Aggregation Of Melanophores Research Articles

TRPM8 thermosensation in poikilotherms mediates both skin colour and locomotor performance responses to cold temperature

Thermoregulation is a homeostatic process to maintain an organism’s internal temperature within a physiological range compatible with life. In poikilotherms, body temperature fluctuates with that of the environment, with both physiological and behavioral responses employed to modify body temperature. Changing skin colour/reflectance and locomotor activity are both well-recognized temperature regulatory mechanisms, but little is known of the participating thermosensor/s. We find that Xenopus laevis tadpoles put in the cold exhibit a temperature-dependent, systemic, and rapid melanosome aggregation in melanophores, which lightens the skin. Cooling also induces a reduction in the locomotor performance. To identify the cold-sensor, we focus on transient receptor potential (trp) channel genes from a Trpm family. mRNAs for several Trpms are present in Xenopus tails, and Trpm8 protein is present in skin melanophores. Temperature-induced melanosome aggregation is mimicked by the Trpm8 agonist menthol (WS12) and blocked by a Trpm8 antagonist. The degree of skin lightening induced by cooling is correlated with locomotor performance, and both responses are rapidly regulated in a dose-dependent and correlated manner by the WS12 Trpm8 agonist. We propose that TRPM8 serves as a cool thermosensor in poikilotherms that helps coordinate skin lightening and behavioural locomotor performance as adaptive thermoregulatory responses to cold.

Taisho-Sanshoku koi have hardly faded skin and show attenuated melanophore sensitivity to adrenaline and melanin-concentrating hormone.

Koi carp, an ornamental fish derived from the common carp Cyprinus carpio (CC), is characterized by beautiful skin color patterns. However, the mechanism that gives rise to the characteristic vivid skin coloration of koi carp has not been clarified. The skin coloration of many teleosts changes in response to differences in the background color. This change in skin coloration is caused by diffusion or aggregation of pigment granules in chromatophores and is regulated mainly by sympathetic nerves and hormones. We hypothesized that there would be some abnormality in the mechanism of skin color regulation in koi carp, which impairs skin color fading in response to background color. We compared the function of melanin-concentrating hormone (MCH), noradrenaline, and adrenaline in CC and Taisho-Sanshoku (TS), a variety of tri-colored koi. In CC acclimated to a white background, the skin color became paler and pigment granules aggregated in melanophores in the scales compared to that in black-acclimated CC. There were no clear differences in skin color or pigment granule aggregation in white- or black-acclimated TS. The expression of mch1 mRNA in the brain was higher in the white-acclimated CC than that in the black-acclimated CC. However, the expression of mch1 mRNA in the brain in the TS did not change in response to the background color. Additionally, plasma MCH levels did not differ between white- and black-acclimated fish in either CC or TS. In vitro experiments showed that noradrenaline induced pigment aggregation in scale melanophores in both CC and TS, whereas adrenaline induced pigment aggregation in the CC but not in the TS. In vitro administration of MCH induced pigment granule aggregation in the CC but not in the TS. However, intraperitoneal injection of MCH resulted in pigment granule aggregation in both CC and TS. Collectively, these results suggest that the weak sensitivity of scale melanophores to MCH and adrenaline might be responsible for the lack of skin color change in response to background color in the TS.

Coinfections of Aeromonas spp., Enterococcus faecalis, and Vibrio alginolyticus isolated from farmed Nile tilapia and African catfish in Egypt, with an emphasis on poor water quality

