Prenatal cocaine exposure: effects on play behavior in the juvenile rat

Chronic modafinil administration to preadolescent rats impairs social play behavior and dopaminergic system

Some clinical trials are investigating modafinil (Mod) as a treatment for attentional deficit and hyperactivity disorder (ADHD) in children and adolescents. Mod increases dopamine (DA) levels in the reward system by blocking dopamine transporter (DAT). Social interactions are rewarding behaviors and evidence reveals the importance of reward circuitry in social interactions. Chronic psychostimulant treatments alter DA neurotransmission and associated behaviors. The aim of this work was to evaluate the effects of chronic Mod treatment during preadolescence on social play behavior, locomotor activity, and DA in nucleus accumbens (NAc). Preadolescent male Sprague-Dawley rats were injected with Mod (75 mg/kg i.p.) or vehicle for 14 days (PND22 to PND35). After that, we measured social play behavior, content and DA release in NAc by HPLC coupled to electrochemical detection, protein levels of DA type 2 receptor (D₂) by Western blot and DA kinetic by fast-scan cyclic voltammetry (FSCV) in NAc. Regarding social play, the total number of pinning events decreased in the Mod group compared with the vehicle. The K⁺-stimulated DA release in NAc was significantly lower in Mod-treated rats compared with vehicle group. Also, Mod increases locomotor activity at the first injection, but this effect is almost completely lost at day 14 of Mod treatment. Chronic Mod treatment during preadolescence in rats impairs dopaminergic neurotransmission in NAc and decreases the capacity of rats to perceive rewarding effects of social play. Importantly, as Mod is being evaluated to treat ADHD in children and adolescents, potential effects on social behavior should be considered since this kind of behavior in this particular stage is crucial for neurodevelopment.

Methamphetamine exposure during the first, but not the second half of prenatal development, affects social play behavior

Methamphetamine (MA), as a psychostimulant drug that crosses the placental barrier, may disrupt the development of social play. The present study aims to examine the effect of prenatal MA (5 mg/kg) exposure during the first (gestational day (GD) 1-11) or second (GD 12-22) halves of prenatal development of rats on social play behavior. To investigate an acute effect of MA on social play in adulthood, juvenile rats were exposed to a dose of 1 mg/kg MA or saline on the test day and tested for social play for 15 min. Prenatal exposure to MA during GD 1-11 increased social play behavior during 5-10 min interval of the test in males but not females. Prenatal MA during GD 12-22 did not influence social play in males nor females. However, social play occurred to a greater extent in GD 12-22 groups compared with GD 1-11. Acute exposure to MA eliminated playful behavior in all groups and decreased social exploration in GD 1-11. Our results suggest that manipulation of prenatal development during the first half of the gestational period has a greater impact on social play behavior than during the second half.

Cocaine-induced neurodevelopmental deficits and underlying mechanisms

Exposure to drugs early in life has complex and long-lasting implications for brain structure and function. This review summarizes work to date on the immediate and long-term effects of prenatal exposure to cocaine. In utero cocaine exposure produces disruptions in brain monoamines, particularly dopamine, during sensitive periods of brain development, and leads to permanent changes in specific brain circuits, molecules, and behavior. Here, we integrate clinical studies and significance with mechanistic preclinical studies, to define our current knowledge base and identify gaps for future investigation. Birth Defects Research (Part C) 108:147-173, 2016. © 2016 Wiley Periodicals, Inc.

Neuropeptidergic regulation of pair-bonding and stress buffering: Lessons from voles

This article is part of a Special Issue "SBN 2014". Interpersonal attachment is a critical component of the human experience. Pair-bonding ameliorates the severity of several mental and physical diseases. Thus, a better understanding of how the central nervous system responds to and encodes social-buffering during stress is a valuable research enterprise. The prairie vole (Microtus ochrogaster), as a laboratory animal model, provides the gold standard for the investigation of the neurobiology underlying attachment. Furthermore, emerging research in voles, additional laboratory rodents, transgenic mice, primates, and humans has provided novel insight into the neurochemical mechanisms underlying the therapeutic effects of social bonds reducing anxiety, depression, and drug abuse liability. In the present review, we highlight the work from this burgeoning field and focus on the role(s) of the neuropeptides oxytocin (OT), vasopressin (AVP), and corticotrophin releasing hormone (CRH) mediating stress buffering. Together, the data suggest that OT underlies social bonding to reduce stress-induced psychological illness while AVP and CRH facilitate arousal to enhance autonomic reactivity, increasing susceptibility to adverse mental and physical health.

Neonatal exposure to amphetamine alters social affiliation and central dopamine activity in adult male prairie voles

The prairie vole (Microtus ochrogaster) is a socially monogamous rodent species that forms pair bonds after mating. Recent data have shown that amphetamine (AMPH) is rewarding to prairie voles as it induces conditioned place preferences. Further, repeated treatment with AMPH impairs social bonding in adult prairie voles through a central dopamine (DA)-dependent mechanism. The present study examined the effects of neonatal exposure to AMPH on behavior and central DA activity in adult male prairie voles. Our data show that neonatal exposure to AMPH makes voles less social in an affiliation test during adulthood, but does not affect animals' locomotor activity and anxiety-like behavior. Neonatal exposure to AMPH also increases the levels of tyrosine hydroxylase (TH) and DA transporter (DAT) mRNA expression in the ventral tegmental area (VTA) in the brain, indicating an increase in central DA activity. As DA has been implicated in AMPH effects on behavioral and cognitive functions, altered DA activity in the vole brain may contribute to the observed changes in social behavior.

Oxytocin reverses amphetamine-induced deficits in social bonding: evidence for an interaction with nucleus accumbens dopamine

Drug addiction has devastating consequences on social behaviors and can lead to the impairment of social bonding. Accumulating evidence indicates that alterations in oxytocin (OT) and dopamine (DA) neurotransmission within brain reward circuitry may be involved. We investigated this possibility, as well as the therapeutic potential of OT for drug-induced social deficits, using the prairie vole (Microtus ochrogaster)-a socially monogamous rodent that forms enduring pair bonds between adult mates. We demonstrate that repeated exposure to the commonly abused psychostimulant amphetamine (AMPH) inhibits the formation of partner preferences (an index of pair bonding) in female prairie voles. AMPH exposure also altered OT and DA neurotransmission in regions that mediate partner preference formation: it decreased OT and DA D2 receptor immunoreactivity in the medial prefrontal cortex (mPFC) and nucleus accumbens (NAcc), respectively, and increased NAcc DA levels. Administration of OT directly into the mPFC of AMPH-exposed voles restored partner preferences, and altered NAcc DA levels, and this effect was dependent on OT receptor activation. Together, these data suggest that repeated AMPH exposure impairs pair bonding through an OT-mediated mechanism, and that OT and DA systems within brain reward circuitry may interact to mediate the complex relationship between drug abuse and social bonding. Further, these results provide empirical support for the idea that the central OT system may represent an important target for the treatment of social deficits in addiction.

