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PubMed1999

Visual thalamotelencephalic pathways in the sturgeon Acipenser, a non-teleost actinopterygian fish.

Terrestrial vertebrates (amphibians, reptiles, birds, and mammals) possess two visual systems, the geniculate and extrageniculate pathways to the telencephalon. In cartilaginous fishes (e.g. sharks) both retinal and tectal neurons project to neurons in the thalamus, which themselves project to a single area in the telencephalon. The condition in ray-finned fishes (Actinopterygii) is ambiguous. In many teleosts there is a well developed extrageniculate pathway but no obvious geniculate system. This study reports on the thalamotelencephalic projections of a sturgeon, a non-teleost ray-finned fish. Several tract tracing methods (e.g., HRP, WGA-HRP, biocytin, BDA, DiI) were employed in conjunction with normal techniques for identifying neural structures (e.g., Nissl, Golgi). After injections of tracer into retinal and tectal recipient areas of the thalamus, labeled terminals were observed in the ventrolateral region of the caudal telencephalon, an area referred to as the thalamic projection area. After injections of tracer into the telencephalon, populations of retrogradely filled neurons were located in both the dorsal and ventral thalamus. These data demonstrate that thalamic neurons in both retinal and tectal pathways project directly to the telencephalon. These results support the view that two visual pathways are a primitive feature of vertebrate brain organization. These results are also consistent with the hypothesis that the ancestor of Acipenser and Teleostei (Actinopteri) acquired a novel visual pathway to the telencephalon through the ventral portion of the thalamus.

Animals↗
PubMed2003

Spatio-temporal distribution of microglia/macrophages during regeneration in the cerebellum of adult teleost fish, Apteronotus leptorhynchus: a quantitative analysis.

In contrast to mammals, adult teleost fish exhibit an enormous capacity to replace damaged neurons with newly generated ones after injuries in the central nervous system. In the present study, the role of microglia/macrophages, identified by tomato lectin binding, was examined in this process of neuronal regeneration in the corpus cerebelli of the teleost fish Apteronotus leptorhynchus. In the intact corpus cerebelli, or after short survival times following application of a mechanical lesion to this cerebellar subdivision, microglia/macrophages were virtually absent. Conversely, approximately 3 days after application of the lesion, the areal density of microglia/macrophages started to increase at and near the lesion site in the ipsilateral hemisphere, as well as in the contralateral hemisphere, and reached maximum levels at approximately 10 days post lesion. The density remained elevated until it reached background levels approximately one month after the injury. By comparing the time course of the appearance of microglia/macrophages with that of other regenerative events occurring within the first few weeks of wound healing in this model system, we hypothesize that one possible function of microglia/macrophages might be to remove debris of cells that have undergone apoptotic cell death at the lesion site.

Animals↗
PubMed2003

Expression of nitric oxide synthase in the preoptic-hypothalamo-hypophyseal system of the teleost Oreochromis niloticus.

In the present study, we have analyzed the expression of nitric oxide synthase (NOS) in the preoptic-hypothalamo-hypophyseal system of the teleost Oreochromis niloticus. The assay for enzyme activity demonstrated that a constitutive NOS activity is present both in soluble and particulate fractions of the homogenates of diencephalons. Western blot analysis using an antibody against the N-terminus of human nNOS revealed two bands both in the supernatant and in the pellet. One band co-migrates at approximately 150 kDa with that detected in the rat cerebellum homogenates and presumably corresponds to neuronal NOS (nNOS) of mammals. The additional band, which migrates at approximately 180 kDa, might be attributed to an alternatively spliced nNOS isoform. Using NADPH diaphorase (NADPHd) histochemistry in combination with NOS immunohistochemistry, nNOS expression has been detected in preoptic nuclei, hypophysiotrophic nuclei of the ventral hypothalamus, and the pituitary gland. Various degrees of dissociation of NADPHd activity and nNOS immunoreactivity have been detected that could be attributed to the expression of different subtypes of nNOS in the preoptic/hypothalamo/hypophysial system of tilapia. In this paper, we also investigated the colocalization of nNOS with arginine-vasotocin (AVT) by means of immunolabeling of consecutive sections. Results suggest that NO may be colocalized with AVT in a subpopulation of neurosecretory neurons. Present findings suggest that nitric oxide (NO) is implicated in the modulation of hormone release in teleosts in a similar way to mammals.

