Demonstration of horseradish peroxidase and fluorescent catecholamines in the same neuron

The demonstration of the presence of catecholamines and horseradish peroxidase (HRP) in the same neuron has been achieved by submitting vibratome sections to a modified glyoxylic acid fluorescence method followed by the usual procedure to reveal HRP. After HRP injection into the striatum or into the nucleus accumbens of the rat, both fluorescent dopaminergic neurons labelled with HRP and non-fluorescent neurons labelled with HRP were observed in the substantia nigra or in the ventral tegmental area, respectively.