Description:

The synapse is a specialized structure containing pre and postsynaptic elements that regulate the transfer of information by chemical synaptic transmission. A neuron must be able to change the strength of its contacts depending on whether it participates in a well-used pathway. This aspect of synaptic function is an important element of plasticity that most likely underlies changes in behavior and learning.

The focus of this study is on hippocampal neurons that are known to play an important role in learning and memory. The hypothesis is that the well-known anti-cell death mitochondrial protein BCL-xL is an important effecter of the signaling that results from the synaptic contact of a nerve cell with its partner. We suggest that BCL-xL increases the number of mitochondria, targets mitochondria to synaptic sites, and regulates the opening of ion channels in mitochondrial membranes. These changes may cause the regulated and targeted production and/or release of ATP in the synapse, resulting in activity-dependent development of chemical transmission. The findings have implications for improving the function of neuronal synapses during stroke or in neurodegenerative conditions such as Alzheimer's Disease.

Progress:

At the BRC we undertook the study of ATP levels in cultured hippocampal neurons heterologously expressing BCL-xL-GFP or mitochondrially targeted GFP alone. Using a plate luminometer, we monitored the ATP levels of the neurons growing on coverslips at day 7-10 after transfection (transfected using calcium phosphate on day 5 in culture). ATP levels were monitored using the firefly Luciferin/luciferase system, after permeabilizing the cells in the presence of 0.1% Triton-X 100. The results revealed that the culture coverslips containing cells expressing BCL-xL produced significantly more ATP than cells from control coverslips (N=8 BCL-xL, N=7 Control, p= 0.03).

In addition, we undertook a study in which an oxygen-sensing electrode was used to monitor oxygen uptake from single hippocampal neurons expressing BCL-xL-GFP or from control cells in the same dish. The results, although preliminary, recapitulated the results found with the luminometer.