Smell the potassium: Surprising find in study of sex- and aggression-triggering vomeronasal organ

July 29, 2012, Stowers Institute for Medical Research
In an unexpected finding, Ron Yu and his team revealed that potassium channels contribute to the primary activation of the vomeronasal organ, which detects pheromones. Credit: Illustration: Courtesy of Dr. Ron Yu, Stowers Institute for Medical Research

The vomeronasal organ (VNO) is one of evolution's most direct enforcers. From its niche within the nose in most land-based vertebrates, it detects pheromones and triggers corresponding basic-instinct behaviors, from compulsive mating to male-on-male death matches. A new study from the Stowers Institute for Medical Research, published online in Nature Neuroscience on July 29, 2012, extends the scientific understanding of how pheromones activate the VNO, and has implications for sensory transduction experiments in other fields.

"We found two new ion channels—both of them —through which VNO are activated in mice," says Associate Investigator C. Ron Yu, Ph.D., senior author of the study. "This is quite unusual; potassium channels normally don't play a direct role in the activation of sensory neurons."

Humans have shrunken, seemingly vestigial VNOs, but still exhibit instinctive, pre-programmed behaviors relating to reproduction and aggression. Scientists hope that an understanding of how the VNO works in mice and other lower mammals will provide clues to how these innate behaviors are triggered in humans.

The VNO works in much the same way as the main olfactory organ that provides the sense of smell. Its neurons and their input stalks, known as dendrites, are studded with specialized receptors that can be activated by contact with specific messenger-chemicals called pheromones, found mostly in body fluids. When activated, VNO receptors cause adjacent ion channels to open or close allowing ions to flood into or out of a neuron. These inflows and outflows of electric charge create voltage surges that can activate a VNO neuron, so that it signals to the brain to turn on a specific behavior.

In 2002, as a postdoctoral researcher at Columbia University, Yu was a member of one of the first teams to find that VNO receptors rely heavily on a calcium channel called TRPC2. But there were hints that VNO neurons use other ion channels too; and in a study reported last November in Nature Communications, Yu's team at Stowers, including first author SangSeong Kim, Ph.D., a postdoctoral researcher, found evidence for the role of a chloride-specific channel, CACC.

In the new study, Yu, Kim and their colleagues looked for VNO potassium channels, which admit positively charged . They began by setting up whole-cell patch clamp tests, in which tiny electrodes measure the net flow of charged ions through the membranes of neurons in a slice of mouse VNO tissue. To determine the contribution of potassium ions to these currents, they replaced the potassium ions in the neurons with chemically similar cesium ions, which cannot get through potassium channels. When these potassium-depleted VNO neurons were exposed to pheromone-containing mouse urine, the usual net inward flow of positive charge was significantly greater than it had been when the neurons contained potassium.

That and other experiments with the VNO tissue slices suggested that potassium ions normally flow out of VNO neurons through potassium channels when a VNO receptor is activated. This was not completely unexpected; neurons typically have a greater concentration of potassium ions inside than outside, leading to an outward flow when potassium channels are opened. The outward flow originates mostly from the main bodies of neurons and helps reset neurons to a resting state voltage. However, in the VNO neurons a strong outward flow of potassium also occurred within the dendrites, directly countering the inward flow of positive ions that would activate the neurons. "It seemed a bit bizarre that such an important system would work against itself in this way," Yu says.

The team was able to zero in on the two potassium channels responsible, which are known as SK3 and GIRK. But when they set up experiments to evaluate these channels not in VNO tissue slices but "in vivo"—in the working VNOs of live mice—they found a very different result: On balance the potassium channels now sent potassium ions in the inward direction. In fact, these two newly discovered channels seemed to account for more than half of the VNO-activating current.

This inflowing-potassium phenomenon is known to occur in another type of sensory neuron, the sound-sensitive cochlear hair cell, whose external environment contains relatively high levels of potassium. "This made us wonder whether the VNO also has a high level of potassium in the fluid surrounding its dendrites," says Kim.

