δ13C and δ15N Signatures in Muscle and Fin Tissues: Nonlethal Sampling Methods for Stable Isotope Analysis of Salmonid

Stable isotope analysis has emerged as an important tool in aquatic ecology. For fish, dorsal muscle from sacrificed individuals has traditionally been used in stable isotope studies; however, there are many instances when lethal sampling is undesirable. We evaluated the feasibility of using adipose and caudal fin clips as alternatives to muscle in stable isotope studies for five species of salmonids. Because fish size and water temperature can affect stable isotope ratios, we also determined whether fish length and sampling date affected the difference in isotope signatures between fins and muscle. Biopsied muscle plugs and fin clips were collected from rainbow trout Oncorhynchus mykiss, brook trout Salvelinus fontinalis, and lake trout S. namaycush as well as lake whitefish Coregonus clupeaformis and pygmy whitefish Prosopium coulterii and analyzed for stable isotopes of carbon and nitrogen. The isotope signatures of both adipose and caudal fins were significantly correlated (0.33 , R2 , 0.97) with those of dorsal muscle from the five salmonid species studied, and in some cases the signatures of fins did not differ from those of muscle. Fish length and sampling date occasionally had a small effect (0.042 , R2 , 0.49) on the relationship between the isotope signatures of fin and muscle. Although muscle biopsy provides a viable, nonlethal method of collecting muscle tissue from suitably sized fish, the strong relationships between the isotope signatures of fin and muscle demonstrate that fin clips should be considered good surrogates for muscle in stable isotope studies of salmonids

Complex littoral habitat influences the response of native minnows to stocked trout: evidence from whole-lake comparisons and experimental predator enclosures

Strong negative effects of introduced predatory fishes on native species are frequently reported but may not be universal. Recent research from productive lakes, for example, has documented few serious negative effects. Our objective was to determine how complex littoral habitat mediates the response of adult and young-of-year (YOY) native dace (Chrosomus spp.) and fathead minnow (Pimephales promelas) to the introduction of rainbow trout (Oncorhynchus mykiss) in productive lakes in Alberta, Canada. We first quantified inshore–offshore habitat use of native fish in stocked and unstocked lakes with heavily vegetated littoral zones. We then manipulated the presence or absence of trout and densities of macrophytes within enclosures in an unstocked lake and assessed the behavioral response of native fish. Our whole-lake comparisons revealed that adult and YOY fishes occurred in vegetated inshore areas to a greater extent in stocked relative to unstocked lakes. In the enclosure experiment, native fishes did not respond to the introduction of trout at natural macrophyte densities, but dace significantly reduced their occupation of enclosures with reduced macrophytes once trout were added. Our results suggest that complex littoral macrophyte beds provide important refuge habitat for native fishes, which can potentially mitigate negative effects associated with introductions of a piscivorous predator. </jats:p

The tyrosine kinase inhibitor AG126 restores receptor signaling and blocks release functions in activated microglia (brain macrophages) by preventing a chronic rise in the intracellular calcium level

We recently reported that lasting activation of mouse microglial cells with bacterial lipopolysaccharide (LPS) chronically elevated the basal intracellular calcium concentration ([Ca 2+] i). This correlated to an attenuated calcium signaling of complement (C5a) and purinergic (UTP) receptors as well as to the capacity for effective production of cytokines-chemokines. Here, we demonstrate that these adjustments in the [Ca 2+] i regulation require a critical protein tyrosine kinase (PTK) function - even in varying stimulation scenarios. Changes in basal [Ca 2+] i and calcium signaling are not restricted to Gram-negative bacterial confrontation. Pneumococcal cell wall (PCW) modelling Gram-positive infection causes virtually the same effects. Moreover, decreases in calcium signaling efficacy are neither associated with altered receptor expression, nor mediated by autocrine loops. Administration of microglial release products, transfer of conditioned supernatant or presence of a radical scavenger during LPS or PCW treatments have no consequence. However, both the elevation in basal [Ca 2+] i as well as the suppression of C5a- and UTP-evoked calcium signals are selectively and dose-dependently reversed by tyrphostin AG126, a PTK inhibitor that, moreover, blocks inducible nitric oxide and cytokine-chemokine release. The findings suggest that the AG126-sensitive PTK critically controls both sensory and executive features of the microglial activation process via sustained up-regulation of basal [Ca 2+] i

Interferon-γ differentially modulates the release of cytokines and chemokines in lipopolysaccharide- and pneumococcal cell wall-stimulated mouse microglia and macrophages

During bacterial infections of the CNS, activated microglia could support leucocyte recruitment to the brain through the synthesis of cyto- and chemokines. In turn, invading leucocytes may feedback on microglial cells to influence their chemokine release pattern. Here, we analyzed the capacity of interferon-{gamma} (IFN{gamma}) to serve as such a leucocyte-to-microglia signal. Production of cyto- and chemokines was stimulated in mouse microglia cultures by treatments with lipopolysaccharide (LPS) from Gram-negative Escherichia coli or cell walls from Gram-positive Streptococcus pneumoniae (PCW). IFN{gamma} presence during the stimulation (0.1-100 ng/mL) modulated the patterns of LPS- and PCW-induced cyto- and chemokine release in a dose-dependent, potent and complex manner. While amounts of TNF{alpha} and IL-6 remained nearly unchanged, IFN{gamma} enhanced the production of IL-12, MCP-1 and RANTES, but attenuated that of KC, MIP-1{alpha} and MIP-2. Release modulation was obtained with IFN{gamma} preincubation (treatment of cells before LPS or PCW administration), coincubation and even delayed addition to an ongoing LPS or PCW stimulation. Together the changes observed for the microglial chemokine release under IFN{gamma} would shift the chemoattractive profile from favouring neutrophils to a preferential attraction of monocytes and T lymphocyte populations - as actually seen during the course of bacterial meningitis. The findings support the view of activated microglia as a major intrinsic source for an instant production of a variety of chemokines and suggest that leucocyte-derived IFN{gamma} could potentially regulate the microglial chemokine release pattern

Expression of proteinase-activated receptors in mouse microglial cells

Microglia are the resident immune cells of the CNS: they are activated rapidly by CNS damage and perform the function of tissue macrophages. The first steps during microglial activation are currently under intense study, and it is widely believed that substances released from damaged brain tissue can trigger this process. We recently reported that the blood coagulation factor thrombin, which enters the CNS during breakdown of the blood–brain barrier, activates microglial cells. The cellular effects of thrombin and trypsin-like proteases are mediated by proteinase-activated receptors (PARs). Based on our prior data we hypothesized that microglial cells express these receptors. Using RT-PCR and flow cytometry, we report that primary mouse microglial cells, as well as the murine microglial cell lines BV-2 and N9, indeed express PARs, albeit at different levels. Demonstrating multiple PARs on microglia may enhance the attractiveness of PARs as therapeutic targets in neuroinflammatory disorders