On the interaction between drugs of abuse and adolescent social behavior

RATIONALE

Social factors influence drug abuse. Conversely, drugs of abuse alter social behavior. This is especially pertinent during post-weaning development, when there are profound changes in the social repertoire, and the sensitivity to the positive and negative effects of drugs of abuse is altered.

OBJECTIVES

This study aimed to provide an overview of our current understanding of the interaction between drugs of abuse and juvenile/adolescent social behavior.

METHODS

We first provide evidence that a characteristic form of juvenile and adolescent social behavior, i.e., social play behavior, has reinforcing properties and is affected by drugs of abuse. Next, social risk factors for drug use and addiction are described, including antisocial personality traits and early social insults. Last, we discuss research that investigates social influences on drug use, as well as the consequences of perinatal drug exposure on later social interactions.

RESULTS

Social play behavior is highly rewarding in laboratory animals, and it is affected by low doses of opioids, cannabinoids, ethanol, nicotine, and psychostimulants. In humans, antisocial personality traits, most prominently in the form of conduct disorder, are a prominent risk factor for drug addiction. Preclinical studies have consistently shown altered sensitivity to drugs as a result of social isolation during post-weaning development. The social environment of an individual has a profound, but complex, influence on drug use, and perinatal drug exposure markedly alters later social interactions.

CONCLUSIONS

The studies reviewed here provide a framework to understand the interaction between drugs of abuse and adolescent social interaction, at the preclinical and the clinical level.

Empathic responsivity at 3 years of age in a sample of cocaine-exposed children

This study examined the association between prenatal exposure to cocaine and behavioral and physiological responsivity. Participants were 216 mother-infant dyads (116 cocaine exposed-CE, 100 nonexposed-NCE) recruited at birth. Measures of heart rate (HR) and respiratory sinus arrhythmia (RSA) were obtained during baseline and during a task designed to elicit empathy (exposure to infant crying). When the effects of prenatal cocaine use were examined in the context of polydrug use, results of model testing indicated that lower gestational age, prenatal exposure to cocaine and postnatal exposure to alcohol were each associated with a reduced suppression of RSA during the empathy task. These findings provide additional support for an association between prenatal cocaine exposure and dysregulation during early childhood during affect-eliciting environmental challenges.

Prenatal and gestational cocaine exposure: Effects on the oxytocin system and social behavior with implications for addiction

Drug abuse during pregnancy is a major public health concern, with negative consequences throughout development. Prenatal cocaine exposure (PCE) in rats produces social behavior deficits with corresponding changes in neuroendocrine and monoaminergic signaling. The relevance of parental care in social behavior maturity cannot be ignored, and gestational exposure to cocaine severely disrupts parental care, thus impacting the early environment of the offspring. Oxytocin (Oxt) is critical in regulating social behaviors and central levels are disrupted following acute and chronic cocaine (CC) treatment in postpartum rat dams, coincident with deficits in maternal care. We will discuss studies aimed to determine the relative contribution of PCE and CC-induced deficits in maternal care to social behaviors and Oxt signaling across development. PCE results in decreased social (including parental) behaviors in adolescence and adulthood. PCE is also associated with increased aggression in adults. Rearing by CC-exposed mothers synergistically increases the behavioral effects of PCE. Rearing by CC-exposed mothers, but not PCE, disrupts Oxt levels and mRNA in regions relevant to social behavior, but does not affect receptors in postpartum adult offspring. Preliminary work indicates that PCE/CC rearing has dynamic effects on Oxt levels and receptors in neonatal rat pups, suggesting very early regulation of Oxt signaling. This work highlights how the interactive role of Oxt signaling and behavioral context throughout development can be derailed by drug abuse during pregnancy. The relevance of disrupted Oxt to intergenerational transmission of addiction is briefly discussed.

Prenatal Cocaine Disrupts Serotonin Signaling-Dependent Behaviors: Implications for Sex Differences, Early Stress and Prenatal SSRI Exposure

Prenatal cocaine (PC) exposure negatively impacts the developing nervous system, including numerous changes in serotonergic signaling. Cocaine, a competitive antagonist of the serotonin transporter, similar to selective serotonin reuptake inhibitors (SSRIs), also blocks dopamine and norepinephrine transporters, leaving the direct mechanism through which cocaine disrupts the developing serotonin system unclear. In order to understand the role of the serotonin transporter in cocaine's effect on the serotonergic system, we compare reports concerning PC and prenatal antidepressant exposure and conclude that PC exposure affects many facets of serotonergic signaling (serotonin levels, receptors, transporters) and that these effects differ significantly from what is observed following prenatal SSRI exposure. Alterations in serotonergic signaling are dependent on timing of exposure, test regimens, and sex. Following PC exposure, behavioral disturbances are observed in attention, emotional behavior and stress response, aggression, social behavior, communication, and like changes in serotonergic signaling, these effects depend on sex, age and developmental exposure. Vulnerability to the effects of PC exposure can be mediated by several factors, including allelic variance in serotonergic signaling genes, being male (although fewer studies have investigated female offspring), and experiencing the adverse early environments that are commonly coincident with maternal drug use. Early environmental stress results in disruptions in serotonergic signaling analogous to those observed with PC exposure and these may interact to produce greater behavioral effects observed in children of drug-abusing mothers. We conclude that based on past evidence, future studies should put a greater emphasis on including females and monitoring environmental factors when studying the impact of PC exposure.

Cocaine Exposure and Children's Self-Regulation: Indirect Association via Maternal Harshness

OBJECTIVES

This study examined the association between prenatal cocaine exposure and children's self-regulation at 3 years of child age. In addition to direct effects of prenatal cocaine exposure on children's self-regulation, we hypothesized there would be indirect associations between cocaine exposure and self-regulation via higher maternal harshness and poor autonomic regulation in infancy.

METHODS

The sample consisted of 216 mother-infant dyads recruited at delivery from local area hospitals (116 cocaine-exposed, 100 non-exposed). Infant autonomic regulation was measured at 7 months of age during an anger/frustration task, maternal harshness was coded from observations of mother-toddler interactions at 2 years of age, and children's self-regulation was measured at 3 years of age using several laboratory paradigms.

