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PubMed2006

Schistosome infection in deer mice (Peromyscus maniculatus): impacts on host physiology, behavior and energetics.

Animals routinely encounter environmental stressors and may employ phenotypic plasticity to compensate for the costs of these perturbations. Parasites represent an ecologically important stressor for animals, which may induce host plasticity. The present study examined the effects of a trematode parasite, Schistosomatium douthitti, on deer mouse (Peromyscus maniculatus) physiology, behavior and energetics. Measures were taken to assess direct parasite pathology as well as potential host plasticity used to reduce the costs of these pathologies. Parasitized mice had increased liver and spleen masses, as well as decreased liver protein synthesis. Parasitism also led to increased gastrointestinal (GI) mass, either directly due to parasite presence or as host compensation for decreased GI function. No additional plasticity was recorded - infected animals did not consume more food, decrease in body mass or reduce their activity. Parasitism led to reduced thermoregulation during short-term cold exposure, indicating that there may be fitness costs of parasitism. There were no changes in the other measures of energetics taken here, namely basal metabolic rate (BMR) and cold-induced maximal metabolic rate (MR(max)). Together, the results suggest that many costs of parasite infection are largely ameliorated through physiological or morphological compensatory mechanisms.

Animals↗
PubMed1986

Heat loss from deer mice (Peromyscus): evaluation of seasonal limits to thermoregulation.

This paper investigates the influence of seasonal adaptations to thermoregulatory heat loss for deer mice (Peromyscus) during summer and winter. A general, mechanistic model of heat transfer through fur was evaluated for the structural properties of the fur of deer mice. The model was validated against heat production determined from mice exposed to a range of radiative (wall) temperatures (tr) at air temperatures (ta) of 15, 27 and 34 degrees C. Calculated heat loss from the appendages was subtracted from the measured heat production to yield heat loss from the furred torso. This calculated torso heat loss agreed closely with the predicted fur heat loss for all conditions, as shown by a regression slope near 1 (0.99). Simulations using models of fur and appendage heat loss reveal that the winter increase in thermogenic (heat production) capacity has a greater effect than changes in fur properties in expanding the limits to thermoregulation. Both wind and a clear night sky increase heat loss and can limit thermoregulation to air temperatures above those found in deer mice habitats during winter (-25 degrees C). Thus, despite seasonal adaptations, these simulations indicate that thermoregulation is not possible under certain winter conditions, thereby restricting deer mice to within the protected environment of the leaf litter or snow tunnels.

Acclimatization↗
PubMed1996

Sexually dimorphic spatial learning in meadow voles Microtus pennsylvanicus and deer mice Peromyscus maniculatus.

A number of studies examining developmental, neural and hormonal aspects of sexually dimorphic spatial learning (Morris water-maze) in meadow voles (Microtus pennsylvanicus) and deer mice (Peromyscus maniculatus) are described. We found that, in adult deer mice, female spatial performance decreased during the breeding season relative to the non-breeding season, whereas the reverse pattern was observed in male performance. There was a sex difference favouring males in spatial learning during the breeding season, but not during the non-breeding season. In adult meadow voles, females with low levels of oestradiol and males performed better in the water-maze than females with high levels of oestradiol. Postweaning voles (20 and 25 days after birth) acquired the water-maze task more quickly than preweaning voles (day 10). No sex difference in water-maze performance was evident at any of these juvenile ages. When these same voles were tested again as adults to investigate retention and re-acquisition of the water-maze, both males and females from male-biased litters re-acquired the task better than males and females from female-biased litters. Together, the results of these studies indicate that sexually dimorphic spatial ability is dependent on the organization (in utero) and activational effects of gonadal hormones. These studies provide the first demonstration of the influence of natural changes in reproductive status on spatial learning of deer mice and meadow voles. The results also demonstrate that spatial performance of males and females is differentially affected by changes in reproductive status and that group differences in the laboratory are associated with group differences in space utilization in the wild. These findings help to clarify previous apparently contradictory findings about sex differences in spatial ability.

