Mother-infant interactions in two strains of rats: Implications for dissociating mechanism and function of a maternal pattern

Automated maternal behavior during early life in rodents (AMBER) pipeline

Mother-infant interactions during the early postnatal period are critical for infant survival and the scaffolding of infant development. Rodent models are used extensively to understand how these early social experiences influence neurobiology across the lifespan. However, methods for measuring postnatal dam-pup interactions typically involve time-consuming manual scoring, vary widely between research groups, and produce low density data that limits downstream analytical applications. To address these methodological issues, we developed the Automated Maternal Behavior during Early life in Rodents (AMBER) pipeline for quantifying home-cage maternal and mother-pup interactions using open-source machine learning tools. DeepLabCut was used to track key points on rat dams (32 points) and individual pups (9 points per pup) in postnatal day 1-10 video recordings. Pose estimation models reached key point test errors of approximately 4.1-10 mm (14.39 pixels) and 3.44-7.87 mm (11.81 pixels) depending on depth of animal in the frame averaged across all key points for dam and pups respectively. Pose estimation data and human-annotated behavior labels from 38 videos were used with Simple Behavioral Analysis (SimBA) to generate behavior classifiers for dam active nursing, passive nursing, nest attendance, licking and grooming, self-directed grooming, eating, and drinking using random forest algorithms. All classifiers had excellent performance on test frames, with F1 scores above 0.886. Performance on hold-out videos remained high for nest attendance (F1 = 0.990), active nursing (F1 = 0.828), and licking and grooming (F1 = 0.766) but was lower for eating, drinking, and self-directed grooming (F1 = 0.534-0.554). A set of 242 videos was used with AMBER and produced behavior measures in the expected range from postnatal 1-10 home-cage videos. This pipeline is a major advancement in assessing home-cage dam-pup interactions in a way that reduces experimenter burden while increasing reproducibility, reliability, and detail of data for use in developmental studies without the need for special housing systems or proprietary software.

Marked sexual dimorphism in neuroendocrine mechanisms for the exacerbation of paclitaxel-induced painful peripheral neuropathy by stress

Chemotherapy-induced neuropathic pain is a serious adverse effect of chemotherapeutic agents. Clinical evidence suggests that stress is a risk factor for development and/or worsening of chemotherapy-induced peripheral neuropathy (CIPN). We evaluated the impact of stress and stress axis mediators on paclitaxel CIPN in male and female rats. Paclitaxel produced mechanical hyperalgesia, over the 4-day course of administration, peaking by day 7, and still present by day 28, with no significant difference between male and female rats. Paclitaxel hyperalgesia was enhanced in male and female rats previously exposed to unpredictable sound stress, but not in rats that were exposed to sound stress after developing paclitaxel CIPN. We evaluated the role of the neuroendocrine stress axes: in adrenalectomized rats, paclitaxel did not produce hyperalgesia. Intrathecal administration of antisense oligodeoxynucleotides (ODN) reduced expression of β2-adrenergic receptors on nociceptors, and paclitaxel-induced hyperalgesia was slightly attenuated in males, but markedly attenuated in females. By contrast, after intrathecal administration of antisense ODN to decrease expression of glucocorticoid receptors, hyperalgesia was markedly attenuated in males, but unaffected in females. Both ODNs together markedly attenuated paclitaxel-induced hyperalgesia in both males and females. We evaluated paclitaxel-induced CIPN in stress-resilient (produced by neonatal handling) and stress-sensitive (produced by neonatal limited bedding). Neonatal handling significantly attenuated paclitaxel-induced CIPN in adult male, but not in adult female rats. Neonatal limited bedding did not affect the magnitude of paclitaxel-induced CIPN in either male or female. This study provides evidence that neuroendocrine stress axis activity has a marked, sexually dimorphic, effect on paclitaxel-induced painful CIPN.

How strain differences could help decipher the neurobiology of mammalian playfulness: What the less playful Fischer 344 rat can tell us about play

Play is common among the young of many mammalian species. How that play is exhibited results from a dynamic interplay between genetic framework and experiential influences that, in turn, operate on hard-wired brain systems. One approach towards understanding how genes and environment interact with brain substrates to yield a particular playful phenotype is to take advantage of inbred strains of rats that come with a known genetic identity and assess the effects of varying early social experiences and targeted neurobiological interventions on rats of these strains. This paper primarily summarizes research utilizing the F344 inbred strain, a rat that consistently plays less than most other strains.

Age-dependent differences on neurochemistry and behavior in rats raised with low and high levels of maternal care

In laboratory rats, naturally-occurring variations in maternal care have been used to study the neurobehavioral consequences of maternal nursing and to model the early-life adversity associated with many psychiatric disorders. This study aimed to determine the role of maternal care on behavior and monoamine concentrations at the prepubertal and young adulthood ages. We observed the licking/grooming (LG) behavior of Sprague-Dawley (SD) dams and assigned the litter to either low (LLG) or high (HLG) LG groups. Behavioral testing in the male offspring consisted of the open-field test, the elevated plus-maze, and the forced swimming test. Afterward, neurotransmitters contents were measured in the prefrontal cortex, the nucleus accumbens, the amygdala, and the hippocampus. We found that at the prepubertal stage, the effects of maternal care were only noticeable in the elevated plus-maze and the serotonin concentration in the nucleus accumbens. At adulthood, body weight and monoamines contents increased substantially in LLG rats. Specifically, they showed higher serotonin contents with a reduced turnover in almost all brain regions, followed by higher contents of norepinephrine and dopamine, especially in the nucleus accumbens. Changes in monoamines concentrations seem to be independent of the behavioral phenotype shaped by variations in maternal care, as behavioral effects were somewhat weak in both experiments. If higher monoamines contents in LLG rats represent an adaptive mechanism to deal with further adverse events, the behavioral paradigms used here were insufficiently challenging to bring out noticeable differences, at least in SD rats.

Prenatal vitamin D deficiency does not exacerbate behavioural impairments associated with prenatal ethanol exposure in juvenile male mice

There is a high prevalence of vitamin D deficiency and exposure to low levels of ethanol in pregnant women. However, there are a paucity of studies that have addressed the impact of both vitamin D deficiency and ethanol exposure on the offspring's vulnerability to neurodevelopmental disorders later in life. The aim of this study was to examine whether the absence of vitamin D during gestation in mice would alter the effects of prenatal exposure to low dose ethanol on the behaviour and dopaminergic gene expression patterns of juvenile mice. Four-week old female C57BL/6J mice were placed on a prenatal vitamin D deficient (PVD) or standard diet for 6 weeks and mated at 10 weeks of age. Females were exposed to either 10%(v/v) ethanol or water between gestational days 0-8 and all were offered water thereafter. We found that blood ethanol concentration in the dams was not affected by maternal diet. Behavioural analyses of the offspring included ultrasonic vocalizations (USV) at postnatal day (P) 7, locomotion and social interaction at P21. The main findings were increased USV calling rate and impaired social interaction in males with prenatal ethanol exposure (PrEE). Gene expression analysis of transcripts involved in dopamine regulation revealed a main effect of ethanol exposure on dopamine- and cyclic adenosine monophosphate- regulated neuronal phosphoprotein (Darpp-32), a main effect of vitamin D diet on Dopamine 2 Receptors (D2R) and a main effect of Sex on Tyrosine Hydroxylase (TH) expression. The combination of PVD-PrEE did not exacerbate the alterations resulting from PVD or PrEE. Despite the limited evidence to support the interaction of PVD and PrEE during the postnatal period, males were more vulnerable than female offspring to the detrimental effects of PrEE. Therefore, based on these studies in mice we suggest that maintenance of optimal vitamin D levels and abstinence from ethanol during pregnancy would reduce risk of later disruption to brain function and behaviour in the offspring.

