Alterations in behavioral and striatal dopamine asymmetries induced by prenatal stress

Behavioral lateralization of mice varying in serotonin transporter genotype

In humans, non-right-handedness is associated with a higher incidence of psychiatric disorders. Since serotonin seems to be involved in both, the development of psychiatric disorders and lateralization, the present study focuses on the effect of the serotonin transporter (5-HTT) gene on behavioral lateralization. For this, we used the 5-HTT knockout mouse model, a well-established animal model for the study of human depression and anxiety disorders. For female mice from all three 5-HTT genotypes (wild type, heterozygous, and homozygous knockout), we repeatedly observed the direction and strength of lateralization of the following four behaviors: grid climbing (GC), food-reaching in an artificial test situation (FRT), self-grooming (SG), and barrier crossing (BC), with the FRT being the standard test for assessing behavioral lateralization in mice. We found no association between behavioral lateralization and 5-HTT genotype. However, in accordance with previous findings, the strength and temporal consistency of lateralization differed between the four behaviors observed. In conclusion, since the 5-HTT genotype did not affect behavioral lateralization in mice, more research on other factors connected with behavioral lateralization and the development of symptoms of psychiatric disorders, such as environmental influences, is needed.

Extra food provisioning does not affect behavioural lateralization in nestling lesser kestrels

Costs and benefits of brain lateralization may depend on environmental conditions. Growing evidence indicates that the development of brain functional asymmetries is adaptively shaped by the environmental conditions experienced during early life. Food availability early in life could act as a proxy of the environmental conditions encountered during adulthood, but its potential modulatory effect on lateralization has received little attention. We increased food supply from egg laying to early nestling rearing in a wild population of lesser kestrels Falco naumanni, a sexually dimorphic raptor, and quantified the lateralization of preening behaviour (head turning direction). As more lateralized individuals may perform better in highly competitive contexts, we expected that extra food provisioning, by reducing the level of intra-brood competition for food, would reduce the strength of lateralization. We found that extra food provisioning improved nestling growth, but it did not significantly affect the strength or direction of nestling lateralization. In addition, maternal body condition did not explain variation in nestling lateralization. Independently of extra food provisioning, the direction of lateralization differed between the sexes, with female nestlings turning more often towards their right. Our findings indicate that early food availability does not modulate behavioural lateralization in a motor task, suggesting limited phenotypic plasticity in this trait.

Maternal immune activation leads to atypical turning asymmetry and reduced DRD2 mRNA expression in a rat model of schizophrenia

Atypical asymmetries have been reported in individuals diagnosed with schizophrenia, linking higher symptom severity to weaker lateralization. Furthermore, both lateralization and schizophrenia are influenced by the dopaminergic system. However, whether a direct link between the etiology of schizophrenia and atypical asymmetries exists is yet to be investigated. In this study, we examined whether maternal immune activation (MIA), a developmental animal model for schizophrenia and known to alter the dopaminergic system, induces atypical lateralization in adolescent and adult offspring. As the dopaminergic system is a key player in both, we analyzed neuronal dopamine D2 receptor (DRD2) mRNA expression. MIA was induced by injecting pregnant rats with 10 mg/kg polyinosinic:polycytidylic (PolyI:C) at gestational day 15. Controls were injected with 0.9 % NaCl. Offspring were tested at adolescence or early adulthood for asymmetry of turning behavior in the open field test. The total number of left and right turns per animal was assessed using DeepLabCut. Strength and preferred side of asymmetry were analyzed by calculating lateralization quotients. Additionally, DRD2 mRNA expression in the prefrontal cortex of offspring at both ages was analyzed using real-time PCR. MIA was associated with a rightward turning behavior in adolescents. In adults, MIA was associated with an absence of turning bias, indicating reduced asymmetry after MIA. The analysis of DRD2 mRNA expression revealed significantly lower mRNA levels after MIA compared to controls in adolescent, but not adult animals. Our results reinforce the association between atypical asymmetries, reduced DRD2 mRNA expression, and schizophrenia. However, more preclinical research is needed.

Zebrafish (Danio rerio) behavioral laterality predicts increased short-term avoidance memory but not stress-reactivity responses

Once considered a uniquely human attribute, behavioral laterality has proven to be ubiquitous among non-human animals, and is associated with several neurophenotypes in rodents and fishes. Zebrafish (Danio rerio) is a versatile vertebrate model system widely used in translational neuropsychiatric research owing to their highly conserved genetic homology, well-characterized physiological responses, and extensive behavioral repertoire. Although spontaneous left- and right-biased responses, and associated behavioral domains (e.g., stress reactivity, aggression, and learning), have previously been observed in other teleost species, no information relating to whether spontaneous motor left–right-bias responses of zebrafish predicts other behavioral domains has been described. Thus, we aimed to investigate the existence and incidence of natural left–right bias in adult zebrafish, exploiting an unconditioned continuous free movement pattern (FMP) Y-maze task, and to explore the relationship of biasedness on performance within different behavioral domains. This included learning about threat cues in a Pavlovian fear conditioning test, and locomotion and anxiety-related behavior in the novel tank diving test. Although laterality did not change locomotion or anxiety-related behaviors, we found that biased animals displayed a different search strategy in the Y-maze, making them easily discernable from their unbiased counterparts, and increased learning associated to fear cues. In conclusion, we showed, for the first time, that zebrafish exhibit a natural manifestation of motor behavioral lateralization which can influence aversive learning responses.

Estradiol does not affect spasms in the betamethasone-NMDA rat model of infantile spasms

OBJECTIVE

This study attempted to validate the effects of neonatal estradiol in ameliorating the spasms in the prenatally betamethasone-primed N-methyl-d-aspartate (NMDA) model of infantile spasms in rats as shown previously in a mouse Arx gene knock-in expansion model of infantile spasms.

METHODS

Neonatal rats prenatally exposed to betamethasone (on day 15 of pregnancy) were treated with subcutaneous 40 ng/g estradiol benzoate (EB) between postnatal days (P)3-P10 or P0-P5. A synthetic estrogen analogue, diethylstilbestrol, was used between P0 and P5 (2 μg per rat, s.c.). On P12, P13, and P15, the rats were subjected to NMDA-triggered spasms, and latency to onset and number of spasms were evaluated. Rats with EB on P3-P10 were tested after spasms in the open field, novel object recognition, and elevated plus maze to determine effects of treatment on behavior. Additional rats with P3-P10 or P0-P5 EB were investigated for γ-aminobutyric acid (GABA)ergic neurons (glutamate decarboxylase [GAD]67 expression) in the neocortex. As a positive control, a group of rats received either subcutaneous adrenocorticotropic hormone (ACTH) (2 × 0.3 mg/kg on P12 and 3 × 0.3 mg/kg on P13 and P14) or vehicle after the first episode of spasms on P12.

