Effects of maternal L-tryptophan depletion and corticosterone administration on neurobehavioral adjustments in mouse dams and their adolescent and adult daughters

Hyperglycemia and cognitive impairments anticipate the onset of an overt type 2 diabetes-like phenotype in TALLYHO/JngJ mice

Type 2 Diabetes mellitus (T2DM) is a metabolic disorder characterized by chronic hyperglycemia, resulting from deficits in insulin secretion, insulin action, or both. Whilst the role of insulin in the peripheral nervous system has been ascertained in countless studies, its role in the central nervous system (CNS) is emerging only recently. Brain insulin has been lately associated with brain disorders like Alzheimer's disease, obsessive compulsive disorder, and attention deficit hyperactivity disorder. Thus, understanding the role of insulin as a common risk factor for mental and somatic comorbidities may disclose novel preventative and therapeutic approaches. We evaluated general metabolism (glucose tolerance, insulin sensitivity, energy expenditure, lipid metabolism, and polydipsia) and cognitive capabilities (attention, cognitive flexibility, and memory), in adolescent, young adult, and adult male and female TALLYHO/JngJ mice (TH, previously reported to constitute a valid experimental model of T2DM due to impaired insulin signaling). Adult TH mice have also been studied for alterations in gut microbiota diversity and composition. While TH mice exhibited profound deficits in cognitive flexibility and altered glucose metabolism, we observed that these alterations emerged either much earlier (males) or independent of (females) a comprehensive constellation of symptoms, isomorphic to an overt T2DM-like phenotype (insulin resistance, polydipsia, higher energy expenditure, and altered lipid metabolism). We also observed significant sex-dependent alterations in gut microbiota alpha diversity and taxonomy in adult TH mice. Deficits in insulin signaling may represent a common risk factor for both T2DM and CNS-related deficits, which may stem from (partly) independent mechanisms.

Disrupted serotonin system development via early life antidepressant exposure impairs maternal care and increases serotonin receptor expression in adult female offspring

Manipulating serotonin (5-HT) levels in the developing brain elicits a range of effects on brain function and behavior. For example, early-life exposure to selective 5-HT reuptake inhibitor (SSRI) antidepressants disrupts dorsal raphe function and triggers aberrant adult behaviors such as increased passive stress coping and anhedonia. However, much less is understood about how alterations in 5-HT signaling in early life impact outcomes in female offspring, including critical social functions such as maternal care. The present study shows that early-life SSRI exposure disrupts adult female offspring's maternal behavior. Pregnant/postpartum female Sprague-Dawley rats were treated with the SSRI citalopram in drinking water or provided regular tap water as control. Female offspring were raised to adulthood and mated with treatment-naïve males. Following parturition, we observed maternal behavior during portions of the light and dark phases of postnatal days (P)1-14. Relative to controls, dams with a history of early-life SSRI exposure exhibited decreased maternal care, including diminished arched-back nursing, reduced licking and grooming of pups, and increased behavioral inconsistency. Brains were collected from dams with and without a history of early-life SSRI exposure to measure relative mRNA expression of select 5-HT receptor transcripts (5HTR1A, -1B, -2A, -2C) in regions involved in maternal care. Early-life SSRI exposure augmented expression of 5-HTR1A in the medial preoptic area and 5-HTR1B, 5-HTR2A, and 5-HTR2C in the prefrontal cortex. These results demonstrate that early alterations to 5-HT signaling through SSRI exposure may disrupt nurturing parental behaviors and 5-HT receptor expression in affected female rat offspring.

Perspective: Gestational Tryptophan Fluctuation Altering Neuroembryogenesis and Psychosocial Development

Tryptophan, as the sole precursor of serotonin, mainly derived from diets, is essential for neurodevelopment and immunomodulation. Gestational tryptophan fluctuation may account for the maternal-fetal transmission in determining neuroembryogenesis with long-lasting effects on psychological development. Personality disorders and social exclusion are related to psychosocial problems, leading to impaired social functioning. However, it is not clear how the fluctuation in mother-child transmission regulates the neuroendocrine development and gut microbiota composition in progeny due to that tryptophan metabolism in pregnant women is affected by multiple factors, such as diets (tryptophan-enriched or -depleted diet), emotional mental states (anxiety, depression), health status (hypertension, diabetes), and social support as well as stresses and management skills. Recently, we have developed a non-mammal model to rationalize those discrepancies without maternal effects. This perspective article outlines the possibility and verified the hypothesis in bully-victim research with this novel model: (1). Summarizes the effects of the maternal tryptophan administration on the neuroendocrine and microbial development in their offspring; (2). Highlights the inconsistency and limitations in studying the relationship between gestational tryptophan exposure and psychosocial development in humans and viviparous animals; and (3). Evidences that embryonic exposure to tryptophan and its metabolite modify bullying interactions in the chicken model. With the current pioneer researches on the biomechanisms underlying the bully-victim interaction, the perspective article provides novel insights for developing appropriate intervention strategies to prevent psychological disorders among individuals, especially those who experienced prenatal stress, by controlling dietary tryptophan and medication therapy during pregnancy.