Aspirin pre-treatment modulates ozone-induced fetal growth restriction and alterations in uterine blood flow in rats

Prenatal exposure to ozone has been linked to low birth weight in people and fetal growth restriction in rats. Clinical recommendations suggest use of low dose aspirin to lower risk of preeclampsia and intrauterine growth restriction in high-risk pregnancies, yet its utility in mitigating the postnatal effects of gestational ozone exposure is unknown. The present study investigated the possibility of low dose aspirin to mitigate the effects of ozone exposure during pregnancy. Exposure to ozone impaired uterine arterial flow and induced growth restriction in fetuses of both sexes. Aspirin treatment induced marginal improvements in ozone-induced uterine blood flow impairment. However, this resulted in a protection of fetal weight in dams given aspirin only in early pregnancy. Aspirin administration for the entirety of gestation increased placental weight and reduced antioxidant status, suggesting that prolonged exposure to low dose aspirin may induce placental inefficiency in our model of growth restriction.

Nesting Environment Provides Sex-Specific Neuroprotection in a Rat Model of Neonatal Hypoxic-Ischemic Injury

Hypoxic-ischemic (HI) encephalopathy is a devastating injury that occurs when the fetal brain is deprived of oxygen and blood to a degree that may lead to neurological damage, seizing and cerebral palsy. In rodents, early environmental enrichment that promotes maternal care-taking behavior (mCTB) can improve neurobehavioral outcomes and protect against neurological decline. We hypothesized that an enhanced nesting environment would improve mCTB as measured by pup weight gain, and support greater HI recovery in developing rats. Pregnant dams (E15-16) were introduced to either control Standard Facility (SF) housing or closed nestbox (CN) conditions and maintained in larger cages through pup weaning. On postnatal day (PND) 7, male and female Long-Evans rat pups (N = 73) were randomly sorted into one of two surgical conditions: control and HI. HI pups received isoflurane anesthesia and right carotid artery ligation, a 2-h rest followed by 90 min exposure to a moist hypoxic (92% N, 8% O2) chamber. Pups (PND 8) were weighed daily, and tested on the Morris Water Maze (MWM) task (PND 35-50). Results demonstrate significant differences afforded to male and female pups based on weight measure, where CN-rearing modifies pre-weaning adolescent weights in females and increases post-weaning weights in males and females by an average of 10 g. Following successful MWM training and acquisition (PND 35-37), both male and female CN-raised animals demonstrated faster latency to find the hidden platform (HP) during HP trials (PND 38-42) and appeared to freely explore the MWM pool during an additional probe trial (PND 43). Moreover, after sacrifice (PND 60), CN rearing created sex-specific alterations in brain-derived neurotrophic factor (BDNF), glial-derived neurotrophic factor (GDNF) immunopositive cell staining of the dorsomedial striatum and CA1 of the hippocampus. CN-rearing afforded HI males higher BDNF levels in the striatum and produced greater GDNF levels in the hippocampus of HI-injured females. These results suggest that early life environmental enrichment positively modifies nesting environment, increases weight gain, as well as spatial learning and memory in a sex-specific directionality. Our findings also implicate correlative changes in corticolimbic neurotrophin protein levels in the CN-reared animals that may contribute to these benefits.

Early life stress in rats sex-dependently affects remote endocrine rather than behavioral consequences of adult exposure to contextual fear conditioning

Exposure to electric foot-shocks can induce in rodents contextual fear conditioning, generalization of fear to other contexts and sensitization of the hypothalamic-pituitary-adrenal (HPA) axis to further stressors. All these aspects are relevant for the study of post-traumatic stress disorder. In the present work we evaluated in rats the sex differences and the role of early life stress (ELS) in fear memories, generalization and sensitization. During the first postnatal days subjects were exposed to restriction of nesting material along with exposure to a "substitute" mother. In the adulthood they were exposed to (i) a contextual fear conditioning to evaluate long-term memory and extinction and (ii) to a novel environment to study cognitive fear generalization and HPA axis heterotypic sensitization. ELS did not alter acquisition, expression or extinction of context fear conditioned behavior (freezing) in either sex, but reduced activity in novel environments only in males. Fear conditioning associated hypoactivity in novel environments (cognitive generalization) was greater in males than females but was not specifically affected by ELS. Although overall females showed greater basal and stress-induced levels of ACTH and corticosterone, an interaction between ELS, shock exposure and sex was found regarding HPA hormones. In males, ELS did not affect ACTH response in any situation, whereas in females, ELS reduced both shock-induced sensitization of ACTH and its conditioned response to the shock context. Also, shock-induced sensitization of corticosterone was only observed in males and ELS specifically reduced corticosterone response to stressors in males but not females. In conclusion, ELS seems to have only a minor impact on shock-induced behavioral conditioning, while affecting the unconditioned and conditioned responses of HPA hormones in a sex-dependent manner.

Neonatal Handling Produces Sex Hormone-Dependent Resilience to Stress-Induced Muscle Hyperalgesia in Rats

Neonatal handling (NH) of male rat pups strongly attenuates stress response and stress-induced persistent muscle hyperalgesia in adults. Because female sex is a well established risk factor for stress-induced chronic muscle pain, we explored whether NH provides resilience to stress-induced hyperalgesia in adult female rats. Rat pups underwent NH, or standard (control) care. Muscle mechanical nociceptive threshold was assessed before and after water avoidance (WA) stress, when they were adults. In contrast to male rats, NH produced only a modest protection against WA stress-induced muscle hyperalgesia in female rats. Gonadectomy completely abolished NH-induced resilience in male rats but produced only a small increase in this protective effect in female rats. The administration of the antiestrogen drug fulvestrant, in addition to gonadectomy, did not enhance the protective effect of NH in female rats. Finally, knockdown of the androgen receptor by intrathecal antisense treatment attenuated the protective effect of NH in intact male rats. Together, these data indicate that androgens play a key role in NH-induced resilience to WA stress-induced muscle hyperalgesia.

PERSPECTIVE

NH induces androgen-dependent resilience to stress-induced muscle pain. Therefore, androgens may contribute to sex differences observed in chronic musculoskeletal pain and its enhancement by stress.

