Effect of Hypophysectomy on the Synaptic Ribbons in the Pineal Organ of the Killifish Fundulus heretoclitus

Abstract

The Pineal organ of the killifish was investigated by electron microscopy under experimental light and dark conditions and after hypophysectomy. Significant changes were detected in the number and length of the synaptic ribbons in the pineal organ. The pineal synaptic ribbons in-creased in number and length during darkness at night, but decreased during the day in light. Hypophysectomy showed a prominent effect on the decrease in number and lengh of the synaptic ribbons. Tish result suggests that the pineal synaptic ribbons function as receptors for the infor-mation from the pituitary. Meanwhile, the intact fish kept in continuous darkness showed a con-spicuous decrease in number and length of the synaptic ribbons during day time. This means that changes of synaptic ribbons (number and length) might be involved in circadian rhythm rather than light and dark conditions.