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Deermice (Peromyscus maniculatus) did not increase their food intake above baseline following treatment with 2-deoxy-D-glucose (2DG, 500 or 1000 mg/kg). They did eat more following food deprivation or treatment with insulin at a high dose (100 U/kg). House mice (Mus musculus) showed hyperphagia to 2DG, low dose of insulin (5 U/kg) and deprivation.
Resonance light:dark cycles (LD 6:18, 6:30, 6:42, or 6:54) were used to establish that a circadian rhythm of light sensitivity is involved in the thermoregulatory and reproductive responses to a short day photoperiod in the mouse, Peromyscus leucopus. A fifth group was maintained on the long day photoperiod of LD 16:8. After 19 weeks animals presented with LD 6:18 or 6:42 exhibited short day photoperiod responses: gonadal regression, incidence of spontaneous daily torpor and molt to the winter pelage. In contrast animals responded to LD 6:30 and 6:54 as long day photoperiods: maintenance of gonadal system, no incidence of spontaneous daily torpor, and summer pelage. In a second study a T-experiment was conducted to determine that more than one circadian system may regulate these multiple photoperiodic effects. Mice were exposed to 1 of 8 LD cycles for 15 weeks (1:22.00, 1:22.25, 1:22.50, 1:23.00, 1:23.50, 1:23.75, 9:15, or 16:8), Entrained wheel-running activity occurred under all LD regimes. Mice on LD 1:22.50, 1:23.00, and 1:23.50, however, exhibited activity patterns similar to mice on LD 9:15, and they exhibited gonadal regression. Mice on LD 1:22.00, 1:22.25, and 1:23.75 exhibited activity patterns similar to LD 16:8 animals, and most of these animals remained reproductively competent. There was also a close association between occurrence of reproductive regression and daily torpor. In contrast, molt to the winter pelt occurred under all non-24-hr LD cycles. This dysynchrony in response suggests that at least 2 circadian systems are involved in photoperiodic time measurement in P. leucopus.
Reproductive responses and thermogenic properties of brown adipose tissue (BAT) were evaluated in individuals from an outbred population of deer mice (Peromyscus maniculatus nebrascensis) after 10 weeks exposure to short photoperiod (8:16 light:dark) and cold ambient temperature (2 degrees C). Deer mice populations are composed of phenotypes that differ in their reproductive response to environmental cues. These phenotypes also differ in body temperature regulation as indicated by their use of daily torpor. By comparing BAT responses among individuals of different phenotypes, we were able to assess the association between environmentally induced changes in reproduction and metabolism. Short/cold days caused increased proliferation of BAT and higher cytochrome oxidase activity. However, the magnitude of these changes varied with reproductive phenotype and use of daily torpor. BAT weight in short/cold day exposed males with normal sized testes more than doubled while total cytochrome oxidase activity increased by 30% as compared to controls. In contrast, short/cold day exposed deer mice with atrophic testes that employed daily torpor exhibited a 64% increase in BAT weight and 100% increase in total cytochrome oxidase activity, compared to control mice. Cytochrome oxidase activity in nontorpid deer mice with atrophic testes was intermediate to these two groups. Our results demonstrate a response of BAT to short/cold days that varies with individual reproductive response. This finding suggests that there exists a common integrative mechanism for temperature and photoperiod to regulate both seasonal reproductive and metabolic adjustments.
