Prenatal oxazepam enhances mouse maternal aggression in the offspring, without modifying acute chlordiazepoxide effects

Developmental exposure to chlorpyrifos alters reactivity to environmental and social cues in adolescent mice

Neonatal mice were treated daily on postnatal days (pnds) 1 through 4 or 11 through 14 with the organophosphate pesticide chlorpyrifos (CPF), at doses (1 or 3 mg/kg) that do not evoke systemic toxicity. Brain acetylcholinesterase (AChE) activity was evaluated within 24 h from termination of treatments. Pups treated on pnds 1-4 underwent ultrasonic vocalization tests (pnds 5, 8, and 11) and a homing test (orientation to home nest material, pnd 10). Pups in both treatment schedules were then assessed for locomotor activity (pnd 25), novelty-seeking response (pnd 35), social interactions with an unfamiliar conspecific (pnd 45), and passive avoidance learning (pnd 60). AChE activity was reduced by 25% after CPF 1-4 but not after CPF 11-14 treatment. CPF selectively affected only the G(4) (tetramer) molecular isoform of AChE. Behavioral analysis showed that early CPF treatment failed to affect neonatal behaviors. Locomotor activity on pnd 25 was increased in 11-14 CPF-treated mice at both doses, and CPF-treated animals in both treatment schedules were more active when exposed to environmental novelty in the novelty-seeking test. All CPF-treated mice displayed more agonistic responses, and such effect was more marked in male mice exposed to the low CPF dose on pnds 11-14. Passive avoidance learning was not affected by CPF. These data indicate that developmental exposure to CPF induces long-term behavioral alterations in the mouse species and support the involvement of neural systems in addition to the cholinergic system in the delayed behavioral toxicity of CPF.

Sensory, hormonal, and neural control of maternal aggression in laboratory rodents

Parental animals of many rodent species display fierce and persistent aggression toward unfamiliar conspecifics that appears to protect their often altricial and defenseless young. We herein review studies of the sensory, hormonal, neuroanatomical, and neurochemical mechanisms underlying maternal aggression in laboratory rodents. The relationship between maternal aggression and fearfulness or anxiety is also discussed.

The developmental psychobiology of behavioural plasticity in mice: the role of social experiences in the family unit

Small perturbations of young animals' sensory experience or hormonal milieu have been shown to alter ontogenetic pathways and to potentially produce huge effects on CNS functioning and behaviour later in life. From a social point of view, variables such as the expression of affiliative bonding and of playful interactions among littermates, the quantity/quality of maternal care, or episodes of maternal or sibling deprivation during critical phases in development, seem to interfere as epigenetic factors with the rigidly ordered temporal sequences of events that occur during the ontogenesis of CNS. This leads to the onset of adaptive neurodevelopmental changes, which are observable within a continuum that encompasses both "normal" individual variability and potential behavioural disorganisation, which in turn will probably be related to profound alteration in the establishment of adult social competence. The present review summarises the more recent work in mice dealing with short-term, as well as long-term modifications, in naturally occurring species-typical social and non-social responses as a function of the early manipulation of social characteristics of the family unit (such as litter gender composition and time of weaning). These analyses were carried out on infant animals, i.e. during the ontogenetic stage of the establishment of social bonding, as well as on pre-pubertal and adult mice and on lactating adult females. Critical issues, such as the respective roles of sibling-sibling and dam-offspring interactions in the shaping of "sibling effects", are also addressed. Overall, these studies indicate that, within their natural range of variation, early patterns of social stimulation are powerful determinants of subsequent behaviour of developing altricial rodents, and confirm that early social life events warrant attention because they can strongly affect neurobehavioural development. Evidence of a relationship between social events occurring during early rearing (i.e. when dramatic transitions in neuroendocrine and neurochemical CNS systems occur) and individual behavioural variability in the infant and adult response to the effects of psychostimulants abused by humans is presented. A better understanding of the mechanisms that mediate such remarkable plasticity might have great psychobiological as well as clinical importance, especially when considering the issue of vulnerability to drug abuse.

