Sexual dimorphism among calbindin-D28K immunoreactive cells in the rat pineal body

Calbindin antibodies have been used in neuroanatomical studies to give excellent cytoarchitectural staining and visualization of a Golgi-like cellular morphology. Calbindin-D28K immunoreactivity used in rat pineal gland as a marker detected two classes of pineal cells. One class of small cells representing exclusively glial cells was strongly immunoreactive, and presented a large variety of individual shapes. The majority were a pyramidal shape with one or more processes while others displayed a cytoplasmic lipid droplet. Some small cells occurred around pericapillary spaces. The second class of calbindin-D28K positive cells corresponding to type II pinealocytes were characterized by their large size and less intensive labelling. Type II pinealocytes were round or rectangular; the nucleus was infolded and large with a prominent nucleolus. These large cells were preferentially distributed in the vicinity of vessels and assembled in a cluster of more than ten cells. The lack of S-100 and myeloperoxidase immunoreactivities in large calbindin-D28K cells excluded their possible characterization as glial cells and mononuclear phagocytes, while their size (> 15 microns) excluded microglial cells. A sex difference was detected between large calbindin-D28K positive cells. The mean calculated number of large positive cells for males was 6361 +/- 1504 (n = 8) compared to 2162 +/- 1235 (n = 7) for females. No significative difference was detected between males and females for small calbindin-D28K positive cells.