Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Olfactory System Detects Pheromones that Control Reproduction

11.11.2005


Howard Hughes Medical Institute researchers have discovered that pheromones essential for mating behavior in mice are recognized by the nose and not by the vomeronasal system, as researchers had long suspected.



The new studies demonstrate that the main olfactory epithelium, which was presumed to be mostly involved with the sense of smell, plays a critical role in pheromone detection.

Howard Hughes Medical Institute investigator Catherine Dulac and colleagues Hayan Yoon, an HHMI predoctoral fellow, and Lynn W. Enquist published their findings in an immediate early publication on November 10, 2005, in the journal Cell. Yoon and Dulac are at Harvard University, and Enquist is at Princeton University. Related studies by HHMI investigator Linda B. Buck are published in the same issue.


The pheromone communication system, which is found in a wide range of mammals, involves detection of chemical odorants released by animals. Pheromones are chemicals that are involved in changing behavior or hormone secretion. According to most biology textbooks, detection of pheromones takes place in a specialized structure, called the vomeronasal organ (VNO). Although the VNO resides in the nasal cavity, the pheromone sensory system is distinct from the sense of smell, as are the chemical receptors involved. In animals possessing a pheromone sensory system — including mice, dogs, cats, and elephants — the system governs a range of genetically preprogrammed mating, social ranking, maternal, and territorial defense behaviors.

In their experiments, Dulac and her colleagues sought to determine whether sensory neurons in the main olfactory epithelium and the VNO were connected to neurons in the brain that synthesize luteinizing hormone releasing hormone (LHRH). LHRH controls the onset of puberty. In females it also stimulates ovulation and controls the estrus cycle. In males, the hormone controls gonad function, including spermatogenesis and testosterone production.

“One of the classical dogmas is that LHRH neurons receive inputs from the vomeronasal system. For example, textbooks on reproductive physiology say that pheromonal modulation of reproductive behavior depends on these connections,” said Dulac. “However, our studies show that this idea is wrong.”

Previous experiments designed to tease out the routes of neurons used techniques that depended heavily on dyes that could not label specific populations of neurons. These experiments suggested that neurons of the vomeronasal system are directly connected with LHRH neurons, and thus carry the modulatory effect of pheromonal cues on LHRH release. But because classical tracing techniques could not specifically identify the connection of neuronal subsets, they ended up tracing the routes of groups of undefined neuronal populations clustered around LHRH producing neurons, Dulac said.

In the experiments reported in Cell, Dulac and her colleagues used a genetically altered version of a pseudorabies virus that is a highly specific tracer, permitting the researchers to label neurons with a fluorescent protein marker. This technique relied on a conditional approach that caused the pseudorabies virus to replicate only when it was triggered by a specific genetic signal. The researchers also created a transgenic mouse in which neurons expressing LHRH provided that signal, making the viral tracer highly specific.

“So, whenever we saw a signal from the conditional virus, we knew we were seeing connections to neurons expressing LHRH and nothing else,” said Dulac. As a control, the researchers also used a “non-conditional” strain of pseudorabies virus that infected all types of neurons.

The researchers chose pseudorabies virus for their studies because it could be introduced into a neuron and infect its way upstream along the network of axons that connect neurons. The virus could also jump the synapses between neurons, as it moved from one neuron to the next. As a result, the researchers could use the pseudorabies virus to obtain a detailed look at all of the neurons that were connected to each other.

“Our conditional tracing studies showed a major projection to LHRH neurons from the main olfactory epithelium and the structures that comprise the primary olfactory complex,” said Dulac. “This major route was never suspected. In addition, we were quite surprised when we realized we could not identify any connections with the vomeronasal system, which led us to attempt to confirm the experiment on a wide range of mice,” she said.

As a control, the researchers performed a separate set of experiments using a non-conditional strain of the pseudorabies virus. These studies confirmed that the virus was capable of infecting all nuclei comprising the vomeronasal system.

Next, the researchers postulated that one should be able to identify functional correlates of the anatomical circuit linking olfactory neurons and LHRH-producing neurons. They studied the sexual behavior of mutant mouse strains that lacked either a functional olfactory epithelium or vomeronasal organ. They also studied the behavior of normal mice in which the olfactory epithelium had been selectively destroyed by a drug.

They found that the male mice that lacked a functioning olfactory epithelium showed little interest in females, with greatly reduced investigatory or mounting behavior. By contrast, male mice lacking a vomeronasal organ were able to mate. The researchers also discovered that LHRH neurons in the olfactory-deficient male mice were no more activated by exposure to female urine — which normally elicits sexual behavior — than exposure to water.

Future studies will aim at further characterizing the network of connections from the olfactory system to LHRH neurons in many brain structures, said Dulac. Also, the researchers plan to explore how olfactory and vomeronasal neurons work together in mice to control reproductive behavior.

Dulac said that extending the conclusions from their studies in mice to humans is “totally speculative, but extremely interesting. There have been many observations of behavior in humans that suggest we react to pheromones,” she said. “For example, it is known that women who live in close quarters tend to have synchronized menstrual cycles. But it was also believed that humans would need a functional vomeronasal organ in order to sense pheromones — and there is no evidence for such an organ in humans.

“But now that we have identified an olfactory circuit that plays a role in sexual behavior in rodents, this requires us to rethink how mammals detect pheromones. It is quite tempting to speculate that there might be such a circuit in humans,” said Dulac. “We must also rethink the simplistic division of olfaction, in which the main olfactory system governs cognitively based behavior and the vomeronasal system governs hard-wired, pheromone-triggered behaviors.”

Jim Keeley | EurekAlert!
Further information:
http://www.hhmi.org/news/dulac20051110.html

More articles from Studies and Analyses:

nachricht New study: How does Europe become a leading player for software and IT services?
03.04.2017 | Fraunhofer-Institut für System- und Innovationsforschung (ISI)

nachricht Reusable carbon nanotubes could be the water filter of the future, says RIT study
30.03.2017 | Rochester Institute of Technology

All articles from Studies and Analyses >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Fighting drug resistant tuberculosis – InfectoGnostics meets MYCO-NET² partners in Peru

28.04.2017 | Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

 
Latest News

Wireless power can drive tiny electronic devices in the GI tract

28.04.2017 | Medical Engineering

Ice cave in Transylvania yields window into region's past

28.04.2017 | Earth Sciences

Nose2Brain – Better Therapy for Multiple Sclerosis

28.04.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>