The Effects of Extracellular Matrix Compliance and Protein Expression on Neurons

Extracellular and intracellular cues affect neuronal morphology and contribute to brain diseases, such as schizophrenia, and injury. First, we examined how extracellular cues influence branching parameters of hippocampal neurons. Brain injury or disease can initiate changes in local or global stiffness of brain tissue. While stiffness of the extracellular environment is known to affect the morphology and function of many cell types, little is known about how the dendrites of neurons respond to changes in brain stiffness. We cultured hippocampal neurons on hydrogels composed of polyacrylamide of varying rigidities to mimic the effects of extracellular matrix stiffness on dendrite morphology. At 12 days in vitro, dendrite branching was altered by stiffness; i.e. branching peaked in neurons grown on gels of intermediate stiffness (8 kPa). Furthermore, we found that ionotropic glutamate receptors play roles in regulating dendrite morphology. AMPA receptors play a role in dendritc arborization for harder stiffness, >2kPa, at all distances from the cell body. NMDA receptors play a role in dendritic arborization for a range of rigidities (1-25 kPa), at only proximal and intermediate distances from the cell body. However, a caveat to these studies is that cell adhesion is affected by the rigidity of these substrates. Addressing this caveat is of great iii importance because cell density affects dendrite branching. Thus, we also determined whether substrate stiffness plays a critical role in determining dendrite branching independent of cell density. We concluded that substrate stiffness does play a crucial role in determining dendrite branching patterns independent of cell number; however, the density of cells plated on substrates also influences the dendrite branching pattern of neurons. In the second chapter of my thesis, we looked at how intracellular proteins in different sections of the human brain are affected in schizophrenia. By Western blotting, we examined human, postmortem brain samples. NOS1AP protein expression increased in the dorsal lateral prefrontal cortex of patients with schizophrenia and not in the occipital lobe, medial temporal lobe, or cerebellum. Thus, this thesis demonstrates how extracellular and intracellular cues affect disease states, such as brain injury and schizophrenia. iv ACKNOWLEDGMENTS