RESULTS

Contrary to hypotheses, there were no direct associations between maternal cocaine use during pregnancy and children's self-regulation. However, results from testing our conceptual model including the indirect effects via maternal harshness or infant parasympathetic regulation indicated that this model fit the data well, χ(2) (23) = 34.36, p > 0.05, Comparative Fit Index = 0.95, RMSEA = 0.05. Cocaine using mothers displayed higher intensity of harshness toward their toddlers during lab interactions across a variety of tasks at 2 years of age (β = 0.23, p < 0.05), and higher intensity of harshness at 2 years was predictive of lower self-regulation at 3 years (β = -0.36, p < 0.01). Maternal cocaine use was also predictive of a non-adaptive increase in respiratory sinus arrhythmia (RSA) from baseline to the negative affect task, but RSA change in infancy was not predictive of self-regulation at 3 years.

CONCLUSION

RESULTS are supportive of animal models indicating higher aggression among cocaine treated dams, and indicate that higher maternal harshness among cocaine using mothers is predictive of child self-regulatory outcomes in the preschool period.

Social behavior of offspring following prenatal cocaine exposure in rodents: a comparison with prenatal alcohol

Clinical and experimental reports suggest that prenatal cocaine exposure (PCE) alters the offsprings' social interactions with caregivers and conspecifics. Children exposed to prenatal cocaine show deficits in caregiver attachment and play behavior. In animal models, a developmental pattern of effects that range from deficits in play and social interaction during adolescence, to aggressive reactions during competition in adulthood is seen. This review will focus primarily on the effects of PCE on social behaviors involving conspecifics in animal models. Social relationships are critical to the developing organism; maternally directed interactions are necessary for initial survival. Juvenile rats deprived of play behavior, one of the earliest forms of non-mother directed social behaviors in rodents, show deficits in learning tasks and sexual competence. Social behavior is inherently complex. Because the emergence of appropriate social skills involves the interplay between various conceptual and biological facets of behavior and social information, it may be a particularly sensitive measure of prenatal insult. The social behavior surveyed include social interactions, play behavior/fighting, scent marking, and aggressive behavior in the offspring, as well as aspects of maternal behavior. The goal is to determine if there is a consensus of results in the literature with respect to PCE and social behaviors, and to discuss discrepant findings in terms of exposure models, the paradigms, and dependent variables, as well as housing conditions, and the sex and age of the offspring at testing. As there is increasing evidence that deficits in social behavior may be sequelae of developmental exposure alcohol, we compare changes in social behaviors reported for prenatal alcohol with those reported for prenatal cocaine. Shortcomings in the both literatures are identified and addressed in an effort to improve the translational value of future experimentation.

Prenatal cocaine exposure increases anxiety, impairs cognitive function and increases dendritic spine density in adult rats: influence of sex

Cocaine exposure during pregnancy can impact brain development and have long-term behavioral consequences. The present study examined the lasting consequences of prenatal cocaine (PN-COC) exposure on the performance of cognitive tasks and dendritic spine density in adult male and female rats. From gestational day 8 to 20, dams were treated daily with 30 mg/kg (ip) of cocaine HCl or saline. At 62 days of age, offspring were tested consecutively for anxiety, locomotion, visual memory and spatial memory. PN-COC exposure significantly increased anxiety in both sexes. Object recognition (OR) and placement (OP) tasks were used to assess cognitive function. Behavioral tests consisted of an exploration trial (T1) and a recognition trial (T2) that were separated by an inter-trial delay of varying lengths. Male PN-COC subjects displayed significantly less time investigating new objects or object locations during T2 in both OR and OP tasks. By contrast, female PN-COC subjects exhibited impairments only in OR and only at the longest inter-trial delay interval. In addition, gestational cocaine increased dendritic spine density in the prefrontal cortex and nucleus accumbens in both genders, but only females had increased spine density in the CA1 region of the hippocampus. These data reveal that in-utero exposure to cocaine results in enduring alterations in anxiety, cognitive function and spine density in adulthood. Moreover, cognitive deficits were more profound in males than in females.

Teens with heavy prenatal cocaine exposure respond to experimental social provocation with escape not aggression

Preclinical data show that, compared to no exposure, prenatal cocaine exposure (PCE) has age-dependent effects on social interaction and aggression. The aim of this clinical study was to determine how heavy/persistent PCE--after controlling for other prenatal drug exposures, sex and postnatal factors--predicts behavioral sensitivity to provocation (i.e., reactive aggression) using a well-validated human laboratory model of aggression. African American teens (mean=14.2 years old) with histories of heavy/persistent PCE (maternal cocaine use ≥ 2 times/week during pregnancy, or positive maternal or infant urine/meconium test at delivery; n=86) or none/some exposure (NON: maternal cocaine use < 2 times/week during pregnancy; n=330) completed the Point Subtraction Aggression Paradigm. In this task, teens competed in a computer game against a fictitious opponent. There were three possible responses: (a) earn points, to exchange for money later; or (b) "aggress" against the fictitious opponent by subtracting their points; or (c) escape temporarily from point subtraction perpetrated by the fictitious opponent. The PCE group responded significantly more frequently on the escape option than the NON group, but did not differ in aggressive or money-earning responses. These data indicate that PCE-teens provoked with a social stressor exhibit a behavioral preference for escape (negative reinforcement) than for aggressive (retaliatory) or appetitive (point- or money-reinforced) responses. These findings are consistent with preclinical data showing that social provocation of adolescent or young adult offspring after PCE is associated with greater escape behavior, inferring greater submission, social withdrawal, or anxiety, as opposed to aggressive behavior.

The role of mesocorticolimbic dopamine in regulating interactions between drugs of abuse and social behavior

The use of addictive drugs can have profound short- and long-term consequences on social behaviors. Similarly, social experiences and the presence or absence of social attachments during early development and throughout life can greatly influence drug intake and the susceptibility to drug abuse. The following review details this reciprocal interaction, focusing on common drugs of abuse (e.g., psychostimulants, opiates, alcohol and nicotine) and social behaviors (e.g., maternal, sexual, play, aggressive and bonding behaviors). The neural mechanisms underlying this interaction are discussed, with a particular emphasis on the involvement of the mesocorticolimbic dopamine system.

The effects of prenatal cocaine exposure on problem behavior in children 4-10 years

BACKGROUND

Children prenatally exposed to cocaine may be at increased risk for behavioral problems due to disruptions of monaminergically regulated arousal systems and/or environmental conditions.

