EURON and THEME joint PhD meeting

49
EURON and THEME joint meeting 2011
Labelling and optogenetic manipulation of learningrelated
neuronal assemblies.
Holger Dannenberg, Milan Pabst, Karen van Loo, Albert Becker, Susanne Schoch,
Heinz Beck
Department of Epileptology and Life&Brain Center, University Bonn, Sigmund-Freud-Str. 25, 53105 Bonn,
Germany.
Learning is thought to correlate with an initial change in the dynamics of a
specific assembly of neurons and a subsequent sustained change in the synaptic
connections between them. The propensity of this particular assembly of neurons
to be recruited into synchronized activity can then be viewed as a memory trace.
However, identifying these neuronal assemblies has been challenging.
Immediate early gene promoters (IEGs) could be good candidates to genetically
label cell populations active in-vitro, and to subsequently drive expression of
fluorescent markers or light-sensitive channels that allow specific millisecondscale
modulation of cellular activity. We have first compared the hippocampal
expression patterns of the IEGs Arc (also known as Arg3.1), Egr1 (also known as
zif268) and c-fos after a spatial learning paradigm in rats. We found an increase
in the number of cells in the hippocampus of trained rats and/or rats having
explored a novel environment compared to a cage control group. The expression
patterns showed a partial overlap with subregional differences between each of
the IEGs.
We first chose a core promoter from the Arc gene (termed synaptic-activityresponsive
element, SARE) to drive expression of the light-activated inhibitory
chloride-pump halorhodopsin (eNpHR3.0) fused to EYFP. We show that the
adenoviral approach is suitable to express eNpHR3.0-EYFP in principal cells of the
hippocampus and characterized the SARE activation pattern by comparing it with
the expression pattern of Arc, Egr1, and c-fos. eNpHR3.0-EYFP expressing cells
could be inhibited by photo-activation in acute hippocampal slices, confirming
its functionality in vitro. These approaches may permit the light-based activation
or inhibition of neurons participating in the neuronal engram, both in-vitro and
in-vivo.