Iridovirus infections among Missouri River sturgeon: initial characterization, transmission, and evidence for establishment of a carrier state.

Iridovirus infections of the integument were associated with disease and mortality among hatchery-reared populations of juvenile pallid sturgeon Scaphirhynchus albus and shovelnose sturgeon S. platorynchus from the Missouri River. Virus-infected cells in the integument of fins and body were greatly enlarged, possessed pleomorphic and eccentric nuclei, and exhibited an amphophilic to eosinophilic staining of the cytoplasm in hematoxylin-and-eosin-stained sections. Virus particles found in the host cell cytoplasm were composed of an outer hexagonal capsid measuring 254 nm in diameter and surrounding a dense nucleoid. Despite numerous attempts, the virus could not be propagated on routine cell lines used in fish viral diagnostics or from established cell lines from white sturgeon Acipenser transmontanus, pallid sturgeon, or shovelnose sturgeon. Bath exposures of healthy juvenile pallid sturgeon to a crude extract or a 0.45-microm-filtered extract from the fins of infected fish resulted in transmission of the virus and mortality. At water temperatures of 15 degrees C, the first deaths occurred at approximately 1 month; mortality peaked between 50 and 60 d postexposure, after which surviving fish recovered. Presence of the virus was confirmed among dead and moribund pallid sturgeon by both histology and detection of viral DNA by polymerase chain reaction methods. Feeding of infected tissues and cohabitation with virus-infected shovelnose sturgeon also resulted in successful virus transmission to juvenile pallid sturgeon. Virus infections among experimentally exposed pallid sturgeon that recovered from clinical episodes persisted for at least 8.5 months, and these apparently healthy fish transmitted the virus and disease to juvenile pallid sturgeon by cohabitation. The newly described Missouri River sturgeon iridovirus (MRSIV) as found in pallid sturgeon and shovelnose sturgeon shares many properties with a group of iridoviruses associated with serious skin and gill infections in several species of sturgeon.

Development of PCR assays to detect iridovirus infections among captive and wild populations of Missouri River sturgeon.

The Missouri River sturgeon iridovirus (MRSIV) is an important factor contributing to losses during the hatchery rearing of juvenile pallid Scaphirhynchus albus and shovelnose S. platorynchus sturgeon. As the virus has not been isolated in cell culture, current detection procedures rely upon a combination of light and electron microscopy. Detection of characteristic virus-infected cells in the integument, usually of the fins, in hematoxylin and eosin (H&E)-stained tissue sections provides a presumptive finding. Confirmation requires observation by electron microscopy of characteristic doubly enveloped hexagonal virions of the appropriate size in the host cell cytoplasm. To improve these diagnostic procedures, a conventional polymerase chain reduction (PCR) assay was developed as a sensitive and specific method for detection of MRSIV DNA as found in numerous tissues of both naturally and experimentally infected pallid and shovelnose sturgeon. Sequences of amplicons obtained from testing of wild-caught shovelnose sturgeon and juvenile pallid sturgeon during hatchery outbreaks were identical, suggesting that the viruses found in both sturgeon are similar or closely related. In addition, a TaqMan PCR was developed that allowed estimates of the concentrations of MRSIV DNA present in the tissues of pallid and shovelnose sturgeon during acute and persistent infection. These new PCR assays are improved methods to detect MRSIV, but equally importantly, they provide insights into to the biology of the agent for more effective management of viral diseases in captive and wild Missouri River sturgeon populations.

Evaluation of a range of doses of ultraviolet irradiation to inactivate waterborne actinospore stages of Myxobolus cerebralis.

The ability of a range of doses of ultraviolet irradiation (UV) to inactivate the waterborne actinospore or triactinomyxon stages (TAMs) of Myxobolus cerebralis was evaluated by infectivity for juvenile rainbow trout Oncorhynchus mykiss. TAMs were UV-irradiated using a low pressure mercury vapour lamp collimated beam apparatus. All doses 40, 80, 120 and 160 mJ cm(-2) were found to completely inactivate the TAMs as demonstrated by the absence of microscopic lesions, myxospores and parasite DNA detected by quantitative PCR (qPCR) among rainbow trout 5 mo post-exposure. In contrast, rainbow trout receiving the same concentrations of untreated TAMs (1000 fish(-1)) developed clinical signs of whirling disease at 2 mo post-exposure and had severe microscopic lesions, high myxospore counts and high qPCR values when examined at 5 mo following exposure to the parasite.

