Home' Trinidad and Tobago Guardian : February 16th 2017 Contents B26 body & soul
guardian.co.tt Thursday, February 16, 2017
Scientists illuminate the
neurons of social attraction
The ancient impulse to procreate is necessary for
survival and must be hardwired into our brains.
Now scientists from the University of North Car-
olina School of Medicine have discovered an im-
portant clue about the neurons involved in that
Using advanced deep brain imaging techniques and
optogenetics, the UNC scientists found that a small
cluster of sex-hormone-sensitive neurons in the mouse
hypothalamus are specialised for inducing mice to "no-
tice" the opposite sex and trigger attraction.
This study, led by Garret Stuber, PhD, associate pro-
fessor of psychiatry and cell biology & physiology, and
Jenna McHenry, PhD, a postdoctoral research associate
in Stuber's lab, identified a hormone-sensitive circuit in
the brain that controls social motivation in female mice.
"These neurons essentially take sensory and hor-
monal signals and translate them into motivated so-
cial behaviour," said Stuber, who is also a member of
the UNC Neuroscience Center. The findings, reported
in Nature Neuroscience, illuminate the neural roots of
opposite-sex social behaviour in mammals, and may
also be relevant to certain psychiatric illnesses.
"These neural circuits that bridge social and reward
processing should also provide important insights for
disorders that impair social motivation," said McHenry,
the first author of the paper. In the study, Stuber and
colleagues examined the medial preoptic area (mPOA)
of the brain. This clump of neurons sits within the hy-
pothalamus, an evolutionarily ancient structure at the
bottom-centre of the brain. Prior research showed that
the mPOA is important for social and reproductive be-
haviour in all vertebrate species studied from fish to
human, but it has been unclear whether this area drives
social motivation through circuit connections with re-
ward systems in the brain.
The researchers focused on one of the mPOA's major
connections, through which it sends neural signals to
another brain structure called the ventral tegmental area
(VTA)---known to be a powerful contributor in motivat-
ing behaviour and the release of the neurotransmitter
dopamine. The researchers injected the VTAs of female
mice with special fluorescent beacon molecules that, like
some viruses, tend to move "upstream" along nerve con-
nections. When these tiny beacons reached the mPOA,
they ended up highlighting VTA-projecting neurons
that express a gene called neurotensin. Analyses of these
VTA-projecting neurons showed that most of them also
express estrogen receptors and are therefore likely to be
sensitive to rises and falls of ovarian hormones in the
mouse fertility cycle, also known as the estrus cycle.
The researchers next studied this specific set of mPOA
neurons in living mice, which was a considerable chal-
lenge. The microscopy techniques that permit imaging
of brain cells in awake mice generally can't visualise an-
ything deeper than a fraction of a millimetre below the
brain's surface, whereas the mPOA is several millimetres
deep. To get around this problem, Stuber's team used
tiny tubular lenses connected from their microscope,
in effect, to the mPOA. With a technique known as
two-photon calcium imaging, the scientists were
then able to visualise the activity of mPOA neurons in
awake, behaving female mice. To enhance the accuracy
of the technique, the researchers used mice that had
been genetically engineered so that only their mPOA
neurotensin neurons could be imaged.
"With our setup, we could image the mice a couple of
times a week and each time find the same cells that we
previously recorded brain activity from," Stuber said.
The team found that when the female mice were ex-
posed to the odour of male mouse urine---but not the
odour of female mouse urine or other attractive odours,
like appetising food---a large subset of the mPOA neu-
rotensin neurons was excited into greater activity. The
researchers also found that these neurons responded
more robustly to male mouse urine when females had
high circulating levels of estrogen or a combination of
These are neurotensin cells in the medial preoptic
brain area, imaged by Jenna McHenry, PhD, through a
2-photon microscope attached to a live mouse.
estrogen/progesterone, which surges
before the mice become fertile.
"This suggests that certain neurons
in the brain may be specialised to prefer
social rewards over nonsocial rewards,
and that the processing of social cues
is sensitive to circulating hormones,"
McHenry said. Using optogenetics, the
scientists artificially stimulated the ac-
tivity of the mPOA neurotensin neurons
using light. They observed that this stim-
ulation triggered the release of the VTA
neurotransmitter dopamine in a key mo-
tivation-related structure downstream
from the VTA. Both male and female mice
whose mPOA neurotensin neurons were
artificially driven this way showed a pref-
erence in standard tests for moving closer
to mice of the opposite sex.
"On the whole, the data suggest that
these mPOA neurons help drive social
attraction toward a potential mate,"
(University of North Carolina Health Care)
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