Nitric Oxide Synthase and NADPH Diaphorase Distribution in the Bullfrog (Rana catesbeiana) CNS: Pathways and Functional Implications

Expression and localization of neuronal nitric oxide synthase in the brain and sensory tissues of the African cichlid fish Astatotilapia burtoni

Nitric oxide (NO) produced by the enzyme neuronal nitric oxide synthase serves as an important neurotransmitter in the central nervous system that is involved in reproductive regulation, learning, sensory processing, and other forms of neural plasticity. Here, we map the distribution of nnos-expressing cells in the brain and retina of the cichlid fish Astatotilapia burtoni using in situ hybridization. In the brain, nnos-expressing cells are found from the olfactory bulbs to the hindbrain, including within specific nuclei involved in decision-making, sensory processing, neuroendocrine regulation, and the expression of social behaviors. In the retina, nnos-expressing cells are found in the inner nuclear layer, presumably in amacrine cells. We also used quantitative PCR to test for differences in nnos expression within the eye and olfactory bulbs of males and females of different reproductive states and social statuses. In the eye, males express more nnos than females, and socially dominant males express more nnos than subordinate males, but expression did not differ among female reproductive states. In the olfactory bulbs, dominant males had greater nnos expression than subordinate males. These results suggest a status-specific function for NO signaling in the visual and olfactory systems that may be important for sensory perception related to mating or territorial interactions to maintain the social hierarchy. The widespread distribution of nnos-expressing cells throughout the cichlid brain is similar to that in other teleosts, with some conserved localization patterns across vertebrates, suggesting diverse functions for this important neurotransmitter system.

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

This study reports for the first time the distribution and morphological characterization of nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d; a reliable marker of nitric oxide synthase activity) positive elements in the central nervous system of the adult river lamprey (Lampetra fluviatilis) on the framework of the neuromeric model and compares their cytoarchitectonic organization with that of gnathostomes. Both NADPH-d exhibiting cells and fibers were observed in all major divisions of the lamprey brain as well as in the spinal cord. In the secondary prosencephalon, NADPH-d positive cells were observed in the mitral cell layer of the olfactory bulb, evaginated pallium, amygdala, dorsal striatum, septum, lateral preoptic nucleus, caudal paraventricular area, posterior entopeduncular nucleus, nucleus of the stria medullaris, hypothalamic periventricular organ and mamillary region sensu lato. In the lamprey diencephalon, NADPH-d labeled cells were observed in several nuclei of the prethalamus, epithalamus, pretectum, and the basal plate. Especially remarkable was the staining observed in the right habenula and several pretectal nuclei. NADPH-d positive cells were also observed in the following mesencephalic areas: optic tectum (two populations), torus semicircularis, nucleus M5 of Schöber, and a ventral tegmental periventricular nucleus. Five different cell populations were observed in the isthmic region, whereas the large sensory dorsal cells, some cells located in the interpeduncular nucleus, the motor nuclei of most cranial nerves, the solitary tract nucleus, some cells of the reticular nuclei, and small cerebrospinal fluid-contacting (CSF-c) cells were the most evident stained cells of the rhombencephalon proper. Finally, several NADPH-d positive cells were observed in the rostral part of the spinal cord, including the large sensory dorsal cells, numerous CSF-c cells, and some dorsal and lateral interneurons. NADPH-d positive fibers were observed in the olfactory pathways (primary olfactory fibers and stria medullaris), the fasciculus retroflexus, and the dorsal column tract. Our results on the distribution of NADPH-d positive elements in the brain of the adult lamprey L. fluviatilis are significantly different from those previously reported in larval lampreys and demonstrated that these animals possess a complex nitrergic system readily comparable to those of other vertebrates, although important specific differences also exist.

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

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.

Characterization of NADPH Diaphorase- and Doublecortin-Positive Neurons in the Lizard Hippocampal Formation

The lizard cortex has remarkable similarities with the mammalian hippocampus. Both regions process memories, have similar cytoarchitectural properties, and are important neurogenic foci in adults. Lizards show striking levels of widespread neurogenesis in adulthood and can regenerate entire cortical areas after injury. Nitric oxide (NO) is an important regulatory factor of mammalian neurogenesis and hippocampal function. However, little is known about its role in nonmammalian neurogenesis. Here, we analyzed the distribution, morphology, and dendritic complexity (Neurolucida reconstructions) of NO-producing neurons through NADPH diaphorase (NADPHd) activity, and how they compare with the distribution of doublecortin-positive (DCX+) neurons in the hippocampal formation of the neotropical lizard Tropidurus hispidus. NADPHd-positive (NADPHd+) neurons in the dorsomedial cortex (DMC; putatively homologous to mammalian CA3) were more numerous and complex than the ones in the medial cortex (MC; putatively homologous to the dentate gyrus). We found that NADPHd+ DMC neurons send long projections into the MC. Interestingly, in the MC, NADPHd+ neurons existed in 2 patterns: small somata with low intensity of staining in the outer layer and large somata with high intensity of staining in the deep layer, a pattern similar to the mammalian cortex. Additionally, NADPHd+ neurons were absent in the granular cell layer of the MC. In contrast, DCX+ neurons were scarce in the DMC but highly numerous in the MC, particularly in the granular cell layer. We hypothesize that NO-producing neurons in the DMC provide important input to proliferating/migrating neurons in the highly neurogenic MC.

