A methodological approach to rapid and sensitive monoamine histofluorescence using a modified glyoxylic acid technique: the SPG method

A modified approach of the glyoxylic acid (GA) condensation reaction for the visualization of biogenic amines in tissue is described. Cryostat sections are used from brain or extracerebral tissue in dog, monkey, rat and mouse and exposed for 3 s to a room temperature solution containing sucrose-potassium phosphate-glyoxylic acid (SPG). The tissues are air dried and heated in an oven for 5 min. The complete precessing time from fresh tissue to microscopic examineation takes 18 min. Morphologically sharp and brightly fluorescent monoamine-containing neurons, pre- and terminal axons are seen against a dark parenchymal background without drug pre-treatment. The SPG method retains the high specific sensitivity for monoamines previously described in the original technique but is, in addition, more rapid and simple and is easily accissible as a research tool to investigators inexperienced in histofluoresecence techniques.