Big Picture: Human Mind

My long-term or life-term goal is to answer what is human mind. Maybe this question can never be answered, but I hope to further our understanding of human behavior at the molecular or cellular level, and to improve our health by increasing our knowledge of the nervous system.

Human mind and intelligence are performed by nervous system. And I believe that to understand mind, it is necessary to understand nervous system at two levels: one is the molecular and cellular or intra-cellular level; and the other is the neural network or the inter-cellular level. I also believe that there are some basic prolems, solvement of which will lead to answer of a lot of other questions. I need to find such "central" questions and work on them.

Current Research: How Neural Circuits Control Animal Behavior

Previous Research: Molecular Mechanism in Synaptic Transmission

Synaptic transmission is a bridge between intra and inter cellular levels, where a central role is performed by regulated vesicle exocytosis. Typically, the vesicles have to dock at their release site, and a fraction of the docked vesicles are primed to be release ready, that is, the vesicle membrane can fuse with the plasma membrane in response to calcium trigger without further maturation steps. It is generally accepted that exocytosis is mediated by SNARE proteins, whose function is fine tuned through interaction with other proteins. But, how exocytosis is regulated by these proteins remains unclear.

[ Click the figure above to view the vesicle cycle animation (Galli, T. and Haucke, V., 2001) ]

Three SNARE proteins comprise the minimal machinery underlying vesicle fusion: one vesicle membrane protein synaptobrevin (also called VAMP) and the two plasma membrane proteins, syntaxin and SNAP-25. These three proteins form a stable four-helical bundle, called SNARE core complex, to drives membrane fusion. Although in vitro studies have shown that these three SNARE proteins alone suffice to fuse the membranes of artificial liposomes, the rate of such fusions is orders of magnitude slower (the half-life is ~10 min) than fusion in regulated exocytosis (which takes place as rapidly as less than a millisecond), suggesting additional factors or mechanisms are involved in fast regulated secretion. Complexin (CPX) is a small neuronal protein that binds in a 1:1 stoichiometry to the SNARE core complex, very rapidly (~5x107M-1S-1) and with high affinity, which makes it an attractive candidate to regulate fast exocytosis.

Here we use adrenal chromaffin cell, a well-characterized and extensively used model system for studying Ca2+-triggered exocytosis, to study the role of complexin in regulated exocytosis. Chromaffin cells secrete catecholamine through the fusion of large dense core vesicles (LDCVs) with the plasma membrane, employing the same conserved fusion machinery that also mediates synaptic transmitter release from neurons. Another major advantage of chromaffin cells is that these cells express only one major CPX isoform -- CPX II (Four CPX isoforms have been identified in vertebrates). Thus, we can explore the function of complexin with the chromaffin cells from CPX II knock out mice without the interference of other isoforms.

The major approaches that we used include membrane capacitance measurement, which tracks membrane addition and removal; amperometry, which is a quantitative electrochemical measurement of the released catecholamines; and total internal reflection fluorescence (TIRF) microscopy, which is an optical sectioning approach that allows selective imaging of vesicles near the plasma membrane.