Predator Odor Exposure Research Articles

Threat bias in mice with inactivating mutations of Prkar1a

Anxiety disorders are associated with abnormalities in the neural processing of threat-related stimuli. However, the neurobiological mechanisms underlying threat bias in anxiety are not well understood. We recently reported that a Prkar1a heterozygote (Prkar1a+/−) mouse with haploinsufficiency for the main regulatory subunit (R1α) of protein kinase A (PKA) exhibits an anxiety-like phenotype associated with increased cAMP signaling in the amygdala. Prkar1a+/− mice provide a novel model to test the direct effect of altered PKA expression and subsequent anxiety-like behavioral phenotype on the response to threat. We hypothesized that Prkar1a+/−mice would exhibit a bias in threat detection since increased amygdala activity during emotional stimuli is associated with a maladaptive response. We measured behavior and PKA activity in brain areas after exposure to predator or control odor exposure in male Prkar1a+/− and wild-type (WT) littermates. Indeed, there were significant differences in the behavioral response to threat detection; WT mice showed the expected response of decrease in exploratory behavior during predator vs. control odor exposure, while Prkar1a+/− mice did not alter their behavior between conditions. Basal and total PKA activity was independently associated with genotype, with an interaction between genotype and threat condition. Prkar1a+/− mice had higher PKA activity in amygdala and ventromedial hypothalamus in response to predator odor. In contrast, WT mice had higher PKA activity in amygdala and orbitofrontal cortex after exposure to control odor.Dysregulated PKA activity in the amygdala–prefrontal cortex circuitry in Prkar1a+/− mice is associated with behavioral phenotype of anxiety and a bias for threat. This is likely related to a failure to inhibit the amydgala response, which is an effect of the genotype. These results suggest that the alteration in PKA signaling in Prkar1a+/− mice is not ubiquitous in the brain; tissue-specific effects of the cAMP/PKA pathway are related to threat detection and fear sensitization.

Genetic predisposition to anxiety-related behavior predicts predator odor response

While rodents have a keen sense of smell and largely depend on olfactory cues for operating in their environment, most of the widely used tests to assess anxiety-related behavior largely ignore the olfactory system, being primarily based on fear of brightly lit, novel and open spaces. Here, we aimed at testing whether the genetic predisposition to anxiety predicts the predator odor response in mice. In the first experiment, using the 3-chamber avoidance test in CD-1 mice, trimethylthiazoline (TMT), a synthetic fox fecal odor, was shown to induce stronger behavioral and neuroendocrine effects than cat odor and butyric acid, respectively, and was therefore chosen as aversive odor for the following series of experiments. In this series, bidirectionally, selectively inbred CD-1 mice with either high (HAB), intermediate (NAB) or low (LAB) anxiety-related behavior responded differently to TMT, with HABs spending significantly less time than both NABs and LABs in the chamber harbouring the predator odor. Importantly, this result is not confounded by any deficit of the olfactory system, as LAB and NAB mice, while not or only moderately responding to TMT, responded to both the pleasant odor of female urine and the repugnant odor of butyric acid. Probably due to the strength of TMT, a similar increase in corticosterone levels upon predator odor exposure was observed in all three groups. Together, the results suggest that, dependent on the genetic predisposition to extremes in anxiety-related behavior, mice differentially interpret the odor of a potential predator, making this type of avoidance behavior highly predictable.

Activation of phenotypically-distinct neuronal subpopulations of the rat amygdala following exposure to predator odor

Exposure of rats to an odor of a predator can elicit an innate fear response. In addition, such exposure has been shown to activate limbic brain regions such as the amygdala. However, there is a paucity of data on the phenotypic characteristics of the activated amygdalar neurons following predator odor exposure. In the current experiments, rats were exposed to cloth which contained either ferret odor, butyric acid, or no odor for 30 min. Ferret odor-exposed rats displayed an increase in defensive burying versus control rats. Sections of the brains were prepared for dual-labeled immunohistochemistry and counts of c-Fos co-localized with Ca2+/calmodulin-dependent protein kinase II (CaMKII), parvalbumin, or calbindin were made in the basolateral (BLA), central (CEA), and medial (MEA) nucleus of the amygdala. Dual-labeled immunohistochemistry showed a significant increase in the percentage of CaMKII-positive neurons also immunoreactive for c-Fos in the BLA, CEA and MEA of ferret odor-exposed rats compared to control and butyric acid-exposed groups. Further results showed a significant decrease in calbindin-immunoreactive neurons that were also c-Fos-positive in the anterior portion of the BLA of ferret odor-exposed rats compared to control and butyric acid-exposed rats, whereas the MEA expressed a significant decrease in calbindin/c-Fos dual-labeled neurons in butyric acid-exposed rats compared to controls and ferret odor-exposed groups. These results enhance our understanding of the functioning of the amygdala following exposure to predator threats by showing phenotypic characteristics of activated amygdalar neurons. With this knowledge, specific neuronal populations could be targeted to further elucidate the fundamental underpinnings of anxiety and could possibly indicate new targets for the therapeutic treatment of anxiety.

