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

Maternal prolactin during late pregnancy is important in generating nurturing behavior in the offspring

Although maternal nurturing behavior is extremely important for the preservation of a species, our knowledge of the biological underpinnings of these behaviors is insufficient. Here we show that the degree of a mother's nurturing behavior is regulated by factors present during her own fetal development. We found that Cin85-deficient (Cin85^-/-) mother mice had reduced pituitary hormone prolactin (PRL) secretion as a result of excessive dopamine signaling in the brain. Their offspring matured normally and produced their own pups; however, nurturing behaviors such as pup retrieval and nursing were strongly inhibited. Surprisingly, when WT embryos were transplanted into the fallopian tubes of Cin85^-/- mice, they also exhibited inhibited nurturing behavior as adults. Conversely, when Cin85^-/- embryos were transplanted into the fallopian tubes of WT mice, the resultant pups exhibited normal nurturing behaviors as adults. When PRL was administered to Cin85^-/- mice during late pregnancy, a higher proportion of the resultant pups exhibited nurturing behaviors as adults. This correlates with our findings that neural circuitry associated with nurturing behaviors was less active in pups born to Cin85^-/- mothers, but PRL administration to mothers restored neural activity to normal levels. These results suggest that the prenatal period is extremely important in determining the expression of nurturing behaviors in the subsequent generation, and that maternal PRL is one of the critical factors for expression. In conclusion, perinatally secreted maternal PRL affects the expression of nurturing behaviors not only in a mother, but also in her pups when they have reached adulthood.

Preweaning sensorimotor deficits and adolescent hypersociability in Grin1 knockdown mice

Mice with knockdown of the N-methyl-D-aspartate (NMDA) receptor NR1 subunit, encoded by the gene Grin1, have been investigated as a model for the intrinsic NMDA hypofunction hypothesized for schizophrenia. Previous work has shown that adult Grin1 mutant mice have overt deficits in habituation and sensorimotor gating, exaggerated reactivity to environmental stimuli, reduced social approach, and other alterations that reflect behavioral manifestations of schizophrenia. In humans, the emergence of overt symptoms of the disorder typically occurs in adolescence or early adulthood, suggesting a role for aberrant maturation of NMDA receptor signaling in symptom onset. The following study evaluated Grin1 mutant mice for abnormal behavioral phenotypes during the preweaning, adolescent, and adult periods. Measures included open field activity, prepulse inhibition of acoustic startle responses, and social preference in a three-chamber choice task. Mice from the C57BL/6J inbred strain, one of the parental strains for the Grin1 line, were also tested. The results showed that developmental reduction of NMDA receptor function led to significant alterations in behavior during the second and third weeks of life, including exaggerated startle responses and sensorimotor gating deficits on postnatal day 13, and pronounced hypersociability in adolescence. Male Grin1 mutant mice were more susceptible than female mice to the detrimental effects of decreased NMDA signaling. Overall, these findings provide evidence that reduced Grin1 function leads to abnormal phenotypes in the preweaning period, and that deficient NMDA signaling can lead to both overt hypersociability or marked asociality, dependent upon sex and age.

Long-term effects of environmentally relevant doses of 2,2',4,4',5,5' hexachlorobiphenyl (PCB153) on neurobehavioural development, health and spontaneous behaviour in maternally exposed mice

Background

Polychlorinated biphenyls (PCBs) are widespread in the environment, human food and breast milk. Seafood is known to contain nutrients beneficial for the normal development and function of the brain, but also contaminants such as PCBs which are neurotoxic. Exposure to non-coplanar PCBs during brain development can disrupt spontaneous behaviour in mice and lead to hyperactive behaviour. Humans are chronically exposed to the highest relative levels of organochlorines in early childhood during brain development, though usually at doses which do not give clinical symptoms of toxicity. This study aimed to elucidate the developmental and behavioural effects of 2,2',4,4',5,5' hexachlorobiphenyl (PCB153) in mice, mimicking human exposure during gestation and lactation.

Methods

Environmentally relevant doses of PCB153 were added to the experimental diets. Feed concentrations were approximately 0.5, 6.5, and 1500 μg PCB153/kg feed, representing a realistic and a worst case scenario of frequent consumption of contaminated fish. The study also investigated the effects of maternal nutrition, i.e. a standard rodent diet versus a high inclusion of salmon. Mice pups were examined for physical- and reflex development, sensorimotor function and spontaneous behaviour from five days after birth until weaning. A selection of pups were followed until 16 weeks of age and tested for open field behaviour and the acoustic startle response (ASR) with prepulse inhibition (PPI). Blood thyroid hormones and liver enzymes, blood lipids and PCB153 content in fat were examined at 16 weeks. Statistical analyses modelled the three way interactions of diet, PCB exposure and litter size on behaviour, using generalized linear models (GLM) and linear mixed effect models (LME). The litter was used as a random variable. Non-parametric tests were used for pair wise comparisons of biochemical analyses.

