Early adversity alters attention and locomotion in adult Sprague-Dawley rats

Developmental Manipulation-Induced Changes in Cognitive Functioning

Schizophrenia is a complex neurodevelopmental disorder with as-yet no identified cause. The use of animals has been critical to teasing apart the potential individual and intersecting roles of genetic and environmental risk factors in the development of schizophrenia. One way to recreate in animals the cognitive impairments seen in people with schizophrenia is to disrupt the prenatal or neonatal environment of laboratory rodent offspring. This approach can result in congruent perturbations in brain physiology, learning, memory, attention, and sensorimotor domains. Experimental designs utilizing such animal models have led to a greatly improved understanding of the biological mechanisms that could underlie the etiology and symptomology of schizophrenia, although there is still more to be discovered. The implementation of the Research and Domain Criterion (RDoC) has been critical in taking a more comprehensive approach to determining neural mechanisms underlying abnormal behavior in people with schizophrenia through its transdiagnostic approach toward targeting mechanisms rather than focusing on symptoms. Here, we describe several neurodevelopmental animal models of schizophrenia using an RDoC perspective approach. The implementation of animal models, combined with an RDoC framework, will bolster schizophrenia research leading to more targeted and likely effective therapeutic interventions resulting in better patient outcomes.

Tactile stimulation prevents disruptions in male rat copulatory behavior induced by artificial rearing

Early life social interactions in gregarious mammals provide an important source of stimulation required for the development of species-typical behaviors. In the present study, complete deprivation of maternal and littermate contact through artificial rearing was used to examine the role of early social stimulation on copulatory behavior and the ejaculate in adult rats. We found that artificially reared naïve male rats were sexually motivated; nevertheless, they did not acquire the level of sexual experience that typically occurs during copulatory training. Disrupted expression of sexual experience of artificially reared rats was demonstrated by an inconsistent pattern of ejaculatory behavior across training tests. Artificial tactile stimulation applied during isolation prevented this disruption and rats achieved ejaculation in most copulatory tests. Despite the irregularity of ejaculatory behavior in isolated rats, their sperm count and seminal plug were similar to control maternally reared (sexually experienced) and artificially-reared rats that received tactile stimulation. These results suggest that tactile sensory information provided by the mother and/or littermates to the offspring is crucial for the development of copulatory behavior. The absence of social and/or tactile stimulation during early life compromises the ability of male rats to gain sexual experience in adulthood.

How do established developmental risk-factors for schizophrenia change the way the brain develops?

The recognition that schizophrenia is a disorder of neurodevelopment is widely accepted. The original hypothesis was coined more than 30 years ago and the wealth of supportive epidemiologically data continues to grow. A number of proposals have been put forward to suggest how adverse early exposures in utero alter the way the adult brain functions, eventually producing the symptoms of schizophrenia. This of course is extremely difficult to study in developing human brains, so the bulk of what we know comes from animal models of such exposures. In this review, I will summarise the more salient features of how the major epidemiologically validated exposures change the way the brain is formed leading to abnormal function in ways that are informative for schizophrenia symptomology. Surprisingly few studies have examined brain ontogeny from embryo to adult in such models. However, where there is longitudinal data, various convergent mechanisms are beginning to emerge involving stress and immune pathways. There is also a surprisingly consistent alteration in how very early dopamine neurons develop in these models. Understanding how disparate epidemiologically-validated exposures may produce similar developmental brain abnormalities may unlock convergent early disease-related pathways/processes.

Maternal predator odour exposure programs metabolic responses in adult offspring

A cardinal feature of the reaction to stress is the promotion of energy mobilization, enabling appropriate behavioural responses. Predator odours are naturalistic and ecologically relevant stressors present over evolutionary timescales. In this study, we asked whether maternal predator odour exposure could program long-term energy mobilization in C57BL/6 mice offspring. To test this hypothesis, we measured rates of oxygen consumption in prenatally predator odour exposed mice in adulthood while controlling for levels of locomotor activity at baseline and under stress. Circulating thyroid hormone levels and the transcript abundance of key regulators of the hypothalamic-pituitary-thyroid axis within the periventricular nucleus (PVN) of the hypothalamus and in the liver, including carriers and receptors and thyrotropin-releasing hormone, were measured as endocrine mediators facilitating energy availability. Prenatally predator odour exposed mice of both sexes mobilized more energy during lower energy demand periods of the day and under stressful conditions. Further, prenatally predator odour exposed mice displayed modifications of their hypothalamic-pituitary-thyroid axis through increased circulating thyroxine and thyroid hormone receptor α within the PVN and decreased transthyretin in the liver. Overall, these results suggest that maternal exposure to predator odour is sufficient to increase long-term energy mobilization in adult offspring.

Postnatal separation prevents the development of prenatal stress-induced anxiety in association with changes in oestrogen receptor and oxytocin immunoreactivity in female mandarin vole (Microtus mandarinus) offspring

Oestrogen has both anxiogenic and anxiolytic effects because of variation in opposing action on alpha (ERα) and beta (ERβ) estrogen receptors in the medial preoptic area (mPOA), bed nucleus of the stria terminalis (BNST) and medial amygdala (MeA). Oxytocin (OT) reverses some of the anxiogenic effects of oestrogen in the hypothalamic paraventricular nucleus (PVN) and supraoptic nucleus (SON). Because anxiety disorders are twice as common in women as in men, and oestrogen and OT are more important in females, we examined interactions between prenatal restraint stress (GS) and postnatal early short-term maternal separation (MS) and female mandarin vole behaviour, estrogen receptors and OT. The results show that adult female offspring from GS/noMS mothers showed increased anxiety in open-field and elevated plus-maze tests and had lower serum 17-beta-oestradiol (E₂ ) levels than female offspring from GS/MS, noGS/MS and noGS/noMS mothers. GS/noMS females had more immunoreactive neurons for ERα in several brain regions and less ERβ- and OT-immunoreactive neurons in brain areas compared to GS/MS, noGS/MS and noGS/noMS offspring. Interestingly, noGS/MS and GS/MS offspring were similar to noGS/noMS offspring in that they did not develop anxiety as adults. We propose that MS alters the serum concentration of E₂ and that the ERβ/ERα ratio and OT level in the brain may be responsible for the decrease in anxiety-like behaviour in adult female offspring initially exposed to anxiety-inducing conditions via an adverse foetal environment.

