Melanin in the Pineal Gland of Species in the Family Canidae.

Objective. To analyze the presence of melanin and to assess the frequency of pigmented pineal glands (PG) in dogs of different age groups. Material and methods. Studies were performed on racoon dogs (Nyctereutes procyonoides Grey), foxes (Vulpes L.), and Arctic foxes (V. lagopus L.). PG pigmentation was assessed visually in immature or juvenile (6–8 months) and mature (1.5–3.5 years) female animals of each species and the proportions (%) of pigmented and nonpigmented glands were determined. The numbers of immature and adult animals of each species were as follows: racoon dogs (n = 4, n = 15), foxes (n = 15, n = 28), and Arctic foxes (n = 4, n = 14, respectively). The morphological characteristics of the PG were studied using histological methods on sections stained with eosin and by the Fontana–Masson method. Results. The PG of the study species showed accumulations of the pigment melanin both at the periphery of the gland and around blood vessels. A high level of variability in gland pigmentation was noted visually, from unpigmented to intensely pigmented. The frequency of pigmented glands was influenced by age and species. In racoon dogs, pigmented PG were seen only in immature individuals (25%), while in foxes only in adults (21.4%). In Arctic foxes, pigmented PG were characteristic of both age groups, though the proportion decreased with age (from 21.4% to 7.1%). Conclusions. Extensive variability was seen in the extent of PG pigmentation in canids. Pigmented PG frequencies were species-specific and age-dependent. [ABSTRACT FROM AUTHOR]