OBJECTIVE

To assess behavioral outcomes of cocaine (CE) and non-cocaine-exposed (NCE) children, 4 through 10 years old, controlling for other prenatal drug exposures and environmental factors.

METHODS

Low socioeconomic status (SES), primarily African American children (n=381 (193 (CE), 188 (NCE)) were recruited from birth. Generalized Estimating Equation (GEE) analyses were used to assess the predictive relationship of prenatal cocaine exposure to odds of caregiver reported clinically elevated behavioral problems at 4, 6, 9 and 10y ears of age, controlling for confounders.

RESULTS

Prenatal cocaine exposure was associated with increased rates of caregiver reported delinquency (OR=1.93, CI: 1.09-3.42, p<0.02). A significant prenatal cocaine exposure by sex interaction was found for delinquency indicating that only females were affected (OR=3.57, CI: 1.67-7.60, p<0.001). There was no effect of cocaine on increased odds of other CBCL subscales. Higher prenatal tobacco exposure was associated with increased odds of externalizing symptoms at 4, 9 and 10 years of age. For CE children, those in foster or adoptive care were rated as having more behavior problems than those in biologic mother or relative care. Greater caregiver psychological distress was associated with increased behavioral problems. There were no independent effects of elevated blood lead level on increased behavior problems after control for prenatal drug exposure and other environmental conditions.

CONCLUSION

Prenatal cocaine and tobacco exposure were associated with greater externalizing behavior after control for multiple prenatal drug exposures, other environmental and caregiving factors and lead exposure from 4 through 10 years of age. Greater caregiver psychological distress negatively affected caregiver ratings of all CBCL domains. Since cocaine and tobacco use during pregnancy and maternal psychological distress have the potential to be altered through prenatal educational, drug treatment and mental health interventions, they warrant attention in efforts to reduce rates of problem behaviors in children.

Biobehavioral Outcomes in Adolescents and Young Adults Prenatally Exposed to Cocaine: Evidence From Animal Models

Cocaine has been a popular illicit drug among drug-using pregnant women over the last three decades. Prenatal cocaine exposure (PCE) has significant effects on children's development throughout early childhood. Very few human studies, however, report the effects of PCE on adolescent or early-adult development. As knowledge about early childhood effects in human children was informed by animal studies, this review considers the effects of PCE on behavioral outcomes in adolescent and young adult animals and provides potential guidance for research in human children. Animal models prenatally exposed to cocaine manifest play deficits, decreased social interaction, and increased aggression during competition in adolescence and young adulthood. Altered behavioral adaptation after stress exposure, including hormonal response change, is also evident. Attention deficits are reported in adult offspring with PCE, not only in a novel environment, but also in a final task session, indicating effects of PCE on transition and maintenance of attention. Animal studies support that PCE effects may extend beyond early childhood and continue to adolescence and adulthood. Additionally, some studies highlight that behavioral changes in offspring with PCE born without teratogenesis remain latent and reveal themselves during adulthood when animals are under stress conditions. Based on the evidence from animal models, well-designed human studies are needed to elucidate the effects of PCE on older human children. Research models that combine behavioral measures with stressful challenges may hold potential in discerning a longer term influence of PCE.

Intergenerational effects of cocaine on maternal aggressive behavior and brain oxytocin in rat dams

Gestational cocaine treatment results in significantly increased maternal aggression towards an intruder by postpartum day six, while acute postpartum treatment dose dependently decreases maternal aggressive (MA) behavior. Both increased and decreased aggression in the cocaine-treated dams are correlated with either decreased or increased levels of oxytocin in the amygdala, respectively. The current study was an effort to determine whether the effect of gestational cocaine on maternal aggression is transient or would continue into the postpartum period; whether an intermittent cocaine treatment regimen, which incorporates gestational and postpartum intermittent cocaine treatment, would differ from chronic daily gestational treatment; and finally, whether next generation female offspring of cocaine-treated or control dams would have altered MA behavior and oxytocin system changes attributable to either prenatal drug exposure, rearing condition or both. We now report no increase in maternal aggression following chronic gestational treatment and significantly lower levels of aggression in intermittently treated dams on postpartum day eight, with no significant effects in either group on postpartum day 12. Young adult female offspring of the cocaine-treated and control dams, who reared their own natural litters and were tested on postpartum day eight for maternal aggression, had higher levels of maternal aggression towards an intruder attributable to both prenatal cocaine exposure and rearing condition. Higher aggression in cocaine-reared next generation dams was associated with lower levels of oxytocin in the amygdala. Intergenerational effects of cocaine were apparent with respect to aggression and oxytocin system changes.

Postnatal exposure to cocaine in rats housed in an enriched environment: effects on social interactions

This study was undertaken to evaluate the effects of environmental enrichment (EE) in rats exposed to cocaine during the first month of postnatal life by examining several categories of social behaviour (play fighting, social investigation, comfort behaviours and invitation to play). Wistar rats were divided in four groups: pups exposed to cocaine hydrochloride (15 mg/kg body weight/day), sc, in two daily doses, from postnatal day (PND) 1 to 28 and reared in EE; exposed to cocaine as previously described and reared in standard environment (SE); saline-exposed and reared in EE; pups saline-exposed and reared in SE. On PND 21, 24 and 28, social interactions were examined for 10 min. Results show that cocaine animals reared in SE decreased the frequency of play solicitation. Control animals reared in EE exhibited decreased play fighting and social investigation behaviours compared to SE-reared rats. Animals postnatally exposed to cocaine when reared in EE displayed more comfort and invitation to play behaviours and decreased social investigation compared with SE-reared animals. The results suggest that in rats postnatally exposed to cocaine, EE rearing elicited differences in both processing of environmental stimuli and a response to social challenges.

Cocaine disrupts pup-induced maternal behavior in juvenile and adult rats

Impaired onset of maternal behavior in first generation rat dams was previously correlated with rearing by cocaine-treated dams and prenatal cocaine exposure. Pup-induced maternal behavior in non-lactating rats has not been examined with regard to cocaine exposure and rearing conditions. First generation male and female juveniles and young adult males reared by cocaine-treated or control dams and prenatally exposed to either cocaine or control conditions were tested for pup-induced maternal behavior at postnatal days 28 and 60. We now report disruptions in pup-induced maternal behavior in both 28 and 60 day old first generation offspring attributable to rearing condition and prenatal cocaine exposure.

