PubMed Health⌕ Search

Biomedical subjects

D M Neil

Publications and source records attributed to D M Neil.

At least 19 recordsLinked to original sources
PubMed2006

Differences in enzyme activities between two species of Hematodinium, parasitic dinoflagellates of crustaceans.

Parasitic dinoflagellates of the genus Hematodinium infect several commercially important decapod crustaceans. Different species of Hematodinium have different levels of virulence in their respective hosts. Enzyme activities were studied from two species of Hematodinium, one isolated from the Norway lobster (Nephrops norvegicus) and the other from the American blue crab (Callinectes sapidus). We report the identification of differences in secretion of acid phosphatase (AP) and leucine arylamidase from two parasite species. Leucine arylamidase was only contained and secreted by the species infecting the blue crab. Both parasite species contained AP, but only the species infecting the Norway lobster secreted this enzyme. In this species, AP activity was predominantly in the soluble fraction (69.5%). AP activity was localized to cytoplasmic granules and on the membranes surrounding the cell nucleus. In addition to providing information on the cellular metabolism of the parasite, the pattern of activities of these enzymes may also be useful in distinguishing among different species of Hematodinium.

Acid Phosphatase↗
PubMed2006

Molecular detection of Hematodinium spp. in Norway lobster Nephrops norvegicus and other crustaceans.

The Norway lobster Nephrops norvegicus (L.) from the coastal waters of Scotland is seasonally infected by a parasitic dinoflagellate of the genus Hematodinium. Methods used to detect infection include a morphological index (pleopod diagnosis) and several immunoassays. The present study describes the development and application of a set of Hematodinium-specific polymerase chain reaction (PCR) primers and DNA probes based on Hematodinium ribosomal DNA (rDNA). In the PCR assay, a diagnostic band of 380 bp was consistently amplified from total genomic DNA isolated from Hematodinium-infected N. norvegicus. The sensitivity of the assay was 1 ng DNA, which is equivalent to 0.6 parasites. The primer pair also detected Hematodinium DNA in preparations of the amphipod Orchomene nanus, indicating that the amphipod may be infected with the same Hematodinium sp. infecting N. norvegicus. DNA probes detected Hematodinium parasites in heart, hepatopancreas and gill tissues from N. norvegicus, and hepatopancreas and gill tissues from Carcinus maenas, confirming Hematodinium infection in the latter.

Amphipoda↗
PubMed2005

Identification and partial characterisation of metalloproteases secreted by a Mesanophrys-like ciliate parasite of the Norway lobster Nephrops norvegicus.

A ciliate parasite, tentatively identified as Mesanophrys sp. of Norway lobsters Nephrops norvegicus, is demonstrated to secrete several proteases into the culture medium (modified Nephrops saline). Analyses using substrate-impregnated sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) revealed 12 activity bands differing greatly in mobility in the gels. The complete inhibition of proteolytic activity by 1,10-phenanthroline indicated that the proteases are of the metallo class. The proteases were active at the physiological temperature (8 degrees C) and haemolymph pH (7.8) of the host. The proteases were selective in the degradation of several host proteins, including the myosin heavy chain, which is a major structural component of lobster muscle. Consequently, these proteases may have important roles in several aspects of the host-parasite interaction including invasion, nutrient uptake by the ciliate, and pathogenesis.

Animals↗
PubMed2005

A parasitic scuticociliate infection in the Norway lobster (Nephrops norvegicus).

A histophagous ciliate infection was discovered in a number of Norway lobsters (Nephrops norvegicus) from the Clyde Sea Area, Scotland. Silver-carbonate staining of cultured ciliates revealed an oral apparatus and additional structural features that are morphologically similar to scuticociliates in the genus Mesanophrys, which are known to parasitize crustaceans. However, ribosomal DNA sequences (ITS1/5.8S/ITS2) of the ciliate were identical to Orchitophyra stellarum, a parasitic scuticociliate of sea stars with a different morphology from Mesanophrys spp. and to the ciliate from N. norvegicus. Associated pathology included degeneration and necrosis of the myocardial heart muscle, and large numbers of ciliates in the gill filaments.

