dIV in ftplysia sensory neuron: processes vs« cell bodii 29.2 
Before 5~HT 19» after 50 mM 5-HT 49s after B-HT 
Concentrations of the intracellular messenger cAMP (cyclic adenosine 3' ,5' monophosphate) 
within a single neuron from the sea snail Aplysia californica. 77?^ cAMP is detected by its ability to 
affect an enzyme, cAMP- dependent protein kinase. This enzyme was produced by recombinant 
DNA technology, labeled with fluorescent dyes, and injected into the neuron, which was then 
grown in tissue culture. The cAMP-sensitive signal from the enzyme was imaged by confocal 
fluorescence microscopy, a technique that can isolate one plane of focus within a live specimen. 
The concentrations of cAMP are denoted by a rainbow of colors, with blues and reds representing 
the lowest and highest levels, respectively. 
The upper left panel shows the neuron before stimulation. The upper middle panel shows the 
same cell shortly after addition of 5 hydroxytryptamine ( 5-HT, also known as serotonin ) to the 
medium. Although applied to the entire cell, 5 HT, an important neurotransmitter, elevates cAMP 
to a much greater extent in the fine dendrites. Over the next 100 seconds (upper right, lower left 
panels ), the cAMP shows some spread to the main cell body, but the dendrites continue to have the 
highest cAMP levels. The cAMP response begins to decay even while the 5-HT is still present (lower 
middle panel ) and returns to baseline when it is removed (lower right). These images are the first 
direct visualization of local generation of c AMP in the fine outgrowths and its diffusion toward 
the cell body and nucleus. It is known to be a key controller of both short- and long-term plasticity 
in many neurons. 
Research of Brian Bacskai, Benny Hochner, Martyn Mahaut-Smith, Stephen Adams, Bong-kiun 
Kaang, Eric Kandel, and Roger Tsien. 
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