Acetylcholinesterase-positive neurons in the pineal and parapineal organs of the rainbow trout, Salmo gairdneri (with special reference to the pineal tract).

Abstract

About 1500 nerve cells were demonstrated in the pineal organ of the rainbow trout, Salmo gairdneri, by means of the acetylcholinesterase (AChE) reaction (Karnovsky and Roots, 1964). The diameter of these elements is 10–15 μm in the end vesicle of the pineal organ and only 5–8 μm in the pineal stalk. The number of the AChE-positive neurons per unit area increases from the pineal end vesicle to the pineal stalk; most of them belong to the pseudounipolar type. An intrapineal ganglion with large, multipolar neurons occupies a rostromedial position. These cells exhibit a strong AChE reaction and are surrounded by a dense network of fibers. Thin bundles of axons form fiber pathways in the lateral walls of the pineal end vesicle. These roots converge to the pineal tract that is located in the dorsal portion of the pineal stalk and runs toward the posterior commissure.