Area dorsalis pars lateralis of the telencephalon in a teleost (Sebastiscus marmoratus) can be divided into dorsal and ventral regions.

Abstract

Area dorsalis pars lateralis was shown to be subdivided into a dorsal region and a ventral region by a shallow groove on the telencephalic surface. In the dorsal region, three layers were distinguished by Nissl staining; a surface layer I, a middle layer II, and a deep layer III. Although a three-layered structure was also observed in the ventral region, it was not as clear as that in the dorsal region. Cells in area dorsalis pars lateralis were classified by Golgi-Cox staining into 5 types; small cells, horizontal cells, pyriform cells, inverted cells, and multipolar cells. The distribution of zinc was examined by the Neo-Timm method and found to be present in layers I and II and weakly in layer III of the dorsal region but not in layers I and II of the ventral region. The presence of zinc in synaptic terminals in the dorsal region was verified by analytical electron microscopy. Following separate and localized injections of horseradish peroxidase into dorsal and ventral regions, some different fiber connections were revealed. Both dorsal and ventral regions had reciprocal connections with ipsilateral area dorsalis pars centralis, area ventralis pars supracommissuralis, area ventralis pars dorsalis, area ventralis pars posterior, nucleus prethalamicus, and had afferent connections from area ventralis pars lateralis, area ventralis pars intermedia, raphe nuclei, and locus ceruleus. Only the dorsal region, however, received projections from contralateral area dorsalis pars centralis, ipsilateral area dorsalis pars dorsalis, area dorsalis pars medialis, and area dorsalis pars posterior and sent fibers to the inferior lobe, nucleus paracommissuralis, and optic tectum. Although area dorsalis pars lateralis had been thought to be a homogeneous region of the primary visual area of the telencephalon, histochemistry of zinc and fiber connections of the region indicates that the area is subdivided into two regions: dorsal and ventral.