The high mortality rate among Nile tilapia (Oreochromis niloticus) and African catfish (Clarias gariepinus) polycultured in earthen ponds in Manzala, Egypt, was investigated. Mortality has been linked to poor water quality parameters accompanied with bacterial infections. Moribund farmed fishes exhibited general septicemic signs. Fish from both species (45 each) were sampled and analyzed bacteriologically. Vibrio alginolyticus (32.3%), Enterococcus faecalis (29.4%), Aeromonas caviae (23.5%), and A. veronii (14.7%) were isolated from moribund fishes using selective media and further identified by biochemical tests. 16S rRNA gene sequencing and phylogenetic analysis confirmed the identity of these isolates. Experimental infection of O. niloticus with different bacterial isolates resulted in clinical signs of hemorrhagic septicemia and mortality rates of 80%, 60%, 40%, and 30%, respectively, for E. faecalis, A. veronii, V. alginolyticus, and A. caviae. Water parameter analysis revealed marked divergence from typical values. In addition, different bacterial isolates (including Staphylococcus sciuri, S. aureus, E. faecalis, A. veronii, A. caviae, and V. alginolyticus) were identified and isolated from water samples. BLAST analysis of water bacterial isolates displayed a 100% similarity score with relevant fish isolates, indicating that the water was the likely source of infections. Histopathological examination revealed signs of bacterial infection in both fish species. In addition, common circulatory and degenerative changes with melanophore aggregation, and lymphocytic depletion in hematopoietic organs were recorded.

Ergasilus extensusand bacterial co‐infection in flathead grey mullet,Mugil cephalus(Linnaeus, 1758), are associated with pathological changes and immunological gene expression alterations

We studied the ectoparasite, Ergasilus extensus or gill lice in gills from farmed grey mullet, Mugil cephalus. Streptococcus agalactiae and Enterococcus faecalis were also studied and isolated from infected fish. We identified these pathogens using 16S rRNA gene sequencing. Our analyses revealed high homology percentages with identical sequences in GenBank. Moreover, phylogenetic tree analysis confirmed S. agalactiae and E. faecalis from other close related pathogens. We also used quantitative real-time polymerase chain reaction (qRT-PCR) to investigate cell-mediated immunity in infected fish with this co-infection. Enhanced cell-mediated immunity was observed as a function of increased interleukin 1 β (IL-1β) and tumour necrosis factor-α (TNFα) levels. Histopathological examinations revealed the presence of haemorrhaging and many parts of the parasite near infected gill lamellae. Also, bacteria aggregated as multiple cocci close to areas of parasite attachment, together with eosinophilic granular cell infiltration. Hepatic tissue showed haemorrhaging and melanophore aggregation with vacuolar degeneration observed in hepatocytes.

The regulation of skin pigmentation in response to environmental light by pineal Type II opsins and skin melanophore melatonin receptors

Coupling skin colour with the light/dark cycle helps regulate body temperature in ectotherms. In X. laevis, nocturnal release of melatonin from the pineal complex induces pigment aggregation and skin lightening. This nocturnal blanching is initiated by a sensor (type II opsin) that triggers melatonin release when light intensity falls below a minimum threshold, and an effector (melatonin receptor) in the skin which induces pigment aggregation. The sensor/s and effector/s belong to two families of G-protein coupled receptors that originated from a common ancestor, but diverged with subsequent evolution. The aim of this work was to identify candidate sensor/s and effector/s that regulate melatonin-mediated skin colour variation. In X. laevis, we identified a developmental time (stage 43/44) when skin lightening depends on pineal complex photosensitivity alone. At this stage, the pineal complex comprises the frontal organ and pineal gland. A total of 37 type II opsin (14 duplicated) and 6 melatonin receptor (3 duplicated) genes were identified through a full genome analysis of the allotetraploid, X. laevis. These genes were grouped into subfamilies based on their predicted amino acid sequences and the presence of specific amino acids essential for their function. The pineal complex expresses mainly blue light sensitive opsins [pinopsin, parietopsin, opn3, and melanopsins (opn4 and opn4b)] and UV-light sensitive opsins (opn5 and parapinopsin), while visual opsins and va-ancient opsin are absent, as determined by RT-PCR and in situ hybridization. The photoisomerase retinal G-protein coupled receptor, and an uncharacterized opn6b opsin, are also expressed. The spectral sensitivity that triggers melatonin secretion, and therefore melanophore aggregation, falls in the visible spectrum (470–650 ηm) and peaks in the blue/green range, pointing to the involvement of opsins with sensitivities therein. The effector-melatonin receptors expressed in skin melanophores are mtnr1a and mtnr1c. Our data point to candidate proteins required in the neuroendocrine circuit that underlies the circadian regulation of skin pigmentation, and suggest that multiple initiators and effectors likely participate.