Bidirectional Effects of Mother-Young Contact on the Maternal and Neonatal Brains

Adaptive plasticity occurs intensely during the early postnatal period through processes like proliferation, migration, differentiation, synaptogenesis, myelination and apoptosis. Exposure to particular stimuli during this critical period has long-lasting effects on cognition, stress reactivity and behavior. Maternal care is the main source of social, sensory and chemical stimulation to the young and is, therefore, critical to "fine-tune" the offspring's neural development. Mothers providing a low quantity or quality of stimulation produce offspring that will exhibit reduced cognitive performance, impaired social affiliation and increased agonistic behaviors. Transgenerational transmission of such traits occurs epigenetically, i.e., through mechanisms like DNA methylation and post-translational modification of nucleosomal histones, processes that silence or increase gene expression without affecting the DNA sequence. Reciprocally, providing maternal care profoundly affects the behavior, learning, memory and fine neuroanatomy of the adult female. Such effects are in many cases permanent and sometimes they involve the hormones of pregnancy and lactation. The above evidence supports the idea that the mother-young dyad exerts profound and permanent effects on the brains of both adult and developing organisms, respectively. Effects on the latter can be explained by the neural developmental processes taking place during the early postnatal period. In contrast, little is known about the mechanisms mediating the plasticity of the adult maternal brain. The bidirectional effects that mother and young exert on each other's brains exemplify a remarkable plasticity of this organ for organizing itself and provide an immense source of variability for adaptation and evolution in mammals.

Paternal calorie restriction prior to conception alters anxiety-like behavior of the adult rat progeny

The maternal environment influences a broad range of phenotypic outcomes for offspring, with anxiety-like behavior being particularly susceptible to maternal environmental perturbations. Much less is known regarding paternal environmental influences. To investigate this, adult male rats were exposed to 25% calorie restriction (CR) or glucocorticoid elevation (CORT; 200 μg/ml of corticosterone in drinking water) for ∼ 6 weeks prior to breeding. Elevated plus maze (EPM), open field (OF), predator odor (cat urine), and acoustic startle/pre-pulse inhibition (AS/PPI) were characterised in the adult male offspring. Plasma concentrations of corticotrophin-releasing hormone (CRF), adrenocorticotropin hormone (ACTH), and serum leptin were characterised in both sires and offspring. Maternal care received by litters was additionally observed. Expectedly, CR and CORT treatment attenuated weight gain, whilst only CR induced anxiolytic behavior in the EPM. The adult offspring sired by CR males also demonstrated a reduction in weight gain, food intake and serum leptin levels when compared to controls. Moreover, CR offspring demonstrated an anxiolytic-like profile in the EPM and OF, enhanced habituation to the AS pulse, reduced PPI, but no alteration to predator odor induced defensiveness compared to control. CORT offspring failed to demonstrate any behavioral differences from controls, however, exhibited a trend towards reduced ACTH and leptin concentration. Collectively, the results indicate that a reduction in calories in males prior to conception can affect the behavior of adult offspring. The phenotypic transmission of CR experiences from fathers to the progeny could potentially be mediated epigenetically. The role of glucocorticoid elevation and maternal care are also discussed.

Deconstructing the function of maternal stimulation in offspring development: Insights from the artificial rearing model in rats

This article is part of a Special Issue on "Parental Care". Maternal behavior has an important function in stimulating adequate growth and development of the young. Several approaches have been used in primates and rodents to deconstruct and examine the influence of specific components of maternal stimulation on offspring development. These approaches include observational studies of typical mother-infant interactions and studies of the effects of intermittent or complete deprivation of maternal contact. In this review, we focus on one unique approach using rats that enables the complete control of maternal variables by means of rearing rat pups artificially without contact with the mother or litter, while maintaining stable nutrition, temperature and exposure to stressful stimuli. This artificial rearing model permits the removal and controlled replacement of relevant maternal and litter stimuli and has contributed valuable insights regarding the influence of these stimuli on various developmental outcomes. It also enables the analysis of factors implicated in social isolation itself and their long-term influence. We provide an overview of the effects of artificial rearing on behavior, physiology, and neurobiology, including the influence of replacing maternal tactile stimulation and littermate contact on these outcomes. We then discuss the relevance of these effects in terms of the maternal role in regulating different aspects of offspring development and implications for human research. We emphasize that artificial rearing of rats does not lead to a global insult of nervous system development, making this paradigm useful in investigating specific developmental effects associated with maternal stimulation.

Attachment and parental reflective functioning features in ADHD: enhancing the knowledge on parenting characteristics

Attention-Deficit/Hyperactivity Disorder (ADHD) is a disorder characterized by a chronic, pervasive, and developmentally inappropriate levels of impulsivity and in attention. It is associated with adverse academic and social functions and stress to families. Studies provide evidence that family variables are correlated with this disorder and that parenting styles play an important role in its complexity. However, a thorough investigation of the impact of parental affective and relational aspects on the ADHD child's areas of functioning is still needed. In designing future research on ADHD, we suggest to investigate parenting characteristics to a greater extent by adopting an attachment perspective with a focus on parental reflective functioning as it pertains to the child's ADHD clinical condition.

Parenting begets parenting: A neurobiological perspective on early adversity and the transmission of parenting styles across generations

The developing brains of young children are highly sensitive to input from their social environment. Nurturing social experience during this time promotes the acquisition of social and cognitive skills and emotional competencies. However, many young children are confronted with obstacles to healthy development, including poverty, inappropriate care, and violence, and their enhanced sensitivity to the social environment means that they are highly susceptible to these adverse childhood experiences. One source of social adversity in early life can stem from parenting that is harsh, inconsistent, non-sensitive or hostile. Parenting is considered to be the cornerstone of early socio-emotional development and an adverse parenting style is associated with adjustment problems and a higher risk of developing mood and behavioral disorders. Importantly, there is a growing literature showing that an important predictor of parenting behavior is how parents, especially mothers, were parented themselves. In this review, we examine how adversity in early-life affects mothering behavior in later-life and how these effects may be perpetuated inter-generationally. Relying on studies in humans and animal models, we consider evidence for the intergenerational transmission of mothering styles. We then describe the psychological underpinnings of mothering, including responsiveness to young, executive function and affect, as well as the physiological mediators of mothering behavior, including hormones, brain regions and neurotransmitters, and we consider how development in these relevant domains may be affected by adversity experienced in early life. Finally, we explore how genes and early experience interact to predict mothering behavior, including the involvement of epigenetic mechanisms. Understanding how adverse parenting begets adverse parenting in the next generation is critical for designing interventions aimed at preventing this intergenerational cycle of early adversity.

