Mental retardation syndromes and age-related cognitive diseases are disorders that degrade the quality of life of afflicted individuals and apply a serious toll on society in general. While the causes of some of these conditions are known, the basis for cognitive impairment is generally not understood. Current theories suggest that many forms of impairment arise from aberrant spine morphology and synaptic plasticity and that facilitation of these processes will enhance cognitive function. The endogenous neurotrophin, brain derived neurotrophic factor (BDNF) modulates spine shape and facilitates synaptic plasticity in adult brain. These and other results suggest that BDNF may be critical for structural changes that underlie functional synaptic plasticity. The proposed research will investigate the role of endogenous BDNF signaling via its TrkB receptor in activity-induced remodeling of the dendritic spine actin cytoskeleton and synapse size in association with long term potentiation (LTP), a form of plasticity thought to underlie learning. Studies will use adult rat hippocampal slices to test the hypothesis that theta burst afferent stimulation (TBS) elicits BDNF-dependent activation of spine TrkB which, in turn, signals through the actin regulatory protein cofilin to increase spine F-actin levels and the size of synapses involved in LTP.
Aim 1 will test if TBS activates TrkB in spines engaged in LTP: immunocytochemistry and restorative deconvolution microscopy will be used to test if TBS activates TrkB (i.e., increases Trk autophosphorylation) in the lamina of afferent stimulation.
Aim 2 will use similar techniques to test if TBS effects on phospno-Trk depend on both extracellular TrkB ligands and signaling from integrins (the latter known to modulate receptor tyrosine kinase activities in other systems).
Aim 3 will test the hypothesis that TBS-induced Trk signaling contributes to activation of an actin signaling cascade and to an increase in synapse size. The separate studies under Aim 3 will test (3A) if TBS increases the size of PSD95-immunoreactive synapses associated with phospho- Trk, (3B) if TBS-induced increases phospho-Trk are upstream to changes in the spine filamentous (F)-actin (i.e. are not blocked by latrunculin A which prevents actin filament assembly) and (3C) if signaling through TrkB is needed for TBS-induced increases in spine phospho-PAK, spine phospho-cofilin, and increases in synapse size thought to underlie stable LTP. This project will serve as the first direct analysis of BDNF-to actin signaling involved in adult synaptic plasticity. Understanding this process may provide insight into a shared basis of learning impairments associated with several neuro-cognitive diseases and identify therapeutic targets for enhancing function with these disorders. ? ?

Agency
National Institute of Health (NIH)
Institute
National Institute of Mental Health (NIMH)
Type
Predoctoral Individual National Research Service Award (F31)
Project #
1F31MH083396-01
Application #
7486417
Study Section
Special Emphasis Panel (ZRG1-F03A-M (20))
Program Officer
Curvey, Mary F
Project Start
2008-04-16
Project End
2011-04-15
Budget Start
2008-04-16
Budget End
2009-04-15
Support Year
1
Fiscal Year
2008
Total Cost
$30,225
Indirect Cost
Name
University of California Irvine
Department
Anatomy/Cell Biology
Type
Schools of Medicine
DUNS #
046705849
City
Irvine
State
CA
Country
United States
Zip Code
92697
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Seese, Ronald R; Chen, Lulu Y; Cox, Conor D et al. (2013) Synaptic abnormalities in the infralimbic cortex of a model of congenital depression. J Neurosci 33:13441-8
Babayan, Alex H; Kramár, Enikö A; Barrett, Ruth M et al. (2012) Integrin dynamics produce a delayed stage of long-term potentiation and memory consolidation. J Neurosci 32:12854-61
Kramár, Enikö A; Chen, Lulu Y; Lauterborn, Julie C et al. (2012) BDNF upregulation rescues synaptic plasticity in middle-aged ovariectomized rats. Neurobiol Aging 33:708-19
Chen, Lulu Y; Rex, Christopher S; Babayan, Alex H et al. (2010) Physiological activation of synaptic Rac>PAK (p-21 activated kinase) signaling is defective in a mouse model of fragile X syndrome. J Neurosci 30:10977-84
Rex, Christopher S; Gavin, Cristin F; Rubio, Maria D et al. (2010) Myosin IIb regulates actin dynamics during synaptic plasticity and memory formation. Neuron 67:603-17
Chen, Lulu Y; Rex, Christopher S; Sanaiha, Yas et al. (2010) Learning induces neurotrophin signaling at hippocampal synapses. Proc Natl Acad Sci U S A 107:7030-5
Chen, Lulu Y; Rex, Christopher S; Pham, Danielle T et al. (2010) BDNF signaling during learning is regionally differentiated within hippocampus. J Neurosci 30:15097-101
Lauterborn, J C; Pineda, E; Chen, L Y et al. (2009) Ampakines cause sustained increases in brain-derived neurotrophic factor signaling at excitatory synapses without changes in AMPA receptor subunit expression. Neuroscience 159:283-95
Kramár, Enikö A; Chen, Lulu Y; Brandon, Nicholas J et al. (2009) Cytoskeletal changes underlie estrogen's acute effects on synaptic transmission and plasticity. J Neurosci 29:12982-93

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