Animals↗
PubMed2003

Temperature-dependent developmental variation in lobster muscle myosin heavy chain isoforms.

The temperature- and developmental-regulation of myosin heavy chain (MyHC) expression and primary sequence was investigated in the abdominal musculature of developing Homarus gammarus larvae acclimated to 10, 14 and 19+/-1 degrees C. MyHC loop 1 (ATP binding) and loop 2 (actin binding) regions were sequenced and compared. The deduced amino acid sequence of MyHC loop 1 showed a development-related increase in net charge from +1 to +2 between larval stages 1 and 2, which was not temperature-dependent. In post-settled stage 9 larvae, minor shifts in amino acid sequence occurred at 19 degrees C, and corresponded to a significant up-regulation of fast myosin mRNA expression. However, no temperature-specific loop 1 isoforms were detected. The deduced amino acid sequence of MyHC loop 2 was not affected by temperature, and the net charge remained +4 throughout development. These findings contrast to previous studies using the common carp, in which temperature-specific MyHC isoform genes were expressed in response to disparate thermal regimes. This raises the question as to whether arthropods do not express specific temperature isoforms but instead rely on shifts in fibre type to accommodate alterations in thermal environment.

Amino Acid Sequence↗
PubMed2002

Detection of the parasitic dinoflagellate Hematodinium in the Norway lobster Nephrops norvegicus by ELISA.

Norway lobsters Nephrops norvegicus from the coastal waters of Scotland are seasonally infected by a parasitic dinoflagellate of the genus Hematodinium. An enzyme-linked immunosorbent assay (ELISA) has been developed for the detection of the parasite in the haemolymph of N. norvegicus. The ELISA is simple to perform with a detection limit of 5 x 10(4) parasites ml(-1) haemolymph. The ELISA is currently being used to study the prevalence and seasonality of Hematodinium infection in N. norvegicus and other crustacean hosts.

Animals↗
PubMed2002

Infection by a Hematodinium-like parasitic dinoflagellate causes Pink Crab Disease (PCD) in the edible crab Cancer pagurus.

The edible crab (Cancer pagurus) supports a large and valuable fishery in UK waters. Much of the catch is transported live to continental Europe in specially designed live-well ('vivier') vehicles. During the winter of 2000/2001, many trap-caught crabs from Guernsey, Channel Islands, UK, were reportedly moribund and pink in colour. These crabs generally died before and during vivier transportation. We provide histological, immunological, and molecular evidence that this condition is associated with infection by a Hematodinium-like dinoflagellate parasite similar to that previously reported in C. pagurus and to an infection causing seasonal mass mortalities of the Norway lobster (Nephrops norvegicus). Pathologically, every altered host bore the infection, which was characterised by very large numbers of plasmodial and vegetative stages in the haemolymph and depletion of reserve cells in the hepatopancreas. Due to the hyperpigmentation of the carapace and appendages, we have called this infection 'Pink Crab Disease' (PCD). Similar Hematodinium infections cause 'Bitter Crab Disease' in tanner and snow crabs, which has had a negative effect on their marketability. At present, little is known about the seasonality, transmission, and market impact of this infection in C. pagurus.

Animals↗
PubMed2001

Development and application of an immunoassay diagnostic technique for studying Hematodinium infections in Nephrops norvegicus populations.

Patent Hematodinium infections of the Norway lobster Nephrops norvegicus can be detected with a morphological method (pleopod diagnosis), but this fails to identify low-level haemolymph (sub-patent) and any tissue-based (latent) infections. The current study describes the development and application of an immunoassay for the detection of antigens of the parasite Hematodinium in the Norway lobster N. norvegicus. Infected tissue and haemolymph samples were detected as multiple-band reactions to a polyclonal antibody (anti-Hematodinium). The sensitivity limit of the method was 204 parasites mm(-3), approximately 10 times more sensitive than the pleopod diagnosis method. Use of the immunoassay on tissue samples taken from catches in the Clyde Sea area, Scotland, UK, showed that the pleopod method considerably under-diagnosed infection prevalence in the early part of the season, though this under-diagnosis decreased as infected lobsters in the field progressed from latent and sub-patent to patent infections. However, the immunoassay failed to detect any infected lobsters during the summer months, suggesting that infection may not be carried over from one season to the next. The data presented suggest that this immunoassay allows for the accurate estimation of Hematodinium infection prevalence in the field and should be employed, where possible, for the routine monitoring of infection prevalence in N. norvegicus.

