Developmental exposure to vasopressin increases aggression in adult prairie voles. (9/710)

Although the biological roots of aggression have been the source of intense debate, the precise physiological mechanisms responsible for aggression remain poorly understood. In most species, aggression is more common in males than females; thus, gonadal hormones have been a focal point for research in this field. Although gonadal hormones have been shown to influence the expression of aggression, in many cases aggression can continue after castration, indicating that testicular steroids are not completely essential for the expression of aggression. Recently, the mammalian neuropeptide arginine vasopressin (AVP) has been implicated in aggression. AVP plays a particularly important role in social behavior in monogamous mammals, such as prairie voles (Microtus ochrogaster). In turn, the effects of social experiences may be mediated by neuropeptides, including AVP. For example, sexually naive prairie voles are rarely aggressive. However, 24 h after the onset of mating, males of this species become significantly aggressive toward strangers. Likewise, in adult male prairie voles, central (intracerebroventricular) injections of AVP can significantly increase intermale aggression, suggesting a role for AVP in the expression of postcopulatory aggression in adult male prairie voles. In this paper, we demonstrate that early postnatal exposure to AVP can have long-lasting effects on the tendency to show aggression, producing levels of aggression in sexually naive, adult male prairie voles that are comparable to those levels observed after mating. Females showed less aggression and were less responsive to exogenous AVP, but the capacity of an AVP V(1a) receptor antagonist to block female aggression also implicates AVP in the development of female aggression.  (+info)

Water vole (Arvicola terrestris scherman) density as risk factor for human alveolar echinococcosis. (10/710)

Concern is growing in Europe about alveolar echinococcosis (AE) with the increase in grassland rodent and red fox populations, intermediate and definitive hosts for Echinococcus multilocularis, respectively. The objective of this study was to assess the influence of rodent densities on human AE distribution. Spatial Poisson regression analyses were performed with geomorphologic features, landscape composition, climatic characteristics, and water vole density as independent variables. The outcome consisted of AE cases diagnosed over the period 1980-1992. High vole density yielded a 10-fold risk (relative risk [RR] = 10.34, 95% confidence interval [CI] = 2.78-38.39), and the first plateau (400-700 m altitude) compared with the plain (200-400 m) was associated with a large increase in risk (RR = 7.10, 95% CI = 1.30-38.63). These results confirm that human AE is strongly influenced by the densities of arvicolid species. Foxes feeding almost exclusively on grassland rodents when the latter expand could mediate this relation.  (+info)

Role of steroid hormones in Trichinella spiralis infection among voles. (11/710)

Males are generally more susceptible to parasite infection than females. This sex difference may reflect the suppressive effects of testosterone and enhancing effects of estradiol on immune function. This study characterized the role of circulating steroid hormones in sex differences after infection with the nematode Trichinella spiralis. Because testosterone suppresses immune function and because polygynous males have higher circulating testosterone concentrations than monogamous males, sex differences in parasite burden were hypothesized to be exaggerated among polygynous meadow voles compared with monogamous prairie voles. As predicted, sex differences in response to T. spiralis infection were increased among meadow voles; males had higher worm numbers than females. Male and female prairie voles had equivalent parasite burden. Overall, prairie voles had higher worm numbers than meadow voles. Contrary to our initial prediction, differences in circulating estradiol concentrations in females, testosterone concentrations in males, and corticosterone concentrations in both sexes were not related to the observed variation in T. spiralis infection. Taken together, these data suggest that not all sex differences in parasite infection are mediated by circulating steroid hormones and that adaptive-functional explanations may provide new insight into the causes of variation in parasite infection.  (+info)

Transmission dynamics of a zoonotic pathogen within and between wildlife host species. (12/710)

The transmission dynamics of the cowpox virus infection have been quantified in two mixed populations of bank voles (Clethrionomys glareolus) and wood mice (Apodemus sylvaticus), through analyses of detailed time-series of the numbers of susceptible, infectious and newly infected individuals. The cowpox virus is a zoonosis which circulates in these rodent hosts and has been shown to have an adverse effect on reproductive output. The transmission dynamics within species is best described as frequency dependent rather than density dependent, contrary to the 'mass action' assumption of most previous studies, both theoretical and empirical. Estimation of a transmission coefficient for each species in each population also allows annual and seasonal variations in transmission dynamics to be investigated through an analysis of regression residuals. Transmission between host species is found to be negligible despite their close cohabitation. The consequences of this for the combining ability of hosts as zoonotic reservoirs, and for apparent competition between hosts, are discussed.  (+info)