Prenatal sulfur dioxide exposure induces changes in the behavior of adult male mice during agonistic encounters

Sulfur dioxide (SO2) is one of the most important pollutants of the western countries, responsible for several cardiopulmonary diseases in humans. SO2 affects both young and adult people, causing low work productivity with social and economical costs extremely high for the communities. To test whether or not SO2 produces changes in social and/or agonistic behavior of laboratory animals, outbred CD-1 male mice were prenatally exposed to different SO2 concentrations (0, 5, 12, or 30 ppm) up to pregnancy day 14. At adulthood, following a 4-week isolation period, they underwent an aggressive encounter with CD-1 male opponents of the same age, body weight, and isolation condition (single 20-min session). The levels of several responses such as tail rattling, freezing, and defensive postures were reduced by the treatment, particularly during the initial period of the agonistic encounter, whereas offensive and attack behaviors were not significantly modified. In addition, rearing and social investigation increased. Overall, the present results indicate that prenatal SO2 exposure can alter mouse social/agonistic behavior, apparently acting on the approach phase toward the opponent and suggestive of changes in the animals' capability to cope with threatening dangerous situations.

On mouse pups and their lactating dams: behavioral consequences of early exposure to oxazepam and interacting factors

Behavioral analysis in animal models appears to be a valuable and sensitive tool for detecting subtle alterations in CNS function, which can be produced by early exposure to small perturbations of sensory experience, hormonal milieu, or exposure to psychotropic agents devoid of major teratogenic potential. Concerning anxiolytics, the more recent work in mice, which is here summarized, was carried out by putting the emphasis on changes in naturally occurring species-typical social responses as a function of early exposure to benzodiazepines. For adult females, on the behavior expressed during the early postpartum period, whereas for infant subjects, on the ontogenetic stage of the establishment of social bonding. Critical issues such as the choice of fostering procedure and rearing conditions are also addressed. Evidences of relationships between changes in social milieu taking place during early rearing-i.e., when dramatic transitions in the neurochemical target system occur- and the adult behavioral response to challenges with BDZ agents are presented. These data strengthen the notion that the modes of reaction of adult animals to the joint influence of physiological and environmental (stimulus) variables are under the influence of events in early ontogenesis. Therefore, a better understanding of the mechanisms-as unveiled by an appropriate use of drug tools-that mediate such a plasticity might have considerable psychobiological and clinical-therapeutical relevance.

A comparison of behavioural effects of prenatally administered oxazepam in mice exposed to open-fields in the laboratory and the real world

Prenatal benzodiazepine exposure has been reported to result in abnormal neurobehavioural development in laboratory animals but little is known about the behavioural relevance of this effect ina naturalistic environment. In this study, outbred CD-1 male mice were prenatally exposed to oxazepam (15 mg/kg per os, twice daily) on days 12-16 of fetal life and fostered at birth to untreated dams. At adulthood, each mouse was fitted with a radio collar and its first reactions assessed. Three hours later, behavioural and exploratory activities were recorded in a laboratory open field, and 24 h later in a natural setting. Immediate reactions to the radio collar were higher in the oxazepam-treated mice than in controls consisting of more attempts to remove it and an increase of push-digging. The attempts to remove the collar were still evident in oxazepam treated mice tested in the laboratory open-field 3 h later. Moreover, oxazepam increased the frequency of grooming and reduced walking in both the laboratory and the natural settings. In the natural settings running was increased during the initial 30-min test, while a pronounced level of grooming and a lower frequency of eating were observed 140 min after release. Frequency of sniffing, grooming, and rearing behaviours were higher in the laboratory test when compared to the natural settings. On the other hand, prolonged bouts of sniffing were recorded in the natural environment. These findings permit separation of robust drug effects (increased grooming, reduced walking) from situation-dependent effects, the natural environment revealing, in addition, more subtle effects.

Prenatal oxazepam affects passive avoidance performance of preweaning mice

CD-1 outbred mice were exposed to oxazepam on fetal days 12-16 by maternal administration (per os of 15 mg/kg twice daily at 8 a.m. and 8 p.m.) and fostered at birth to untreated dams, while control mice received vehicle solution. Mice were then tested on postnatal day 14 and 15 in a passive avoidance apparatus for their ability to withhold a step-down response from a vibrating platform. The step-down response was punished with a mild footshock. Each animal was subjected to a maximum of 15 trials. Mice prenatally treated with oxazepam showed an impairment in the acquisition of the task as indicated by shorter latencies to step-down throughout the 15 trials in both sessions (days 14 and 15). As control nonreinforced animals prenatally treated with oxazepam did not show a similar alteration in latency to step-down, these data suggest that prenatal exposure to oxazepam influences behavioral performance of preweaning mice in an aversively motivated task.