The Flavor Enhancer Maltol Increases Pigment Aggregation in Dermal and Neural Melanophores in Xenopus laevis Tadpoles.

Melanophores are pigmented cells that change the distribution of melanosomes, enabling animals to appear lighter or darker for camouflage, thermoregulation, and protection from ultraviolet radiation. A complex series of hormonal and neural mechanisms regulates melanophore pigment distribution, making these dynamic cells a valuable tool to screen toxicants as they rapidly respond to changes in the environment. We found that maltol, a naturally occurring flavor enhancer and fragrance agent, induces melanophore pigment aggregation in a dose-dependent manner in Xenopus laevis tadpoles. To determine if maltol affects camouflage adaptation, we placed tadpoles into maltol baths situated over either a white or a black background. Maltol induced pigment aggregation in a similar dose-dependent pattern regardless of background color. We also tested how maltol treatment compares to melatonin treatment and found that the degree of pigment aggregation induced by maltol is similar to treatment with melatonin but that maltol induces over a much longer time course. Last, maltol had no effect on mRNA expression in the brain of genes that regulate camouflage-related pigment aggregation. The present results suggest that maltol does not exert its effects via the camouflage adaptation mechanism or via melatonin-related mechanisms. These results are the first to identify a putative toxicological effect of maltol exposure in vivo and rule out several mechanisms by which maltol may exert its effects on pigment aggregation. Environ Toxicol Chem 2020;39:381-395. © 2019 SETAC.

Understanding the role of melatonin in cancer metabolism

Oncogenes alters metabolic pathways while the resulted metabolites, in turn,
 modifies the expression and production of oncogenes or tumor suppressors. Metabolic
 reprogramming has been considered as a consequence of oncogenes’ activity more
 than a phenotypic change of cancer cells. Currently, three different metabolic
 alterations for cancer cells, i.e. an increased ability to acquire nutrients,
 preferred metabolic pathways or differentiation pathways, have been described.
 Melatonin is a molecule which has been extensively investigated since it was
 discovered more than 60 years ago. From the aggregation of melanophores to
 antioxidant chain reactions, melatonin has been proposed to be an important
 molecule affecting the physiology of mammals but also the biology of
 unicellular organisms. Thus, the decrease in melatonin synthesis in humans with
 age has been related to several diseases including neurodegeneration and
 cancer. For many years, it has been believed that melatonin crosses biological
 membranes easily to exert its functions. However, this notion has been
 challenged by recent discovery that majority of melatonin might cross biological
 membranes through glucose transporters. This initial observation has generated a
 new important idea about melatonin’s function, that is, the membrane transportation
 of melatonin and glucose by the same transporter in cancer cells would be a new
 promising mechanism of this indole by either reprogramming glucose metabolism,
 impeding nutrients uptake or assigning preferred metabolic pathways in cancer
 cells. In this review, we will focus the role of melatonin as an
 antiproliferative agent, and its connection with metabolic changes due to
 melatonin competition with glucose.

Fluorine substituted methoxyphenylalkyl amides as potent melatonin receptor agonists.

A series of fluorine substituted methoxyphenylalkyl amides were prepared with different orientations of the fluorine and methoxy groups with respect to the alkylamide side chain and with alkyl sides of differing lengths (n = 1-3). β-Dimethyl and α-methyl derivatives were also synthesised. The compounds were tested as melatonin agonists and antagonists using the pigment aggregation of Xenopus melanophores as the biological assay. A number of these compounds were potent melatonin agonists, the potency depending on the length of the alkyl chain, the orientation of the methoxy and fluorine substituents, the amide chain length and, for the ethyl side-chain analogues, the presence of β-substituents.

