Xenon Impairs Reconsolidation of Fear Memories in a Rat Model of Post-Traumatic Stress Disorder (PTSD)

Xenon (Xe) is a noble gas that has been developed for use in people as an inhalational anesthestic and a diagnostic imaging agent. Xe inhibits glutamatergic N-methyl-D-aspartate (NMDA) receptors involved in learning and memory and can affect synaptic plasticity in the amygdala and hippocampus, two brain areas known to play a role in fear conditioning models of post-traumatic stress disorder (PTSD). Because glutamate receptors also have been shown to play a role in fear memory reconsolidation – a state in which recalled memories become susceptible to modification – we examined whether Xe administered after fear memory reactivation could affect subsequent expression of fear-like behavior (freezing) in rats. Male Sprague-Dawley rats were trained for contextual and cued fear conditioning and the effects of inhaled Xe (25%, 1 hr) on fear memory reconsolidation were tested using conditioned freezing measured days or weeks after reactivation/Xe administration. Xe administration immediately after fear memory reactivation significantly reduced conditioned freezing when tested 48 h, 96 h or 18 d after reactivation/Xe administration. Xe did not affect freezing when treatment was delayed until 2 h after reactivation or when administered in the absence of fear memory reactivation. These data suggest that Xe substantially and persistently inhibits memory reconsolidation in a reactivation and time-dependent manner, that it could be used as a new research tool to characterize reconsolidation and other memory processes, and that it could be developed to treat people with PTSD and other disorders related to emotional memory.     

Generation and Characterization of a Mouse Model Harboring the Exon-3 Deletion in the Cardiac Ryanodine Receptor

A large genomic deletion in human cardiac ryanodine receptor (RYR2) gene has been detected in a number of unrelated families with various clinical phenotypes, including catecholaminergic polymorphic ventricular tachycardia (CPVT). This genomic deletion results in an in-frame deletion of exon-3 (Ex3-del). To understand the underlying disease mechanism of the RyR2 Ex3-del mutation, we generated a mouse model in which the RyR2 exon-3 sequence plus 15-bp intron sequences flanking exon-3 were deleted. Heterozygous Ex3-del mice (Ex3-del^+/−) survived, but no homozygous Ex3-del mice were born. Unexpectedly, the Ex3-del^+/− mice are not susceptible to CPVT. Ex3-del^+/− cardiomyocytes exhibited similar amplitude but altered dynamics of depolarization-induced Ca²⁺ transients compared to wild type (WT) cells. Immunoblotting analysis revealed markedly reduced expression of RyR2 protein in the Ex3-del^+/− mutant heart, indicating that Ex3-del has a major impact on RyR2 protein expression in mice. Cardiac specific, conditional knockout of the WT RyR2 allele in Ex3-del^+/− mice led to bradycardia and death. Thus, the absence of CPVT and other phenotypes in Ex3-del^+/− mice may be attributable to the predominant expression of the WT RyR2 allele as a result of the markedly reduced expression of the Ex3-del mutant allele. The effect of Ex3-del on RyR2 protein expression is discussed in relation to the phenotypic variability in individuals with the RyR2 exon-3 deletion.     

Survival of dispersing versus philopatric juvenile snowshoe hares: do dispersers die?

We used radio-telemetry to monitor the survival of dispersing and philopatric juvenile snowshoe hares ( Lepus americanus ) in southwestern Yukon Territory, Canada, during a cyclic population increase. Neither 28-d survival nor the proportion of hares surviving to breed differed significantly between juvenile hares that dispersed and those that did not, nor was there a significant relationship between dispersal distance and fate (dead or alive). Our results indicate that the overall survival cost associated with natal dispersal is low for snowshoe hares during the early increase of the hare cycle.     

