In recent decades, considerable efforts have been made to understand the mechanism of memory, cognition, and relevant neurodegenerative diseases in the human brain. Several studies have shown the importance of microtubule proteins in the memory mechanism and memory dysfunction. Microtubules possess dynamicity, which is essential for functions of neuronal networks. Microtubule-associated proteins, i.e., tau, play vital roles in microtubule stability. On the other hand, the ferromagnetic mineral magnetite (Fe(3)O(4)) has been detected in the normal human brain, and elevated levels of magnetite are also observed in the brains of Alzheimer's disease patients. Therefore, we propose that a relationship between microtubule organization in axons and brain magnetite nanoparticles is possible. In this study we found alterations of microtubule polymerization in the presence of increasing concentrations of magnetite through transmission electron microscopy images and a turbidimetry method. Structural changes of microtubule and tau protein, as an essential microtubule-associated protein for tubulin assembly, were detected via circular dichroism spectroscopy, intrinsic fluorescence, and 8-anilino-1-naphthalenesulfonic acid fluorometry. We predicted three possible binding sites on tau protein and one possible binding site on tubulin dimer for magnetite nanoparticles. Magnetite also causes the morphology of PC12 cells to change abnormally and cell viability to decrease. Finally, we suggest that magnetite changes microtubule dynamics and polymerization through two paths: (1) changing the secondary and tertiary structure of tubulin and (2) binding to either tubulin dimer or tau protein and preventing tau-tubulin interaction.

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Recently, the hypothesis in which memory and information would be stored as magnetic forms in astrocytes is expanding and neuromagnetic interactions between neurons and neighboring astrocytes in neocortex have potential to be the basis of memory formation. It has been proposed that all sorts of information may be maintained in form of neuronal activity-associated magnetic fields (NAAMFs) and thereby alterations of magnetic fields in the brain may potentially affect the memory function. On the other hand, microtubules (MTs), the most essential elements of cytoskeleton, are crucial in regulation of spine development and morphology, brain cognitive behavior, consciousness and information storage. Because of MT dynamic nature, it can produce local magnetic field in neurons through vibration. According to size, number, structure and function of microtubule proteins, they are the most eligible components of neurons to be affected by endogenous and exogenous magnetic fields. In this study we tried to investigate the possible effects of exogenous static magnetic fields (SMFs) on memory through examining the structural and functional changes in MT dynamic activity and neural cell morphology. MT activity results revealed that MT polymerization process was not attained to steady state at the right time in the presence of SMF at 300 mT and the ascending slope at the steady state phase was found as abnornmal. In addition, MT structure was relatively changed. On the influence of SMF, PC12 neuron-liked cells' spines decreased significantly and their morphology altered to pyramidal form.

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