Periventricular efferent neurons in the optic tectum of rainbow trout

Abstract

The efferent connections and axonal and dendritic morphologies of periventricular neurons were examined in the optic tectum of rainbow trout to classify periventricular efferent neurons in salmonids. Among the target nuclei of tectal efferents, tracer injections to the following four structures labeled periventricular neurons: the area pretectalis pars dorsalis (APd), nucleus pretectalis superficialis pars magnocellularis (PSm), nucleus ventrolateralis of torus semicircularis (TS), and nucleus isthmi (NI). Two types of periventricular neurons were labeled by injections to the APd. One of them had an apical dendrite ramifying at the stratum fibrosum et griseum superficiale (SFGS), with an axon that bifurcated into two branches at the stratum griseum centrale (SGC), and the other had an apical dendrite ramifying at the SGC. Two types of periventricular neurons were labeled after injections to the TS. One of them had an apical dendrite ramifying at the boundary between the stratum opticum (SO) and the SFGS, and the other had dendritic branches restricted to the stratum album centrale or stratum periventriculare. Injections to the PSm and NI labeled periventricular neurons of the same type with an apical dendrite ramifying at the SO and a characteristic axon that split into superficial and deep branches projecting to the PSm and NI, respectively. This cell type also possessed axonal branches that terminated within the tectum. These results indicate that periventricular efferent neurons can be classified into at least five types that possess type-specific axonal and dendritic morphologies. We also describe other tectal neurons labeled by the present injections.

Visual, lateral line, and auditory ascending pathways to the dorsal telencephalic area through the rostrolateral region of the lateral preglomerular nucleus in cyprinids

“…In a salmonid the preglomerular nuclei have been reported to receive fibers from the optic tectum (Kinoshita et al, 2006) as well as the semicircular torus and to project to the Dm and Dd plus dDl (Folgueira et al, 2005). These connections appear similar to those of the PGlr in cyprinids (Northcutt, 2006;present study).…”

“…Recent studies suggest the presence of tectopreglomerulo-dorsal telencephalic pathways also in salmonids (rainbow trout: Folgueira et al, 2005;Kinoshita et al, 2006). Also importantly, another recent study in goldfish reported that the rostrolateral region of the PGl (PGlr) receives tectal fibers in addition to octavolateral inputs (Northcutt, 2006).…”

“…According to the latter goldfish report, the PGlr can be subdivided into dorsal (PGlr-d) and ventral (PGlr-v) regions, and the PGlr-d receives tectal and ventrolateral toral (presumed lateral line) fibers, whereas the PGlr-v receives auditory fibers from the medial pretoral nucleus of Finger and Tong (1984). However, the morphology of tectopreglomerular neurons remained unclear, and it is unknown whether the tectopreglomerular pathway in cyprinids conveys visual inputs or other modalities that reach the optic tectum (Meek and Nieuwenhuys, 1998;Kinoshita et al, 2006).…”

Somatosensory nucleus in the torus semicircularis of cyprinid teleosts

“…Labeled terminals in the NLVpl were cupshaped and appeared to envelop target neurons in this nucleus (Fig. 4C), a feature shared by afferents to the NLV from various sources (carp: Yoshimoto and Ito, 1993;Ito et al, 1997;Xue et al, 2006b, tilapia: Yang et al, 2004Xue et al, 2005Xue et al, , 2006a; rainbow trout: Kinoshita et al, 2006). Cerebellar injections label this population of granular cells (Fig.…”

Pattern of Nitrergic Neuronal System Organization in the Brain of Two Holostean Fishes (Actinopterygii: Ginglymodi)

“…They possessed long apical processes directed toward the pial surface (spv; Fig. 5d-g) and were identified as neurons of type XIV [according to Meek and Nieuwenhuys, 1998;Kinoshita et al, 2006]. The apical processes ramified es- pecially in the stratum album centrale (sac; Fig.…”