Primary culture of astrocytic glial cells from rainbow trout, Salmo gairdneri L., brain

Derivation and osmotolerance characterization of three immortalized tilapia (Oreochromis mossambicus) cell lines

Fish cell cultures are becoming more widely used models for investigating molecular mechanisms of physiological response to environmental challenge. In this study, we derived two immortalized Mozambique tilapia (Oreochromis mossambicus) cell lines from brain (OmB) and lip epithelium (OmL), and compared them to a previously immortalized bulbus arteriosus (TmB) cell line. The OmB and OmL cell lines were generated without or with Rho-associated kinase (ROCK) inhibitor/3T3 feeder layer supplementation. Although both approaches were successful, ROCK inhibitor/feeder layer supplementation was found to offer the advantages of selecting for epithelial-like cell type and decreasing time to immortalization. After immortalization (≥ passage 5), we characterized the proteomes of the newly derived cell lines (OmB and OmL) using LCMS and identified several unique cell markers for each line. Subsequently, osmotolerance for each of the three cell lines following acute exposure to elevated sodium chloride was evaluated. The acute maximum osmotolerance of these tilapia cell lines (>700 mOsm/kg) was markedly higher than that of any other known vertebrate cell line, but was significantly higher in the epithelial-like OmL cell line. To validate the physiological relevance of these tilapia cell lines, we quantified the effects of acute hyperosmotic challenge (450 mOsm/kg and 700 mOsm/kg) on the transcriptional regulation of two enzymes involved in biosynthesis of the compatible organic osmolyte, myo-inositol. Both enzymes were found to be robustly upregulated in all three tilapia cell lines. Therefore, the newly established tilapia cells lines represent valuable tools for studying molecular mechanisms involved in the osmotic stress response of euryhaline fish.

The isolation and culture of microglia-like cells from the goldfish brain

We have developed a method for isolating goldfish microglia. Cells were identified as microglia immunohistochemically with NN-2, a monoclonal antibody (MAb) raised against teleost retinal microglial cells, and by their phagocytic abilities. Morphological characterization of the cells identified round, phase-bright cells as well as flattened macrophage-like cells. Ramified cells were also seen but they were rare. Fusion of macrophage-like cells occurred in high density cultures and resulted in the formation of giant cells that disintegrated a few days later. Immunohistochemical studies demonstrated that virtually all of the cells in our cultures were NN-2+ and did not label with either antiGFAP (an astrocyte marker) or MAb 6D2 (an oligodendrocyte marker). Cells identified as microglia were intensely phagocytic and ingested latex microspheres, DiIAcLDL and goldfish myelin in vitro. In addition, we labelled microglial cells in vivo with intracranial injections of fluorescent dextran and found that microglia isolated from these animals contained the dextran and phagocytosed microspheres. We also studied the effect of myelin on microsphere uptake and compared the effect of myelin and opsonized myelin on the phagocytic activity of the cells. Our results showed a clear increase in the phagocytic activity of microglia when incubated with myelin, with an enhanced effect of opsonized myelin.

ACTH occurrence in teleosts supramedullary neuron clusters: a neuron-glial common language?

The cross-talk between neurons and glia is receiving increased attention because of its potential role in information processing in the nervous system. We choose the cluster of supramedullary neurons (SN) and glial cells of pufferfish as a suitable model for studying neuron-glial interactions, identifying the implicated cell types and the signalling involved. In particular, among proopiomelanocortin (POMC)-derived peptides, adrenocorticotrope hormone (ACTH)-immunopositivity was found both in SN and in microglial cells. The present results for the first time show the presence of ACTH in microglia of a vertebrate. The role of ACTH is discussed, including its possible neuroprotective function. Moreover, SN immunoreactivity supports the idea that ACTH participates in neurotransmission and/or neuromodulation. In addition to these possible functions, the hypothesis is put forward that ACTH represents a common language by which neurons and glial cells communicate with each other.

Culturing and characterization of astrocytes isolated from juvenile rainbow trout (Oncorhynchus mykiss)

An access to brain cell cultures from fish would enable screening of possible neurotoxic chemicals contaminating the aquatic environment. In the present study, a protocol for a successful routine isolation and culturing of brain cells from juvenile rainbow trout was worked out. The coating material was shown to be of importance for cell proliferation. Cells grow better on a surface coated with laminin than on those coated with poly-L-lysine (PLL), poly-D-lysin (PDL) or poly-L-ornithine (PLO). The best cell growth was obtained on double-coated surfaces (PLL, PDL or PLO plus laminin). On such a culture substrate and with a seeding density of 1 x 10(7) cells/cm(2) confluence was obtained within 3-4 weeks at an incubation temperature of 18 degrees C. Approximately 95% of the cells were identified as astrocytes on the basis of a positive staining with antibodies against the astrocyte specific glial protein (GFAP). No oligodendrocytes or fibroblasts were identified in the cultures, and despite several efforts, neurons did not grow under the culture conditions used. When challenged with ligands known to awake a calcium transient in mammalian astrocytes, 44% of the cells responded to ATP with an increase in [Ca 2+](i), 38% to norepinephrine, 27% to 5-hydroxytryptamine, 7% to histamine and 6% to glutamate. Kainate, quisqualate and gamma-aminobutyric acid did not awake a calcium transient in the cells. Using a proper protocol, it is thus quite easy to get an almost pure culture of astrocyte, whereas neurones proved to very difficult to culture.