Cocaine exposure during adolescence affects anxiety in adult mice

Psychostimulant drugs such as cocaine have profound and long-lasting neurobiological effects, which may affect anxiety or social behaviors. These actions could be greater when cocaine is administered during a developmental period such as adolescence. The present work attempts to further clarify the long-lasting effects of cocaine administration on mice, examining three major variables: age; pattern of drug administration; and housing conditions. Adolescent (postnatal day 26) or early adult mice (postnatal day 46) were exposed to a daily or binge cocaine administration and 15 days later their behavior was evaluated, the mice being housed either in isolation or in groups during this stage. After a period free of drug, the behaviors evaluated were: spontaneous and cocaine-induced motor activity; anxiety, using the elevated plus maze; the social profile, assessed in a social interaction test. Daily cocaine administration increased avoidance and flee in isolated adolescent-treated mice and decreased social contacts in those which were grouped. On the other hand, the binge pattern modified the anxiety of the grouped adolescent-treated mice evidenced by the increase in time spent on the open arms of the plus maze. An increase in spontaneous and cocaine-induced motor activity was shown in animals after a daily pre-treatment. The results are discussed in terms of presenting cocaine-induced behavioral changes within a specific temporal window and depending on the three variables studied.

Prenatal Exposure to Cocaine and Enriched Environment: Effects on Social Interactions

Exposure to cocaine throughout gestation may produce several deleterious outcomes in the offspring that include effects on neurotransmitter systems and structure of the central nervous system. Such changes are most likely correlated with behavioral alterations. Environmental enrichment (EE) in early stages is a factor that affects structural and behavioral development. This article examines the effects, upon social interactions, of EE during the first month of life in rats prenatally exposed to cocaine. Wistar dams were subcutaneously exposed to 60 mg/kg of cocaine divided in two daily doses from gestational day (GD)8 to GD22. Pair-fed controls were given saline vehicle in the same protocol. Offspring were distributed to the different environments in four experimental groups. Group 1: offspring from dams prenatally exposed to cocaine as previously described and reared in EE from postnatal day (PND)1 to PND28; Group 2: pups from cocaine-exposed dams and reared in a standard environment (SE); Group 3: pups from pair-fed saline-exposed dams and reared in EE; Group 4: offspring from saline-exposed dams and reared in SE. On PND21, 24, and 28, rats were examined in several social behavioral categories (play fighting, social investigation, comfort behaviors, and solicitation to play) for 10 min. Animals reared in SE do not display any differences due to treatment in the behavioral categories analyzed. Control offspring reared in EE presented decreased play fighting, decreased solicitation to play, and decreased social investigation compared to the control SE group, while cocaine-exposed animals reared in EE did not present these variations. These results suggest that EE rearing may unmask hidden effects of prenatal cocaine exposure.

The effects of selective breeding for infant ultrasonic vocalizations on play behavior in juvenile rats

For over 25 generations, two lines of rats (High and Low USV lines) have been selectively bred for extreme rates of infantile (45 kHz) ultrasonic vocalizations (USV) in response to maternal separation at postnatal day (P)10. High and low line juveniles (P30-P40) were socially isolated and allowed to play in same-sex sibling pairs for 10 min per day over three days. Measures of play were nape contacts and pinning. Other social and nonsocial behaviors were also scored during the three sessions; two of these, 55 kHz USV and walk-overs, were statistically associated with play. Compared to the Random control line, both High and Low line juveniles showed deficits in play behavior. In the High line, play initiatory behavior (nape contacts) was reduced, but pinning, USV and walk-overs were relatively unchanged. In contrast, nape contacts, pinning, USV and walk-overs were all reduced in Low line juveniles compared to Random line controls. The results suggest that selection for extremes of infant USV rates has produced temperamental differences that are expressed in juvenile play in the High and Low USV lines.

Cocaine treatment and prenatal environment interact to disrupt intergenerational maternal behavior in rats

The link between impaired maternal behavior (MB) and cocaine treatment could result from drug-induced decreases in maternal reactivity to offspring, prenatal drug exposure (PDE) in offspring that could alter their ability to elicit MB, or the interaction of both, which could subsequently impair MB of the 1st-generation dams. Following chronic or intermittent cocaine or saline treatment during gestation, rat dams rearing natural or cross-fostered litters were compared along with untreated dams for MB. Untreated 1st-generation females with differentially treated rearing dams and PDE were tested for MB with their natural litters. The authors report disruptions in MB in dams and their 1st-generation offspring, attributable to main and interaction effects of maternal treatment, litter PDE, and rearing experience.

Early postnatal protein malnutrition changes the development of social play in rats

Early protein malnutrition produces structural and functional alterations in the brain and changes the organism-environment interactions. Rats from 26 to 76 days of age were used to study the effects of early postnatal protein malnutrition on the development of social play. During lactation phase the litters were fed diet containing 16% protein (well-nourished) or 6% protein (malnourished). From weaning to the end of behavioral tests well-nourished animals were fed a commercial lab chow diet (well-nourished--W) and the malnourished rats were divided into 2 groups: one was maintained on 6% protein diet (malnourished--M) and the other was fed a commercial lab chow diet (previously malnourished--PM). Pairs of male rats of same diet conditions were tested, at different ages, for three consecutive days. During sessions the following behaviors were recorded: pinning, wrestling, walk-over and rear. The frequency of wrestling and walk-over was significantly higher in malnourished as compared to well-nourished animals (p<0.05). Early protein malnutrition also changed the ontogeny of play behaviors (pinning and wrestling) with developmental retards in M and PM as compared with W animals, especially at 46 and 56 days of age. These results suggest that early protein malnutrition can affect the development of neural mechanisms underlying social play in rats.

Prenatal cocaine exposure alters spontaneous and cocaine-induced motor and social behaviors

The abuse of cocaine in pregnant women could affect emotional behaviors in their descendents. The aim of this work was to evaluate the effects of prenatal cocaine exposure on spontaneous and cocaine-induced motor and social behaviors in mice. Three kinds of prenatal treatment were used: non-treated animals; mice treated daily with physiological saline during the last week of pregnancy; and finally, those treated with cocaine (25 mg/kg) during the same period. Behavioral studies took place on adult males, which were housed in two different conditions: grouped (non-aggressive), or isolated (aggressive). Cocaine-pretreated animals exhibited slight differences in spontaneous motor activity, but alterations in their social relationship with conspecifics were presented, with decreases in isolated but increases in grouped mice. The cocaine challenge increased aggression specifically in grouped prenatally cocaine-treated mice, but increases in motor activity or avoidance and flee behavior were presented in those animals pretreated with either saline or cocaine. Isolated saline-or cocaine-treated animals exhibited greater concentrations of DA and DOPAC than those grouped. A decrease in 5-HIAA concentrations was presented in pretreated animals, irrespective of their housing conditions. In conclusion, cocaine administration during pregnancy induces long lasting effects on the offspring, for both behavioral abnormalities and cocaine response, which last to adult life.