Production and Purification of Recombinant Somatolactin and its Effects on Insulin-like Growth Factors Gene Expression in Tilapia Hepatocytes

Somatolactin (SL), the member of the growth hormone (GH)/prolactin (PRL) family, is fish-specific pituitary hormone with diverse functions. However, little is known about its biological function in fish hepatocytes. Using tilapia as a model, SLtranscripts were shown to be widely expressed in various extrapituitary tissues with the relatively high expression level in liver. To explore the biological action of SL in hepatocytes, we produced and purified recombinant tilapia SL protein which could induce pigment aggregation in tilapia melanophores. Further, the antiserum for the SL was produced and its specificity was confirmed by antiserum preabsorption. During 4 week starvation, hepatic SL transcripts in starved fish were significantly higher than the control fish starting on the 1st week of starvation until 4th week. After re-feeding, the SL transcripts level returned to normal. Using primary cultures of tilapia hepatocytes, insulin-like growth factors (IGF1 and IGF2) gene expression were elevated by static incubation with recombinant tilapia SL. In contrast, removal endogenous SL by immunoneutralization using SL antiserum was shown to inhibit IGF1 and IGFgene expression. These findings, taken together, provide evidence for the first time that SL may serve as a novel regulator in fish stimulating IGF1 and IGF gene expression in hepatocytes.

Developmental changes in melanophores and their asymmetrical responsiveness to melanin-concentrating hormone during metamorphosis in barfin flounder (Verasper moseri)

Barfin flounder larvae exhibit unique black coloration, as well as left–right asymmetry in juvenile stage as in other flatfish. In this study, we first assessed the changes in melanophores with development and then investigated their responsiveness to melanin-concentrating hormone (MCH) during metamorphosis. Larval-type melanophores appeared on both sides of the body before metamorphosis, whereas adult-type melanophores appeared only on the ocular side after metamorphosis. Even in the individuals of this species displaying black coloration, the density of larval-type melanophores was similar to that in transparent larvae of other species. However, unlike in transparent larvae, larval-type melanophores completely dispersed in the black larvae of this species. Therefore, the black coloration during larval stages was mainly due to dispersion, and not the density, of larval-type melanophores. In vitro MCH treatment revealed, for the first time, the responsiveness of melanophores in larval stages. On the ocular side, larval-type melanophores aggregated against MCH during larval stages, while, in the larvae at later metamorphic stages and in juveniles, larval-type melanophores did not aggregate, although aggregation of adult-type melanophores was noted. In contrast, on the blind side, the responsiveness of larval-type melanophores to MCH was consistently present from larval to juvenile stages. The metamorphic transition of MCH responsiveness from larval- to adult-type melanophores only on the ocular side suggests the larval (therefore, immature) nature of the blind side skin. We propose that the inhibited development, and thus the retention of the larval-type skin leads to the formation of the blind side characteristics and is the central mechanism for the flatfish asymmetry.

Designing Microdevices Operated through Self-Organizations of Microtubules and Kinesin Motors

Fish melanocytes change their colors through aggregation and dispersion of melanophores. The aggregation and dispersion of melanophores make the appearances of fish melanocytes bright and dark, respectively. The movements of malanophores are driven by biological molecular motors, motor proteins. Inspired by this mechanism, we have envisioned an optical microdevice powered by motor proteins. That is, in arrays of microscale chambers, melanophore-imitated particles, whose surfaces are covered with kinesin motors, are aggregated and dispersed through formations and disassemblies of microtubule asters, respectively. In order to realize such optical device, exploring possible designs of the device is required to test the feasibility of the device. However, laborious experimental procedures hamper such explorations. An alternative way of the exploring would be use of computer simulations. Previously, we have shown the power of computer simulations in designing Lab-on-a-Chip devices powered by motor proteins. Here, we performed systematic explorations of designs of the envisioned device. To this end, we modeled a microtubule as the Kramers chain of a linear polymer, and performed Brownian dynamics simulations. The simulations showed aster formations of microtubules in chambers of various shapes, such as thin triangle, square and hexagonal prisms. We will discuss effects on the aster formations of the size of microscopic chambers, microtubule properties, and motor protein properties. Through the computer simulation, we will show design guidelines for the optical device.

