Fátima Adrio

Distribution of choline acetyltransferase (ChAT) immunoreactivity in the central nervous system of a chondrostean, the siberian sturgeon (Acipenser baeri)

All studies to date of cholinergic systems of bony fishes have been done in teleosts. To gain further insight into the evolution of the cholinergic systems of bony fishes, we have studied the brain of a chondrostean fish, the Siberian sturgeon (Acipenser baeri, Brandt), by using an antibody against choline acetyltransferase (ChAT). This study showed the presence of ChAT‐immunoreactive (ChAT‐ir) neurons in the preoptic region (parvocellular and magnocellular preoptic nuclei and suprachiasmatic nucleus), the periventricular and tuberal hypothalamus, the saccus vasculosus, the dorsal thalamus, and the habenula. The mesencephalic tegmentum contained ChAT‐ir cells in the torus semicircularis and torus lateralis. The isthmus contained several cholinergic populations: the nucleus isthmi, the lateral nucleus of the valvula, the secondary visceral nucleus, and the dorsal tegmental nucleus. The motor neurons of the cranial nerves and the spinal motor column were strongly immunoreactive. The medial (sensory) trigeminal nucleus also contained a ChAT‐ir neuronal population. The distribution of ChAT‐ir neurons in the sturgeon brain showed some notable differences with that observed in teleosts, such as the absence of cholinergic cells in the telencephalon and the optic tectum. Several brain regions were richly innervated by ChAT‐ir fibers, particularly the telencephalon , optic tectum, thalamus, posterior tubercle, and interpeduncular nucleus. The hypothalamo‐hypophyseal tract, the tract of the saccus vasculosus, the fasciculus retroflexus, and an isthmo‐mesencephalo‐thalamic tract were the most conspicuous cholinergic bundles. Comparative analysis of these results suggests that teleosts have conserved most traits of the cholinergic system of the sturgeon, having acquired new cholinergic populations during evolution. J. Comp. Neurol. 426:602–621, 2000.

Synthesis of estrogens in progenitor cells of adult fish brain : Evolutive novelty or exaggeration of a more general mechanism implicating estrogens in neurogenesis?

In contrast to other vertebrates, in which the adult brain shows limited adult neurogenesis, teleost fishes exhibit an unparalleled capacity to generate new neurons as adults, suggesting that their brains present a highly permissive environment for the maintenance and proliferation of adult progenitors. Here, we examine the hypothesis that one of the factors permitting establishment of this favourable environment is estradiol. Indeed, recent data showed that radial glial cells strongly expressed one of two aromatase duplicated genes. Aromatase is the estrogen-synthesizing enzyme and this observation is of great interest, given that radial glial cells are progenitor cells capable of generating new neurons. Given the well-documented roles of estrogens on cell fate, and notably on cell proliferation, these data suggest that estradiol could be involved in maintaining and/or activating these progenitors. Examination of recent data in birds and mammals suggests that the situation in fish could well be an exaggeration of a more general mechanism implicating estrogens in neurogenesis. Indeed, there is accumulating evidence that estrogens are involved in embryonic, adult or reparative neurogenesis in other vertebrates, notably in mammals.

New insights on Saccus vasculosus evolution: a developmental and immunohistochemical study in elasmobranchs.

