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Although melanoctyes appear to be limited to the hair folilcles of adult belly skin of the PET mouse, they are found throughout the integument of the newborn. Trauma applied to the ventral belly skin of newborn PET mice results in the maintenance and augmentation of the melanocytes within the skin, even after the formation and growth of hair. The area immediately surrounding the site of trauma shows an increase in the number of melanocytes, apparently due in part to the disruption of the developing follicles and the consequent release of their pigment cells to the skin. UV irradiation also maintains a system of melanocytes within the ventral belly skin of PET mice.The significance of the maintenance and augmentation of melanocytes from the newborn into the adult by surgical trauma or UV radiation is discussed.Mice of the PET strain have been de-,scribed with particular respect to the occurrence of extra-epidermal melanocytes (Nichols and Reams, '60). Mayer and Reams ('62) have given a detailed account of the melanocyte system within the musculature of the leg. However, little attention has been paid to the melanocytes of the skin of PET mice.Int erf ollicul ar melanocyte s generally are considered to be lacking in the hair-covered areas of the skin of mice. However SteinerWourlisch ('25) has made mention of the occurrence of melanocytes in the skin of pigmented mice, and Mayer and Reams ('62) have described dense melanocyte populations in the posterior skin of the leg of PET mice. Although interfollicular melanocytes can be observed to a limited extent in the dorsal skin of pigmented mice, they are usually lacking in the ventral belly skin. Even though adult mouse skin may be deficient in visible melanocytes, Reynolds ('54) reported the presence of dopanegative amelanotic melanocytes in the hair-covered skin of adult pigmented mice. Thus, the apparent absence of melanocytes does not necessarily imply that the skin is devoid of pigment cells.Exposure of adult pigmented mice to ultraviolet radiation provokes hyperpigmentation (Blum, '61; Quevedo and McTague, '63) through a hyperproduction of melanin plus an increased number of active melanocytes (Staricco, '63). Apparently, therefore, latent pigment cells within the skin can be activated to become melanotic melanocytes (Szabo, '63).The purpose of the present study was to investigate the effects of surgical trauma on the melanocyte system of the ventral belly skin of the PET mouse. In seeking an understanding of this problem, a comparison was made between the effects of surgical trauma and ultraviolet radiation on ventral belly skin. Since little information was available concerning the melanocyte population in the ventral belly skin of PET mice, a descriptive analysis was made as the first phase of the investigation. Normal melanocyte population in various aged PET miceThe normal melanocyte population of the ventral belly skin of PET mice of various ages was determined by a microscopic study of whole mounts. Mice were sacrificed by cervical displacement at ...

Mammals, as a rule, are described as having melanocytes of neural crest origin confined almost entirely to the skin. Of the organs other than skin which have been described as possessing melanocytes are portions of the gonado-genital apparatus of the Opossum (Burns, 1939), and, in the house mouse, tissues of the nictitans, the meninges of the brain, the parathyroids, the thymus and harderian glands (Markert & Silvers, 1956), and the parathyroids of C58 mice (Dunn, 1949). The present investigation has been made in a strain of mice in which melanocytes are found in the connective tissues throughout much of the body. This strain originated several years ago in the Department of Genetics, Medical College of Virginia, from a cross between inbred C3H and black mice of unknown breed obtained from a local pet shop. Because of the latter circumstance, the line-bred progeny have been termed the PET/MCV strain.