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

Abstract

Chondrychthyans (cartilaginous fishes) are key to understanding the ancestral gnathostome condition since they provide an outgroup to sarcopterygians and actinopterygians. To gain comparative knowledge about the development of the vertebrate serotoninergic systems, we studied by immunohistochemistry the origin, spatiotemporal organization, and migration patterns of serotonin-containing neurons and the growth of axonal pathways in the central nervous system of a shark, the lesser spotted dogfish. Hindbrain serotonin-immunoreactive cells arose close to the floor plate and most populations migrated ventrally and mediolaterally to form the various raphe and reticular groups. The order of appearance of serotoninergic populations in the rhombencephalon and spinal cord (first the superior groups and then the inferior and spinal populations) roughly matched with that reported in other vertebrates but important differences were noted in the formation of prosencephalic groups in fishes. In addition to preoptic and hypothalamic areas, serotoninergic cerebrospinal fluid-contacting cells were observed in the isthmus (raphe dorsalis anterioris). Transient serotonin-immunoreactive cells were noted in the pineal organ, habenula, and pretectum. Further, we provide a revised anatomical framework for reticular and raphe serotoninergic populations considering their origin and segmental organization. Two distinct phases of development of the serotoninergic innervation were distinguished, that of the formation of the main axonal pathways and that of the branching of fibers. The development of main serotoninergic ascending pathways in dogfish was notably similar to that described in mammals. Our findings suggest the conservation of developmental patterns in serotoninergic systems and enhance the importance of elasmobranchs for understanding the early evolution of this system in vertebrates.

Organization of the Serotonergic System in the Central Nervous System of Two Basal Actinopterygian Fishes: the Cladistians <b><i>Polypterus senegalus</i></b> and <b><i>Erpetoichthys calabaricus</i></b>

“…No differences were observed between the immunolabeling of the sections treated with the antiserum alone or preadsorbed with BSA, thus indicating that the antibody does not cross-react with the carrier molecule alone. The antiserum has previously been used in several nonmammalian species, including different fishes and amphibians, and it has shown no cross-reaction with other monoamines [Stuesse and Cruce, 1992;Marín et al, 1998;Adrio et al, 1999;Antri et al, 2006;Abalo et al, 2007;Carrera et al, 2008;López et al, 2009;. The specificity of ChAT, CB, and CR antisera has been previously described in Polypterus [Graña et al, 2013;, and the distribution patterns for these markers are similar in the brain of Erpetoichthys (present results).…”

“…Thus, detailed distribution maps of 5-HT neurons and fibers were described in the brains of representative species of different groups [primates: Schofield and Everitt, 1981;Baker et al, 1991a, b;rodents: Steinbusch, 1981;Törk, 1990;monotremes: Manger et al, 2002;birds: Meneghelli et al, 2009;reptiles: Ueda et al, 1983;Smeets and Steinbusch, 1988;Bennis et al, 1990;Challet et al, 1991]. In addition, numerous studies revealed the 5-HT system in anamniotes, particularly in amphibians [Ueda et al, 1984;Corio et al, 1992;Clairambault et al, 1994], lungfishes , ray-finned fishes [Kaslin and Panula, 2001;Rink and Guo, 2004;see Lillesaar, 2011, for more references], cartilaginous fishes [Stuesse et al, 1995;Carrera et al, 2008], and jawless fishes [Pierre et al, 1992;Antri et al, 2006]. Therefore, from an evolutionary and comparative perspective, the 5-HT system is one of the best-known neurotransmitter systems in the brain.…”

“…750256E;Immunostar). Immunolabeling was completely eliminated in the sections treated with the primary antibody at the working dilution preadsorbed with serotonin-BSA conjugated at a concentration of 10 μg/ml at 4 ° C for 24 h [see Carrera et al, 2008]. In addition, we tested whether the BSA (carrier molecule) affects immunolabeling by preadsorbing the antiserum at the working dilution with 10 mg/ml BSA for 4 h at room temperature.…”

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

“…The catecholaminergic cells of the hypothalamus of the Lesser Spotted Dogfish differentiates early (stage 26), compared to structures of the mesencephalon and the rhombencephalon (stages 30-31) [Carrera et al, 2005]. The opposite happens with the hypothalamic serotoninergic cells, which differentiate late (stage 31) in relation to the rhombencephalic serotoninergic cells (stage 26) [Carrera et al, 2008b]. From stage 31, the hypothalamus in this species contains abundant serotoninergic and catecholamine-synthesizing (TH-immunoreactive) cells.…”

“…During the first and second periods of forebrain development, GABA, which is considered a subpallial marker in early developmental stages, is synthesized in most cells that extend through the basal part of the forebrain, from a level just anterior to the optic stalk (the presumptive preoptic area) to a very rostral telencephalic level, where the sharp decrease in GABA might represent the pallial-subpallial boundary. Because the density of GABAergic somata decreases during the third period of forebrain development, differences between preoptic and subpallial territories cannot be discerned with this marker, but when an embryo enters the prehatching phase (stages 33 and 34) serotoninergic cells differentiate in the walls of the preoptic recess to form a small population that is also observed in adults [Carrera et al, 2008b]. The preoptic area of this dogfish has been well studied in relation to the neurosecretory system [Vallarino et al, 1990;Meur ling et al, 1996] because it is in this region that one finds the neurons of the magnocellular preoptic nucleus, which forms part of the classical neurosecretory system, together with several populations of cells that contain diverse hypophysiotropic neuropeptides [for a review, see Smeets, 1998].…”