Calcitonin gene-related peptide immunoreactivity selectively labels accessory optic nuclei and pathways of the rat visual system.

The present study shows the distribution of calcitonin gene-related peptide (CGRP)-immunolabeled neuronal somata and fibers in the accessory optic system of adult rats. CGRP-immunoreactive cell bodies were small to medium-sized and mostly fusiform or oval-shaped. Both immunolabeled somata and fibers were found in the dorsal and lateral terminal nuclei as well as in the interstitial nucleus of the superior fasciculus (posterior fibers); whereas only immunoreactive fibers were found in the ventral division of the medial terminal nucleus, particularly its rostral portion. These results indicate that CGRP-containing neurons are present in all nuclear components of the accessory optic system and suggest that this neuropeptide may play a neuromodulative role in eye movements.

An autoradiographic study of the projections of visual cortical area 1 to the thalamus, pretectum and superior colliculus of the rabbit.

The projections of visual cortical area 1 (vl) to the thalamus, pretectum and superior colliculus of the rabbit have been studied by Giolli and Guthrie ('67, '71) using the Nauta and Fink-Heimer methods to determine the course and distribution of degenerating nerve fibers. The present study represents a reinvestigation of these same projections utilizing the tracing method of autoradiography. An injection of 3H leucine was produced within a small region of vl in each of 18 adult albino rabbits, and the brains were subsequently processed for autoradiography by the method of Cowan et al. ('72). The results have confirmed the observations of Giolli and Guthrie ('67, '71) (1) by showing that vl of the rabbit projects to the thalamic reticular nucleus, the ventral lateral geniculate nucleus, the dorsal lateral geniculate nucleus; the pulvinar, the anterior and posterior pretectal nuclei and the superior colliculus and (2) by showing that a particular retinotopic organization is present in each of these projections. However, unlike Giolli and Guthrie ('67, '71), the present autoradiographic study has further revealed (1) that both the ventrolateral and the posterior thalamic nuclei receive inputs from vl and (2) that the nucleus of the optic tract is not innervated by axons originating from vl.

The accessory optic fiber system of the golden hamster with special reference to retinohypothalamic projection.

The hamster accessory optic fiber system has been investigated with the use of de Olmos-Ingram and Fink-Heimer silver methods following the production of unilateral ocular enucleation. It was found that this fiber system consists of both crossed and uncrossed inferior and superior fasciculi. The fibers of the inferior fasciculus (anterior accessory optic tract) run along the medial edge of the cerebral peduncle and terminate within the medial terminal nucleus of the accessory optic system. The fibers of the superior fasciculus (posterior accessory optic tract) leave the main optic tract, pass superficially over the medial geniculate nucleus and the cerebral peduncle; they synapse within the dorsal, the lateral and the medial terminal accessory optic nuclei. The presence of a retinohypothalamic tract could not be confirmed.