Results

Litter size consistently influenced pup development and behaviour. Few lasting PCB153 related changes were observed, but results indicated effects on synchronization of physical development. Perinatal PCB153 exposure appeared to reduce habituation and cause aggression in males, though not statistically significant.

Conclusions

Litter size and maternal diet influenced physical development and function more than PCB153 in perinatally exposed mouse pups and supports the developmental importance of maternal care and the social environment.

Repeated acute exposures to hypergravity during early development subtly affect CD-1 mouse neurobehavioural profile

Exposure to altered gravitational environment, especially during critical ontogenetic phases, may induce persistent nervous system modifications and behavioural anomalies. This study evaluated the effects of hypergravity exposure on the development of the nervous system and assessed the relevance of parity in the mother's responses to altered gravitational stimuli. CD-1 mouse pups of both sexes delivered by primiparous and biparous dams were exposed to 1h of 2 G rotationally induced hypergravity from PND2 to PND9. Sensorimotor responses and somatic growth were daily measured (PND2-PND15), ultrasonic vocalisations recorded on PNDs 2, 5 and 9, and homing behaviour evaluated on PND12. In addition, spatial orientation ability was assessed in a T-maze on PND18, while mice exploratory behaviour and locomotor activity were evaluated in an open-field test (PND21). Long-term effects of hypergravity exposure on both spatial learning (Morris water-maze test) and brain levels of NGF and BDNF were also investigated at adulthood. Rotation per se induced a delay in somatic growth, sensorimotor responses and ultrasonic vocalisation profile, while hypergravity highlighted sex differences in open-field behaviour. Strategies to solve a spatial learning task, rather than learning per se, were affected by early exposure to rotation, while hypergravity selectively altered behavioural profile in the reversal phase of the test. Early exposure to rotation per se also decreased hypothalamic BDNF levels, while hypergravity reduced NGF levels in the frontal cortex. Previous maternal experience did not interact with hypergravity exposure, while differences between offspring of primiparous and biparous dams were observed in sensorimotor development and exploratory behaviour.

Structural Effects and Neurofunctional Sequelae of Developmental Exposure to Psychotherapeutic Drugs: Experimental and Clinical Aspects

The advent of psychotherapeutic drugs has enabled management of mental illness and other neurological problems such as epilepsy in the general population, without requiring hospitalization. The success of these drugs in controlling symptoms has led to their widespread use in the vulnerable population of pregnant women as well, where the potential embryotoxicity of the drugs has to be weighed against the potential problems of the maternal neurological state. This review focuses on the developmental toxicity and neurotoxicity of five broad categories of widely available psychotherapeutic drugs: the neuroleptics, the antiepileptics, the antidepressants, the anxiolytics and mood stabilizers, and a newly emerging class of nonprescription drugs, the herbal remedies. A brief review of nervous system development during gestation and following parturition in mammals is provided, with a description of the development of neurochemical pathways that may be involved in the action of the psychotherapeutic agents. A thorough discussion of animal research and human clinical studies is used to determine the risk associated with the use of each drug category. The potential risks to the fetus, as demonstrated in well described neurotoxicity studies in animals, are contrasted with the often negative findings in the still limited human studies. The potential risk fo the human fetus in the continued use of these chemicals without more adequate research is also addressed. The direction of future research using psychotherapeutic drugs should more closely parallel the methodology developed in the animal laboratories, especially since these models have already been used extremely successfully in specific instances in the investigation of neurotoxic agents.

Polybrominated diphenyl ethers: neurobehavioral effects following developmental exposure

Polybrominated diphenyl ethers (PBDEs), a class of widely used flame retardants, are becoming widespread environmental pollutants, as indicated by studies on sentinel animal species, as well as humans. Of particular concern are the reported increasingly high levels of PBDEs in human milk, as should be given that almost no information is available on their potential effects on developing organisms. In order to address this issue, studies have been conducted in mice and rats to assess the potential neurotoxic effects of perinatal exposure to PBDEs (congeners 47, 99, 153 and the penta-BDE mixture DE-71). Characteristic endpoints of PBDE neurotoxicity are, among others, endocrine disruption (e.g. decreased thyroid hormone levels), alteration in cholinergic system activity (behavioral hyporesponsivity to nicotine challenge), as well as alterations of several behavioral parameters. In particular, the main hallmark of PBDE neurotoxicity is a marked hyperactivity at adulthood. Furthermore, a deficit in learning and memory processes has been found at adulthood in neonatally exposed animals. Some of neurotoxic effects of PBDEs are comparable to those of polychlorinated biphenyls (PCBs), though the latter class of compounds seems to exert a stronger toxic effect. Available information on PBDE neurotoxicity obtained from animal studies and the possibility of neonatal exposure to PBDEs via the mother's milk suggest that these compounds may represent a potential risk for neurobehavioral development in humans.