Binding, internalization, and intracellular localization of interleukin-1 beta in human diploid fibroblasts

This study demonstrates internalization of interleukin-1 (IL-1) via its cell surface receptor on human diploid fibroblasts and shows intracellular localization of IL-1 beta. Binding experiments at 8 degrees C using confluent fibroblast monolayers revealed 5,000-15,000 IL-1 receptors/cell that bound both IL-1 alpha and IL-1 beta. Incubation of monolayers with 125I-IL-1 beta (10(-9) M) at 8 degrees C and then at 37 degrees C for various times up to 8 h revealed a t1/2 for internalization of receptor-bound IL-1 beta of about 1.5 h. In addition, it was shown that IL-1 beta internalized via receptors was undegraded and retained binding activity. Electron microscopic autoradiography of monolayers incubated with 125I-IL-1 beta, as above, showed a progressive increase in the ratio of cytoplasmic to cell surface-associated grains. Grains at the cell surface were primarily localized at cell processes or attachment sites, frequently close to intra- and extracellular filamentous material. During incubation at 37 degrees C, most grains were free in the cytoplasm, with few present in lysosomes or vesicles. After 1 h, approximately 15% of the grains were over nuclei. Control cultures incubated at 37 degrees C with 125I-IL-1 beta and 100-fold excess unlabeled IL-1 beta showed increased uptake of label into lysosomes and little into nuclei. This study shows that IL-1 receptors are primarily located at fibroblast processes and that receptor-mediated internalization of the ligand is slow. Nuclear localization apparently requires IL-1 receptor-specific internalization of IL-1 beta, suggesting a possible role for this process in eliciting the IL-1 signal.     

Ca(2+) binding to cardiac troponin C: effects of temperature and pH on mammalian and salmonid isoforms

A reduction in temperature lowers the Ca(2+) sensitivity of skinned cardiac myofilaments but this effect is attenuated when native cardiac troponin C (cTnC) is replaced with skeletal TnC. This suggests that conformational differences between the two isoforms mediate the influence of temperature on contractility. To investigate this phenomenon, the functional characteristics of bovine cTnC (BcTnC) and that from rainbow trout, Oncorhynchus mykiss, a cold water salmonid (ScTnC), have been compared. Rainbow trout maintain cardiac function at temperatures cardioplegic to mammals. To determine whether ScTnC is more sensitive to Ca(2+) than BcTnC, F27W mutants were used to measure changes in fluorescence with in vitro Ca(2+) titrations of site II, the activation site. When measured under identical conditions, ScTnC was more sensitive to Ca(2+) than BcTnC. At 21 degrees C, pH 7.0, as indicated by K(1/2) (-log[Ca] at half-maximal fluorescence, where [Ca] is calcium concentration), ScTnC was 2.29-fold more sensitive to Ca(2+) than BcTnC. When pH was kept constant (7.0) and temperature was lowered from 37.0 to 21.0 degrees C and then to 7.0 degrees C, the K(1/2) of BcTnC decreased by 0.13 and 0.32, respectively, whereas the K(1/2) of ScTnC decreased by 0.76 and 0.42, respectively. Increasing pH from 7.0 to 7.3 at 21.0 degrees C increased the K(1/2) of both BcTnC and ScTnC by 0.14, whereas the K(1/2) of both isoforms was increased by 1.35 when pH was raised from 7.0 to 7.6 at 7.0 degrees C.     