Using cross-species comparisons and a neurobiological framework to understand early social deprivation effects on behavioral development

Building upon the transactional model of brain development, we explore the impact of early maternal deprivation on neural development and plasticity in three neural systems: hyperactivity/impulsivity, executive function, and hypothalamic-pituitary-adrenal axis functioning across rodent, nonhuman primate, and human studies. Recognizing the complexity of early maternal-infant interactions, we limit our cross-species comparisons to data from rodent models of artificial rearing, nonhuman primate studies of peer rearing, and the relations between these two experimental approaches and human studies of children exposed to the early severe psychosocial deprivation associated with institutional care. In addition to discussing the strengths and limitations of these paradigms, we present the current state of research on the neurobiological impact of early maternal deprivation and the evidence of sensitive periods, noting methodological challenges. Integrating data across preclinical animal models and human studies, we speculate about the underlying biological mechanisms; the differential impact of deprivation due to temporal factors including onset, offset, and duration of the exposure; and the possibility and consequences of reopening of sensitive periods during adolescence.

Propagation of maternal behavior across generations is associated with changes in non-maternal cognitive and behavioral processes

Over a number of years we have studied the phenomenology of maternal behavior from endocrine, neural, experiential, and ontogenetic perspectives. Here, we focus on the effects of early life experiences with and without the mother on subsequent maternal and non-maternal behaviors of the offspring. We have used an artificial rearing procedure, which entails removing rat pups from their mother and raising them in isolation, while controlling and manipulating several aspects of their upbringing. As adults, mother-reared (MR) and artificially-reared (AR) rats are assessed on their own maternal behavior, as well several other behaviors. While both AR and MR rats nurse and successfully wean their young, the AR rats spend less time licking, grooming, and crouching over their young. Hence, being raised in social isolation does not seem to affect primary maternal motivational dynamics. Instead, isolation rearing produces alterations in the ongoing execution of the behavior and its effective organization. Here, we present evidence that changes in maternal behavior, as a result of social isolation from mother and siblings, are due to changes in top-down (e.g., sustained attention, flexibility) and bottom-up process (e.g., increased stimulus-driven behavior). These changes are likely due to alterations in brain dopamine systems, which are sensitive to early life manipulations and are modulators of bottom-up and top-down processes. Finally, we draw parallels between the rat and human maternal behavior. This article is part of a Special Issue entitled: In Honor of Jerry Hogan.

Role of sensory, social, and hormonal signals from the mother on the development of offspring

For mammals, sensory, social, and hormonal experience early in life is essential for the continuity of the infant's development. These experiences come from the mother through maternal care, and have enduring effects on the physiology and behavior of the adult organism. Disturbing the mother-offspring interaction by maternal deprivation (neglect) or exposure to adverse events as chronic stress, maltreatment, or sexual abuse has negative effects on the mental, psychological, physiological, and behavioral health. Indeed, these kinds of negative experiences can be the source of some neuropsychiatric diseases as depression, anxiety, impulsive aggression, and antisocial behavior. The purpose of this chapter is to review the most relevant evidence that supports the participation of cues from the mother and/or littermates during the postnatal preweaning period for the development of nervous system of the offspring. These findings come from the most frequently utilized experimental paradigms used in animal models, such as natural variations in maternal behavior, handling, partial maternal deprivation, and total maternal deprivation and artificial rearing. Through the use of these experimental procedures, it is possible to positively (handling paradigm), or negatively (maternal deprivation paradigms), affect the offspring's development. Finally, this chapter reviews the importance of the hormones that pups ingest through the maternal milk during early lactation on the development of several physiological systems, including the immune, endocrine systems, as well as on the adult behavior of the offspring.

The effects of prenatal stocking densities on the fear responses and sociality of goat (Capra hircus) kids

Prenatal stress (stress experienced by a pregnant mother) and its effects on offspring have been comprehensively studied but relatively little research has been done on how prenatal social stress affects farm animals such as goats. Here, we use the operational description of ‘stress’ as “physical or perceived threats to homeostasis.” The aim of this study was to investigate the prenatal effects of different herd densities on the fear responses and sociality of goat kids. Pregnant Norwegian dairy goats were exposed to high, medium or low prenatal animal density treatments throughout gestation (1.0, 2.0 or 3.0 m² per animal, respectively). One kid per litter was subjected to two behavioral tests at 5 weeks of age. The ‘social test’ was applied to assess the fear responses, sociality and social recognition skills when presented with a familiar and unfamiliar kid and the ‘separation test’ assessed the behavioral coping skills when isolated. The results indicate goat kids from the highest prenatal density of 1.0 m² were more fearful than the kids from the lower prenatal densities (i.e. made more escape attempts (separation test: P < 0.001) and vocalizations (social test: P < 0.001; separation test: P < 0.001). This effect was more pronounced in females than males in the high density (vocalizations; social test: P < 0.001; separation test: P  =  0.001) and females were generally more social than males. However, goat kids did not differentiate between a familiar and an unfamiliar kid at 5 weeks of age and sociality was not affected by the prenatal density treatment. We conclude that high animal densities during pregnancy in goats produce offspring that have a higher level of fear, particularly in females. Behavioral changes in offspring that occur as an effect of prenatal stress are of high importance as many of the females are recruited to the breeding stock of dairy goats.

The effects of prenatal and postnatal environmental interaction: prenatal environmental adaptation hypothesis

Adverse antenatal maternal environments during pregnancy influence fetal development that consequently increases risks of mental health problems including psychiatric disorders in offspring. Therefore, behavioral and brain alterations caused by adverse prenatal environmental conditions are generally considered as deficits. In this article, we propose a novel hypothesis, along with summarizing a body of literatures supporting it, that fetal neurodevelopmental alterations, particularly synaptic network changes occurring in the prefrontal cortex, associated with adverse prenatal environmental conditions may be adaptation to cope with expected severe postnatal environments, and therefore, psychiatric disorders may be able to be understood as adaptive strategies against severe environmental conditions through evolution. It is hoped that the hypothesis presented in this article stimulates and opens a new venue on research toward understanding of biological mechanisms and therapeutic treatments of psychiatric disorders.

Maternal exercise during pregnancy ameliorates the postnatal neuronal impairments induced by prenatal restraint stress in mice

Clinical and preclinical studies have demonstrated that prenatal stress (PS) induces neuronal and behavioral disturbances in the offspring. In the present study, we determined whether maternal voluntary wheel running (VWR) during pregnancy could reverse the putative deleterious effects of PS on the neurodevelopment and behavior of the offspring. Pregnant CF-1 mice were randomly assigned to control, restraint stressed or restraint stressed+VWR groups. Dams of the stressed group were subjected to restraint stress between gestational days 14 and delivery, while control pregnant dams remained undisturbed in their home cages. Dams of the restraint stressed+VWR group were subjected to exercise between gestational days 1 and 17. On postnatal day 23 (P23), male pups were assigned to one of the following experimental groups: mice born from control dams, stressed dams or stressed+VWR dams. Locomotor behavior and pyramidal neuronal morphology were evaluated at P23. Animals were then sacrificed, and Golgi-impregnated pyramidal neurons of the parietal cortex were morphometrically analyzed. Here, we present two major findings: first, PS produced significantly diminished dendritic growth of parietal neurons without altered locomotor behavior of the offspring; and second, maternal VWR significantly offset morphological impairments.