RESULTS

Neither EB treatment nor diethylstilbestrol consistently affected expression of spasms in this model, although we found a significant increase in GAD67-immunopositive cells in the neocortex after P3-P10 and P0-P5 EB treatment, consistent with a study in mice. Behavioral tests showed increase in lateralization in male rats treated with P3-P10 EB, a behavioral trait usually associated with female sex. Diethylstilbestrol treatment in male rats resulted in arrested pubertal descent of testes. ACTH had robust effects in suppressing spasms.

SIGNIFICANCE

Treatment of infantile spasms (IS) using neonatal EB may be justified in those cases of IS that present with detectable deficits in GABAergic neurons. In other types of IS, the efficacy of neonatal EB and its analogues is not supported.

Long-term consequences of prenatal stress and neurotoxicants exposure on neurodevelopment

There is a large consensus that the prenatal environment determines the susceptibility to pathological conditions later in life. The hypothesis most widely accepted is that exposure to insults inducing adverse conditions in-utero may have negative effects on the development of target organs, disrupting homeostasis and increasing the risk of diseases at adulthood. Several models have been proposed to investigate the fetal origins of adult diseases, but although these approaches hold true for almost all diseases, particular attention has been focused on disorders related to the central nervous system, since the brain is particularly sensitive to alterations of the microenvironment during early development. Neurobiological disorders can be broadly divided into developmental, neurodegenerative and neuropsychiatric disorders. Even though most of these diseases share genetic risk factors, the onset of the disorders cannot be explained solely by inheritance. Therefore, current understanding presumes that the interactions of environmental input, may lead to different disorders. Among the insults that can play a direct or indirect role in the development of neurobiological disorders are stress, infections, drug abuse, and environmental contaminants. Our laboratories have been involved in the study of the neurobiological impact of gestational stress on the offspring (Dr. Antonelli's lab) and on the effect of gestational exposure to toxicants, mainly methyl mercury (MeHg) and perfluorinated compounds (PFCs) (Dr. Ceccatelli's lab). In this focused review, we will review the specialized literature but we will concentrate mostly on our own work on the long term neurodevelopmental consequences of gestational exposure to stress and neurotoxicants.

Prenatal stress induces vulnerability to nicotine addiction and alters D2 receptors' expression in the nucleus accumbens in adult rats

Prenatal stress (PS) can induce several long-lasting behavioral and molecular abnormalities in rats. It can also be considered as a risk factor for many psychiatric diseases like schizophrenia, depression or PTSD and predispose to addiction. In this study, we investigated the effect of prenatal stress on the reinforcing properties of nicotine in the CPP paradigm. Then, we examined the mRNA expression of the D2 dopaminergic receptors using the quantitative real-time PCR technique in the nucleus accumbens (NAcc). We found that prenatally stressed rats exhibited a greater place preference for the nicotine-paired compartment than the control rats. Moreover, we observed an overexpression of the DRD2 gene in adult offspring stressed in utero and a downregulation in the PS NIC group (PS rats treated with nicotine) compared with their control counterparts (C NIC). These data suggest that maternal stress can permanently alter the offspring's addictive behavior and D2 receptors' expression.

Prenatal restraint stress decreases the expression of alpha-7 nicotinic receptor in the brain of adult rat offspring

Prenatal stress (PS) strongly impacts fetal brain development and function in adulthood. In normal aging and Alzheimer's disease, there is hypothalamic-pituitary-adrenal axis dysfunction and loss of cholinergic neurons and neuronal nicotinic acetylcholine receptors (nAChRs). This study investigated whether prenatal restraint stress affects nAChR expression in the brain of adult offspring. For PS, pregnant dams were placed in a plastic restrainer for 45 min, three times daily during the last week of pregnancy; controls were undisturbed. Male offspring were analyzed at postnatal day (PND) 60 (n = 4 rats per group). Western blot (WB) and fluorescence microscopy showed that PS decreased α7-AChR subunit expression (∼50%) in the frontal cortex in the adult offspring. PS decreased significantly the number of α7-AChR-expressing cells in the medial prefrontal cortex (by ∼25%) and in the sensory-motor cortex (by ∼20%) without affecting the total cell number in those areas. No alterations were found in the hippocampus by quantitative polymerase chain reaction (qPCR), or WB analysis, but a detailed fluorescence microscopy analysis showed that PS affected α7-AChR mainly in the CA3 and dentate gyrus subfields: PS decreased α7-AChR subunit expression by ∼25 and ∼30%, respectively. Importantly, PS decreased the number of α7-AChR-expressing cells and the total cell number (by ∼15 and 20%, respectively) in the dentate gyrus. PS differently affected α4-AChR: PS impaired its mRNA expression in the frontal cortex (by ∼50%), without affecting protein levels. These results demonstrate that disturbances during gestation produce long-term alterations in the expression pattern of α7-AChR in rat brain.

Prenatal stress and adult drug-seeking behavior: interactions with genes and relation to nondrug-related behavior

Addiction inflicts large personal, social, and economic burdens, yet its etiology is poorly defined and effective treatments are lacking. As with other neuropsychiatric disorders, addiction is characterized by a core set of symptoms and behaviors that are believed to be influenced by complex gene-environment interactions. Our group focuses on the interaction between early stress and genetic background in determining addiction vulnerability. Prior work by our group and others has indicated that a history of prenatal stress (PNS) in rodents elevates adult drug seeking in a number of behavioral paradigms. The focus of the present chapter is to summarize work in the area of PNS and addiction models as well as our recent studies of PNS on drug seeking in different strains of mice as a strategy to dissect gene-environment interactions underlying cocaine addiction vulnerability. These studies indicate that ability of PNS to elevate adult cocaine seeking is strain dependent. Further, PNS also alters other nondrug behaviors in a fashion that is dependent on different strains and independent from the strain dependence of drug seeking. Thus, it appears that the ability of PNS to alter behavior related to different psychiatric conditions is orthogonal, with similar nonspecific susceptibility to prenatal stress across genetic backgrounds but with the genetic background determining the specific nature of the PNS effects. Finally, the advent of recombinant inbred mouse strains is allowing us to determine the genetic bases of these gene-environment interactions. Understanding these effects will have broad implications to determining the nature of vulnerability to addiction and perhaps other disorders.

