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PubMed1975

Elimination of 137-Cs and 59-Fe and its relationship to metabolic rates of wild small rodents.

Elimination of 137-Cs and 59-Fe by three species of wild rodents was measured in laboratory and field experiments to determine whether excretion rates of these nuclides are influenced directly by general metabolic (CO-2 production) rates. Sigmodon hispidus and Peromyscus leucopus were used in both field and laboratory experiments, and Reithrodontomys humulis was investigated only in the laboratory. Final-component biological half-lives (Tb) of 59-Fe for Sigmodon averaged 108 days in winter, 144 days in spring, and means ranged from 176 to 242 days under various laboratory conditions (ambient temperature, cold-exposure, irradiation, and chemical metabolic inhibition); for Peromyscus, values were 50 days in winter 47 days in spring, and 289 days (at ambient temperature only) in the laboratory; for Reithrodontomys mean values ranged from 121 to 178 days at different laboratory treatment levels. Biological half-lives of final-component 137-Cs elimination for Sigmodon averaged 7.5 days in winter, 7.9 days in spring, and means ranged from 7.7 to 8.6 days at the different treatment levels in the laboratory. Laboratory mean values for Reithrodontomys ranged from 3.5 to 3.9 days. For Peromyscus, Tb values averaged 3.4 days in winter, 3.6 days in spring, and 3.5 days in the laboratory. The data suggested that elimination of 59-Fe is influenced by metabolic rates of rodents in the field, but laboratory experiments were unable to demonstrate any predictable relationship. Neither did the rate of final-component 137-Cs loss from rodents appear to be influenced by metabolic rate in the laboratory or in the field. However, final-component Y-axis intercept values of 137-Cs exhibited a linear correlation with metabolic rates, and equations were derived from these intercept values to predict metabolism in the field for two species: for Sigmodon, Daily Average CO-2 Production (ml/hr/g, STP) [5.24-0.9172 (log-ea)] [0.886]; and for Reithrodontomys, = [12.51-1.80 (log-ea)] [0.886].

Animals↗
PubMed2004

Habitat-related variation in infestation of lizards and rodents with Ixodes ticks in dense woodlands in Mendocino County, California.

During the spring and early summer of 2002, we examined the relative importance of Borrelia-refractory lizards (Sceloporus occidentalis, Elgaria spp.) versus potential Borrelia burgdorferi sensu lato (s.l.)-reservoirs (rodents) as hosts for Ixodes pacificus immatures in 14 woodland areas (six oak, five mixed oak/Douglas fir, and three redwood/tanoak areas) distributed throughout Mendocino County, California. Lizards were estimated to serve as hosts for 93-98% of all larvae and > or =99.6% of all nymphs infesting lizards or rodents in oak woodlands and oak/Douglas fir sites in the southern part of the county. In redwood/tanoak woodlands and oak/Douglas fir sites in northern Mendocino County, the contribution of rodents to larval feedings reached 36-69% but lizards still accounted for 94-100% of nymphal bloodmeals. From late April to mid-June, I. pacificus larvae were recovered from 95 to 96% of lizards and dusky-footed woodrats (Neotoma fuscipes) and from 59% of Peromyscus spp. mice. In contrast, 99% of lizards but few woodrats (15%) and none of the mice were infested by nymphs. Comparisons of tick loads for 19 lizard-Peromyscus spp. mouse pairings, where the lizard and mouse were captured within 10m of each other, revealed that the lizards harbored 36 times more larvae and >190 times more nymphs than the mice. In oak woodlands, loads of I. pacificus larvae decreased from late April/early May to late June for S. occidentalis lizards but increased for Peromyscus spp. mice. We conclude that the relative utilization of Borrelia-refractory lizards, as compared to rodents, by I. pacificus larvae was far higher in dry oak woodlands than in moister habitats such as redwood/tanoak and oak/Douglas fir woodlands in northern Mendocino County. Non-lizard-infesting potential enzootic vectors of B. burgdorferi s.l. (I. angustus and I. spinipalpis) were recorded from rodents in three of six oak woodland areas, two of five oak/Douglas fir woodland areas, and two of three redwood/tanoak woodland areas.

Animals↗
PubMed1998

Deer Mice As Laboratory Animals.