Effectiveness of topical anesthetics on reducing tactile sensitivity in the paws of newborn rats

The aim of this study was to evaluate the effectiveness of three local, topical anesthetics on touch response thresholds of the paws of 1-day-old rats. Touch response thresholds were measured using Semmes Weinstein monofilaments after treatment of the paws with EMLA (2.5% lidocaine and 2.5% prilocaine), alcaine (.5% proparacaine), triocaine (20% benzocaine, 6% lidocaine, and 4% tetracaine), or petroleum jelly (treatment control). Touch thresholds significantly increased after treatment with EMLA 18% of the time, and there was no evidence of a systemic effect. Touch thresholds were not significantly altered after treatment with alcaine, triocaine, or petroleum jelly. Therefore, EMLA appears to be a slightly effective topical anesthetic for reducing tactile sensitivity in newborn rats.

Early postnatal experience and DRD2 genotype affect dopamine receptor expression in the rat ventral striatum

Dopamine systems can be altered by experiences such as early life adversity. The intensity of these effects seems to vary as a function of interactions between genetic and environmental influences. In a series of experiments we have investigated the effects of genetic variants and early life adversity on several biobehavioral outcomes. Here we investigated the presence of single nucleotide polymorphisms (SNPs) in the gene coding for dopamine D2 receptors (DRD2) and the interaction between these variants with early life adversity on the expression of D2 receptors in the striatum. Time-mated pregnant female rats underwent restraint stress (gestational days 10-21) or were left undisturbed. Following parturition rat pups were maternally reared (MR) or artificially reared (AR). Subsequent to adult behavioral testing, rats were genotyped and their brains were processed (autoradiography) for D2 receptor expression. We found three variants in the DRD2 gene and these variants interacted with early adversity to affect D2 receptor expression in the nucleus accumbens. Specifically, artificially reared rats with AG DRD2 variant showed significantly higher D2 expression compared to mother reared rats with the AG DRD2 variant as well as the artificially reared rats with a GG DRD2 variant. These findings show that adult D2 expression is significantly influenced by the interaction of DRD2 SNPs and early developmental factors. These finding may explain why there are significant individual differences in the impact of early life adversity on dopamine-dependent processes and disorder vulnerabilities.

Schore's regulation theory: maternal-infant interaction in the NICU as a mechanism for reducing the effects of allostatic load on neurodevelopment in premature infants

Premature infants confront numerous physiologic and environmental stressors in the neonatal intensive care unit (NICU) that have the potential to permanently alter their neurodevelopment. Schore's regulation theory postulates that positive maternal-infant interactions can shape the infant's developmental outcomes through inducing mechanistic changes in brain structure and function. The purposes of this article are to explain the regulation of infant neurobiological processes during interactions between mothers and healthy infants in the context of Schore's theory, to identify threats to these processes for premature infants, and to propose principles of clinical practice and areas of research necessary to establish a supportive environment and prevent or reduce maladaptive consequences for these vulnerable infants. A premature birth results in the disruption of neurodevelopment at a critical time. Chronic exposure to stressors related to the NICU environment overwhelms immature physiologic and stress systems, resulting in significant allostatic load, as measured by long-term neurodevelopmental impairments in the premature infant. Positive maternal-infant interactions during NICU hospitalization and beyond have the potential to reduce neurologic deficits and maximize positive neurodevelopmental outcomes in premature infants. The quality of the maternal-infant interaction is affected not only by the infant's developing neurobiology but also by the mother's responses to the stressors surrounding a premature birth and mothering an infant in the NICU environment. Nurses can empower mothers to overcome these stressors, promote sensitive interactions with their infants, and facilitate neurodevelopment. Research is critically needed to develop and test nursing interventions directed at assisting mothers in supporting optimal neurodevelopment for their infants.

Behavioral animal models of antipsychotic drug actions

Basic research in animals represents a fruitful approach to study the neurobiological basis of brain and behavioral disturbances relevant to neuropsychiatric disease and to establish and evaluate novel pharmacological therapies for their treatment. In the context of schizophrenia, there are models employing specific experimental manipulations developed according to specific pathophysiological or etiological hypotheses. The use of selective lesions in adult animals and the acute administration of psychotomimetic agents are indispensable tools in the elucidation of the contribution of specific brain regions or neurotransmitters to the genesis of a specific symptom or collection of symptoms and enjoy some degrees of predictive validity. However, they may be inaccurate, if not inadequate, in capturing the etiological mechanisms or ontology of the disease needed for a complete understanding of the disease and may be limited in the discovery of novel compounds for the treatment of negative and cognitive symptoms of schizophrenia. Under the prevailing consensus of schizophrenia as a disease of neurodevelopmental origin, we have seen the establishment of neurodevelopmental animal models which aim to identify the etiological processes whereby the brain, following specific triggering events, develops into a "schizophrenia-like brain" over time. Many neurodevelopmental models such as the neonatal ventral hippocampus (vHPC) lesion, methylazoxymethanol (MAM), and prenatal immune activation models can mimic a broad spectrum of behavioral, cognitive, and pharmacological abnormalities directly implicated in schizophrenic disease. These models allow pharmacological screens against multiple and coexisting schizophrenia-related dysfunctions while incorporating the disease-relevant concept of abnormal brain development. The multiplicity of existing models is testimonial to the multifactorial nature of schizophrenia, and there are ample opportunities for their integration. Indeed, one ultimate goal must be to incorporate the successes of distinct models into one unitary account of the complex disorder of schizophrenia and to use such unitary approaches in the further development and evaluation of novel antipsychotic treatment strategies.