Energy metabolism of fish brain

This review focuses on recent research on the metabolic function of fish brain. Fish brain is isolated from the systemic circulation by a blood-brain barrier that allows the transport of glucose, monocarboxylates and amino acids. The limited information available in fishes suggests that oxidation of exogenous glucose and oxidative phosphorylation provide most of the ATP required for brain function in teleosts, whereas oxidation of ketones and amino acids occurs preferentially in elasmobranchs. In several agnathans and benthic teleosts brain glycogen levels rather than exogenous glucose may be the proximate glucose source for oxidation. In situations when glucose is in limited supply, teleost brains utilize other fuels such as lactate or ketones. Information on use of lipids and amino acids as fuels in fish brain is scarce. The main pathways of brain energy metabolism are changed by several effectors. Thus, several parameters of brain energy metabolism have been demonstrated to change post-prandially in teleostean fishes. The absence of food in teleosts elicits profound changes in brain energy metabolism (increased glycogenolysis and use of ketones) in a way similar to that demonstrated in mammals though delayed in time. Environmental factors induce changes in brain energy parameters in teleosts such as the enhancement of glycogenolysis elicited by pollutants, increased capacity for anaerobic glycolysis under hypoxia/anoxia or changes in substrate utilization elicited by adaptation to cold. Furthermore, several studies demonstrate effects of melatonin, insulin, glucagon, GLP-1, cortisol or catecholamines on energy parameters of teleost brain, although in most cases the results are quite preliminary being difficult to relate the effects of those hormones to physiological situations. The few studies performed with the different cell types available in the nervous system of fish allow us to hypothesize few functional relationships among those cells. Future research perspectives are also outlined.

In vivo and in vitro effects of benzothiazole on sheepshead minnow (Cyprinodon variegatus)

Benzothiazole, a common chemical associated with tire manufacturing and industrial wastewater, is a principal component of both fresh water and estuarine tire leachate, a neurotoxicant to larval sheepshead minnows (Cyprinodon variegatus) in in vivo estuarine studies. The neurotoxic potential of benzothiazole was investigated following in vivo and in vitro exposure of sheepshead minnows to 3.75, 7.5, 15, 30 and 60 mg/l benzothiazole. Following benzothiazole exposure, fish were evaluated for survival, growth and histological alterations. Fish mortality occurred after 5 days of exposure to 60 mg/l (LC50 = 41.9). Significant decreases in larval growth were noted at all concentrations. Histologically, gills had cellular alterations but the central nervous system lacked the severe cellular damage seen in previous tire leachate exposure studies. Benzothiazole cytotoxicity to primary cultures of brain cells from sheepshead minnow and tilapia (Oreochromis niloticus) and two epithelial cell lines was evaluated using a tetrazolium salt assay (MTT) at 1 and 4 days. In vitro results indicate primary cultures of brain cells are less sensitive to benzothiazole than epithelial cell lines. Significant cytotoxicity to the epithelial cell lines was noted at 30 and 60 mg/l concentrations. Histologically and cytotoxicologically, the present study indicates that benzothiazole is a gill toxicant and not a neurotoxicant.

Production of eicosanoids derived from 20:4n-6 and 20:5n-3 in primary cultures of turbot (Scophthalmus maximus) brain astrocytes in response to platelet activating factor, substance P and interleukin-1 beta

Primary cultures of turbot (Scophthalmus maximus) brain astroglial cells established in medium containing fetal bovine serum contain increased proportions of 18:1(n-9), total (n-9) and (n-6) polyunsaturated fatty acids (PUFA) and greatly reduced (n-3) PUFA in comparison with turbot brain. Supplementation with a mixture of 5 microM eicosapentaenoic [20:5(n-3)] and 25 microM docosahexaenoic [22:6(n-3)] acids for 4 days significantly increased the percentages of these acids in total cellular lipid of turbot astrocytes and restored the (n-3) PUFA composition of the cells to that found in turbot brain. The production of prostaglandins (PG) E and F of the 2- and 3-series and leukotrienes (LT) C4 and C5 in response to various agonists was determined in PUFA-supplemented astrocytes. Calcium ionophore A23187, platelet activating factor and substance P stimulated the production of both PGF and PGE. Interleukin-1 beta significantly stimulated the production of PGF only. There were differences between the agonists in their effects on the relative levels of 2- and 3-series PGs produced. Only very low amounts of LTC were produced by the turbot astrocytes, with only substance P showing a minor stimulatory effect.