A mouse model of early social interactions after prenatal drug exposure: a genetic investigation

The aim of the present study was to (i) characterise the mouse behavioural profile (particularly social interactions) during the preweaning period, (ii) assess the effects of prenatal exposure to an anticonvulsant drug widely used in clinical practice, (iii) examine possible genetic differences both in baseline behavioural profiles and in sensitivity to drug-induced effects. Following a balanced intra-strain fostering procedure, the offspring of C57BL/6J and CBA inbred mouse strains from mothers exposed during pregnancy to either phenobarbitone (PHB, 60 mg/kg) or vehicle (VEH) given intraperitoneally (IP) during days 10-16 of gestation, were observed for early social interactions in the home cage during the last part of the preweaning period (days 20 and 21). The behavioural repertoires of the two strains differed markedly, in that C57 pups were more involved in Play soliciting, Locomotor-rotational play, and in Maintenance activities, while CBA mice spent much more time being inactive or exploring the environment. C57 and CBA mice also differed in the sensitivity to PHB exposure. On the whole, time spent in Investigative/Affiliative behaviours was increased, while the frequency of Play soliciting patterns was reduced in PHB-treated mice. The treatment of the fostering mother had only negligible effects, suggesting that PHB-induced changes in behaviour were largely due to direct effects of the substance on the foetus. These results indicate that specific items of the preweaning behavioural profile, and particularly social interactions, are influenced by early PHB exposure, and that the responses are heavily affected by the genotype.

Impaired acquisition of swimming navigation in adult mice exposed prenatally to oxazepam

Prenatally administered oxazepam (OX) impairs adult radial maze performance in mice, possibly by permanent hippocampal changes. CDI mice were tested in swimming navigation, a sensitive indicator for hippocampal damage. Ten males and ten females were exposed to OX on fetal days 12-16 by maternal administration PO of 30 mg/kg/day and fostered at birth to untreated dams, while control mice received vehicle solution. All mice were tested at 8-9 weeks for ability to find a submerged platform in a fixed location (acquisition: 18 trials, 6 trials per day) and for capacity to re-orient towards a new platform position (reversal: 12 trials, 6 trials per day). OX mice showed a slight but significant impairment of swimming navigation during the initial part of training, as indicated by longer swimming paths during the fourth and fifth trial (day 1), an impairment due both to delayed habituation to the novel stressfull condition and acquisition of platform climbing but unrelated to navigational abilities. No treatment-dependent differences were observed in the reversal phase. During reversal, both OX and control females spent significantly more time in swimming across the location of the old platform. Unrelated to navigational performance, females showed a slightly but significantly higher swimming speed than males. Due to the absence of any navigational impairment, data suggest that prenatal exposure to oxazepam exerts long-term influence on adult learning capacities primarily through interaction with brain systems located outside the hippocampus.

Developmental aspects of neurobehavioural toxicity

Previous work on the developmental aspects of neurobehavioural toxicity in rats and mice has shown the reliability of a variety of procedures aimed at assessing changes that may have widespread functional consequences, for example: (i) modified Fox batteries to study the maturation of various reflexes and responses after birth, (ii) activity/habituation and analgesia tests with age-specific profiles of reactivity to selected drug challenges, and (iii) simple learning tasks such as active and passive avoidance [1]. We will now summarize more recent work on other portions of the behavioural repertoire which deserve to be thoroughly assessed in "higher-tier" studies.