Exposure to a natural predator, the short-tailed weasel, Mustela erminea, elicited significant increases in the nociceptive responses of wild male white-footed mice, Peromyscus leucopus. A short (30 sec), ecologically relevant, nonvisual exposure to a weasel elicited a relatively brief (15 min) analgesia that was insensitive to the opiate antagonist, naloxone (1.0 mg/kg), and was blocked by either pre- or post-exposure injections of the benzodiazepine antagonist, Ro15-1788 (10 mg/kg), or agonist, diazepam (4.0 mg/kg). A 5 min exposure to the weasel elicited an analgesic response of longer duration (15-30 min) that was sensitive to both naloxone and the benzodiazepine agonist and antagonist. A 15 min exposure to the weasel induced a higher amplitude analgesia that was of relatively long duration (45 min), blocked by naloxone, and insensitive to the benzodiazepine manipulations. Exposures of 5 and 15 min to a nonpredator, the European rabbit, Oryctolagus cuniculus, elicited low amplitude, naloxone-reversible analgesic responses that were unaffected by the benzodiazepine manipulations. Thirty-sec exposures to the rabbit had no significant effects on the nociceptive response of the rabbit. These results indicate that a brief, ecologically appropriate, exposure to a predator elicits a benzodiazepine-mediated analgesia while a more prolonged exposure to a predator induces opioid-mediated analgesia. These results show that the opioid and nonopioid distinction between the effects of long- and short-term laboratory stresses is also evident with a natural, ecologically relevant, stressor.
We measured the resting metabolic rates of Peromyscus maniculatus for 7 days before and 7 days following forced pairing in order to determine whether seasonal light cycles influenced the rates of behavioral and metabolic habituation of deer mice to cohabitation. We had earlier shown that winter photoperiod and/or huddling results in lower resting metabolic rates and core temperatures of deer mice. Seasonal photoperiods were simulated by conditioning wild-caught mice to 24-h light cycles with differing durations of light exposure during the 24 h day. These experiments demonstrated that winter mice adjusted their resting metabolic rates from solitary to huddling levels much more rapidly than summer mice. Initial, high metabolic rate responses of paired mice persisted much longer than expressions of agonistic behaviors between paired mice. We propose that winter photoperiod enables animals to more efficiently make the transition to spontaneous, amicable huddling as a winter acclimatization strategy.
This study examined auditory-evoked brainstem responses (ABR) in the deermouse (Peromyscus maniculatus) during torpor and arousal. The ABR of the euthermic deermouse consisted of five waves occurring in a time frame of 10 ms. During torpor, ABR wave I could be elicited at slow, but not fast stimulation rates indicating variability in neural activity along the auditory pathway. Arousal was heralded by the appearance of all the components of the ABR evoked in response to both slow and fast click rates signaling functional restoration of auditory neural activity during this phase.
There is little solid evidence for specific genetic adaptations in animal populations native to high altitude. There is also continuing debate over what oxygen transport characteristics are truly adaptive at high altitude. We have attempted to elucidate both problems through population genetic and physiological studies of the deer mouse, Peromyscus maniculatus. That species is noteworthy because it inhabits the widest range of altitudes of any North American mammal, and it shows a high degree of genetic variation in hemoglobins. Deer mice were collected from 35 populations representing ten nominal subspecies covering a broad geographical range of the United States. The mice were acclimated to low altitude (340 m); then a mixing method was used to determine P50 and other blood gas parameters on samples pooled from individuals of representative hemoglobin genotypes. When the data from all subspecies wee combined, there was a highly significant negative correlation between P50 and the native altitude of the population. Tests on progeny reared at low altitude indicated that the differences in P50 were primarily genetic. Part of the clinal variation in P50 could be attributed to 2,3-DPG effects; high-altitude populations showed lower baseline DPG/Hb ratios. Surprisingly, within those subspecies which inhabit a wide range of altitudes, there was no correlation between P50 and native altitude. Our tentative conclusion from these data and data presented elsewhere is that deer mouse populations do show genetic adaptations to high altitude. However, because of gene exchange between populations, the genetic characteristics of a population reflect the average altitude over a relatively broad geographic area.
Erythrocyte DPG concentrations were studied in populations of Peromyscus maniculatus native to different altitudes. Deer mice native to, and resident at, high altitude showed higher DPG/Hb ratios than did deer mice native to, and resident at, low altitude. However, after prolonged acclimation to low altitude, the high-altitude natives showed lower DPG/Hb ratios than did low-altitude natives. The differences in baseline DPG levels appear to be determined primarily by genetic factors. The heritability (h2) of DPG/Hb ratios was estimated by two independent methods to be 0.51 and 0.66, but those values are inflated to an unknown extent by environmental correlations between relatives. Mild cold stress did not elicit an increase in DPG/Hb ratios. DPG levels tended to decrease with age, but the aging effect was not consistently observed in all samples. Neither sex nor alpha-globin genotype influenced DPG levels. The adaptive significance of the genetic differences in DPG metabolism between high- and low-altitude populations remains problematic.
