MORPHOLOGICAL DIVERSITY AND GLUTAMATE IMMUNOREACTIVITY OF RETINAL TERMINALS IN THE SUPRACHIASMATIC NUCLEUS OF THE CAT

Although the cat visual system has been the subject of intensive inves tigation, little attention has been given to the morphological feature s of ganglion cell projections to the suprachiasmatic nucleus. The pre sent study has utilized anterograde transport of horseradish peroxidas e and wheat germ agglutinin-conjugated horseradish peroxidase to label ganglion cell terminals in the cat suprachiasmatic nucleus. Visualiza tion of the reaction product was facilitated through the use of gold-s ubstituted silver intensification. Ganglion cell terminals were found to be morphologically diverse, making both asymmetric and symmetric co ntacts with postsynaptic processes. Synaptic vesicles were either scat tered or densely packed, sometimes forming paracrystalline arrays. In contrast to other retinorecipient areas in which ganglion cell termina ls have been characterized by the presence of lightly staining mitocho ndria, many of the retinal terminals in the suprachiasmatic nucleus we re seen to contain darkly stained mitochondria. Postembedding antiglut amate immunocytochemistry was used to evaluate the level of endogenous glutamate in these ganglion cell terminals. Although morphologically diverse, all of the retinal terminals in the suprachiasmatic nucleus w ere glutamate positive, consistent with the postulated role of glutama te as the neurotransmitter of retinal ganglion cells. (C) 1995 Wiley-L iss, Inc.