Effects of environmental enrichment on behavior and dopamine transporter function in medial prefrontal cortex in adult rats prenatally treated with cocaine

The present study determined if environmental enrichment modifies the effects of prenatal cocaine on open field activity, social interaction and dopamine transporter (DAT) function in the medial prefrontal cortex (mPFC) in rats. Cocaine (40 mg/kg) or saline was administered (s.c.) to pregnant dams from gestation days 8 to 20 (PCOC and PSAL, respectively). At postnatal day 25 (PND 25), female offspring from PCOC and PSAL groups were assigned to the enriched condition (EC; PCOC/EC and PSAL/EC) or impoverished condition (IC; PCOC/IC and PSAL/IC). On PND 60, 90 and 120, locomotor activity, rearing behavior and social interactions were assessed in the open field. On PND 345, rats were anesthetized, challenged with nicotine (0.4 mg/kg), and DAT function in medial prefrontal cortex (mPFC) was assessed using in vivo voltammetry. EC groups displayed decreased locomotor activity across test days, while activity in IC groups did not habituate across days. Generally, PCOC groups displayed more rearing behavior than PSAL groups. During social interaction assessment, IC groups followed their social partner more frequently than EC groups. Moreover, the PCOC/IC group initiated more play solicitations and was engaged in mutual rearing less frequently than PCOC/EC, PSAL/IC and PSAL/EC groups, indicating that epigenetic environmental factors decreased the divergent social behaviors displayed by the PCOC/IC group. Results from in vivo voltammetry experiments demonstrated differences in baseline DAT function in response to environmental enrichment in the prenatal saline groups; however, no effect of prenatal cocaine was observed under baseline conditions. Nicotine challenge unmasked an effect of prenatal cocaine on DA clearance rate in mPFC in the IC groups, which was attenuated by environmental enrichment. Taken together, PCOC/IC rats displayed divergent social interaction and altered DAT function in mPFC, whereas the PCOC/EC group generally was not different from PSAL groups, suggesting that environmental enrichment attenuates the behavioral and neurochemical effects of prenatal cocaine.

Prenatal cocaine and/or nicotine exposure produces depression and anxiety in aging rats

The adult use of cocaine and nicotine has been linked to depression and/or anxiety. Changes in emotional behavior were assessed using behavioral paradigms developed as animal analogs of psychiatric disorders in 12-14 month old Sprague-Dawley rats exposed daily on gestational days 8-20 to cocaine and nicotine, either alone or in combination. Results from the elevated plus maze (EPM), used to assess anxiety-related behaviors, indicated that offspring prenatally exposed to either high-dose cocaine (40 mg/kg/day) or high-dose nicotine (5.0 mg/kg/day) were less timid/more impulsive. Animals from these two groups spent the most time on the open arms, and had the highest percentage of entries into the open arms of the EPM. Combined in utero exposure to cocaine and nicotine nullified these effects. Cocaine challenge (20 mg/kg) did not interact with prenatal treatment, but increased activity on all arms of the EPM in all groups. Sucrose preference was used as a measure of anhedonia, a cardinal symptom of depressive illness. Reduced sucrose preference was seen only in the group of offspring prenatally exposed to high-dose cocaine (40 mg/kg) plus low-dose nicotine (2.5 mg/kg/day). Exposure to a water-deprivation stress normalized sucrose preference in this group, without altering preference or intake in the other prenatal treatment groups. Transient hyperactivity was seen in the offspring of dams treated with high-dose nicotine, an effect that was again reversed in combined drug groups. Traditional gender differences in activity levels and sucrose intake, that is, females greater than males, were still evident in this population of aging rats. These data indicate that prenatal exposure to cocaine and/or nicotine has long-term effects on emotional behavior. Combined drug exposure contributed to the development of depressive symptoms, but not anxiety-like behavior, in a dose-dependent manner. In contrast, exposure to high doses of either drug alone reduced cautionary behavior. Data from this line of research could provide insight into the pathogenesis of emotional disorders, especially during the aging process.

Prenatal cocaine exposure alters sensitivity to the effects of idazoxan in a distraction task

The present study was designed to test whether prenatal cocaine (COC) exposure alters sensitivity to the attentional effects of idazoxan (IDZ), an alpha-2 adrenergic antagonist that increases coeruleocortical NE activity. The task assessed subjects' ability to selectively attend to an unpredictable light cue and disregard olfactory distractors. IDZ increased commission errors specifically under conditions of distraction, an effect that was similar in the COC and control groups. In contrast, COC animals were significantly more sensitive than controls to the effects of IDZ on omission errors and nontrials. The pattern of effects suggests that the differential treatment response to IDZ on these latter measures resulted from an alteration in norepinephrine (NE)-modulated dopamine release in the COC animals, reflecting lasting changes in dopaminergic and/or noradrenergic systems as a result of the early cocaine exposure. Based on the behavioral measures that showed a differential response to IDZ in the COC animals, it seems likely that these changes may contribute to the alterations in sustained attention and arousal regulation that have been reported in both animals and humans exposed to cocaine in utero.

Postnatal protein malnutrition affects play behavior and other social interactions in juvenile rats

The effects of postnatal protein malnutrition on juvenile social behaviors were investigated in male and female Wistar rats. During the lactation period (21 days), each litter (six male and two female pups) was provided with 16% (control) or 6% (low protein) casein diets. At weaning, the control group (W) continued to receive the 16% protein diet and the malnourished group was divided into two groups: one continuing to receive a 6% protein diet (malnourished group - M) and the other shifted to a 16% protein diet (previously malnourished group - PM). These conditions lasted until 38 days of age when the behavioral tests ended. To assess social interaction, pairs of rats of the same nutritional condition and same gender were placed in a familiar arena for 3 consecutive days. Playful social behavior (pin), nonplayful social behavior (anogenital sniff, walk-over, side-mount and allogroom) and nonsocial behavior (rear) were recorded in three 10-min sessions. Postnatal protein malnutrition significantly decreased playful social behavior, nonsocial behavior (rear) and nonplayful social behaviors such as side-mount and walk-over. Anogenital sniff and allogroom were increased by early malnutrition. Nutritional rehabilitation from weaning reversed the changes produced by protein malnutrition in nonplayful (side-mount, walk-over, anogenital sniff and allogroom) and nonsocial behaviors (rear) but increased playful social behavior (pin). Gender effects were observed only on side-mount (higher incidence in males) and walk-over (higher incidence in females) indicating that playful behavior and nonsocial behavior were not affected by sex. The present results suggest that behavioral differences described in adulthood may result from changes in social behaviors of juvenile rats induced by early protein malnutrition.