Sex-dependent impact of early-life stress and adult immobilization in the attribution of incentive salience in rats

Early life stress (ELS) induces long-term effects in later functioning and interacts with further exposure to other stressors in adulthood to shape our responsiveness to reward-related cues. The attribution of incentive salience to food-related cues may be modulated by previous and current exposures to stressors in a sex-dependent manner. We hypothesized from human data that exposure to a traumatic (severe) adult stressor will decrease the attribution of incentive salience to reward-associated cues, especially in females, because these effects are modulated by previous ELS. To study these factors in Long-Evans rats, we used as an ELS model of restriction of nesting material and concurrently evaluated maternal care. In adulthood, the offspring of both sexes were exposed to acute immobilization (IMO), and several days after, a Pavlovian conditioning procedure was used to assess the incentive salience of food-related cues. Some rats developed more attraction to the cue predictive of reward (sign-tracking) and others were attracted to the location of the reward itself, the food-magazine (goal-tracking). Several dopaminergic markers were evaluated by in situ hybridization. The results showed that ELS increased maternal care and decreased body weight gain (only in females). Regarding incentive salience, in absolute control animals, females presented slightly greater sign-tracking behavior than males. Non-ELS male rats exposed to IMO showed a bias towards goal-tracking, whereas in females, IMO produced a bias towards sign-tracking. Animals of both sexes not exposed to IMO displayed an intermediate phenotype. ELS in IMO-treated females was able to reduce sign-tracking and decrease tyrosine hydroxylase expression in the ventral tegmental area and dopamine D1 receptor expression in the accumbens shell. Although the predicted greater decrease in females in sign-tracking after IMO exposure was not corroborated by the data, the results highlight the idea that sex is an important factor in the study of the long-term impact of early and adult stressors.

Effects of cross-fostering on play and anxiety in juvenile Fischer 344 and Lewis rats

A cross-fostering design was used to assess the relative involvement of genetic variability and early postnatal experiences on differential levels of playfulness in juvenile Fischer 344 (F344) and Lewis (LEW) rats and the extent to which strain differences in anxiety may influence play in these two strains. F344 dams were found to lick and groom their pups less than LEW dams and this was not dependent upon the strain of the pups in the litter. As expected, F344 rats were less playful than LEW rats as demonstrated by fewer playful contacts directed to the nape of a Sprague-Dawley (SD) partner and a decreased likelihood of rotating completely to a supine position when their nape was contacted by the SD partner. These differences could not be readily explained by parallel strain differences in anxiety. The pattern of effects on play as a function of cross-fostering depended on both the genetic background of the pup and the motivational state of the pup prior to testing. Whereas in-fostered LEW pups solicited more play as isolation prior to testing increased from 4 to 24h, cross-fostered pups of both strains as well as in-fostered F344 pups were relatively insensitive to the motivational modulation of play solicitation. Responsiveness to play solicitations in pups of both strains reared by F344 dams was insensitive to prior isolation whereas pups reared by LEW dams were less likely to respond with a complete rotation to a supine position when solicited as isolation increased from 4 to 24h prior to testing. These data suggest that the overall level of playfulness in a particular strain of rat is fairly resistant to cross-fostering and may be particularly sensitive to genetic variation whereas how this urge is titrated and modified by motivational factors may be influenced more by epigenetic factors.

Cross-fostering: Elucidating the effects of gene×environment interactions on phenotypic development

Cross-fostering of litters from soon after birth until weaning is a valuable tool to study the ways in which gene×environment interactions program the development of neural, physiological and behavioral characteristics of mammalian species. In laboratory mice and rats, the primary focus of this review, cross-fostering of litters between mothers of different strains or treatment groups (intraspecific) or between mothers of different species (interspecific) has been conducted over the past 9 decades. Areas of particular interest have included maternal effects on emotionality, social preferences, responses to stressful stimulation, nutrition and growth, blood pressure regulation, and epigenetic effects on brain development and behavior. Results from these areas of research highlight the critical role of the postnatal maternal environment in programming the development of offspring phenotypic characteristics. In addition, experimental paradigms that have included cross-fostering have permitted investigators to tease apart prenatal versus postnatal effects of various treatments on offspring development and behavior.

Part III: Principal component analysis: bridging the gap between strain, sex and drug effects

Previous work has identified the adolescent period as particularly sensitive to the short- and long-term effects of marijuana and its main psychoactive component Δ9-tetrahydrocannabinol (THC). However, other studies have identified certain backgrounds as more sensitive than others, including the sex of the individual or the strain of the rat used. Further, the effects of THC may be specific to certain behavioural tasks (e.g. measures of anxiety), and the consequences of THC are not seen equally across all behavioural measures. Here, data obtained from adolescent male and female Long-Evans and Wistar rats exposed to THC and tested as adults, which, using standard ANOVA testing, showed strain- and sex-specific effects of THC, was analyzed using principal component analysis (PCA). PCA allowed for the examination of the relative contribution of our variables of interest to the variance in the data obtained from multiple behavioural tasks, including the skilled reaching task, the Morris water task, the discriminative fear-conditioning to context task, the elevated plus maze task and the conditioned place preference task to a low dose of amphetamine, as well as volumetric estimates of brain volumes and cfos activation. We observed that early life experience accounted for a large proportion of variance across data sets, although its relative contribution varied across tasks. Additionally, THC accounted for a very small proportion of the variance across all behavioural tasks. We demonstrate here that by using PCA, we were able to describe the main variables of interest and demonstrate that THC exposure had a negligible effect on the variance in the data set.

Stress in Neonatal Rats with Different Maternal Care Backgrounds: Monoaminergic and Hormonal Responses

The first 2 weeks of life in rats are known as the stress hyporesponsive period because stress responses in pups are diminished as compared to adult animals. However, it is considered a critical period in development in which infant rats are susceptible to environmental events, such as stressful stimuli and quality of maternal care received. These early life events have long-lasting effects, shaping a variety of outcomes, such as stress responsivity. This study investigated the effects of maternal care and sex differences on the response to an aversive stimulus in rat pups from high (HL) and low licking (LL) mothers. Plasma corticosterone, oxytocin, and central monoaminergic activity in 13-day-old rats submitted to cold stress were analyzed. Stress increased plasma corticosterone and marginally decreased hypothalamic dihydroxyphenylacetic acid/dopamine (DOPAC/DA) ratio. HL pups showed higher levels of plasma oxytocin than LL pups. The maternal effect was also detected in the hippocampus, in which 5-hydroxyindole-3-acetic acid/serotonin (5-HIAA/5-HT) ratio was increased in HL pups, independently of the sex and stress. Investigating the early life events is useful not only into understand the neurobiological and hormonal mechanisms underlying maternal and stressful influences on infant development into a healthy or psychopathological adult phenotype, but also to unveil the immediate outcomes on infancy.