The saccus vasculosus (SV) is a circumventricular organ of the hypothalamus of many jawed fishes whose functions have not yet been clarified. It is a vascularized neuroepithelium that consists of coronet cells, cerebrospinal fluid-contacting (CSF-c) neurons and supporting cells. To assess the organization, development and evolution of the SV, the expression of glial fibrillary acidic protein (GFAP) and the neuronal markers γ-aminobutyric acid (GABA), glutamic acid decarboxylase (GAD; the GABA synthesizing enzyme), neuropeptide Y (NPY), neurophysin II (NPH), tyrosine hydroxylase (TH; the rate-limiting catecholamine-synthesizing enzyme) and serotonin (5-HT), were investigated by immunohistochemistry in developing and adult sharks. Coronet cells showed GFAP immunoreactivity from embryos at stage 31 to adults, indicating a glial nature. GABAergic CSF-c neurons were evidenced just when the primordium of the SV becomes detectable (at stage 29). Double immunolabeling revealed colocalization of NPY and GAD in these cells. Some CSF-c cells showed TH immunoreactivity in postembryonic stages. Saccofugal GABAergic fibers formed a defined SV tract from the stage 30 and scattered neurosecretory (NPH-immunoreactive) and monoaminergic (5-HT- and TH-immunoreactive) saccopetal fibers were first detected at stages 31 and 32, respectively. The early differentiation of GABAergic neurons and the presence of a conspicuous GABAergic saccofugal system are shared by elasmobranch and teleosts (trout), suggesting that GABA plays a key function in the SV circuitry. Monoaminergic structures have not been reported in the SV of bony fishes, and were probably acquired secondarily in sharks. The existence of saccopetal monoaminergic and neurosecretory fibers reveals reciprocal connections between the SV and hypothalamic structures which have not been previously detected in teleosts.

Distribution of serotonin (5HT)‐immunoreactive structures in the central nervous system of two chondrostean species (Acipenser baeri and Huso huso)

The distribution of serotonin‐immunoreactive (5HT‐ir) elements was studied in the brain and rostral spinal cord of two chondrosteans, Acipenser baeri and Huso huso, by using an antibody against serotonin. The distribution of these elements was similar in both sturgeon species. In the telencephalon, 5HT‐ir cells were found in the olfactory bulb and in the medioventral wall of the telencephalic ventricle, rostral to the anterior commissure, the latter being cerebrospinal fluid‐contacting (CSF‐C) neurons. The diencephalon contained the highest number of 5HT‐ir cell bodies, most of them of CSF‐C type, located in the preoptic recess organ, paraventricular organ, posterior recess nucleus, and in the ventromedial thalamus. 5HT‐ir non–CSF‐C neurons appeared in the dorsal thalamic nucleus. In the brainstem, 5HT‐ir neurons were located in four raphe nuclei (dorsal, superior, medial and inferior raphe nuclei) and four lateral reticular nuclei. The dorsal raphe nucleus contained 5HT‐ir CSF‐C cells, a type of serotoninergic cell that has not been described before in raphe nuclei of fishes or of other vertebrates. CSF‐C and non–CSF‐C 5HT‐ir cells were observed in the spinal cord. 5HT‐ir fibers were also widely distributed in the central nervous system of both sturgeon species. Comparison of these results with the distribution of serotoninergic systems in lampreys and other vertebrates suggests that widespread distribution of 5HT‐ir cells is a feature of early vertebrate lines. J. Comp. Neurol. 407:333–348, 1999.

DISTRIBUTION OF GABA IMMUNOREACTIVITY IN THE CENTRAL AND PERIPHERAL NERVOUS SYSTEM OF AMPHIOXUS (BRANCHIOSTOMA LANCEOLATUM PALLAS)

On the basis of labeling with an anti‐γ‐aminobutyric acid (GABA) antibody, we report for the first time the presence and distribution of GABA‐immunoreactive cells in the central and peripheral nervous system of amphioxus. In the nerve cord, there is a large dorsorostral group of cerebrospinal‐fluid‐contacting (CSFc) cells at the caudal end of the brain vesicle that gives rise to a large ventral commissure and neuropilar region. In the middle and caudal region of the brain, numerous commissural and CSFc neurons are situated below the region of large dorsal cells. In the spinal cord, several types of GABA‐immunoreactive neurons of different size, appearance, and distribution were observed. In the dorsalmost region, very small commissural cells are scattered regularly along the cord. More ventrally in the cord, GABAergic neurons, both of commissural and CSFc cell types, form segmental groups, but scattered cells are observed throughout. These cells give rise to dense longitudinal fascicles of GABAergic fibers and to scattered commissural fibers. The caudal ampulla lacks GABAergic cells and fibers. Some of the fibers of the most rostral and caudal peripheral (sensory) nerves, as well as some sensory cells of the rostral and caudal epidermis, are GABA immunoreactive. The significance of these results for the understanding of the evolution of GABAergic systems of vertebrates is discussed. J. Comp. Neurol. 401:293–307, 1998.