PCR detection of granulocytic ehrlichiae in Ixodes ricinus ticks and wild small mammals in western Switzerland. (13/710)

The presence of granulocytic ehrlichiae was demonstrated by PCR in Ixodes ricinus ticks and wild small mammals in Switzerland in two areas of endemicity for bovine ehrlichiosis. Six ticks (three females and three nymphs) (1.4%) of 417 I. ricinus ticks collected by flagging vegetation contained ehrlichial DNA. A total of 201 small mammals from five species, wood mouse (Apodemus sylvaticus), yellow-necked mouse (Apodemus flavicollis), earth vole (Pitymys subterraneus), bank vole (Clethrionomys glareolus), and common shrew (Sorex araneus), were trapped. The analysis of I. ricinus ticks [corrected] collected on 116 small mammals showed that nine C. glareolus voles and two A. sylvaticus mice hosted infected tick larvae. In these rodents, granulocytic ehrlichia infection was also detected in blood, spleen, liver, and ear samples. Further examinations of 190 small mammals without ticks or with noninfected ticks showed the presence of ehrlichial DNA in spleen and other tissues from six additional C. glareolus, three A. flavicollis, and one S. araneus mammals. This study suggests that A. sylvaticus, A. flavicollis, S. araneus, and particularly C. glareolus are likely to be natural reservoirs for granulocytic ehrlichiae. Partial 16S rRNA gene sequences of granulocytic ehrlichiae from ticks and rodents showed a high degree of homology (99 to 100%) with granulocytic ehrlichiae isolated from humans. In contrast, groESL heat shock operon sequence analysis showed a strong divergence (approximately 5%) between the sequences in samples derived from rodents and those derived from samples from questing ticks or from other published ehrlichia sequences. Dual infections with granulocytic ehrlichia and Borrelia burgdorferi were found in ticks and small mammals.  (+info)

Experimental tests of predation and food hypotheses for population cycles of voles. (14/710)

Pronounced population cycles are characteristic of many herbivorous small mammals in northern latitudes. Although delayed density-dependent effects of predation and food shortage are often proposed as factors driving population cycles, firm evidence for causality is rare because sufficiently replicated, large-scale field experiments are lacking. We conducted two experiments on Microtus voles in four large predator-proof enclosures and four unfenced control areas in western Finland. Predator exclusion induced rapid population growth and increased the peak abundance of voles over 20-fold until the enclosed populations crashed during the second winter due to food shortage. Thereafter, voles introduced to enclosures which had suffered heavy grazing increased to higher densities than voles in previously ungrazed control areas which were exposed to predators. We concluded that predation inhibits an increase in vole populations until predation pressure declines, thus maintaining the low phase of the cycle, but also that population cycles in voles are not primarily driven by plant-herbivore interactions.  (+info)

The initial pathogenesis of cadmium induced renal toxicity. (15/710)

The novel application of magic angle spinning 1H NMR spectroscopy, coupled with pattern recognition techniques, has identified biochemical changes in lipid and glutamate metabolism that precede classical nephrotoxicity. These changes occurred in the bank vole (Clethrionomys glareolus) after chronic dosing, at a low level of exposure and at a renal Cd(2+) concentration (8.4 microgram/g dry wt) that was nearly two orders of magnitude below the WHO critical organ concentration (200 microg/g wet wt). These early stage effects of Cd(2+) on the biochemistry of renal tissue may reflect adaptation mechanisms to the toxic insult or the preliminary stages of the toxicological cascade.  (+info)

In vitro antibiotic susceptibility of Francisella tularensis isolated from humans and animals. (16/710)

The in vitro susceptibility of 38 strains of Francisella tularensis (biovar F. tularensis palaearctica) was determined using Etests on cysteine heart agar plates with 2% haemoglobin. All strains were susceptible to the antibiotics traditionally used to treat tularaemia, such as streptomycin (MIC(90) 4.0 mg/L), tetracycline (MIC(90) 0.38 mg/L) and chloramphenicol (MIC(90) 0.38 mg/L), and to aminoglycosides, such as tobramycin (MIC(90) 1.5 mg/L) and gentamicin (MIC(90) 1.0 mg/L). The quinolones examined had low MIC(90)s: ciprofloxacin, 0.016 mg/L; levofloxacin, 0.016 mg/L; grepafloxacin, 0.047 mg/L; and trovafloxacin, 0.032 mg/L. In contrast, all the strains were resistant to beta-lactams and azithromycin. Quinolones thus seem to be promising drugs for the treatment of tularaemia.  (+info)