The impact of acidification on diatoms and chemistry of Dutch moorland pools

Summary Moorland pools are shallow oligotrophic soft water lakes on poorly buffered sandy soils. Diatom assemblages of samples from 16 pools taken in 1920 and 1978 were compared by analysis of pH-spectra, diversity, dissimilarity and multivariate statistical techniques.The pH-spectra of pools in the southern (S) and central (C) part of the country indicate a fall in pH from 4.5–6.0 in the old samples to 3.7–4.6 in the recent ones. The pH-spectra of the northern pools (N) do not indicate a significant shift from the original pH (ca 4.5).The number of species in the count and the diversity (indices of Simpson and Shannon) decreased significantly in S+C, and that goes also for the dissimilarity index of Dyer. No changes were found in N.The first component (PC 1) of the principal component analysis explains 61% of total variance. PC 1 is correlated with log [SO₄] (r=0.83, p<0.001) and even better (r=0.95, p<0.001) with the relative sulphate concentration,i.e. the ratio of sulphate to all major anions (sulphate, chloride, bicarbonate). All old samples have low scores on PC 1, recent samples have low scores on the second (PC 2) and third (PC 3) principal component. Old samples have high scores on PC 2 and PC 3, explaining 9 and 6% of total variance, respectively.The orginal variation, caused by regional factors, is replaced by a SO₄ ^2– controlled variation. PC 1 is nearly completely determined by the relative abundance ofEunotia exigua. This species, which is known to be very resistant to pollution by sulphur, aluminium and heavy metals, increased largely from 1920 to 1978.In spite of the rather homogeneous distribution of wet sulphate deposition in the Netherlands, substantial differences in SO₄ ^2– content in the pools are observed, being lowest in N (0.13–0.48 meq.l^–1) and highest in S+C (0.38–1.65 meq.l^–1). Sulphate is positively correlated with calcium, aluminum and magnesium but negatively with factors that characterize humic acid waters (e.g. permanganate-consumption, iron and the ratio of univalent to divalent cations). Sulphate concentration depends on the intensity of sulphate reduction, accumulation by dry deposition in surrounding forests of Scots pine, drought and atmospheric deposition.     

Granulocyte-macrophage colony-stimulating factor augments the primary antibody response by enhancing the function of antigen-presenting cells

Purified, recombinant-derived murine granulocyte-monocyte colony-stimulating factor was found to enhance the primary in vitro immune response to SRBC by murine spleen cells. In determining the mechanism of this augmentation, it was found that only splenic adherent cells and neither resting nor activated T cells nor B cells expressed specific receptors for GM-CSF. When splenic adherent cells were pulsed briefly with GM-CSF before addition to macrophage-depleted cultures, they reconstituted the PFC response to a significantly greater degree than did control macrophages. Splenic adherent cells incubated overnight with SRBC plus GM-CSF were also more efficient antigen-presenting cells than splenic adherent cells incubated with antigen alone. The mechanism of this enhanced antigen presentation was found to be due to a GM-CSF-dependent increase in the level of IL 1 secretion and Ia antigen expression. Consistent with these data was the finding that GM-CSF augmented IL 2 production by splenic T cells in response to suboptimal concentrations of Con A. Finally, the day 5 in vivo antibody response (as measured by serum titers) of mice immunized with a low dose of SRBC was enhanced by two daily inoculations of GM-CSF. Thus, the role that GM-CSF plays in augmenting immune responses may not be solely accounted for by its ability to cause the proliferation or differentiation of macrophages, but more than likely includes its ability to enhance the function of antigen-presenting macrophages.     

Nematode parasitism in a northern European drosophilid community

Many factors may influence the structure of invertebrate communities. Among these is the presence of parasites which attack some or all members of a guild and potentially promote coexistence of competitor species. We assessed the prevalence of nematode (Allantonematidae) parasitism in Dutch woodland drosophilids (Diptera). Nematodes were found in 6 of the 18 drosophilid species sampled (percentage parasitism in parentheses): Drosophila phalerata (16%), D. kuntzei (5.1%), D. immigrans (0.5%), D. testacea (1.2%) and D. transversa (2.8%) were all parasitized by Howardula aoronymphium and D. subobscura (3%) was parasitized by Parazitylenchus diplogenus. This is the first report of nematode parasitism of D. immigrans and D. transversa. There were no important seasonal trends in percentage parasitism. We explored the consequences of nematode parasitism for individual drosophilids. Nematodes did not exert an important influence on the wing length (adult body size) of the drosophilids we sampled, but egg loads (fecundities) of female D. phalerata, D. subobscura and D. kuntzei were reduced by nematode parasitism. Parasitism rates were positively correlated with relative host abundance, in Dutch and other communities, suggesting that species diversity is promoted by a disproportionately high parasitism of more common host species.