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Pico CARONI "Structural remodeling of hippocampal microcircuits in the adult"

Abstract :

Sustained rearrangements of synaptic connections could provide mechanisms
to alter connectivity in neuronal circuits, and encode experience in the brain, but evidence that sustained net rearrangements of connectivity do take place in the adult had been lacking.
We have investigated rearrangements of connectivity between hippocampal mossy fibers and CA3 pyramidal neurons. We found that mossy fibers establish 8-10 local terminal arborization complexes (LMT-Cs) in CA3 exhibiting major differences in size and divergence in adult mice. LMT-Cs exhibited two types of long-term rearrangements in connectivity in the adult: progressive expansion of LMT-C subsets along individual dendrites throughout life, and pronounced increases in LMT-C complexities in response to enriched environment. In organotypic slice cultures, subsets of LMT-Cs also rearranged extensively and grew over weeks and months, altering the strength of preexisting connectivity, and establishing or dismantling connections with pyramidal neurons. LMT-C maintenance and growth were regulated by spiking activity, mGluR2-sensitive transmitter release from LMTs, and PKC.
I will summarize those findings and present very recent results providing evidence for the existence of subtypes of hippocampal granule cells, which differ in their gene expression patterns and their axonal connectivities. Furthermore, I will show how, for each subtype of granule cell, structural plasticity is largely restricted to a very small subset of its presynaptic terminals (one or 2-3, depending on the type of granule cell), and how this striking property leads to a systematic shift in the connectivity of mossy fibers as a function of age and experience. 

Selected publications

Willmann R, Pun S, Stallmach L, Sadasivam G, Santos AF, Caroni P, Fuhrer C.
Cholesterol and lipid microdomains stabilize the postsynapse at the neuromuscular junction.
EMBO J. 2006 Sep 6;25(17):4050-60.
Galimberti I, Gogolla N, Alberi S, Santos AF, Muller D, Caroni P.
Long-term rearrangements of hippocampal mossy fiber terminal connectivity in the adult regulated by experience.
Neuron. 2006 Jun 1;50(5):749-63.
De Paola V, Holtmaat A, Knott G, Song S, Wilbrecht L, Caroni P, Svoboda K.
Cell type-specific structural plasticity of axonal branches and boutons in the adult neocortex.
Neuron. 2006 Mar 16;49(6):861-75.

Pun S, Santos AF, Saxena S, Xu L, Caroni P.
Selective vulnerability and pruning of phasic motoneuron axons in motoneuron disease alleviated by CNTF.
Nat Neurosci. 2006 Mar;9(3):408-19. Epub 2006 Feb 12.