Vagal Lobe Research Articles

Distribution of gamma-aminobutyric acid immunoreactivity in the brain of the Siberian sturgeon (Acipenser baeri): Comparison with other fishes.

Gamma-aminobutyric acid (GABA) is the main inhibitory neurotransmitter in the central nervous system (CNS) of vertebrates. Immunohistochemical techniques with specific antibodies against GABA or against its synthesizing enzyme, glutamic acid decarboxylase (GAD) allowed characterizing GABAergic neurons and fibers in the CNS. However, studies on the CNS distribution of GABAergic neurons and fibers of bony fishes are scant and were done in teleost species. With the aim of understanding the early evolution of this system in bony vertebrates, we analyzed the distribution of GABA-immunoreactive (-ir) and GAD-ir neurons and fibers in the CNS of a basal ray-finned fish, the Siberian sturgeon (Chondrostei, Acipenseriformes), using immunohistochemical techniques. Our results revealed the presence and distribution of GABA/GAD-ir cells in different regions of the CNS such as olfactory bulbs, pallium and subpallium, hypothalamus, thalamus, pretectum, optic tectum, tegmentum, cerebellum, central grey, octavolateralis area, vagal lobe, rhombencephalic reticular areas, and the spinal cord. Abundant GABAergic innervation was observed in most brain regions, and GABAergic fibers were very abundant in the hypothalamic floor along the hypothalamo-hypophyseal tract and neurohypophysis. In addition, GABA-ir cerebrospinal fluid-contacting cells were observed in the alar and basal hypothalamus, saccus vasculosus, and spinal cord central canal. The distribution of GABAergic systems in the sturgeon brain shows numerous similarities to that observed in lampreys, but also to those of teleosts and tetrapods.

Organization of the Catecholaminergic System in the Short-Lived Fish Nothobranchius furzeri.

The catecholaminergic system has received much attention based on its regulatory role in a wide range of brain functions and its relevance in aging and neurodegenerative diseases. In the present study, we analyzed the neuroanatomical distribution of catecholaminergic neurons based on tyrosine hydroxylase (TH) immunoreactivity in the brain of adult Nothobranchius furzeri. In the telencephalon, numerous TH+ neurons were observed in the olfactory bulbs and the ventral telencephalic area, arranged as strips extending through the rostrocaudal axis. We found the largest TH+ groups in the diencephalon at the preoptic region level, the ventral thalamus, the pretectal region, the posterior tuberculum, and the caudal hypothalamus. In the dorsal mesencephalic tegmentum, we identified a particular catecholaminergic group. The rostral rhombencephalon housed TH+ cells in the locus coeruleus and the medulla oblongata, distributing in a region dorsal to the inferior reticular formation, the vagal lobe, and the area postrema. Finally, scattered TH+ neurons were present in the ventral spinal cord and the retina. From a comparative perspective, the overall organization of catecholaminergic neurons is consistent with the general pattern reported for other teleosts. However, N. furzeri shows some particular features, including the presence of catecholaminergic cells in the midbrain. This work provides a detailed neuroanatomical map of the catecholaminergic system of N. furzeri, a powerful aging model, also contributing to the phylogenetic understanding of one of the most ancient neurochemical systems.

Evolutionary Modifications Are Moderate in the Astroglial System of Actinopterygii as Revealed by GFAP Immunohistochemistry.