Animals↗
PubMed2001

Pathogenesis of experimental vesicular stomatitis virus (New Jersey serotype) infection in the deer mouse (Peromyscus maniculatus).

The pathogenesis of vesicular stomatitis virus (VSV) infection has not been investigated previously in native New World rodents that may have a role in the epidemiology of the disease. In the present study, 45 juvenile and 80 adult deer mice (Peromyscus maniculatus) were inoculated intranasally with VSV New Jersey serotype (VSV-NJ) and examined sequentially over a 7-day period. Virus was detected by means of immunohistochemistry and in situ hybridization in all tissues containing histologic lesions. Viral antigen and mRNA were observed initially in olfactory epithelium neurons, followed by olfactory bulbs and more caudal olfactory pathways in the brain. Virus also was detected throughout the ventricular system in the brain and central canal of the spinal cord. These results support both viral retrograde transneuronal transport and viral spread within the ventricular system. Other tissues containing viral antigen included airway epithelium and macrophages in the lungs, cardiac myocytes, and macrophages in cervical lymph nodes. In a second experiment, 15 adult, 20 juvenile, and 16 nestling deer mice were inoculated intradermally with VSV-NJ. Adults were refractory to infection by this route; however, nestlings and juveniles developed disseminated central nervous system infections. Viral antigen also was detected in cardiac myocytes and lymph node macrophages in these animals. Viremia was detected by virus isolation in 35/72 (49%) intranasally inoculated juvenile and adult mice and in 17/36 (47%) intradermally inoculated nestlings and juveniles from day 1 to day 3 postinoculation. The documentation of viremia in these animals suggests that they may have a role in the epidemiology of vector-borne vesicular stomatitis.

Animals↗
PubMed2001

Polyplax guatemalensis sp. n. (Phthiraptera: Anoplura), a new sucking louse from Peromyscus grandis, a montane cloud forest rodent from Guatemala.

The adult male and female of Polyplax guatemalensis sp. n. are described from the sigmodontine murid rodent Peromyscus grandis Goodwin collected in the Reserva de Biosfera, Sierra de las Minas, Guatemala, at an elevation of 2,200 m. The new species extends the number of known native species of Polyplax in the New World to four with none of them recorded south of Panama. Polyplax guatemalensis is morphologically most closely related to Polyplax auricularis which parasitises a cluster of closely related New World sigmodontine rodents from Canada to Panama. These two species can be distinguished from all other known species of Polyplax by the presence of partially overlapping, subtriangular, anterior abdominal plates in both sexes. Polyplax guatemalensis can be separated from P. auricularis by the abundant tergal abdominal setae and longer pseudopenis in males, and by the presence of one fewer anterior abdominal, subtriangular tergite and sternite in females.

Animals↗
PubMed1984

Photosensitive stages in pubertal development of male deer mice (Peromyscus maniculatus).

Male deer mice (Peromyscus maniculatus bairdii) were exposed to a long (15L:9D) or short (6L:18D) photoperiod during four stages of development. At 6 weeks of postnatal age degree of pubertal development was determined by measurement of testis and seminal vesicle weights and area of the androgen-dependent sebaceous gland. Continuous exposure to a short photoperiod beginning before conception (i.e. mother kept in short days), at conception, or at birth markedly retarded pubertal development. Initiation of short-day treatment after weaning at 3 weeks of age was partly effective in inhibiting puberty. Males exposed to long days beginning at weaning were stimulated fully, however, having reproductive organs as large at 6 weeks of age as those of males housed on long days for the entire experiment. These results indicate that pubertal development in male deer mice is regulated by early postnatal, but not prenatal, photoperiod. However, early after weaning, males are more responsive to increasing than to decreasing photoperiod.

Animals↗
PubMed1984

Effect of transitional photoperiods on testicular development and puberty in male deer mice (Peromyscus maniculatus).

