Reproduction and thermoregulation in peromyscus: effects of chronic short days.
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Animals↗
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Ultrasonic vocalizations in male deer mice (Peromyscus maniculatus bairdi): their role in male sexual behavior.
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Animals↗
Disruption of ejaculates by male copulation in deer mice (Peromyscus maniculatus).
Six experiments were conducted to analyze possible disruption of sperm transport occurring when one male deer mouse copulates soon after another male ejaculates. When a second male mated soon after the first, females had significantly fewer uterine sperm 1 hr later than when a delay of 7 or 15 min was imposed between males. However, it was impossible to detect any effect of such disruption on pregnancy initiation. Similarly, artificial stimulation soon after an ejaculation was ineffective in disrupting pregnancy initiation. No effect of a rapid resumption of copulation could be detected on litter composition in a sperm competition situation. Although it is clear, from these and other data, that the phenomenon of ejaculate disruption occurs in deer mice, technical difficulties may interfere with experimental analysis.
Animals↗
The effects of indomethacin on plasma LH levels in female and male deermice (Peromyscus maniculatus).
The purpose of this investigation was to determine (1) the approximate time of the preovulatory LH rise in cyclic deermice, (2) the effect of indomethacin administration on plasma LH levels during the expected preovulatory LH rise, and (3) the effect of indomethacin administration on plasma LH levels in castrated male deermice. The data indicate that the preovulatory LH rise occurred at about 2200 h on proestrus and that indomethacin pretreatment significantly reduced plasma LH levels during that time. In addition, indomethacin significantly reduced plasma LH levels in castrated male deermice. We conclude that plasma LH levels remain low throughout the estrous cycle with the exception of the preovulatory "surge", that plasma LH levels in deermice are comparable to those reported for the rat, and that indomethacin pretreatment reduced plasma LH levels during periods when they were expected to be elevated (in castrated males and during the expected preovulatory LH rise in female deermice). The data are consistent with the hypothesis that the effect of indomethacin on plasma LH levels is due to an inhibitory effect on hypothalamic PG biosynthesis.
Animals↗
Analysis of serotonin, dopamine and their metabolites in the caudate putamen, the suprachiasmatic nucleus and the median raphe nucleus of euthermic and torpid deermice, Peromyscus maniculatus.
Deermice, subjected to food rationing and low ambient temperature, were sacrificed in normothermia or during daily torpor. Levels of monoamines and their metabolites in the caudate putamen (CPN), the suprachiasmatic nuclear area (SCN), and the median raphe nucleus (MRN) were quantified through the use of HPLC with electrochemical detection. Significant elevations in levels (pg/mg protein) of the serotonin (5-HT) metabolite, 5-hydroxyindole-3-acetic acid (5-HIAA) were noted in torpid individuals in all nuclei examined. The dopamine (DA) metabolite, homovanillic acid (HVA) was significantly elevated in the CPN and MRN of torpid individuals. Moreover, a significant increase in the HVA to DA ratio was also noted in the CPN and the MRN. In the SCN, the concentrations of 5-hydroxytryptophan (5-HTP), 5-HT, DA and 3,4-dihydroxyphenylacetic acid (DOPAC) were also increased significantly during torpor. These significant elevations suggest that an increase in the activity of the serotonergic and dopaminergic systems occurs in these nuclei during daily torpor in the deermouse.
Animals↗
Diurnal rhythms of 5-HT1A and 5-HT2 receptor binding in euthermic and torpor prone deermice, Peromyscus maniculatus.