The present paper is the first comparative study on the astroglia of several actinopterygian species at different phylogenetical positions, teleosts (16 species), and non-teleosts (3 species), based on the immunohistochemical staining of GFAP (glial fibrillary acidic protein), the characteristic cytoskeletal intermediary filament protein, and immunohistochemical marker of astroglia. The question was, how the astroglial architecture reflexes the high diversity of this largest vertebrate group. The actinopterygian telencephalon has a so-called ‘eversive’ development in contrast to the ‘evagination’ found in sarcopterygii (including tetrapods). Several brain parts either have no equivalents in tetrapod vertebrates (e.g., torus longitudinalis, lobus inferior, lobus nervi vagi), or have rather different shapes (e.g., the cerebellum). GFAP was visualized applying DAKO polyclonal anti-GFAP serum. The study was focused mainly on the telencephalon (eversion), tectum (visual orientation), and cerebellum (motor coordination) where the evolutionary changes were most expected, but the other areas were also investigated. The predominant astroglial elements were tanycytes (long, thin, fiber-like cells). In the teleost telencephala a ‘fan-shape’ re-arrangement of radial glia reflects the eversion. In bichir, starlet, and gar, in which the eversion is less pronounced, the ‘fan-shape’ re-arrangement did not form. In the tectum the radial glial processes were immunostained, but in Ostariophysi and Euteleostei it did not extend into their deep segments. In the cerebellum Bergmann-like glia was found in each group, including non-teleosts, except for Cyprinidae. The vagal lobe was uniquely enlarged and layered in Cyprininae, and had a corresponding layered astroglial system, which left almost free of GFAP the zones of sensory and motor neurons. In conclusion, despite the diversity and evolutionary alterations of Actinopterygii brains, the diversity of the astroglial architecture is moderate. In contrast to Chondrichthyes and Amniotes; in Actinopterygii true astrocytes (stellate-shaped extraependymal cells) did not appear during evolution, and the expansion of GFAP-free areas was limited.

Characterization of neural stem cells and proliferating cells in the brain of loach (Misgurnus anguillicaudatus)

Loach (Misgurnus anguillicaudatus) is an essential commercial fish in China. We aimed to give some notes on brain histology of loach fish and characterize the sites of stem cells in the brain. As well as, we showed the sites of proliferating cells with detection of their glial property. To this end, we histologically observed the structure of the brain via hematoxylin and eosin stain. We also used fluorescent in situ hybridization to evaluate the localization of Msi1, Bmi1, and Sox2. They are essential genes expressed in brain stem cells of loach. Proliferating cells were evaluated by PCNA immunofluorescence. As well as GFAP immunofluorescence was used for detection of the gial property of proliferating cells. Our results indicated that the neural stem cells were located in the granular cell layer of the cerebellum, vagal lobe, facial lobe, optic tectum, and beside the third ventricle because these sites exhibited expression of Sox2. There were several areas of the brain that contained proliferating cells, including the cerebrum, in the torus longitudinalis, and in between the optic tectum and cerebellum. In the cerebellum, the proliferating cells were present in the molecular cell layer, around the intracerebellar ventricle, in the lobus caudalis cerebella, in the eminentia granularis, and around the rhombencephalic ventricle. Proliferating cells were also observed in the three layers of the vagal lobe and throughout the facial lobe. These proliferating cells were all negative for GFAP. The present study provides valuable insight into neural stem cells in loach brain, and these findings can be used to guide future studies.

In situ localization of vasotocin receptor gene transcripts in the brain-pituitary-gonadal axis of the catfish Heteropneustes fossilis: a morpho-functional study.

In the catfish Heteropneustes fossilis, three vasotocin (VT) receptor subtype genes, v1a1, v1a2, and v2a, were cloned and characterized previously. In the present study, using RNA probes, we localized the distribution of the gene transcripts in the brain-pituitary-gonadal (BPG) axis. The V1a-type receptor, v1a1 and v1a2, genes showed similar and overlapping distribution in the brain. The gene paralogs are distributed in the radial glial cells (RGCs) of the telencephalic ventricle and around the third ventricle in the hypothalamus and thalamus, olfactory tract, nucleus preopticus, nucleus lateralis tuberis, nucleus recessus lateralis and posterioris, nucleus saccus vasculosi, thalamic nuclei, habenular nucleus, habenular commissure, basal part of pineal stalk, accessory pretectal nucleus, optic tectum, corpus and valvula of the cerebellum, and facial and vagal lobes. The V2a receptor gene (v2a) has restricted distribution and is largely confined to the anterior subependymal region of the telencephalon. The localization pattern shows that the V1a-type receptors are distributed in major sensorimotor processing centers and the neuroendocrine/reproductive centers of the brain. In the pituitary, the receptor genes were localized differentially in the three divisions with the V1a-type receptor genes strongly expressed in the rostral pars distalis compared to the v2a paralog. In the ovary, the V1a-type receptor genes were localized in the follicular layer while v2a was localized in the oocyte membrane. In the testis, v1a2 and v2a are densely distributed in the interstitial tissue and seminiferous epithelium but the v1a1 is lowly expressed. The results suggest that the VT receptor genes have an extensive but differential distribution in the BPG axis. Future experimental studies are required to correlate the cellular localizations with specific functions of VT in the BPG axis.

