Study shows how pheromones drive sexual behavior

A new mouse study investigates the effect of pheromones in male and female mice, revealing different brain circuits and various behavioral responses.

By
Ana Sandoiu
 
A new mouse study shows how
different brain circuits for males and females turn chemical signals into
either aggressive or sexual behavior, respectively.
Many of us have heard about
pheromones making some people seem more attractive than others, but little is
known about the exact mechanism that makes this possible.
In animals, sense of smell
plays a key role in regulating instinctive responses, and whether or not they
react to competitors, predators, or potential mates.
A team of researchers led by
Kazushige Touhara, a professor at the University of Tokyo’s Graduate School of
Agricultural and Life Sciences in Japan, set out to examine how male pheromones
enhance sexual behavior in female mice.
Prof. Touhara explains,
“It is widely known that some chemicals, especially odors, can impact an
animal’s instinctive behaviors even on first contact. We assumed there was a
neural mechanism in the brain that correctly connects important sensory
information to appropriate behavioral centers in the brain.”
A look at the sexual behaviour
of mice, our fellow mammals, can bring valuable insights into human
reproductive behavior. The findings were published in the journal Neuron.
Studying
pheromones in mice
Prof. Touhara and team
examined a male pheromone called exocrine gland-secreting peptide 1 (ESP1),
which has been shown in previous studies – referenced by the authors – to drive
sexual behavior in female mice and aggressive behavior in male mice.
ESP1 is different from other
pheromones because it is a single chemical that corresponds to a single
receptor, making it easier for the researchers to track.
To do so, the scientists
infected the ESP1 receptor neurons with a virus. Once the virus had spread, the
scientists marked the infected brain cells with a fluorescent protein, so that
they could see the neural circuit taken by the ESP1.
In other words, the
researchers were able to see how ESP1 signals are conveyed in the brain, as
neurons send electrical impulses to other neurons through the synapses.
Using this fluorescent viral
tracing method, Prof. Touhara and team saw that the circuit taken by the ESP1
signal in the amygdala differed between males and females. The amygdala was
shown to contain another subarea that acted as a “switch,” relaying
ESP1 information to different parts of the hypothalamus depending on the
mouse’s sex.
The amygdala is the part of
the brain’s limbic system, which deals with emotions, emotional behavior, and
motivation.
The researchers mapped how the
“ESP1 information is conveyed from the peripheral receptive organ to the
motor-regulating midbrain via the amygdala-hypothalamus axis.”
In females, sexual behavior
was modulated by a newly discovered pathway from the hypothalamus to the
midbrain.
The hypothalamus is the brain
area responsible for releasing hormones that regulate a variety of bodily
functions, including body temperature, appetite, sex drive, thirst, sleep, and
mood.
The study also revealed that
activating the ESP1 receptor neurons in the brain’s hypothalamus boosted sexual
activity in female mice, even when actual ESP1 was not present.
Different
neurons and predator cues
Additionally, the researchers
tested the response of receptor neurons to snake skin in the same brain area –
more specifically, in the brain’s dorsal ventromedial hypothalamus, which is a
region associated with defensive behavior. Snake skin is a predator cue signal
for mice, which makes them act aggressively in defense.
The scientists found no change
in sexual behavior after activating the neurons that responded to the predator
cue signals.
“This finding suggests
that there are two different types of neurons, ESP1 and predator neurons, and
only the former controls sexual behaviors in female mice,” Prof. Touhara
explains.
The authors note that more
research is needed to better understand how female sexual behavior works, as
well as how it can be regulated. Specifically, researchers could obtain a
strategy for turning male pheromones into a sexual response from the females.
This may provide valuable insight into how sexual dysfunctions arise.
SOURCE:
MEDICAL NEWS TODAY
Kayode Ojo
Kayode Emmanuel Ojo is the Co-Founder and Managing Director at SHEFFA Limited. He is presently studying Computer Science at the National Open University, Victoria Island, Lagos.