Although laboratory mice (Mus) and rats (Rattus) are the most widely used research rodents, deer mice (Peromyscus maniculatus) and their congeneric species are favored as nontraditional alternatives for some purposes. Mice of the native genus Peromyscus are the most abundant and widely distributed rodents in North America. They occur in a great diversity of habitats and play a significant role in natural ecosystems. Because of their abundance, peromyscines are commonly hosts for larva of ticks that transmit Lyme disease bacteria, and they are implicated in several other vector-borne diseases. Deer mice also are the principal carriers of the virus that causes hantaviral pulmonary syndrome, or "Four Corners disease." Deer mice are useful as laboratory models for a variety of other types of pure and applied research. They are easily maintained and bred in captivity using the husbandry protocols developed for other small laboratory rodent species. The Peromyscus Genetic Stock Center at the University of South Carolina maintains more than 50 laboratory-bred, well-characterized stocks of deer mice and other peromyscine species for research and educational use.

Journal Article↗
PubMed1985

Serological and virological evidence of a Hantaan virus-related enzootic in the United States.

The first isolation of a Hantaan-related virus from a feral rat in the United States was made from a Rattus norvegicus caught in New Orleans. The strain, designated Tchoupitoulas virus, is antigenically related to, but distinct from, the prototype strain 76-118 of Hantaan virus and is the first Hantaan-like virus isolated from the pancreas of a naturally infected animal. Serosurveys of wild rodents from urban and rural areas in the United States indicated that Hantaan-related viruses infected urban rats in coastal and inland cities and infected five species of New World rodents in the western United States (Peromyscus maniculatus, Peromyscus difficilis, Peromyscus californicus, Neotoma mexicana, and Neotoma cinerea). Serosurveys disclosed no evidence of Hantaan-virus infection in rats in large-scale breeding colonies.

Animals↗
PubMed2004

Detection and characterization of Borrelia bissettii in rodents from the central California coast.

This is the first report of Borrelia burgdorferi sensu lato in rodents from San Luis Obispo county, with most isolates obtained from a previously unreported host, Neotoma lepida Thomas. B. burgdorferi sensu lato was identified in seven rodent species, including the California vole, Microtus californicus Peale; dusky-footed woodrat, Neotoma fuscipes Baird; desert woodrat, Neotoma lepida Thomas; brush mouse, Peromyscus boylii Baird; California mouse, Peromyscus californicus Gambel; deer mouse, Peromyscus maniculatus Wagner; and western harvest mouse, Reithrodontomys megalotis Baird. Ear punch biopsies were cultured in BSK-H medium from 179 rodents trapped at six different study sites. Overall, prevalence of rodent infection was 44/179 (24.6%), with 34 of these isolates from N. lepida. Spirochete isolates were obtained from rodents at all study sites, indicating widespread prevalence of B. burgdorferi sensu lato across rodent species and habitats. Nucleotide sequences for 14 of these isolates have been submitted to GenBank. Isolates from three N. lepida and one P. boylii had identical flagellin gene sequences, and phylogenetic analysis placed these spirochetes in B. burgdorferi sensu lato group DN127, now known as B. bissettii Postic, Marti Ras, Lane, Hendson & Baranton. Additional sequencing of the intergenic spacer regions between the 5S and 23S ribosomal genes was performed on three of these isolates. Phylogenetic analysis separated these isolates into two clusters that grouped with Colorado or California isolates. The role of B. bissettii and related species other than B. burgdorferi sensu stricto Johnson, Schmid, Hyde, Steigerwalt & Brenner as human pathogens in the United States warrants further investigation.

Animals↗
PubMed2004

Rodent-flea-plague relationships at the higher elevations of San Diego County, California.