Differential methylation of genes in the medial prefrontal cortex of developing and adult rats following exposure to maltreatment or nurturing care during infancy

Quality of maternal care in infancy is an important contributing factor in the development of behavior and psychopathology. One way maternal care could affect behavioral trajectories is through environmentally induced epigenetic alterations within brain regions known to play prominent roles in cognition, emotion regulation, and stress responsivity. Whereas such research has largely focused on the hippocampus or hypothalamus, the prefrontal cortex (PFC) has only just begun to receive attention. The current study was designed to determine whether exposure to maltreatment or nurturing care is associated with differential methylation of candidate gene loci (bdnf and reelin) within the medial PFC (mPFC) of developing and adult rats. Using a within-litter design, infant male and female rats were exposed to an adverse or nurturing caregiving environment outside their home cage for 30 min per day during the first postnatal week. Additional littermates remained with their biological caregiver within the home cage during the manipulations. We observed that infant rats subjected to caregiver maltreatment emitted more audible and ultrasonic vocalizations than littermates subjected to nurturing care either within or outside of the home cage. While we found no maltreatment-induced changes in bdnf DNA methylation present in infancy, sex-specific alterations were present in the mPFC of adolescents and adults that had been exposed to maltreatment. Furthermore, while maltreated females showed differences in reelin DNA methylation that were transient, males exposed to maltreatment and both males and females exposed to nurturing care outside the home cage showed differences in reelin methylation that emerged by adulthood. Our results demonstrate the ability of infant-caregiver interactions to epigenetically mark genes known to play a prominent role in cognition and psychiatric disorders within the mPFC. Furthermore, our data indicate the remarkable complexity of alterations that can occur, with both transient and later emerging DNA methylation differences that could shape developmental trajectories and underlie gender differences in outcomes.

Early life manipulations alter learning and memory in rats

Much research shows that early life manipulations have enduring behavioral, neural, and hormonal effects. However, findings of learning and memory performance vary widely across studies. We reviewed studies in which pre-weaning rat pups were exposed to stressors and tested on learning and memory tasks in adulthood. Tasks were classified as aversive conditioning, inhibitory learning, or spatial/relational memory. Variables of duration, type, and timing of neonatal manipulation and sex and strain of animals were examined to determine if any predict enhanced or impaired performance. Brief separations enhanced and prolonged separations impaired performance on spatial/relational tasks. Performance was impaired in aversive conditioning and enhanced in inhibitory learning tasks regardless of manipulation duration. Opposing effects on performance for spatial/relational memory also depended upon timing of manipulation. Enhanced performance was likely if the manipulation occurred during postnatal week 3 but performance was impaired if it was confined to the first two postnatal weeks. Thus, the relationship between early life experiences and adulthood learning and memory performance is multifaceted and decidedly task-dependent.

Prenatal stress produces sex differences in nest odor preference

Prenatal stress (PS) and early postnatal environment may alter maternal care. Infant rats learn to identify their mother through the association between maternal care and familiar odors. Female Wistar rats were exposed to restraint stress for 30 min, 4 sessions per day, in the last 7 days of pregnancy. At birth, pups were cross-fostered and assigned to the following groups: prenatal non-stressed mothers raising non-stressed pups (NS:NS), prenatal stressed mothers raising non-stressed pups (S:NS), prenatal non-stressed mothers raising stressed pups (NS:S), prenatal stressed mothers raising stressed pups (S:S). Maternal behaviors were assessed during 6 postpartum days. On postnatal day (PND) 7, the behavior of male and female pups was analyzed in the odor preference test; and noradrenaline (NA) activity in olfactory bulb (OB) was measured. The results showed that restraint stress increased plasma levels of corticosterone on gestational day 15. After parturition, PS reduced maternal care, decreasing licking the pups and increasing frequency outside the nest. Female pups from the NS:S, S:NS, S:S groups and male pups from the S:S group showed no nest odor preference. Thus, at day 7, female pups that were submitted to perinatal interventions showed more impairment in the nest odor preference test than male pups. No changes were detected in the NA activity in the OB. In conclusion, repeated restraint stress during the last week of gestation reduces maternal care and reduces preference for a familiar odor in rat pups in a sex-specific manner.

Sex Differences in Pain Responses at Maturity Following Neonatal Repeated Minor Pain Exposure in Rats

There is mounting evidence of long-lasting changes in pain sensitivity in school-age children who were cared for in a neonatal intensive care unit. Such care involves multiple pain exposures, 70% of which are accounted for by heel lance to monitor physiological well-being. The authors sought to model the repeated brief pain resulting from heel lance by administering repeated paw needle stick to neonatal rat pups. Repeated needle stick during the first 8 days of life was sex-specific in altering responses to mechanical and inflammatory stimuli, but not to a thermal stimulus, at maturity. Specifically, neonatal paw needle stick males exhibited significantly greater mechanical sensitivity in response to von Frey hair testing, whereas neonatal paw needle stick females exhibited significantly greater pain behavior scores following hindpaw formalin injection. This is the first study to show such sex-dependent changes in pain responsiveness at maturity in animals having experienced repeated neonatal needle stick pain. These findings support existing evidence that there are long-term sensory sequelae following neonatal pain experiences in rats and further suggest that there are sex-linked differences in the nature of the consequences. If these relationships hold in humans, these findings suggest that even mild painful insults early in life are not without sensory consequences.

Immediate and enduring effects of neonatal isolation on maternal behavior in rats

Previously, we showed that neonatal isolation (1-hisolation/day from dam, litter, and nest on PND 2-9) facilitates cocaine self-administration and increases extracellular dopamine responses in ventral striatum after stimulant administration in adulthood. Recent studies suggest that enduring alterations in neurobehavioral responses associated with early life manipulations reflect changes in maternal behavior. Thus, we sought to determine if neonatal isolation alters maternal care and if dams with neonatal isolation experience as pups showed differential maternal care towards their pups. In Experiment 1, litters were assigned to one of three conditions: neonatal isolation, handled (5-min separation of dam from litter), or non-handled (no separation). Maternal behaviors were rated on PND 2-9 for 60-min immediately following reunion of mother and litter. In Experiment 2, female rats with or without neonatal isolation experience were assigned to either the neonatal isolation or non-handled litter condition and maternal behaviors rated. Dams of isolated and handled litters spent more time licking pups and less time picking up pups to put outside the nest than dams of non-handled litters. Further, dams of isolated and handled vs. non-handled litters showed less non-maternal behaviors of burrowing and grooming. Neonatal isolation-experienced dams with isolated litters failed to increase pup-licking and decrease non-maternal behaviors. Rather, these dams picked up pups to place outside the nest more than non-handled-experienced dams. Neonatal isolation alters maternal behavior that, in turn, may shape neurobehavioral responses of offspring including effects on maternal care. Such changes may reflect epigenetic effects resulting from changes in maternal behavior.

Agmatine reduces ultrasonic vocalization deficits in female rat pups exposed neonatally to ethanol

Rat pups, in isolation, produce ultrasonic vocalizations (USVs). These USVs have been used as a diagnostic tool for developmental toxicity. We have shown that neonatal ethanol (ETOH) exposure produces deficits in this behavior. The current study was designed to examine whether agmatine (AG), which binds to imidazoline receptors and modulates n-methyl-d-aspartate receptors (NMDAR), could reduce these deficits. In addition, this study examined critical periods for ETOH's effects on USVs by administering ETOH during either the 1st or 2nd postnatal week. Neonatal rats received intragastric intubations of either ETOH (6g/kg/day), ETOH and AG (6g/kg/day and 20mg/kg/day), AG (20mg/kg/day), or maltose on postnatal days (PND) 1-7 or 8-14. A non-intubated control was also included. Subjects were tested on PND 15. Neonatal ETOH exposure significantly increased the latency to vocalize for females and reduced the rate of USVs in both males and females exposed to ETOH on PND 1-7. Agmatine reduced these deficits, in female but not male pups. Subjects exposed to ETOH on PND 8-14 showed no evidence of abnormal USVs. These findings suggest that there may be gender differences in response to AG following neonatal ETOH exposure and also provide further support that the first neonatal week is a particularly sensitive time for the developmentally toxic effects of ETOH in rodents.

