The use of stereological counting methods to assess immediate early gene immunoreactivity

The issue of whether profile and stereological counting methods are interchangeably accurate when assessing immediate early gene expression still needs to be resolved. To compare these two counting techniques, we quantified the expression of c-fos in the nucleus accumbens core and shell, and in the lateral septum as a control structure, of rats treated with neuroleptics. With the profile counting method, which relies on selective placement of a counting grid within a structure, we evaluated the density of c-fos labeled cells within a box of fixed dimension. With stereology, which applies random and systematic sampling methods, we used the optical fractionator method and counted the absolute number of c-fos labeled cells within the contours of each structure examined. Our results showed that the substantial increase in c-fos expression in the shell and core induced by haloperidol treatment was detected by both stereological and profile counting methods; in contrast, the weaker effect of clozapine on c-fos expression was detected differentially by the two methods. Whereas the profile counting method reported a reduction of c-fos in the core by clozapine, and an increase in c-fos in the lateral septum, these effects were not replicated using stereology. These findings suggest that stereological and profile counting methods do not always produce equivalent results. This may be particularly relevant when a measured effect is relatively small, and it is not distributed homogeneously within a structure. In this respect, the random and systematic sampling methods of stereology may yield more accurate and unbiased results than the profile counting method, and therefore may be preferred for a more accurate and thorough investigation of a treatment effect on immediate early gene expression in a specific brain region.