Aromatase, estrogen receptors and brain development in fish and amphibians

Estrogens affect brain development of vertebrates, not only by impacting activity and morphology of existing circuits, but also by modulating embryonic and adult neurogenesis. The issue is complex as estrogens can not only originate from peripheral tissues, but also be locally produced within the brain itself due to local aromatization of androgens. In this respect, teleost fishes are quite unique because aromatase is expressed exclusively in radial glial cells, which represent pluripotent cells in the brain of all vertebrates. Expression of aromatase in the brain of fish is also strongly stimulated by estrogens and some androgens. This creates a very intriguing positive auto-regulatory loop leading to dramatic aromatase expression in sexually mature fish with elevated levels of circulating steroids. Looking at the effects of estrogens or anti-estrogens in the brain of adult zebrafish showed that estrogens inhibit rather than stimulate cell proliferation and newborn cell migration. The functional meaning of these observations is still unclear, but these data suggest that the brain of fish is experiencing constant remodeling under the influence of circulating steroids and brain-derived neurosteroids, possibly permitting a diversification of sexual strategies, notably hermaphroditism. Recent data in frogs indicate that aromatase expression is limited to neurons and do not concern radial glial cells. Thus, until now, there is no other example of vertebrates in which radial progenitors express aromatase. This raises the question of when and why these new features were gained and what are their adaptive benefits. This article is part of a Special Issue entitled: Nuclear receptors in animal development.

Distribution of tyrosine hydroxylase (TH) and dopamine β-hydroxylase (DBH) immunoreactivity in the central nervous system of two chondrostean fishes (Acipenser baeri and Huso huso)

To obtain a better understanding of the evolution of the brain catecholaminergic systems of fishes, we have examined the distribution of catecholamine‐synthesizing enzymes in two species of sturgeon (Acipenser baeri and Huso huso) using antibodies against tyrosine hydroxylase (TH) and dopamine‐β ‐hydroxylase (DBH; only analyzed in Acipenser). Both sturgeons showed TH‐immunoreactive (THir) neurons widely distributed in most regions of the brain, the highest number of THir cells being located in the forebrain (olfactory bulb, preoptic area, and posterior tuberculum). THir cells were also seen in other forebrain areas (retrobulbar area, dorsal and ventral telencephalic areas, hypothalamus, ventral thalamus, pretectal area) and in the brainstem (locus coeruleus, viscerosensory area, caudal reticular formation, and area postrema). Immunoreactive fibers and varicosities showed a wide distribution, being particularly abundant in the diencephalon and mesencephalon. DBH‐immunoreactive (DBHir) cells were observed in the anterior tuberal nucleus, where these cells were TH‐negative, and in the locus coeruleus and the caudal rhombencephalon (vagal reticular formation), where the DBHir cells were also THir. DBHir fibers were scarce in the telencephalon and very abundant in the diencephalon, mesencephalon, and rhombencephalon. The comparative analysis of the catecholaminergic systems of chondrosteans and those observed in other groups of fishes and tetrapods indicate a similar organization of many nuclei, as well as characteristics that are probably primitive, such as the presence of a large number of forebrain catecholaminergic groups. J. Comp. Neurol. 448:280–297, 2002.

THE NEURONAL SYSTEM OF THE SACCUS VASCULOSUS OF TROUT (SALMO TRUTTA FARIO AND ONCORHYNCHUS MYKISS) : AN IMMUNOCYTOCHEMICAL AND NERVE TRACING STUDY