Prenatal cocaine exposure increases sensitivity to the attentional effects of the dopamine D1 agonist SKF81297

Sensitivity to the attentional effects of SKF81297, a selective full agonist at dopamine D(1) receptors, was assessed in adult rats exposed to cocaine prenatally (via intravenous injections) and controls. The task assessed the ability of the subjects to monitor an unpredictable light cue of either 300 or 700 msec duration and to maintain performance when presented with olfactory distractors. SKF81297 decreased nose pokes before cue presentation and increased latencies and response biases (the tendency to respond to the same port used on the previous trial), suggesting an effect of SKF81297 on the dopamine (DA) systems responsible for response initiation and selection. The cocaine-exposed (COC) and control animals did not differ in sensitivity to the effects of SKF81297 on these measures. In contrast, the COC animals were significantly more sensitive than were controls to the impairing effect of SKF81297 on omission errors, a measure of sustained attention. This pattern of results provides evidence that prenatal cocaine exposure produces lasting changes in the DA system(s) subserving sustained attention but does not alter the DA system(s) underlying response selection and initiation. These findings also provide support for the role of D(1) receptor activation in attentional functioning.

Enduring effects of prenatal cocaine administration on emotional behavior in rats

The present studies sought to determine whether prenatal cocaine administration (15 mg/kg b.i.d. between gestational ages 1-20) had enduring effects on emotional behavior of rats. Rats prenatally treated with cocaine interacted less with other rats in the social interaction test of anxiety at both 30 and 120 days of age. However, there were no differences in the elevated plus maze test of anxiety. Rats prenatally treated with cocaine were significantly more immobile in the forced-swim test at 60 and 120 days of age. In addition, animals exposed to prenatal cocaine were more sensitive to the enhancing effect of phencyclidine (2.0 mg/kg) on startle responses to an acoustic stimulus. The cocaine-treated animals tested at 50 to 60 days of age showed higher levels of prepulse inhibition, in comparison to the saline group, after vehicle pretreatment, but not after phencyclidine. Although there were gender differences in the expression of some of these behavioral tasks, there were no gender differences in the effects of cocaine. These findings indicate that when emotional behavior is altered by prenatal cocaine administration, the effects are enduring.

Fetal and neonatal exposure to trimethylolpropane phosphate alters rat social behavior and emotional responsivity

The proconvulsant compound trimethylolpropane phosphate (TMPP) was evaluated for its effects on motor, social, and emotional behaviors. Long Evans rats were treated prenatally for 13 days and/or neonatally for 10 days. Behavioral tests were performed during treatment and several days after treatment. Beginning on gestation day 9, and continuing for 13 days, 20 dams received once daily i.p. injections. Half were treated with distilled water, the other 10 received 0.2 mg TMPP/kg body weight. No external malformations were observed in the live-born offspring of TMPP- or vehicle-exposed dams. On postnatal day 3 one-half the pups were cross-fostered to dams that had the opposite treatment as their biological mothers. Also on postnatal day 3, pups were divided into two groups, one receiving injections of distilled water, the other receiving injections of 0.2 mg TMPP/kg body weight. Ten daily injections were administered i.p., beginning postnatal day 3. Motor behaviors were evaluated in step-down and paw lift tasks and no group differences were found. At 18 days of age, one half the pups were separated from the dam and their littermates. The other half of the pups continued to be housed with the dam and remaining littermates until postnatal day 50. Social interaction was measured in juvenile play and adult social investigation. Emotional responsivity was assessed in open field activity, elevated plus-maze exploration, and ultrasonic distress vocalizations. Complex interactions were found for measures of social interaction and emotional responsivity related to drug treatment, housing condition, and sex. Due to the observed sex differences. it is hypothesized that the action of TMPP may involve a change in the hormonal systems that control the differentiation of related sex-typical behaviors.

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.

The effects of neonatal cocaine exposure on a play-rewarded spatial discrimination task in juvenile rats

This study examined the effects of neonatal cocaine exposure on the rewarding properties of play in a modified T-maze. Animals were artificially reared from postnatal day (PND) 4-9 with drug concentrated in four daily feeds. There were four treatment groups, 40 mg/kg/day cocaine, 20 mg/kg/day cocaine, an artificially reared control and a surgery control. From PND 38-42, subjects were tested with a food reward (EXP 1) or a play reward (EXP 2). No deficits in learning were seen when the reward was food. The 20 mg/kg/day cocaine group, however, showed impaired learning and altered play behavior when the reward was access to a play partner. Neonatal cocaine exposure thus appears to differentially affect learning based on the type of reward presented.

Development of spatial navigation following prenatal cocaine and malnutrition in rats: lack of additive effects

The effects of prenatal cocaine exposure and protein malnutrition on the development of spatial navigation were assessed in rats. Sprague-Dawley dams were fed a low-protein (6% casein), adequate protein (25% casein), or a laboratory chow diet prior to mating and throughout pregnancy. Within each diet group, rats received either cocaine injections (30 mg/kg i.p. two times per week prior to mating and then 30 mg/kg s.c. daily from day 3 to 18 of pregnancy) or saline injections. All litters were fostered on the day of birth to saline-injected mothers fed either the 25% casein diet or the chow diet. Gestation length was decreased by prenatal cocaine exposure whereas litter size was reduced by prenatal malnutrition. On postnatal days 21, 25, 30, or 70, rats were tested for their ability to locate a submerged platform in a Morris water maze. In well-nourished rats, prenatal cocaine increased the mean distance swum during acquisition over days 21-30, a difference that was abolished in rats with prenatal malnutrition. In the absence of drug exposure (saline groups), prenatal malnutrition was itself associated with longer swim paths. Neither prenatal insult affected the accuracy of the spatial navigation at these ages, as determined by their search pattern when the platform was removed. On postnatal day 25, rats raised on the chow diet exhibited superior performance to that of rats raised on the 25% casein diet, but by day 30 these two well-nourished groups were comparable. At day 70, prenatal cocaine impaired spatial performance on the first session, in well-nourished rats only. Thus, these results provide no support for the hypothesis that prenatal cocaine and protein malnutrition combine to produce a greater effect on behavioral development than either insult alone.