Epigenetic effects of glucocorticoids

The early nurturing environment has persistent influences on developmental programming of inter-individual differences in metabolic and endocrine function that contribute to emotional and cognitive performance through life. These effects are mediated, in part, through neonatal programming of hypothalamic-pituitary-adrenal (HPA) axis function. Animal models support this hypothesis. For example, in the rat natural variations in maternal care influence HPA axis stress reactivity in the offspring via long-term changes in tissue-specific gene expression. Studies in vivo and in vitro show that maternal licking and grooming increases glucocorticoid receptor expression in the offspring via increased hippocampal serotonergic tone accompanied by increased histone acetylase transferase activity, histone acetylation and DNA demethylation mediated by the transcription factor nerve growth factor-inducible protein-A. These effects are reversed by early postnatal cross-fostering and by pharmacological manipulations, including trichostatin A (TSA) and l-methionine administration in adulthood. These studies demonstrate that an epigenetic state of a gene can be established through early in life experience, and is potentially reversible in adult life. Accordingly, epigenetic modifications in target gene promoters in response to environmental demand may ensure stable yet dynamic regulation that mediates persistent changes in biological and behavioral phenotype over the lifespan.

Neonatal handling and the maternal odor preference in rat pups: involvement of monoamines and cyclic AMP response element-binding protein pathway in the olfactory bulb

Early-life environmental events, such as the handling procedure, can induce long-lasting alterations upon several behavioral and neuroendocrine systems. However, the changes within the pups that could be causally related to the effects in adulthood are still poorly understood. In the present study, we analyzed the effects of neonatal handling on behavioral (maternal odor preference) and biochemical (cyclic AMP response element-binding protein (CREB) phosphorylation, noradrenaline (NA), and serotonin (5-HT) levels in the olfactory bulb (OB)) parameters in 7-day-old male and female rat pups. Repeated handling (RH) abolished preference for the maternal odor in female pups compared with nonhandled (NH) and the single-handled (SH) ones, while in RH males the preference was not different than NH and SH groups. In both male and female pups, RH decreased NA activity in the OB, but 5-HT activity increased only in males. Since preference for the maternal odor involves the synergic action of NA and 5-HT in the OB, the maintenance of the behavior in RH males could be related to the increased 5-HT activity, in spite of reduction in the NA activity in the OB. RH did not alter CREB phosphorylation in the OB of both male and females compared with NH pups. The repeated handling procedure can affect the behavior of rat pups in response to the maternal odor and biochemical parameters related to the olfactory learning mechanism. Sex differences were already detected in 7-day-old pups. Although the responsiveness of the hypothalamic-pituitary-adrenal axis to stressors is reduced in the neonatal period, environmental interventions may impact behavioral and biochemical mechanisms relevant to the animal at that early age.

Difluoromethylornithine (DFMO) reduces deficits in isolation-induced ultrasonic vocalizations and balance following neonatal ethanol exposure in rats

Neonatal ethanol (EtOH) exposure is associated with central nervous system dysfunction and neurotoxicity in rats. Increases in polyamine levels have been implicated as one underlying mechanism for some of EtOH's effects on the developing brain. In this study we addressed whether the inhibition of polyamine biosynthesis by alpha-difluoromethylornithine (DFMO) could reduce behavioral deficits induced by early EtOH exposure. Male and female rat pups received ethanol (6 g/kg/day EtOH i.g.), or isocaloric maltose (control) from postnatal days (PND) 1-8. On PND 8, animals were injected with either saline or DFMO (500 mg/kg, s.c.) immediately following the final neonatal treatment. Subjects were tested for isolation-induced ultrasonic vocalizations (USV) on PND 16; spontaneous activity in an open field apparatus on PND 20 and 21; and balance on PND 31. Animals exposed to EtOH neonatally displayed an increased latency to the first USV and reduced frequencies of USV, hyperactivity and preference for the center of the open field and poorer balance relative to controls. DFMO minimized these deficits in latency to the first USV and balance. These data provide further support that polyamines play a role in some of the functional deficits associated with EtOH exposure during early development and that reducing polyamine activity can improve outcome.

Maternal care affects male and female offspring working memory and stress reactivity

Variations in maternal care affect the development of individual differences in learning and memory and neuroendocrine responses to stress in adult male offspring, but it is not known how variations in maternal care affect adult female offspring. The present study investigated the performance of adult Sprague-Dawley male and female offspring exposed to either low or high levels of maternal licking/grooming on a spatial memory task (Experiment 1) and the effects of acute stress on corticosterone levels and spatial memory performance (Experiment 2). In Experiment 1 rats were trained for 24 days on the spatial working/reference memory version of the radial arm maze (RAM). In Experiment 2, rats were trained on the same RAM task, exposed to an acute stress, and the effect of stress on corticosterone levels and subsequent spatial memory was examined. In Experiment 1, adult female offspring of low licking/grooming dams had enhanced working memory compared to all other groups. In Experiment 2, all groups of male and female offspring had enhanced working memory 24 h after exposure to acute 2 h restraint stress while reference memory was enhanced after stress in male and female offspring of low licking/grooming dams. Furthermore, female offspring of low licking/grooming dams showed the largest corticosterone response to the acute restraint stress compared to all other groups. Male offspring of low licking/grooming dams showed a flattened corticosterone response to stress. Thus variations in maternal care differentially affect working memory and stress reactivity in male and female offspring.

Effects of maternal care on the development, emotionality, and reproductive functions in male and female rats

Variations in maternal behavior induce long-lasting effects on behavioral and neuroendocrine responses to stress. The aim of this study was to analyze developmental parameters, reproductive function, and anxiety-related behaviors of male and female rats raised by mothers that naturally display high and low levels of maternal licking behavior. Results showed that an increase in licking behavior received by the pups accelerated their eye opening and reduced fear behavior assessed in the open field test. Additionally, female offspring of high licking (HL) mothers showed decreased ovulation and lordosis intensity. In contrast, males from HL and low licking (LL) mothers did not differ in their reproductive function, suggesting a gender difference in maternal effects. Present results showed that individual differences in maternal behavior appear not only to be predictive of later emotionality and stress-responsivity in the offspring, but can also modulate the reproductive function of females. Maternal genetic factors, differences in the prenatal intrauterine milieu, or a combination of these cannot be excluded to explain the effects observed.

