Parietal Eye-Pineal Gland Interactions in the Lizard Sceloporus occidentalis (Reptilia, Lacertilis, Iguanidae)

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Abstract
The effect of light on pineal gland weight and pineal hydroxyindole-O-methyltransferase (HIOMT) activity was monitored in parietalectomized and/or blinded lizards during the winter and spring. The average weight of the gland increased in winter but enzyme activity was higher in the spring. Sexual differences were evident with females generally having heavier pineal glands than males during both seasons. Light intensity in the test environment was inversely related to pineal HIOMT activity, but parietal eye removal partially reduced this effect, especially in brighter environments. The light simulated parietal eye will cause decreases in pineal HIOMT activity. This effect is similar to that of the lateral eye but does not occur to as great a degree. Besides causing highly significant increases in pineal HIOMT activity, blinding also resulted in pineal weight gain, an effect not seen upon parietalectomy. Removal of the parietal eye in blinded animals did not significantly increase activity of the melatonin forming enzyme. The parietal eye of certain lizards can effect alterations in pineal gland HIOMT activity but the influence of this photoreceptor on pineal function is more subtle and more restricted than that of the lateral eyes. The possible significance of parietal eye-pineal gland interactions in lizards is discussed.

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