Effect of supplementation with 20:3(n-6), 20:4(n-6) and 20:5(n-3) on the production of prostaglandins E and F of the 1-, 2- and 3-series in turbot (Scophthalmus maximus) brain astroglial cells in primary culture

The production of prostaglandins E and F of the 1-, 2- and 3-series was determined in primary cultures of turbot (Scophthalmus maximus) brain astroglial cells after supplementation with 25 microM dihomo-gamma-linolenic (20:3(n-6)), arachidonic (20:4(n-6)) and eicosapentaenoic (20:5(n-3)) acids. Supplementation by 20:3(n-6), 20:4(n-6) and 20:5(n-3) for 4 days significantly increased the percentages of the respective acids in the total cellular lipid of the turbot astrocytes. The predominant prostaglandins formed by turbot astrocytes in response to stimulation with calcium ionophore A23187 were prostaglandin E2 and prostaglandin F2 alpha under all experimental conditions. The production of prostaglandin E2 was stimulated 2.6-fold, but prostaglandin F2 alpha production was unaffected after supplementation of cultures with 20:4(n-6). However, prostaglandin E2 production in astrocytes was significantly inhibited 3- and 4-fold, and prostaglandin F2 alpha was inhibited 1.6- and 14.6-fold by supplementation with 20:3(n-6) and 20:5(n-3), respectively. Supplementation with 20:3(n-6) also significantly increased the production of prostaglandin E1 (almost 4-fold) and prostaglandin F1 alpha (2.2-fold) whereas supplementation with 20:5(n-3) did not significantly increase the production of prostaglandin E3. Prostaglandin F3 alpha but not prostaglandin E1 were significantly reduced in 20:5(n-3)-supplemented cultures.

Elongation predominates over desaturation in the metabolism of 18:3n-3 and 20:5n-3 in turbot (Scophthalmus maximus) brain astroglial cells in primary culture

The origin of docosahexaenoic acid (DHA, 22:6n-3) that accumulates in turbot brain during development was investigated by studying the incorporation and metabolism via the desaturase/elongase pathways of [1-14C]-labelled polyunsaturated fatty acids (PUFA) in primary cultures of brain astrocytic glial cells. There was little specificity evident in the total incorporation of PUFAs into the turbot astrocytes. However, specificity was apparent in the distribution of the various PUFAs among the individual lipid classes. In particular, there was very specific incorporation of [14C]arachidonic acid (AA, 20:4n-6) into phosphatidylinositol balanced by a lower incorporation of this acid into total diradyl glycerophosphocholines. [14C]-Linolenic acid (LNA, 18:3n-3) and [14C]eicosapentaenoic acid (EPA, 20:5n-3) were metabolized via the desaturase/elongase pathways to a significantly greater extent than [14C]linoleic acid (18:2n-6) and [14C]AA. The turbot astrocytes expressed very little delta 5 desaturase activity and only low levels of delta 4 desaturation activity. Although the percentages were small, approximately 4-5 times as much labelled DHA was produced from [14C]EPA compared with [14C]LNA. However, it was concluded that very little DHA in the turbot brain could result from the metabolism of LNA and EPA in astrocytic glial cells.

Incorporation of [3H]arachidonic and [14C]eicosapentaenoic acids into glycerophospholipids and their metabolism via lipoxygenases in isolated brain cells from rainbow trout Oncorhynchus mykiss

The incorporation of [3H]arachidonate [( 3H]AA) and [14C]eicosapentaenoate [( 14C]EPA) into glycerophospholipids was studied in isolated brain cells from rainbow trout, a teleost fish whose lipids are rich in (n-3) polyunsaturated fatty acids (PUFAs). EPA was incorporated into total lipid to a greater extent than AA, but the incorporation of both PUFAs into total glycerophospholipids was almost identical. The incorporation of both AA and EPA was greatest into phosphatidylethanolamine (PE). However, when expressed per milligram of individual phosphoglycerides, both AA and EPA were preferentially incorporated into phosphatidylinositol (PI), the preference being significantly greater with AA. On the same basis, significantly more EPA than AA was incorporated into phosphatidylcholine (PC). When double-labelled cells were challenged with calcium ionophore A23187, the 3H and 14C released from the cells closely paralleled each other, peaking at 10 min after addition of ionophore. The 12-monohydroxylated derivative was the pre-dominant lipoxygenase product from both AA and EPA with a rank order of 12-hydroxyeicosatetraenoic acid (12-HETE) greater than leukotriene B4 (LTB4) greater than 5-HETE greater than 15-HETE for the AA products and 12-hydroxyeicosapentaenoic acid (12-HEPE) greater than 5-HEPE greater than LTB5 greater than 15 HEPE for EPA products. The 3H/14C (dpm/dpm) ratios in the glycerophospholipids, total released radioactivity, and the lipoxygenase products suggested that PC rather than PI was the likely source of eicosanoid precursors in trout brain cells.