Gustatory and general visceral centers and their connections in the brain of adult zebrafish: a carbocyanine dye tract-tracing study.

The central connections of the gustatory/general visceral system of the adult zebrafish (Danio rerio) were examined by means of carbocyanine dye tracing. Main primary gustatory centers (facial and vagal lobes) received sensory projections from the facial and vagal nerves, respectively. The vagal nerve also projects to the commissural nucleus of Cajal, a general visceral sensory center. These primary centers mainly project on a prominent secondary gustatory and general visceral nucleus (SGN/V) located in the isthmic region. Secondary projections on the SGN/V were topographically organized, those of the facial lobe mainly ending medially to those of the vagal lobe, and those from the commissural nucleus ventrolaterally. Descending facial lobe projections to the medial funicular nucleus were also noted. Ascending fibers originating from the SGN/V mainly projected to the posterior thalamic nucleus and the lateral hypothalamus (lateral torus, lateral recess nucleus, hypothalamic inferior lobe diffuse nucleus) and an intermediate cell- and fiber-rich region termed here the tertiary gustatory nucleus proper, but not to a nucleus formerly considered as the zebrafish tertiary gustatory nucleus. The posterior thalamic nucleus, tertiary gustatory nucleus proper, and nucleus of the lateral recess gave rise to descending projections to the SGN/V and the vagal lobe. The connectivity between diencephalic gustatory centers and the telencephalon was also investigated. The present results showed that the gustatory connections of the adult zebrafish are rather similar to those reported in other cyprinids, excepting the tertiary gustatory nucleus. Similarities between the gustatory systems of zebrafish and other fishes are also discussed. J. Comp. Neurol. 525:333-362, 2017. © 2016 Wiley Periodicals, Inc.

Krüpple-like factors 7 and 6a mRNA expression in adult zebrafish central nervous system

Krüpple-like factors (KLFs) are transcription factors with zinc finger DNA binding domains known to play important roles in brain development and central nervous system (CNS) regeneration. There is little information on KLFs expression in adult vertebrate CNS. In this study, we used in situ hybridization to examine Klf7 mRNA (klf7) and Klf6a mRNA (klf6a) expression in adult zebrafish CNS. Both klfs exhibit wide and similar expression in the zebrafish CNS. Brain areas containing strongly labeled cells include the ventricular regions of the dorsomedial telencephalon, the ventromedial telencephalon, periventricular regions of the thalamus and hypothalamus, torus longitudinalis, stratum periventriculare of the optic tectum, granular regions of the cerebellar body and valvula, and superficial layers of the facial and vagal lobes. In the spinal cord, klf7- and klf6a-expressing cells are found in both the dorsal and ventral horns. Numerous sensory structures (e.g. auditory, lateral line, olfactory and visual) and several motor nuclei (e.g. oculomotor, trigeminal, and vagal motor nuclei) contain klf7- and/or klf6a-expressing cells. Our results may provide useful information for determining these Klfs in maintenance and/or function in adult CNS.

Brain Mapping of Ghrelin O-Acyltransferase in Goldfish (Carassius Auratus): Novel Roles for the Ghrelinergic System in Fish?

