Lordosis behavior

Lordosis behavior by a female cat during copulation.

Lordosis behavior, also known as mammalian lordosis (Greek lordōsis, from lordos "bent backward"[1]) or presenting, is a body posture adopted by some mammals including humans, elephants, rodents, felines and others, usually associated with female receptivity to copulation. The primary characteristics of the behavior are a lowering of the forelimbs but with the rear limbs extended and hips raised, ventral arching of the spine and a raising, or sideward displacement, of the tail. During lordosis, the spine curves dorsoventrally so that its apex points towards the abdomen. In human physiology, the term "lordosis" is sometimes used to describe an abnormal forward curvature of the spine in the lumbar region.[1]

Description

Lordosis is a reflex action that causes many non-primate female mammals to adopt a body position that is often crucial to reproductive behavior. The posture moves the pelvic tilt in an anterior direction, with the posterior pelvis rising up, the bottom angling backward and the front angling downward. Lordosis aids in copulation as it elevates the hips, thereby facilitating penetration by the penis. It is commonly seen in female mammals during estrus (being "in heat"). Lordosis occurs both during pre-copulatory behavior and during copulation itself.

Neurobiology

Simplified diagram of the neurobiological circuits modulating lordosis.[2][3][4][5]

Lordosis brain circuits are connected with other neural circuits, especially the olfactory and reward systems.

The main phases of reproductive behavior are:

  1. Odors, especially pheromones, make it possible to exchange sexual signals between potential partners.[6]
  2. Olfactory circuits (red arrows in the above diagram) make it possible to recognize the partner of the opposite sex[2][7] and to trigger sexual arousal,[3][8] which induces vaginal lubrication, erection and copulation.
  3. When the male mounts the female, the male's tactile stimuli on the female's rump trigger the lordosis reflex.[4][9]
  4. The lordosis circuits cause the ventral arching of the spine, which elevates the hips and presents the vagina to the male, thereby facilitating penetration by the penis.[4][9]

  1. The tactile contact between the penis and the genital area triggers the reflex movements of the male's pelvis (pelvic thrusts), then intromission. After intromission, the penis's movements in the vagina trigger the reflex of ejaculation.[10][11]
  2. Tactile stimulation of the clitoris (and the penis for the male) during copulation is transmitted to the brain (blue arrows).[12]
  3. Activation of the reward system induces learning which optimizes copulation, particularly by the development of sexual motivation.[13] Moreover, olfactive, auditory and visual signals perceived during the copulation may by conditioning become sexual signals,[14] which optimizes the innate pheromonal signals.[3]

There is thus, in the innate neurobiological organization of the organism, a true heterosexual reproductive behavior in non-primate mammals.[5][15]

Simplified diagram of the neurobiological circuits of the lordosis reflex in female mammals.[4][5][9] Lordosis is hardwired in the spinal cord and receives modulatory afferents from the forebrain. a) Median preoptic nucleus; b) Anterior hypothalamic nucleus; c) Ventromedial hypothalamic nucleus; d) Midbrain reticular formation; e) Vestibulo-spinal tract; f) Reticulo-spinal tract; g) Dorsal roots L1, L2, L5, L6 and S1

During estrus, the estrogen hormone, estradiol, regulates sexual receptivity by the neurons in the ventromedial nucleus[16] of the hypothalamus, the periaqueductal gray, and other areas of the brain. Sexual stimuli trigger activity in a number of brain areas, including the ventromedial hypothalamus, which 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 afferent nerve fibers in the spinal cord (L1-L6). These cause muscles along the spine to contract, thereby producing the lordosis posture. Because these afferent fibers are also part of a reflex arc, lordosis can be triggered reflexively.[17]

Lordosis can also be elicited by manual cutaneous stimulation of the flanks followed by the rump-tail base-perineum region,[17] or induced by injections of estradiol benzoate and progesterone.[18]

Lordosis is particularly marked among felines
Lordosis in lions

More precisely, the lordosis sexual reflex is mainly hardwired in the spinal cord, at the level of the lumbar and sacral vertebrae (L1, L2, L5, L6 and S1).[4] 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. For this reason, in general, the lordosis reflex is not functional.[9] 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.[19] The female is ready for copulation and fertilization.

During the copulation, when a male approaches the female, male pheromones (part 1 of the above diagram) are detected by the olfactory circuits (part 2). The pheromonal signals stimulate, among other things, the hypothalamus, which facilitates the lordosis reflex.[20] Then, when the male mounts the female (part 3), 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, 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 (part 4).[4] The lordosis position which results from it makes it possible to present the vagina properly to the male (part 5), facilitating penile intromission. Then, during intromission, tactile and deep sensations from the genital area and clitoris accentuate the lordosis reflex (part 6).[21] It is thus observed that the physiological and neurobiological organization of the lordosis behavior reflex is specifically adapted to heterosexual copulation.

Evolution, from rodent to human

Increased corticalization of the brain induces several changes in the control of sexual behavior, including lordosis.[15] Sexual reflexes, such as the motor reflex of lordosis, become secondary and are apparently no longer functional in human women.