Hypothalamic Pituitary Adrenal Axis Responses to Low‐Intensity Stressors are Reduced After Voluntary Wheel Running in Rats

Regular physical exercise is beneficial for both physical and mental health. By contrast, stress is associated with deleterious effects on health and there is growing evidence that regular physical exercise counteracts some of the effects of stress. However, most previous studies have suggested that prior exercise does not alter the acute hypothalamic pituitary adrenal (HPA) axis responses to stress. The present series of studies provides evidence that in rats, 6 weeks (but not 1 or 3 weeks) of voluntary wheel running reduces the HPA axis responses to lower-intensity stressors such as an i.p. saline injection, exposure to a novel environment or exposure to moderate intensity noise, but not to more intense stressors such as predator odour exposure or restraint. Daily exercise does not appear to be necessary for the reduction in HPA axis responses, with intermittent access (24 h out of each 72-h period) to a running wheel for 6 weeks, resulting in similar decrements in adrenocorticotrophic hormone and corticosterone release in response to 85 dBA noise exposure. Data from in situ hybridisation for c-fos mRNA are consistent with the hypothesis that voluntary exercise results in a decrease in HPA axis responsiveness to a low-intensity stressor at a central level, with no changes in primary sensory processing. Together, these data suggest that 6 weeks of daily or intermittent exercise constrains the HPA axis response to mild, but not more intense stressors, and that this regulation may be mediated at a central level beyond the primary sensory input.

Application of a naturalistic psychogenic stressor in periadolescent mice: effect on serum corticosterone levels differs by strain but not sex

BackgroundAs a first step in determining whether psychogenic stressors might be incorporated into periadolescent mouse models of stress, we evaluated whether a commonly used psychogenic stressor, exposure to red fox urine, alters serum corticosterone levels in periadolescent C57BL/6J and DBA/2J mice.FindingsIn a 1-day experiment, forty-eight 38-day-old C57BL/6J (N = 12 males; N = 12 females) and DBA/2J (N = 12 males; N = 12 females) mice were exposed to 10-min of red fox urine via cotton ball (N = 12 C57BL/6J mice; N = 12 DBA/2J mice) or to a non-saturated cotton ball (N = 12 C57BL/6J mice; N = 12 DBA/2J mice). All mice were sacrificed 15-min after cotton ball exposure and serum was collected for corticosterone assessment. Overall, there was a main effect for strain such that C57BL/6J male and female mice displayed higher corticosterone levels than did male and female DBA/2J mice. There were no main effects for sex or odor exposure. However, there was a significant strain by odor exposure interaction, whereby, within odor-exposed mice, DBA/2J mice displayed lower corticosterone levels (ng/mL) compared to C57BL/6J mice, regardless of sex. Further, among DBA/2J mice, predator odor exposure reduced corticosterone levels compared to no odor exposure.ConclusionsFindings indicate that mouse strain, but not sex, may play an important role in the efficacy of a predator odor among periadolescent mice.