Animals↗
PubMed2001

Carbohydrate dynamics and the crustacean hyperglycemic hormone (CHH): effects of parasitic infection in Norway lobsters (Nephrops norvegicus).

The effects of a dinoflagellate parasite (Hematodinium sp.) on carbohydrate metabolism were examined in the Norway lobster, Nephrops norvegicus. Five stages of infection were observed. These included uninfected (Stage 0), subpatently infected (SP), and patently infected (Stage 1-4) lobsters. During patent infection, the concentration of glucose in the hemolymph was reduced significantly from its value of 180 microg ml(-1) in uninfected (Stage 0) lobsters to 25.3 microg ml(-1) in Stage 3-4. These changes were accompanied by significantly lower levels of hepatopancreatic glycogen in lobsters at Stage 2 (2.01 mg g(-1)) and Stage 3-4 (0.84 mg g(-1)) of infection than in those at Stage 0 (16.19 mg g(-1)) and Stage 1 (14.71 mg g(-1)). Due to disruption of the normal feedback loops which control the release of crustacean hyperglycemic hormone (CHH), plasma concentrations increased with the severity of infection from 32.2 fmol ml(-1) in Stage 0 to 106.6 fmol ml(-1) in Stage 3-4. The increased CHH concentrations occurred concomitantly with reduced concentrations of plasma glucose and tissue glycogen. A significantly increased hemolymph CHH titer (107.7 fmol ml(-1)) was also observed during SP infection. It is concluded that the parasite places a heavy metabolic load on the host lobster.

Animal Diseases↗
PubMed2000

Alterations in the biochemistry and ultrastructure of the deep abdominal flexor muscle of the norway lobster Nephrops norvegicus during infection by a parasitic dinoflagellate of the genus Hematodinium.

Changes in various biochemical and ultrastructural characteristics of the deep abdominal flexor (DAF) muscles were studied in Norway lobster Nephrops norvegicus (L.) from the Clyde estuary, Scotland, UK, at different stages of infection by a parasitic dinoflagellate of the genus Hematodinium. Abdominal DAF muscles from infected lobsters showed slight, significant increases in total water content, along with greatly depleted glycogen reserves and an altered free amino acid profile. However, protein concentration and composition remained unchanged. Ultrastructurally, parasitic infection of DAF muscle fibres caused alterations in sarcolemmal structure, and localized disruption of myofibrillar bundles around the periphery, but not throughout the centre of the fibres. Overall, the reduction in swimming performance previously reported for N. norvegicus during Hematodinium infection reflect an alteration in carbohydrate supply to the active muscle and some subtle disruption of muscle structure. The altered carbohydrate titre could reflect the Hematodinium parasites acting as a carbohydrate sink in the haemolymph, a disruption of normal tissue glycogenesis, or some alteration in the host's hormonal regulation. These changes could also adversely affect the taste, texture and marketability of infected meat.

Amino Acids↗
PubMed1999

Shortening properties of two biochemically defined muscle fibre types of the Norway lobster Nephrops norvegicus L.

Mechanical properties of myofibrillar bundles from single chemically skinned fibres from the superficial abdominal flexor muscle of the Norway lobster Nephrops norvegicus were measured, and the protein content of these fibres was analysed by SDS-PAGE. Two slow fibre phenotypes (S1, S2) were distinguished on the basis of their myofibrillar protein assemblages. Data from 9 S1 and 8 S2 fibres obtained at similar sarcomere length demonstrate significant differences between the fibre types in maximal tension (N cm-2, S1: 10.5 +/- 3.9; S2: 3.1 +/- 0.8), in the delay of the peak of stretch activation (ms, S1: 122 +/- 18; S2: 412 +/- 202), in fibre stiffness (N cm-2 per nm half sarcomere, S1: 0.36 +/- 0.19; S2: 0.09 +/- 0.03) and in maximal shortening velocity (fibre length s-1, S1: 0.53 +/- 0.10; S2: 0.27 +/- 0.06). Furthermore, the maximal power output of the type S1 fibres was about five times larger than that of S2 fibres. The power output was maximal at lower loads in S1 fibres (relative load = 0.37 +/- 0.04) than in S2 fibres (relative load = 0.44 +/- 0.05). This study represents a comprehensive investigation of two slow muscle fibre types which are thought to be specialized for slow movements (S1 fibres) and for the postural control of the abdomen (S2 fibres).