Ghrelin O-acyltransferase (GOAT) is the enzyme responsible for acylation of ghrelin, a gut-brain hormone with important roles in many physiological functions in vertebrates. Many aspects of GOAT remain to be elucidated, especially in fish, and particularly its anatomical distribution within the different brain areas has never been reported to date. The present study aimed to characterize the brain mapping of GOAT using RT-qPCR and immunohistochemistry in a teleost, the goldfish (Carassius auratus). Results show that goat transcripts are expressed in different brain areas of the goldfish, with the highest levels in the vagal lobe. Using immunohistochemistry, we also report the presence of GOAT immunoreactive cells in different encephalic areas, including the telencephalon, some hypothalamic nuclei, pineal gland, optic tectum and cerebellum, although they are especially abundant in the hindbrain. Particularly, an important signal is observed in the vagal lobe and some fiber tracts of the brainstem, such as the medial longitudinal fasciculus, Mauthneri fasciculus, secondary gustatory tract and spinothalamic tract. Most of the forebrain areas where GOAT is detected, particularly the hypothalamic nuclei, also express the ghs-r1a ghrelin receptor and other appetite-regulating hormones (e.g., orexin and NPY), supporting the role of ghrelin as a modulator of food intake and energy balance in fish. Present results are the first report on the presence of GOAT in the brain using imaging techniques. The high presence of GOAT in the hindbrain is a novelty, and point to possible new functions for the ghrelinergic system in fish. Anat Rec, 299:748-758, 2016. © 2016 Wiley Periodicals, Inc.

Periprandial changes and effects of short- and long-term fasting on ghrelin, GOAT, and ghrelin receptors in goldfish (Carassius auratus).

The periprandial profile and effects of short- (7days) and long-term (30days) fasting on the ghrelinergic system were studied in goldfish (Carassius auratus). Plasma levels of acyl-ghrelin, desacyl-ghrelin, and ghrelin O-acyl transferase (GOAT) were analyzed by enzymoimmunoassays, and expression of preproghrelin, goat and growth hormone secretagogue receptors (ghs-r) was quantified by real-time PCR. Circulating levels of acyl-ghrelin and GOAT rise preprandially, supporting the role of acyl-ghrelin as a meal initiator in this teleost. Consistently, preproghrelin and ghs-r1a1 expression increases 1h before feeding time in intestinal bulb, suggesting that this receptor subtype might be involved in the preprandial action of ghrelin in this tissue. Significant postfeeding variations are detected for preproghrelin in telencephalon, goat in telencephalon and hypothalamus, ghs-r1a1 in vagal lobe, ghs-r1a2 and ghs-r2a1 in hypothalamus and ghs-r2a2 in telencephalon and vagal lobe, especially in unfed fish. Short- and long-term fasting significantly increase preproghrelin expression in telencephalon and gut. Goat expression is upregulated by short-term fasting in telencephalon and hypothalamus, and by both short- and long-term fasting in gut. Expression of ghs-r increases by fasting in telencephalon, while an upregulation of type 2, but not type 1, receptors is observed in vagal lobe. In intestinal bulb, ghs-r1a2 transcripts increase after both short- and long-term fasting. These results show a high dependence of the ghrelinergic system on feeding and nutritional status in fish, and demonstrate for the first time a differential implication of the various components of this system suggesting different roles for the four ghrelinergic receptor subtypes.

Two cholecystokinin receptor subtypes are identified in goldfish, being the CCKAR involved in the regulation of intestinal motility

Cholecystokinin (CCK) plays a key role in the digestive physiology of vertebrates. However, very little is known about the role of CCK on intestinal functions in fish. The present study identifies two CCK receptor subtypes in a stomachless teleost, the goldfish (Carassius auratus), and investigates by using an in vitro system their involvement mediating the effects of the sulfated octapeptide of CCK (CCK-8S) on the motility of isolated proximal intestine. Partial-length mRNAs encoding two CCK receptor isoforms (CCKAR and CCKBR.I) were sequenced and the structural analysis showed that both receptors belong to the G-protein coupled receptor superfamily. Both goldfish CCK receptor sequences were more closely related to zebrafish sequences, sharing the lowest similarities with cavefish and tilapia. The highest expression of goldfish CCKAR was observed along the whole intestine whereas the CCKBR gen was predominantly expressed in the hypothalamus, vagal lobe and posterior intestine. Application of CCK-8S to the organ bath evoked a concentration-dependent contractile response in intestine strips. The contractions were not blocked by either tetrodotoxin or atropine, suggesting that CCK-8S acts on the gut smooth muscle directly. Preincubations of intestine strips with devazepide and L365,260 (CCKAR and CCKBR receptor selective antagonists) showed that the CCK-8S-induced contraction could be partially mediated by the CCKAR receptor subtype, which is also the most abundant CCK receptor found in gastrointestinal tissues. In conclusion, two CCK receptors with a differential distribution pattern has been identified in goldfish, and the CCKAR subtype is mainly involved in the regulation of intestinal motility by the CCK-8S.