Ability of predator odour exposure to elicit conditioned versus sensitised post traumatic stress disorder-like behaviours, and forebrain ΔFosB expression, in rats

At present, exposure of a rodent to the odour of a predator is one of the most common animal models of post traumatic stress disorder (PTSD). Despite this, the model remains incompletely characterized, particularly in regard to within subject assessment of major PTSD-like behaviours. In an attempt to redress this situation, we have extensively characterized the two broad categories of behaviour that are considered to characterize PTSD, that is sensitized behaviours such as social withdrawal and hypervigilance and conditioned behaviours such as avoidance of trauma linked cues. Specifically, we determined the presence and duration of both conditioned and sensitized behaviours, in the same cohort of animals, after three exposures to predator odour. Conditioned fear was assessed on the basis of inhibition of locomotor activity upon return to context 2, 7, 14, 21, and 28 days after the last odour exposure session. To assess the impact on sensitization behaviours, we monitored acoustic startle responses and social interaction behaviour 4, 9, 16, 23, and 30 days after the last exposure session. In addition to examining the behavioural consequences associated with odour exposure, we also determined the key brain regions that were activated using ΔFosB immunohistochemistry. Our results show that the two groups of behaviours thought to characterize PTSD (conditioned and sensitized) do not travel together in the predator odour model, with clear evidence of enduring changes in conditioned fear but little evidence of changes in social interaction or acoustic startle. With regard to associated patterns of activity in the brain, we observed that odour-exposed animals exhibited significantly higher numbers of FosB-positive nuclei in only the medial prefrontal cortex (mPFC), a finding that can be viewed as being consistent with the observed behavioural changes.

Disruption of neuroendocrine stress responses to acute ferret odor by medial, but not central amygdala lesions in rats

Investigations of the neural pathways associated with responses to predators have implicated the medial amygdala (MeA) as an important region involved in defensive behaviors. To our knowledge, however, the involvement of the MeA in neuroendocrine responses to predator odor exposure has not been investigated. Therefore, the present study examined the effects of MeA disruption in rats exposed to ferret or control odor on hypothalamo-pituitary-adrenocortical (HPA) axis activation. Bilateral lesions of the MeA were made in Sprague–Dawley rats with the neurotoxin ibotenic acid (10 μg/μl; 0.3 μl / side). As a control for regional specificity, additional groups of rats were given lesions in the central amygdala (CeA). One week after recovery, the rats were exposed to ferret or strawberry control towels in small cages to examine HPA axis responses as determined by plasma corticosterone and adrenocorticotropin hormone (ACTH) levels. Rats with complete bilateral MeA but not CeA lesions displayed significantly less corticosterone and ACTH release compared to sham-operated control rats only in the ferret odor conditions. These results suggest that the MeA is an important structure involved in the HPA axis responses to predator odors, in support of previous studies investigating behavioral responses under similar conditions.

Periadolescent stress exposure exerts long-term effects on adult stress responding and expression of prefrontal dopamine receptors in male and female rats

Recent research has demonstrated that experiential/environmental factors in early life can program the adult stress response in rats, and this is manifest as altered hypothalamic-pituitary-adrenocortical activity and behavior in response to a stressor. Very little work has been devoted to investigating whether the environment during adolescence plays a similar role in modulating ongoing developmental processes and how this might affect adult stress responding. Periadolescent predator odor (PPO) exposure was used here as a naturalistic model of repeated psychological stress. Behavioral and endocrine responses to PPO changed across the exposure period, and behavioral alterations persisted into adulthood. While adolescent rats showed pronounced avoidance responses upon initial PPO exposure, hyperactivity increased across the exposure period, especially in females. Corticosterone (cort) responses to stressor exposure also changed in females, with higher physiological baseline levels observed at the end of the exposure period. In adulthood, relative to rats who had received a control manipulation during adolescence, PPO-exposed rats were more fearful in a novel open field and displayed altered responses to a predator odor stress test in adulthood. Moreover, lower levels of the D2 dopamine (DA) receptor were measured in prefrontal (infralimbic and dorsopeduncular) cortices of PPO-exposed rats. These findings suggest that the adolescent period may represent a sensitive period during which developmental programming of the stress response occurs.