Hormonal modulation of catecholaminergic neurotransmission in a prenatal stress model

Our laboratory has a long-standing interest in the effects of prenatal stress (PS) on various neurotransmitter pathways and the morphology of the developing brain as well as in behavioural aspects of the offspring. Employing a commonly used PS paradigm in which the dams were subjected to restraint stress during the last week of gestation, we observed that several of these pathways were altered in the offspring brain. In this chapter, we will summarize and discuss the results obtained with the main catecholaminergic pathways, namely dopamine (DA) and norepinephrine (NE). In our hands, PS produces an increase in dopamine D2-type receptors in limbic areas, a decreased DA release after amphetamine stimulation in prefrontal cortex (PFC) and an increase in NE release in the same area of the adult offspring brain. In addition, DA uptake is altered at prepubertal stages that persist through adulthood. However, the expression of the step-limiting enzyme of the DA synthesis, tyrosine hydroxylase (TH), is only impaired at early stages of development after PS in the neuronal bodies. At the nuclear regulation level, dopaminergic transcription factors Nurr1 and Ptx3 showed a high vulnerability to PS showing changes along the lifespan. It was striking to observe that many impairments observed in most of these pathways differed depending on whether they were tested before or after puberty indicating a particular sensitivity of the systems to variations in gonadal hormones peaks. In fact, we observed that PS induced long-term effects on the male offspring reproductive system and spermatogenesis development, particularly by inducing a long-term imbalance of circulating sexual hormone levels. Our findings suggest that PS exerts long-term effects on various neurotransmitter pathways altering the normal connectivity between brain areas. Since the developing forebrain was shown to be influenced by androgen exposure, and PS was shown to disrupt prenatal testosterone surges, our results suggest that prenatal insults might be affecting the organizational role of androgens during brain development and differentially modulating their activational role during pubertal brain maturation.

Maternal administration of flutamide during late gestation affects the brain and reproductive organs development in the rat male offspring

We have previously demonstrated that male rats exposed to stress during the last week of gestation present age-specific impairments of brain development. Since the organization of the fetal developing brain is subject to androgen exposure and prenatal stress was reported to disrupt perinatal testosterone surges, the aim of this research was to explore whether abnormal androgen concentrations during late gestation affects the morphology of the prefrontal cortex (PFC), hippocampus (HPC) and ventral tegmental area (VTA), three major areas that were shown to be affected by prenatal stress in our previous studies. We administered 10-mg/kg/day of the androgen receptor antagonist flutamide (4'nitro-3'-trifluoromethylsobutyranilide) or vehicle injections to pregnant rats from days 15-21 of gestation. The antiandrogenic effects of flutamide were confirmed by the analysis of androgen-dependent developmental markers: flutamide-exposed rats showed reduced anogenital distance, delay in the completion of testis descent, hypospadias, cryptorchidism and atrophied seminal vesicles. Brain morphological studies revealed that prenatal flutamide decreased the number of MAP2 (a microtubule-associated protein type 2, present almost exclusively in dendrites) immunoreactive neuronal processes in all evaluated brain areas, both in prepubertal and adult offspring, suggesting that prenatal androgen disruption induces long-term reductions of the dendritic arborization of several brain structures, affecting the normal connectivity between areas. Moreover, the number of tyrosine hydroxylase (TH)-immunopositive neurons in the VTA of prepubertal offspring was reduced in flutamide rats but reach normal values at adulthood. Our results demonstrate that the effects of prenatal flutamide on the offspring brain morphology resemble several prenatal stress effects suggesting that the mechanism of action of prenatal stress might be related to the impairment of the organizational role of androgens on brain development.

Prenatal stress induces increased striatal dopamine transporter binding in adult nonhuman primates

BACKGROUND

To determine the effects in adult offspring of maternal exposure to stress and alcohol during pregnancy, we imaged striatal and midbrain dopamine transporter (DAT) binding by positron emission tomography in rhesus monkeys (Macaca mulatta). We also evaluated the relationship between DAT binding and behavioral responses previously found to relate to dopamine D2 receptor density (responsivity to tactile stimuli, performance on a learning task, and behavior during a learning task).

METHODS

Subjects were adult offspring derived from a 2 × 2 experiment in which pregnant monkeys were randomly assigned to control, daily mild stress exposure (acoustic startle), voluntary consumption of moderate-level alcohol, or both daily stress and alcohol. Adult offspring (n = 38) were imaged by positron emission tomography with the DAT ligand [(18)F]2β-carbomethoxy-3β-(4-chlorophenyl)-8-(2-fluoroethyl)-nortropane ([(18)F]FECNT).

RESULTS

Results showed that prenatal stress yielded an overall increase of 15% in [(18)F]FECNT binding in the striatum (p = .016), 17% greater binding in the putamen (p = .012), and 13% greater binding in the head of the caudate (p = .028) relative to animals not exposed to prenatal stress. Striatal [(18)F]FECNT binding correlated negatively with habituation to repeated tactile stimulation and positively with tactile responsivity. There were no significant effects of prenatal alcohol exposure on [(18)F]FECNT binding.

CONCLUSIONS

Maternal exposure to mild daily stress during pregnancy yielded increases in striatal DAT availability that were apparent in adult offspring and were associated with behavioral characteristics reflecting tactile hyperresponsivity, a condition associated with problem behaviors in children.

Gestational restraint stress and the developing dopaminergic system: an overview

Prenatal stress exerts a strong impact on fetal brain development in rats impairing adaptation to stressful conditions, subsequent vulnerability to anxiety, altered sexual function, and enhanced propensity to self-administer drugs. Most of these alterations have been attributed to changes in the neurotransmitter dopamine (DA). In humans; dysfunction of dopaminergic system is associated with development of several neurological disorders, such as Parkinson disease, schizophrenia, attention-deficit hyperactivity disorder, and depression. Evidences provided by animal research, as well as retrospective studies in humans, pointed out that exposure to adverse events in early life can alter adult behaviors and neurochemical indicators of midbrain DA activity, suggesting that the development of the DA system is sensitive to disruption by exposure to early stressors. The purpose of this article is to provide a general overview of published studies and our own study related to the effect of prenatal insults on the development of DA metabolism and biology, focusing mainly in articles involving prenatal-restraint stress protocols in rats. We will also attempt to make a correlation between theses alterations and DA-related pathological processes in humans.