Androgen receptor is essential for sexual differentiation of responses to olfactory cues in mice

During sexual differentiation males and females are exposed to different levels of testosterone, which promotes sex differences in the adult brain and in behavior. Testosterone can act after aromatization or reduction via a number of steroid hormone receptors. Here we provide new evidence that the androgen receptor (AR) is essential for sexual differentiation in mice. We used mice carrying the testicular feminization (Tfm) mutation of the AR. Adult Tfm males, wild-type male and female littermates were gonadectomized and given subcutaneous estradiol implants. In all sexually dimorphic traits, Tfm males had responses equivalent to females and different from males. In simultaneous choice tests, males spent significantly more time investigating female-soiled bedding, whereas females and Tfm males preferred to investigate male-soiled bedding. Tfm males and females did not have a partner preference in tests with awake stimulus animals, whereas males showed a preference for females over males. Exposure to male-soiled, but not clean, bedding produced a significant increase in c-Fos-immunoreactive cells in the medial preoptic area and bed nucleus of the stria terminalis in Tfm males and females, no increase was noted in males. Masculine sexual behavior (mounting and thrusting) was not sexually dimorphic, and all groups displayed these behaviors. Our results support data collected in humans suggesting a role for the androgen receptor in sexual differentiation of social preferences and neural responses to pheromones.

Can knowledge of developmental processes illuminate the evolution of parental care?

There are two levels of investigation for elucidating the evolution of parental behavior. The macro level focuses on how parental behavior can evolve as an aspect of reproduction. The micro level focuses on how species variations in parental behavior evolve. Recently, modern evolutionary biology has turned to developmental biology as a source for information about how trait variability (the substrate upon which natural selection and other evolutionary mechanisms can operate) can emerge during development (called "evo-devo"). Application of this evo-devo approach to the phenomenon of parental behavior requires identification of those mechanisms that produce variations in developmental pathways leading to parental behavior. It is these variations that provide the phenotypes for the potential evolution of different parental behavior systems. Variations in rodent maternal behavior affect the development of the HPA and HPG axes in their offspring. These mechanisms are examined to reveal how such developmental variations could underlie the evolution of biparental behavior. Knowledge of the developmental mechanisms responsible for species variations in mammalian parental behavior systems may provide insight into those mechanisms that may have been involved in the evolution of parental behavior itself.

Maternal behavior deficits in nulliparous oxytocin knockout mice

The first observations of postpartum oxytocin knockout (OTKO) mice found no maternal behavior deficits. However, it is unclear how detailed those observations were. In this study, we compared maternal behavior exhibited by OTKO and wild-type (WT) nullipara toward six 2-4-day-old foster pups during test sessions conducted on 3 successive days. Each day, subjects were placed in a clean cage 30 min prior to introduction of pups which were deposited in a clump adjacent to the middle of a long wall of each test cage. Behavior was measured for 3.5 h after which pups and test subjects were returned to their home cages. On test days 1 and 3, a significantly smaller proportion of OTKO females retrieved pups to a corner of their cage. Also, significantly fewer pups were retrieved to corners by OTKO females. In contrast to most WTs, most OTKO females mothered pups in the center of the cage where they were initially deposited. Pup-licking frequencies were significantly lower in OTKO females. Their self-grooming frequencies also trended toward being lower. Latencies to retrieve and lick pups, latencies to and frequencies of still crouching over pups and proportion of time in nest did not differ between groups. Our findings suggest that OT stimulates a significant proportion of pup-licking in nulliparous mice, a situation similar to lactating rat mothers. Our results also indicate that OT may play a role in the motivation to retrieve pups to a more secure location.

Neonatal ethanol exposure but not neonatal cocaine selectively reduces specific isolation-induced vocalization waveforms in rats

This study was designed to examine the interaction of neonatal ethanol and cocaine exposure on isolation induced ultrasonic vocalizations using an oral gavage method of drug administration. There were 5 neonatal treatment groups including 3.0 g/kg ethanol, 20 mg/kg cocaine, both 3.0 g/kg ethanol and 20 mg/kg cocaine, an intubated control and a nonintubated control. Drug was administered twice daily from postnatal days (PND) 4 - 10. On PND 14, subjects were tested for a 6 min test to assess the rate and type of ultrasonic vocalizations displayed. As previously reported using an intragastric "artificial rearing" administration procedure, pups exposed to ethanol displayed reductions in the number of ultrasonic vocalizations across the test session. Pups exposed to both drugs showed similar deficits to those pups receiving ethanol alone. In contrast, cocaine had no effect on this outcome measure. Sonographic analysis of the vocalizations revealed that ethanol's effects appeared to be selective to certain waveforms rather than a general reduction across all wave types and again, cocaine had no impact on the proportion of the various wave types. These findings provide further support that neonatal ethanol exposure can have significant effects on maternal/infant communication and may play a role in many of the long-term effects associated with ethanol exposure during development.

Postnatal environment affects behavior of adult transgenic mice

Behavioral phenotypes of knockout mice are often interpreted as the effects of the absence of the gene product on adult behavior, yet behavioral differences among genotypes may be exaggerated or blurred by the postnatal environment. For example, mice develop in litters of varying sex ratios and genotypes, and it is possible that some of these behavioral differences may result from the composition of the litter. To determine whether these factors might play a role in the development of the behavioral characteristics that have become diagnostic of the knockout, offspring of parents heterozygous for a null mutation of estrogen receptor alpha (ERKO) were sexed and genotyped within 2 days of birth. Litters were then reconstituted, forming same-sex litters of equal numbers of ERKO and wild-type (WT) individuals that were tested in a standard resident-intruder paradigm. In this manner the effect of genotype would be evident without the potential confound of the presence of the opposite sex in the litter. Behavioral differences between the genotypes were more sharply defined than reported previously. ERKO females displayed only aggressive behavior whereas their WT littermates displayed only mounting behavior; both aggression and mounting behavior were greatly reduced in ERKO males. These data suggest that the postnatal environment such as litter composition may influence the development of sociosexual behaviors in ERKO mice.

Early Deprivation Alters the Vocalization Behavior of Neonates Directing Maternal Attention in a Rat Model of Child Neglect

Animal models of child neglect (known as maternal separation or early deprivation) have suggested a causal link to subsequent depression and/or anxiety in children. In this experiment, the acoustical features of the ultrasonic calls emitted by a rat pup when separated from its dam were analyzed as well as the maternal behavior when the dam was allowed to retrieve the pup. Bout structure and harmonic double shifts did differ between controls and "neglected" pups, as did maternal attention. This model will be used to determine neural mechanisms underlying deficits in attachment behavior.

The relative playfulness of juvenile Lewis and Fischer-344 rats

The relative playfulness of inbred Lewis and Fischer-344 rats was characterized. Fischer rats were consistently less playful than Lewis rats, with rats of this strain less likely to initiate playful interactions with either responsive or unresponsive partners and also less likely to respond playfully when playful solicitations were directed to them. While less playful, Fischer rats were more socially inquisitive than Lewis rats when tested with an unresponsive partner, suggesting that Fischer rats are less likely to escalate a social encounter into a playful one. Strain differences in playful responsiveness were present with or without prior social isolation, suggesting that this aspect of play represents a relatively stable trait difference. Unlike play responsiveness, strain differences in play solicitation were only apparent after a period of social isolation. Low levels of play were still present in Fischer rats that had been reared by Lewis dams, suggesting a genetic source for the altered play in rats of this strain. Further studies of play behavior in Lewis and Fischer rats could illuminate relevant neural involvement in rough-and-tumble play and also help understand the genetic bases for this complex social behavior.