Chronic exposure of cat odor enhances aggression, urinary attractiveness and sex pheromones of mice

To test whether predator odor exposure negatively affects the behavior of prey, we exposed three groups of male house mice (Mus musculus) to the odors of cat (Felis catus) urine, rabbit (Oryctolagus cuniculus) urine and water (control), respectively, for consecutive 58 days and investigated how the treatments affected the response, aggressiveness, dominance, urinary attractiveness to females and pheromone composition of male mice. Compared to mice exposed to rabbit urine or water, those exposed to cat odor did not show any response habituation to the cat odor and became more aggressive, increased mark urine production and were more attractive to females when the latter were tested with their urine. Furthermore, gas chromatography coupled with mass spectrometry analysis revealed coincident elevations of the well-known male pheromones, E,E-α-farnesene, E-β-farnesene, R,R-dehydro-exo-brevicomin or S-2-sec-butyl-dihydrothiazole. In addition, rabbit urine exposure increased urinary attractiveness to females and pheromonal levels of the males in comparison with the mice exposed to water. This could be related to olfactory enrichment of heterospecific chemosignals, suggesting that predator odors were more beneficial. In light of these anti-intuitional findings in the chemical interaction between cats and mice, we conclude that predator odor affects prey more profoundly than previously believed and that its impact may not always be negative.

Vulnerability to mild predator stress in serotonin transporter knockout mice

Effect of predator stress on rat and mouse anxiety-like behavior may model aspects of post traumatic stress disorder (PTSD). A single cat exposure of wild type (C57, CFW) mice can produce lasting anxiety-like effects in the elevated plus maze, light/dark box tests and startle. In addition, female but not male C57 mice are made more anxious in the plus maze by exposure to predator odors alone, suggesting differential vulnerability to predator stressors of differing intensity. There is a link between genetic variation in the serotonin (5-HT) transporter (SERT) and anxiety in humans. This prompted the generation of SERT knockout mice [see Holmes A, Murphy DL, Crawley JN. Biol Psychiatry 2003;54(10):953–9]. Present work used these mice to determine if there was a link between vulnerability to the anxiogenic effects of predator odors and abnormalities of 5-HT transmission induced by a life long reduction in 5-HT reuptake. Wild type (WT, C57 background), heterozygous (SERT +/−, HET) mice and homozygous knockout (SERT −/−, KO) were assigned to handled control groups or groups exposed for 10 min to a large testing room rich in cat odor. One week after handling or room exposure, anxiety testing took place in the dark phase of the light/dark cycle, in red light. Predator odor exposure was selectively anxiogenic in the plus maze and light/dark box tests in SERT −/− mice. Exposure to predator odor did not potentiate startle. Findings suggest a role for abnormalities in 5-HT transmission in vulnerability to some of the lasting anxiogenic effects of species relevant stressors and possibly in vulnerability to PTSD.

Predator threat, copulation effort and immunity in male rats (Rattus norvegicus)

AbstractParental investment theory predicts that organisms should increase their current reproductive investments when they perceive a threat to future reproduction. In such a situation, animals are expected to pay the cost of reproduction by committing a terminal reproductive effort (TRE). We aimed to induce a TRE in male Wistar rats by exposing experimental animals to predator (cat) odour, while the control group was exposed to the odour of rabbit. As response variables, we measured the parameters of male copulatory activity (copulation effort) and resistance to the experimental infection with a neurotropic nematode, Toxocara canis. Contrary to our expectations, control animals received a greater average number of ejaculations in ad libitum copulation trials than predator‐exposed animals. Other parameters of copulatory activity (intromission and ejaculation latencies, numbers of mounts and intromissions, ejaculation efficiency, duration of post‐ejaculatory interval) did not differ between treatment groups. Exposure to predator odour resulted in growth retardation and immune suppression as revealed by the elevated urinary corticosterone levels and higher parasite counts in brain and muscle tissues as compared with control animals. We failed to detect any immunological cost of increased copulatory activity as no significant correlations between measures of copulatory activity and immune parameters could be found. Individual mount number correlated positively with urine creatinine concentration (an index of muscular activity), suggesting that this aspect of male copulatory behaviour is energetically most demanding. Our experiment thus failed to support the hypotheses that exposure to predator odour increases copulatory activity in male rats and that intense copulatory activity leads to immune suppression. The hypothesis that predator odour exposure leads to immune suppression and reduced infection resistance was supported.