It does. It turns out that the standard preparation of tissue slices for the initial patch-clamp experiments had washed away that naturally high concentration. The resulting low concentration had misleadingly caused potassium ions to be sucked out of VNO neuron dendrites when the SK3 and GIRK potassium channels were opened. "It's a cautionary tale that shows the importance of doing in vivo experiments," Yu says.

The finding that potassium channels contribute to the primary activation of the VNO could be a clue to the origins of the organ. "We speculate that the VNO may have evolved to have a high extracellular concentration of ions, as well as multiple , so that it remains functional even when it comes into contact with various ion-rich bodily fluids," Yu says. "The diversity of signaling pathways perhaps make it more robust in triggering innate behaviors."

Explore further: Rival, predator, mate: Mapping the molecules that detect chemical cues

Related Stories

Rival, predator, mate: Mapping the molecules that detect chemical cues

September 29, 2011
(Medical Xpress) -- The chemical cues that signal animals’ identity are so important to letting other individuals know how to behave in the presence of a member of their own species – whether to mate or fight, for ...

Neuroscientists' discovery could bring relief to epilepsy sufferers

June 21, 2011
Researchers at the University of California, Riverside have made a discovery in the lab that could help drug manufacturers develop new antiepileptic drugs and explore novel strategies for treating seizures associated with ...

Recommended for you

Research reveals atomic-level changes in ALS-linked protein

January 18, 2018
For the first time, researchers have described atom-by-atom changes in a family of proteins linked to amyotrophic lateral sclerosis (ALS), a group of brain disorders known as frontotemporal dementia and degenerative diseases ...

Fragile X finding shows normal neurons that interact poorly

January 18, 2018
Neurons in mice afflicted with the genetic defect that causes Fragile X syndrome (FXS) appear similar to those in healthy mice, but these neurons fail to interact normally, resulting in the long-known cognitive impairments, ...

How your brain remembers what you had for dinner last night

January 17, 2018
Confirming earlier computational models, researchers at University of California San Diego and UC San Diego School of Medicine, with colleagues in Arizona and Louisiana, report that episodic memories are encoded in the hippocampus ...

Recording a thought's fleeting trip through the brain

January 17, 2018
University of California, Berkeley neuroscientists have tracked the progress of a thought through the brain, showing clearly how the prefrontal cortex at the front of the brain coordinates activity to help us act in response ...

Midbrain 'start neurons' control whether we walk or run

January 17, 2018
Locomotion comprises the most fundamental movements we perform. It is a complex sequence from initiating the first step, to stopping when we reach our goal. At the same time, locomotion is executed at different speeds to ...

Neuroscientists suggest a model for how we gain volitional control of what we hold in our minds

January 16, 2018
Working memory is a sort of "mental sketchpad" that allows you to accomplish everyday tasks such as calling in your hungry family's takeout order and finding the bathroom you were just told "will be the third door on the ...

4 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

JVK
5 / 5 (1) Jul 29, 2012
Whether receptor-mediated signal transduction occurs via a VNO and AOS or through the main olfactory system (MOS) it is the molecular biology common to all species which assures us that olfaction and odor receptors provide a clear evolutionary trail that can be followed from unicellular organisms to insects to humans. The adaptive evolution of a common response to food odors and mammalian pheromones, including human pheromones, is the GnRH-directed luteinizing hormone (LH) response that links the epigenetic effects of human pheromones and food odors directly to the socioaffective nature of evolved behaviors, as detailed in: Kohl, J.V. (2012) Human pheromones and food odors: epigenetic influences on the socioaffective nature of evolved behaviors. Socioaffective Neuroscience & Psychology, 2: 17338.
http://dx.doi.org...i0.17338
Osiris1
not rated yet Jul 29, 2012
Next all the fourteen years old boys will be asking how to "activate" the VNO's in their girlfriends.
JVK
not rated yet Jul 29, 2012
There is no functional human VNO, which means it is obviously not required for the response to human pheromones that can be measured in assays of luteinizing hormone (LH).
JVK
not rated yet Jul 29, 2012
A mixture of androstenol and androsterone appears to alter the LH response in women and increases their ovulatory phase observed flirtatious behavior, and self-reported level of attraction. See for example: Human pheromones, epigenetics, physiology, and the development of animal behavior http://posters.f1000.com/P1387

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.