Retrograde fluorescent neuronal tracing combined with acetylcholinesterase histochemistry

The retrograde fluorescent tracing technique was combined with the di-isopropylfluorophosphate (DFP) histochemical procedure for acetylcholinesterase (AChE). Three fluorescent tracers (True blue Fast blue and Evans blue) were injected into the rat striatum. After the appropriate survival time and after the administration of DFP, AChE reaction products could be observed in the fluorescent retrogradely labeled substantia nigra neurons. The fluorescent retrograde labeling and the AChE brown reaction products were observed in the same cell bodies by simply turning on and off the bright-field illumination while observing with fluorescence. The sensitivity of the method appeared to be related to the length of the survival time after the tracer injection as well as after the DFP administration. This combined method allows to study the efferent connections of AChE-containing neurons in the central nervous system.