In a series of five experiments, young male deer mice (Peromyscus maniculatus bairdii) were exposed to photoperiods ranging in length from 3 to 19 h per 24-h period, as well as to constant light and constant darkness. Reproductive organ growth as measured at 6 weeks of age was inhibited by less than or equal to 11.5 h of light. In males receiving 11.5-19 h of light, there was a quantitative increase in reproductive organ size as a function of photoperiod. Rather than a 'critical' photoperiod partitioning reproductive inhibition and stimulation, there was a zone of gradual transition from inhibition to full stimulation. Histological analysis of testes demonstrated that spermatogenesis was stimulated by long photoperiods. Examination of the epidermal surface of the penis by scanning electron microscopy indicated that penile spine development was also regulated by photoperiod.

Animals↗
PubMed1984

Influence of melatonin on pubertal development in male deer mice (Peromyscus maniculatus).

The role of melatonin in pubertal development was assessed in male deer mice (Peromyscus maniculatus bairdii) exposed to photoperiodic and social stimuli. Exogenous melatonin retarded puberty in males reared in a long photoperiod, but was without effect in males reared in short days. Melatonin did not retard pubertal development induced by exposure of short-day males to an adult female. These results suggest that pineal melatonin mediates photoperiodic, but not social, control of pubertal development.

Animals↗
PubMed1998

Phenotypic differences in the GnRH neuronal system of deer mice Peromyscus maniculatus under a natural short photoperiod.

The neural mechanisms by which short photoperiod induces gonadal regression among seasonally breeding mammals are not well understood. One hypothesis suggests that the proximate cause of seasonal gonadal regression is a photoperiod-induced modification in GnRH secretion. This hypothesis is indirectly supported by our recent findings using immunocytochemistry which identified specific photoperiod-induced adjustments in the number and morphology of GnRH containing neurones between reproductively competent and reproductively regressed laboratory housed male deer mice. Herein, we report that the GnRH neuronal system is similarly affected in reproductively responsive and nonresponsive wild male deer mice Peromyscus maniculatus exposed to a natural short photoperiod. The distribution of immunoreactive (IR)-GnRH neurones was nearly identical in field caught animals and those housed under artificial photoperiod in the laboratory. Compared with reproductively nonresponsive males, reproductively responsive mice from the field population possessed a greater total number of IR-GnRH neurones, a greater number of IR-GnRH neurones within the lateral hypothalamus, and a greater proportion of bipolar IR-GnRH neurones. Each of these distributional and morphological characters was consistent with our findings in laboratory housed male deer mice exposed to an artificial short photoperiod. Taken together, these data underscore the validity of using an artificial photoperiod to evaluate seasonal adjustments in reproductive function in the laboratory.

Animals↗
PubMed2005

Photoperiod-induced differential expression of angiogenesis genes in testes of adult Peromyscus leucopus.

Non-pathological angiogenesis in adults is rare and is largely thought to be restricted to wound healing and female reproductive cycles. Adult male rodents, however, display seasonal angiogenesis to support seasonal changes in reproductive tissue morphology. Non-tropical rodents use photoperiod (day length) to determine the time of year. During short days, the reproductive system undergoes involution and mating behaviours stop, adaptations which presumably allow energy resources to be shifted to processes necessary for winter survival. We compared the patterns of gene expression involved in angiogenesis in testes of white-footed mice (Peromyscus leucopus) following 7, 14, 21 or 34 weeks of long or short day lengths. Short days decreased body mass, reproductive tract mass and seminiferous tubule diameter. Potential genes involved in seasonal angiogenesis were screened by hybridizing testicular RNA from each group to angiogenesis-specific microarrays. Genes that were > or =6-fold different between long- and short-day testes (i.e. hypoxia-inducible factor 1alpha(Hif1alpha), plasminogen activator inhibitor 1 (Serpine1), transforming growth factor beta receptor 3 (Tgfbetar3) and tumour necrosis factor (Tnf )) were sequenced and expression differences were compared throughout gonadal regression and recrudescence using quantitative RT-PCR. Our results suggest that short days trigger expression of Hif1alpha, Serpine1, and Tgfbetar3 to inhibit angiogenesis or promote apoptosis during testicular regression, and also trigger expression of Tnf to promote angiogenesis during testicular recrudescence.

