Uchiyama H ; Ito H ;

Brain Res vol. 298 (1)   pp. 11-24, 23 Avr 1984

Neuron cell bodies of the preoptic retinopetal nucleus (PRN), located in the diencephalon of the filefish , Navodon modestus, project axons to the retina. In the present study, the fiber connections and synaptic organization of the preoptic retinopetal nucleus (PRN) were investigated light- and electron-microscopically. The majority of neural cell bodies are located in the rostral half of this rostro- caudally elongated nucleus. Four types of synaptic terminals are distinguishable. The first (L) consists of large, irregularly shaped terminals that contain electron-dense mitochondria and numerous synaptic vesicles. These profiles make asymmetrical multi-synaptic contacts and gap junctions with somata and dendrites. The L terminals are also presynaptic to a second class of terminals (P), which have pleomorphic synaptic vesicles and form synapses onto dendrites. F terminals which have flat synaptic vesicles were also seen PRN. Very few S terminals were also seen in PRN. This type of terminal contains spherical synaptic vesicles of various sizes and a few pale mitochondria. S terminals form asymmetrical synapses with somata, dendrites and P terminals. Following unilateral tectal ablation, degenerating fibers from the lesion were traced into PRN bilaterally, although ipsilateral projections were far more numerous. L terminals exhibit degenerative changes after large tectal resection, whereas S terminals degenerate after contralateral eye enucleation. Therefore, a tecto-PRN-retinal circuit and a reciprocal connection between the retina and PRN have been documented. The similarity between PRN in the filefish and retinopetal nuclei in other classes of vertebrates, especially the isthmo-optic nucleus in birds, is discussed.

Animal ;  Birds: anatomy # histology ;  Brain Mapping ;  Comparative Study ;  Diencephalon: anatomy & histology ;  Efferent Pathways: anatomy & histology ;  Fishes: anatomy & histology ;  Retina: anatomy & histology ;  Species Specificity ;  Superior Colliculus: anatomy & histology ;  Support,Non-U.S.Gov't ;  Telencephalon: anatomy & histology ;  Visual Pathways: anatomy & histology ;  57320 ;