Rodent-flea-plague relationships were examined at sites located at higher elevations of San Diego County during 1991-2002. The most frequently sampled rodents were the California ground squirrel, Spermophilus beecheyi, and white-footed mice, Peromyscus spp. Higher seasonal mean dependent variables (prevalences of squirrels and indices of O. montana), higher mean amounts of seasonal rainfall, and lower seasonal mean ambient temperatures were found at sites during 1991--1993 compared with 2000--2002. Levels of plague antibody indicate that squirrels seroconverted at most sites during spring/early summer when exposed to infected fleas when cleaning out burrows following hibernation, when interacting more with other squirrels occurred establishing home ranges, and when dispersing juveniles occupied abandoned burrows containing old nests. The majority of squirrels (35/41) were reported seropositive at Heise County Park (elev. 1,281 m) during 1996, 2001, and 2002. This may reflect fewer fleas biting squirrels more often when squirrels spent more time below-ground in order to avoid higher ambient temperatures. In contrast, most squirrels (12/13) were reported seropositive at two higher sites (elev. 1,584 and 1,641 m) on Palomar Mountain during 1993--1996 when there were higher mean dependent variables and amounts of seasonal rainfall compared with 1999--2002. This increased rainfall may have benefited host and flea populations and thus plague transmission. Seasonal indices were usually reduced after dusting squirrel burrows with 2% diazinon dust. Findings also indicated that S. beecheyi is a primary reservoir for plague at the higher elevations of these and other sites in southern California, and that the deer mouse, Peromyscus maniculatus, and other Peromyscus spp. were not major host reservoirs at the sites sampled.

Analysis of Variance↗
PubMed1993

Biochemical correlates of longevity in two closely related rodent species.

The objective of this study was to explore the basis of variations in the life span and metabolic potential, i.e., total amount of energy consumed during life, between different species, in context of the free radical hypothesis of aging. A comparison was made between the house mouse (Mus musculus) and the white-footed mouse (Peromyscus leucopus): the latter has > 2-fold greater life span and metabolic potential than the former. Longer life span and higher metabolic potential of Peromyscus were associated with low rates of mitochondrial O2.- and H2O2 generation, higher activities of catalase and glutathione peroxidase and low levels of protein oxidative damage as well as low susceptibility to oxidative damage in response to experimental oxidative stress. Results support the role of oxidative stress in aging.

Aging↗
PubMed1999

A direct repeat sequence at the Rasgrf1 locus and imprinted expression.

Genomic imprinting is an epigenetic modification that can lead to parental-specific monoallelic expression of specific autosomal genes. While methylation of CpG dinucleotides is thought to be a strong candidate for this epigenetic modification, little is known about the establishment or maintenance of parental origin-specific methylation patterns. We have recently identified a portion of mouse chromosome 9 containing a paternally methylated region associated with a paternally expressed imprinted gene, Ras protein-specific guanine nucleotide-releasing factor 1 (Rasgrf1). This area of chromosome 9 also contains a short, direct tandem repeat in close proximity to a paternally methylated NotI site 30 kb upstream of Rasgrf1. Short, direct tandem repeats have been found associated with other imprinted genes and may act as important regulatory structures. Here we demonstrate that two rodent species (Mus and Rattus) contain a similar direct repeat structure associated with a region of paternal-specific methylation. In both species, the Rasgrf1 gene shows paternal-specific monoallelic expression in neonatal brain. A more divergent rodent species (Peromyscus) appears to lack a similar repeat structure based on Southern Blot analysis. Peromyscus animals show biallelic expression of Rasgrf1 in neonatal brain. These results suggest that direct repeat elements may play an important role in the imprinting process.

Animals↗
PubMed1993

Relative utilization of reptiles and rodents as hosts by immature Ixodes scapularis (Acari: Ixodidae) in the coastal plain of North Carolina, USA.

The interaction of immature black-legged ticks, Ixodes scapularis, with reptiles and rodents was investigated in various woodland habitats in the coastal plain of North Carolina. Reptiles were sampled from April 1 to September 30, 1991. No ticks were found on 95 specimens representing 16 species of snakes. Ticks were found on 54 (36.7%) of 147 lizards. I. scapularis was the only tick recovered from lizards. Some lizards were collected in drift fence traps each month of the study except August. Capture rates averaged one lizard per 16 trap-days. Larvae and nymphs of I. scapularis were removed from the southeastern five-lined skink (Eumeces inexpectatus), the ground skink (Scincella lateralis), the broad-headed skink (E. laticeps) and the eastern glass lizard (Ophisaurus ventralis), but ticks were not found on three other lizard species. Tick infestation rates and loads for parasitized species are presented. Ticks were almost exclusively attached at the base or in the axils of forelimbs of skinks and in the lateral grooves of eastern glass lizards. Rodents were live-trapped at sites where lizards were sampled and at other sites from 1 July, 1990 to 30 January, 1992. Capture rates averaged one rodent per 47 trap-nights. Ticks were found on 23 (17.8%) of 129 animals inspected. Five species of rodents were examined but only four species were found to be tick-infested. In contrast to lizards, few I. scapularis were collected. Rodents, principally the white-footed mouse (Peromyscus leucopus) and cotton mouse (P. gossypinus) were most frequently infested with immature American dog ticks, Dermacentor variabilis, during winter and early spring months. Burdens of D. variabilis on these rodents averaged 0.3 ticks per rodent. Effects of the diversion of ticks from feeding on Peromyscus mice on the transmission of the Lyme disease spirochete are discussed.