Child health, developmental plasticity, and epigenetic programming

Plasticity in developmental programming has evolved in order to provide the best chances of survival and reproductive success to the organism under changing environments. Environmental conditions that are experienced in early life can profoundly influence human biology and long-term health. Developmental origins of health and disease and life-history transitions are purported to use placental, nutritional, and endocrine cues for setting long-term biological, mental, and behavioral strategies in response to local ecological and/or social conditions. The window of developmental plasticity extends from preconception to early childhood and involves epigenetic responses to environmental changes, which exert their effects during life-history phase transitions. These epigenetic responses influence development, cell- and tissue-specific gene expression, and sexual dimorphism, and, in exceptional cases, could be transmitted transgenerationally. Translational epigenetic research in child health is a reiterative process that ranges from research in the basic sciences, preclinical research, and pediatric clinical research. Identifying the epigenetic consequences of fetal programming creates potential applications in clinical practice: the development of epigenetic biomarkers for early diagnosis of disease, the ability to identify susceptible individuals at risk for adult diseases, and the development of novel preventive and curative measures that are based on diet and/or novel epigenetic drugs.

Prenatal Stress Alters Progestogens to Mediate Susceptibility to Sex-Typical, Stress-Sensitive Disorders, such as Drug Abuse: A Review

Maternal-offspring interactions begin prior to birth. Experiences of the mother during gestation play a powerful role in determining the developmental programming of the central nervous system. In particular, stress during gestation alters developmental programming of the offspring resulting in susceptibility to sex-typical and stress-sensitive neurodevelopmental, neuropsychiatric, and neurodegenerative disorders. However, neither these effects, nor the underlying mechanisms, are well understood. Our hypothesis is that allopregnanolone, during gestation, plays a particularly vital role in mitigating effects of stress on the developing fetus and may mediate, in part, alterations apparent throughout the lifespan. Specifically, altered balance between glucocorticoids and progestogens during critical periods of development (stemming from psychological, immunological, and/or endocrinological stressors during gestation) may permanently influence behavior, brain morphology, and/or neuroendocrine-sensitive processes. 5α-reduced progestogens are integral in the developmental programming of sex-typical, stress-sensitive, and/or disorder-relevant phenotypes. Prenatal stress (PNS) may alter these responses and dysregulate allopregnanolone and its normative effects on stress axis function. As an example of a neurodevelopmental, neuropsychiatric, and/or neurodegenerative process, this review focuses on responsiveness to drugs of abuse, which is sensitive to PNS and progestogen milieu. This review explores the notion that allopregnanolone may effect, or be influenced by, PNS, with consequences for neurodevelopmental-, neuropsychiatric-, and/or neurodegenerative- relevant processes, such as addiction.

The impact of perinatal stress on the functional maturation of prefronto-cortical synaptic circuits: implications for the pathophysiology of ADHD?

Enriched as well as impoverished or adverse perinatal environment plays an essential role in the development and refinement of neuronal pathways, which are the neural substrate of intellectual capacity and socioemotional competence. Perinatal experience and learning events continuously interact with the adaptive shaping of excitatory, inhibitory, and neuromodulatory synaptic as well as the endocrine stress systems, including the neuronal corticotropin-releasing factor (CRF) pathways. Adverse environments, such as stress and emotional deprivation can not only delay experience-dependent maturation of these pathways, but also induce permanent changes in prefronto-cortical wiring patterns. We assume that such dysfunctional connections are the neuronal basis for the development of psychosocially induced mental disorders during later life. The aim of this review is to focus on the impact of perinatal stress on the neuronal and synaptic reorganization during brain development and possible implications for the etiology and therapy of mental disorders such as ADHD.

Ontogenetic expression of dopamine-related transcription factors and tyrosine hydroxylase in prenatally stressed rats

The development of the central nervous system can be permanently affected by insults received during the perinatal period, predisposing the organism to long-term behavioral and neurochemical abnormalities. Rats exposed to different types of stress during the last week of gestation produce offspring that show several alterations, many of which have been attributed to changes in dopamine (DA) neurotransmission that could serve as the neurochemical basis for the development of neuropsychiatric disorders. Employing an immunocytochemical approach, we studied the expression levels of two transcription factors Nurr1 and Pitx3 which are expressed at critical moments of DA neurons differentiation as well as the expression of the rate limiting enzyme in DA synthesis, tyrosine hydroxylase (TH) in mesencephalic areas of the brains of prenatally stressed (PS) offspring at different postnatal ages. Main results show that stress exerted to the gestant mother produces permanent effect in the ontogenetic expression of key factors related to the DA metabolism mainly in the ventral tegmental area (VTA) of the mesencephalon. The immunocytochemical expression of the transcription factor Nurr1 shows an increase at postnatal days (PNDs) 7, 28, and 60 whereas Pitx3 shows a decrease at PND 28 and an increase at 60 PND. The rate limiting step in DA synthesis, the enzyme TH shows a decrease at PND 7 to reach control levels at PNDs 28 and 60. The increase of TFs might be up-regulating TH in order to restore DA levels that were previously seen to be normal before puberty. The area selectivity of the increase of the TFs toward VTA and the mesolimbic pathway indicates that an insult received during the prenatal period will exert mainly motivational, emotional, and reward behavior impairments in the adult life.

Maternal and early life stress effects on immune function: relevance to immunotoxicology

Stress is triggered by a variety of unexpected environmental stimuli, such as aggressive behavior, fear, forced physical activity, sudden environmental changes, social isolation or pathological conditions. Stressful experiences during very early life (particularly, maternal stress during fetal ontogeny) can permanently alter the responsiveness of the nervous system, an effect called programming or imprinting. Programming affects the hypothalamic-pituitary-adrenocortical (HPA) axis, brain neurotransmitter systems, sympathetic nervous system (SNS), and the cognitive abilities of the offspring, which can alter neural regulation of immune function. Prenatal or early life stress may contribute to the maladaptive immune responses to stress that occur later in life. This review focuses on the effect of maternal and early life stress on immune function in the offspring across life span. It highlights potential mechanisms by which prenatal stress impacts immune functions over life span. The literature discussed in this review suggests that psychosocial stress during pre- and early postnatal life may increase the vulnerability of infants to the effects of immunotoxicants or immune-mediated diseases, with long-term consequences. Neural-immune interactions may provide an indirect route through which immunotoxicants affect the developing immune system. A developmental approach to understanding how immunotoxicants interact with maternal and early life stress-induced changes in immunity is needed, because as the body changes physiologically across life span so do the effects of stress and immunotoxicants. In early and late life, the immune system is more vulnerable to the effects of stress. Stress can mimic the effects of aging and exacerbate age-related changes in immune function. This is important because immune dysregulation in the elderly is more frequently and seriously associated with clinical impairment and death. Aging, exposure to teratogens, and psychological stress interact to increase vulnerability and put the elderly at the greatest risk for disease.