Animals↗
PubMed1995

The population of GnRH-containing neurons showing socially mediated size changes project to the pituitary in a teleost, Haplochromis burtoni.

Reproductive function in all vertebrates is controlled by the brain-pituitary-gonadal axis. In teleost fish, endocrine cells within the adenohypophysis are grouped together and each collection of cells is innervated by specific neuropeptide fibers. An important regulatory step in reproductive control is gonadotropin-releasing hormone (GnRH), whose delivery to the pituitary is responsible for its release of gonadotropins. The hormone GnRH has been shown to play a critical role in the social control of reproduction in a teleost fish, Haplochromis burtoni. However, there has been no direct evidence that the preoptic area GnRH neurons project to the pituitary. In this study, we used a retrograde tracer and immunohistochemistry to identify those GnRH containing neurons that project to the adenohypophysis. We compared reproductively active territorial males with quiescent non-territorial males to discover whether the connectivity of the preoptic area GnRH neurons depends on the reproductive status of the male. We found that, irrespective of reproductive status, most GnRH neurons in the preoptic area project to the pituitary and that all of these GnRH neurons show the soma size change that has been associated with reproductive status in Haplochromis burtoni. Based on these data, we propose that there is a single population of GnRH containing cells in the preoptic area that change size as a function of reproductive state and that this entire population projects to the pituitary. This is the first direct demonstration that this essential circuit, linking GnRH neurons in the preoptic area to the pituitary, exists.

Agonistic Behavior↗
PubMed1994

Descending telencephalic information reaches longitudinal torus and cerebellum via the dorsal preglomerular nucleus in the teleost fish, Pantodon buchholzi: a case of neural preaptation?

The weakly electric mormyrids are known to have an ascending neuronal pathway that reaches the diencephalon and carries information concerned with electrolocation. The recipient diencephalic center, the dorsal preglomerular nucleus, receives a massive telencephalic input and projects to the corpus and valvula cerebelli. This circuitry has been interpreted as a uniquely derived (autapomorphic) feature for mormyrids. In the present study, we demonstrate with the fluorescent neuronal tracer DiI that the closely related, but non-electroreceptive, teleost Pantodon buchholzi possesses a dorsal preglomerular nucleus with similar telencephalo-cerebellar circuitry. The projection to the cerebellum only reaches the corpus, however, not the valvula cerebelli. Further, the dorsal preglomerular nucleus of Pantodon displays a descending pathway via the torus longitudinalis. Two phylogenetic interpretations for the presence of telencephalo-cerebellar pathways in both mormyrids and Pantodon are possible: if such a pathway existed as a preaptation in the common ancestor of mormyrids and Pantodon, it must be an exaptation for electroreception in mormyrids, since this sensory modality evolved anew in this teleost group; alternatively, the pathway evolved in parallel homoplasy, once in Pantodon, as part of a descending premotor pathway, and independently in mormyrids, where the system gains access to ascending electrosensory information.

Animals↗
PubMed1989

Tyrosine hydroxylase immunoreactivity in a subpopulation of granule cells in the olfactory bulb of teleost fish.

The distribution of tyrosine hydroxylase (TH)-like immunoreactivity in the olfactory bulb was studied in three species of teleosts, the tench Tinca tinca, the Mediterranean barbel Barbus meridionalis and the rainbow trout Salmo gairdneri, by using an indirect immunoperoxidase method. The antiserum used displayed a characteristic pattern of immunostaining in the three species, and four main conclusions can be drawn: (1) there is a large population of TH-like positive cell bodies and fibers in the olfactory bulb in fish, mainly in the granule cell and plexiform layers; (2) the immunolabeled cells are identified as granule cells, but only one group of granule cells is positive; (3) specific quantitative variations exist in the pattern of TH immunoreactivity, with use of the same fixative, antibody and localization method, among the three species studied, and (4) the pattern of TH immunoreactivity in the olfactory bulb in teleosts is completely different from that described previously in amniotes.