Increase in telencephalic dopamine and cerebellar norepinephrine contents by hydrostatic pressure in goldfish: the possible involvement in hydrostatic pressure-related locomotion

Fish are faced with a wide range of hydrostatic pressure (HP) in their natural habitats. Additionally, freshwater fish are occasionally exposed to rapid changes in HP due to heavy rainfall, flood and/or dam release. Accordingly, variations in HP are one of the most important environmental cues for fish. However, little information is available on how HP information is perceived and transmitted in the central nervous system of fish. The present study examined the effect of HP (water depth of 1.3m) on the quantities of monoamines and their metabolites in the telencephalon, optic tectum, diencephalon, cerebellum (including partial mesencephalon) and vagal lobe (including medulla oblongata) of the goldfish, Carassius auratus, using high-performance liquid chromatography. HP affected monoamine and metabolite contents in restricted brain regions, including the telencephalon, cerebellum and vagal lobe. In particular, HP significantly increased the levels of dopamine (DA) in the telencephalon at 15min and that of norepinephrine (NE) in the cerebellum at 30min. In addition, HP also significantly increased locomotor activity at 15 and 30min after HP treatment. It is possible that HP indirectly induces locomotion in goldfish via telencephalic DA and cerebellar NE neuronal activity.

Differential expression of protocadherin-19, protocadherin-17, and cadherin-6 in adult zebrafish brain.

Cell adhesion molecule cadherins play important roles in both development and maintenance of adult structures. Most studies on cadherin expression have been carried out in developing organisms, but information on cadherin distribution in adult vertebrate brains is limited. In this study we used in situ hybridization to examine mRNA expression of three cadherins, protocadherin-19, protocadherin-17, and cadherin-6 in adult zebrafish brain. Each cadherin exhibits a distinct expression pattern in the fish brain, with protocadherin-19 and protocadherin-17 showing much wider and stronger expression than that of cadherin-6. Both protocadherin-19 and protocadherin-17-expressing cells occur throughout the brain, with strong expression in the ventromedial telencephalon, periventricular regions of the thalamus and anterior hypothalamus, stratum periventriculare of the optic tectum, dorsal tegmental nucleus, granular regions of the cerebellar body and valvula, and superficial layers of the facial and vagal lobes. Numerous sensory structures (e.g., auditory, gustatory, lateral line, olfactory, and visual nuclei) and motor nuclei (e.g., oculomotor, trochlear, trigeminal motor, abducens, and vagal motor nuclei) contain protocadherin-19 and/or protocadherin-17-expressing cell. Expression of these two protocadherins is similar in the ventromedial telencephalon, thalamus, hypothalamus, facial, and vagal lobes, but substantially different in the dorsolateral telencephalon, intermediate layers of the optic tectum, and cerebellar valvula. In contrast to the two protocadherins, cadherin-6 expression is much weaker and limited in the adult fish brain.