Deermice display both spontaneous and induced daily torpor bouts, attaining minimum body temperatures of 15-20 degrees C. There is evidence that brain serotonin may be involved in the initiation and/or maintenance of torpor. Inhibition of serotonin [5-hydroxytryptamine (5-HT)] synthesis markedly reduces the duration and depth of torpor. Because a certain percentage of deermice will not enter torpor under any circumstances, we were able to compare 5-HT receptor subtypes in deermice that readily enter into torpor (TP) and in non-torpor prone (NTP) animals. Deermice were trapped in the wild and subjected to food rationing and low ambient temperature and then sacrificed either in a normothermic or torpid state at 11:00 p.m. or 11:00 a.m. Whole brain was assayed for 5-HT1A and 5-HT2 receptor differences using [3H]8-OH-DPAT and [3H]ketanserin, respectively. The Bmax values for 5-HT1A receptors were significantly greater in both TP and NTP animals sacrificed at 11:00 p.m. compared to animals sacrificed at 11:00 a.m. In contrast, the density of 5-HT2 receptors was significantly greater in animals sacrificed at 11:00 a.m. compared to animals sacrificed at 11:00 p.m. This is consistent with the opposing functions of these receptors in the regulation of temperature and sleep. The affinity (Kd) of each receptor was unchanged. A comparison of TP and NTP animals sacrificed at the same time of day revealed no significant differences in either Bmax or in Kd values, indicating that differences in 5-HT1A and 5-HT2 receptors may not explain the heterogeneity of deermice in their ability to enter torpor.(ABSTRACT TRUNCATED AT 250 WORDS)
8-Hydroxy-2-(di-n-propylamino)tetralin↗
Water economy of the canyon mouse Peromyscus crinitus stephensi.
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Acclimatization↗
A possible role for the thyroid in reproductive inhibition in laboratory populations of the prairie deermouse (Peromyscus maniculatus).
Serum thyroxine concentrations were determined and found to be reduced in reproductively inhibited deermice selected from controlled growth laboratory populations. Daily injections of 1 microgram thyroxine in reproductively inhibited male deermice were shown to significantly increase testis weight and the number of spermatids with acrosome formation. Daily feeding of thyroxine to a controlled growth population promoted an increase in the mean weights of the reproductive organs of both sexes that was intermediate between reproductively inhibited and capable deermice. Also, two females in the population produced the first surviving young after 250 days of inhibition.
Adrenal Glands↗
Serum ACTH and adrenal histology in reproductively inhibited male prairie deermice (Peromyscus maniculatus bairdi).
Exogenous ACTH will cause adrenal hypertrophy and gonad dysfunction in reproductively capable male deermice. The ultrastructure of the zona fasciculata of inhibited animals is substantially different from ACTH stimulated animals which suggests that ACTH alone does not produce the inhibition. Although ACTH concentrations were variable, there was no clear demonstration that any differences existed between reproductively capable vs inhibited animals at the time when corticosterone is known to be elevated in the inhibited animals. A contributory role for ACTH in promoting inhibition is not ruled out, but neither is it likely that elevated ACTH alone accounts for the observed reproductive inhibition in animals taken from populations.
Adrenal Glands↗
Metabolic and thermoregulatory effects of photoperiod and melatonin on Peromyscus maniculatus acclimatization.
A photoperiod-related seasonal rhythm in active period (scotophase), metabolic rate and core temperature was documented for animals held at 21.0 +/- 0.1 degrees C ambient; animals that were habituated to long nights (10:14LD) had a greater metabolic reserve than those held in summer photoperiods (14:10LD). While relative weights of gonads and sex accessory tissues of mice show typical "winter" regression, interscapular brown adipose tissue mass was unaffected by photoperiod; moreover, IBAT beta adrenergic responses under "winter" photoperiods did not differ from "summer" photoperiods in the absence of cold stimulus. Thermogenic efficiency, measured as the increment of active temperature level achieved per increment of active period metabolic effort, was highest for animals exposed to short photoperiods. Thermal conductance was reduced in animals exposed to short (10:14LD) photoperiods. Heat conservation and thermogenic response capacity was enhanced by melatonin treatment and short photoperiod.
Acclimatization↗
Bioenergetic benefits of huddling by deer mice (Peromyscus maniculatus).
Both short photoperiod and communal social living conserve metabolic energy by deer mice held in thermal neutral ambient temperatures. Initial socialization was energetically more costly than solitary living, but huddling behaviors reduced thermal conductance and mass specific metabolic rate by 30% within 5 days. While short photoperiod reduced metabolic energy expenditure by decreasing thermoregulatory demand, huddling mediated behavioral conservation was achieved with hyperthermic core temperatures.