Neurobehavior effects in four strains of mice offspring exposed prenatally to alprazolam

OBJECTIVE

This study was performed to determine whether prenatal exposure to alprazolam affects offspring behavior in different strains of mice.

STUDY DESIGN

Eight to 11 gravid mice of the C3H/He, C57BL/6, A/J, and DBA/2 strains were given either an anxiolytic dose of alprazolam (0.32 mg/kg) or a placebo by gavage on day 18 of an anticipated 19- to 21-day gestation. Neurobehavior tasks were conducted to assess anxiety, learning and memory, and social interaction. Data were analyzed by analysis of variance or a Fisher exact probability test.

RESULTS

Anxiety in alprazolam-exposed offspring was reduced in C3H/He (P <.05) and A/J (P <.05) newborn infants by separation vocalization but may be increased in the C3H/He adult strain on the plus maze task. Learning was slower among C57BL/6 mice exposed to alprazolam (P <.01), whereas memory was reduced in exposed A/J and DBA/2 offspring (P <.05). Alprazolam exposure was associated with more aggression among C3H/He and C57BL/6 male offspring (P <.01) and with less group activity by C57BL/6 offspring (P <.05).

CONCLUSION

Altered behaviors in several mouse strains after prenatal exposure to alprazolam suggests a vulnerability of GABA-benozdiazepine receptor formation in fetal brain development.

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.

Methodological analysis in behavioral toxicology: an ethotoxicological approach

A constraint in the development of laboratory animal models of human disease conditions is their applicability to the natural environment in which a given animal species evolved. The range of behavioral patterns that can be carefully assessed and quantified in the laboratory is sometimes limited. Although field studies reflect behavioral responses in natural settings, they may also have methodological limitations. Laboratory techniques are not applicable to wild species since natural conditions cannot be brought into a laboratory in an inexpensive or reliable way. However, it is possible to create near-natural settings which may not fulfill all the criteria of the actual context of evolution, but which can be controlled by the experimenter. We recommend an integrative style of approach considering laboratory constraints and, at the same time, the ecological niche in which a given behavioral pattern evolved. This type of ethological assessment may be useful when carrying out toxicological studies on both wild and laboratory mammals.

Long-term consequences of neonatal exposure to diazepam on cerebral glucose utilization, learning, memory and anxiety

The long-term consequences of neonatal exposure to diazepam (DZP) on behavioral abilities and local cerebral glucose utilization (LCGU) in 12 brain regions involved in the control of memory and anxiety were studied in adult rats. Rat pups received a daily subcutaneous injection of 10 mg/kg DZP or of the dissolution vehicle from postnatal day (P) 2 to 21. Learning and memory were tested in P60-P70 rats over 5 consecutive days in a T maze and an eight-arm maze while anxiety and reaction to novelty were tested in a two-compartment box with a two-step staircase on the enriched side. LCGU was measured in the P60 rat by the quantitative autoradiographic [14C]deoxyglucose method. In the T maze, when performed without delay between the two trials, the rate of alternation was significantly lower in DZP- than in vehicle-exposed rats on the first 2 days of testing and similar in both groups on days 3-5. In the procedure with a 30 s intertrial delay, the rate of alternation was similar in DZP- and vehicle-treated rats on all days of testing. In the eight-arm maze, DZP-treated rats were more active, i.e., entered more arms per minute than control animals. The number of arms entered before the first error was lower on day 1 and higher on day 3 in DZP- compared to vehicle-exposed rats. In the two-compartment box, DZP-treated rats crossed more often and spent more time than controls on the lower step of the staircase while control rats made more rearings and spent more time than DZP-exposed rats in the well protected corner of the box. LCGU were decreased by early DZP exposure in six regions which were mammillary body, septum, visual and prefrontal cortices, dorsomedian caudate nucleus and mediodorsal thalamus. In conclusion, postnatal DZP treatment induced at adulthood an increase in activity, a delay in task acquisition but no learning-memory impairment and reduced the level of anxiety allowing active responding to novelty. These quite subtle behavioral changes were accompanied by discrete metabolic decreases in regions mediating anxiety, reflecting a change in the level of anxiety and emotionality.