The neurobiology of social play behavior in rats

Social play behavior is one of the earliest forms of non-mother-directed social behavior appearing in ontogeny in mammalian species. During the last century, there has been a lot of debate on the significance of social play behavior, but behavioral studies have indicated that social play behavior is a separate and relevant category of behavior. The present review provides a comprehensive survey of studies on the neurobiology of social play behavior. Evidence is presented that opioid and dopamine systems play a role in the reward aspect of social play behavior. The role of cholinergic, noradrenergic and opioid systems in attentional processes underlying the generation of social play behavior and the involvement of androgens in the sexual differentiation of social play behavior in rats is summarized. It is concluded that there is not only behavioral, but also neurobiological evidence to suggest that social play behavior represents a separate category of behavior, instead of a precursor for adult social, sexual or aggressive behavior.

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.

Perinatal cocaine reduces responsiveness to cocaine and causes alterations in exploratory behavior and visual discrimination in young-adult rats

Lister hooded female rats were exposed to either saline or cocaine (20 mg/kg s.c.) from gestational day 10 every other day until weaning (postnatal day 25). The effects of maternal cocaine exposure on novelty-induced exploration and on spontaneous and cocaine-induced motor activity were evaluated in young-adult male offspring (4 weeks after weaning). Rats exposed to cocaine during development spent less time exploring two novel objects. Lack of habituation upon the second presentation of the objects and failure in the ability to discriminate between the novel and familiar object were also found in cocaine exposed offspring. Moreover, maternal cocaine treatment did not affect spontaneous motor activity (active time, average speed and rearing) in rats subjected to an open field test. Furthermore, perinatal exposure to cocaine significantly attenuated acute cocaine (15 mg/kg i.p.)-induced hyperactivity. These data indicate that developmental exposure to cocaine, at dose levels below those producing gross malformations and/or overt signs of neurotoxicity, causes behavioral changes characterized by an altered responsiveness to environmental and pharmacological challenges.

Prenatal protein malnutrition affects the social interactions of juvenile rats

The effects of prenatal protein malnutrition on juvenile social behavior was investigated in male and female rats. Animals were provided with 25% (control) or 6% (low protein) casein diets before and during pregnancy. After birth eight pups in each litter (six males and two females) were fostered to lactating control mothers. After weaning (21 days of age) all animals received a lab chow diet until behavioral testing began at 45 days of age. To assess social interaction, pairs of rats of the same gender, consisting of one malnourished and one control rat, were placed in a familiar rectangular arena on 3 consecutive days. Playful social behavior (pin), nonplayful social behaviors (anogenital sniff, walk-over, side-mount, and allogroom), and nonsocial behavior (rear) were recorded in 10-min sessions. Prenatal malnutrition significantly decreased both playful and nonplayful social behaviors, and increased nonsocial rearing. No significant gender differences were observed. The finding that early social behavior is altered by prenatal malnutrition opens the possibility that such changes may play an important role in determining some of the later behavioral differences described in the adult animal.

Play behavior and stress responsivity in periadolescent offspring exposed prenatally to cocaine

Play behavior and stress responsiveness were examined in offspring exposed gestationally to cocaine. The subjects were offspring of Sprague-Dawley rat dams given s.c. injections of 40 mg/kg/3 cc cocaine HC1 daily from gestational days 8-20 (C40), pair-fed dams injected daily with saline (PF), and untreated control dams (LC). Periadolescent (postnatal day (P) 30-36) male and female rats were assigned to either pretest Stress or No Stress conditions. Every other day Stress animals were exposed to a stressor (on P30--foot shock; P32--white noise; P34--forced swim; P36--foot shock), with each stressor being administered 4 h prior to a play session. Immobility during one of the stressors, foot shock, was used to assess stress responsiveness. Play sessions consisted of pairing each experimental animal with a same-sex, nonexperimentally manipulated conspecific for 7 min. The results indicated that periadolescent offspring exposed gestationally to cocaine differed from controls in their stress responsivity, as evidenced by a failure to show increased immobility during the final foot shock session. Also, while cocaine-exposed juveniles did not differ from controls in their own play behavior, these offspring elicited less play solicitation from conspecifics, as evidenced by an increased latency to be pounced, and decreased frequency and duration of being pounced. These findings parallel earlier evidence for altered stress responsiveness in adult cocaine-exposed rats and also suggest that prenatal exposure to cocaine results in altered social cues.

Prenatal cocaine but not prenatal malnutrition affects foster mother-pup interactions in rats

The separate and combined effects of prenatal cocaine exposure and malnutrition on mother-pup interactions in rats were assessed daily from postnatal day 2 to day 21. Sprague-Dawley dams were fed a diet of low protein content (6% casein), an isocaloric diet of adequate protein content (25% casein, control), or a laboratory chow diet prior to mating and throughout pregnancy. Within each diet group, rats received either cocaine injections (30 mg/kg IP two times per week prior to mating and then 30 mg/kg SC daily from days 3 to 18 of pregnancy) or saline injections. Litters were fostered on the day of birth to control mothers (i.e., nondrug-exposed dams fed the control or chow diet). Foster mothers fed the 25% casein diet showed increased contact with cocaine-exposed pups compared with nondrug-exposed pups in the second postnatal week but lower levels as the pups approached weaning. Passive nursing was increased in dams caring for prenatally malnourished, cocaine-exposed pups compared with those caring for similar pups with no drug exposure. Chow-fed mothers did not differ in their behavior towards pups with or without prenatal cocaine treatment. Prenatal cocaine and malnutrition independently compromised birth weight and various reflexive milestones but the attainment of physical milestones was affected only by prenatal cocaine. There were no additive effects of the two prenatal insults on any measure of mother-pup interaction or pup development.

Prenatal cocaine exposure affects social behavior in Sprague-Dawley rats

Children prenatally exposed to cocaine are reported to exhibit inappropriate social behavior, including aggression. We have recently observed a similar phenomenon in rats prenatally exposed to cocaine. Pregnant females were injected twice daily with 15 mg/kg cocaine hydrochloride or saline on gestation days 1-20. Offspring were tested for social behavior towards two unfamiliar, untreated rats of the same age and sex. Cocaine-treated males (90 PND) took longer to reciprocate contact and cocaine-treated females (60 PND) spent more time rough grooming unfamiliar females. Male cocaine offspring (180 PND) tested for aggression exhibited an increased frequency and duration and decreased latency to chase an intruder. ACTH was lower in cocaine-treated males (150-180 PND) following plus-maze exposure or exposure to an unfamiliar male. Our data indicate that prenatal cocaine treatment in rats increases fear or aggression responses, dependent on sex and stimulus situation.