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8 INSIDE SALK

SUMMER 2016

WWW.SALK.EDU

When tweaking its architecture, the

adult brain works like a sculptor—

starting with more than it needs so it

can carve away the excess to achieve an

ideal design. That’s the conclusion of a

new study that tracked developing cells

in an adult mouse brain in real time.

New brain cells began with a period of

overgrowth before the brain pruned

back its connections. The observation,

describedMay 2016 in

Nature

Neuroscience

, suggests that novel cells

in the adult brain have more in common

with those in the embryonic brain than

scientists previously thought.

While most of the brain’s billions of cells

are formed before birth, Salk Professor

Rusty Gage and others previously

showed that in a few select areas of the

mammalian brain, stem cells develop

into new neurons during adulthood. In

this study, his group focused on cells

in the dentate gyrus, an area thought

to be responsible for the formation of

memories.

Gage and first author Tiago Gonçalves

followed—on a daily basis—the growth

of neurons over several weeks. When

mice were housed in environments

with lots of stimuli, the new cells grew

quickly, sending out dozens of branches

called dendrites which receive electrical

signals from surrounding neurons.

When kept in empty housing, new

neurons grew slightly slower and sent

out less dendrites. But, in both cases, the

new dendrites began to be pruned back.

Defects in the dendrites of neurons

have been linked to brain disorders like

schizophrenia, Alzheimer’s, epilepsy and

autism. Charting how the brain shapes

these branches—both during embryonic

development and in adulthood—may be

the key to understanding mental health.

DISCOVERIES

ADULT BRAIN

PRUNES

BRANCHED

CONNECTIONS

OF NEW

NEURONS

Defects in the dendrites

of neurons have been

linked to numerous

brain disorders

including Alzheimer’s

and schizophrenia.

Charting how the

brain shapes these

branches may be the

key to understanding

mental health.

NEUROSCIENCE

Over a period of about a month, the Salk team

kept track of each new neural branch, called

a dendrite, on growing neurons, as well as

each dendrite that was pruned away. Here, the

branches of one cell are shown—new dendrites

are in green, those pruned away are orange, and

dendrites that both developed and were pruned

away since the last snapshot are in pink.