1. Cyclic Voltametry for the Detection of Dopamine in vivo

2. Dopamine Neurotransmitter Important for motor and cognitive functions
small molecule chemical messenger
Important for motor and cognitive functions
Deficts in dopamine levels cause Parkinson Disease
Regulates reward
Dopamine increases after drugs of abuse like cocaine
Venton, B. J. and Wightman, M. R. “Psychoanalytical Chemistry: Dopamine and Behavior.” Analytical Chemistry (2003):
Structure of Dopamine.
4-(2-aminoethyl)
benzene-1,2-diol

3. Dopaminergic Neurons
Dopamine is synthesized in dopaminergic neurons and packaged into membrane bound vesicles
Electrical action potential initiates the release of dopamine
Dopamine vesicles undergo exocytosis
Spills out into the extracellular space
Can be detected
Venton, B. J. and Wightman, M. R. “Psychoanalytical Chemistry: Dopamine and Behavior.” Analytical Chemistry (2003):
The dompaminergic neuron can release dopamine into the extracellular space where its contents can be detected by target neurons.

4. Detection of Dopamine
Exocytosis of dopamine from vesicle occurs on a millisecond time scale
Sensor must be fast, sensitive, and selective since dopamine concentrations are low
Fast scan cyclic voltametry is the dominant electrochemical technique used
Venton, B. J. and Wightman, M. R. “Psychoanalytical Chemistry: Dopamine and Behavior.” Analytical Chemistry (2003):
Dopamine
Dopamine-o-quinone
+ 2 H+

5. Carbon Fiber Microelectrodes
Carbon Fiber Microelectrodes (CFME) are electrodes in which a carbon fibers serve as the electroactive area
Advantages:
Carbon fibers are biological compatible to cells
Small size (less than 10um in diameters) allows for implantation in vivo
Commonly used with cyclic voltametry
Huffman, M.L. and Venton, B.J. “Carbon fiber Microelectrodes for in vivo applications.” Analyst (2009):
Image:
Carbon Fiber Microelectrode

6. Voltammetry
Electrochemical technique in which the current (I) is measured as a function of voltage (Eapp).
There are several kinds:
Linear Scan voltametry (Polarography)
Differential pulse polarography
Square-wave voltametry
Cyclic Voltametry

7. Fast-scan Cyclic Voltametry
400 V/s
-0.4 V
100 ms
8.5 ms
Scan electrode from a holding potential to a switching potential and back at a
high scan rate. Repeat these scans every 100 ms.
Dopamine
Dopamine-o-quinone
+ 2 H+
As potential is ramped up, dopamine is oxidized to dopamine-o-quinone.
As potential is ramped down, dopamine-o-quinone reduced back to dopamine.

8. Fast-Scan Cyclic Voltametry
Cyclic voltammograms
Background-subtracted
cyclic voltammogram of dopamine
No dopamine
Dopamine present
oxidation
reduction
Fast scan rate cause a large background
charging current due to charging
the double layer.
When dopamine is added (red line),
the differences are small.
The background current is stable and can
be subtracted out to obtain a background-
subtracted cyclic voltammogram for dopamine.
The position of the peaks help identify the
molecule being detected.

9. Fast-scan cyclic voltametry-5 3
i, nA
E vs Ag/AgCl
dopamine
reduction
dopamine
oxidation
dopamine present
Data can also be depicted as a color plot to show many CVs over time.
Current is in color and shows when dopamine is present.

10. Results Electrically-Stimulated release in a rat
Addy, N. A. et. al. "Sensitization of Rapid Dopamine Signaling in the Nucleus Accumbens Core and Shell After Repeated Cocaine in Rats." Journal of Neurophysiology (2010). 104:
Carbon-fiber microelectrode implanted in nucleus accumbens
Nucleus accumbens regulates reward
Electrically stimulate cell bodies in ventral tegmental area
Size of dopamine evoked depends on frequency of stimulation
Color plots look like dopamine

11. Results Spontaneous dopamine transients in a rat
Spontaneous dopamine transients in a rat after cocaine
Aragona, J.B, et. al. “Preferential Enhancement of Dopamine Transmission within the Nucleus Accumbens Shell by Cocaine is Attributed to a Direct Increase in Phasic Dopamine Release Events.” Journal of Neuroscience (2008). 28:
Cocaine increases the concentration and the length of time for dopamine signaling.

12. Advantages Allows real-time detection of dopamine in behaving animals
Can determine during what behaviors dopamine is released
Can determine how drugs affect dopamine signaling in the brain