Animals↗
PubMed1998

Accumulation of manganese in the haemolymph, nerve and muscle tissue of Nephrops norvegicus (L.) and its effect on neuromuscular performance.

Exposure of Norway lobsters, Nephrops norvegicus (L.) for 3 weeks to manganese concentrations, (5 & 10 mg Mn l(-1) (90-180 microM)), led to its accumulation in various body tissues. The highest concentration was in nerve tissue (brain and abdominal ganglia) which had up to 6 times (on wet wt. basis) the manganese concentration of the exposure concentration, whereas the haemolymph accumulated 3 times and the muscle tissue only 0.5 times the exposure concentration. In the haemolymph the manganese was bound mainly to protein, predominantly (80-90%) to the respiratory protein haemocyanin, as the concentration was 14 times higher in the protein fraction than in the supernatant. Manganese did not substitute for copper in the haemocyanin, as the copper concentration remained constant despite the manganese exposure. The possibility that manganese exposure induced neurotoxic effects sufficient to reduce neuromuscular performance was assessed from the kinematics of free tail-flip swimming, and from measures of the forces produced by abdominal movements in tethered animals. No significant reduction in tail flip velocity or flexion force, but a significant reduction in the maximum post-flip extension force was found. No correlation was found between the manganese concentration in a single tissue or different fractions of the haemolymph and the post-flip extension, except for a weak negative correlation with the manganese concentration in the abdominal ganglion. The ecophysiological implications of these results are discussed.

Abdomen↗
PubMed1998

Activation of skinned muscle fibres from the Norway lobster Nephrops norvegicus L. by manganese ions.

Effects of Mn2+ and Ca2+ on the mechanical properties of glycerinated myofibrillar bundles originating from slow S1 type muscle fibres of superficial flexor muscles of the lobster Nephrops norvegicus were investigated. Mn2+ (5-20 microM) activated the preparations in a dose-dependent manner. The sensitivity of myofibrillar force generation for Mn2+ was around 30 times lower than that for Ca2+. The maximal tension produced under Mn2+ activation was about 75% of that under Ca2+ activation. At higher free Mn2+ concentrations (>2 mM), the steady-state force decreased; it was completely abolished at 30 mM free Mn2+. These high Mn2+ solutions were accompanied by changed in MgATP and MnATP concentrations, and in the ionic strength. Control experiments have shown that none of these parameters seemed fo account fully for the observed force depression in high Mn2+ solutions. It is likely that direct effects of Mn2+ such as a change of the myofilament surface charges are responsible. The maximal unloaded shortening velocity of the myofibrillar preparations was shown to be similar under maximal Mn2+ and Ca2+ activation. Conversely, the kinetics of stretch-induced delayed force increase were about two to three times faster under Mn2+ activation. These results suggest that certain steps of the cross-bridge cycle depend on the ion species bound to the regulatory proteins.

Adenosine Triphosphate↗
PubMed1994

Calcium-activated and stretch-induced force responses in two biochemically defined muscle fibre types of the Norway lobster.

