Effects of Early Postnatal Pinealectomy on Adult Braln and Divisional Pituitary Weights in Relation to Type of Illumination

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Abstract
Female S1 rats, pinealectomized (p), sham-operated (s) or not operated (n-o) 2–4 days postnatally, were placed at weaning (age = 20–23 days) in individual activity-monitoring cages under blue, green or red fluorescent lights. Photoperiod (LD 12:12) timing was reversed at 2–3 week intervals until autopsy at 293–299 days. In p as compared with s and n-o animals, the brains were lighter and the pituitary glands were heavier. This difference was significant in pars distalis, pars intermedia and the colloid in the residual lumen. Neurohypophyseal weight, however, was significantly greater in both p and n-o than in s animals, suggesting a reversal of a traumatic effect by pinealectomy. Although most of these effects were most significant or marked in the blue-lighted animals, the results are not inconsistent with dependence on known spectral sensitivity of the rat's retinal rhodopsin. However, the results contradict the idea that all effects of pinealectomy are necessarily greater in, or depend upon, reduced illumination intensity or photoperiod length.