Evaluation of malacosporean life cycles through transmission studies.

Myxozoans, belonging to the recently described Class Malacosporea, parasitise freshwater bryozoans during at least part of their life cycle, but no complete malacosporean life cycle is known to date. One of the 2 described malacosporeans is Tetracapsuloides bryosalmonae, the causative agent of salmonid proliferative kidney disease. The other is Buddenbrockia plumatellae, so far only found in freshwater bryozoans. Our investigations evaluated malacosporean life cycles, focusing on transmission from fish to bryozoan and from bryozoan to bryozoan. We exposed bryozoans to possible infection from: stages of T. bryosalmonae in fish kidney and released in fish urine; spores of T. bryosalmonae that had developed in bryozoan hosts; and spores and sac stages of B. plumatellae that had developed in bryozoans. Infections were never observed by microscopic examination of post-exposure, cultured bryozoans and none were detected by PCR after culture. Our consistent negative results are compelling: trials incorporated a broad range of parasite stages and potential hosts, and failure of transmission across trials cannot be ascribed to low spore concentrations or immature infective stages. The absence of evidence for bryozoan to bryozoan transmissions for both malacosporeans strongly indicates that such transmission is precluded in malacosporean life cycles. Overall, our results imply that there may be another malacosporean host which remains unidentified, although transmission from fish to bryozoans requires further investigation. However, the highly clonal life history of freshwater bryozoans is likely to allow both long-term persistence and spread of infection within bryozoan populations, precluding the requirement for regular transmission from an alternate host.

Exogenous nerve growth factor attenuates opioid-induced inhibition of voltage-activated Ba2+ currents in rat sensory neurons.

Nerve growth factor (NGF) promotes the survival of embryonic sensory neurons and maintains the phenotypic characteristics of primary nociceptive neurons postnatally. NGF also contributes to nociceptor activation and hyperalgesia during inflammatory pain states. The purpose of this study was to determine whether NGF might have an additional pronociceptive action by interfering with opioid-mediated analgesia in primary nociceptive neurons. Sensory neurons were isolated from the dorsal root ganglia of weanling rats and kept in standard culture conditions either with or without exogenous NGF (50 ng/ml). Currents through voltage-gated calcium channels were recorded from individual neurons using the whole cell patch clamp technique with Ba(2+) as the charge carrier (I(Ba)). The micro-opioid agonist fentanyl (1 microM) and the GABA(B) agonist baclofen (50 microM) were used to test G protein-dependent inhibition of I(Ba). Fentanyl inhibited I(Ba) by an average of 38+/-4% in untreated cells vs. 25+/-2% in NGF-treated cells (P<0.01). NGF had no effect on I(Ba) current magnitude or kinetics. The NGF-induced attenuation of opioid action was observed as early as 4 h after exposure, but was not seen when NGF was applied by bath perfusion for up to 40 min, suggesting that the effect was not mediated by a rapid phosphorylation event. The effect of NGF was prevented by K-252a (100 nM), an inhibitor of TrkA autophosphorylation. Baclofen-induced inhibition of I(Ba), on the other hand, was not affected by NGF treatment, suggesting that NGF modulation of opioid-mediated inhibition occurred upstream from the G protein. This was supported by the finding that GTP-gamma-S, an agonist independent G protein activator, inhibited I(Ba) similarly in both untreated and NGF treated cells. The results show that NGF selectively attenuated opioid-mediated inhibition of I(Ba) via TrkA receptor activation, possibly by altering opioid receptor function.

HSP90 inhibitors alter capsaicin- and ATP-induced currents in rat dorsal root ganglion neurons.

Heat shock proteins (HSPs) are major components of eukaryotic and prokaryotic cells with particularly high levels of expression in neurons. HSPs control protein folding, transport of proteins to and from the nucleus, incorporation of proteins into the cell membrane, and maintenance of the functional activity of several proteins involved in transcriptional control. In this study we demonstrate that inhibitors of HSP90 alter currents mediated by the ligand gated channels, P2X and VR1. P2X and VR1 are membrane receptors activated by ATP and capsaicin, respectively, and are thought to be involved in inflammation-related nociception. The HSP90 inhibitors geldanamycin (GLD), radicicol (RAD) herbimycin A (HERB) potentiated ATP induced currents, whereas only GLD altered capsaicin-induced currents in isolated DRG neurons. At low (< 1 microM) concentrations, GLD potentiated the capsaicin-induced current, while at high concentrations (10-25 microM) it inhibited it. The results suggest a potential involvement of HSPs in nociception.