Immunocytochemical expression of dopamine-related transcription factors Pitx3 and Nurr1 in prenatally stressed adult rats

Rats exposed to different types of stress during the last week of pregnancy produce offspring that show severe anomalies in neural development and brain morphology. We have previously reported that prenatal stress (PS) induced by immobilization increases D2-type dopamine (DA) receptor levels in the adult offspring, with a concomitant reduction in DA release in prefrontal cortex after amphetamine stimulation. Recently, two transcription factors, Nurr1 and Pitx3, have been identified that are expressed at critical moments of DA neuron differentiation. Their genetic expression is activated immediately after these neuron determinations and maintained through adult life. Nurr1 regulates several proteins that are required for dopamine synthesis and regulation, and Pitx3 is specifically involved in the terminal differentiation and maintenance of dopamine neurons. By means of an immunocytochemistry approach, we studied the expression of Nurr1 and found an ubiquitous distribution in cerebral cortex, hippocampus, thalamus, amygdala, and midbrain, whereas Pitx3 remains restricted to the mesencephalic DA neurons such as substantia nigra and ventral tegmental area. Our results show that the expression of both Nurr1 and Pitx3 increased in prenatally stressed adult offspring in the ventral tegmental area, whereas no changes were observed in the substantia nigra area. It might be hypothesized that the increase of the specific dopaminergic transcription factors might be a compensatory mechanism to counteract the reduction in dopamine levels previously observed as a consequence of prenatal stress.

Perplexities and provocations of eating disorders

BACKGROUND

Etiological hypotheses of eating disorders, anorexia nervosa and bulimia nervosa have not produced informative research for predictably effective treatment.

METHODS

The rationale for applying a model of allostasis, a dysregulation of reward circuits with activation of brain and hormonal stress responses to maintain apparent stability, is developed for eating disorders.

RESULTS

The neurotransmitter systems involved in the allostatic state of a reward system in anorexia nervosa and bulimia nervosa may be similar to those present in drug addiction.

CONCLUSION

The biological vulnerabilities underlying the unique features of eating disorders should be intensively investigated with the advancing techniques in genetics and neuroimaging. Preventing chronicity with early diagnosis and adequate treatment before age 18 is necessary.

Sensory processing disorder in a primate model: evidence from a longitudinal study of prenatal alcohol and prenatal stress effects

Disrupted sensory processing, characterized by over- or underresponsiveness to environmental stimuli, has been reported in children with a variety of developmental disabilities. This study examined the effects of prenatal stress and moderate-level prenatal alcohol exposure on tactile sensitivity and its relationship to striatal dopamine system function in thirty-eight 5- to 7-year-old rhesus monkeys. The monkeys were from four experimental conditions: (a) prenatal alcohol exposed, (b) prenatal stress, (c) prenatal alcohol exposed + prenatal stress, and (d) sucrose controls. Increased D(2) receptor binding in the striatum, evaluated using positron emission tomography neuroimaging, was related to increased withdrawal (aversion) responses to repetitive tactile stimuli and reduced habituation across trials. Moreover, prenatal stress significantly increased overall withdrawal responses to repetitive tactile stimulation compared to no prenatal stress.

Prenatal stress suppresses cell proliferation in the early developing brain

Although prenatal stress has been repeatedly shown to inhibit adult neurogenesis in the dentate gyrus of offspring, its effects on embryonic and early postnatal brain development are not well described. Here, using the cell proliferation marker 5-bromo-2'-deoxyuridine, we examine for the first time the effect of prenatal stress at the embryonic stage on cell proliferation in the hippocampus, nucleus accumbens and amygdala. We show that prenatal stress induces a significant decrease in density of 5-bromo-2'-deoxyuridine-positive cells in the nucleus accumbens (40%) and hippocampus (60%), and a nonsignificant decrease in the amygdala (30%). Taken together, these results demonstrate the adverse effects of prenatal maternal stress on early development in limbic brain regions and the potential mechanisms are discussed.

Schizophrenia: a unique translational opportunity in behavioral neuroendocrinology

Schizophrenia is a complex and debilitating neuropsychiatric disease in which both environmental and genetic factors contribute to the pathophysiology of the disease. Epidemiological data point to the importance of the prenatal period in the genesis of schizophrenia and suggest that environmental factors, such as stress and hormones of the hypothalamic-pituitary-adrenal axis, may establish a vulnerability to the disease. Unfortunately, the exact cause of this neurodevelopmental disease is unclear. In this review, data on the importance of gestational stress exposure to the etiology of schizophrenia-like behavioral, endocrine and molecular phenotypes will be presented and differences will be highlighted between the preparations that are commonly used in most laboratory investigations.

Changes of spine density and dendritic complexity in the prefrontal cortex in offspring of mothers exposed to stress during pregnancy

Both chronic stress in adulthood and episodes of stress in the early postnatal period have been shown to interfere with neuronal development in limbic prefrontal cortical regions. The present study in rats showed for the first time that the development of layer II/III pyramidal neurons in the dorsal anterior cingulate (ACd) and orbitofrontal cortex (OFC) is significantly affected in offspring of mothers exposed to stress during pregnancy. In prenatally stressed (PS) male rat pups the ACd and OFC showed significantly lower spine densities on the apical dendrite (ACd, -20%; OFC, -25%), on basal dendrites reduced spine densities where found only in the OFC (-20% in PS males). Moreover, in both cortical areas a significant reduction of dendritic length was observed in PS males compared to control offspring, which was confined to the apical dendrites (ACd, -30%, OFC, -26%). Sholl analysis revealed that these alterations were accompanied by a significantly reduced complexity of the dendritic trees in both cortical regions. PS females displayed reductions of dendritic spine densities in the ACd and OFC on both the basal (ACd, -21%; OFC, -20%) and apical dendrites (ACd, -21%; OFC, -21%), however, in contrast to the findings in PS males, no dendritic atrophy was detected in the PS females. These findings demonstrate that gestational stress leads to significant alterations of prefrontal neuronal structure in the offspring of the stressed mothers in a sex-specific manner.

