Evolution Update

Evolution Update

Scientists Identify Pheromones That Elicits Sexual Response in Male Mice

Irma Shaboian January 18, 2016

Researchers develop a new technique that allowed them to elucidate the structure of two chemicals in female urine that were responsible for sexual interest and behaviour in male mice.

Communication between species is understood to be mediated in some way by pheromones. First coined in 1959, pheromones are chemical substances excreted/secreted by an animal into the environment which triggers a response in another animal of the same species—typically of the opposite sex. The odourless airborne compound typically conveys information subconsciously, such as mood or sex, about its provider to the receiver, often resulting in sexual interest.

The regulation of the receiver’s behaviour is mediated by the accessory olfactory system (AOS), more commonly known as an animal’s sense of smell. When an airborne chemical substance is detected in the cells of the nose, a message is sent to the brain about it. Simply put, pheromones function as chemical stimuli that serves a communicatory role between two animals when processed by the brain. Once the information is processed by the receiving animal, they are able to respond.

While the mechanism through which pheromonal communication occurs and the accompanied social cues that follow it are understood, the specific chemical compounds and their structure is less well-known.

Scientists at Washington University School of Medicine in St.Louis created a unique technique to identify the molecular compounds in female mice urine that are responsible for instigating both investigation of the female urine and mounting behaviour. The newly developed technique referred to as CAM (for component-activity matching) takes advantage of the fact that different urine samples result in different patterns of excitement in nerve cells in the nose.

In what could be described as a process of elimination, the researchers picked among compounds whose concentrations in the urine of the female mice matched the pattern of activity in the male mice’s nerve cells. Doing so allowed for the identification of two molecular compounds (titled as M377 and M361) that were responsible for the examination of female urine and sexual excitement in male mice.

Both compounds are categorized as carboxylic acid steroid metabolites, which are the waste products of hormone metabolism that are unique to female mice.

The researchers observed that when M377 was added to male urine, which originally does not contain it, other male mice increased the time they spent investigating the urine. Similarly, when the female mice that did not contain the metabolites originally (due to a lack of ovaries) had the metabolites added to their urine, male mice increased their investigation of the urine and sexual excitement was observed.

The identification of the chemical compounds that were responsible for the observed effects was unique to female mice. That is, researchers examined the urine of hamsters and rabbits for M377 and it was not present. This suggested that M377 is a female-specific cue for mice and its utility could be a means of species recognition between the sexes.

For humans, the effect of pheromones is still an on-going debate. Unlike mice, some research suggests that human body odour may influence the selection of a partner or sexual preference. But because of the large and complex human brain in comparison to other mammals, it becomes more difficult to discern the ability of pheromones to influence the behaviour of the receiver—especially since human odor is typically masked.

Nevertheless, the CAM technique developed by scientists at Washington University may serve as a tool for understanding the molecular identify of pheromones in future studies when exploring neurobiology and sexual selection.

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