OBSERVATIONS ON THE PINEAL-GLAND OF THE BIG BROWN BAT, EPTESICUS-FUSCUS - POSSIBLE CORRELATION OF MELANIN INTENSIFICATION WITH CONSTANT DARKNESS

Background: Our initial observation of the macroscopically pigmented p ineal gland of the big brown bat, Eptesicus fuscus, led to this study. Information has been lacking on pigmentation in the pineal and its si gnificance in mammals in general and bats in particular. This report b egins to address this situation.Methods: Bats were examined both in th e wild and after exposure to various experimental conditions. The pine als were examined macroscopically as well as with light and electron m icroscopy. The pigment was identified as melanin by its color, the ult rastructure of its granules, and their reaction with hydrogen peroxide . Results: Gross observations showed the pineals to be variably pigmen ted, which were subjectively scored from unpigmented to heavily pigmen ted. Pineals from bats exposed to a continuous 24 h light regimen or t hose from a summer population contained very little, if any, externall y visible melanin. Such pineals are considered unpigmented in this stu dy. In contrast, pineals from 74% of 156 animals taken together, eithe r subjected to constant darkness or hibernation (simulated or natural) , exhibited very heavily pigmented pineals. The pigment in these cases even extended to the juxtapineal meningeal covering. The pineal was p igmented even in a newborn Eptesicus. Conclusions: The pineal pigmenta tion in the big brown bat appears to intensify with constant darkness and may vary seasonally. The observation of macroscopically pigmented pineals in some other bats (Myotis lucifugus, Pipistrellus subflavus, and Lasiurus borealis) suggests that this phenomenon may be of taxonom ic value for the family Vespertilionidae (Order Chiroptera). (C) 1994 Wiley-Liss, Inc.