Origin, development, function, and evolution of cypriniform trophic novelties

Cypriniform fishes are characterized by a number of evolutionary trophic novelties. These feeding novelties have allowed cypriniforms to take full advantage of a number of unique trophic niches. One such feeding innovation, the palatal organ, is a complex muscular structure located on the pharyngeal roof of cypriniform fishes. The palatal organ is a dorsal mass of complexly arranged muscle fibers within the buccopharyngeal cavity innervated by the vagal lobe and covered by a taste bud coated epithelium. Here we use developmental data from zebrafish, functional data from carp and goldfish, and histological data and modeling approaches from assorted cypriniform species to address how the palatal organ developed and explain some of its functional evolution. Using zebrafish we first describe the origin and ontogenetic development of the palatal organ. Comparative data on histological structure and myosin composition of the palatal organ across a wide phylogenetic sampling of cypriniforms is then used to determine the variation in structure and potential function of the palatal organ across Cypriniformes. The general assumption has been that the function of the palatal organ is conserved across cypriniforms, and requires the careful sensory control made possible by a hypertrophied vagal lobe to function properly. Few have considered the possibility that the palatal organ may have become adapted for different functions during the course of cypriniform evolution. Its possible role in other feeding modes has been largely overlooked as it has been presumed that the palatal organ's only function is in sorting during benthic feeding events. Using electromyography and high‐speed video to examine palatal organ activity in the common carp and goldfish, muscle activation patterns demonstrate that the palatal organ is likely employed just prior to suction generation, during suction feeding behaviors, during prey processing events, and may even play a role in respiration during stressful conditions. Furthermore, the palatal organ shows behavioral modulation when different food types and positions are used. These data suggest that the palatal organ is a multi‐functional structure with a much wider range of functional repertoires than previously shown. While sorting during benthic feeding may have been the primitive function of the palatal organ, it has likely been secondarily adapted for increasing dietary breadth during the course of cypriniform evolution. This muscular pad has become secondarily modified for different forms of feeding but may even play a more generalized role in suction feeding and prey processing within cypriniforms.

Connections of the commissural nucleus of Cajal in the goldfish, with special reference to the topographic organization of ascending visceral sensory pathways.

The primary general visceral nucleus of teleosts is called the commissural nucleus of Cajal (NCC). The NCC of goldfish has been divided into the medial (NCCm) and lateral (NCCl) subnuclei that receive inputs from subdiaphragmatic gastrointestinal tract and the posterior pharynx, respectively. Fiber connections of the NCC were examined by tract-tracing methods in the goldfish Carassius auratus. Tracer injections into the NCC suggested that the NCC projects directly not only to the secondary visceral sensory region in the rhombencephalic isthmus and other brain stem centers, but also to the forebrain, similar to the situations in mammals, birds, and the Nile tilapia. Although fiber connections of the NCCm and NCCl were basically similar, the NCCm was the more important source of ascending general visceral fibers to the forebrain. Topographic organization was recognized regarding projections to the isthmic secondary visceral sensory zone; input from the NCCm is represented in the secondary general visceral sensory nucleus, while input from the NCCl in the lateral edge of the secondary gustatory nucleus. Moreover, specific injections into different regions of the vagal lobe revealed that the dorsomedio-ventrolateral axis of the lobe is represented in the lateromedial axis of the secondary gustatory nucleus. These observations suggest fine topographic organization of ascending visceral sensory pathways to the isthmic secondary centers. It should also be noted that the reception of primary afferents from the posterior pharynx and projections to the secondary gustatory nucleus suggest that the NCCl may be regarded as a gustatory rather than a general visceral sensory structure.

Sensory-specific modulation of adult neurogenesis in sensory structures is associated with the type of stem cell present in the neurogenic niche of the zebrafish brain.

Teleost fishes retain populations of adult stem/progenitor cells within multiple primary sensory processing structures of the mature brain. Though it has commonly been thought that their ability to give rise to adult-born neurons is mainly associated with continuous growth throughout life, whether a relationship exists between the processing function of these structures and the addition of new neurons remains unexplored. We investigated the ultrastructural organisation and modality-specific neurogenic plasticity of niches located in chemosensory (olfactory bulb, vagal lobe) and visual processing (periventricular grey zone, torus longitudinalis) structures of the adult zebrafish (Danio rerio) brain. Transmission electron microscopy showed that the cytoarchitecture of sensory niches includes many of the same cellular morphologies described in forebrain niches. We demonstrate that cells with a radial-glial phenotype are present in chemosensory niches, while the niche of the caudal tectum contains putative neuroepithelial-like cells instead. This was supported by immunohistochemical evidence showing an absence of glial markers, including glial fibrillary acidic protein, glutamine synthetase, and S100β in the tectum. By exposing animals to sensory assays we further illustrate that stem/progenitor cells and their neuronal progeny within sensory structures respond to modality-specific stimulation at distinct stages in the process of adult neurogenesis - chemosensory niches at the level of neuronal survival and visual niches in the size of the stem/progenitor population. Our data suggest that the adult brain has the capacity for sensory-specific modulation of adult neurogenesis and that this property may be associated with the type of stem cell present in the niche.

