GABAergic system of the pineal organ of an elasmobranch (Scyliorhinus canicula): a developmental immunocytochemical study

Abstract

The present immunocytochemical study provides evidence of a previously unrecognized, rich, gamma-aminobutyric acid (GABA)-ergic innervation of the pineal organ in the dogfish (Scyliorhinus canicula). In this elasmobranch, the pineal primordium is initially detected at embryonic stage 24 and grows to form a long pineal tube by stage 28. Glutamic acid decarboxylase (GAD)-immunoreactive (-ir) fibers were first observed at stage 26, and by stage 28, thin GAD-ir fibers were detectable at the base of the pineal neuroepithelium. In pre-hatchling embryos, most fibers gave rise to GAD-ir boutons that were localized in the basal region of the neuroepithelium, although a smaller number of labeled terminals ascended to the pineal lumen. A few pale GAD-ir perikarya were observed within the pineal organ of stage 29 embryos, but GAD-ir perikarya were not observed at other developing stages or in adults. In contrast, GABA immunocytochemistry revealed the presence of GABAergic perikarya and fibers in the pineal organ of late stage embryos and adults. Although high densities of GABAergic cells were observed in the paracommissural pretectum, posterior tubercle, and tegmentum of dogfish embryos (regions previously demonstrated to contain pinealopetal cells), the presence of GABA-ir perikarya in the pineal organ strongly suggests that the rich GABAergic innervation of the elasmobranch pineal organ is intrinsic. This contrasts with the central origin of GABAergic fibers in the pineal gland of some mammals.

Early development of GABAergic cells of the retina in sharks: An immunohistochemical study with GABA and GAD antibodies

“…GABA and GAD immunoreactivities were absent from retina of embryos prior to the stage 26, which contrasts with the abundance of GABA and GAD immunoreactive cells in the brain at earlier stages (Carrera et al, 2006). Strikingly, the onset of GABA and GAD expression in the retina occurred when it was just a neuroepithelium without any apparent layering.…”

Development of the serotoninergic system in the central nervous system of a shark, the lesser spotted dogfish Scyliorhinus canicula

“…Although this group is a key for understanding the early evolutionary history of vertebrates, developmental studies are rather scarce. Knowledge of the development of neurotransmitter systems in Chondrichthyes is limited to a few studies of catecholaminergic and GABAergic systems in the lesser spotted dogfish Scyliorhinus canicula (Sueiro et al, 2003(Sueiro et al, , 2004(Sueiro et al, , 2007Carrera et al, 2005Carrera et al, , 2006Carrera et al, , 2008FerreiroGalve et al, 2008a,b). This dogfish has also been used in studies of gene expression during very early brain development (Sauka-Spengler et al, 2001Derobert et al, 2002a,b).…”

A Developmental Approach to Forebrain Organization in Elasmobranchs: New Perspectives on the Regionalization of the Telencephalon

“…2 B), and the zona limitans intrathalamica is recognized as the wedge of GABAergic cells that extends between prosomeres p2 and p3 ( fig. 3 A, B) [see also Carrera et al, 2006;Ferreiro-Galve et al, 2008]. This transverse boundary can be identified also by the presence of sonic hedgehog protein.…”

“…The use of immunomarkers of the GABAergic system as antibodies against GABA and the synthesis enzyme, the glutamic acid decarboxylase (GAD), has shed light on forebrain regionalization in this dogfish, as they seem to be good markers for some boundaries and domains [Carrera et al, 2006[Carrera et al, , 2008aFerreiro-Galve et al, 2008]. Moreover, the expression of the Pax6 gene, which is considered one of the genes responsible for forebrain regionalization in vertebrates, reveals a pattern consistent with that observed in other fishes [Wullimann and Rink, 2001] and highlights the presence of longitudinal and transverse boundaries, such as the alar-basal, diencephalic-mesencephalic, and pallial-subpallial boundaries, as well as some prosomeric domains.…”