Retrograde and Transganglionic Anterograde Transport of an HRP-Wheat Germ Acclutinin Conjugate as Studied with Tetramethyl Benzidine Ultracyto-chemistry

Abstract

The protein tracer horseradish peroxidase (HRP) is a primary component in the current method of choice for the anatomical demonstration of neuronal connections. Recently the performance of HRP as a neuronal tracer was improved significantly by conjugating the HRP to wheat germ agglutinin (WGA). When compared to HRP alone, the conjugate was observed to label larger numbers of neurons following comparable injections. In addition, the conjugate has been shown to be transported through peripheral ganglia and into the central projections of the ganglion neurons. However, the ability of the conjugate to demonstrate neuronal connections, as with HRP alone, is greatly dependent on the cytochemical method used to localize the HRP activity. It was previously shown by light microscopy, that the tetramethyl benzidine (TMB) method provided the highest degree of sensitivity when tested against eight other commonly used HRP cytochemical methods. Only recently have the conditions necessary to render the TMB reaction product suitable for electron microscopy been described.