Animals↗
PubMed1985

Sonic motor pathways in teleost fishes: a comparative HRP study.

Among marine teleost fishes, one neuroeffector pathway for sonic communication consists of two components: a peripheral effector organ that consists of a swimbladder with associated 'drum' muscles, and a swimbladder or 'sonic' motor nucleus (SMN) located at the junction of the spinal cord and the medulla oblongata. Here, the organization of the SMN is compared in two unrelated groups of teleosts, the midshipmen, Porichthys notatus and P. myriaster, and the sea robin, Prionotus carolinus. Horseradish peroxidase (HRP), used as a retrograde tracer, revealed the position of the SMN in each species. While the SMN is a fused midline structure in midshipmen, it is bilateral in sea robins. The functional significance of these two contrasting patterns of organization remains to be explored. A third study group included mormyrid freshwater electric fish, which are also sonic. Mormyrids were included in part because an earlier study identified androgen-binding cells at a brain level comparable to that of the SMN of marine fishes. Using HRP methods, a swimbladder motor nucleus was identified at the caudal pole of the vagal motor column. However, the nucleus in mormyrids lies dorsal to the fourth ventricle and central canal, not ventral as it does in midshipmen and sea robins. Its position corresponds to the steroid-concentrating cells identified in a previous study.

Air Sacs↗
PubMed1975

Hypothalamohypophysial vascular and neurosecretory link in the teleost Bagarius bagarius (Ham.).

A three-dimensional picture of the hypothalamohypophysial neurosecretory system of B. bargarius could be obtained by adopting in situ staining techniques. The paired NPO give rise to left and right neurosecretory tracts which, although they approximate as a common tract, maintain their individuality till entering the pars intermedia. The ventral hypothalamic and the hypophysial arteries take their origin from the internal carotid artery. The former contributes to the formation of the primary plexus of the median eminence and the latter enters the pituitary directly, giving rise to the neuroadreno-interface vasculature. The vasculature of the median eminence lies in close contact with the long common neurosecretory tract. Morphological evidence suggests that in B. bagarius there are three pathways of hypothalamic control of the hypophysis: (1) A direct neuroglandular pathway, where the neurosecretory axons come directly in contact with the adrenohypophysial cells. (2) An indirect neurovasculoglandular pathway, where the blood exposed to the NSM at the median eminence comes in contact with gland cells. (3) Another indirect neurovasculoglandular pathway, where the blood is exposed to NSM at the neurohypophysis prior coming in contact with the gland cells. Thus, B. bagarius has the 'median eminence equivalent' neuroadeno-interface vasculature typical of the teleosts and the median eminence comparable to the Elasmobranchs, Holocephali and primitive Actinopterygians. This shows that the pituitary portal system of teleosts is in general agreement with that of other fish groups, except that in some it is restricted to the neuroadreno-interface, whereas in others like B. bagarius it extends to the hypothalamus also. These may be termed anterior and posterior median eminence.

Animals↗
PubMed1989

Chronic inflammatory cells with epithelial cell characteristics in teleost fishes.

Certain cells that participate in the chronic inflammatory response of teleost fishes have many features typical of epithelioid cells of mammals. Such features include high metabolic activity, frequent phagolysosomes, and cytoplasmic interdigitations between adjacent cells; however, the epithelioid granulomas formed in response to certain diseases in teleost fishes also have several features associated with epithelial cells. Cases of ulcerative mycosis or acid-fast bacterial infection in Atlantic menhaden (Brevoortia tyrannus), fungal infection in silver perch (Bairdiella chrysoura), and mycobacteriosis in Mozambique tilapia (Oreochromis mossambicus) had epithelioid cells that were joined together by well-formed desmosomes with tonofilaments. "Mature granulomas" of the ulcerative mycosis-infected menhaden stained positively for cytokeratin, a cytoskeletal protein that is considered to be highly specific for epithelial cells. The consistent presence of these heretofore unrecognized epithelial features suggest that they may be characteristic of certain types of cells participating in piscine chronic inflammation.

