Optical controlling reveals timedependent roles for adult-born
dentate granule cells
Yan Gu, Maithe Arruda-Carvalho, Jia Wang, Stephen
R Janoschka, Sheena A Josselyn，
Paul W Frankland & Shaoyu Ge
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Background
The adult hippocampus continues to give rise to several
thousand new dentate granule cells everyday.
Studies using global perturbation or ablation of adult
hippocampal neurogenesis has revealed deficits in some
forms of hippocampal memory.
.
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Background
As the morphological and physiological phenotypes of
adult-born cells change markedly as they mature, they
may have distinct roles at different stages following
integration into hippocampal circuits.
Adult-born dentate granule cells (DGCs) extend dendrites
receive functional input from the existing neural circuits
as early as 2 weeks after birth.
Input (dendritic) synapses of adult-born neurons show
enhanced plasticity between 4–6 weeks after birth
compared with other stages.
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Questions
What is the precise timing for these adult-born
functional output synapse formation and maturation?
Whether do output synapses, if formed and functional,
also exhibit heightened plasticity around the same time?
What is its functional role?
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Methods
Retroviral birth-dating + Gene delivery
(EGFP+ Light gated ion channels)
Optogenetic stimulation
Electrophysiological
experiments
Synaptic transmission efficiency,
Capability of LTP
Behavioral
experiments
Water maze
Classical fear conditioning
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Results
Birth-dating and labeling newborn DGCs
Labeling specificity of newborn DGCs
with high-titer retrovirus
No mature DGC-like cells at 1 and 2 wpi
Experimental timeline
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Results
Adult-born neurons form functional synapses on
CA3 pyramidal neurons
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Adult-born DGCs fully integrate into the hippocampal trisynaptic circuits by ~4 wpi
Results
Heightened synaptic plasticity of young adult-born neurons
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Results
Output synapses of mature newborn DGCs remain plastic,
but have a higher induction threshold
Young newborn neurons exhibit heightened plasticity that peaks at ~4 wpi
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Conclusion 1
• Adult-born DGCs fully incorporate into the
hippocampal trisynaptic neural circuit
around 4 wpi and DGCs at this age have
more excitable membranes and enhanced
input/output synaptic plasticity.
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Results
Optical silencing of newborn DGCs does not
influence acquisition of spatial memory
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Results
Silencing young newborn neurons affects
spatial memory retrieval
labeled ~4-week-old adult-born DGCs regulate spatial memory retrieval. 12
Results
Silencing young newborn neurons impairs
retrival of contextural fear memory
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Results
The behavioral role for newborn DGCs relies on their age
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Results
Heightened plasticity in young newborn
neurons may be important for memory
retrieval
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Results
Silencing newborn neurons at 4 wpi, but not 8 wpi,
disrupted memory retrieval in both tasks
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Conclusion 2
• Adult-born neurons may be transiently
critical for memory retrieval, but the effect,
at least in spatial and contextual memory
retrieval, may decline as these adult-born
neurons continue to mature.
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Thank you
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