Effects of chronic maternal stress on hypothalamo-pituitary-adrenal (HPA) function and behavior: no reversal by environmental enrichment

Maternal stress during pregnancy is linked to increased risk for impaired behavioral and emotional development and affective disorders in children. In animal models, acute periods of prenatal or postnatal stress have profound effects on HPA function and behavior in adult offspring. However, few animal studies have determined the impact of chronic exposure to stress throughout the perinatal period. The objective of this study was to determine the effects of chronic maternal stress (CMS) during the 2nd half of pregnancy and nursing on HPA function, locomotor behavior and prepulse inhibition in adult guinea pig offspring, as well as to determine whether environmental enrichment (EE) could reverse the effects of CMS. Guinea pigs were exposed to a random combination of variable stressors every other day over the 2nd half of gestation and from postnatal day (pnd) 1 until weaning (pnd25). Following weaning, offspring were housed in either standard conditions or EE. In both adult male and female offspring, there was no effect of CMS on basal or activated HPA function. CMS significantly increased locomotor activity in an open-field in male offspring, though no effect was observed in females. In female offspring, CMS disrupted PPI; however there was no effect on male PPI. EE had a number of effects on HPA function and behavior but in most cases these were independent of the influence of CMS. EE significantly elevated basal cortisol levels in male offspring at pnd70, whereas in female offspring, EE interacted with CMS to elevate basal cortisol levels from pnd35 to pnd70. In female offspring, EE decreased locomotor activity. In males, EE enhanced PPI; however in female offspring EE disrupted PPI. In conclusion, while CMS had minimal effects on HPA function, there were significant long-term sex-specific effects on behavior. EE did not reverse the effects observed as a result of CMS, but rather modified HPA function and behavior independently of CMS. Further, there was significant interaction of CMS with EE that resulted in elevation of basal HPA function in female offspring. These data, combined with previous studies from our laboratory, suggest that acute phases of maternal stress in late pregnancy may have greater long-term effects on HPA function and related behaviors than prolonged chronic maternal stress.

Effects of motherless rearing on basal and stress-induced corticosterone secretion in rat pups

Rearing of rat pups without a mother, artificial rearing (AR), produces substantial changes in the pups' behavior in later life. These changes are similar to those produced by the stress of repeated mother-pup separations. The predominant interpretation is that the long-term effects of disruptions to the mother-pup relationship are mediated by exposure to elevated levels of corticosterone which affect the development of neurobiological systems underlying cognition and behavior. Indeed, repeated separation of pups from the mother sensitizes the pups' corticosterone response to stress. This study examined basal and stress-induced corticosterone release in AR pups. Corticosterone levels were increased immediately following implantation of feeding cannulae. One day after the start of AR, circulating concentrations of corticosterone were not increased unless AR pups were challenged with an additional stressor (injection). Corticosterone levels were lowest when cannulation and AR started on postnatal day (PND) 5 compared with earlier PNDs. On PND 12, there was no evidence of increased corticosterone levels in AR pups at baseline or in response to stress, indicating that AR did not result in persistent sensitization of corticosterone release. The long-term effects of motherless rearing on rat behavior are mediated by mechanisms that are independent of sustained early corticosterone exposure.

Accumbal dopamine function in postpartum rats that were raised without their mothers

Postpartum rats that had been previously raised in an artificial rearing (AR) apparatus, without their mothers or siblings during the preweaning period, show altered maternal responses towards their own offspring in adulthood. In mother-reared (MR) rats, nucleus accumbens (NAC) dopamine (DA) responses to pups evoke a robust sustained rise during the postpartum period and following treatment with estrogen/progesterone parturient-like hormones (Afonso et al., 2009). These MR females had siblings that received AR rearing with varying amounts of preweaning tactile stimulation (ARmin; ARmax). The present study examined NACshell DA responses to pup and food stimuli in these AR rats, and statistically compared them to their MR siblings. Microdialysis samples were collected from adult (90 days postnatal) AR females in different parity states (cycling vs. postpartum, Exp. 1), or after ovariectomy with different hormone treatments (sham vs. hormone, Exp. 2. After basal sample collection, pup and then food stimuli were individually presented to the females in the dialysis chamber. As with their MR siblings, basal DA concentrations were lower and pup-evoked DA responses greater in hormonally-primed AR females than in non-primed AR controls. Compared to their postpartum MR sisters (Exp. 1), AR rats had increased basal DA levels, reduced pup related DA elevations, and disrupted maternal behavior. The postpartum AR impairment in pup-evoked DA was reversed by additional pre-weaning tactile stimulation. Exogenous hormones (Exp. 2) eliminated AR impairments on pup-evoked DA responses. Although MR and AR siblings had comparable DA responses to food stimuli, upon reanalyzing MR data it was found that only postpartum dams had DA responses to pups greater than to food. These data suggest that that the hormonally induced suppression of basal DA levels may reflect saliency of pups which was greater in MR than in AR dams. Preweaning tactile stimulation could partially reverse these effects only in naturally cycling or parturient animals.

Infantile experience and play motivation

Fully-fledged affective systems in mature animals are in part the result of the impact of infantile experience on brain development. The present experimental series examines whether tactile stimulation in infancy (early handling) influences rough-and-tumble play (R&T) throughout the juvenile period, using a testing regime of 17 days divided into five parts where handled (H) and nonhandled (NH) Wistar rats are assessed daily. In Parts 1 and 2 (age range at the start: 30-33 days) the objective is to study the amount of R&T that the rats are capable of exhibiting under varying lengths of social deprivation. In Part 3 (37-40 days) the objective is to determine whether familiarity with the experimental situation has independent or interactive effects with early handling. In Part 4 (40-43 days) the objective is to obtain evidence of the suppressing effects of an unexpected contextual change. In Part 5 (56-59 days) the objective is to study whether the effects of early handling can still be present at an age when R&T has practically vanished in NH rats. Results show that early handling invigorates R&T affecting pins (i.e., the most rewarding component) at the expense of dorsal contacts by enhancing play motivation in a specific manner, and that it is able to dilate the inverted-U developmental curve of this behavior, thereby providing strong evidence for a direct effect on the neuropsychological systems for play motivation.

Annual Research Review: All mothers are not created equal: neural and psychobiological perspectives on mothering and the importance of individual differences

Quality of mothering relies on the integrity of multiple physiological and behavioral systems and on two maternal factors, one proximal and one distal, that have a great impact on how a mother mothers: postpartum depression and early experiences. To mother appropriately requires the action of systems that regulate sensation, perception, affect, reward, executive function, motor output and learning. When a mother is at risk to engage in less than optimal mothering, such as when she is depressed or has experienced adversity in childhood, the function of many or all of maternal and related systems may be affected. In this paper, we will review what is currently known about the biological basis of mothering, with attention to literature on hormones but with a particular focus on recent advances in the fields of functional neuroimaging. Instead of discussing strictly 'maternal' brain imaging studies, we instead use a systems approach to survey important findings relevant to brain systems integral to and/or strongly related to the mothering experience: (a) social behavior; (b) reward and affect; (c) executive function; and (d) maternal behavior. We find that there are many commonalities in terms of the brain regions identified across these systems and, as we would expect, all are sensitive to the influence of, or function differently in the context of, depression and adverse early experience. It is likely that the similarity and cross-talk between maternal, affect and stress systems, observed behaviorally, hormonally and in the context of brain function, allows for mood disturbance and early adverse experiences to have a significant impact on the quality of mothering and the motivation to mother.

