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Utilisateur:Crossroads/Brouillon

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Le comportement de lordose est la posture naturelle du corps pour la réceptivité sexuelle à la copulation présente chez la plupart des mammifères, y compris rongeurs, éléphants et chats. Les principales caractéristiques du comportement sont un abaissement des membres antérieurs mais avec les membres arrière étendus et la hanches relevée, ventrale cambrure de la colonne vertébrale et un déplacement ascendant ou latéral, de la queue. Pendant la lordose, la colonne vertébrale se courbe dorsoventrale de façon à ce que son apex pointe vers l'abdomen.

Description

La lordose est une action réflexe qui amène de nombreuses femelles mammifères non primates à adopter une position corporelle souvent cruciale pour le comportement reproducteur. La posture déplace l'inclinaison pelvienne dans une direction antérieure, le bassin postérieur se levant, le bas inclinant vers l'arrière et l'avant inclinant vers le bas. La lordose facilite la copulation en élevant les hanches, facilitant ainsi la pénétration du pénis. Il est couramment observé chez les mammifères femelles pendant l'œstrus (étant «en chaleur»). La lordose survient pendant la copulation elle-même et chez certaines espèces, comme le chat, lors d'un comportement pré-copulatoire[1].

Neurobiology

Lordosis is particularly marked among felines.
Lordosis in lions

The lordosis reflex arc is hardwired in the spinal cord, at the level of the lumbar and sacral vertebrae (L1, L2, L5, L6 and S1).[2] In the brain, several regions modulate the lordosis reflex. The vestibular nuclei and the cerebellum, via the vestibular tract, send information which makes it possible to coordinate the lordosis reflex with postural balance. More importantly, the ventromedial hypothalamus sends projections that inhibit the reflex at the spinal level, so it is not activated at all times.[3] Sex hormones control reproduction and coordinate sexual activity with the physiological state. Schematically, at the breeding season, and when an ovum is available, hormones (especially estrogen) simultaneously induce ovulation and estrus (heat). Under the action of estrogen in the hypothalamus, the lordosis reflex is uninhibited.[4] The female is ready for copulation and fertilization.

When a male mammal mounts the female, tactile stimuli on the flanks, the perineum and the rump of the female are transmitted via the sensory nerves in the spinal cord. In the spinal cord and lower brainstem, they are integrated with the information coming from the brain, and then, in general, a nerve impulse is transmitted to the muscles via the motor nerves. The contraction of the longissimus and transverso-spinalis muscles causes the ventral arching of the vertebral column.[2]

Hormonal and cerebral regulation

Sexual behaviour is optimized for reproduction, and the hypothalamus is the key brain area which regulates and coordinates the physiological and behavioural aspects of reproduction.[5] Most of the time, the ventromedial nucleus of the hypothalamus (VMN) inhibits lordosis. But when environmental conditions are favorable and the female is in estrus, the estrogen hormone, estradiol, induces sexual receptivity by the neurons in the ventromedial nucleus,[6] the periaqueductal gray, and other areas of the brain. The ventromedial hypothalamus sends impulses down axons synapsing with neurons in the periaqueductal gray. These convey an impulse to neurons in the medullary reticular formation which project down the reticulospinal tract and synapse with the neurobiological circuits of the lordosis reflex in the spinal cord (L1–L6). These neurobiological processes induced by estradiol enable the tactile stimuli to trigger lordosis.

The mechanisms of regulation of this estrogen-dependent lordosis reflex have been identified through different types of experiments. When the VMN is lesioned lordosis is abolished; this suggests the importance of this cerebral structure in the regulation of lordosis. Concerning hormones, displays of lordosis can be affected by avariectomy, injections of estradiol benzoate and progesterone,[7] or exposure to stress during puberty.[8][9] Specifically, stress can suppress the hypothalamic-pituitary-gonadal (HPG) axis and therefore decrease concentrations of gonadal hormones. Consequently, these reductions in exposure to gonadal hormones around puberty can result in decreases in sexual behavior in adulthood, including displays of lordosis.[8]

In humans

Lordosis behavior is non-functional in humans, although lordosis-like positions can be observed in women being mounted from behind.[10]

References

  1. ↑ « Female Cat in Heat - signs, symptoms and behavioral changes of feline estrus. », sur www.pet-informed-veterinary-advice-online.com (consulté le )
  2. ↑ a et b Pfaff D. W. , Schwartz-Giblin S., Maccarthy M. M., Kow L-M (1994). "Cellular and molecular mechanisms of female reproductive behaviors", in Knobil E., Neill J. D. The physiology of reproduction, Raven Press, 2nd edition.
  3. ↑ Kow L.M., Florea C., Schwanzel-Fukuda M., Devidze N., Kami K.H., Lee A., Zhou J., Maclaughlin D., Donahoe P., Pfaff D., « Development of a sexually differentiated behavior [lordosis] and its underlying CNS arousal functions », Curr. Top. Dev. Biol., vol. 79,‎ , p. 37–59 (ISBN 9780123739131, PMID 17498546, DOI 10.1016/S0070-2153(06)79002-0)
  4. ↑ Flanagan-Cato L.M., « Sex differences in the neural circuit that mediates female sexual receptivity », Frontiers in Neuroendocrinology, vol. 32, no 2,‎ , p. 124–136 (PMID 21338620, PMCID 3085563, DOI 10.1016/j.yfrne.2011.02.008)
  5. ↑ Plant T., Zeleznik A. (Eds). Knobil and Neill's Physiology of Reproduction. Academic Press, 4th edition, 2015
  6. ↑ « Mapping of neural and signal transduction pathways for lordosis in the search for estrogen actions on the central nervous system », Behav. Brain Res., vol. 92, no 2,‎ , p. 169–180 (PMID 9638959, DOI 10.1016/S0166-4328(97)00189-7, S2CID 28276218)
  7. ↑ Olster, D.H. et Blaustein, J.D., « Development of steroid-induced lordosis in female guinea pigs: effects of different estradiol and progesterone treatments, clonidine, and early weaning. », Hormones and Behavior, vol. 23, no 1,‎ , p. 118–129 (PMID 2538389, DOI 10.1016/0018-506x(89)90079-2, S2CID 26078948)
  8. ↑ a et b Jasmina Kercmar, Stuart Tobet et Gregor Majdic, « Social Isolation during Puberty Affects Female Sexual Behavior in Mice », Frontiers in Behavioral Neuroscience, vol. 8,‎ , p. 337 (PMID 25324747, PMCID 4179611, DOI 10.3389/fnbeh.2014.00337)
  9. ↑ D. Daniels et LM. Flanagan-Cato, « Social Isolation during Puberty Affects Female Sexual Behavior in Mice », Journal of Neurobiology, vol. 45, no 1,‎ , p. 1–13 (PMID 10992252, DOI 10.1002/1097-4695(200010)45:1<1::AID-NEU1>3.0.CO;2-W)
  10. ↑ Pfaus, J. G.; Flanagan-Cato, L. M.; Blaustein, J. D. "Female sexual behavior". in Plant T., Zeleznik A. (Eds). Knobil and Neill's Physiology of Reproduction. Academic Press, 4th edition, 2015
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