Long-lasting changes in morphine-induced locomotor sensitization and tolerance in Long-Evans mother rats as a result of periodic postpartum separation from the litter: a novel model of increased vulnerability to drug abuse?

Daily postpartum separations from the litter produce enduring changes in anxiety and sensitivity to the antinociceptive effects of morphine in Long-Evans dams. We tested whether postpartum experience alters sensitivity to the effects of morphine on locomotor activity. Dams were tested 4-6 weeks after their pups were weaned, and had one of the following backgrounds: daily separation from the litter on postpartum days 2-14 for either 3 h (prolonged separation-LS) or 15 min (brief separation-BS), or no separation (nonhandled control-NH). After 2 consecutive days (B1-2) of baseline activity measurements, subjects were tested daily after s.c. injections of either morphine (10 mg/kg) or saline for 7 days and again on day 10. Beginning 5 days later, saline and 1.0-10 mg/kg of morphine were tested in all dams. On B1, LS and BS dams habituated slower than NH controls, yielding higher horizontal counts. LS dams failed to habituate across baseline days and were more active than other dams on B2. Sensitization, a progressive increase in horizontal activity, was more rapid and robust in LS and BS dams compared to NH animals. LS was the only group that developed tolerance to morphine-induced decreases in vertical activity. In LS dams with the history of morphine treatment, injection of saline resulted in higher horizontal activity and center time compared to saline-treated counterparts, indicative of conditioning. Among animals with a history of saline treatment, LS dams were more sensitive to morphine challenges than BS and NH dams. As a result of the robust and long-lasting increases in the ability of morphine to induce behavioral sensitization in litter-separated dams, periodic postpartum separation may represent a new animal model of increased vulnerability to substance abuse.

Long-lasting changes in stress-induced corticosterone response and anxiety-like behaviors as a consequence of neonatal maternal separation in Long-Evans rats

Early neonatal environmental factors appear to have powerful and long-lasting influences on an organism's physiology and behavior. Long-Evans male rats separated from their dam for 3 h daily over the first 2 weeks of life (maternally separated, MS rats) when tested as adults exhibit exaggerated behavioral and neuroendocrine responses to stress compared to 15-min separated (handled, H) animals. The purpose of this study was to compare male and female adult rats that were MS, H or were undisturbed (nonhandled, NH) as neonates in anxiety-like behaviors, in the elevated plus-maze, and in response to startle-inducing auditory stimuli. We confirmed that MS males oversecrete corticosterone (CORT; 2.5-5 times) in response to mild handling stress. MS males and females were less likely to explore open arms of the plus-maze. MS males exhibited 35% higher startle amplitudes compared to controls. Furthermore, MS males were more likely to emit ultrasonic vocalizations in response to startle than were H controls. However, MS and control females did not differ in auditory startle response or in startle-induced ultrasonic vocalizations. Therefore, experiencing maternal separation results in a long-lasting increase in anxiety-like behaviors that occurs in a sex-dependent manner.

Age-related changes in paternal responses of gerbils parallel changes in their testosterone concentrations

Results of previous studies in our laboratory have shown that testosterone (T) inhibits parental response in adult male Mongolian gerbils. Here, we examined developmental changes in parental responses of male gerbils before, during, and after a naturally occurring surge in T that peaks on Day 75 postpartum. On the hypothesis that T inhibits parental response in male gerbils, we predicted that (a) 75-day-old male gerbils would be less responsive to neonates than would either younger or older male gerbils, and (b) young male gerbils whose T titers were rising as the litters that they were helping to rear matured would show a decrease over days in parental effort relative to older male gerbils whose T titers were falling as the litters that they were helping to rear matured. Both predictions were confirmed, providing evidence consistent with the view that naturally occurring, developmental changes in circulating concentrations of T play a role in age-related changes in the level of parental response of male Mongolian gerbils.

Repeated neonatal maternal separation alters morphine-induced antinociception in male rats

Recent studies indicate that Long-Evans rats separated from their dam for 3 h daily over the first 2 weeks of life (maternally separated [MS] rats) exhibit exaggerated behavioral and neuroendocrine responses to stress as adults compared to handled (H) or non-handled (NH) control animals. Our aim was to determine whether repeated neonatal maternal separation results in altered sensitivity to the opioid agonist morphine in male and female adult rats. Sensitivity to morphine was assessed using hot-plate and tail-flick tests. Morphine was less potent inducing antinociception in MS males compared to same-sex controls in the hot-plate, but not in the tail-flick test. Decrease in sensitivity to morphine in MS females compared to same-sex controls was present only as a trend in the hot-plate, but not in the tail-flick test. These results suggest that neonatal maternal separation results in long-lasting changes in opioid responsiveness primarily in male rats.

Maternal behaviour in lactating rats stimulates c-fos in glutamate decarboxylase-synthesizing neurons of the medial preoptic area, ventral bed nucleus of the stria terminalis, and ventrocaudal periaqueductal gray

Increased activity of the immediate-early gene c-fos can be observed in many areas of the lactating rat brain after dams physically interact with pups and display maternal behaviour. These sites include the medial preoptic area, ventral bed nucleus of the stria terminalis, and the ventrolateral caudal periaqueductal gray, each of which is critical for the normal performance of particular maternal behaviours. The phenotype of cells in these areas that show increased c-fos activity after maternal behaviour, however, is unknown. Via double-label immunocytochemistry, we determined if the population of cells in these sites that express c-fos after maternal behaviour in lactating rats overlaps with the population that expresses the 67,000 mol. wt isoform of glutamate decarboxlyase, the synthesizing enzyme for the inhibitory neurotransmitter GABA. Lactating rats were separated from pups beginning on day 5 postpartum, and 48h later half were allowed to interact with a litter of pups for 60min whereas the other half were not. Dams re-exposed to pups were highly maternal, retrieving and licking them as well as displaying prolonged nursing behaviour that included milk letdown. Both groups of dams had a similar number of 67,000 mol. wt glutamate decarboxylase-immunoreactive cells in each site, although the number of 67,000 mol. wt glutamate decarboxylase-immunoreactive cells per microscopic field was significantly greater in the caudal ventrolateral periaqueductal gray than in the ventral bed nucleus of the stria terminalis, which in turn was greater than the medial preoptic area. In pup-stimulated dams, two to fourfold more Fos-immunoreactive cells were found in these three sites compared with non-stimulated controls. Labeling for Fos immunoreactivity and 67,000 mol. wt glutamate decarboxylase immunoreactivity was heterogeneous within each site. In the medial preoptic area, more Fos-immunoreactive and 67,000 mol. wt glutamate decarboxylase-immunoreactive cells (either single or dual-labeled) were found dorsally than ventrally. In the ventral bed nucleus of the stria terminalis, more Fos-immunoreactive and 67,000 mol. wt glutamate decarboxylase-immunoreactive cells were found medially than laterally. Within the caudal ventrolateral periaqueductal gray, 67,000 mol. wt glutamate decarboxylase-immunoreactive labeling was greatest ventromedially, while high numbers of Fos-immunoreactive nuclei were found both ventromedially and ventrolaterally. In pup-stimulated dams, more than half (53% in the medial preoptic area, 59% in the ventral bed nucleus of the stria terminalis, and 61% in the caudal ventrolateral periaqueductal gray) of the total population of Fos-immunoreactive cells also expressed 67,000 mol. wt glutamate decarboxylase. These results suggest that many of the neurons in these sites that show elevated c-fos activity after maternal behaviour are either local inhibitory interneurons or provide inhibitory input to other neural sites. These inhibitory mechanisms may be critical for the display of postpartum nurturance, possibly facilitating maternal behaviour by removing tonic inhibition on sites necessary for maternal responding or by restricting activity in neural sites that inhibit it.