Mechanical properties of thin (< 80 microns) myofibrillar bundles from single rehydrated freeze-dried fibres of the superficial abdominal flexor muscle of the lobster Nephrops norvegicus have been measured, and subsequently the protein content of these fibres has been analysed by SDS-PAGE. Two slow fibre phenotypes can be distinguished on the basis of their myofibrillar assemblages and sarcomere length (type S1: 6.0-7.5 microns, type S2: 8.0-10.9 microns). Differences (means +/- SD, average of seven fibres of each type) were observed in the kinetics for Ca2+ activation (half time of force development (ms); S1: 416 +/- 174; S2: 762 +/- 199 plus a delay of 280 +/- 130) and relaxation (half time of force decay (ms); S1: 162 +/- 75, S2: 257 +/- 53), for Ca2+ sensitivity of force generation (-log [Ca2+] for half maximal activation; S1: 5.40 +/- 0.12; S2: 5.55 +/- 0.08), and of the kinetics of stretch activation (delay of the peak of stretch-induced force increase (ms); S1: 91 +/- 30; S2: 493 +/- 436). From these results and partly also in combination with previously obtained mechanical data on intact fibres it can be concluded (1) that S2 fibres are specialized for long-lasting force maintenance whereas S1 fibres are adapted for slow movements; (2) intrinsic myofibrillar kinetics is not the main time-limiting factor for either activation or relaxation of intact fibres under physiological conditions; (3) processes which precede crossbridge cycling seem to be the main time-limiting factors for the Ca2+ activation of the myofibrils.

Animals↗
PubMed1993

Interaction and synchronization between two abdominal motor systems in crayfish.

1. Extracellular and intracellular recordings from an isolated thoraco-abdominal preparation of the crayfish, Pacifastacus leniusculus, demonstrate that the swimmeret and the abdominal positioning systems can at times be spontaneously coordinated with each other. 2. Two forms of coordination were encountered between these two motor systems. First, some flexor and extensor motor neurons can burst in phase with the swimmeret power-stroke motor neurons. Second, when the flexor motor neurons displayed irregular bursting, the swimmeret rhythm was often inhibited. 3. Both of these two forms of coordination between the swimmeret and the abdominal positioning systems can be induced by depolarization of certain abdominal interneurons. 4. Bath application of oxotremorine increases the frequency of the swimmeret rhythm in a dose-dependent manner. The threshold concentration for this effect is 10(-8) M, and it persists for as long as oxotremorine is present in the bathing solution. 5. At a concentration of 10(-5) M, oxotremorine also induces slow rhythmic activity in the abdominal positioning system consisting of opposite firing between the flexor and extensor motor neurons. 6. Bath application of 10(-5) M oxotremorine also induces two types of interaction between these two abdominal motor systems. In cycle-by-cycle coordination the flexor motor neurons and one extensor motor neuron display rhythmic activity in phase with that of power-stroke motor neurons of the swimmeret system. A slow coordination also occurs with an inhibition of the swimmeret rhythm during the extensor bursts and an excitation during the flexor bursts. 7. Injection of similar doses of oxotremorine into the haemolymph of intact crayfish produces rhythmic abdominal movements that are comparable to the fictive pattern induced in the isolated preparation.

Abdominal Muscles↗
PubMed1992

Histochemical heterogeneity of fibers in the abdominal superficial flexor muscles of the Norway lobster, Nephrops norvegicus (L.).

The superficial flexor muscle in the abdomen of the Norway lobster Nephrops norvegicus (L.), comprises medial and lateral bundles with distinct fiber type composition. Fibers of the medial bundle have long sarcomeres (> 9 microns) and a thick fringe of subsarcolemmal mitochondria. In histochemical tests they have a low total myofibrillar ATPase activity, a pH-stable isoform of myosin ATPase, and a high level of oxidative enzyme activity. A few fibers of the lateral bundle also display these morphological and histochemical properties. However, the majority of lateral fibers have shorter sarcomeres (< 8 microns), no subsarcolemmal mitochondria, but a well-developed tubular system. They also have a higher total myofibrillar ATPase activity, a pH-labile isoform of myosin ATPase, and a low level of oxidative enzyme activity. The heterogeneous pattern of different fiber types in the lateral bundle of this muscle is similar but not identical in the different abdominal segments and in different individuals.

Abdominal Muscles↗
PubMed1976

The structure and function of thoracic exopodites in the larvae of the lobster Homarus gammarus (L.).

The first three larval stages of the lobster Homarus gammarus are pelagic swimming animals. A description is given of the exopodite apparatus of the thoracic appendages that provide lift and propulsive power in these stages. Setal arrangement and display provides greater surface area during power strokes. Musculature is peculiar to the exopodites and concerned with rotational movements of the appendage. Metachronal beating takes place with the segmental appendages moving in a variable sequence.

Animals↗