In vitro uptake and metabolism of [3H]indole compounds in the pineal organ of the pike. II. A radioautographic study.

In a previous radiobiochemical study [Falcón et al., 1985] it was demonstrated that the pineal organ of the pike incubated in vitro takes up and metabolizes [3H]serotonin and [3H]melatonin. Parallel to this experiment (present work), pineal organs were investigated by use of light and electron microscopic radioautography to investigate the cell types involved in indole metabolism. Irrespective of the tracer and experimental conditions used, the radioautographic reactions were mainly found in cone-like and modified photoreceptor cells of the pineal parenchyma. Taking into account the limits of the method used as well as previous data concerning the direct photosensitivity of the organ, the localization of exogenous indoles, and the localization and circadian variations of endogenous ones, it is concluded that the photoperiodic information is translated into both nervous and indolic signals in cone-like photoreceptor cells and into indolic signals in modified photoreceptor cells.