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Return to Table of Contents
 Calcium Imaging Suggests
Dendrite Plasticity
Research may lead to better understanding of epilepsy and other neurological disorders
The idea that changes in the strength of a synapse, or junction between nerve cells, underlies learning and memory is a cornerstone of modern neuroscience. Work related to ‘synaptic plasticity’ even won the Nobel Prize in Physiology or Medicine in 2000. “But that’s clearly not the whole story,” says Dr. Daniel Johnston, a Professor at Baylor College of Medicine who spends his summers conducting research at the MBL and a member of the Laboratory’s newly established Neuroimaging Cluster. Based on work using a sophisticated research technique known as ‘calcium imaging,’ Johnston and colleagues believe that there may be a parallel and complementary plasticity within dendrites, the parts of neurons to first receive information from the synapses.
“We have found a lot of ion channels in the dendrites, which no one thought were there,” says Johnston. These channels appear to control the flow of sodium, potassium, and calcium ions within the neurons. Increases in calcium concentrations inside the neuron lead to changes in synaptic strength. Molecules known to be important for learning and memory, such as cyclic AMP and protein kinases, also regulate these ion channels. Changes in the channels and the resulting flow of ions in dendrites may be as important to learning and memory as are changes at the synapses.
To investigate the dendrites, Johnston and fellow researchers inject dyes into individual living rat hippocampal neurons, and then illuminate the cell with light of a certain wavelength. The dyes, which bind available calcium ions, rapidly emit light of a different wavelength when the concentration of calcium ions increases inside the cell. Digital cameras and sensitive photodetectors record the emitted light hundreds of times per second, and allow researchers to see changes in calcium concentrations over very short periods of time and in very precise locations within the cell.
Johnston believes that his imaging work on the cellular mechanisms of neuroplasticity may also lead to a better understanding of neurological disorders such as aging and epilepsy as well as certain types of psychiatric and cognitive dysfunction. “We’re just touching the tip of the iceberg of knowing how dendrites work in normal and abnormal brain activity,” he says. “New methods in neuroimaging are what make these types of studies possible.”
The Neuroimaging Cluster is a collaboration among leading summer researchers at the MBL who image live tissues to better understand basic mechanisms of nervous systems. By bringing together some of the best researchers and imagers in the world, the MBL hopes to sustain a high level of interaction and collaboration in this exciting area of biology. Additional research by members of the Cluster includes mapping the output of the olfactory bulb, signal integration in single vertebrate dendrites; basic mechanisms of neuronal communication; transmitter release in the squid giant synapse; and mechanisms of short-term memory.
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