Animals↗
PubMed2003

Multiple corticosteroid receptors in a teleost fish: distinct sequences, expression patterns, and transcriptional activities.

Corticosteroid hormones, including the mineralocorticoids and the glucocorticoids, regulate diverse physiological functions in vertebrates. These hormones act through two classes of corticosteroid receptors (CR) that are ligand-dependent transcription factors: type I or mineralocorticoid receptor (MR) and type II or glucocorticoid receptor (GR). There is substantial overlap in the binding of these two receptor types to hormones and to DNA. In fish, the overlap in processes controlled by CRs may be different from that in other vertebrates, as fish are thought to synthesize only glucocorticoids, whereas they express both GR and MR. Here we describe the characterization of four CRs in a cichlid fish, Haplochromis burtoni: a previously undescribed GR (HbGR1), another GR expressed in two splice isoforms (HbGR2a and HbGR2b), and an MR (HbMR). Sequence comparison and phylogenetic analysis showed that these CRs sort naturally into GR and MR groups, and that the GR duplication we describe will probably be common to all teleosts. Quantitative PCR revealed differential patterns of CR tissue expression in organs dependent on corticosteroid action. Trans-activation assays demonstrated that the CRs were selective for corticosteroid hormones and showed that the HbMR was similar to mammalian MRs in being more sensitive to both cortisol and aldosterone than the GRs. Additionally, the two HbGR2 isoforms were expressed uniquely in different tissues and were functionally distinct in their actions on classical GR-sensitive promoters. The identification of four CR subtypes in teleosts suggests a more complicated corticosteroid signaling in fish than previously recognized.

Amino Acid Sequence↗
PubMed2004

Electrotonic coupling in the anterior pituitary of a teleost fish.

The anterior pituitary of teleost fish contains a variety of endocrine cells, which, under control from the hypothalamus, release trophic hormones and thereby play a major role in reproduction, social behavior, and growth. In fish, hypothalamic fibers directly innervate the pituitary. The hypothalamic hormones released from these fibers bind to membrane receptors on pituitary cells, triggering action potentials, a rise in cytosolic calcium, and exocytosis. It is unclear whether these activities are confined to the stimulated cell or propagate to adjacent cells. We addressed this issue using whole cell and perforated patch-clamp techniques in a novel, hypothalamo-pituitary slice preparation from the tilapia fish (Oreochromis niloticus). Pituitary cells at rest generated occasional spontaneous spikes and sharp depolarizations of lower amplitude. The latter probably represented spikes in neighboring, electrotonically coupled cells. The presence of electrotonic communication, probably mediated by gap junctions, was also supported by the finding that Lucifer Yellow diffuses between cells. To quantify this connectivity, we performed simultaneous recording from pairs of adjacent cells. Thirty-three percent of the cells exhibited strong reciprocal coupling. Coupling coefficients ranged between 0.18 and 0.31, and coupling resistances ranged between 16 and 39 GOhm. The electrical junctions were effective low pass filters, attenuating action potentials much more than low frequency waveforms. We conclude that electrical activities of anterior pituitary cells in teleost fish are synchronized by coupling through gap junctions. Regulation of this coupling may play a critical role in determining complex patterns of pituitary hormone secretion.

Action Potentials↗
PubMed1983

Urotensin I, a CRF-like neuropeptide, stimulates acth release from the teleost pituitary.

Intraperitoneal injections of urotensin I, a CRF-like neuropeptide isolated from the caudal neurosecretory system of the teleost Catostomus commersoni, ovine CRF and sauvagine all produced significant increases in circulating levels of plasma cortisol in goldfish in which endogenous ACTH secretion was suppressed with betamethasone. In vitro, urotensin I was 2-3 times more potent than CRF or sauvagine in stimulating ACTH release from a superfused goldfish anterior pituitary cell column. These results demonstrate that urotensin I stimulates ACTH release in the goldfish, which suggests that urotensin I or a urotensin I-like peptide may serve as a CRF in teleost fishes.

