Cyclic Voltammetry for the Detection of Dopamine in vivo

Download this lesson

Dopamine


Structure of Dopamine.
4-(2-aminoethyl)
benzene-1,2-diol
  • Neurotransmitter
    • 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

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







The dompaminergic neuron can release dopamine into the extracellular space where its contents can be detected by target neurons. (Venton & Wightman 2003)

Detection of Dopamine


Volametry
There are several kinds:
Cyclic Voltametry
Carbon Fiber Microelectrodes


http://www.clinchem.org/cgi/content/full/49/10/1763
Carbon Fiber Microelectrode
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

Fast Scan Cyclic Voltametry



Scan electrode from a holding potential to a switching potential and back at a
high scan rate.  Repeat these scans every 100 ms.  



As potential is ramped up, dopamine is oxidized to dopamine-o-quinone.
As potential is ramped down, dopamine-o-quinone reduced back to dopamine.

Cyclic Voltammogram



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. 
Background-subtracted
cyclic voltammogram of dopamine



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. 




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. 

Experimental Results
Electrically-Stimulated release in a rat

(Addy, et al.  2010)
Spontaneous dopamine transients in a rat


Spontaneous dopamine transients in a rat after cocaine


Cocaine increases the concentration and the length of time for dopamine signaling (Aragona et. al. 2008).

Advantages
References

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: 922-931.

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: 8821-8831.


Huffman, M.L. and Venton, B.J.  "Carbonfiber Microelectrodes for in vivo applications." Analyst (2009): 18-24. 


Venton, B. J. and Wightman, M. R. "Psychoanalytical Chemistry: Dopamine and Behavior.Analytical Chemistry (2003): 414-421. 


http://www.cem.msu.edu/~cem333/Week12.pdf

http://www.cartage.org.lb/en/themes/sciences/chemistry/analyticalchemistry/methodsinstrumentation/Electrochemical/Electrochemical.htm

www.chem.uic.edu/chem421/cv.PDF