Figure 2.

Importance of fixation for small molecule immunohistochemistry. A and B, To generate specific antibodies, the immunogen was linked to a larger protein by carbodiimide. Only when carbodiimide is used with the fixative (4% formaldehyde) (panel B), will the antigen be presented to the antibody in the “right” form. C, Serotonin is not fixed well with strong complexing fixatives such as acrolein (compare panel D, where the mild fixative 4% paraformaldehyde was used). In contrast, the small peptide TRH is only fixed by rapid strong fixation, here using acrolein (cf. panels E and F).