PAP complex: a pitfall in immunocytochemistry of the pig hypothalamus

Use of rabbit peroxidase-antiperoxidase (PAP) complex in immunostaining of the pig hypothalamus resulted in false positive staining of elements of the supraoptic and paraventricular nuclei due to binding of rabbit PAP complex and rabbit immunoglobulins to these structures. This phenomenon seriously hampers immunohistochemical investigation of the pig hypothalamus. Specific binding of swine immune serum against luteinizing hormone-releasing hormone has been detected with the protein A-biotin-streptavidin method employed on paraffin and vibratome sections of fetal and postnatal pig hypothalamus.