Evolution of the main neurobiological factors that control the sexual behavior of mammals.[5][22]

In humans

As a result of these evolved differences, lordosis behavior became secondary in hominidae and is apparently non-functional in humans. When a woman gets onto all fours, curves her back and remains still, it is no longer a reflex movement triggered by sexual stimuli, but a voluntary movement.[5][23][24] The anthropologist Helen Fisher speculates that when a human female wears high-heeled footwear, the buttocks thrust out and the back arches into a pose that simulates lordosis behavior, which is why high heels are considered "sexy".[25]

See also

References

  1. 1 2 "Lordosis". Wordnik. Retrieved December 15, 2013.
  2. 1 2 Stowers L. , Holy T. E. , Meister M. , Dulac C. , Koentges G. (2002) Loss of sex discrimination and male-male aggression in mice deficient for TRP2, Science, 295(5559):1493-1500.
  3. 1 2 3 Moncho-Bogani J., Lanuza E., Hernandez A. , Novejarque A. , Martinez-Garcia F. (2002) Attractive properties of sexual pheromones in mice: innate or learned? Physiology & Behavior, 77(1):167-176.
  4. 1 2 3 4 5 6 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.
  5. 1 2 3 4 5 (French) Wunsch S. (2014) To understand the origins of human sexuality. Neurosciences, ethology, anthropology. Comprendre les origines de la sexualité humaine. Neurosciences, éthologie, anthropologie. L'Esprit du Temps.
  6. ↑ Keller M., Bakker J. (2009) Pheromonal communication in higher vertebrates and its implication on reproductive function. Editorial. Behavioural Brain Research, 200(2):237-238.
  7. ↑ Dulac C. , Torello A. T. (2003) Molecular detection of pheromone signals in mammals: from genes to behaviour, Nat. Rev. Neurosci., 4(7):551-562.
  8. ↑ Yoon H., Enquist L. W., Dulac C. (2005) Olfactory inputs to hypothalamic neurons controlling reproduction and fertility, Cell, 123(4):669-682.
  9. 1 2 3 4 Kow L.M., Florea C., Schwanzel-Fukuda M., Devidze N., Kami K.H., Lee A., Zhou J., Maclaughlin D., Donahoe P., Pfaff D. (2007) Development of a sexually differentiated behavior [lordosis] and its underlying CNS arousal functions. Curr. Top. Dev. Biol., 79:37-59
  10. ↑ Allard J. , Truitt W. A. , Mckenna K. E. , Coolen L. M. (2005) Spinal cord control of ejaculation, World J. Urol., 23(2):119-126.
  11. ↑ Coolen L. M. (2005) Neural control of ejaculation, J. Comp Neurol., 493(1):39-45.
  12. ↑ Matsumoto J., Urakawa S., Hori E., de Araujo M.F., Sakuma Y., Ono T., Nishijo H. (2012) Neuronal responses in the nucleus accumbens shell during sexual behavior in male rats. The Journal of Neuroscience, 32(5):1672-1686.
  13. ↑ Cibrian-Llanderal T., Tecamachaltzi-Silvaran M., Triana-Del R.R., Pfaus J.G., Manzo J., Coria-Avila G.A. (2010) Clitoral stimulation modulates appetitive sexual behavior and facilitates reproduction in rats. Physiology & Behavior, 100(2):148-153.
  14. ↑ Pfaus J.G., Kippin T.E., Coria-Avila G.A., Gelez H., Afonso V.M., Ismail N., Parada M. (2012) Who, what, where, when (and maybe even why)? How the experience of sexual reward connects sexual desire, preference, and performance. Archives of Sexual Behavior, 41(1):31-62.
  15. 1 2 Agmo A. (2007) Functional and dysfunctional sexual behavior
  16. ↑ Kow LM, Pfaff DW (May 1998). "Mapping of neural and signal transduction pathways for lordosis in the search for estrogen actions on the central nervous system". Behav. Brain Res. 92 (2): 169–180. doi:10.1016/S0166-4328(97)00189-7. PMID 9638959.
  17. 1 2 Pfaff, D.W.; Sakuma, Y. (1979). "Facilitation of the lordosis reflex of female rats from the ventromedial nucleus of the hypothalamus" (PDF). Journal of Physiology. 288 (1): 189–202.
  18. ↑ Olster, D.H.; Blaustein, J.D. (1989). "Development of steroid-induced lordosis in female guinea pigs: effects of different estradiol and progesterone treatments, clonidine, and early weaning.". Hormones and Behaviour. 23 (1): 118–129. doi:10.1016/0018-506x(89)90079-2. PMID 2538389.
  19. ↑ Flanagan-Cato L.M. (2011) Sex differences in the neural circuit that mediates female sexual receptivity. Frontiers in Neuroendocrinology, 32(2):124-136.
  20. ↑ Haga S., Hattori T., Sato T., Sato K., Matsuda S., Kobayakawa R., Sakano H., Yoshihara Y., Kikusui T., Touhara K. (2010) The male mouse pheromone ESP1 enhances female sexual receptive behaviour through a specific vomeronasal receptor. Nature, 466(7302):118-122.
  21. ↑ Gonzalez-Flores O., Beyer C., Lima-Hernandez F.J., Gomora-Arrati P., Gomez-Camarillo M.A., Hoffman K., Etgen A.M. (2007) Facilitation of estrous behavior by vaginal cervical stimulation in female rats involves alpha1-adrenergic receptor activation of the nitric oxide pathway. Behavioural Brain Research, 176(2):237-243.
  22. ↑ Nei M., Niimura Y., Nozawa M. (2008) The evolution of animal chemosensory receptor gene repertoires: roles of chance and necessity. Nat. Rev. Genet., 9(12):951-963.
  23. ↑ Wunsch S (2007) PhD thesis about sexual behavior Paris, Sorbonne.
  24. ↑ Georgiadis J.R., Kringelbach M.L., Pfaus J.G. (2012) Sex for fun: a synthesis of human and animal neurobiology. Nat. Rev. Urol., 9(9):486-498.
  25. ↑ Laura T. Coffey (Sep 23, 2009). "Do high heels empower or oppress women?". TODAY msnbc.com.
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