Animals↗
PubMed1980

Differences in activity in cerebral methyltransferases and monoamine oxidases between audiogenic seizure susceptible and resistant mice and deermice.

The specific acitivity of cerebral histamine N-methyltransferase (HMT) was significantly lower in the audiogenic seizure-susceptible (SS) 21-day old DBA/2J mouse when compared to the non-susceptible 70-day old DBA/2J mouse but not when compared to the seizure resistant (SR) C57B1/6J mouse at 21 days of age. There was no significant difference between the two strains at 70 days of age. The lower HMT specific activity was also observed in a SS mutant of the deermouse Peromyuscus maniculatus, relative to the SR, wild-type animal. The activity of cerebral catechol-O-methyltransferase (COMT) was significantly lower in the DBA/2J mice relative to the C57B1/6J at 21 and 70 days while, in Peromyscus, it was higher in the SS mutant than in the SR animal. The activity of MAO, B was lower in the 21-day old, relative to the 70-day old DBA/2J and the 21-day old C57B1/6J mice. There were no differences in MAO A or B between SS and SR Peromyscus. The findings raise the possibility that cerebral methylation may operate at characteristic rates in SS animals.

Acoustic Stimulation↗
PubMed1985

Minimal metabolism, summit metabolism and plasma thyroxine in rodents from different environments.

Rodents were live-trapped in three environments (desert, intermediate and coastal) in Southern California, USA, chosen because of the taxonomic overlap of species. Upon capture, blood samples were taken and plasma thyroxine concentrations were measured. Four species (Dipodomys merriami, Perognathus fallax, Peromyscus eremicus and Peromyscus californicus) were returned to the laboratory for measurement of minimal and summit rates of metabolism. Heteromyid rodents had significantly lower plasma thyroxine concentrations (14-44 nmol l-1) than cricetid rodents (18-93 nmol l-1). Although there was significant habitat difference in plasma thyroxine levels, this influence was not constant between heteromyid and cricetid rodents. In most species, the desert individuals had the lowest plasma thyroxine concentration. Minimal metabolic rates were lower than expected in all four species, as well as in the tropical heteromyid Liomys salvini and summit metabolic rates were similarly reduced in all species. Upon capture there was considerable variation in plasma thyroxine concentration of different species (23-93 nmol l-1). However, following 10 weeks in captivity, the range and variability of plasma thyroxine levels in these species was considerably reduced (32-64 nmol l-1).

Animals↗
PubMed2006

Weak winner effect in a less aggressive mammal: correlations with corticosterone but not testosterone.

We investigated the existence of the "winner effect" (winning an aggressive encounter following previous victories) and an associated rise in testosterone (T) in the white-footed mouse (Peromyscus leucopus) which generally display low levels of aggression and territoriality. We compared the effect of previously winning three, two, one, or zero resident-intruder encounters on the likelihood of winning a subsequent aggressive encounter. Although 50% of males were removed during training because of peaceful encounters, the winner effect was weak and not significant. We hypothesize that territoriality/aggression may be associated with the strength of the winner effect and discuss whether the slight winner effect exhibited by P. leucopus may become significant when population densities increase and males become more territorial. There was also no associated change in T with winning; however, corticosterone (Cort) changed with experience as winners had low Cort levels compared to losers and controls. Furthermore, low Cort levels in winners were associated with quicker attack latencies. These results contrast with findings of a significant winner effect and increase in T in males of the highly territorial and aggressive California mouse (Peromyscus californicus) using an identical methodology. California mice also attacked their opponents at more caudal regions of the body compared to white-footed mice that attacked their opponents at more rostral regions of the body, possibly related to different levels/types of aggression expressed by the two species.

