Perisomatic feedback inhibition underlies cholinergically induced fast network oscillations in the rat hippocampus in vitro

Gamma frequency network oscillations are assumed to be important in cognitive processes, including hippocampal memory operations, but the precise functions of these oscillations remain unknown. Here, we examine the cellular and network mechanisms underlying carbachol-induced fast network oscillations in the hippocampus in vitro, which closely resemble hippocampal gamma oscillations in the behaving rat. Using a combination of planar multielectrode array recordings, imaging with voltage-sensitive dyes, and recordings from single hippocampal neurons within the CA3 gamma generator, active current sinks and sources were localized to the stratum pyramidale. These proximal currents were driven by phase-locked rhythmic inhibitory inputs to pyramidal cells from identified perisomatic-targeting interneurons. AMPA receptor-mediated recurrent excitation was necessary for the synchronization of interneuronal discharge, which strongly supports a synaptic feedback model for the generation of hippocampal gamma oscillations.     

Attraction of the invasive social wasp,Vespula vulgaris,by volatiles from fermented brown sugar

The introduction of invasive social wasp species of the genus Vespula (Hymenoptera: Vespidae) to New Zealand has caused a major ecological problem, particularly in the beech forests (Nothofagus spp.) of the South Island, where they have destabilized the native bird and invertebrate biodiversity. New attractants are under investigation as part of a search for pest management solutions. Fermenting brown sugar has been previously reported as a social wasp attractant. This work was undertaken to identify compounds from fermented brown sugar attractive to social wasps. Raw fermented brown sugar was confirmed to be attractive in a field trial and 10 chemical compounds present in the headspace were positively identified by coupled gas chromatography‐mass spectrometry and synthetic references. During electroantennogram experiments, 3‐methyl‐1‐butanol, 3‐methylbutyl acetate, and ethyl hexanoate elicited high electrophysiological responses from Vespula vulgaris (L.) antennae. These compounds mediated attraction of V. vulgaris wasps in forest margins by trapping. A blend of these compounds could be used as a lure in a monitoring tool, or even a local suppression method if combined with a toxin.     

The effect of a rat plasma high-density lipoprotein subfraction on the synthesis of bile salts by rat hepatocyte monolayers

The effect of a rat high-density lipoprotein subfraction (HDL2) on the synthesis of bile salts by rat hepatocyte monolayers prepared from rats fed a diet containing cholestyramine, was investigated. The synthesis of bile salts as measured by radioimmunoassay of conjugated cholic, chenodeoxycholic and beta-muricholic acids was significantly increased when hepatocytes were incubated with a physiological concentration (500 micrograms HDL2 protein X ml-1) of HDL2.     

Inhibition of cholesterol 7 alpha-hydroxylase by an antibody to a male-specific form of cytochrome P-450 from subfamily P450IIC.

The absence of antibodies to cholesterol 7 alpha-hydroxylase (EC 1.14.13.17), the rate-determining enzyme for bile acid synthesis, has significantly compromised studies on this protein. Nine antibodies raised against proteins from the cytochrome P-450 gene families (P450I, P450IIA, P450IIB, P450IIC and P450III) were tested as inhibitors of 7 alpha-hydroxylase activity. An antibody raised against a male-predominant P-450 (PB2a, P450h) from the P450IIC gene subfamily was an effective inhibitor of activity in liver microsomal fractions from rat, mouse and hamster. The inhibition could be reversed by the addition of PB2a antigen, indicating structural similarity between cholesterol 7 alpha-hydroxylase and proteins within the P450IIC subfamily. Western blot analysis of hepatic microsomal fractions with the PB2a antibody gave three bands, two of which, like cholesterol 7 alpha-hydroxylase, did not inhibit sexual dimorphism. The intensity of one of the bands (apparent Mr 54,000) correlated with changes observed in activity due to diet [Spearman correlation of 0.800 (P less than 0.01)]. These findings suggest that cholesterol 7 alpha-hydroxylase is a form of P-450 which shares structural similarity with cytochromes P-450 in the P450IIC gene subfamily and that its feedback regulation by bile acid involves protein induction rather than simply post-translational modification.     

Evaluation of the synthetic sex pheromone of the obscure mealybug,Pseudococcus viburni,as an attractant to conspecific males,and to females of the parasitoid Acerophagus maculipennis

The obscure mealybug, Pseudococcus viburni (Signoret) (Hemiptera: Pseudococcidae), is a cosmopolitan pest. In New Zealand, recently introduced management tools include the host‐specific parasitoid Acerophagus maculipennis (Mercet) (Hymenoptera: Encyrtidae) established in 2001, and pheromone‐baited monitoring traps available since 2005. Red delta traps baited with rubber septum lures impregnated with 4.0 μg of the mealybug synthetic sex pheromone, placed in apple orchards in Hawke's Bay and Nelson, trapped both male P. viburni and female A. maculipennis. Two generations of both species per year were discernible, but numbers were low in spring and parasitoids were not trapped during winter (June to September). Male P. viburni catches reached a plateau at a pheromone dose of ca. 1.0 μg per lure but numbers of A. maculipennis per trap increased up to 100 μg per lure, the maximum dose tested. A mathematical model showed that the lures had a half‐life of about 7.4 days and were most attractive to P. viburni with a dose of 0.19 μg, and that the trap effectiveness decreased rapidly once the release rate dropped below the optimum. The model also predicted that the initial pheromone dose should be increased from 0.19 to 5.41 μg per lure as the desired period of deployment increased from 0 to 9 weeks. A dose of 4.0 μg had an initial relative effectiveness of about 55%, reached peak effectiveness after about 5 weeks, and fell to 55% relative effectiveness again after about 8.3 weeks. We conclude that an initial pheromone load of 4.0 μg is appropriate for practical monitoring of P. viburni during the New Zealand summer. Future applications of the sex pheromone for managing the pest and parasitoid are discussed.     