We found serological evidence of infection with Prospect Hill virus, a Hantaan-like virus isolated from meadow voles (Microtus pennsylvanicus), in microtine and cricetid rodents trapped in Maryland, West Virginia, Minnesota and California, USA. Fluorescent antibodies were detected in sera from M. pennsylvanicus (74/277), M. californicus (39/185), Clethrionomys gapperi (5/51), Peromyscus maniculatus (4/22) and P. truei (1/11). Sera from seropositive P. maniculatus contained neutralizing antibodies against Prospect Hill virus, confirming that infection with Prospect Hill virus or antigenically related viruses is not restricted to microtine rodents in the USA. Despite the widespread distribution of Prospect Hill virus in indigenous rodents, the recent demonstration that American mammalogists are only rarely infected supports the view that the overall risk of Prospect Hill virus infection in man is low.
The ontogeny of striking, prey-handling and envenomation behavior was studied in the prairie rattlesnake (Crotalus v. viridis). Snakes of three size classes (small, medium, large) were allowed to strike and envenomate deer mice (Peromyscus maniculatus) of corresponding size. The mass of venom expended in a single strike, assayed by enzyme-linked immunosorbent assay (ELISA) of whole-mouse homogenates, increased exponentially with length of the snake. Small snakes embedded their fangs in prey for a longer duration than larger snakes. Mice were always struck and released, regardless of snake or prey size. Latency to immobilization was similar for mice envenomated by medium and large snakes; small mice struck by small snakes were not mobile. Latency to death and death rate (latency to death divided by mass of mouse) were greater for mice envenomated by small snakes as compared to medium and large snakes. These findings further clarify the ontogenetic and functional relationships between venom, morphology, diet and behavior. They also illustrate how behavior may be modified to maximize envenomation and feeding success.
The purpose of this study was to assess through correlation analyses the various factors and consequences associated with the mass of venom injected by prairie rattlesnakes (Crotalus v. viridis) into their natural prey, deer mice (Peromyscus maniculatus). Fifty-seven predator-prey interactions were studied via slow motion videotape review. The mass of venom expended by snakes during biting was quantified by enzyme-linked immunosorbent assay (ELISA) of whole-animal homogenates. The quantity of venom expended was not related to size of prey; however, the range of mouse sizes (13-31 g) was quite narrow. Multiple bites of the same mouse were not associated with incremental increases in venom expenditure; only about 40% more venom was expended by striking prey a second time. The duration of fang contact and site of fang penetration had no discernible effects on venom expenditure. The site of fang penetration of prey appeared to be random, due to evasive actions of the mice. The components of striking (duration of launch, fang contact, and recoil, respectively) and distance of the strike were correlated and appeared to be influenced by the prey's reaction. After striking and releasing mice, the snakes did not attempt to relocate more quickly those prey which succumbed to venom relatively quickly. Both natural (snakebite) and artificial (syringe) injections indicated that the site of venom injection (e.g. anterior, posterior, muscle, vital organ) has a greater influence on subsequent mobility and survival of mice than the quantity of venom injected. It appears that some behavioral aspects of predation (especially the sequential components of striking) are flexible and responsive to prey reactions, while others (venom expenditure and poststrike immobility) are less subject to modification.
To measure directly the accumulation of DNA damage with age, and to understand better the effect of modulators of DNA damage in vivo, the DNA of brain, liver, and kidney of two mice from different families, Mus musculus and Peromyscus leucopus, have been examined for age-dependent accumulation of single-strand breaks plus alkali-labile bonds, by the alkaline sucrose sedimentation method. These two species of small rodents are closely related taxonomically, yet differ significantly in maximum achievable lifespan. Using the reciprocal of the number average molecular weight for estimation of DNA size, these analyses indicate that: (a) DNA damage does not measurably accumulate in brain tissue; (b) the accumulation of DNA damage was more pronounced in hepatic DNA than other tissue DNA; and (c) the rate of accumulation of DNA damage in liver and kidney cells with age was greater in the shorter-lived species (M. musculus) and was inversely proportional to maximum achievable lifespan. There are suggestions that a similar threshold might exist for tolerance of DNA damage in the two species in specific organs, and that these species differ in the rate at which this threshold is reached as a function of maximum achievable lifespan.
