A morphometric and statistical study of the effects of soft laser (He-Ne) irradiation on the pineal gland.

Thirty-six male Wistar rats (225g average b.w.) were studied after direct He-Ne laser irradiation (632.8 nm, 5 mW) of the surgically-exposed pineal gland. Total irradiation time was 5 minutes, with rest intervals of 1 minute for every minute of irradiation. The animals were sacrificed in groups of 4 (controls, irradiated animals and sham-operated rats--i.e., craniotomy without irradiation) on days 3, 7 and 10 postirradiation. A significant increase was seen (p < 0.0001) in the medullary and cortical karyometric indices of the pineal body in all experimental, control and sham-operated animals. The increase was greatest (over 50%) on day 3 postirradiation among the experimental animals, with respect to the control and sham-operated groups. A progressive and significant decrease in karyometric index (p < 0.05) was in turn observed on days 7 and 10 postirradiation, although the values remained higher than among the controls. Ultrastructurally, there were cytoplasmic signs of an increase in metabolic activity in the experimental animals on days 3 and 7, followed by a decrease in activity by day 10 with the appearance of numerous lipid droplets, pericanallicular dark cells and mesoglial cells. We suggest that laser irradiation stimulates cortical and medullary pinealocytes, followed by a decreased effect at day 10 postirradiation. The effect of laser light is in turn determined by experimental action and the duration of exposure.