Eight-arm maze performance, neophobia, and hippocampal cholinergic alterations after prenatal oxazepam in mice

Outbred CD-1 mice were exposed to oxazepam (15 mg/kg PO twice/day) on days 12-16 of fetal life, i.e., at a critical ontogenetic stage of Type II benzodiazepine (BDZ) receptor increase, and fostered at birth to untreated dams. At adulthood, radial arm maze performance, activity-habituation test in an open-field arena (either single 15-min test or three 5-min sessions at 24-h intervals), approach to a novel stimulus object, and amphetamine or scopolamine effects thereon were assessed in male progeny. Overall, the oxazepam exposed (OX) mice were much less efficient in the radial arm maze task than the vehicle exposed (VEH) animals. Pre-test scopolamine injection, but not amphetamine, significantly impaired the arm maze performance of OX mice when compared with the corresponding VEH-scopolamine animals. In separate nonlearned behavioral tasks, prenatal oxazepam did not affect either baseline activity levels in the open field or the response to the amphetamine and the scopolamine challenge, while it considerably increased the latency of first approach to a novel object and produced a deficit of habituation in the course of the subsequent exploratory period. Concomitant investigation at the neurochemical level showed that the adult OX animals had a significant increase in both Bmax and in the affinity (Kd) of cholinergic muscarinic receptors in the hippocampal formation when compared to the vehicle-exposed controls.

Sexual segregation in infancy and bi-directional benzodiazepine effects on hot-plate response and neophobia in adult mice

In the present experiment, the hypothesis that rearing animals in conditions of sexual segregation in infancy (ISS) would affect their adult behavioral reactivity to drug or environmental challenges was tested. Outbred Swiss CD-1 mouse litters were reduced at birth to six pups according to three conditions: MM (all males), MF (sex-balanced composition), and FF (all females). At weaning (day 21), all mice were rehoused in unisexual groups. At adulthood (day 70), animals were challenged either with BDZ agonist chlordiazepoxide (CDP at 2.5- or 5.0-mg/kg dose) or BDZ receptor partial inverse agonist Ro 15-3505 (RO at 3-, 10-, or 30-mg/kg dose) and assessed in sequence for pain reactivity in a hot-plate apparatus (set at 55 +/- 1 degrees C), for locomotor activity in a Varimex apparatus, and finally for neophobia level by measuring the latency to first approach a novel object. As concerns the hot-plate test, lick latency was significantly shortened in MF females receiving CDP (5.0 mg/kg), while RO was either ineffective in MF females or induced a prominent dose-dependent analgesia in FF females. Activity was decreased by CDP (2.5 mg/kg) and enhanced by RO (3.0 mg/kg). For latency to approach a novel object, males as a whole exhibited shorter times than females. Mixed-sex animals of both sexes were less fearful, being also more explorative than their corresponding unisexually reared groups. In particular, MF males receiving either a 5.0-mg/kg CDP dose or a 3.0-mg/kg RO dose explored the object more often than MM males.(ABSTRACT TRUNCATED AT 250 WORDS)

Selective changes in mouse behavioral development after prenatal benzodiazepine exposure: a progress report

1. Animal studies of the effects of early exposure to CNS agents devoid of a major teratogenic potential must assess possible deviations from normal behavioral development in both a stage-specific and a behavior-specific fashion; several experiments on prenatal benzodiazepine (BDZ) exposure are reviewed, illustrating such an assessment strategy and discussing caveats on experimental designs and statistical analysis. 2. The offspring of mouse dams treated in late pregnancy with oxazepam (15 mg/kg p.o. twice daily on days 12-16) show a mild and reversible impairment in somatic and neurobehavioral development which is unlikely to be responsible for a series of other more specific changes. 3. The treatment produces a selective reduction of locomotor activity and amphetamine hyperactivity at the end of the second postnatal week, as well as a selective impairment of active avoidance at the young adult stage, in the absence of similar changes in scopolamine hyperactivity and passive avoidance. 4. The treatment also prevents the appearance at 28 days of morphine hyperactivity and of rebound hyperactivity after muscimol depression, without modifying the developmental profile of pain reactivity and of morphine and muscimol analgesia. 5. Young adult females previously exposed to oxazepam in utero show a marked enhancement of maternal aggression towards male intruders; mother-pup interactions are also modified, leading either to reduced or to exaggerated maternal care as a function of fostering procedures. 6. Overall, several effects of prenatal BDZ exposure appear to be amenable to modifications in monoaminergic system functions and/or to an accelerated development of GABAergic mechanisms; some of the changes in social and parental interactions, however, point to subtle modifications in the balance between different components of the fear-defensive repertoire, possibly due to an altered stimulus reactivity by mechanisms which are still poorly understood.