Local anesthetic inhibition of voltage-activated potassium currents in rat dorsal root ganglion neurons.

BACKGROUND: Local anesthetic actions on the K+ channels of dorsal root ganglion (DRG) and dorsal horn neurons may modulate sensory blockade during neuraxial anesthesia. In dorsal horn neurons, local anesthetics are known to inhibit transient but not sustained K+ currents. The authors characterized the effects of local anesthetics on K+ currents of isolated DRG neurons. METHODS: The effects of lidocaine, bupivacaine, and tetracaine on K+ currents in isolated rat DRG neurons were measured with use of a whole cell patch clamp method. The currents measured were fast-inactivating transient current (I(Af)), slow-inactivating transient current (I(As)), and noninactivating sustained current (I(Kn)). RESULTS: One group of cells (type 1) expressed I(Af) and I(Kn). The other group (type 2) expressed I(As) and I(Kn). The diameter of type 2 cells was smaller than that of type 1 cells. Lidocaine and bupivacaine inhibited all three K+ currents. Tetracaine inhibited I(As) and I(Kn) but not I(Af) For bupivacaine, the concentration for half-maximal inhibition (IC50) of I(Kn) in type 2 cells was lower than that for I(Kn) in type 1 cells (57 vs. 121 microM). Similar results were obtained for tetracaine (0.6 vs. 1.9 mM) and for lidocaine (2.2 vs. 5.1 mM). CONCLUSIONS: Local anesthetics inhibited both transient and sustained K+ currents in DRG neurons. Because K+ current inhibition is known to potentiate local anesthetic-induced impulse inhibition, the lower IC50 for I(Kn) of small type 2 cells may reflect preferential inhibition of impulses in nociceptive neurons. The overall modulatory actions of local anesthetics probably are determined by their differential effects on presynaptic (DRG) and postsynaptic (dorsal horn neurons) K+ currents.

Molecular phylogeny of tubificid oligochaetes with special emphasis on Tubifex tubifex (Tubificidae).

Tubifex tubifex is a cosmopolitan freshwater oligochaete whose presence has been studied as a health indicator of the aquatic environment and as a host for several myxozoan parasites of fish. Unfortunately, current morphological criteria used to distinguish Tubifex spp. (Tubificidae) are inadequate. We therefore developed mitochondrial 16S ribosomal DNA markers to examine phylogenetic relationships among aquatic oligochaetes and to distinguish species of Tubifex that might serve as hosts for a particular myxozoan parasite, Myxobolus cerebralis. Our phylogenetic analyses of oligochaetes based on a 378-bp segment yielded one most parsimonious tree with three major groups that corresponded to the families Lumbricidae, Sparganophilidae, and Tubificidae. T. tubifex and T. ignotus formed a monophyletic assemblage, and a sister relationship between the genera Tubifex and Limnodrilus was strongly supported. A second analysis of the relationship within the genus Tubifex identified six genetically distinct lineages of T. tubifex from North America and Europe that were separated by genetic distances comparable to those found for "well-defined" species of Limnodrilus. Therefore, the existence of several morphologically indistinguishable, thus cryptic, species of Tubifex in North America and Europe is suggested.

Ultraviolet irradiation inactivates the waterborne infective stages of Myxobolus cerebralis: a treatment for hatchery water supplies.

The effects of ultraviolet (UV) irradiation on the viability of the waterborne triactinomyxon stages of Myxobolus cerebralis were evaluated by vital staining and the infectivity for juvenile rainbow trout Oncorhynchus mykiss. A dose of 1300 mWs cm-2 was required to inactivate 100% of the triactinomyxons held under a static collimated beam of UV as determined by vital staining. Juvenile rainbow trout were protected from infections with M. cerebralis when exposed to 14,000 or 1400 triactinomyxon spores per fish that had been treated with the collimating beam apparatus (1300 mWs cm-2). Among all fish receiving UV-treated triactinomyxons, none had clinical signs of whirling disease, or evidence of microscopic lesions or spores of M. cerebralis after 5 mo at water temperatures of 15 degrees C. In contrast, 100% of the fish receiving the higher dose of untreated triactinomyxons developed clinical signs of whirling disease and both microscopic signs of infection and spores were detected in all of the high and low dose trout receiving untreated triactinomyxon exposures. Two additional trials evaluated the Cryptosporidium Inactivation Device (CID) for its ability to treat flow-through 15 degrees C well water to which triactinomyxons were added over a 2 wk period. CID treatments of a cumulative dose exceeding 64,000 triactinomyxons per fish protected juvenile rainbow from infections with M. cerebralis. Rainbow trout controls receiving the same number of untreated triactinomyxons developed both microscopic lesions and cranial spore concentrations up to 10(4.6) per 1/2 head, although no signs of clinical whirling disease were observed. UV (126 mWs cm-2, collimated beam apparatus) was also effective in killing Flavobacterium psychrophilum, the agent causing salmonid bacterial coldwater disease, as demonstrated by the inability of bacterial cells to grow on artificial media following UV treatment.