Animals↗
The relationship between food intake, body fat and reproductive inhibition in prairie deermice (Peromyscus maniculatus bardii).
1. Reproductively-inhibited deermice selected from four laboratory populations consumed significantly less food than reproductively-proven pairs. 2. Reproductively-inhibited animals predominantly, but not consistently, had reduced total body fat compared with reproductively capable deermice. 3. The per capita food consumption rate of two populations followed for 26 weeks since founding, decreased over time to about 65% of the daily intake of the proven animals used to found the populations. 4. An aggregation or "huddling" behaviour with concomitant reduction in thyroid hormone activity, possibly in response to the density of the "huddle", is suggested as an explanation for these observations.
Adipose Tissue↗
The effects of feeding triiodothyronine on reproductively inhibited prairie deermice (Peromyscus maniculatus bairdii) from laboratory populations.
1. Two reproductively inhibited populations were given 250 ng triiodothyronine (T3) per gram of food for 35 days to elevate the reduced serum thyroid hormone concentration previously demonstrated in reproductively inhibited animals and to determine if the treatment would promote recovery. 2. Per capita food intake was significantly increased but per cent body fat tended to decrease and body weight did not significantly increase during T3 treatment. 3. Mean testis and seminal vesicle weights of T3-treated males were significantly increased and testis histology indicated some increase in spermatogenesis. 4. Mean ovary weights of T3-treated females only tended to increase although the uterine weights were significantly increased and ovarian histology revealed a significant increase in preovulatory follicles. 5. The limited recovery of reproductively inhibited animals may indicate that thyroid activity per se is related to, but not the direct cause of, the reproductive inhibition observed in populations.
Animals↗
The interaction of shivering and non-shivering thermogenesis in deer mice (Peromyscus maniculatus).
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Adaptation, Biological↗
N-Nitroso compounds produced in deer mouse (Peromyscus maniculatus) GI tracts following hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) exposure.
Given the potent carcinogenic effects of most N-nitroso compounds, the reductive transformation of the common explosive hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) to a group of N-nitroso derivatives, hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine (MNX), hexahydro-1,3-dinitroso-5-nitro-1,3,5-triazine (DNX), and hexahydro-1,3,5-trinitroso-1,3,5-triazine (TNX) in the environment have caused concerns among the general public. Questions are arising about whether the same transformations also occur in mammals, and if true, to what extent. This study investigated the N-nitroso derivatives production in the deer mouse GI tract following RDX administration. Findings verified that such transformations do occur in the mammalian GI tract at notable levels: the average MNX concentrations in deer mice stomach were 85 microg/kg and 1318 microg/kg for exposure to 10mg/kg and 100mg/kg diet, respectively. DNX in stomach were 217 microg/kg for the 10mg/kg dose group and 498 microg/kg for the 100mg/kg dose group. Changes in other toxic endpoints including body weight gain, food consumption, organ weight, and behavior were also reported.
Animals↗
Differences in hypothalamic 2-[125I]iodomelatonin binding in photoresponsive and non-photoresponsive white-footed mice, Peromyscus leucopus.
Photoperiod is an environmental cue used by many temperate-zone species to regulate their reproductive timing. Within species, the degree of reproductive photoresponsiveness can vary widely both among and within populations. The neuroendocrine mechanisms causing this individual variation in photoresponsiveness are unknown. Using selected lines from a population of white-footed mice known to vary genetically in reproductive photoresponsiveness, we tested the hypothesis that variation in the number and/or location of melatonin receptors is the basis for individual differences in reproductive photoresponsiveness. The brains and pars tuberalis of the pituitary from sixteen mice, (eight mice from each of two lines selected for two generations to respond strongly or weakly to photoperiod), were processed for autoradiography using the radioligand 2-[125I]-iodomelatonin (IMEL). We found significantly higher specific IMEL binding in the medial preoptic area and the bed nucleus of the stria terminalis of non-responsive mice than responsive mice. There were no differences between groups in specific IMEL binding in the suprachiasmatic and dorsomedial nuclei of the hypothalamus, pars tuberalis, or paraventricular nucleus of the thalamus. These results provide support for the hypothesis that individual variation in photoresponsiveness is due in part to differences in the density or affinity of melatonin receptors.