Organization of the nitrergic neuronal system in the primitive bony fishes Polypterus senegalus and Erpetoichthys calabaricus (Actinopterygii: Cladistia)

Cladistians are a group of basal actinopterygian fishes that constitute a good model for studying primitive brain features, most likely present in the ancestral bony fishes. The analysis of the nitrergic neurons (with the enzyme nitric oxide synthase; NOS) has helped in understanding important aspects of brain organization in all vertebrates studied. We investigated the nitrergic system of two cladistian species by means of specific antibodies against NOS and NADPH-diaphorase (NADPH-d) histochemistry, which, with the exception of the primary olfactory and terminal nerve fibers, labeled only for NADPH-d, yielded identical results. Double immunohistochemistry was conducted for simultaneous detection of NOS with tyrosine hydroxylase, choline acetyltransferase, calbindin, calretinin, and serotonin, to establish accurately the localization of the nitrergic neurons and fibers and to assess possible interactions between these neuroactive substances. The pattern of distribution in both species showed only subtle differences in the density of labeled cells. Distinct groups of NOS-immunoreactive cells were observed in pallial and subpallial areas, paraventricular region, tuberal and retromammillary hypothalamic areas, posterior tubercle, prethalamic and thalamic areas, optic tectum, torus semicircularis, mesencephalic tegmentum, interpeduncular nucleus, superior and middle reticular nuclei, magnocellular vestibular nucleus, solitary tract nucleus, nucleus medianus magnocellularis, the spinal cord and amacrine cells in the retina. Large neurons in cranial nerve sensory ganglia were also labeled. The comparison of these results with those from other vertebrates, using a neuromeric analysis, reveals a conserved pattern of organization of the nitrergic system from this primitive fish group to amniotes, including mammals.

A comparative cluster analysis of nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase histochemistry in the brains of amphibians

Nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) is a key enzyme in the synthesis of the gaseous neurotransmitter nitric oxide. We compare the distribution of NADPH-d in the brain of four species of hylid frogs. NADPH-d-positive fibers are present throughout much of the brain, whereas stained cell groups are distributed in well-defined regions. Whereas most brain areas consistently show positive neurons in all species, in some areas species-specific differences occur. We analyzed our data and those available for other amphibian species to build a matrix on NADPH-d brain distribution for a multivariate analysis. Brain dissimilarities were quantified by using the Jaccard index in a hierarchical clustering procedure. The whole brain dendrogram was compared with that of its main subdivisions by applying the Fowlkes-Mallows index for dendrogram similarity, followed by bootstrap replications and a permutation test. Despite the differences in the distribution map of the NADPH-d system among species, cluster analysis of data from the whole brain and hindbrain faithfully reflected the evolutionary history (framework) of amphibians. Dendrograms from the secondary prosencephalon, diencephalon, mesencephalon, and isthmus showed some deviation from the main scheme. Thus, the present analysis supports the major evolutionary stability of the hindbrain. We provide evidence that the NADPH-d system in main brain subdivisions should be cautiously approached for comparative purposes because specific adaptations of a single species could occur and may affect the NADPH-d distribution pattern in a brain subdivision. The minor differences in staining pattern of particular subdivisions apparently do not affect the general patterns of staining across species.

Metabolomic insights into system-wide coordination of vertebrate metamorphosis

Background

After completion of embryogenesis, many organisms experience an additional obligatory developmental transition to attain a substantially different juvenile or adult form. During anuran metamorphosis, the aquatic tadpole undergoes drastic morphological changes and remodelling of tissues and organs to become a froglet. Thyroid hormones are required to initiate the process, but the mechanism whereby the many requisite changes are coordinated between organs and tissues is poorly understood. Metabolites are often highly conserved biomolecules between species and are the closest reflection of phenotype. Due to the extensive distribution of blood throughout the organism, examination of the metabolites contained therein provides a system-wide overview of the coordinated changes experienced during metamorphosis. We performed an untargeted metabolomic analysis on serum samples from naturally-metamorphosing Rana catesbeiana from tadpoles to froglets using ultraperformance liquid chromatography coupled to a mass spectrometer. Total and aqueous metabolite extracts were obtained from each serum sample to select for nonpolar and polar metabolites, respectively, and selected metabolites were validated by running authentic compounds.

Results

The majority of the detected metabolites (74%) showed statistically significant abundance changes (p_adj < 0.001) between metamorphic stages. We observed extensive remodelling of five core metabolic pathways: arginine and purine/pyrimidine, cysteine/methionine, sphingolipid, and eicosanoid metabolism and the urea cycle, and found evidence for a major role for lipids during this postembryonic process. Metabolites traditionally linked to human disease states were found to have biological linkages to the system-wide changes occuring during the events leading up to overt morphological change.

Conclusions

To our knowledge, this is the first wide-scale metabolomic study of vertebrate metamorphosis identifying fundamental pathways involved in the coordination of this important developmental process and paves the way for metabolomic studies on other metamorphic systems including fish and insects.

Neuroplastic and neuropathological changes in the central nervous system of the Gray mussel Crenomytilus grayanus (Dunker) under environmental stress

We studied here neuron ultrastructure, synaptic plasticity and subcellular localization of NADPH-diaphorase (NADPH-d), a cytochemical marker for nitric oxide syntase, in the pedal ganglia of the Gray mussel Crenomytilus grayanus sampled from the polluted and reference sites in Amursky Bay (Sea of Japan) at lower and higher water temperature (in the beginning and the end of August, respectively). At lower temperature, neuroplastic changes in mussel ganglia prevailed: a sharp increase in the number of cytosomes in NADPH-d-positive neurons and a sharp decrease in the number of mitochondria in both NADPH-d-positive and NADPH-d-negative neurons. At higher temperature, neurodegenerative changes prevailed: disruption of a part of NADPH-d-negative axons and interneuronal contacts, formation of concentric lamellar structures in the neuropils, and accumulation of autophagosomes in NADPH-d negative neurons. The results suggest that the stress-induced production of nitric oxide in cytosomes of mussel neurons and plasticity of gap junctions have a neuroprotective effect.