Neuronal Networks in the Pineal Organ Responsible for Regulating Biological Rhythms

Abstract

The photosensory pineal organ of poikilotherm animals has an important role in the biological rhythms. Neuronal mechanisms to process photic information were analyzed on the basis of electrophysiological studies. Achromatic and chromatic systems were referred to be responsible for the intensity and wavelength information processing, respectively. For the achromatic system two types of neuronal networks were proposed. In the first type, photoreceptors make synapses directly with an achromatic ganglion cell, and in the second type, the interneuron participates in the processing. In the latter case, two models were introduced. (1) An interneuron integrates the signals from photoreceptors having different sensitivities and different kinds of transmitters. The interneuron transmitts the information to the ganglion cell. (2) An achromatic ganglion cell receives the signal from photoreceptors which are affected by other photoreceptors having higher sensitivity through an interneuron. For the chromatic process, photoreceptors having high sensitivity at middle wavelengths activate a chromatic ganglion cell through an interneuron, while UV-sensitive photoreceptors directly inhibit the ganglion cell.
Through these neuronal networks in the pineal organ, the daily and annual rhythm in photic environment may be converted to the biological rhythm.