Synthesis of new N-(arylcyclopropyl)acetamides and N-(arylvinyl)acetamides as conformationally-restricted ligands for melatonin receptors

N-(Arylcyclopropyl)acetamides and N-(arylvinyl)acetamides or methyl ureas have been prepared as constrained analogues of melatonin. The affinity of these new compounds for chicken brain melatonin receptors and recombinant human MT1 and MT2 receptors was evaluated using 2-[125I]-iodomelatonin as radioligand. Strict ethylenic or cyclopropyl analogues of the commercialized agonist agomelatine (Valdoxan®) were equipotent to agomelatine in binding bioassays. However, the ethylenic analogue was more effective than the cyclopropyl one in the melanophore aggregation bioassay, but was still less potent than the disubstituted 2,7-dimethoxy-naphtalenic compounds.

Signal transduction mechanisms for autocrine/paracrine regulation of somatolactin-α secretion and synthesis in carp pituitary cells by somatolactin-α and -β

Pituitary hormones can act locally via autocrine/paracrine mechanisms to modulate pituitary functions, which represents an interesting aspect of pituitary regulation other than the traditional hypothalamic input and feedback signals from the periphery. Somatolactin, a member of the growth hormone (GH)/prolactin (PL) family, is a pleiotropic hormone with diverse functions, but its pituitary actions are still unknown. Recently, two SL isoforms, SLα and SLβ, have been cloned in grass carp. Based on the sequences obtained, recombinant proteins of carp SLα and SLβ with similar bioactivity in inducing pigment aggregation in carp melanophores were produced. In carp pituitary cells, SLα secretion and cell content were elevated by static incubation with recombinant carp SLα and SLβ, respectively. These stimulatory actions occurred with a parallel rise in SLα mRNA level with no changes in SLβ secretion, cell content, and gene expression. In contrast, SLα mRNA expression could be reduced by removing endogenous SLα and SLβ with immunoneutralization. At the pituitary cell level, SLα release, cell content, and mRNA expression induced by carp SLα and SLβ could be blocked by inhibiting JAK2/STAT5, PI3K/Akt, MEK1/2, and p38 MAPK, respectively. Furthermore, SLα and SLβ induction also triggered rapid phosphorylation of STAT5, Akt, MEK1/2, ERK1/2, MKK3/6, and p38 MAPK. These results suggest that 1) SLα and SLβ produced locally in the carp pituitary can serve as novel autocrine/paracrine stimulators for SLα secretion and synthesis and 2) SLα production induced by local release of SLα and SLβ probably are mediated by the JAK2/STAT5, PI3K/Akt, and MAPK signaling pathways.

On the role of histamine receptors in regulating pigmentary responses in Oreochromis mossambicus melanophores

Purpose: The present work was carried out to reveal the involvement of histamine receptors at the neuro-melanophore junction of teleost, Oreochromis mossambicus.Methods: The isolated scale melanophores were assayed using the mean melanophore size index and their responses were recorded in presence of various concentrations of histamine along with H1 and H2 receptor specific agonists and antagonist and potentiator compound 48/80.Results: Melanophores showed high sensitivity to histamine and its specific agonists. Histamine caused a dose-dependent pigment aggregation, whereas 2-(2-Pyridyl) ethylamine (PEA), a specific H1R agonist also caused aggregation in a similar manner. Conversely, amthamine, a specific H2R agonist resulted in pigment dispersion. The effects were antagonized by mepyramine; specific H1R antagonist and ranitidine a specific H2R antagonist.Conclusion: It is concluded that O. mossambicus melanophores have both H1 and H2 receptors which mediate melanophore aggregation and dispersion respectively. Compound 48/80 augmented the melanin-aggregating and dispersing effects of PEA and amthamine. It is suggested that the effect of histamine is directly mediated through H1 and H2 receptors, whereas H1Rs may be predominantly involved in the aggregatory responses.