Evidence of multiple introductions and genetic admixture of the Asian brush-clawed shore crab <Emphasis Type="Italic">Hemigrapsus takanoi</Emphasis> (Decapoda: Brachyura: Varunidae) along the Northern European coast

The Asian brush-clawed shore crab Hemigrapsus takanoi is a non-indigenous species along the Northern European coast. Although the history of range expansion of European H. takanoi has been well-documented, little is known about the genetic compositions of either the introduced European populations or the native Asian ones. We therefore collected H. takanoi broadly from their native Asian sites and introduced European ranges, and genotyped them by sequencing the mitochondrial 16S RNA gene and by analyzing nuclear microsatellite loci. Our results revealed that the H. takanoi Bay of Seine (France) populations consisted of a genetic admixture between populations in Japan and those in the Yellow Sea region. These French populations should be carefully monitored in the future, since the genetic admixture of multiple source populations may accelerate range expansion in non-indigenous organisms. Our results also suggested that shipping lines from East Asia were more probable vectors than historical juvenile oyster transportations from Japan for the foundation of present European H. takanoi populations. Interestingly, gene flow between populations in Japan and those in the Yellow Sea region (i.e., domestic invasion) was not observed despite the higher potential for artificial translocations via shipping lines in the native Asian range compared with those from Asia to Europe. The lack of domestic invasions implied that intra-specific priority effects of the resident H. takanoi populations played an important role in preventing the successful colonization of artificially-transferred individuals.     

Apolipoprotein B overproduction by the perfused liver of the St. Thomas' mixed hyperlipidemic (SMHL) rabbit

The St. Thomas' mixed hyperlipidemic (SMHL) rabbit (previously St. Thomas' Hospital rabbit) is a putative model of familial combined hyperlipidemia (FCH). When fed a low (0.08%) cholesterol diet, it exhibits elevations in both plasma cholesterol and triglyceride compared to New Zealand White (NZW) controls. To determine the mechanism for this hyperlipidemia we studied the secretion of apolipoprotein B (apoB)-containing lipoproteins from perfused livers of both young and mature rabbits. During a 3-h perfusion we measured the total cholesterol and triglyceride content of the medium and the cholesterol, triglyceride, and apoB content of very low density lipoprotein (VLDL)(1) (S(f) 60;-400), VLDL(2) (S(f) 20;-60), intermediate (S(f) 12;-20), and low (S(f) 0;-12) density lipoproteins (IDL, LDL). Lipoprotein concentrations increased linearly throughout the perfusion period. The rate of cholesterol output was 3-fold higher (459 vs. 137 ng/g liver/min, P = 0.003) in SMHL versus NZW rabbits whilst that of triglyceride was similar (841 vs. 662 ng/g liver/min, NS). VLDL(1) cholesterol output was elevated 2-fold (232 vs. 123 ng/g liver/min, P < 0.05) and VLDL(2) + IDL + LDL cholesterol output, 4.5-fold (106 vs. 23 ng/g liver/min, P < 0. 005) in SMHL versus NZW rabbits. ApoB output in VLDL1 was 38 ng/g liver per min in SMHL and 14 ng/g liver per min in NZW (NS). In SMHL VLDL(2) + IDL + LDL apoB was increased 9-fold at 53 versus 6 ng/g liver per min in NZW (P < 0.001). We conclude that the SMHL rabbit overproduces apoB-containing lipoproteins particularly in the VLDL(2) + IDL + LDL fraction, a characteristic consistent with its use as a model of FCH.     

Incorporation of lycopene into chylomicron remnant-like particles enhances their induction of lipid accumulation in macrophages

Lipid accumulation in macrophages exposed to chylomicron remnant-like particles containing the dietary antioxidant lycopene was investigated. After incubation with THP-1 macrophages (48 h), chylomicron remnant-like particles containing lycopene (lycCRLPs) as compared to those without (CRLPs) caused significantly more lipid accumulation in the cells, and this was due to increases in both the triacylglycerol (+100%) and cholesterol (+62%) content. In addition, expression of mRNA for diacylglycerol acyltransferase (DGAT), a key enzyme in triacylglycerol synthesis, was significantly decreased by lycCRLPs, but not CRLPs. These findings suggest that lycopene from the diet may promote, rather than retard, lipid accumulation in macrophages during its transport in the blood in chylomicron remnants.     

Interactions of the cholesterol side-chain with egg lecithin. A spin label study.

The effect in egg lecithin liposomes of cholesterol and cholesterol analogues with side-chains of reduced length on the order parameters of two steroid spin labels has been studied. Analogues with side-chains shorter than cholesterol by more than three carbon cause significantly less ordering than cholesterol. Liposomes containing a cholesterol analogue in which the side-chain is absent cause very little increase in the ordering of a new sterol spin label in which the nitroxide is incorporated into the side-chain. The results suggest that the sterol side-chain exerts a great influence on membrane rigidity within its immediate environment.