The Bruce , or block of pregnancy, is a predisposition for female mice to terminate their pregnancy after exposure to the aroma of unfamiliar men. This effect was first recorded in 1959 by Hilda M. Bruce, and was particularly studied in laboratory mice (Mus musculus). In mice, pregnancy can only be stopped before embryo implantation, but other species will interfere with even long-term pregnancy.
The Bruce effect was also observed in mice-deer, rats of prairie, collared leming, and it has also been proposed, but not confirmed, in other non-mouse species such as lions and geladas.
Video Bruce effect
Discovery
In an experiment published in 1959, zoologist Hilda Bruce from the National Institute of Medical Research in London placed pregnant rats with male mice that were not the father of the embryos being carried. As a result, the rate of miscarriage increases, followed by mating with a new male. No increase in miscarriage occurs when pregnant rats are paired with castrated male rats or adolescents. The effect remains when male rats are kept out of sight or hearing of women. This shows that women distinguish men by smell. To test this hypothesis, Bruce and his colleague Alan Parkes recruited perfume to kiss the pieces of cloth from the rat cage. Perfume makers can differentiate the scents of different mouse strains.
Maps Bruce effect
Action mechanism
Pheromone detection
The vomeronasal system serves as a "vascular pump" which, stimulated by the presence of a new male, actively attracts the substance. Male rats urine contains class I MHC peptides that bind to receptors in female vomeronasal organs, structures containing mucus in the nasal septum. These chemical signals, which are specific to every man, are studied by females at mating, or shortly thereafter. The vasopressin hormone is essential in combining chemosensory gestures with appropriate physiological responses. When the vasopressin 1b receptor gene is exposed in women, the presence of unknown men does not trigger a pregnancy disorder.
Get to know a familiar man
Exposure to male urinary pheromones will activate the neuroendocrine pathway leading to failure of pregnancy. However, if the pheromones are related to the memorized by the female (usually male mating pair), noradrenaline release will decrease the receiving power of the olfactory bulb accessory to this pheromone. Pregnancy disorders will, therefore, be avoided. This noradrenaline role has recently been questioned. Oxytocin hormone is also important in the process of this social memory. Women treated with oxytocin antagonists can not recognize their partner's bladder, and will terminate pregnancy when exposed to men, known or unknown.
Neuroendocrine Path
Activation of vomeronasal neuron receptors by male pheromones triggers complex neuroendocrine pathways. The pheromonal information travels through the nerve to an olfactory accessory bulb, and then to the corticomedial amygdala, the accessory olfactory channel, and the stria terminalis. This area stimulates the hypothalamus to increase the release of dopamine, thereby preventing the secretion of prolactin from the anterior pituitary. In the absence of prolactin, hormones are important to maintain the corpus luteum, luteolysis occurs. Because the corpus luteum can no longer release progesterone, the uterus remains untreated for implantation of the embryo, and the pregnancy fails.
The role of estrogen
Androgens and estrogens, especially estradiol (E2), are also important chemosignals that regulate Bruce's effects. However, they are believed to act through a separate path to the ones discussed above. Small steroid molecules such as E2 can enter the bloodstream directly through the ingestion of the nose and travel to the uterus, which has a high receptor density. Normally, E2 is essential in preparing the blastocyst and uterus for implantation. However, excessive E2 will prevent implantation from taking place. Neutered men are unable to stop a woman's pregnancy unless the castrated male is given testosterone. estradiol, a metabolic product of testosterone, is known to interfere with pregnancy in women, and is present in male urine.
Time
The incidence of Bruce's effects depends on the exposure time of pheromone. After mating, females undergo prolactin twice daily. Pregnancy is only terminated if exposure to a new male aroma coincides with two prolactin spikes, one of which occurs in the daytime period.
Evolutionary benefits
In order to be able to evolve and survive in the population, Bruce's effects must provide fitness benefits for the individual. The possible advantages of pregnancy blocks are widely debated.
Men
When given the opportunity, male rats tend to direct their urine toward women. This allows men to improve their fitness success by "sabotaging" a male competitor's pregnancy, and faster returning a woman to estrus. Bruce's effects can also help in maintaining social status, with dominant males leaving more signs of urinal scent, and thus inhibiting pregnancies initiated by subordinate men.
Female
Source of the article : Wikipedia
0 Comments