A Piscirickettsia salmonis-like bacterium associated with mortality of white seabass Atractoscion nobilis.

Mortality among hatchery-reared juvenile white seabass Atractoscion nobilis in southern California, USA, was associated with infections by a Piscirickettsia salmonis-like organism (WSPSLO). Infected fish had no consistent external signs other than pale gills, lethargy and impaired swimming behavior. Internally, the kidney and spleen were enlarged, and some fish had livers with multiple pale foci. Smears from infected kidney, liver, and spleen stained with Wright-Giemsa had intracytoplasmic coccoid organisms, often in pairs, that ranged in size from 0.5 to 1.0 microm. Microscopic lesions included multifocal hepatic, renal, and splenic necrosis, and intralesional macrophages often contained the WSPSLO. The bacterium was isolated from infected fish on cell lines of salmonid (CHSE-214) and white seabass (WSBK) origin. The WSPSLO induced plaque formation and destroyed the cell monolayers within 10 to 14 d incubation at temperatures of 15 and 20 degrees C. The bacterium retained infectivity for cell lines up to 14 d at 4 and 13 degrees C, up to 7 d at 20 degrees C, but it was inactivated at 37 and 56 degrees C within 24 and 1 h, respectively. Freezing at -20 degrees C reduced infectivity by 100-fold. Dehydration and resuspension in distilled water completely inactivated the bacterium. In contrast, the WSPSLO retained nearly all of its infectivity for CHSE-214 cells following a 72 h period in seawater at 20 degrees C. Polyclonal rabbit antibodies made to the WSPSLO reacted specifically in indirect fluorescent antibody tests (IFAT) with the bacterium in cell cultures and smears from infected fish tissues. Tissue smears from infected salmon or CHSE-214 cells with P. salmonis reacted weakly with the anti-WSPSLO serum. Conversely, polyclonal anti-P. salmonis serum produced a weakly positive reaction with the WSPSLO from infected CHSE-214 cells. The WSPSLO as propagated in CHSE-214 cells was highly virulent for juvenile coho salmon Oncorhynchus kisutch, inducing 80% mortality within 10 d of intraperitoneal injection of 10(2.5)-50% tissue culture infectious doses per fish. We conclude that the bacterium from white seabass possesses antigenic differences from P. salmonis yet possesses virulence for salmon equal to known strains of P. salmonis.

Comparative susceptibility of rainbow trout Oncorhynchus mykiss and brown trout Salmo trutta to Myxobolus cerebralis, the cause of salmonid whirling disease.

The susceptibility of rainbow trout Oncorhynchus mykiss and brown trout Salmo trutta to Myxobolus cerebralis, the cause of salmonid whirling disease, was assessed following dosed exposures to the infectious stages (triactinomyxons). Parallel groups of age-matched brown trout and rainbow trout were exposed to 10, 100, 1000 or 10,000 triactinomyxons per fish for 2 h and then placed in aquaria receiving single pass 15 degrees C well water. Severity of infection was evaluated by presence of clinical signs (whirling and/or black tail), prevalence of infection, severity of microscopic lesions, and spore counts 5 mo after exposure. Clinical signs of whirling disease, including a darkened caudal region (black tail) and radical tail chasing swimming (whirling), occurred first among rainbow trout at the highest dose at 6 to 7 wk post exposure. Black tail and whirling occurred among rainbow trout receiving 1000 and 100 triactinomyxons per fish at 8 to 9 wk post exposure. Only 1 of 20 fish had a black tail among rainbow trout receiving 10 triactinomyxons per fish, although 30% of the fish were infected at 5 mo post exposure. Black tails were observed in brown trout at 1000 and 10,000 triactinomyxons per fish beginning at 11 and 7 wk post exposure, respectively. There was no evidence of the tail chasing swimming (whirling) in any group of brown trout. The prevalence of infection, spore numbers, and severity of microscopic lesions due to M. cerebralis among brown trout were less at each exposure dose when compared to rainbow trout. Infections were found among rainbow trout at all doses of exposure but only among brown trout exposed to doses of 100 triactinomyxons per fish or greater. Risk of infection analyses showed that rainbow trout were more apt to be infected at each exposure dose than brown trout. Spore counts reached 1.7 x 10(6) per head among rainbow trout at the highest dose of exposure compared to 1.7 x 10(4) at the same exposure dose among brown trout. Spore numbers increased with dose of exposure in rainbow trout but not in brown trout. As microscopic lesion scores increased from mild to moderate, spore numbers increased in rainbow trout but not brown trout. The mechanisms by which brown trout resist infections with M. cerebralis were not determined. Cellular immune functions, including those of eosinophilic granular leukocytes that were more prominent in brown trout than rainbow trout, may be involved.

