קרן זאבי

תלמידת המחלקה לתואר שני תרצה בנושא:

Cytoplasmic Flow in Neurons

- a theoretical model and an experimental system

Introduction: Axonal transport is a critical process for supplying necessary constituents to different parts of a neuron and maintaining normal neuronal function. Different organelles such as mitochondria and vesicles are transported along the microtubules in the axon by motor proteins (Kinesin and Dynein), anterogradly and retrogradly. Diffusion cannot yield the needed transport through axonal length scales and it is unknown if all the necessary materials (e.g. small soluble molecules) are transported by axonal transport. We suggest that active movement of organelles exerts a drag force on the surrounding medium, which induces cytoplasmic flow. We suggest that this flow facilitates directed movement of soluble materials, as observed in plant cells. Methods: We present a theoretical work and an experimental system. The theoretical work models the flow for any general configuration of organelles moving along the axon. The axon is modeled as a rigid tube filled with a viscous Newtonian fluid while rigid spheres, that represent the organelles, move in straight lines inside the tube. The experimental system, aimed to approve the existence of cytoplasmic flow in the axon, is based on microinjection of inert quantum dots for analysis of single cells within the neuronal network of leeches. The quantum dots propagation velocity along axons is measured and compared between normally functioning neurons and fixed neurons. Results & Conclusions: The theoretical results show that the average fluid velocity is independent on the organelles instantaneous velocity, but is linearly proportional to their rate. In addition, a small negative flow is expected near the membrane wall. The experimental results show that normally functioning neurons posses higher propagation velocity (0.54±0.05) than the fixed neurons (0.21±0.02). This work predicts a noticeable flow that may be an additional mechanism for molecular transport along axons.

העבודה נעשתה בהנחייתו של ד"ר אורי נבו, המחלקה להנדסה ביו-רפואית, הפקולטה להנדסה,

אוניברסיטת תל-אביב

ההרצאה תתקיים ביום ראשון 4.3.2012, בשעה 14:45,

בחדר 315, הבניין הרב תחומי, אוניברסיטת תל אביב