mise à jour du
12 février 2003
 Trends in Neurosciences 2002;25(1):45-50
Hormonal and genetic influences
on arousal sexual and otherwise
Donald Pfaff, Jonathan Frohlich, Maria Morgan
Laboratory of Neurobiology and Behavior, The Rockefeller
University, Box 275, 1230 York Avenue, New York
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Genetic influences on lordosis, a mammalian social behavior, are amenable for study because of the relative simplicity of both stimuli and response. The neural circuit for lordosis involves a supraspinal loop, which is controlled by an estrogen- and progesterone-dependent signal from the medial hypothalamus and results in heightened sexual motivation. In turn, this involves elevated states of arousal, defined by increased sensory alertness, motor activity and emotional reactivity. Mice in which the gene encoding the form of the estrogen receptor (ERa) has been knocked out show that ERa is crucial for lordosis behavior. Comparing ERa, ERb and double knockouts reveals that different patterns of sexual behaviors in mice require different patterns of ER activity. Understanding how hormonal and genetic effects on deep motivational and arousal processes contribute to their effects on specific sexual and aggressive behaviors pose significant challenges for mouse functional genomics.
A large body of reliable neurobiological results has been enabled by the analysis of hormonal and genetic influences on lordosis, a simple reproductive behavior. Lordosis is the vertebral dorsiflexion performed by female quadrupeds in response to adequate stimuli from a reproductively competent male. Biologically it is important because it permits fertilization and, therefore, reproduction. Strategically it is well chosen for analysis because it depends on the activity of estrogenic hormones facilitated by progestins. Therefore it serves as a virtual expression system for the actions of these steroid hormones and research in this field has been enhanced and accelerated by the tools of steroid chemistry and biochemical endocrinology.

Furthermore, the behavior involves simple responses that are triggered by simple stimuli. All are manageable in the laboratory and, crucially, all arerelatively easy to study. Because of these advantages the hormonal, neural and genetic determinants of lordosis have been reported in detail. In addition to the spinal circuitry required, there is an obligatory supraspinal loop that brings somatosensory stimuli involved in this reproductive behavior to the medullary reticular formation and the midbrain central gray. This circuit, which governs female reproductive behavior, is dependent on the interactions of estrogen and progestins with ER and progesterone receptors within hypothalamic neurons. Analysis of the behavioral functions at the molecular level depends upon the activity of these nuclear hormone receptors as transcription factors. Thus estrogenic effects on hypothalamic neurons that govern female reproductive behavior requires the synthesis of mRNA and protein and the molecular actions of estrogens and progestins in the hypothalamus and basal forebrain guarantee a biologically adaptive synchrony between reproductive behavior and the pituitaryÐovarian mechanisms that cause ovulation.

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credit photo : "Asif A. Ghazanfar and Aristides Arrenberg"
Max Planck Institute for Biological Cybernetics
Tuebingen; Germany.
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