Electroantennography

Electroantennogram or EAG is a technique by which we measure the average output of the antenna to the brain for a given odor. It is commonly used in the electrophysiology while studying the function of olfactory pathway in insects. The technique was invented in 1957 by German biologist Dietrich Schneider. [National Academy of sciences (2003). Beyond discovery - Insect pheromones.]

EAG is performed in two ways:
# Remove the antenna from the animal and insert two chlorided silver wires for contact on to the two ends and amplify the voltage between them while applying odor puff to see a deflection as in the figure.
# Leave the animal intact and insert a ground wire (silver/silverchloride) or a glass electrode filled with a buffer solution to some part of the body, usually inserted into an eye, and another to the tip of the antenna. A large bore glass electrode can also be placed directly over the tip of the antenna, such as in "Drosophila melanogaster" (fruit fly)antenna recordings. The later method is useful if one is doing an experiment on the animal as a whole while doing the antennogram.

The technique is widely applied in screening of insect pheromones by examining the responses to fractions of a compound mixture separated using chromatography. [Hummel, H. E. and T. A. Miller (1984). Techniques in pheromone research.Springer-Verlag,New York.]

Usually the wire inserted into the antenna is a thin silver wire which is chlorided in bleach. This is an older practice. Commonly, tungsten wires which have been chemically sharpened are inserted into a single neuron in the antenna.

Further detailed examination of the odor response at the olfactory sensory level can be done by sensilla recording.

See [Carlson Lab] http://pantheon.cis.yale.edu/~jcarlso/index.html

References