Animals↗
Dissociation between spontaneously emitted and apomorphine-induced stereotypy in Peromyscus maniculatus bairdii.
Stereotyped behavior is repetitive, topographically invariant motor activity that lacks an obvious function. We have previously characterized the spontaneous and persistent stereotypies that occur in deer mice housed in standard laboratory cages. Providing these animals with enriched environments markedly reduces their vulnerability to develop stereotypic behavioral repertoires, thus enabling us to generate behaviorally distinct (stereotypic and nonstereotypic) mice of the same species. As stereotypic behaviors are readily induced by systemic administration of a dopamine (DA) agonist, the present study tested whether apomorphine would induce stereotypies in environmentally enriched (nonstereotypic) deer mice that were topographically similar to the stereotypies that are spontaneously emitted by standard-caged (stereotypic) deer mice. The effects of apomorphine were also evaluated in the standard-caged (stereotypic) deer mice. DA agonist-induced behaviors in nonstereotypic mice included stereotypies that were largely topographically distinct from spontaneously emitted stereotypies; apomorphine failed to produce statistically significant elevations in two of the three stereotypic behaviors typical of standard-caged deer mice. Furthermore, there was no evidence of increased DA receptor sensitivity in stereotypic mice. Thus, environmentally related stereotypy is distinct from systemically administered DA agonist-induced stereotypy, and is not exacerbated by such drug treatment. The results obtained do provide support, however, for a limited involvement of the DA system in the mediation of these behaviors.
Animals↗
Modulation of endocrine pathways by 4,4'-DDE in the deer mouse Peromyscus maniculatus.
4,4'-DDT and 4,4'-DDE are widespread environmental contaminants that cause eggshell thinning in birds, altered sex ratios in the American alligator, and changes in the anal-genital distance in rodents. These contaminants are known to cause some of their toxicity by altering steroid receptor-mediated mechanisms. However, chemical-specific alterations in the expression of hormone-metabolizing enzymes may also be a mechanism for endocrine disruption, by altering the half-life of hormones in critical tissues. Previously, we showed that 4,4'-DDE causes a dose-dependent increase in ethoxyresorufin-O-deethylase (EROD) activity, but not pentoxyresorufin-O-dealkylase (PROD) activity, in the deer mouse. In this study, we demonstrated that 4,4'-DDE elicited a corresponding increase in CYP1A protein expression but not CYP2B using Western blotting and immunoprecipitation. 4,4'-DDE-mediated changes in phase II conjugating enzymes; UDP-glucuronosyltransferase (UGT) and phenolsulfotransferase (ST), were also investigated for the first time. Prepubescent female deer mice were dosed with 4,4'-DDE by gavage on days 1 and 2, then euthanized on day 4. As anticipated, dose-dependent increases in hepatic EROD and MROD activities, but not PROD or BROD, were observed. UGT activity was monitored by incubating liver microsomes and 14C-UDP-GA with potential substrates and measuring incorporation of radioactivity into TLC-resolved glucuronides. Dose-dependent increases in conjugation were observed with p-nitrophenol (a general UGT substrate) but not testosterone. Interestingly, a biphasic dose-response curve was observed for ST activity, with a peak at the 3 mg/kg dose. Dose-dependent increases in CYP1A1 and UGT-specific immunoreactive proteins were observed, suggesting de novo synthesis as a consequence of 4,4'-DDE exposure. We also measured Phase I and II enzymes in deer mouse platelets. Preliminary results indicate that the 4,4'-DDE-induced changes in liver Phase I and II enzyme activity were similar, but not identical, to those found in platelets. These results indicate that environmentally-relevant levels of 4,4'-DDE modulate the activity and expression of CYP1A1 and phase II enzymes in the deer mouse and that certain changes may be measured non-lethally.
Animals↗