The effects of endogenous opioid peptides are limited by proteolytic enzymes such as endopeptidase 24.11 ("enkephalinase"), which cleaves the Gly-Phe bonds in Met- and Leu-enkephalin. SCH 34826 [(S)-N-[n-[1-[(2,2-dimethyl-1,3-dioxolan-4- yl)methoxy]carbonyl]-2-phenylethyl]-L-phenyl-alanine-B-alanine] is a potent, highly specific, enkephalinase inhibitor that has marked analgesic effects in laboratory rodents. The present study compared the effects of SCH 34826 on nociception and restraint stress-induced opioid analgesia in reproductive adult male and female deer mice, Peromyscus maniculatus. SCH 34826 had significantly greater antinociceptive actions and facilitatory effects on stress-induced analgesia in male than female mice. These antinociceptive effects of SCH 34826 were reduced by the general opioid antagonist naloxone and completely blocked by the specific delta opioid receptor antagonist, ICI 174,864, and nonsignificantly affected by the mu and kappa opioid receptor antagonists, beta-funaltrexamine and nor-binaltorphimine, respectively. These results show that there are sex differences in the effects of the enkephalinase inhibitor, SCH 34826, on opioid-mediated antinociception and that these sex differences are associated with delta opioid mechanisms.
There is evidence suggesting that the endogenous tetrapeptide, Tyr-MIF-1 (Tyr-Prol-Leu-Gly-amide), has antagonistic or modulatory effects on opioid-mediated analgesia. There is also substantial evidence for sex differences in opioid effects, whereby male rodents display greater levels of opioid-mediated analgesia than females. In the present study, determinations were made of the effects of Tyr-MIF-1 on morphine- and restraint stress-induced opioid analgesia in adult male and female deer mice, Peromyscus maniculatus. Intraperitoneal treatment with Tyr-MIF-1 (0.10-10 mg/kg) reduced morphine- and stress-induced analgesia in both male and female mice, with Tyr-MIF-1 having markedly greater antagonistic effects in male than female mice. These results indicate that there are sex differences in the modulatory (antiopiate) effects of Tyr-MIF-1 on opioid-mediated analgesia.
Recent investigations have detected polychlorinated biphenyl (PCB) body burdens in wild white-footed mice (Peromyscus leucopus) captured at hazardous waste sites. Insufficient information is currently available to interpret the toxicological significance of these body burdens. In an effort to provide this information, we investigated hepatic changes and PCB body burdens in white-footed mice following a 21-day dietary exposure to a PCB mixture, Aroclor 1254. Dietary concentrations tested were 0, 2.5, 25, 50, and 100 mg Aroclor 1254/kg diet (reported as ppm). Liver weights were significantly increased at all concentrations except 2.5 ppm. Ethoxyresorufin O-dealkylase (EROD) activity, an aryl hydrocarbon hydroxylase-type substrate, was significantly increased at all PCB concentrations, but the dose-response tended to plateau above 25 ppm. Pentoxyresorufin O-dealkylase (PROD) activity, a putative phenobarbital-type substrate, was significantly increased in a dose-dependent manner at 25 ppm PCB and above, with no plateau response. Pentobarbital sleep time was significantly decreased at 25 ppm, but not at 2.5 ppm. Results indicate white-footed mice undergo a mixed-type induction pattern following exposure to Aroclor 1254, with EROD the most sensitive indicator of PCB exposure. This investigation identified a no observed effect concentration for liver weights and PROD activity at 2.5 ppm in the diet which is equivalent to a body burden of 2.0 mg Aroclor 1254/kg wet wt of mice; the no observed effect concentration for EROD is below these levels. These results support the use of EROD, PROD, and liver weight as biomarkers of PCB exposure in field-captured rodents.
