Pattern of nitrergic cells and fibers organization in the central nervous system of the Australian lungfish,Neoceratodus forsteri(Sarcopterygii: Dipnoi)

Abstract

The Australian lungfish Neoceratodus forsteri is the only extant species of the order Ceratodontiformes, which retained most of the primitive features of ancient lobe finned‐fishes. Lungfishes are the closest living relatives of land vertebrates and their study is important for deducing the neural traits that were conserved, modified, or lost with the transition from fishes to land vertebrates. We have investigated the nitrergic system with neural nitric oxide synthase (NOS) immunohistochemistry and NADPH‐diaphorase (NADPH‐d) histochemistry, which yielded almost identical results except for the primary olfactory projections and the terminal and preoptic nerve fibers labeled only for NADPH‐d. Combined immunohistochemistry was used for simultaneous detection of NOS with catecholaminergic, cholinergic, and serotonergic structures, aiming to establish accurately the localization of the nitrergic elements and to assess possible interactions between these neurotransmitter systems. The results demonstrated abundant nitrergic cells in the basal ganglia, amygdaloid complex, preoptic area, basal hypothalamus, mesencephalic tectum and tegmentum, laterodorsal tegmental nucleus, reticular formation, spinal cord, and retina. In addition, low numbers of nitrergic cells were observed in the olfactory bulb, all pallial divisions, lateral septum, suprachiasmatic nucleus, prethalamic and thalamic areas, posterior tubercle, pretectum, torus semicircularis, cerebellar nucleus, interpeduncular nucleus, the medial octavolateral nucleus, nucleus of the solitary tract, and the dorsal column nucleus. Colocalization of NOS and tyrosine hydroxylase was observed in numerous cells of the ventral tegmental area/substantia nigra complex. Comparison with other vertebrates, using a neuromeric analysis, reveals that the nitrergic system of Neoceratodus shares many neuroanatomical features with tetrapods and particularly with amphibians.

Pax6 expression highlights regional organization in the adult brain of lungfishes, the closest living relatives of land vertebrates

“…The three main components of the amygdaloid complex (lateral, central, and medial) that are characteristic of tetrapods (Moreno & González, ) have been proposed in lungfishes on the basis of neurochemistry and, to a lesser extent, connectivity (see López, Morona, Moreno, & González, ). Pax6 cells are particularly abundant in the lateral amygdala that would correspond to ventral pallial neurons, located just above the striatal region, as revealed with the Isl1 labeling (Moreno et al, ) and with the strongly reactive nitrergic cell population that is a characteristic feature of the lateral amygdala in amphibians (López et al, ; Moreno & González, , ). The central amygdala, a striatal component labeled with Isl1, and the medial amygdala (or vomeronasal amygdala; González et al, ) also show abundant Pax6 cells in the adult lungfishes.…”

“…The set of nuclei of lungfishes that constitute the amygdala is located in the mid to caudal part of the telencephalon and has been subdivided into three components—lateral, central and medial—on the basis of neurochemical, genoarchitectonic, and hodological data (González & Northcutt, , ; López et al, ; López, Morona, Moreno, & González, ). The most conspicuous population of Pax6 cell was found in the lateral amygdala, which, as mentioned previously, is a region in the ventral pallium that is contacted directly by olfactory fibers originated in the olfactory bulb (Northcutt & Rink, ; Figures c,d, f, and d–f).…”

“…The most conspicuous population of Pax6 cell was found in the lateral amygdala, which, as mentioned previously, is a region in the ventral pallium that is contacted directly by olfactory fibers originated in the olfactory bulb (Northcutt & Rink, ; Figures c,d, f, and d–f). The precise localization of the lateral amygdala can be assessed by its nitrergic and calbindin‐positive cells, which colocalized Pax6 (Figure h; Morona et al, ; López et al, ). The area defined as the central amygdala of lungfishes constitutes the caudal extent of the striatum and is mainly related to autonomic brain centers (see López, Morona, Moreno, & González, ).…”

“…The nomenclature used is essentially the same followed in our recent studies of lungfish brains (López et al, ; ; López, Morona, & González, ; López, Morona, Moreno, et al, ; López & González, , ; López, Morona, & González, ; Morona et al, ), including the terminology of the prosomeric model for the forebrain (Puelles & Rubenstein, , ).…”

Neuromeric Distribution of Nicotinamide Adenine Dinucleotide Phosphate-Diaphorase Activity in the Adult Lamprey Brain

“…In general, there is a conserved pattern of NADPH-d/nNOS positive neurons distribution across vertebrates, with main populations located at pallial/cortical areas, basal ganglia, amygdaloid complex, preoptic area, hypothalamus, optic tectum/superior colliculus region, reticular formation and spinal cord. Among fishes, many studies have described the organization of the nitrergic system in teleosts (Holmqvist et al, 1994(Holmqvist et al, , 2000Arévalo et al, 1995;Brüning et al, 1995;Villani and Guarnieri, 1995a,b;Anken and Rahmann, 1996;Bell et al, 1997;Virgili et al, 2001;Singru et al, 2003;Giraldez-Perez et al, 2008 and more recently for other basal actinopterygian groups (Cladistians: López et al, 2016;Holosteans: López et al, 2017) and the Australian lungfish (Sarcopterygii: Dipnoi; López et al, 2019). However, there is little documentation regarding the presence of this type of neurons in cyclostomes.…”