Prenatal stress: role in psychotic and depressive diseases

RATIONALE

The birth of neurons, their migration to appropriate positions in the brain, and their establishment of the proper synaptic contacts happen predominately during the prenatal period. Environmental stressors during gestation can exert a major impact on brain development and thereby contribute to the pathogenesis of neuropsychiatric illnesses, such as depression and psychotic disorders including schizophrenia.

OBJECTIVE

The objectives here are to present recent preclinical studies of the impact of prenatal exposure to gestational stressors on the developing fetal brain and discuss their relevance to the neurobiological basis of mental illness. The focus is on maternal immune activation, psychological stresses, and malnutrition, due to the abundant clinical literature supporting their role in the etiology of neuropsychiatric illnesses.

RESULTS

Prenatal maternal immune activation, viral infection, unpredictable psychological stress, and malnutrition all appear to foster the development of behavioral abnormalities in exposed offspring that may be relevant to the symptom domains of schizophrenia and psychosis, including sensorimotor gating, information processing, cognition, social function, and subcortical hyperdopaminergia. Depression-related phenotypes, such as learned helplessness or anxiety, are also observed in some model systems. These changes appear to be mediated by the presence of proinflammatory cytokines and/or corticosteroids in the fetal compartment that alter the development the neuroanatomical substrates involved in these behaviors.

CONCLUSION

Prenatal exposure to environmental stressors alters the trajectory of brain development and can be used to generate animal preparations that may be informative in understanding the pathophysiological processes involved in several human neuropsychiatric disorders.

Inadequate early social experience increases the incentive salience of reward-related cues in adulthood

The mechanisms by which childhood abuse and/or neglect become risk factors for the development of drug addiction, problem gambling, and other disorders of behavioral inhibition are unknown. The loss of behavioral inhibition is often triggered by reward-related cues that acquire incentive salience. This study examined whether inadequate early-life social experience in rats affects the incentive salience of reward-related cues. Rats were deprived of early-life social experience with the mother and litter through artificial-rearing (AR). A group of AR rats (AR+STM) received additional tactile stimulation that mimicked maternal licking, a critical component of rat maternal care. Control rats were maternally reared (MR). The incentive salience attributed to a food cue was measured in adult rats using a conditioned approach task, where a conditional stimulus (CS; lever) was paired with food delivery, and in a conditional reinforcement task. The dependent measures were approach towards the CS (sign-tracking) versus approach towards the place of food delivery (goal-tracking) and instrumental responding for the CS. AR rats made significantly more sign-tracking responses than MR rats. AR rats also made more instrumental responses when reinforced with the CS. AR+STM rats' responses were intermediate to MR and AR rats. Thus, inadequate early-life social experience enhanced the incentive salience of a reward-related cue in adulthood. Replacement of maternal licking partially reversed this effect. These results highlight a potential link between early-life social adversity and susceptibility to disorders of behavioral inhibition.

The environment and susceptibility to schizophrenia

In the present article the putative role of environmental factors in schizophrenia is reviewed and synthesized. Accumulating evidence from recent studies suggests that environmental exposures may play a more significant role in the etiopathogenesis of this disorder than previously thought. This expanding knowledge base is largely a consequence of refinements in the methodology of epidemiologic studies, including birth cohort investigations, and in preclinical research that has been inspired by the evolving literature on animal models of environmental exposures. This paper is divided into four sections. In the first, the descriptive epidemiology of schizophrenia is reviewed. This includes general studies on incidence, prevalence, and differences in these measures by urban-rural, neighborhood, migrant, and season of birth status, as well as time trends. In the second section, we discuss the contribution of environmental risk factors acting during fetal and perinatal life; these include infections [e.g. rubella, influenza, Toxoplasma gondii (T. gondii), herpes simplex virus type 2 (HSV-2)], nutritional deficiencies (e.g., famine, folic acid, iron, vitamin D), paternal age, fetal/neonatal hypoxic and other obstetric insults and complications, maternal stress and other exposures [e.g. lead, rhesus (Rh) incompatibility, maternal stress]. Other putative neurodevelopmental determinants, including cannabis, socioeconomic status, trauma, and infections during childhood and adolescence are also covered. In the third section, these findings are synthesized and their implications for prevention and uncovering biological mechanisms, including oxidative stress, apoptosis, and inflammation, are discussed. Animal models, including maternal immune activation, have yielded evidence suggesting that these exposures cause brain and behavioral phenotypes that are analogous to findings observed in patients with schizophrenia. In the final section, future studies including new, larger, and more rigorous epidemiologic investigations, and research on translational and clinical neuroscience, gene-environment interactions, epigenetics, developmental trajectories and windows of vulnerability, are elaborated upon. These studies are aimed at confirming observed risk factors, identifying new environmental exposures, elucidating developmental mechanisms, and shedding further light on genes and exposures that may not be identified in the absence of these integrated approaches. The study of environmental factors in schizophrenia may have important implications for the identification of causes and prevention of this disorder, and offers the potential to complement, and refine, existing efforts on explanatory neurodevelopmental models.

Influence of diurnal phase on startle response in adult rats exposed to dexamethasone in utero

Depression and pathological anxiety disorders are among the most prevalent neurological diseases in the world and can be precipitated and exacerbated by stress. Prenatal stress alters both behavioral and endocrine responses to stressful stimuli in later life. We have previously observed increased basal acoustic startle response (ASR) in Wistar rats exposed to stress or dexamethasone (DEX) in utero when tested during the light phase of the circadian rhythm, and decreased prepulse inhibition (PPI) in similar animals tested during the dark phase of the cycle. We speculated that this observation of increased basal startle might be influenced by diurnal phase. In the present study, adult female Sprague Dawley rats, stressed prenatally with DEX (200 μg/kg, gestational days 14-21) and postnatally by blood sampling under restraint, were tested for the ASR during both circadian phases (light and dark). Basal startle was increased in animals tested both during the light and the dark phases of the cycle. We hereby replicated our earlier findings in a new strain and laboratory, thus strengthening the validity of our model regarding prenatal stress effects on ASR in female offspring. Our results indicate that observation of increased basal ASR is not solely dependent on diurnal phase. We found no difference in hippocampal glucocorticoid and mineral corticoid receptor expression between groups.