Expression of egr-1 ( zif268) mRNA in select fear-related brain regions following exposure to a predator

Research has demonstrated that immediate-early genes/inducible transcriptional factors (e.g., c-fos, egr-1) are increased in amygdala nuclei (lateral, basal and central nuclei) known to be involved in fear conditioning, footshock stress and novelty. Although these data suggest that expression of inducible transcriptional factors are involved in fear, other non-shock ethologically based paradigms (predator or predator odor exposure) do not appear to increase c-fos in the lateral and basal nuclei. While the lack of c-fos expression may indicate that predator stress does not engage the lateral and basal amygdala nuclei, it may be that c-fos in the amygdala is not responsive to predator exposure. Therefore, egr-1, which increases in the lateral nucleus following fear conditioning, footshock and novelty, was assessed to determine if its expression is induced in rats exposed to a cat. Five minutes of cat exposure did not increase expression of egr-1 mRNA in the lateral nucleus of the amygdala. egr-1 was increased in the paraventricular nucleus of the hypothalamus, indicating cat-induced stress, and visual cortex compared to rats that were either confined for 5 min or handled. In the lateral periaqueductal gray, handled rats displayed a left hemisphere dominance, which disappeared in both the cat-exposed and confined group, suggesting that immobility, induced by either cat-induced stress or unstressed confinement, increased right hemisphere egr-1 expression. The results are discussed in a context of differences and similarities in neural circuitry for conditioned and unconditioned fear.

Anxiety levels and wild running susceptibility in rats: assessment with elevated plus maze test and predator odor exposure

It is reported in the literature that nearly 20% of rats are susceptible to displays of wild running (WR) behavior when submitted to high intensity acoustic stimulation. Some characteristics of WR suggest that it can be viewed as a panic-like reaction. This work aimed to test whether WR-sensitive rats show higher levels of anxiety in elevated-plus-maze (EPM) and predator-odor exposure paradigms in comparison with WR-resistant ones. Male adult Wistar rats were submitted to two trials of acoustic stimulation (104 dB, 60 s) in order to assess WR susceptibility. Seven WR-sensitive and 15 WR-resistant rats were evaluated by the EPM test. Other 13 WR-sensitive and 18 WR-resistant animals were submitted to the predator-odor exposure test which consisted of a 10 min-session of free exploration in a specific apparatus containing two odoriferous stimuli: cotton swab imbedded with snake cloacal gland secretion or with iguana feces (control). WR-sensitive rats presented a significantly higher closed-to open-arm-entry ratio in the EPM test. All rats responded with anxiety-like behaviors to the predator odor exposure, although the WR-sensitive ones showed a marked behavioral inhibition regardless of the odor condition. We conclude that WR-sensitive rats present elevated levels of anxiety manifested by means of passive behavioral strategies.

Deficits in sensorimotor gating and tests of social behavior in a genetic model of reduced NMDA receptor function

Reduced NMDA receptor function is hypothesized to contribute to the pathophysiology of schizophrenia. In order to model chronic and developmental NMDA receptor hypofunction, a mouse line was developed that expresses low levels of the NMDA R1 subunit (NR1) of the NMDA receptor. The present study tested the hypothesis that these NR1 hypomorphic mice would exhibit deficits in sensorimotor and conspecific interactions, analogous to deficits observed in schizophrenic patients. F1 hybrid mice homozygous for the NR1 hypomorphic mutation (NR1 −/−) were generated by crossing heterozygous mice (NR1 +/−) from C57BL/6 and 129 Sv/Ev backgrounds. To assess sensorimotor gating, mice were tested in the paradigm of prepulse inhibition of acoustic startle. The NR1 hypomorphic mice exhibited increased acoustic startle responses and also showed deficits in prepulse inhibition. Startle responses were differentially altered by predator odor exposure in the male NR1 −/− mice, in comparison to control mice. In a test of social affiliation, the wild type mice spent significantly more time investigating a novel mouse in comparison to the NR1 −/− mice. In a resident-intruder test, marked deficits were found in sex-specific aggressive behavior between the wild type and mutant mice. These data support the contention that the NR1 hypomorphic mice exhibit alterations in sensorimotor gating and typical conspecific interactions, reminiscent of behavioral disturbances associated with schizophrenia. The NR1 hypomorphic mice could represent a model system to explore novel treatment and preventative strategies for certain symptoms of schizophrenia.

