Background. Colocalization analysis of confocal fluorescence and electron microscopy (EM) are important tools to detect the expression of multiple anterior pituitary hormones within the same cell. Heterozygous (Men1+/-) mice developed pituitary tumors, mostly reported somatolactotrophinomas and ACTH secreting pituitary adenomas but also nonfunctioning tumors.

The aim of the study was to run immunohistochemistry protocols to study colocalization of pituitary hormones in newborn mice in tumoral and non-tumoral tissue in MEN1-KO and wild type control mice.

Methods: Pituitary samples from nine Men1+/- mice, 29-34 days old male mice (n=8) and one year old (n=1) and control group, four new born (1,5 days old) wild type (mus musculus) mice were analyzed by immunofluorescence immunohistochemistry (GH, PRL, gonadotrophs) to find hormonal colocalization in pituitary cell. Moreover, pituitaries were embedded in LRGold for immunogold labeling technique (GH, PRL, gonadotrophs and alpha-SU) also.

Results: Pituitary tumors, immunoreactive only for PRL were found in three MEN1 – KO mice. No sign of pituitary hyperplasia was found in MEN1-KO. MEN1-KO non-tumoral pituitary displayed similar immunoreactivity to wild type pituitary. Colocalization studies revealed individual cells PRL-FSH immunoreactive and GH-FSH immunoreactive in the non-tumoral tissue from MEN1-KO mice and in wild type pituitaries respectively but no colocalization in the tumoral tissue.

In conclusion, colocalization is a feature of neonate mouse pituitary but not in adults. The MEN1-KO pituitary tumors were prolactinomas and unlike non-tumoral pituitary tissue of MEN1-KO, displayed no PRL-FSH colocalization.