Melanocytes are melanin-pigment synthesizing pigment cells derived from neural crest and widely distributed in vertebrates. They are stellate cells with long processes with numerous dark brown or black granules of melanin in their cytoplasm. There function is generally, to prevent light from reaching adjacent cells. In humans, they are present in the epidermis and its appendages, oral epithelium, some mucous membranes, uveal tract of eye ball, parts of middle and internal ear, and parts of leptomeninges in the base of brain. The cells of retinal pigment epithelium, neurons in locus ceruleus and substantia nigra also synthesize melanin. Melanins are high molecular weight polymers, attached to a structural protein, to form melanoproteins, and in the humans, there are two classes, the brown-black eumelanin and red-yellow pheomelanin, both derived from a substrate tyrosine (Dyson 1995).
Pineal gland (epiphysis cerebri) was once considered to be a phylogenic relic, a vestige of a dorsal third eye, and of little functional significance; the mammalian pineal is now regarded and accepted as an endocrine gland of major regulatory importance, modifying the activity of the adenohypophysis, neurohypophysis, endocrine pancreas, parathyroids, adrenal cortex, adrenal medulla, and gonads. (de Vries and Kappers 1971; Klein 1978; Haulica and Coeulescu 1981; Reiter 1983, 1985, 1987; Malendowicz 1985; Dyson 1995).
The pineal in the big brown bat is pigmented and intensified
with constant darkness (Bhatnagar and Hilton 1994). Pigmented cells in the cat pineal gland show a preferential localization at the ventral surface of the pineal gland near its distal end and the pineal pigment is melanin (Calvo et al. 1992). Presence of pigment cells is a constant characteristic in the adult dog pineal gland; the pigment is melanin (Calvo et al. 1988). Embryo ovine pineal gland has pigment cells containing melanin (Regodon et al. 1998). Pineal glands of neonates consist of cords of dark, nucleated cells, which are frequently pigmented (Min et al. 1987). In the human adult, melanin pigments gradually accumulate within the parenchymal cells with increasing age in males, whereas in females, the maximum pigmentation is noticed in 30-40 year age group and then there was a fall (Tapp and Huxley 1972). The present study was done to find whether or not the human adult pineal gland showed gender difference and age changes in the amount of melanin pigments. (Source)