Unique and potent effects of acute ibogaine on zebrafish: The developing utility of novel aquatic models for hallucinogenic drug research

An indole alkaloid, ibogaine is the principal psychoactive component of the iboga plant, used by indigenous peoples in West Africa for centuries. Modulating multiple neurotransmitter systems, the drug is a potent hallucinogen in humans, although its psychotropic effects remain poorly understood. Expanding the range of model species is an important strategy for translational neuroscience research. Here we exposed adult zebrafish (Danio rerio) to 10 and 20mg/L of ibogaine, testing them in the novel tank, light–dark box, open field, mirror stimulation, social preference and shoaling tests. In the novel tank test, the zebrafish natural diving response (geotaxis) was reversed by ibogaine, inducing initial top swimming followed by bottom dwelling. Ibogaine also attenuated the innate preference for dark environments (scototaxis) in the light–dark box test. While it did not exert overt locomotor or thigmotaxic responses in the open field test, the drug altered spatiotemporal exploration of novel environment, inducing clear preference of some areas over others. Ibogaine also promoted ‘mirror’ exploration in the mirror stimulation test, disrupted group cohesion in the shoaling test, and evoked strong coloration responses due to melanophore aggregation, but did not alter brain c-fos expression or whole-body cortisol levels. Overall, our results support the complex pharmacological profile of ibogaine and its high sensitivity in zebrafish models, dose-dependently affecting multiple behavioral domains. While future investigations in zebrafish may help elucidate the mechanisms underlying these unique behavioral effects, our study strongly supports the developing utility of aquatic models in hallucinogenic drug research. High sensitivity of three-dimensional phenotyping approaches applied here to behavioral effects of ibogaine in zebrafish provides further evidence of how 3D reconstructions of zebrafish swimming paths may be useful for high-throughput pharmacological screening.

Melanin inhibitory and melanin stimulatory effects of extracts of Chlorophytum tuberosum and Chlorophytum borivilianum on isolated fish scale melanophores

The epidermal scale melanophores of fishes are disguised type of smooth muscle cells and behave differently when exposed to certain hormones and drugs; however, their responses to plant extracts have not been studied. Chlorophytum species holds an important position in Indian herbal medicine; hence, in the present investigation, effects of extracts of two species of Chlorophytum, that is, Chlorophytum tuberosum and Chlorophytum borivilianum have been studied on the isolated scale melanophores of the teleost fish, Channa punctatus. The lyophilized extract of tubers of C. tuberosum had a melanin aggregating effect causing paling of the skin; the action seems to be mediated through alpha adrenergic receptors present dominantly on fish melanophores. On the other hand, the extract of tubers of C. borivilianumhad a melanin dispersing effect within the fish melanophores inducing darkening of the skin and the responses seem to be mediated probably through beta adrenergic receptors. Key words: Channa punctatus, melanophore aggregation, Chlorophytum tuberosum, Chlorophytum borivilianum.

The Effects of Crude Oil on Skin Histology of Poecilia sphenops (Valenciennes, 1846) (Cyprinidae, Teleostei)

Summary As being the main energy source that is needed for all of the industrial processes, crude oil is evaluated as a widely investigated ecotoxicant. In order to identify the effects of crude oil on the skin of teleosts, Poecilia sphenops specimens were exposed to three different concentration of soluble part of crude oil (10%, 20%, 40%) at four different exposure time (24, 48, 72, 96 h); and the histopathological changes were reported. A slight epidermis corrosion and melanophore aggregation in dermis were observed at low concentration and short exposure time. As estimated, the striking effects of the crude oil; such as dermis disintegration, necrotic areas and fibrosis in subcutaneous muscle layer; were extended prominently in parallel with increasing concentrations and exposure time.