Effect of water temperature on the development, release and survival of the triactinomyxon stage of Myxobolus cerebralis in its oligochaete host.

The development of the triactinomyxon stage of Myxobolus cerebralis and release of mature spores from Tubifex tubifex were shown to be temperature dependent. In the present work, the effect of temperature over a range of 5-30 degrees C on the development and release of the triactinomyxon stages of M. cerebralis was studied. Infected T. tubifex stopped releasing triactinomyxon spores 4 days after transfer from 15 degrees C to 25 degrees C or 30 degrees C. Transmission electron microscopic examinations of the tubificids held at 25 degrees C and 30 degrees C for 3 days showed that all developmental stages degenerated and transformed to electron-dense clusters between the gut epithelial cells of T. tubifex. In contrast, tubificid worms held at 5 degrees C and 10 degrees C examined at the same time were heavily infected with many early developmental stages of triactinomyxon. At 15 degrees C, the optimal temperature for development, maturing and mature stages of the parasite were evident. Infected T. tubifex transferred from 15 degrees C to 20 degrees C stopped producing triactinomyxon spores after 15 days. However, 15 days at 20 degrees C was not sufficient to destroy all developmental stages of the parasite. When the tubificid worms were returned to 15 degrees C, the one-cell stages and the binucleate-cell stages resumed normal growth. It was also demonstrated that T. tubifex cured of infection by holding at 30 degrees C for 3 weeks and shifted to 15 degrees C could be re-infected with M. cerebralis spores. The waterborne triactinomyxon spores of M. cerebralis did not appear to be as short-lived as previously reported. More than 60% of experimentally produced waterborne triactinomyxon spores survived and maintained their infectivity for rainbow trout for 15 days at water temperatures up to 15 degrees C. In natural aquatic systems, the triactinomyxon spores may survive and keep their infectivity for periods even longer than 15 days.

Whirling disease: host specificity and interaction between the actinosporean stage of Myxobolus cerebralis and rainbow trout Oncorhynchus mykiss.

Scanning electron microscopic studies were conducted on rainbow trout Oncorhynchus mykiss in the first 60 min after their exposure to the triactinomyxon spores of Myxobolus cerebralis. The results demonstrated that as early as 1 min post exposure the whole process, from the attachment of the triactinomyxon spores to the complete penetration of their sporoplasm germs, had occurred. The triactinomyxon spores sought out the secretory openings of mucous cells of the epidermis, the respiratory epithelium and the buccal cavity of trout and used them as portals of entry. Exposure experiments of the triactinomyxon spores of M. cerebralis to non-salmonid fish, such as goldfish Carassius auratus, carp Cyprinus carpio, nose Chondrostoma nasus, medaka Oryzias latipes, guppy Poecilia reticulata and also the amphibian tadpole Rana pipiens as well as to rainbow trout fry indicated a specificity for salmonids. Attempts to activate the triactinomyxon spores by exposure to mucus prepared from cyprinid and salmonid fish showed no significant differences from those conducted in tap water. The results suggest that the simultaneous presence of both mechano- and chemotactic stimuli was required for finding the salmonid fish host.

Volatile anesthetic sensitivity of T-type calcium currents in various cell types.

