Positron emission tomography: measurement of the activity of second messenger systems.

Phosphoinositide turnover is closely connected to modulation of synaptic function and is part of an important second messenger-producing system. New radioligands for imaging second messenger systems by positron emission tomography have been developed: carbon-11-labeled 1,2-diacylglycerols. The theoretical background of second messenger imaging is described in detail and the relation between the biologically active compounds and potential tracers for imaging second messenger systems is discussed. We report informative findings on postsynaptic biological responses in the living human brain of healthy normal subjects and with various diseases.