Scents and social preference: Neuroscientists ID the roots of attraction

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Media Release
A baby lamb is separated from
its family. Somehow, in vast herds of sheep that look virtually identical, the
lost youngling locates its kin. Salmon swim out to the vast expanses of the sea
and migrate back home to their precise spawning grounds with bewildering
Scientists have long known
about such animal kinship attachments, some known as “imprinting,”
but the mechanisms underlying them have been hidden in a black box at the
cellular and molecular levels. Now biologists at the University of California
San Diego have unlocked key elements of these mysteries, with implications for
understanding social attraction and aversion in a range of animals and humans.
Davide Dulcis of UC San
Diego’s Psychiatry Department at the School of Medicine, Giordano Lippi, Darwin
Berg and Nick Spitzer of the Division of Biological Sciences and their
colleagues published their results in the online issue of the journal Neuron.
In a series of neurobiological
studies stretching back eight years, the researchers examined larval frogs
(tadpoles), which are known to swim with family members in clusters. Focusing
the studies on familial olfactory cues, or kinship odors, the researchers
identified the mechanisms by which two- to four-day old tadpoles chose to swim
with family members over non-family members. Their tests also revealed that
tadpoles that were exposed to early formative odors of those outside of their
family cluster were also inclined to swim with the group that generated the
smell, expanding their social preference beyond their own true kin.
The researchers discovered
that this change is rooted in a process known as “neurotransmitter
switching,” an area of brain research pioneered by Spitzer and further
investigated by Dulcis in the context of psychostimulants and the diseased
brain. The dopamine neurotransmitter was found in high levels during normal
family kinship bonding, but switched to the GABA neurotransmitter in the case
of artificial odor kinship, or “non-kin” attraction.
“In the reversed
conditions there is a clear sign of neurotransmitter switching, so now we can
see that these neurotransmitters are really controlling a specific
behavior,” said Dulcis, an associate professor. “You can imagine how
important this is for social preference and behavior. We have innate responses
in relationships, falling in love and deciding whether we like someone. We use
a variety of cues and these odorants can be part of the social preference
The scientists took the study
to a deeper level, seeking to find how this mechanism unfolds at the genetic
Sequencing helped isolate two
key microRNAs, molecules involved in coordinating gene expression. Sifting through
hundreds of possibilities they identified microRNA-375 and microRNA-200b as the
key regulators mediating the neurotransmitter switching for attraction and
aversion, affecting the expression of genes known as Pax6 and Bcl11b that
ultimately control the tadpole’s swimming behavior.
“MicroRNAs were ideal
candidates for the job,” said Lippi, a project scientist in Berg’s
laboratory in the Division’s Neurobiology Section. “They are
post-transcriptional repressors and can target hundreds of different mRNAs to
consolidate specific genetic programs and trigger developmental switches.”
The study began in 2009 and
deepened in size and scope over the years. Reviewers of the paper were
impressed with the project’s breadth, including one who commended the authors
“for this heroic study which is both fascinating and comprehensive.”
“Social interaction,
whether it’s with people in the workplace or with family and friends, has many
determinants,” said Spitzer, a distinguished professor in the Division of
Biological Sciences, the Atkinson Family Chair and co-director of the Kavli
Institute for Brain and Mind at UC San Diego. “As human beings we are
complicated and we have multiple mechanisms to achieve social bonding, but it
seems likely that this mechanism for switching social preference in response to
olfactory stimuli contributes to some extent.”
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.