Electron microscopic demonstration of intracellular promethazine accumulation sites by a precipitation technique: Application to the cerebellar cortex of the mouse

Abstract

A method is described that allows electron microscopic identification of the phenothiazine neuroleptic promethazine after supravital intracardiac injection of high drug concentrations (≥3%). The cerebellar cortex of the mouse was used for the investigation. This procedure is based on simultaneous fixation of drug and tissue by immersion in a paraformaldehyde glutaraldehyde solution with the addition of phosphomolybdic acid. The electron microscopic investigation revealed that the drug could easily be identified as an electron-dense precipitate. Subpopulations of neurons exhibited a higher affinity for the drug than others, but no preference for any nerve cell type was detected. Closer study showed that promethazine accumulated primarily within the cytoplasm, where it was bound to the endoplasmic reticulum. Furthermore, promethazine storage was observed within mitochondria and vesicular structures. Drug binding was also seen in the regions of synapses but without any predilection for these structures. Because this precipitation technique also appears to be well-suited for the ultrastructural identification of other drugs, it offers multiple possibilities for application.