Abstract.The neuronal system of the saccus vasculosus of two species of trout was studied with immunocytochemical methods and carboindocyanine-dye (DiI) tract-tracing. The cerebrospinal-fluid-contacting neurons of the saccus were immunoreactive for gamma-aminobutyric acid (GABA), glutamic acid decarboxylase (GAD), and neuropeptide Y (NPY). Immunostaining of alternate sections of the saccus vasculosus of fry with anti-GAD and anti-NPY indicated that these substances were colocalized. The tractus sacci vasculosi and the neuropil of the nucleus sacci vasculosi were also immunoreactive to these substances. The GABA, GAD, and neuropeptide Y immunoreactivity of the saccus vasculosus system appeared early in trout ontogeny. After applying DiI to various levels of the tractus sacci vasculosi of adult trout, we observed massive bilateral saccular projections to the nucleus sacci vasculosi and could follow the course of the sacco-thalamic tract. This tract extended in the subependymal region of the thalamus rostral to the nucleus sacci vasculosi and split into two small tracts that reached the subhabenular-preoptic region. Sacco-thalamic fibers formed extensive periependymal plexuses along their trajectory. Interestingly, no clear evidence of the existence of a saccopetal system was obtained. On the basis of these results, we postulate that the saccus vasculosus system modulates the function of centers of the posterior tubercle and periventricular thalamus.

Organization of cholinergic systems in the brain of different fish groups: a comparative analysis

Using choline acetyltransferase immunocytochemistry, we compared the cholinergic systems of the brains of four groups of fishes (lampreys, elasmobranchs, chondrosteans, and teleosts). Cholinergic nuclei were classified in four groups according to their distribution in vertebrates. The cranial motor nuclei and the habenulo-interpeduncular system were cholinergic in all vertebrates. The cholinergic nuclei of the isthmus of fishes showed many similarities with those of tetrapods. The magnocellular preoptic neurosecretory cells were cholinergic in most fishes, whereas in neurosecretory nuclei of tetrapods, cholinergic cells were only observed adjacent to the magnocellular cells. In the subpallium, cholinergic cells were observed in all fishes, with the exception of elasmobranchs, which suggests that they might be secondarily lost. In the pallium of fishes, cholinergic neurons were only observed in elasmobranchs. Because pallial cholinergic cells were only observed in lizard and mammals, they could have appeared several times during evolution. The same is suggested for the presence of cholinergic cells in the optic tectum of only a few vertebrate groups, including teleosts. This preliminary analysis enlarges our knowledge of the cholinergic systems of fishes, although more species and groups need to be studied to provide a more complete scenario of their evolution.

Distribution of glycinergic neurons in the brain of glycine transporter-2 transgenic Tg(glyt2:Gfp) adult zebrafish: Relationship to brain–spinal descending systems

We used a Tg(glyt2:gfp) transgenic zebrafish expressing the green fluorescent protein (GFP) under control of the glycine transporter 2 (GLYT2) regulatory sequences to study for the first time the glycinergic neurons in the brain of an adult teleost. We also performed in situ hybridization using a GLYT2 probe and glycine immunohistochemistry. This study was combined with biocytin tract tracing from the spinal cord to reveal descending glycinergic pathways. A few groups of GFP+/GLYT2− cells were observed in the midbrain and forebrain, including numerous pinealocytes. Conversely, a small nucleus of the midbrain tegmentum was GLYT2+ but GFP−. Most of the GFP+ and GLYT2+ neurons were observed in the rhombencephalon and spinal cord, and a portion of these cells showed double GLYT2/GFP labeling. In the hindbrain, GFP/GLYT2+ populations were observed in the medial octavolateral nucleus; the secondary, magnocellular, and descending octaval nuclei; the viscerosensory lobes; and reticular populations distributed from trigeminal to vagal levels. No glycinergic cells were observed in the cerebellum. Tract tracing revealed three conspicuous pairs of GFP/GLYT2+ reticular neurons projecting to the spinal cord. In the spinal cord, GFP/GLYT2+ cells were observed in the dorsal and ventral horns. GFP+ fibers were observed from the olfactory bulbs to the spinal cord, although their density varied among regions. The Mauthner neurons received very rich GFP+ innervation, mainly around the axon cap. Comparison of the zebrafish glycinergic system with the glycinergic systems of other adult vertebrates reveals shared patterns but also divergent traits in the evolution of this system. J. Comp. Neurol. 521:389–425, 2013.