Critical analysis of the neural systems organizing innate fear responses

Unconditioned emotional responses elicited by exposure to a predator have served as the prototypical exemplar for analyses of the behavioral biology of fear-related emotionality. However, the primary research model for the study of fear has involved shock-based cue and context conditioning. While these shock-based models have provided a good understanding of neural systems regulating specific conditioned fear-related behaviors (typically freezing), it is not known if the neural systems underlying an array of defensive responses to innate, unconditioned, painless threat stimuli, and conditioning to these stimuli, are the same as those involved in foot shock and its conditioning sequellae. Recent work involving lesions and c-Fos activation in conjunction with predator or predator odor exposure suggest specific neural systems for response to these, potentially different from the systems outlined in Pavlovian fear conditioning studies. As outlined in the present review, these systems include the medial hypothalamic defensive circuit; specific amygdalar and septo-hippocampal territories, involved in processing, respectively, cues related to the predator presence and environmental contextual analysis; and the periaqueductal gray, known to be critically involved in the expression of predator-induced responses. This information may be potentially important in analysis of defense-related psychopathologies and in the design of therapeutic interventions for them.

Odor-Induced Variation in Anxiety-Like Behavior in Mice is Associated with Discrete and Differential Effects on Mesocorticolimbic Cholecystokinin mRNA Expression

The present investigation assessed alterations in mesocorticolimbic cholecystokinin (CCK) mRNA following novel predator and non-predator odor exposure and light-dark testing in CD-1 mice. In brief, acute exposure of CD-1 mice to the predator odor, 2,5-dihydro-2, 4,5-trimethylthiazoline (TMT; the major component of the anal gland secretions of the red fox), or the control odor, butyric acid (BA), suppressed rearing behavior during odor presentation, subsequently induced anxiety in the light dark test, and was associated with increased mesocorticolimbic CCK mRNA relative to saline treated mice. Only mice exposed to TMT displayed elevated freezing behaviors during odor treatment. In the light-dark test, mice exposed to either BA or TMT took longer to reenter the light section of the apparatus and spent less cumulative time in the light relative to mice exposed to saline. The decreased time spent in the light as well as light dark transitions were exaggerated among mice exposed to fox odor. Odor presentation was associated with increased CCK mRNA in mesocorticolimbic sites. Butyric acid was associated with enhanced CCK gene expression in the VTA, while both BA and TMT were associated with increased medial prefrontal cortex (mPFC) CCK mRNA levels. Increased CCK mRNA within the VTA and mPFC was evident among mice despite testing in the light-dark box. In contrast, basolateral nucleus of the amygdala (BLA) CCK mRNA was enhanced following odor exposure among mice in the light dark test relative only to saline treated mice which demonstrated a natural decrease in BLA CCK mRNA following the light dark test. The differential pattern of CCK mRNA associated with discrete psychogenic stressor manipulations and the provocation of anxiety-like behavior associated with such experiences is discussed.

Brief Exposure to Female Odors “Emboldens” Male Mice by Reducing Predator-Induced Behavioral and Hormonal Responses

In rodents, where chemical signals play a particularly important role in determining intersexual interactions, various studies have shown that male behavior and physiology is sensitive to female odor cues. Here we examined the effects of brief (1 min) and more prolonged (60 min) preexposure to the odors of a novel estrous female on the behavioral and hormonal responses of sexually experienced and inexperienced male mice, Mus musculus, to subsequent predator (cat and weasel) odor exposure and potential predator risk. Brief, but not prolonged, preexposure to the odors of an estrous female decreased the aversion and avoidance responses of male mice to cat odor in a Y-maze preference test, with the extent of responses being affected by a males prior sexual experience. Similarly, brief, but not prolonged, preexposure to female odors markedly attenuated the analgesic responses elicited in male mice by weasel odor. Brief exposure to a novel estrous female by itself had no significant immediate effects on either corticosterone or testosterone levels in the males. However, brief, but not prolonged, preexposure to the odors of an estrous female attenuated the marked increase in corticosterone and decrease in testosterone that were induced in males by exposure to weasel odor. The decreases in aversive responses to, and effects of, predator odor exposure that are induced by brief exposure to a novel estrous female may reflect a greater risk taking and boldness in males that could directly facilitate access to an immediately, and possibly transiently, available novel sexually receptive female.