Exposure of male Syrian hamsters (Mesocricetus auratus) for 10 weeks to short photoperiod (SP) providing 10 hr light: 14 hr darkness (10:14 LD) produced a significant reduction in the weights of the reproductive organs, plasma thyroxine (T4) levels and free T4 index (FT4I) compared to the values of animals exposed to long photoperiod (LP, 14:10 LD). C57bl male house mice (Mus musculus) kept in SP (10:14 LD) had reproductive organ weights equivalent to those of mice kept in long days (14:10 LD) and lower T3 uptake (T3U) values. Male gerbils (Meriones unguiculatus) exposed to 13 weeks of SP (10:14 LD) had lower body weights, testes and seminal vesicle weights and higher T3U values compared to LP (14:10 LD) controls. However, no effect was seen on plasma T4 and triiodothyronine (T3) values nor the FT4I and free T3 index (FT3I). White-footed male mice (Peromyscus leucopus) exposed to SP (8:16 LD) had significantly lower testes and seminal vesicle weights while plasma T4 and T3 levels were unaffected. Snell strain house mice (Mus musculus) exposed to SP (8:16 LD) had normal reproductive organ weights compared to the values of LP-exposed (16:8 LD) control animals. However, there was a significant depression in T3 and in the FT3I in the SP animals.
Swim stress-induced analgesia (SSIA) was examined in photoperiodically induced 'breeding' (reproductive) and 'non-breeding' (non-reproductive) adult male and female deer mice, Peromyscus maniculatus. Nociceptive responses (50 degrees C, hot-plate) of breeding and non-breeding deer mice were determined after either a 1- or 3-min swim in 20 degrees C water. The 1-min swim induced an immediate and relatively short-lasting naloxone (1.0 mg/kg) insensitive 'non-opioid' -mediated SSIA that was antagonized by the N-methyl-D-aspartate (NMDA) antagonist, MK-801 (0.10 mg/kg) in all of the groups of mice except the breeding (reproductive) females. Breeding females displayed a non-opioid analgesia that was insensitive to MK-801. The 3-min swim induced a relatively more prolonged mixed opioid and 'non-opioid' SSIA of which the initial portion was sensitive to antagonism by MK-801 in all groups of the mice except the breeding females, while the latter portion (15 min after swim) was induced by naloxone in all of the groups of mice. Overall, the breeding males displayed greater levels of SSIA than the breeding females, with no consistent sex differences in the non-breeding mice. Within sexes, the breeding males displayed greater levels of opioid and non-opioid SSIA than the non-breeding males, while the non-breeding females displayed greater levels of SSIA than the breeding females. These results show that both sex and reproductive status affect the expression and neurochemical mediation of non-opioid SSIA. These findings also suggest that reproductive females may have an unique or novel hormonally (estrogen) dependent mechanism associated with the expression of SSIA.
Warbles induced by the rodent bot fly larvae, Cuterebra fontinella, developed over a period of 3.5-4 weeks in the deer mouse Peromyscus maniculatus. Warble location, structure and dynamics were examined. Clustering of warbles occurred primarily within the inguinal region of the deer mouse with a significant number favoring the area between the anus and genital organ. No differences in warble production were found in hosts of either sex. On two occasions, a warble was encountered forming directly in the genitals. Warble structure consisted of a pore, cavity and capsule, all of which changed in shape and size as the larvae grew. A new pore was formed during the first larval molt and was commonly bordered by a yellowish precipitate. A bi-layered warble capsule surrounded the cavity as a thin layer and a thick diffuse outer layer. The growing warble expanded into the subcutaneous tissue of the inguinal area and stretched the hide caudally. Subcutaneous tissue surrounding developing warbles became relegated to small areas, leaving only a thin muscle to separate the warble from the peritoneum. Widening of the pore at the time of larval emergence is described. Linear relationships are given describing warble growth and pore enlargement as a factor of time. The location of warbles and the morphology of the pore are discussed in relationship to larval protection. Damage to the host due to warble formation is also addressed.