Effect and mechanism of action of resveratrol: a novel melanolytic compound from the peanut skin of Arachis hypogaea

Purpose: The present work was carried out to determine the effects of ethanolic extracts of Arachis hypogaea and its active ingredient resveratrol on the isolated tail melanophores of the Bufo melanostictus to find the mechanism of skin lightening at the cellular level.Methods: The tail melanophores of the tadpole B. melanostictus were assayed using the mean melanophore size index and their responses were recorded in presence of various concentrations of the plant extract and its active ingredient along with specific antagonists and potentiator.Results: Significant skin lightening activity of the extract of A. hypogaea and its active ingredient resveratrol was observed on the tail melanophores of tadpole. The pigment cells responded by distinct aggregation leading to skin lightening, this effect was reversible, as re-immersion in physiological saline made the melanophores return to their normal intermediate state. These melanin aggregating effects were completely blocked by propanolol (beta blocker) and partially blocked by prazosin (alpha blocker) and were also found to be highly potentiated by reserpine.Conclusion: These studies suggest that the active ingredient of A. hypogaea such as resveratrol can act as a sympathomimetic compound and induce aggregation of melanophores of tadpole B. melanostictus via the induction of beta type of the adrenoceptors. The present study opens new vistas for the use of A. hypogaea and its active ingredient, resveratrol for its clinical application as a nontoxic melanolytic compound for the treatment of hyperpigmentation.

Physiology and mRNA expression in rainbow trout (Oncorhynchus mykiss) after long-term exposure to the new antifoulant medetomidine

Medetomidine is under evaluation for use as an antifouling agent, and its effects on non-target aquatic organisms are therefore of interest. In this study, rainbow trout was exposed to low (0.5 and 5.0nM) concentrations of medetomidine for up to 54days. Recently we have reported on effects on paleness and melanophore aggregation of medetomidine in these fish. Here, specific growth rates were investigated together with a broad set of physiological parameters including plasma levels of growth hormone (GH), insulin-like growth factor-I (IGF-I) and leptin, glucose and haemoglobin (Hb), hematocrit (Ht), condition factor, liver and heart somatic indexes (LSI, HSI). Hepatic enzyme activities of CYP1A (EROD activity), glutathione S-transferases (GST) and glutathione reductase (GR) were also measured. Additionally, hepatic mRNA expression was analysed through microarray and quantitative PCR in fish sampled after 31days of exposure. Medetomidine at both concentrations significantly lowered blood glucose levels and the higher concentration significantly reduced the LSI. The mRNA expression analysis revealed few differentially expressed genes in the liver and the false discovery rate was high. Taken together, the results suggest that medetomidine at investigated concentrations could interfere with carbohydrate metabolism of exposed fish but without any clear consequences for growth.

Nitric oxide inhibited the melanophore aggregation induced by extracellular calcium concentration in snakehead fish, Channa punctatus

We studied the role of nitric oxide (NO) and extra-cellular Ca(2+) on the melanophores in Indian snakehead teleost, Channa punctatus. Increase of Ca(2+) level in the external medium causes pigment aggregation in melanophores. This pigment-aggregating effect was found to be inhibited when the external medium contained spontaneous NO donor, sodium nitro prusside (SNP) at all the levels of concentration tested. Furthermore, it has been observed that SNP keeps the pigment in dispersed state even after increasing the amount of Ca(2+). In order to test whether NO donor SNP causes dispersion of pigments or not is checked by adding the inhibitor of nitric oxide synthase, N-omega-Nitro-L-arginine (L-NNA) in the medium. It has been noted that the inhibitor L-NNA blocked the effect of NO donor SNP causing aggregation of pigments. In that way NO is inhibiting the effect of extracellular Ca(2+), keeping the pigment dispersed.