UNLABELLED: We evaluated the effects of volatile anesthetics on T-type calcium current (ICa,T) present in four different cell types using the whole cell version of the patch clamp technique. In dorsal root ganglion neurons and in two neuroendocrine cells--adrenal glomerulosa cells (AG) and thyroid C-cells--ICa,T was reversibly decreased by volatile anesthetics at clinically relevant concentrations, with isoflurane and enflurane being more potent that halothane. In AG cells, the most sensitive cell type tested, ICa,T was reduced 47%+/-4% (n = 6) by isoflurane (0.7 mM) and 56%+/-2% (n = 5) by enflurane (1.2 mM), but by only 24%+/-1% (n = 5; P < 0.05) by halothane (0.7 mM). Isoflurane caused a significant increase in the rate of deactivation of ICa,T in AG cells. In ventricular myocytes, however, ICa,T was much less sensitive to both isoflurane and halothane. The differential sensitivity of ICa,T in various cell types to the anesthetics may reflect differences in the channels expressed in these tissues or differences in the cellular intermediates involved in anesthetic action. Depression of ICa,T in neuronal cells may contribute to anesthetic action through decreases in cellular excitability. IMPLICATIONS: Using the patch clamp technique, we showed that T-type calcium channels, which promote cellular excitability, are inhibited by volatile anesthetics in neuronal and neuroendocrine cells, but not in ventricular myocytes. Inhibition of neuronal T-type channels may contribute to the mechanism of action of volatile anesthetics.

Intubation via the LMA using a Cook retrograde intubation kit.

PURPOSE: We report two cases of difficult intubation where a laryngeal mask airway (LMA) was used and changed to a conventional endotracheal tube using a retrograde intubation set. CLINICAL FINDINGS: In two patients, following induction of anaesthesia, the trachea could not be intubated in the conventional fashion with a blade. In both patients an LMA was inserted to achieve an airway. In both patients intubation with a conventional endotracheal tube was required. A Cook Retrograde Intubation Kit and fibreoptic bronchoscope were used to change the LMA to conventional endotracheal tube without problems. CONCLUSION: The Cook retrograde intubation allows an LMA to be replaced with an endotracheal tube with an ID greater than 6 mm with a #3 or 7 mm with a #5 LMA. This technique places an exchange stylet into the airway which is superior to a conventional guidewire. This method allows the airway to be maintained until the LMA is exchanged with an endotracheal tube. Anaesthesia may be maintained and the airway instrumented without difficulty using this technique.

Volatile anesthetics reduce low-voltage-activated calcium currents in a thyroid C-cell line.

BACKGROUND: Volatile anesthetics may act in part by inhibiting voltage-dependent calcium channels. The effects of several volatile agents on three types of calcium channels in a thyroid C-cell line were examined. METHODS: Whole-cell calcium currents were recorded using standard patch clamp techniques. Current-voltage relationships were derived before, during, and after application of isoflurane, enflurane, or halothane. Low-voltage-activated (LVA; T type) calcium currents were isolated based on the voltage range of activation. High-voltage-activated (HVA) calcium currents were separated into L and N types using omega-conotoxin GVIA (omega-CTX) and nicardipine. RESULTS: All three agents reversibly decreased both LVA and HVA currents at clinically relevant concentrations. Isoflurane and enflurane both reduced peak LVA current more than peak HVA current: -33 +/- 6% (mean +/- SE) versus -22 +/- 4% for 0.71 mM isoflurane (n = 6), and -46 +/- 6% versus -35 +/- 5% for 1.21 mM enflurane (n = 6). In contrast, halothane depressed LVA and HVA currents to a similar extent: -22 +/- 4% versus -29 +/- 3% for 0.65 mM halothane (n = 6). Isoflurane had no effect on LVA whole-cell current kinetics. Pretreatment with either omega-CTX (400 nM) or nicardipine (1 microM) did not change the sensitivity of HVA current to isoflurane. CONCLUSIONS: Isoflurane and enflurane block LVA calcium channels more potently than either L-type or N-type calcium channels, but halothane shows no such preferential effect. These results may have implications for the mechanism action of volatile anesthetics.

Properties of iridoviruses from ornamental fish.