Postnatal stimulation of the pups counteracts prenatal stress-induced deficits in hippocampal neurogenesis

BACKGROUND

Prenatal stress constitutes a developmental risk factor for later psychopathology. The behavioral disorders are sustained by neurobiological alterations including long-term reduction of hippocampal neurogenesis; its deregulation has been involved in cognitive impairments, mood disorders and addiction. A major goal is to define periods in development and strategies for intervening to prevent the effects of early stressful events. We investigated the ability of a postnatal infantile stimulation to prevent prenatal stress-induced alteration in hippocampal neurogenesis.

METHODS

The influence of postnatal handling on prenatal stress-induced changes in hippocampal neurogenesis was examined in 4 and 26 month-old male rats. Three distinct phases of the neurogenesis were studied: proliferation, survival and neuronal differentiation.

RESULTS

Prenatal stress reduced hippocampal cell proliferation all throughout life. Furthermore, the survival rate of newborn cells, the number of immature neurons and the number of differentiated new neurons were reduced in young and old prenatally-stressed rats. All those deleterious effects were counteracted by neonatal handling.

CONCLUSIONS

These data show that finer aspects of brain shaping can be rewired by environmental influences occurring at sensitive phase of development. They also suggest that infantile stimulation may reverse the appearance of behavioral disorders induced by early life stress.

The marriage-related risk factors during maternal pregnancy in children with attention-deficit hyperactivity disorder

BACKGROUND

The purpose of this research was to investigate the relationship between marriage-related risk factors during maternal pregnancy and subsequent development of attention-deficit hyperactivity disorder (ADHD).

METHODS

The research design was a retrospective case-control study. The case group included 60 patients that fulfilled the ADHD criteria of Fourth Edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV). The controls were normal children randomly selected and matched for their sex and age. Their biological mothers completed a questionnaire about marital adaptation, marital satisfaction and the incidence of stressful life events during pregnancy.

RESULTS

The results showed that the incidence of positive life events, marital adaptation and marital satisfaction during maternal pregnancy was significantly lower in the case group, and conditional logistic regression analysis showed that marital adaptation during pregnancy and pregnancy before marriage were important risk factors for ADHD.

CONCLUSION

Negative emotion during maternal pregnancy may be an important risk factor for ADHD.

The effects of prenatal social stress on behaviour: mechanisms and function

In this review, we summarise experimental animal studies on the effects of the social environment during pregnancy on the offsprings' behaviour, brain, and neuroendocrine function. We show that in non-human mammals the stability of the social environment in which the pregnant females live is critical for the offsprings' social and sexual behaviour later in life as well as for reproductive functioning, endocrine state and androgen and estrogen receptor distribution in specific parts of the brain. Based on these findings, we discuss different neuroendocrine mechanisms mediating the influence of the social environment during pregnancy on the offsprings' behaviour. We conclude that maternal steroids play a decisive role in shaping foetal brain development. However, a pituitary adrenocortical pathway need not always be involved. At least in some cases an involvement of the sympathetic adrenomedullary system seems to be possible. Concerning function, we favour the hypothesis that the behavioural effects of prenatal social stress are not necessarily the 'pathological' consequences of adverse social conditions (non-adaptive explanation). Contrarily, mothers could be adjusting their offspring to the environment in which they live during pregnancy in an efficient way (adaptive explanation).

Prenatal stress reduces interneuronal connectivity in the rat cerebellar granular layer

The development and functioning of the central nervous system have been shown to be affected by maternal stress. To investigate the effects of prenatal stress on the cerebellar interneuronal connectivity, rat embryos are exposed to stress on their embryonic day (E) 7 and 14, by keeping the dam in close-fitting wire mesh cylinders, for 6 h. After completion of the cerebellar development at postnatal day (P) 30, stereological procedures were used at the light and electron microscopic level to analyze growth parameters of the granule cells and synapse-to-neuron ratios. Neither the volume fraction (V(V)) of the granular layer to whole cortex, nor the numerical density of granule cells (N(Vg)) per unit volume of granular layer was affected by exposure to stress. However, the mean granule cell nuclear diameter was significantly decreased in stressed animals. Within the neuropil region, the number and mean diameter of synaptic disc profiles were used to estimate the numerical density of synapses (N(Vs)). Synapse-to-neuron ratio was obtained by dividing N(Vs) with N(Vg), and found significantly lower in the stressed group than the control group. In addition, synaptophysin immunoreactivity showed a significant decrease (41%) in the granular layer of the cerebellum. Collectively, these results demonstrate that intrauterine stress alters the morphology of granule cells and causes a profound and fairly long-lasting deficit in their interneuronal connectivity.

Antenatal maternal anxiety is linked with atypical handedness in the child

BACKGROUND

Animal studies have shown that prenatal stress is linked with altered laterality in the offspring.

AIMS

The aim of this study was to test the hypothesis that antenatal maternal anxiety was associated with altered lateralisation in children, as demonstrated by mixed handedness.

STUDY DESIGN AND SUBJECTS

We used the Avon Longitudinal Study of Parents and Children (ALSPAC), a prospective longitudinal study that has followed women since pregnancy. The final analysis included data on 7431 mother-child pairs. Maternal anxiety was measured at 18- and 32-week gestation and 8 weeks postnatally using a self-report inventory. Child handedness was assessed at 42 months using an established maternal report scale. Information on maternal and paternal handedness, as well as data on possible confounding variables such as obstetric and antenatal risks, were also assessed.

RESULTS

Univariable analysis showed that antenatal anxiety at 18 weeks was associated with mixed-handedness in the child, OR=1.28 (95% CI 1.09-1.50, p<0.01). Although boys were more likely than girls to be mixed handed, the link with antenatal anxiety was similar. There was no significant association with antenatal anxiety at 32 weeks. Multivariable analyses indicated that maternal anxiety at 18 weeks of pregnancy predicted an increased likelihood of mixed-handedness in the child (OR=1.23, 95% CI 1.02-1.48, p<0.05), independently of parental handedness, obstetric and other antenatal risks, and postnatal anxiety.

