Photoreception in pineal organs of larval and adult lampreys,Lampetra japonica

Summary

A comparative study of the larval and adult pineal organs, which are sensitive to incident light, was carried out in the river lampreyLampetra japonica, using intracellular recording from the pineal photoreceptors.

• 1. The tissue overlying the larval pineal organ is transparent, whereas that over the adult pineal is translucent. The optical density of this oval pineal window in the adult lamprey was 1.2.

• 2. In order to elucidate the early development of the larval pineal, the ratior of the diameter (μm) of the pineal to the body-length (cm) was measured. The value ofr was 62.5 in a small larva of 2.8 cm, 29.7 in a larger one of 14.3 cm, and 9.3 in an adult of 54 cm body-length.

• 3. The intracellular response to light of the larval pineal was a hyperpolarization, showing fundamentally the same pattern as that of the adult pineal. It was possible to record a typical response even from the pineal of the smallest larva, 2.8 cm in body length, used in this study.

• 4. The intensity-amplitude relationship was analysed after Naka-Rushton's hyperbolic equation. The value ofσ of isolated larval pineals was 0.88 log unit higher than that of adults. The value ofn was larger in larvae, suggesting a sensitive reaction to changing photic stimulus.

• 5. The spectral sensitivity was compared. The peak was at 505 nm in the larva, but 525 nm in the adult. A change of visual pigment in the pineal during metamorphosis is suggested.