Animals↗
PubMed2003

Vector competence of Ixodes pacificus and I. spinipalpis (Acari: Ixodidae), and reservoir competence of the dusky-footed woodrat (Neotoma fuscipes) and the deer mouse (Peromyscus maniculatus), for Borrelia bissettii.

We investigated the experimental vector competence of Ixodes pacificus Cooley and Kohls and Ixodes spinipalpis Hadwen and Nuttall, and the reservoir competence of the dusky-footed woodrat (Neotoma fuscipes Baird) and the deer mouse (Peromyscus maniculatus [Wagner]), for Borrelia bissettii Postic, Marti Ras, Lane, Hendson, and Baranton. Both rodent species are capable reservoirs for B. bissettii; infection rates for I. pacificus or I. spinipalpis nymphs fed as larvae on infected animals ranged from 50 to 57%. Moreover, both I. pacificus and I. spinipalpis are efficient vectors of B. bissettii. Viable infections were recorded from all rodents known to be exposed to one or more infected nymphs of I. spinipalpis (seven deer mice, two white mice) or I. pacificus (seven deer mice). In contrast, none of four New Zealand white rabbits fed upon by 90 I. pacificus nymphs with a probable B. bissettii infection rate of >50% became infected or seroconverted. The attachment and feeding success of laboratory-reared nymphs similarly confined with deer mice in muslin-covered wire-mesh cages for 24 h ranged from 0% for I. pacificus to 17-73% for I. spinipalpis. Notably, the I. pacificus nymphs were physiologically capable of feeding; nymphs failing to attach to rodents fed readily when placed in feeding capsules upon rabbits. We conclude that the dusky-footed woodrat and the deer mouse are capable experimental reservoir hosts of B. bissettii, and that both I. spinipalpis and I. pacificus are efficient experimental vectors of B. bissettii. However, the reluctance of I. pacificus nymphs to feed on certain rodents may limit its importance as an enzootic vector of B. burgdorferi sensu lato spirochetes.

Animals↗
PubMed2002

Effects of Trichinella spiralis on survival, total mass, and organ mass of oldfield mice (Peromyscus polionotus).

Trichinella spiralis is a parasitic nematode that infects many mammals, including humans. Hosts may experience significant physiological changes or may die because of acute inflammatory immune responses toward the parasite. In this study, oldfield mice (Peromyscus polionotus) were used as a new experimental host for T. spiralis. Males of P. polionotus were infected with increasing doses of T. spiralis to determine the effect infection had on survival, mass change, total mass, and relative organ masses. Total juvenile worm burden increased in an asymptotic fashion with infective dose. Large doses (> or = 600 juveniles) significantly reduced survival. There were significant negative correlations between infection intensity (log10[juveniles]/g) and both mass gain and final total mass. Infection had no effect on liver or spleen size. But there were significant negative correlations between T. spiralis intensity and both testis and seminal vesicle masses. These effects on male size and reproductive organs may help explain behavioral changes, such as the elimination of male dominance, seen in previous studies on mice infected with T. spiralis.

Animals↗
PubMed2006

Reproductive effects of hexahydro-1,3,5-trinitroso-1,3,5-triazine in deer mice (Peromyscus maniculatus) during a controlled exposure study.