CONCLUSION

This result provides further evidence for a link between antenatal anxiety and fetal programming in humans.

Very mild stress of pregnant rats reduces volume and cell number in nucleus accumbens of adult offspring: some parallels to schizophrenia

Pregnant rats subjected to very mild stress give birth to pups who, when examined as adults, exhibited behavioral and anatomical anomalies that resemble some aspects of schizophrenia. The nucleus accumbens (NAcc) is reduced in volume by 20.7 +/- 3.4% (p = 0.003) in pups born to mothers who were stressed during pregnancy by injections of either saline or amphetamine in saline. The total number of cells is decreased in proportion to the reduction in volume, so the volume cell density of the NAcc is not changed with treatment. The affected volume is localized in the ventral rostral area of the NAcc. Both males and females are affected, but males are slightly more sensitive to the challenge to the mother. Rats born to mothers stressed in mid-pregnancy appear to provide useful parallels to the fetal developmental hypothesis of schizophrenia and to the brain abnormalities seen in this disease.

Impact of asymmetric intrauterine growth restriction on organ function in newborn piglets

Fetal malnutrition may induce asymmetric intrauterine growth restriction (aIUGR) with long-lasting consequences. Understanding the organ-specific structural and functional effects aIUGR may have on the newborn, and understanding the potential impact on the neonatal response to compromising conditions, appears to be essential for adequate treatment. Therefore, a survey is given of some organ-specific alterations in newborns, which have suffered from aIUGR. We studied these effects in a model of asymmetric intrauterine growth restriction based on the spontaneous occurrence of runting in pigs. We wish to demonstrate that experimental studies in animal models are necessary and helpful to elucidate pathogenetic mechanisms. aIUGR seems to have both beneficial and detrimental effects on the newborn. The development of skeletal muscles (conversion to oxidative type I fibers) and of their vascular supply as well as of the brain dopaminergic activity is accelerated. Also, aIUGR apparently improves the ability to withstand critical periods of gradual oxygen deficit as shown by the maintenance of renal blood flow during severe systemic hypoxia, and by improved cerebrovascular autoregulation in hemorrhagic hypotension. On the other hand, aIUGR leads to the reduction of the number of nephrons and to impaired renal excretory functions with arterial hypertension and chronic renal failure.

Theory, methods and new directions in the psychophysiology of the schizophrenic process and schizotypy

Theoretical and methodological issues in the psychophysiology of the schizophrenic process are reviewed. These include the importance of schizotypy with its compensatory abilities as well as deficits for elucidating the processes of development and prevention of schizophrenia. The importance of individual differences, syndromes and single case studies. The recognition that this is a dynamic and fluctuating illness and hence the relevance of functional neurophysiology, including the role of imbalances in hemispheric activation in ontogeny, developmental course, expression of symptoms, the effects of neuroleptics and recovery process, and the influence of stress a precipitant of breakdown. The role of thalamo-cortical activation systems. The particular value of electrocortical measures including the interrelations of electroencephalographic rhythms throughout the spectrum, and relations of gamma, dynamic core neuronal complexity, connectivity and sensory gating with experiences of unreality and disturbances of consciousness.

Effects of prenatal stress on stress-induced changes in behavior and macrophage activity of mice

The present study analyzed the effects of maternal stress on behavior and macrophage activity of mice. Pregnant mice received a daily footshock (0.2 mA) from gestational days 15 (GD15) to 19. Experiments were performed on male offspring, challenged or not with another footshock (0.2 mA) on postnatal day 30 (PND30) or 60. The following results were obtained for maternal stress: (1) increment in locomotor activity of juvenile but not of adult mice observed in both open-field and plus-maze; (2) increment in rearing frequency of juvenile but not of adult mice observed in the open-field; (3) decrement in macrophage spreading of adult but not of juvenile mice; (4) abolishment of postnatal footshock effects in both macrophage spreading on PND30 and macrophage nitric oxide (NO) production on PND60; (5) reversion of postnatal footshock effects on H(2)O(2) spontaneous and PMA-induced release by macrophage on PND30; (6) modification of postnatal stress effects on macrophage phagocytosis on PND60. These changes were unrelated to differences in gestational parameters and did not reflect altered maternal-pup interactions or nutritional factors. The observed data provide experimental evidence that maternal stress alters behavior, and macrophage activity at the same time and in the same litter. These data were discussed in the light of possible neuroimmune interactions that involve catecholaminergic pathways.

The role of prenatal stress in the etiology of developmental behavioural disorders

Substantial evidence from preclinical laboratory studies indicates that prenatal stress (PS) affects the hormonal and behavioural development of offspring. In the following review, the effects of PS in rodents and non-human primates on hypothalamic-pituitary-adrenal (HPA) reactivity to stress, morphological changes in the brain, motor behaviour and learning are surveyed. PS has been found to alter baseline and stress-induced responsivity of the HPA axis and levels and distribution of regulatory neurotransmitters, such as norepinepherine, dopamine, serotonin and acetylcholine and to modify key limbic structures. In rodents and non-human primates, PS affected learning, anxiety and social behaviour. The relevance of these findings to humans is discussed with respect to (a) the effect of administration of exogenous corticosteroids in pregnancy and (b) maternal state and trait anxiety during gestation and its relation to foetal autonomic regulation as putative predisposing factors in the pathogenesis of behavioural developmental delays in children.

Alterations induced by gestational stress in brain morphology and behaviour of the offspring

Retrospective studies in humans suggest that chronic maternal stress during pregnancy, associated with raised plasma levels of CRH, ACTH and cortisol may increase the likelihood of preterm birth, developmental delays and behavioural abnormalities in the children. In adulthood, it may contribute to the significant association between the incidence of schizophrenia, increased left or mixed handedness, reduction in cerebral asymmetry and anomalies in brain morphology. Our studies and others have shown that prenatal stress in rats can mimic these developmental and behavioural alterations. These rats show a reduced propensity for social interaction, increased anxiety in intimidating or novel situations and a reduction in cerebral asymmetry and dopamine turnover, consistent with those in schizophrenic humans. Prenatally-stressed (PS) rats also show behaviour consistent with depression, including a phase-shift in their circadian rhythm for corticosterone, sleep abnormalities, a hedonic deficit and greater acquisition of learned helplessness under appropriate conditions. These behavioural abnormalities are associated with impaired regulation of the hypothalamic-pituitary-adrenal axis response to stress and increased CRH activity. PS males may show demasculinisation and feminisation of their sexual behaviour. The developmental and behavioural abnormalities in PS offspring could occur through sensitisation of the foetal brain by maternal stress hormones to the action of glucocorticoid and CRH and to neurotransmitters affected by them. This may have long-lasting consequences and could explain the precipitation of depressive symptoms or schizophrenia by psychosocial stress in later life. The character of the behavioural abnormalities probably depends on the timing of the maternal stress in relation to development of the particular neuronal systems.