Adrenocorticotropic Hormone↗
PubMed1985

Multiple forms of human pancreatic growth hormone releasing factor-like immunoreactivity in teleost brain and pituitary.

Two anatomically distinct neuronal GRF systems in the brain-pituitary of the teleost codfish (Gadus morhua), immunohistochemically localized by use of antisera directed against hpGRF1-44NH2 and hpGRF1-40OH are described. Chromatographic analysis additionally revealed the presence of three molecular variants of immunoreactive hpGRF1-44NH2, two of which differ from the authentic human material. However, all three forms released GH from rat pituitary cells in dispersed culture. These findings indicate that hpGRF is highly conserved in nature and suggest that peptides closely related to this human hypothalamic releasing hormone regulate the teleost pituitary.

Animals↗
PubMed1993

Experimental diabetes mellitus in a teleost fish. II. Roles of insulin, growth hormone (GH), insulin-like growth factor-I, and hepatic GH receptors in diabetic growth inhibition in the goby, Gillichthys mirabilis.

Insulin-dependent diabetes mellitus (IDDM), when untreated or poorly controlled in mammals, results in growth retardation. To determine whether the same relationship exists in an ectothermic vertebrate, IDDM-like symptoms were induced in a teleost fish, the goby Gillichthys mirabilis, by surgical removal of its pancreatic endocrine (islet) organ. Isletectomized (Ix) gobies lost body weight, their skeletal growth was retarded, as measured by changes in body length, and they exhibited a 50% reduction in cartilage 35SO4 incorporation in vitro, consistent with changes that occur in mammals with IDDM. Injections of bovine insulin into the Ix fish restored body growth parameters to control levels and stimulated cartilage 35SO4 incorporation in a dose-related manner. In contrast to mammals with IDDM, which are resistant to GH action, injection of teleost GH stimulated cartilage 35SO4 incorporation in the Ix fish. Furthermore, whereas cartilage from rats with IDDM is resistant to stimulation by insulin-like growth factor-I (IGF-I) in vitro, cartilage explants from the Ix fish were highly responsive to recombinant bovine IGF-I, exhibiting a dose-dependent stimulation of 35SO4 incorporation. As far as we are aware, these results represent the first demonstration of diabetic growth inhibition in an ectothermic vertebrate. This inhibition is similar to that which occurs in mammals with IDDM in some respects, but is different in others, as the diabetic fish did not develop resistance to growth stimulation by either GH or IGF-I. While these results support a role for insulin in maintaining the GH-IGF-I-growth axis in this ectothermic vertebrate, there may be important differences in the role of insulin in the promotion of anabolic processes.

Animals↗
PubMed1998

Transcripts encoding two melatonin synthesis enzymes in the teleost pineal organ: circadian regulation in pike and zebrafish, but not in trout.

In this report the photosensitive teleost pineal organ was studied in three teleosts, in which melatonin production is known to exhibit a daily rhythm with higher levels at night; in pike and zebrafish this increase is driven by a pineal clock, whereas in trout it occurs exclusively in response to darkness. Here we investigated the regulation of messenger RNA (mRNA) encoding serotonin N-acetyltransferase (AA-NAT), the penultimate enzyme in melatonin synthesis, which is thought to be primarily responsible for changes in melatonin production. AA-NAT mRNA was found in the pineal organ of all three species and in the zebrafish retina. A rhythm in AA-NAT mRNA occurs in vivo in the pike pineal organ in a light/dark (L/D) lighting environment, in constant lighting (L/L), or in constant darkness (D/D) and in vitro in the zebrafish pineal organ in L/D and L/L, indicating that these transcripts are regulated by a circadian clock. In contrast, trout pineal AA-NAT mRNA levels are stable in vivo and in vitro in L/D, L/L, and D/D. Analysis of mRNA encoding the first enzyme in melatonin synthesis, tryptophan hydroxylase, reveals that the in vivo abundance of this transcript changes on a circadian basis in pike, but not in trout. A parsimonious hypothesis to explain the absence of circadian rhythms in both AA-NAT and tryptophan hydroxylase mRNAs in the trout pineal is that one circadian system regulates the expression of both genes and that this system has been disrupted by a single mutation in this species.