Contamination with hexahydro-1,3,5-trinitro-1,3,5-triazine (Royal Demolition Explosive [RDX]) has been identified at areas of explosive manufacturing, processing, storage, and usage. Thus, the potential exists for exposure to N-nitroso compounds, hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine, hexahydro-1,3-dinitroso-5-nitro-1,3,5-triazine, and hexahydro-1,3,5-trinitroso-1,3,5-triazine (TNX), formed via anaerobic transformation of RDX. Following exposure, reproductive toxicity of TNX was evaluated in three consecutive litters of deer mice (Peromyscus maniculatus). Hexahydro-1,3,5-trinitroso-1,3,5-triazine was administered ad libitum via drinking water at four doses: 0 (control), 1, 10, and 100 microg/L. Endpoints investigated included reproductive success, offspring survival, offspring weight gain, offspring organ weights, and liver TNX residues. Data from the present study indicate that TNX bioaccumulates in the liver and is associated with postpartum mortality, dose-dependent decrease in body weight from birth to weaning, and decrease in kidney weight of deer mice offspring.

Animals↗
PubMed2001

Naturally occurring periodontal bone loss in the wild deer mouse, genus Peromyscus.

BACKGROUND: Historically, animal models for the study of periodontal diseases have incorporated surgically created defects, plaque retentive ligatures, as well as soft and high-sucrose diets which may not accurately reflect progression of the natural disease. Spontaneous periodontal disease is seen in a few animal species, but these are often expensive to maintain and are unsuitable for manipulation using advanced molecular biology techniques. Mice are inexpensive, easy to maintain, and are routinely used for transgenic experiments and are therefore an optimal animal for research purposes. However, it is commonly accepted that mice do not spontaneously develop periodontal disease. The purpose of this study was to determine if a mouse population that exhibits periodontal breakdown in the wild could be found, allowing for genetic manipulation of naturally occurring periodontal disease. METHODS: We examined over 2,500 dry skulls of several Peromyscus species from various locations and habitats on the west coast of North America for periodontal bone loss in the molars, using furcation involvement as an indicator of disease severity. Alveolar bone loss was classified as Grade I) horizontal component of bone loss in the furcations; II) through-and-through furcations; and III) through-and-through furcations with alveolar bone loss into the apical third of the root. RESULTS: The proportions of individual mice experiencing bone loss were 3.8% for Class I-III involvement, 1.3% for Class II-III involvement, and 0.5% for Class III alone. Three subspecies of P. keeni and one subspecies of P. maniculatus had periodontal disease prevalences in 7% to 13.5% of their samples. Mice from isolated islands had 1.8- to 4.7-fold higher disease prevalence than those located on the mainland, with even greater prevalence on small islands. No statistically significant differences between genders were found. CONCLUSIONS: It appears that periodontal disease is far more common in this mouse genus than previously believed. Some of the subspecies demonstrated severe periodontal disease at a prevalence comparable to that found in humans.

Alveolar Bone Loss↗
PubMed1988

Melatonin acts in the brain to mediate seasonal steroid inhibition of luteinizing hormone secretion in the white-footed mouse (Peromyscus leucopus).

A melatonin-induced supersensitivity of the gonadotropin-secretory system to the negative feedback action of sex steroids is thought to be important to the timing of seasonal reproduction. However, little is known concerning this action of melatonin. In the present study the antigonadal action of melatonin in the anterior hypothalamus (AH) of the white-footed mouse, Peromyscus leucopus, was used to examine the neuroendocrine mechanism whereby melatonin enhances the sensitivity to sex steroid negative feedback. Mice received a melatonin-containing pellet in the AH for 14 weeks, at which time they were castrated and treated sc with a Silastic testosterone (T) capsule for 3 weeks. At the time of castration, weight of the testes and the concentration of T in the blood of mice with a melatonin pellet were greatly reduced compared to mice with a blank (melatonin-free) implant in the AH (P less than 0.01). In mice treated with melatonin the physiological dose of T significantly reduced the concentrations of LH in blood and pituitary (P less than 0.05). This dose of T, however, had little effect on LH in mice with a blank pellet in the AH. Melatonin in the AH markedly increased the content of gonadotropin-releasing hormone (GnRH) in the mediobasal hypothalamus (P less than 0.05) in mice treated with T; however, there was little effect of melatonin and/or T in any other region examined. Melatonin and T had little effect on the contents of immunoreactive beta-endorphin (B-EP) in the hypothalamus, but T alone increased the content of B-EP in the preoptic area. These results are evidence that melatonin and T act in concert to induce the reproductively-quiescent state by suppressing secretion of GnRH from the hypothalamus.

