Contribution to the Study of the Pineal Stalk Nerve Fibres in the Rat

Abstract

Publisher Summary The problem whether the rat pineal gland is innervated via its stalk from the central nervous system has never been satisfactorily answered. Most authors admit that the gland is uniformly innervated by orthosympathetic fibres coming from the superior cervical ganglia, the only rare fibres seen in the stalk and coming from the epithalamus being aberrant and without any functional significance. However, some experiments carried out in the last few years pointed to the persistence of nerve fibers and of electrical reactivity in the pineal gland after bilateral superior cervical ganglionectomy. For these reasons and for describing the pathways of these fibers, a multi-aspect histological approach was undertaken in which serial paraffin sections of rat brains, especially stained to show nerve fibers, as well as semithin and ultrathin sections of the pineal complex were studied. From these experiments, it appeared that the stalk is composed of at least two types of nerve fibers: (1) afferent unmyelinated fibers originating in the superior cervical ganglia and directed to the deep pineal and the habenula and (2) Efferent myelinated and unmyelinated fibers coming from the habenular and posterior commissures and entering the superficial pineal, which lose their sheet and break up into many axonal branches ending in intercellular spaces with small bulbs containing clear synaptosomes. This morphological approach has been completed by a detection of acetylcholinesterase and catecholamines.