Changes in Pinealocytes type I and II of Adult Albino Rat Exposed to Different Wavelengths of Light or Confined to Constant Darkness: A Morphological and Electron Microscopic Study

Introduction: the pineal gland is a neuro-endocrine gland that secretes melatonin hormone which
regulates the circadian rhythm, psychiatric disorder and age changes resulting from exposure to different
light wavelengths or darkness. Intensity, duration and wavelength of light control the activity of pineal
gland.
Aim of work: the purpose of this study was to monitor the morphological and electron microscopic
changes in the pinealocytes type I and II of albino rats exposed to either constant (24hrs/day) red light
(long wavelength) or blue light (short wavelength) as well as confined to constant darkness as compared
to control group subjected to normal diurnal conditions.
Material and methods: forty adult male albino rats were divided into four subgroups. Group I (GI):
the rats were kept under normal diurnal conditions, group II (GII): the rats were confined to constant
darkness, group III (GIII): the rats were exposed to constant red light (long wavelength; 670nm) and
group IV (GIV): the rats were subjected to constant blue light (short wavelength, 450nm); for four weeks
continuously.
Results: morphological findings of pinealocytes type I (PI) were analyzed statistically and revealed an
increase in the nuclear number of PI in GII, decrease in the nuclear number of PI in GIV and nonsignificant
difference in nuclear number of PI in GIII as compared to the control group. In addition,
rats of GIV reported a statistically significant increase in the amount of collagen fibers between loosely
packed parenchymal cells. Electron microscopic results of the cytoplasm of PI in GII showed abundant
cell organelles such as mitochondria, numerous ribosomes and multiple lipid droplets together with
well-developed Golgi bodies, scarce dense core vesicles (DCV), few cisternae of smooth endoplasmic
reticulum (SER) and rough endoplasmic reticulum (RER). GIII demonstrated similar results to that of
GI. On the other hand, GIV showed scarce cytoplasmic organelles such as few mitochondria; mostly
distended with disturbed cristae, scattered lipid droplets with abundant DVC and numerous cisternae
of SER. Ultrastructurally, PI nuclei of GII exhibited infolded nuclear envelope with heterochromatic
karyoplasm and prominent nucleoli while GIV revealed reduction of the nuclear chromatin with rupture
of nuclear envelope at certain sites. However, GIII nuclei demonstrated results similar to that of GI. No
observable changes were detected by light and electron microscopy of PII in the different experimental
groups apart from the presence of statistically significant increase in the nuclear number of PII in GII.
Moreover, the PII cytoplasm showed scarce mitochondria in GI, II and RER in GIV. The glial cells
demonstrated statistically significant increase in GIV but non-significant differences were noticed in the
other groups as compared to GI.
Conclusion: it could be concluded that the morphological and electron microscopic changes of
pinealocyte type I indicate decrease in the activity of pinealocytes type I on exposure to constant short
wavelength blue light and increase in the activity of PI confined to constant darkness. While the exposure
to constant long wavelength red light demonstrates results similar to the control group. There were no
changes in the structure of pinealocytes type II in the different experimental groups, exposed to different
light wavelengths or confined to darkness.