Animals↗
PubMed1994

Role of gonadal steroids and inhibitory photoperiod in regulating body weight and food intake in deer mice (Peromyscus maniculatus).

We investigated the role of declining daylength and gonadal steroids on body weight and food intake in male deer mice (Peromyscus maniculatus). This species was chosen for study because individual males display different reproductive responses to inhibitory daylength. About one-third of all mice exposed to short days undergo testicular regression and exhibit reduced circulating levels of luteinizing hormone and testosterone (reproductive responsive males). In contrast, testicular function and circulating levels of both these hormones remain unaffected in an equal number of mice (reproductive nonresponsive males). Previous studies have shown that each phenotype exhibits a distinct set of metabolic responses to short days, including adjustments in body weight. These characteristics make deer mice a useful animal model in which to study the interactive effects of gonadal steroids and photoperiod on neural substrates regulating body weight. A gonadectomy/steroid replacement experimental model was used to test the role of testosterone in regulating body weight and food intake in short day-housed male deer mice. Among gonad-intact males, short daylength caused a decline in body weight in both reproductive responsive and nonresponsive individuals. However, reproductive responsive mice lost significantly more body weight than did nonresponsive mice. Furthermore, while the weight loss was accompanied by a significant reduction in food intake in responsive mice, the relatively minor weight loss in nonresponsive mice was not accompanied by a change in food intake. Because changes in body weight and food intake (data not shown) occurred nearly simultaneously during the 8-week exposure to short daylength, results suggest that modifications in body weight are not responsible for the decline in food consumed, and vice versa. Gonadectomized reproductive responsive mice lost the same amount of weight as intact responsive mice but ate significantly more food. Among nonresponsive males, gonadectomy led to significantly greater weight loss, relative to intact mice, but caused an increase in food intake per gram body weight. Steroid replacement prevented weight loss and increased food intake in both gonadal phenotypes. Despite the observations that food intake was steroid dependent and the magnitude of the effect differed between reproductive phenotypes, changes in food consumption do not fully explain the inhibitory effects of short days on body weight in either phenotype. Taken together with previous studies, these results suggest that reproductive quiescence confers significant metabolic benefits to individual deer mice by reducing the amount of daily energy requirements via a reduction in body weight.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗
PubMedDate not supplied

Population dynamics of the deer mouse (Peromyscus maniculatus) and Sin Nombre virus, California Channel Islands.

Hantavirus pulmonary syndrome, first documented in 1993, is caused by Sin Nombre virus (SNV), which is carried by the Peromyscus species. In 1994, high SNV antibody prevalence was identified in deer mice from two California Channel Islands. We sampled two locations on three islands to estimate mouse population density and SNV prevalence. Population flux and SNV prevalence appear to vary independently.

Animals↗
PubMed2002

Bear Canyon virus: an arenavirus naturally associated with the California mouse (Peromyscus californicus).

Thirty-four rodents captured in southern California were studied to increase our knowledge of the arenaviruses indigenous to the western United States. An infectious arenavirus was isolated from 5 of 27 California mice but none of the 7 other rodents. Analyses of viral nucleocapsid protein gene sequence data indicated that the isolates from the California mice are strains of a novel Tacaribe serocomplex virus (proposed name "Bear Canyon") that is phylogenetically most closely related to Whitewater Arroyo and Tamiami viruses, the only other Tacaribe serocomplex viruses known to occur in North America. The discovery of Bear Canyon virus is the first unequivocal evidence that the virus family Arenaviridae is naturally associated with the rodent genus Peromyscus and that a Tacaribe serocomplex virus occurs in California.

Animals↗