Amino Acid Sequence↗
PubMed1991

Characterization of complementary DNA encoding the precursor for gonadotropin-releasing hormone and its associated peptide from a teleost fish.

Reproductive maturity among male African cichlids Haplochromis burtoni is cued by a series of environmental and social interactions and is mediated physiologically by GnRH. A cDNA clone encoding the precursor for GnRH was isolated from this teleost. The molecular architecture of the predicted prohormone is analogous to that of the previously characterized mammalian forms; however, the predicted sequence of the associated peptide is strikingly different. Attempts to isolate a putative second precursor using low stringency hybridization were not successful despite evidence that a second related decapeptide exists in at least some teleost species.

Amino Acid Sequence↗
PubMed2005

Mutations in half baked/E-cadherin block cell behaviors that are necessary for teleost epiboly.

Epiboly, the spreading of the blastoderm over the large yolk cell, is the first morphogenetic movement of the teleost embryo. Examining this movement as a paradigm of vertebrate morphogenesis, we have focused on the epiboly arrest mutant half baked (hab), which segregates as a recessive lethal, including alleles expressing zygotic-maternal dominant (ZMD) effects. Here we show that hab is a mutation in the zebrafish homolog of the adhesion protein E-cadherin. Whereas exclusively recessive alleles of hab produce truncated proteins, dominant alleles all contain transversions in highly conserved amino acids of the extracellular domains, suggesting these alleles produce dominant-negative effects. Antisense oligonucleotides that create specific splicing defects in the hab mRNA phenocopy the recessive phenotypes and, surprisingly, some of the ZMD phenotypes as well. In situ analyses show that during late epiboly hab is expressed in a radial gradient in the non axial epiblast, from high concentrations in the exterior layer of the epiblast to low concentrations in the interior layer of the epiblast. During epiboly, using an asymmetric variant of radial intercalation, epiblast cells from the interior layer sequentially move into the exterior layer and become restricted to that layer; there they participate in subtle cell shape changes that further expand the blastoderm. In hab mutants, when cells intercalate into the exterior layer, they tend to neither change cell shape nor become restricted, and many of these cells 'de-intercalate' and move back into the interior layer. Cell transplantation showed all these defects to be cell-autonomous. Hence, as for the expansion of the mammalian trophoblast at a similar developmental stage, hab/E-cadherin is necessary for the cell rearrangements that spread the teleost blastoderm over the yolk.

Alleles↗
PubMed2003

The representation of conspecific sounds in the auditory brainstem of teleost fishes.

Temporal patterns of sounds are thought to be the most important carriers of acoustic information in teleost fishes. In order to investigate how conspecific sounds are processed by the auditory system, auditory brainstem responses (ABRs) elicited by conspecific sounds were recorded in five species of teleosts. In the catfishes Platydoras costatus and Pimelodus pictus, the loach Botia modesta and the labyrinth fish Trichopsis vittata, all of which are hearing specialists, each pulse within the sounds elicited a separate brainwave that closely followed the temporal structure. The ABRs of P. costatus and B. modesta also represent amplitude patterns of conspecific sounds. By contrast, ABRs of the sunfish Lepomis gibbosus, a hearing non-specialist, consisted of long series of waves that could not be attributed to specific sound pulses. A more detailed analysis, however, indicated that each stimulus pulse contributed to the compound ABR waveform. Spectral analysis of low-pitched drumming sounds of P. pictus and corresponding ABRs showed peaks in the ABR spectra at the harmonics of the sound. Our results indicate that, besides temporal patterns, amplitude fluctuations and the frequency content of sounds can be represented in the auditory system and help the fish to extract important information for acoustic communication.

Animal Communication↗