The effects of neonatal ethanol and/or cocaine exposure on isolation-induced ultrasonic vocalizations

Isolation-induced ultrasonic vocalizations (USVs) are emitted by young rat pups when isolated from their dam and conspecifics. These USVs play an important role in maternal/offspring interactions, and have been used as an indicator of response to stress and isolation. This study examined the effects of neonatal ethanol and/or cocaine exposure on USVs in neonatal rats. The neonatal exposure paradigm serves as a model for the "human third trimester of pregnancy" in terms of CNS development. There were five treatment groups including an artificially reared (AR) ethanol-exposed group (6 g/kg/day), an AR cocaine-exposed group (60 mg/kg/day), an AR ethanol- and cocaine-exposed group (6 g/kg/day+60 mg/kg/day), an AR isocaloric control, and a normally reared control. Both groups that received ethanol took longer to vocalize, and displayed fewer vocalizations than non-ethanol-exposed pups when tested on clean bedding (Experiment 1) or on chips from the nest of a lactating dam (Experiment 2). These results suggest that neonatal ethanol exposure alters the pup's immediate response to isolation. This could have direct effects on maternal/infant interactions, and might help explain some of the long-term effects of ethanol exposure on social behaviors.

The role of corticotropin-releasing factor--norepinephrine systems in mediating the effects of early experience on the development of behavioral and endocrine responses to stress

Naturally occurring variations in maternal care in early postnatal life are associated with the development of individual differences in behavioral and hypothalamic-pituitary-adrenal responses to stress in the rat. These effects appear to be mediated by the influence of maternal licking and grooming on the development of central corticotropin-releasing factor (CRF) systems, which regulate the expression of behavioral, endocrine, and autonomic responses to stress through activation of forebrain noradrenergic systems. These findings provide a neurobiologic basis for the observed relationship between early life events and health in adulthood. In more recent studies, we explored the behavioral transmission of individual differences in stress reactivity, and thus, vulnerability to stress-induced illness, across generations.

Effect of gestational stress on maternal behavior in response to cage transfer and handling of pups in two strains of rat

The influence of gestational stress was determined on the mother's behavior in two rat strains after a disturbance in her routine. Daily 10 min observations were made for 9 days postpartum in Sprague-Dawley (S-D) and Sabra (SB) rats after transfer of the maternal cage to another room or transient pup removal. In response to cage transfer, SB spent much more time than S-D rats in nursing, licking and sitting on their pups, but less time in individual activities. The direction of effect of gestational stress depended on the strain and particular behavior. The duration of nursing was increased in S-D but decreased in SB rats, while that of pup-licking was increased in SB and unchanged or decreased in S-D. Pup-removal reduced the total amount of pup-directed behavior in control and stressed mothers of both strains and eliminated any differences resulting from gestational stress seen in response to cage transfer. It is concluded that the degree and direction of effect of gestational stress on the partition of time by a nursing mother between pup-directed and other behaviors during the early postnatal period is strongly influenced by the strain of rat and the conditions under which it is assessed.

Persistent effects of prenatal, neonatal, or adult treatment with flutamide on the hypothalamic-pituitary-adrenal stress response of adult male rats

To explore the role of androgens in early development on adult hypothalamic-pituitary-adrenal (HPA) function in males, we administered flutamide or vehicle injections: (1) to pregnant dams on embryonic days 15-20; (2) to neonatal pups on days 0-5; or (3) to adults on days 55-60. At approximately 70 days of age, trunk blood was collected to determine corticosterone levels (1) upon removal from the home cage, (2) immediately after 30 min of restraint stress, or (3) 60 min after return to home cage following the stressor. Flutamide treatment resulted in higher basal levels of testosterone and stress levels of corticosterone compared to vehicle treatment, and there was no interaction of treatment with age at time of treatment. This suggests that testosterone is less effective at inhibiting HPA function in flutamide-treated males. In addition, prenatally treated males had higher stress levels of corticosterone than neonatally and adult-treated males, regardless of the type of treatment. There were no differences in CBG levels among the groups. The results suggest that, in males, flutamide treatment has a long-lasting effect on HPA function. These results are consistent with our previous research on neonatally gonadectomized males and the hypothesis of organizational effects of sex hormones on HPA function.

Developmental effects on intersexual and intrasexual variation in growth and reproduction in a lizard with temperature-dependent sex determination

The mechanisms that control growth and reproduction have received considerable attention by molecular and cellular endocrinologists, yet there has been relatively little effort to link these two aspects of physiology. On the other hand, evolutionary biologists have long commented on the relationship between growth and reproduction in many species, yet have generally neglected the mechanisms underlying such complex traits. An approach that integrates the multiple proximate levels promises to provide significant insight into the evolution of neuroendocrine control mechanisms. In this chapter, we take this approach in reviewing environmental influences on growth and reproduction in the leopard gecko, Eublepharis macularius. In this species, incubation temperature during embryonic development not only determines gonadal sex, but also underlies within-sex differences in growth, adult morphology, aggressiveness, reproductive physiology and behaviour, and brain organization. Thus, the leopard gecko is an excellent model to elucidate the developmental interactions among the environment and the endocrine and nervous systems that control growth and reproduction.

Effects of lactation on sodium intake in Fischer-344 and Long-Evans rats

Rats of most strains are attracted to salt in low concentrations, and this attraction is increased by pregnancy and lactation. Nonreproducing Fischer-344 (F344) rats are unusual in that they avoid saline at all concentrations, raising the question of whether lactation alters their sodium appetite. Therefore, lactating and cycling Long-Evans and F344 rats were compared in their relative consumption of water and several concentrations of saline. We found that Long-Evans rats preferred saline, but F344 rats preferred plain water. In comparison with cycling rats, lactating Long-Evans rats markedly increased saline intake whereas F344 rats exhibited only a modest increase. Lactating rats of both strains increased total fluid intake, but this increase was primarily from water in F344 rats and from saline in Long-Evans rats. It was concluded that the aversion to saline characteristic of nonreproducing adult F344 rats continues during lactation. Their aversion to sodium in pup urine may account for the low levels of maternal anogenital licking observed in the F344 strain.