Ciguatoxins: Cyclic polyether modulators of voltage-gated Iion channel function

Ciguatoxins are cyclic polyether toxins, derived from marine dinoflagellates, which are responsible for the symptoms of ciguatera poisoning. Ingestion of tropical and subtropical fin fish contaminated by ciguatoxins results in an illness characterised by neurological, cardiovascular and gastrointestinal disorders. The pharmacology of ciguatoxins is characterised by their ability to cause persistent activation of voltage-gated sodium channels, to increase neuronal excitability and neurotransmitter release, to impair synaptic vesicle recycling, and to cause cell swelling. It is these effects, in combination with an action to block voltage-gated potassium channels at high doses, which are believed to underlie the complex of symptoms associated with ciguatera. This review examines the sources, structures and pharmacology of ciguatoxins. In particular, attention is placed on their cellular modes of actions to modulate voltage-gated ion channels and other Na+-dependent mechanisms in numerous cell types and to current approaches for detection and treatment of ciguatera.

Laboratory evaluation of the effect of alternative prey and vegetation on predation of Culex annulirostris immatures by Australian native fish species

The impact of alternative prey and simulated vegetation on Culex annulirostris Skuse predation efficacy by Australian smelt, Retropinna semoni (Retropinnidae); crimson-spotted rainbowfish, Melanotaenia duboulayi (Melanotaeniidae); empire gudgeon, Hypseleotris compressa (Eleotridae); estuary perchlet, Ambassis marianus (Ambassidae); firetail gudgeon, Hypseleotris galii (Eleotridae); fly-specked hardyhead, Craterocephalus stercusmuscarum (Atherinidae); and Pacific blue-eye, Pseudomugil signifer (Atherinidae), was evaluated in Queensland, Australia. The presence of chironomid midge larvae and tusked frog, Adelotus brevis (Leptodactylidae), tadpoles did not have a significant negative impact on the predation rates of Cx. annulirostris by these 7 fish species. Hypseleotris galii, M. duboulayi, and R. semoni demonstrated strong preference for larvae of Cx. annulirostris over both alternative prey species. In the presence of alternative prey species, the mean predation rate of M. duboulayi on larvae of Cx. annulirostris remained greater than that of other fish species tested. When evaluated at varying densities of simulated vegetation, predation rates of all fish species were similar to those reported in open conditions.

Mechanisms involved in the swelling of erythrocytes caused by Pacific and Caribbean ciguatoxins

The mechanisms underlying the swelling of frog red blood cells (RBC), induced by Pacific (P-CTX-1) and Caribbean (C-CTX-1) ciguatoxins (CTXs), were investigated by measuring the length, width and surface of their elliptic shape. P-CTX-1 (0.5 to 5 nM) and C-CTX-1 (1 mu M) induced RBC swelling within 60 min. The CTXs-induced RBC swelling was blocked by apamin (1 mu M) and by Sr2+ (1 mu M). P-CTX-1-induced RBC swelling was prevented and inhibited by H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one(27 mu M), an inhibitor Of Soluble guanylate cyclase (sGC), and NOS blockade by NG methyl-L-arginine (L-NMA; 10 mu M). Cytochalasin D (cytD, 10 mu M) increased RBC surface and mimicked CTX effect but did not prevent the P-CTX-1-induced L-NMA-sensitive extra increase. Calculations revealed that P-CTX-1 and cytD increase RBC total surface envelop and volume. These data strongly suggest that the molecular mechanisms underlying CTXs-induced RBC swelling involve the NO pathway by an activation of the inducible NOS, leading to sGC activation which modulates intracellular cGMP and regulates L-type Ca2+ channels. The resulting increase in intracellular Ca2+ content, in turn, disrupts the actin cytoskeleton, which causes a water influx and triggers a Ca2+-activated K+ current through SK2 isoform channels. (c) 2005 Elsevier Inc. All rights reserved.

Phosphoinositide regulation of neuroexocytosis: adding to the complexity

Exocytosis of neurotransmitter containing vesicles supports neuronal communication. The importance of molecular interactions involving specific lipids has become progressively more evident and the lipid composition of both the synaptic vesicle and the pre-synaptic plasma membrane at the active zone has significant functional consequences for neurotransmitter release. Several classes of lipids have been implicated in exocytosis including polyunsaturated fatty acids and phosphoinositides. This minireview will focus on recent developments regarding the role of phosphoinositides in neurosecretion.

Short- and long-term consequences of thermal variation in the larval environment of anurans

To survive adverse or unpredictable conditions in the ontogenetic environment, many organisms retain a level of phenotypic plasticity that allows them to meet the challenges of rapidly changing conditions. Larval anurans are widely known for their ability to modify behaviour, morphology and physiological processes during development, making them an ideal model system for studies of environmental effects on phenotypic traits. Although temperature is one of the most important factors influencing the growth, development and metamorphic condition of larval anurans, many studies have failed to include ecologically relevant thermal fluctuations among their treatments. We compared the growth and age at metamorphosis of striped marsh frogs Limnodynastes peronii raised in a diurnally fluctuating thermal regime and a stable regime of the same mean temperature. We then assessed the long-term effects of the larval environment on the morphology and performance of post-metamorphic frogs. Larval L. peronii from the fluctuating treatment were significantly longer throughout development and metamorphosed about 5 days earlier. Frogs from the fluctuating group metamorphosed at a smaller mass and in poorer condition compared with the stable group, and had proportionally shorter legs. Frogs from the fluctuating group showed greater jumping performance at metamorphosis and less degradation in performance during a 10-week dormancy. Treatment differences in performance could not be explained by whole-animal morphological variation, suggesting improved contractile properties of the muscles in the fluctuating group.

A late Pleistocene predator-accumulated avifauna from Kids Cave, West Coast, South Island, New Zealand

A fossil deposit excavated from the floor of Kids Cave, West Coast, South Island, New Zealand, is interpreted as having been primarily accumulated by New Zealand falcon Falco novaeseelandiae, with some contribution by Haast's eagle Harpagornis moorei. The fauna is rich: 3699 bones represented 41 bird species, two frog species, unspecified geckoes and skinks, and one bat species. Fossil deposition was mainly within the Last Glacial Maximum from about 22,000 cal yr bp to about 15,000 cal yr bp, with a marked change in sediment characteristics at the onset of the LGM's coldest period. Chronological control is given by three Uranium-series dates for a speleothem and radiocarbon AMS dating of four avian eggshell samples and one bone. The fauna is the first extensive predator accumulation of LGM age described from the West Coast of the South Island, and it indicates a palaeoenvironment of a mosaic of shrublands with forest patches. The onset of the coldest part of the LGM (Aurora 3 glacial advance, 19,500 - 19,000 cal yrs bp) saw marked climate cooling/drying affecting the site, but the avifauna indicates that although open-country taxa became more common in this period, some forest persisted nearby throughout the remainder of the LGM.