Aggression↗
PubMed1997

Role of small mammals in the ecology of Borrelia burgdorferi in a peri-urban park in north coastal California.

The role of small mammals other than woodrats in the enzootiology of the Lyme disease spirochete, Borrelia burgorferi, was assessed in the peri-urban park. Mammals were collected monthly from September through to April. Following tick removal, the animals were tested for B. burgdorferi by culture of ear-punch biopsies. Larvae and nymphs that were intermediate in morphology between Ixodes spinipalpis and Ixodes neotomae occurred on several species of rodents (Peromyscus truei, Peromyscus californicus, Microtus californicus, Rattus rattus and Reithrodontomys megalotis) and the brush rabbit (Sylvilagus bachmani). Morphometric analyses of these I. spinipalpis-like ticks and the offspring from two I. neotomae females from the site suggest that I. neotomae may bo conspecific with I. spinipalpis. Borrelia burgdorferi was isolated from eight out of 109 (7.3%), three out of 16 (18.8%), two out of 38 (5.3%) and two out of six (33.3%) P. truei, P. maniculatus, M. californicus and R. rattus, respectively. One bush rabbit yielded the first isolate of B. burgdorferi from a lagomorph in western North America. This isolate and three others derived from unfed I. spinipalpis-like nymphs failed to produce infection when inoculated intradermally into 11-12 P. maniculatus each. Likewise, no spirochetes were detected in 420 Ixodes pacificus nymphs derived from larvae fed on animals inoculated with these isolates. An additional isolate, derived from an I. spinipalpis-like nymph, was recovered by ear-punch biopsies from five our of 12 (42%) needle-inoculated P. maniculatus. However, spirochetes were not detected in 20 I. pacificus nymphs fed as larvae on each of five mice (two infected and three uninfected) inoculated with this isolate. We conclude that brush rabbits and several species of rodents besides woodrats may contribute to the maintenance of B. burgdorferi because they harbour the spirochete and are fed upon by competent enzootic vectors.

Animals↗
PubMed2002

Experimental evaluation of rodent exclusion methods to reduce hantavirus transmission to residents in a Native American community in New Mexico.

We conducted a pilot study to evaluate the efficacy of rodent proofing continuously occupied homes as a method for lowering the risk for hantavirus pulmonary syndrome (HPS) among residents of a Native American community in northwestern New Mexico. Rodent proofing of dwellings was paired with culturally appropriate health education. Seventy homes were randomly assigned to treatment or control categories. Treatment homes were rodent-proofed by sealing openings around foundations, doors, roofs, and pipes and repairing screens and windows. Repairs to each dwelling were limited to $500 US. After repairs were completed, 15-20 snap traps were placed in each treatment and control home and checked approximately every 2 days for an average of 3-4 weeks. During 23,373 trap nights, one house mouse (Mus musculus) was captured in one treatment home, and 20 mice (16 deer mice, Peromyscus maniculatus, two Pinyon mice, Peromyscus truei, and two unidentified mice) were captured in five control homes (one house had 14 captures, two had two captures, and two had one capture). Trap success was 0.01% in treatment homes and 0.15% in controls. Intensity of infestation (mean number of mice captured per infested home) was 1 in treatment homes and 4 in controls. Observations of evidence of infestation (feces, nesting material, gnaw marks, or reports of infestation by occupant) per 100 days of observation were 1.2 in treatment homes and 3.1 in controls. Statistical power of the experiment was limited because it coincided with a period of low rodent abundance (August-November 2000). Nevertheless, these results suggest that inexpensive rodent proofing of occupied rural homes can decrease the frequency and intensity of rodent intrusion, thereby reducing the risk of HPS among rural residents in the southwestern United States.

Animals↗
PubMed2006

Mammal diversity and infection prevalence in the maintenance of enzootic Borrelia burgdorferi along the western Coastal Plains of Maryland.