Effects of maternal stress on anxiety levels, macrophage activity, and Ehrlich tumor growth

The present study analyzed the effects of maternal stress on behavior and immune function of mice. Pregnant mice received a daily footshock (0.4 mA) from gestational day 15 (GD 15) to GD 19. Experiments were performed on male offspring aged 2 months. The following results were obtained for offspring from dams stressed during pregnancy: (1) decreased locomotor activity observed in the open-field central zone; (2) decreased number of entries into the open arms of the plus-maze and decreased time spent in the exploration of these arms; (3) decreased macrophage spreading and phagocytosis, but no changes in macrophage NO(2)(-) production; (4) increased growth of both the ascitic and solid forms of Ehrlich tumor. These changes were unrelated to differences in gestational parameters and did not reflect altered maternal-pup interactions or nutritional factors. The observed data provide experimental evidence that maternal stress alters stress/anxiety levels, macrophage activity and Ehrlich tumor growth at the same time and in the same litter. The data were discussed in the light of possible neuroendocrine-immune system interactions.

Prenatal stress alters early neurobehavior, stress reactivity and learning in non-human primates: a brief review

In this paper we review three prospective longitudinal studies from our laboratory examining the effects of prenatal stress on early neuro behavior, stress reactivity and learning performance in rhesus monkeys. Either a noise stressor or ACTH treatment was administered to pregnant monkeys during specific periods of pregnancy and offspring were examined repeatedly across development. In all three studies, the prenatally stressed monkeys showed reduced attention and impaired neuromotor functioning during the first month of life compared to controls from undisturbed pregnancies. When the monkeys were separated from their mothers or peers at 6-8 months of age, prenatally stressed monkeys exhibited more disturbance behavior and showed hypothalamic-pituitary-adrenal axis dysregulation. During adolescence, they exhibited impairments in learning, compared to controls.

Effects of maternal stress on development and behaviour in rat offspring

Retrospective studies suggest that gestational stress in humans can delay the attainment of developmental milestones, increase the incidence of allergic reactions and respiratory infections and cause behavioural abnormalities in the children. Our studies and others have shown that prenatal stress in rats can mimic several of these developmental and behavioural alterations. These include a suppression of immune function, but also enhanced sensitivity to allergens. Prenatally-stressed rats, like children, show a reduced propensity for social interaction and increased anxiety in intimidating or novel situations. They have physiological and behavioural alterations consistent with depressive symptoms, including a phase-shift in their circadian rhythm for corticosterone, sleep abnormalities, and greater acquisition of learned helplessness under appropriate conditions. Prenatally-stressed male rats also show demasculinisation and feminisation of their sexual behaviour. The developmental and behavioural abnormalities in prenatally-stressed offspring may be mediated by alterations in the activity of endogenous opioids or neurosteroids, since several of them can be corrected by maternal administration of an opioid antagonist or by drugs like diazepam and allopregnanolone that modulate GABA transmission.

Long term neurodevelopmental and behavioral effects of perinatal life events in rats

Modern neurosciences are now able to open new avenues concerning an experimental approach to clinical neurosciences and psychiatry. Detection and prediction of potential vulnerabilities such as behavioral disturbances and neurodegenerative diseases, are urgent tasks leading to prevention that must be encouraged in parallel to the enormous efforts displayed for treatments. Besides possible genetic origins of diseases, environmental factors are now coming under scrutiny, and especially deleterious and challenging life events and stress occurring during prenatal and postnatal critical periods may orient brain functions towards deleterious developments. The hypothesis that will be examined is that early events might be at the origin of pathological transformations and symptoms after long periods of apparent normal abilities and behavioral homeostasis. We used models of prenatal stress and postnatal manipulations such as cross-fostering. It will be demonstrated that such events induce long-term changes, cognitive and emotional modifications appearing first, when offspring are adults, followed by cognitive defects later in life. Increased sensitivity of the hypothalamic pituitary-adrenal axis (HPA), the endocrine system controlling the secretion of stress hormones (corticoids), appears to be a major element of pathogenesis. HPA axis dysfunction appears very early after birth (3 days) and lasts for months. Cumulative exposure to high levels of hormones seems to be detrimental for some brain regions, especially the hippocampus and major neurotransmitter systems such as dopamine neurons. We evidenced that neuronal modifications in hippocampal region are correlated with behavioral and cognitive defects, relating environment, stress in early life, hormonal changes, long-term neuropathological processes and impaired cognition in aging. Moreover appears in offspring, when adults, a proneness to engage in drug dependence. These data emphasize the need to consider early environmental life events as etiological factors for delayed neuropsychiatric disturbances, neurodegenerative defects included. Moreover, they strengthen the interest for a longitudinal approach to promote experimental psychopathology.

Laterality of tail resting posture in three species of New World primates

A variety of mammalian species including prosimian and simian primates wrap their tails around their bodies as a means of thermoregulation and for reasons of comfort during resting or sleep. Adopting such a resting posture requires an animal to move its tail either to the right or to the left of the midline of its body, and thus to perform a lateralized behavior. The purpose of this study was to assess the occurrence of lateral biases in tail resting posture in three species of New World primates. Twenty squirrel monkeys, spider monkeys, and howler monkeys, respectively, were observed and data on tail resting posture were collected and analyzed. The results demonstrate (1) that individual squirrel monkeys and spider monkeys exhibit highly significant lateral biases in tail resting posture; (2) a lack of a lateral bias at the group level; (3) that howler monkeys fail to show side preferences in tail wrapping; (4) a lack of sex differences in this behavior in all three species; and (5) a lack of significant correlations between preferred side of tail resting posture and preferred side of hand use in simple reaching tasks which had been assessed with a subset of animals in previous studies. Thus, the present study provides evidence for a behavioral asymmetry which is well-known to occur in rats but has not been described so far in nonhuman primates, and which might offer an additional approach to the investigation of the mechanisms underlying functional cerebral asymmetries.