The antidepressant tranylcypromine alters cellular proliferation and migration in the adult goldfish brain.

The goldfish (Carassius auratus) is a widely studied vertebrate model organism for studying cell proliferation in the adult brain, and provide the experimental advantage of growing their body and brain throughout their ∼30-year life time. Cell proliferation occurs in the teleost brain in widespread proliferation zones. Increased cell proliferation in the brain has been linked to the actions of certain antidepressants, including tranylcypromine (TCP), which is used in the treatment of depression. We hypothesized that proliferation zones in the adult goldfish brain can be used to determine the antidepressant effects on cellular proliferation. Here, we report that bromodeoxyuridine (BrdU) labeling over a 24-hr period can be used to rapidly identify the proliferation zones throughout the goldfish brain, including the telencephalon, diencephalon, optic tectal lobes, cerebellum, and facial and vagal lobes. In the first 24 hr of BrdU administration, TCP caused an approximate and significant doubling of labeled cells in the combined brain regions examined, as detected by BrdU immunohistochemistry. TCP caused the greatest increase in cell proliferation in the cerebellum. The normal migratory paths of the proliferating cells within the cerebellum were not affected by TCP treatment. These results indicate that the goldfish provide significant advantages as a vertebrate model for rapidly investigating the effects of antidepressant drugs on cellular proliferation and migration in the normal and injured brain.

Estudio Morfológico y Morfométrico del Cerebro del Bagre Tigrito Pimelodus Pictus (Pimelodidae) Steindachner (1876)

<p>En el presente trabajo se realizó una descripción de la anatomía externa del cerebro de <em>Pimelodus pictus, </em>identificando las principales estructuras que lo conforman. Posteriormente, se realizó un análisis morfométrico de algunas regiones del cerebro (bulbos olfativos, hemisferios telencefálicos, lóbulos ópticos, corpus cerebelar, válvula cerebelar, lóbulos vagales, lóbulos faciales y lóbulos inferiores) para determinar diferencias en tamaño, realizando mediciones de área y longitud. De acuerdo a los resultados obtenidos, el cerebro de <em>P. pictus </em>presenta una morfología acorde con el patrón de organización general descrito para teleósteos pertenecientes al orden Siluriformes, siendo la válvula cerebelar la estructura más grande del cerebro. De acuerdo a los resultados morfométricos obtenidos esta especie podría clasificarse como generalista, debido a que parece utilizar primordialmente tres sistemas sensoriales para explorar su hábitat: el tacto, la vista y el gusto. El tacto, debido a la válvula cereberal de gran tamaño, la cual está relacionada directamente con la presencia de la línea lateral, que es un órgano sensorial cutáneo. La visión, teniendo en cuenta que los lóbulos ópticos de <em>P. pictus </em>presentaron un gran tamaño lo que puede deberse a una especialización visual de esta especie de acuerdo con el ambiente en el que se desenvuelve. Y por ultimo, el gusto, porque los lóbulos vagales y faciales de <em>P. pictus </em>en comparación con otras especies de peces son grandes, esto por la presencia de barbillones, que son estructuras especializadas en integrar señales cutáneas y gustativas.</p>

Glycine‐immunoreactive neurons in the brain of a shark (Scyliorhinus canicula L.)

