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

Abstract

Introduction: the pineal gland is a neuro-endocrine gland that secretes melatonin hormone whichregulates the circadian rhythm, psychiatric disorder and age changes resulting from exposure to differentlight wavelengths or darkness. Intensity, duration and wavelength of light control the activity of pinealgland.Aim of work: the purpose of this study was to monitor the morphological and electron microscopicchanges 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 comparedto 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 constantdarkness, group III (GIII): the rats were exposed to constant red light (long wavelength; 670nm) andgroup IV (GIV): the rats were subjected to constant blue light (short wavelength, 450nm); for four weekscontinuously.Results: morphological findings of pinealocytes type I (PI) were analyzed statistically and revealed anincrease in the nuclear number of PI in GII, decrease in the nuclear number of PI in GIV and nonsignificantdifference 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 looselypacked parenchymal cells. Electron microscopic results of the cytoplasm of PI in GII showed abundantcell organelles such as mitochondria, numerous ribosomes and multiple lipid droplets together withwell-developed Golgi bodies, scarce dense core vesicles (DCV), few cisternae of smooth endoplasmicreticulum (SER) and rough endoplasmic reticulum (RER). GIII demonstrated similar results to that ofGI. On the other hand, GIV showed scarce cytoplasmic organelles such as few mitochondria; mostlydistended with disturbed cristae, scattered lipid droplets with abundant DVC and numerous cisternaeof SER. Ultrastructurally, PI nuclei of GII exhibited infolded nuclear envelope with heterochromatickaryoplasm and prominent nucleoli while GIV revealed reduction of the nuclear chromatin with ruptureof nuclear envelope at certain sites. However, GIII nuclei demonstrated results similar to that of GI. Noobservable changes were detected by light and electron microscopy of PII in the different experimentalgroups 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 cellsdemonstrated statistically significant increase in GIV but non-significant differences were noticed in theother groups as compared to GI.Conclusion: it could be concluded that the morphological and electron microscopic changes ofpinealocyte type I indicate decrease in the activity of pinealocytes type I on exposure to constant shortwavelength blue light and increase in the activity of PI confined to constant darkness. While the exposureto constant long wavelength red light demonstrates results similar to the control group. There were nochanges in the structure of pinealocytes type II in the different experimental groups, exposed to differentlight wavelengths or confined to darkness.