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.

Economical test methods for developmental neurobehavioral toxicity

The assessment of behavioral changes produced by prenatal or early postnatal exposure to potentially noxious agents requires both the designing of ad hoc tests and the adaptation of tests for adult animals to the characteristics of successive developmental stages. The experience in designing tests is still more limited than in the adaptation of tests, but several tests have already proven their usefulness; some examples are the suckling test, the homing test, and evaluations of dam-pup and pup-pup interactions. Functional observational batteries can exploit the development at specified postnatal ages of several reflexes and responses that are absent at birth in altricial rodent species with a short pregnancy such as the rat and the mouse. In neonates, the assessment of early treatment effects can rely not only on deviations from normal responding but also on changes in the time of appearance of otherwise normal response patterns. The same applies to other end points such as responses to pain and various types of spontaneous motor/exploratory activities, including reactivity to a variety of drug challenges that can provide information on the regulatory systems whose development may be affected by early treatments. In particular, the analysis of ontogenetic dissociations (i.e., differential early treatment effects depending jointly on developmental stage at the time of exposure, age of testing, and response end point) can be of considerable value in the study of treatments' mechanisms of action. Overall, it appears that behavioral teratological assessments can be effectively used both proactively, i.e., in risk assessment prior to any human exposure, and reactively. In the latter case, these assessments could have special value in the face of agents suspected to produce borderline changes in developing humans, whose innocuousness or noxiousness can be difficult to establish in the absence of hard evidence of teratogenicity.

Coloboma hyperactive mutant exhibits delayed neurobehavioral developmental milestones

The coloboma mutation (Cm) is a neutron-irradiation induced gene deletion located on the distal portion of mouse chromosome 2. This deletion region includes a gene encoding the synaptic vesicle docking fusion protein, synaptosomal-associated protein of 25 kDa (SNAP-25). The resulting mutation is semi-dominant with heterozygote mice exhibiting a triad of phenotypic abnormalities that comprise profound spontaneous hyperactivity, head bobbing and a prominent eye dysmorphology. Because the expression pattern of two SNAP-25 isoforms begins to change during the first postnatal week, neurobehavioral developmental milestones were examined in order to determine if the expression of the coloboma behavioral phenotype could be detected during this period of postnatal development. The early classification of coloboma mutant offspring may help to further describe the penetrance of this mutation as well as the contribution of developmental changes to the adult behavioral phenotype. The coloboma mutation resulted in delays in some tests of complex motor skills including righting reflex and bar holding. In addition, coloboma mutants were characterized by body weight differences (first appearance day 7) and hyperreactivity to touch (day 11) and head bobbing (day 14). These data demonstrate disruptions in the time course of attaining developmental milestones in coloboma mutants and provide further evidence supporting the hypotheses that alterations in Snap gene expression are associated with functional behavioral consequences in developing offspring.

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.

Induction of maternal behavior by mouse neonates: influence of dam parity and prenatal oxazepam exposure

The aim of the present report was to investigate the influence of pup stimulus properties and female parity on mouse maternal behavior. Outbred CD-1 mouse pups, prenatally exposed to either the vehicle (VEH) or oxazepam (OX, 15 mg/kg twice/day on pregnancy days 12-16) and fostered to untreated dams at birth, were offered as a stimulus on postnatal days 4, 6, and 8 to four groups of females that differed in maternal experience: virgin, experienced virgin females, primiparae, and biparae. Maternal behavior was observed during a 15-min session each day. Virgin females were less involved in crouching behavior than primiparae. Pups, age, and prenatal oxazepam showed interactive effects on maternal care, particularly by increasing licking and nest-building activities and decreasing still-out behavior. Moreover, dams receiving younger pups showed high levels of both locomotor activity and rearing. The present findings point to the need for a better understanding of mother-pup interactions in studies aimed at characterizing drug and toxicant effects on both animal and human development.

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.

Behavioral changes produced in rats by developmental exposure to flumazenil, a benzodiazepine receptor antagonist

1. Prolonged administration of a benzodiazepine receptor antagonist, such as flumazenil (given to the mother at a dose of 3 mg/kg s.c. from day 14 to day 20 of gestation), produced subtle behavioral changes in rat pups. 2. Flumazenil treatment decreased the rate of ultrasonic vocalization in 15-day old male pups removed from their nest. 3. No significant changes in the locomotor activity of the flumazenil-treated group with respect to controls was found at the end of the second and fourth postnatal week. 4. These results suggest that late prenatal exposure to flumazenil induces in rat offspring behavioral changes characterized by decreased emotional responsiveness to environmental challenges.

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.