Topographical mapping of GnRH receptors on dispersed mouse pituitary cells by backscattered electron imaging

Mouse anterior pituitary cells cultured for 2 days were stimulated with one of three biotinylated‐GnRH probes ([biotinyl‐Lys⁶]‐[D‐Lys⁶]GnRH, [biotinyl‐Ser⁴]‐[D‐Lys⁶]GnRH, [biotinyl‐Ser⁴]‐[D‐Trp⁶, des‐Gly¹⁰]GnRH) in the cold (4°C) for 1 hr. These cells were subsequently fixed and an avidin‐gold complex was conjugated to the bound GnRH. After a second fixation, the gold label was silver‐enhanced for viewing with a scanning electron microscope. Gonadotropes were identified as a result of the labeling procedure, measured for size, and the number of GnRH receptor sites counted. Gonadotropes ranged from 3 to 13 μm in diameter and contained from 23.2 ± 3.3 to 338.4 ± 25.2 sites per cell depending upon the size of the cell and the ligand employed. The methods described should be applicable for studying the topographical distribution of a variety of cellular receptors. © 1992 Wiley‐Liss, Inc.