Building the Molecular Machinery of Memory: Local Protein Synthesis in Hippocampal Neurons

Citation

Aakalu, Girish Nanda (2002) Building the Molecular Machinery of Memory: Local Protein Synthesis in Hippocampal Neurons. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/CAY9-6643. https://resolver.caltech.edu/CaltechTHESIS:01232012-132700275

Abstract

Synaptic plasticity is the most widely accepted cellular and molecular model for learning and memory. Although the idea that information is encoding through changes in synaptic strength is simple, the requirement for new protein synthesis to maintain long-lasting forms of plasticity threatens to make this model untenably complex. This complexity arises from the fact that an individual neuron can have thousands of connections, small groups of which change strength independently of others. Since the necessary proteins are likely the effectors of long-term plasticity, non-specific delivery would lead to loss of plasticity-encoded information. Thus it is critical that the effector proteins be faithfully delivered only to the correct sites.

One way to accomplish this task would be to allow the synapses local control over the necessary protein synthesis and delivery. Previous studies have suggested this possibility of dendritic local protein synthesis (LPS). In this thesis we describe the visualization, in real time, of the synthesis of a GFP-based reporter in the dendrites of cultured rat hippocampal neurons. By utilizing a number of physical, optical and molecular manipulations we have insured that the observed synthesis was free of any somatic contribution thereby providing the first definitive evidence for the existence of dendritic LPS in mature vertebrate neurons.

We also describe the regulation of dendritic LPS by two forms of plasticity-inducing stimuli. First, we show that dendritic LPS can be stimulated by brain derived neurotrophic factor (BDNF), a molecule capable of causing persistent synaptic enhancement. Second, we show that a chronic blockade of synaptic activity, which results in a form of synaptic enhancement termed "disuse hypersensitivity", appears to enhance dendritic LPS.

Finally, we discuss a technique that can facilitate the study of the necessity of dendritic LPS for long-lasting plasticity. By using a "caged" protein synthesis inhibitor, we are able to abolish protein synthesis in a spatially restricted manner. Thus it is now possible to conduct experiments where dendritic LPS is inhibited while somatic synthesis is permitted. If plasticity is not maintained under these conditions, we will have satisfying evidence of the necessity of dendritic LPS for long-lasting plasticity.

Thesis Files