Diagnosing schizophrenia in the initial prodromal phase

Prenatal stress mediated through the mother can lead to long-term adaptations in stress-related phenotypes in offspring. This study tested the long-lasting effect of prenatal exposure to predator odor, an ethologically relevant and psychogenic stressor, in the second half of pregnancy. As adults, the offspring of predator odor-exposed mothers showed increased anxiety-like behaviors in commonly used laboratory tasks assessing novelty-induced anxiety, increased defensive behavior in males and increased ACTH stress reactivity in females in response to predator odor. Female offspring from predator odor-exposed dams showed increased transcript abundance of glucocorticoid receptor (NR3C1) on the day of birth and FK506 binding protein 5 (FKBP5) in adulthood in the amygdala. The increase in FKBP5 expression was associated with decreased DNA methylation in Fkbp5 intron V. These results indicate a sex-specific response to maternal programming by prenatal predator odor exposure and a potential epigenetic mechanism linking these responses with modifications of the stress axis in females. These results are in accordance with the mismatch hypothesis stating that an animal's response to cues within its life history reflects environmental conditions anticipated during important developmental periods and should be adaptive when these conditions are concurring.

Sex differences in opioid and N-methyl- d-aspartate mediated non-opioid biting fly exposure induced analgesia in deer mice

There is evidence for sex differences in responses to noxious stimuli and in the expression and mediation of analgesia. In particular, results of investigations with swim stress and the more ethologically appropriate stress of predator odor exposure have suggested sex differences in N-methyl- d-aspartate (NMDA) receptor system involvement in the mediation of analgesia. Whether or not this sex difference generalizes to other environmental stressors is, however, not clear. Biting flies are a natural aversive stimuli commonly encountered by wild and domestic animals and humans. The present study examined the opioid and non-opioid mediated nociceptive (50°C hot plate) responses of reproductive male and female deer mice, Peromyscus maniculatus, exposed to biting fly attack. A 30 min exposure to biting flies (stable flies, Stomoxys calcitrans (L.)) elicited a naloxone sensitive, opioid-mediated analgesia that was of a greater magnitude in males than in female deer mice. In contrast, a 5 min exposure to biting flies elicited a `on-opioid' analgesia that was of similar magnitude in both sexes and insensitive to both naloxone and the specific kappa opiate antagonist, nor-binaltorphimine. In male mice this non-opioid analgesia was antagonised by the competitive NMDA antagonist, NPC 1262, while in reproductive females the biting fly-induced analgesia was insensitive to NPC 12626. These results show that there are sex differences in NMDA involvement in the mediation of the non-opioid analgesia arising from brief exposure to the stress of biting fly attack. These data from a common, natural environmental challenge support the presence of basic sex difference in NMDA involvement in the mediation of stress-induced analgesia.

Effect of illumination condition on risk assessment behaviors of mice

Levels of risk assessment evoked by either a synthetic predator odor or noncontact exposure to live rats were examined under white or red light conditions. Defensive responses to the predator odor were infrequent in white light and showed a modest, but reliable, increase under red light. Noncontact exposure to rats, in contrast, produced considerably higher levels of risk assessment than did odors in white light, and these levels were nearly doubled under red light. Judicious selection of eliciting and background stimuli may provide considerable control over the intensity of risk assessment. Such procedures may prove useful for the study of anxiety-like states. Risk assessment is a popular tool for the study of anxiety-like states (e.g., Blanchard & Blanchard, 1988, 1990) but the variables controlling the intensity of these behaviors are not well characterized. Presentation of various odors, for example, regularly evokes modest elevations in the levels of these defensive responses (e.g., Blanchard et aI., 1990; Garbe, Kemble, & Rawleigh, 1994; Williams & Scott, 1989) which are sensitive to both anxiolytic and anxiogenic drug treatments (Blanchard et aI., 1990; Blanchard, Tauklis, Rodgers, Magee, & Blanchard, 1993; Garbe, Kemble, & Strunk, 1993; Kemble & Gordon, 1996; Zangrossi & File, 1992). Although this experimental manipulation is clearly useful, it should be noted that a reasonably wide range of both predator and nonpredator odors have roughly equivalent effects on risk assessment (Garbe et aI., 1994). Furthermore, repeated prior defeat experience (Kemble & Bolwahnn, in press) does not increase odor reactivity. If odor­ induced risk assessment is generally insensitive to major experimental manipulations, then its usefulness for the study of defensiveness may be somewhat compromised. Alternatively, it is possible that some relevant stimulus conditions remain untested. Illumination condition appears to be a likely candidate. Not only is open field activity affected by illumination levels (e.g., Welker, 1959) but Lester and Faneslow (1992) find that light