Organization of the torus longitudinalis in the rainbow trout (Oncorhynchus mykiss): An immunohistochemical study of the GABAergic system and a DiI tract‐tracing study

Abstract

The torus longitudinalis (TL) is a tectum-associated structure of actinopterygian fishes. The organization of the TL of rainbow trout was studied with Nissl staining, Golgi methods, immunocytochemistry with antibodies to gamma-aminobutyric acid (GABA), glutamic acid decarboxylase (GAD), and the GABA(A) receptor subunits delta and beta2/beta 3, and with tract tracing methods. Two types of neuron were characterized: medium-sized GABAergic neurons and small GABA-negative granule cells. GABA(A) receptor subunit delta-like immunoreactivity delineated two different TL regions, ventrolateral and central. Small GABAergic cells were also observed in marginal and periventricular strata of the optic tectum. These results indicate the presence of local GABAergic inhibitory circuits in the TL system. For tract-tracing, a lipophilic dye (DiI) was applied to the TL and to presumed toropetal nuclei or toral targets. Toropetal neurons were observed in the optic tectum, in pretectal (central, intermediate, and paracommissural) nuclei, in the subvalvular nucleus, and associated with the pretectocerebellar tract. Torofugal fibers were numerous in the stratum marginale of the optic tectum. Toropetal pretectal nuclei also project to the cerebellum, and a few TL cells project to the cerebellar corpus. The pyramidal cells of the trout tectum were also studied by Golgi methods and local DiI labeling. The connections of trout TL revealed here were more similar to those recently reported in carp and holocentrids (Ito et al. [2003] J. Comp. Neurol. 457:202-211; Xue et al. [2003] J. Comp. Neurol. 462:194-212), than to those reported in earlier studies. However, important differences in organization of toropetal nuclei were noted between salmonids and these other teleosts.

Anatomical distribution and daily profile ofgper1bgene expression in brain and peripheral structures of goldfish (Carassius auratus)

“…In the rainbow trout, clock is expressed in cells of the periventricular gray zone of the optic tectum (Mazurais et al, 2000). In addition, these areas have been reported to be intercommunicated and to be connected with the retina (Folgueira et al, 2007;Mazurais et al, 2000;Yáñ ez et al, 2009), and then, being able to receive photoperiodic information.…”

Development of the cerebellum and cerebellar neural circuits

“…The crest cells also receive afferent input from the lateral line afferents. In the optic tectum, Type I neurons (or pyriform cells) function as the principal cells and extend their dendrites superficially into the marginal layer (or stratum marginale; SM) to receive parallel fibers from a medially located granule cell mass known as the torus longitudinalis (TL) [TL-SM-Type I neuron circuitry]; they also receive input from the retina (Bell, 2002;Ito et al, 2003;Folgueira et al, 2007;Bell et al, 2008) (see Fig. 5).…”

Krüpple-like factors 7 and 6a mRNA expression in adult zebrafish central nervous system

“…Other klf7 - and klf6a -expressing structures implicated in the control of movement include the superior raphe nucleus (SR), nucleus of the lateral lemniscus (NLL), reticular formation and motor neurons in the spinal cord (Wullimann et al, 1996). Finally, klf7 - and klf6a -expressing cells are found in structures belonging to a premotor network containing the telencephalon, pretectum, torus longitudinalis (TL), optic tectum, dorsal tegmental nucleus (DTN), lateral valvular nucleus (NLV), cerebellum and spinal cord (Wullimann, 1994; Ikenaga et al, 2002; Folgueira et al, 2007). …”