrogen in the Male Rat Medial Amygdala: Infusion of an Aromatase Inhibitor Lowers Mating and Bovine Serum Albumin-Conjugated Estradiol Implants Do Not Promote Mating , 2006, Neuroendocrinology.