Seasonal Changes in Melatonin and Immunological Adaptations in Birds

Abstract

Birds in general have not been frequently examined for the immunological influences of melatonin or pineal gland, as it has been potentially noted with the mammals including human being. There are only few reports suggesting that melatonin may play some role in the development and function of the immune system in the birds. The diurnal pattern of the melatonin synthesis is the same In almost all vertebrate groups so far examined, though differences exist in structure or anatomy of the pineal gland and seasonal variation in the peripheral melatonin level. Since functional relationship between neuroendocrine pineal gland and immune systems appears as to be diverse, it is logical that immunomodulatory effects of melatonin may be different in different seasons. The seasonal variation In melatonin level has been proved to improve the status of Immunity in seasonal tropical birds to bear the natural challenges. The level of peripheral melatonin minimizes some inflammatory diseases and sudden death syndrome in some poultry birds. The effect of melatonin also depends upon the phases of the inflammatory reaction/process. Pinealectomy in birds demonstrated functional interrelationship between the development of pineal gland, ontogeny of the melatonin secretion and immune system and/or neuroendocrine network. Bursectomy could influence the diurnal rhythm of melatonin and may abolish the effect of immunization on serum melatonin level. Specificities of avian immune system may be, however, very useful for understanding numerous phylogenetic and evolutionary mysteries. In this way a reciprocal functional connection between the avain immune system and the pineal gland seems to exist, but the mechanisms involved in maintaining the immune status by melatonin in avain group Is still not clear and needs to be elucidated.