The glycinergic cell populations in the brain of the lesser spotted dogfish were studied by a glycine immunofluorescence method. Numerous glycine-immunoreactive (Gly-ir) neurons were observed in different brain nuclei. In the telencephalon, Gly-ir cells were observed in the olfactory bulb, telencephalic hemispheres, and preoptic region. In the hypothalamus, cerebrospinal fluid-contacting Gly-ir neurons were observed in the lateral and posterior recess nuclei. Coronet cells of the saccus vasculosus were Gly-ir. In the diencephalon, Gly-ir neurons were observed in the prethalamus and pretectum. In the midbrain, both the optic tectum and lateral mesencephalic nucleus contained numerous Gly-ir neurons. In the cerebellum, many Golgi cells were Gly-ir. In the rhombencephalon, Gly-ir cells were observed in the medial and ventral octavolateral nuclei, vagal lobe, visceromotor nuclei, and reticular formation, including the inferior raphe nucleus. In the spinal cord, some neurons of the marginal nucleus and some cells of the dorsal and ventral horns were Gly-ir. Comparison of dogfish Gly-ir cell populations with those reported for the sea lamprey, Siberian sturgeon, and zebrafish revealed some shared features but also notable differences. For example, Gly-ir cells were observed in the dogfish cerebellum, unlike the case in the Siberian sturgeon and zebrafish, whereas the absence of Gly-ir neurons in the isthmus is shared by all these species, except for lampreys. Gly-ir populations in the dogfish hypothalamus and telencephalon are notable in comparison with those of the other jawed vertebrates investigated to date. Together, these results reveal a complex and divergent evolution of glycinergic systems in the major groups of fishes.

Development of tyrosine hydroxylase‐immunoreactive cell populations and fiber pathways in the brain of the dogfish Scyliorhinus canicula: New perspectives on the evolution of the vertebrate catecholaminergic system

Developmental studies of the central catecholaminergic (CA) system are essential for understanding its evolution. To obtain knowledge about the CA system in chondrichthyans, an ancient gnathostome group, we used immunohistochemical techniques for detecting tyrosine hydroxylase (TH), the initial rate-limiting enzyme of the CA synthesis, to study: 1) the neuromery of developing TH-immunoreactive (ir) neuronal populations, 2) the development of TH-ir innervation, and 3) the organization of TH-ir cells and fibers in the brain of postembryonic stages of the shark Scyliorhinus canicula. The first TH-ir cells appeared in the hypothalamus and rostral diencephalon (suprachiasmatic, posterior recess and posterior tubercle nuclei at embryonic stage 26, and dorsomedial hypothalamus at stage 28); then in more caudal basal regions of the diencephalon and rostral mesencephalon (substantia nigra/ventral tegmental area); and later on in the anterior (locus coeruleus/nucleus subcoeruleus) and posterior (vagal lobe and reticular formation) rhombencephalon. The appearance of TH-ir cells in the telencephalon (pallium) was rather late (stage [S]31) with respect to the other TH-ir prosencephalic populations. The first TH-ir fibers arose from cells of the posterior tubercle (S30) and formed recognizable ascending (toward dorsal and rostral territories) and descending pathways at S31. When the second half of embryonic development started (S32), TH-ir fibers innervated most brain areas, and nearly all TH-ir cell groups of the postembryonic brain were already established. This study provides key information about the evolution of the developmental patterns of central CA systems in fishes and thus may help in understanding how the vertebrate CA systems have evolved.

Correlation between medulla oblongata and feeding habits in two teleosts

A comparative study of hindbrain was analysed on medulla oblongata especially facial, vagal and somatic sensory lobe in two teleost namely Aplocheilus lieneatus, a carnivorous surface feeder and Nemachilus rupecola a bottom feeder. The former feed largely by sight and correspondingly large eyes and upwardly directed mouth, facial and vagal lobes are poorly developed; Whereas, in N. rupicola, being a bottom feeder and downwardly directed mouth and poorly developed eyes. Surface feeders are constantly exposed to external sound at the surface of water, their auditory centres in the brain especially the central acoustic area is well developed in A. lieneatus and this area is poorly developed in N. rupicola. Keywords: Fish, Feeding habit, Medulla oblongata, Facial lobe, Vagal lobe, Central acoustic area.