Testosterone is involved in mediating the effects of prenatal stress in male guinea pig offspring

A link exists between stress during pregnancy and altered hypothalamic–pituitary–adrenal (HPA) activity and behaviour in children. In the guinea pig, male offspring born to mothers that were exposed to stress during pregnancy demonstrated increased anxiety, basal cortisol levels and decreased testosterone concentrations. Testosterone is known to inhibit HPA function and anxiety behaviours. Therefore, we hypothesized that restoring plasma testosterone would ameliorate the differences observed in HPA function and behaviour. Pregnant guinea pigs were exposed to a stressor during the period of rapid fetal brain growth (prenatal stress, PS) or left undisturbed (control, C). Behaviour in an open-field and prepulse inhibition (PPI) of the acoustic startle reflex (ASR) was assessed in juvenile offspring. In adulthood, male offspring were divided into four groups: Control + sham gonadectomy (GDX), control + GDX + testosterone replacement, PS + sham GDX and PS + GDX + testosterone. Male offspring were retested in the open-field and PPI. Basal HPA activity was also assessed. As juveniles, PS males exhibited significantly lower ASR (P < 0.05) and elevated PPI. In adulthood, PS male offspring exhibited significantly decreased PPI (P < 0.02) and this was reversed by administration of testosterone. We also found that adult PS offspring exhibited significantly less activity in the open-field (P < 0.05) and administration of testosterone increased ambulatory activity in PS animals. Basal plasma adrenocorticotrophin hormone (ACTH) levels were significantly greater in PS animals and there was a trend towards reversal by administration of testosterone in PS males. In conclusion, prenatal stress results in male guinea pig offspring that exhibit age-dependent differences in ambulatory activity, sensorimotor gating and HPA activity. In adulthood, the behavioural changes are reversed by replacement of plasma testosterone.

Motherless rats show deficits in maternal behavior towards fostered pups

Complete maternal deprivation in rats, through artificial rearing (AR), produces deficits in subsequent maternal behavior of the offspring. These deficits are partially reversed when isolated pups are provided with additional tactile stimulation designed to simulate maternal licking (e.g., Gonzalez et al. [2001] Developmental Psychobiology, 38, 11-32). These findings highlight the importance of the early maternal environment in subsequent development. However, given the possibility that prenatal environments may differ between AR and maternally reared (MR) offspring, the deficits in the behavior of AR mothers may be driven by the characteristics of their pups derived from the effects of an altered prenatal environment. Hence differences in the neonatal pups of AR mothers may produce the alterations in the AR maternal behavior. To rule out this possibility, we employed a fostering paradigm where AR and MR mothers received cross-fostered mother-reared pups. AR mothers showed the same level of deficits in maternal behavior towards MR foster pups as they do with their own pups and these deficits were partially reversed with additional tactile stimulation. Hence, maternal behavior deficits reported in mothers who had been reared in isolation are due primarily to the direct effects of the earlier experience on mechanisms regulating their maternal behavior and not to the effects on their offspring.

Prenatal stress alters spine density and dendritic length of nucleus accumbens and hippocampus neurons in rat offspring

Prenatal stress alters neuronal morphology of mesocorticolimbic structures such as frontal cortex and hippocampus in the adult offspring. We investigated here the effects of prenatal stress on the spine density and the dendrite morphology of hippocampal pyramidal neurons and medium spiny cells from nucleus accumbens in prepubertal and adult male offsprings. Sprague-Dawley pregnant dams were stressed by restraining movement daily for 2 hours from gestational day 11 until delivery. Control mothers remained free in their home cage without water and food during the stressful event. Male offsprings from immobilized and control rats were left to grow until postnatal day (PD) 35 for the prepubertal group, and until PD 65 for the adult group. Spontaneous locomotor activity was assessed and then brains were removed to study the dendritic morphology by the Golgi-Cox stain method followed by Sholl analysis. Prenatally stressed animals demonstrated increased locomotion and alterations in spine density in the hippocampus and nucleus accumbens at both ages. However, prepubertal males showed an increase in spine density in the CA1 hippocampus with a decrease in CA3 hippocampus, whereas the adult group showed a decrease in the spine density in both of the regions studied. These results suggest that prenatal stress carried out during the middle of pregnancy affect the spine density and basal dendrites of pyramidal neurons of hippocampus, as well as the dendritic morphology of nucleus accumbens which may reflect important changes in the mesocorticolimbic dopaminergic transmission and behaviors associated with the development of psychiatric diseases such as schizophrenia.

Artificial rearing of rat pups reveals the beneficial effects of mother care on neonatal inflammation and adult sensitivity to pain

Repeated pain during brain development can have long-term consequences in both humans and animals. We previously showed that maternal care provided to pups experiencing pain reduced adult pain sensitivity. This study tested whether sensory stimulation was responsible for this effect. Rat pups were either mother-reared controls (MR-CON) or artificially reared (AR) with minimal (AR-MIN) or maximal (AR-MAX) stimulation provided daily. In each rearing condition, pups were either uninjected or injected from postnatal day (PND) 4 to 14 with saline (0.9%) or formalin (0.2-0.4%). Pain behavior and paw inflammation were scored. Thermal sensitivity and responses to formalin were tested in adulthood (PND 70). AR neonates, irrespective of sensory stimulation received, exhibited a pain response (p < 0.001), even with a mild formalin dose. Maternal rearing reduced inflammation during the second week of life compared with AR pups (p < 0.05). Early pain exposure did not modify adult pain sensitivity. However, rearing altered adult pain sensitivity such that uninjected MR-CON rats had lower pain sensitivities than uninjected AR rats (p < 0.05). This suggests that the beneficial effects of maternal rearing can be obliterated if additional stimulation/stress occurs during the early neonatal period. In addition, this suggests that optimal level of maternal stimulation exists that determines adult pain sensitivity.

Realistic expectations of prepulse inhibition in translational models for schizophrenia research

INTRODUCTION

Under specific conditions, a weak lead stimulus, or "prepulse", can inhibit the startling effects of a subsequent intense abrupt stimulus. This startle-inhibiting effect of the prepulse, termed "prepulse inhibition" (PPI), is widely used in translational models to understand the biology of brainbased inhibitory mechanisms and their deficiency in neuropsychiatric disorders. In 1981, four published reports with "prepulse inhibition" as an index term were listed on Medline; over the past 5 years, new published Medline reports with "prepulse inhibition" as an index term have appeared at a rate exceeding once every 2.7 days (n=678). Most of these reports focus on the use of PPI in translational models of impaired sensorimotor gating in schizophrenia. This rapid expansion and broad application of PPI as a tool for understanding schizophrenia has, at times, outpaced critical thinking and falsifiable hypotheses about the relative strengths vs. limitations of this measure.

