Freie Universität Berlin
Charité University Medicine Berlin
Humboldt University Berlin
Max-Delbrück-Center for Molecular Medicine, Berlin-Buch
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GRK 1123:

Cellular Mechanisms of Learning and Memory Consolidation
in the Hippocampal Formation

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This Research Training Group is funded by the German Research Council DFG

©2006, FU Berlin
GRK 1123

Imprint & Disclaimer
AG Ahnert-Hilger AG Behr AG Braunewell AG Haucke AG Heinemann
AG Kempermann AG Kempter/Schmitz AG Kuhl AG Multhaup AG Nitsch

PD Dr. Karl-Heinz Braunewell
Institut für Physiologie, Neurophysiologie
Charité, Universitätsmedizin Berlin
Tucholskystr. 2
10117 Berlin
karl-heinz.braunewell@charite.de


Title

Investigations on the influence of the neuronal calcium sensor VILIP-1 and the cGMP signalling cascade on synaptic plasticity in the rat hippocampus in vitro

Question of the project

The observed activity-dependent expression of VILIP-1 in the hippocampus following plasticity induction together with the effects of VILIP-1 on neuronal signalling pathways have led to the proposal of the following working hypothesis: the main function of VILIP-1 is the calcium-dependent modulation of neuronal signalling cascades i.e. the cAMP- or the cGMP-pathway, that are key components of learning and memory processes. Thus, VILIP-1 may together with a signal effector molecule, e.g. GC-B, form a coincidence detection complex where it acts as a molecular short (calcium-myristoyl switch) or long term (increased gene expression) memory for calcium and thus, is implicated at different levels in the associative models of cellular plasticity, LTP and LTD, in the rat hippocampus.

Scientific background

Learning and memory mechanisms such as synaptic plasticity in form of LTP and LTD have been described in different areas of the brain including the hippocampus (Abraham and Tate 1997). Calcium plays a central role for the induction and the maintenance of synaptic plasticity (Abraham and Tate 1997, Braunewell and Manahan-Vaughan, 2001). Thus, a major current interest is the not yet fully understood link between calcium-binding proteins, neuronal excitability and induction of different forms of synaptic plasticity. In the nervous system a family of neuronal calcium sensor (NCS) proteins (Braunewell and Gundelfinger, 1999) exists which belongs to the super family of EF-hand calcium-binding proteins. One family member, NCS-1, has previously been implicated in learning and memory processes (Gomez et al., 2001), it shows a changed expression level following induction of synaptic plasticity in the hippocampus (Genin et al., 2001) and modulates synaptic plasticity in hippocampal neurons (Sippy et al., 2003). Also other NCS proteins, such as VILIP-1, may be of functional importance during learning and memory.


Previous work of the group in the field

Following induction of synaptic plasticity in the hippocampus an increase in protein expression occurs for VILIP-1 (Braunewell et al., 2003) implying a possible involvement in long-term synaptic plasticity. However, the molecular mechanisms of how VILIP-1 influences synaptic plasticity are not yet known. VILIP-1 associates with neuronal membranes in an activity-dependent and reversible manner in hippocampal neurons, a so-called calcium-myristoyl switch, which constitutes a novel and fast cellular signaling mechanism (Spilker et al., 2002). This enables VILIP-1 to form a signaling complex with membrane localized signaling cascades such as adenylyl and guanylyl cyclases (Braunewell et al., 2001). VILIP-1 interacts with the guanylyl cyclase B (GC-B) and is a physiologic modulator of GC-B function in cerebellar neurons (Braunewell et al., 2001). The VILIP-1-induced cAMP- and possibly also cGMP-accumulation in cell lines (Braunewell et al., 2001) leads to an inactivation of the small GTPase rhoA (Mahloogi et al., 2003), which is able to influence the actin cytoskeleton and may change dendritic spine function and morphology. Therefore, VILIP-1 is likely to be of importance for normal synaptic plasticity (Braunewell et al., 2003) and disturbed plasticity in Alzheimer disease and schizophrenia with reduced VILIP-1-expression (Schnurra et al., 2001; Bernstein et al., 2002).

Goals

We will (i) characterize the effect of GC-B signaling on hippocampal plasticity and we will (ii) analyze the GC-B/VILIP-1 signaling complex as a novel molecular mechanism for synaptic plasticity in electrophysiological experiments in acute hippocampal slices. Although GC-B is strongly expressed in hippocampal neurons and the second messenger cGMP is known to play a decisive role in synaptic plasticity, so far no investigations on the role of GC-B in plasticity have been performed. However, our preliminary results in subiculum slices suggest modulatory activity. Thus, in acute hippocampal slices, we will test whether CNP, a GC-B-agonist, influences induction and/or maintenance of LTP and LTD in the hippocampal CA1 region. Since (ii) in cultured hippocampal neurons VILIP-1 is able to modulate cGMP-production following GC-B stimulation with CNP (Brackmann et al., in prep.) it is expected that VILIP-1 also modulates an observed GC-B effect on plasticity. Therefore, we will perturb VILIP-1 expression by the use of specific interfering RNA and the effect on plasticity with and without GC-B stimulation will be measured. In addition, we will use VILIP-1 transgenic animals to investigate the effect of an increased VILIP-1 expression on GC-B-induced synaptic plasticity. Finally, a VILIP-1 mutant, deficient in calcium-dependent membrane association and thus, VILIP-1/GC-B complex formation, allows the investigation of the role of the calcium-myristoyl switch as a signaling mechanism.

Methods

hippocampal culture, western blotting, cGMP-assays, fluorescence microscopy, transgenic animals, viral expression vectors, siRNA, hippocampal slice, electrophysiological recordings

Dissertation topics

Cooperation with other Members


Scholarship Holder:

 

AG Ahnert-Hilger AG Behr AG Braunewell AG Haucke AG Heinemann
AG Kempermann AG Kempter/Schmitz AG Kuhl AG Multhaup AG Nitsch