An iridovirus from 2 species of freshwater tropical imported fish was examined for its antigenic and biochemical properties and virulence for 3 species of food fish. The virus was found in both guppy (Poecilia reticulata) and doctor fish (Labroides dimidatus). The virus replicated in numerous fish cell lines including BF-2, CCO and EPC. Virus titers reached 10(8) TCID50/ml in each cell line. The virions had similar size and morphology to those previously reported to cause systemic infections among catfish in Europe and from redfin perch and rainbow trout in Australia. A comparison of the ornamental fish iridovirus with these systemic agents indicated that all share common antigens detected by indirect fluorescent antibody tests and Western blots. Additionally, polymerase chain reactions using primer sets developed for the red fin perch virus, amplified a segment of genomic DNA from the ornamental fish isolate. An examination of the virulence of the ornamental fish isolate for 2 important food fish species, rainbow trout (Oncorhynchus mykiss) and channel catfish (Ictalurus punctatus), indicated the former species was susceptible although mortality was low. Dead fish had significant lesions in the liver and kidney and had titers of virus greater than 10(8) TCID50/g. We speculate that these iridoviruses, first detected in Australia in redfin perch, are all related strains in the Ranavirus genus that may have reached these geographically distant sites by movements of ornamental fish.

Baroreflex dysfunction in diabetes mellitus. I. Selective impairment of parasympathetic control of heart rate.

The purpose of this study was to determine the effect of diabetes mellitus on baroreflex control of heart rate. Diabetes (blood glucose = 378 +/- 21 mg/dl) was induced in rabbits by alloxan (n = 9). Alloxan-treated rabbits that remained normoglycemic (n = 9) and rabbits given saline instead of alloxan (n = 5) served as controls. Baroreflex control of heart rate was evaluated in conscious rabbits by measuring changes in heart rate during phenylephrine-induced increases and nitroglycerin-induced decreases in arterial pressure. In diabetic rabbits, the gain of the baroreflex-mediated bradycardia in response to increased pressure decreased significantly from -1.8 +/- 0.3 beats.min-1 x mmHg-1 before alloxan (n = 9) to -0.9 +/- 0.1 and -0.9 +/- 0.3 beats.min-1 x mmHg-1 after 12 and 24 wk of diabetes, respectively (n = 8; P < 0.05). There was no significant change in baroreflex gain in either alloxan-treated or saline-treated normoglycemic rabbits. Baroreflex-mediated bradycardia was not influenced significantly after beta-adrenergic blockade with propranolol (1 mg/kg) and was still impaired in diabetic vs. control rabbits after propranolol. The gain of the baroreflex-mediated tachycardia in response to decreased pressure was not altered in any of the three groups. Propranolol significantly decreased but did not abolish baroreflex-mediated tachycardia. Neither the vagal nor the sympathetic component of the tachycardia was altered significantly by diabetes.(ABSTRACT TRUNCATED AT 250 WORDS)

Baroreflex dysfunction in diabetes mellitus. II. Site of baroreflex impairment in diabetic rabbits.

In our companion paper [T. S. McDowell, M. W. Chapleau, G. Hajduczok, and F. M. Abboud, Am. J. Physiol. 266 (Heart Circ. Physiol. 35): H235-H243, 1994] we report that baroreflex-mediated bradycardia is impaired in diabetic rabbits. The purpose of the present study was to identify the site of impairment. Diabetes was induced in rabbits by alloxan (90-100 mg/kg iv; n = 7). Alloxan-treated rabbits that remained normoglycemic (n = 8) and rabbits given saline instead of alloxan (n = 4) served as controls. Twenty-four weeks after administration of alloxan or saline, rabbits were anesthetized with alpha-chloralose. Aortic baroreceptor and renal sympathetic nerve activity (RSNA) were recorded during phenylephrine- and nitroglycerin-induced changes in arterial pressure. The slope of the baroreceptor pressure-activity relation was not significantly different in diabetic rabbits (1.3 +/- 0.3%/mmHg, n = 7) compared with either alloxan-treated (1.3 +/- 0.1%/mmHg) or saline-treated normoglycemic rabbits (1.2 +/- 0.2%/mmHg). The slope of the arterial pressure-RSNA relation was not significantly different in diabetic rabbits (-3.5 +/- 0.3%/mmHg, n = 7) compared with the alloxan-treated normoglycemic rabbits (-3.0 +/- 0.4%/mmHg, n = 8) and was greater than that in saline-treated normoglycemic rabbits (-1.9 +/- 0.3%/mmHg, n = 4; P < 0.05). The decreases in heart rate in response to electrical stimulation (10 V, 2 ms, 0.5-16 Hz) of the cut peripheral end of the right cervical vagus were similar in diabetic and alloxan-treated normoglycemic rabbits.(ABSTRACT TRUNCATED AT 250 WORDS)