OBJECTIVES

This review enumerates the realistic expectations for PPI in translational models for schizophrenia research, and provides cautionary notes for the future applications of this important research tool.

CONCLUSION

In humans, PPI is not "diagnostic"; levels of PPI do not predict clinical course, specific symptoms, or individual medication responses. In preclinical studies, PPI is valuable for evaluating models or model organisms relevant to schizophrenia, "mapping" neural substrates of deficient PPI in schizophrenia, and advancing the discovery and development of novel therapeutics. Across species, PPI is a reliable, robust quantitative phenotype that is useful for probing the neurobiology and genetics of gating deficits in schizophrenia.

Prenatal restraint stress and motherless rearing disrupts expression of plasticity markers and stress-induced corticosterone release in adult female Sprague–Dawley rats

This study investigated the effects of prenatal stress and complete maternal deprivation, using the artificial rearing (AR) paradigm, on the expression of neural plasticity markers and hypothalamic-pituitary-adrenal (HPA) axis responsivity to stress. Rats were exposed to stress during gestation (day 10-21) and postnatally were either artificially reared (AR) or mother reared (MR). AR involves complete separation of the pup from both the dam and the litter throughout the pre-weaning period. In adulthood, we measured levels of corticosterone (CORT) in response to restraint stress. Also, we examined the expression of synaptophysin (SYN) and brain-derived neurotrophic factor (BDNF) in the medial prefrontal cortex (MPFC) and the nucleus accumbens (Nacc), areas of the brain that mediate behavioral activation and attention, among other behaviors. Earlier work on the same rats indicated that these behavioral endpoints, such as locomotor activity and sensorimotor gating, are affected by our prenatal and postnatal manipulations. Prenatal stress decreased CORT at 20 and 90 min post-stressor in MR, but not in AR, animals. Also, in comparison to MR groups, AR decreased SYN and BDNF expression in the MPFC and Nacc. Additional somatosensory 'licking-like' stroking stimulation partially reversed the effects of AR. Prenatal stress did not have a robust main effect but affected the impact of the postnatal rearing condition on SYN expression and stress-induced CORT. These results suggest that both prenatal and postnatal adversities have an influence on HPA axis responsivity and alter the expression of plasticity related neuronal proteins.

Maternal isolation alters the expression of neural proteins during development: 'Stroking' stimulation reverses these effects

Rat pups reared apart from their siblings, mother, and nest environment in the 'pup-in-a-cup' regime show many alterations in behavior reminiscent of the Institutional Inattention/Overactivity Syndrome that characterizes children whose first few months are spent in institutions. In this report, we compare mother-reared (MR) and artificially reared (AR) male rats in concentrations and distributions of brain proteins that are involved in normal brain development. When assessed during the juvenile period and in adulthood, AR animals showed elevations in Neu-N (a neuronal marker) and in S-100 (an astrocyte marker) but reductions in synaptophysin (synapse protein), N-CAM (cell-adhesion molecule), GAP-43 (axon elongation protein), and BDNF (brain derived neurotrophic factor) in comparison to MR controls in many brain sites involved in attention, impulsivity, activity, and social behavior. Daily 'licking-like' stimulation provided to AR animals (AR-MAX) throughout early development that reverses many of the behavioral deficits, also reverses many of the isolation effects on brain proteins. Study 2 showed that elevations in the number of neurons in combination with decreases in functionality are associated with a reduction in neuronal pruning and apoptosis during the very early post-partum period in AR animals and their reversal through daily 'licking-like' stimulation.

Gender differences in the effects of prenatal stress on brain development and behaviour

An increased incidence of anxiety, depression and attention deficits in children has been linked to psychological stress during pregnancy. Subjection of a pregnant rat to stress at a time when the foetal limbic and hypothalamic pituitary adrenal (HPA) axes develop results in anxiogenic and depressive behaviour and learning and attention deficits in the offspring, which depend on its gender, intensity and timing of the maternal stress and behaviour being tested. Maternal stress increases corticosterone levels in the foetal brain, decreases foetal testosterone and brain aromatase activity in males, and alters brain catecholamine activity to that in females. Learning deficits, reductions in hippocampal neurogenesis, LTP and dendritic spine density in the prefrontal cortex are more readily seen in prenatally-stressed males, while anxiety, depression and increased response of the HPA axis to stress are more prevalent in females. Genders may differ in the sensitivity of developing brain areas to stress hormones.

Early life tactile stimulation changes adult rat responsiveness to amphetamine

Previously, we have found that total maternal deprivation of rat pups, achieved through artificial rearing, leads to a number of behavioral and neurophysiological changes, suggesting a change in the dopamine system. The purpose of this study was to further investigate possible changes in the functioning of dopamine systems, associated with artificial rearing, by examining the locomotor stimulant effects of the dopamine releaser amphetamine and the dopamine reuptake inhibitor methylphenidate. Rats were mother-reared or artificially reared. Some of those artificially reared rats were provided with either a maximum level (artificially reared maximal stimulation) or a minimal level of maternal licking-like tactile stimulation (artificially reared minimal stimulation). In adulthood, rats' locomotion was measured after an injection of d-amphetamine (0, 0.25, 0.5 and 1.0 mg/kg) or methylphenidate (0, 2, 5 and 10 mg/kg). Locomotor activity in response to a novel environment was enhanced in artificially reared rats, although this effect habituated over three daily 1-h sessions. Both amphetamine and methylphenidate dose dependently increased locomotor activity. The effect of amphetamine, but not methylphenidate was greatly enhanced in artificially reared minimally stimulated rats. The enhancement of the effect of amphetamine by artificial rearing was not apparent in artificially reared maximal stimulation rats.

A classification of sociomedical health indicators: perspectives for health administrators and health planners

The conceptualization and operationalization of measures of health status are considered. Health indicators are conceived as a subset of social indicators, and therefore, as any social indicator, they are viewed as derivative from social issues. The interrelationships of different frames of reference for defining and measuring health that have accompained three distinct health problem patterns in the United States are viewed from a developmental perspective. Mortality and morbidity rates, the traditional health indicators, by themselves no longer serve to assess health status in developed nations. Their deficiencies as indicators serve as background for a classification schema for sociomedical health status indicators that relates health definition frames of reference, measures of health status, and health problems. The role of a group of health indicators-sociomedical heath indicators-in the current formulation of health status measures is assessed.