I will be doing a 5HT immunohistochemical procedure on Long-Evans rat brains in the near future and am following a procedure that implements primary and secondary antibodies for staining (procedure attached). 

As is noted in the article (and there are images depicting the results) I can either opt to use no primary antibody and use 5HT antibodies as a secondary, or use 5HT antibodies for both primary and secondary. 

What implications come from using 5HT antibodies for both primary and secondary versus not using a primary? And should I use a brightfield or darkfield?

http://www.sciencedirect.com/science/article/pii/S0165022X03001490