The primary vector of Borrelia burgdorferi in North America, Ixodes scapularis, feeds on various mammalian, avian, and reptilian hosts. Several small mammal hosts; Peromyscus leucopus, Tamias striatus, Microtus pennsylvanicus, and Blarina spp. can serve as reservoirs in an enzootic cycle of Lyme disease. The primary reservoir in the northeast United States is the white-footed mouse, P. leucopus. The infection prevalence of this reservoir as well as the roles of potential secondary reservoirs has not been established in southern Maryland, a region of low to moderate Borrelia infection in humans. Intensive trapping at 96 locations throughout the western Coastal Plains of Maryland was conducted and we found that 31.6% of P. leucopus were infected with B. burgdorferi. Sequence and phylogenetic analysis revealed that only B. burgdorferi sensu stricto circulated in southern Maryland. Feral house mice and voles also were infected and may serve as secondary hosts. Peromyscus gender, age and month of capture were significantly associated with infection status. Larval I. scapularis were the dominant ectoparasite collected from captured rodents even though host seeking A. americanum and D. variabilis were collected in greater numbers across the sampling region. Our findings illustrate that the enzootic cycle of LD is maintained in the western Coastal Plains region of southern Maryland between I. scapularis and P. leucopus as the dominant reservoir.

Animals↗
PubMed1999

Effects of morphine on electrically evoked contractions of the vas deferens in two congeneric rodent species differing in sperm competition intensity.

An early prediction of sperm competition theory was that males should adjust the number of sperm they deliver according to the risk of double mating and this has received empirical support in recent years. It has been suggested that adaptive regulation of sperm delivery in mammals may depend on changes in vas deferens contractility. In laboratory mice, the vas deferens is sensitive to opioid agonists and the secretion of endogenous opioid peptides can be affected by social interactions that may be predictive of sperm competition risk. The present experiment was conducted to determine whether morphine, an opioid agonist (at the mu-receptor), has different effects on electrically evoked contractions of the isolated vas deferens in two congeneric rodent species differing in sperm competition intensity. Morphine inhibited contractions of the vas deferens in the non-monogamous deer mouse (Peromyscus maniculatus) but not the monogamous California mouse (Peromyscus californicus). This implies that the vas deferens of P. maniculatus possesses functional mu-receptors and, thus, should be able to respond to changes in the circulating levels of endogenous agonists whose secretion can be affected by social interactions predictive of sperm competition risk.

Animals↗
PubMed1991

Survey for Ixodes spp. and Borrelia burgdorferi in southeastern Wisconsin and northeastern Illinois.

Forested areas adjacent to Milwaukee, Wis., and Chicago, Ill., were investigated for rodents and ticks infected with Borrelia burgdorferi, the causative agent of Lyme disease. White-footed mice (Peromyscus leucopus or Peromyscus maniculatus), meadow voles (Microtus pennsylvanicus), and eastern chipmunks (Tamias striatus) were captured; and specimens from these animals were cultured for B. burgdorferi to define whether the midwestern Lyme disease area currently encompasses these large metropolitan centers. During 1988, B. burgdorferi was successfully cultured from the tissues of two M. pennyslvanicus voles captured from the Chicago area. However, no Ixodes spp. ticks were captured. None of 274 animals captured from sites I3 and 12 additional sites in Wisconsin and Illinois during the summer of 1989 were infected with B. burgdorferi or Ixodes spp. In addition, no ticks were recovered when the underbrush in 11 contiguous areas was flagged. Apparently, B. burgdorferi is rarely found in these areas because of the absence of the appropriate tick vectors. Further studies are needed to monitor the dispersal of B. burgdorferi-infected Ixodes dammini into this heavily populated midwestern region.

Animals↗
PubMed1992

Antibodies to Borrelia burgdorferi in rodents in the eastern and southern United States.

Serologic studies were conducted to determine whether white-footed mice (Peromyscus leucopus) and cotton mice (Peromyscus gossypinus) contained serum antibodies to Borrelia burgdorferi, the causative agent of Lyme borreliosis. Enzyme-linked immunosorbent assays detected antibodies to this spirochete in 35.7 and 27.3% of 56 P. leucopus and 535 P. gossypinus serum samples, respectively, collected in Connecticut, North Carolina, South Carolina, Georgia, Florida, Alabama, and Mississippi. Antibody titers ranged from 1:160 to greater than or equal to 1:40,960. On the basis of adsorption tests, the antibodies detected appeared to be specific to Borrelia spirochetes. Seropositive rodents in the eastern and southern United States, areas where human cases of Lyme borreliosis have been reported, indicate a widespread geographic distribution of B. burgdorferi or a closely related spirochete.

Animals↗