Effects of temperature and bright light on myeloid bodies in the retinal pigment epithelium of the newt, Notophthalmus viridescens.

Myeloid bodies (MBs) are specialized regions of endoplasmic reticulum which occur in the retinal pigment epithelium of a number of vertebrate species. In the newt, Notophthalmus viridescens, the effects of temperature and brief exposure to bright flashed-light on myeloid bodies have been studied. Morphometric analysis has shown that in animals sampled at 06.30 h, myeloid body sectional area remained unchanged in animals maintained in the cold (1 degree C), compared with control animals at 15 degrees C, whereas phagosome area was significantly increased. At higher temperatures (30 degrees C), myeloid body area was observed to decline from control values, while phagosome area was substantially increased. During the first 2 h of the light phase of a normal (15 degrees C) 12:12 LD lighting cycle, myeloid-body sectional area dropped significantly from values recorded in the latter part of the dark phase. This reduction of MB area at the normal time of "lights-on" was greatly reduced when animals experienced an extended period of darkness. When animals experienced a bright flashed-light at the normal time of "lights-on", followed by a period of extended darkness, reduction in MB area was less pronounced when compared to cycled control animals. These results are discussed in the context of the hypothesis (Yorke and Dickson 1984) that MBs represent a temporary storage site for lipids entering the pigment epithelium after phagocytosis of shed outer segment tips, prior to their permanent storage in lipid droplets.(ABSTRACT TRUNCATED AT 250 WORDS)