Exposure to 3'Sialyllactose-Poor Milk during Lactation Impairs Cognitive Capabilities in Adulthood

Breast milk exerts pivotal regulatory functions early in development whereby it contributes to the maturation of brain and associated cognitive functions. However, the specific components of maternal milk mediating this process have remained elusive. Sialylated human milk oligosaccharides (HMOs) represent likely candidates since they constitute the principal neonatal dietary source of sialic acid, which is crucial for brain development and neuronal patterning. We hypothesize that the selective neonatal lactational deprivation of a specific sialylated HMOs, sialyl(alpha2,3)lactose (3′SL), may impair cognitive capabilities (attention, cognitive flexibility, and memory) in adulthood in a preclinical model. To operationalize this hypothesis, we cross-fostered wild-type (WT) mouse pups to B6.129-St3gal4^tm1.1Jxm/J dams, knock-out (KO) for the gene synthesizing 3′SL, thereby providing milk with approximately 80% 3′SL content reduction. We thus exposed lactating WT pups to a selective reduction of 3′SL and investigated multiple cognitive domains (including memory and attention) in adulthood. Furthermore, to account for the underlying electrophysiological correlates, we investigated hippocampal long-term potentiation (LTP). Neonatal access to 3′SL-poor milk resulted in decreased attention, spatial and working memory, and altered LTP compared to the control group. These results support the hypothesis that early-life dietary sialylated HMOs exert a long-lasting role in the development of cognitive functions.

Aberrant Early in Life Stimulation of the Stress-Response System Affects Emotional Contagion and Oxytocin Regulation in Adult Male Mice

Results over the last decades have provided evidence suggesting that HPA axis dysfunction is a major risk factor predisposing to the development of psychopathological behaviour. This susceptibility can be programmed during developmental windows of marked neuroplasticity, allowing early-life adversity to convey vulnerability to mental illness later in life. Besides genetic predisposition, also environmental factors play a pivotal role in this process, through embodiment of the mother's emotions, or via nutrients and hormones transferred through the placenta and the maternal milk. The aim of the current translational study was to mimic a severe stress condition by exposing female CD-1 mouse dams to abnormal levels of corticosterone (80 µg/mL) in the drinking water either during the last week of pregnancy (PreCORT) or the first one of lactation (PostCORT), compared to an Animal Facility Rearing (AFR) control group. When tested as adults, male mice from PostCORT offspring and somewhat less the PreCORT mice exhibited a markedly increased corticosterone response to acute restraint stress, compared to perinatal AFR controls. Aberrant persistence of adolescence-typical increased interest towards novel social stimuli and somewhat deficient emotional contagion also characterised profiles in both perinatal-CORT groups. Intranasal oxytocin (0 or 20.0 µg/kg) generally managed to reduce the stress response and restore a regular behavioural phenotype. Alterations in density of glucocorticoid and mineralocorticoid receptors, oxytocin and µ- and κ-opioid receptors were found. Changes differed as a function of brain areas and the specific age window of perinatal aberrant stimulation of the HPA axis. Present results provided experimental evidence in a translational mouse model that precocious adversity represents a risk factor predisposing to the development of psychopathological behaviour.

Recovering from depression with repetitive transcranial magnetic stimulation (rTMS): a systematic review and meta-analysis of preclinical studies

Repetitive transcranial magnetic stimulation (rTMS) has gained growing interest for the treatment of major depression (MDD) and treatment-resistant depression (TRD). Most knowledge on rTMS comes from human studies as preclinical application has been problematic. However, recent optimization of rTMS in animal models has laid the foundations for improved translational studies. Preclinical studies have the potential to help identify optimal stimulation protocols and shed light on new neurobiological-based rationales for rTMS use. To assess existing evidence regarding rTMS effects on depressive-like symptoms in rodent models, we conducted a comprehensive literature search in accordance with PRISMA guidelines (PROSPERO registration number: CRD42019157549). In addition, we conducted a meta-analysis to determine rTMS efficacy, performing subgroup analyses to examine the impact of different experimental models and neuromodulation parameters. Assessment of the depressive-like phenotype was quite homogeneous whilst rTMS parameters among the 23 included studies varied considerably. Most studies used a stress-induced model. Overall, results show a largely beneficial effect of active rTMS compared to sham stimulation, as reflected in the statistically significant recovery of both helplessness (SDM 1.34 [1.02;1.66]) and anhedonic (SDM 1.87 [1.02;2.72]) profiles. Improvement of the depressive-like phenotype was obtained in all included models and independently of rTMS frequency. Nonetheless, these results have limited predictive value for TRD patients as only antidepressant-sensitive models were used. Extending rTMS studies to other MDD models, corresponding to distinct endophenotypes, and to TRD models is therefore crucial to test rTMS efficacy and to develop cost-effective protocols, with the potential of yielding faster clinical responses in MDD and TRD.

Zebrafish exhibit associative learning for an aversive robotic stimulus

Zebrafish have quickly emerged as a species of choice in preclinical research, holding promise to advance the field of behavioral pharmacology through high-throughput experiments. Besides biological and heuristic considerations, zebrafish also constitute a fundamental tool that fosters the replacement of mammals with less sentient experimental subjects. Notwithstanding these features, experimental paradigms to investigate emotional and cognitive domains in zebrafish are still limited. Studies on emotional memories have provided sound methodologies to investigate fear conditioning in zebrafish, but these protocols may still benefit from a reconsideration of the independent variables adopted to elicit aversion. Here, we designed a fear-conditioning paradigm in which wild-type zebrafish were familiarized over six training sessions with an empty compartment and a fear-eliciting one. The fearful stimulus was represented by three zebrafish replicas exhibiting a fully synchronized and polarized motion as they were maneuvered along 3D trajectories by a robotic platform. When allowed to freely swim between the two compartments in the absence of the robotic stimulus (test session), zebrafish displayed a marked avoidance of the stimulus-paired one. To investigate whether fear conditioning was modulated by psychoactive compounds, two groups of zebrafish were administered ethanol (0.25% and 1.00%, ethanol/water, by volume) a few minutes before the test session. We observed that ethanol administration abolished the conditioned avoidance of the stimulus-paired compartment. Ultimately, this study confirms that robotic stimuli may be used in the design of fear-conditioning paradigms, which are sensitive to pharmacological manipulations.

Extreme enhancement or depletion of serotonin transporter function and serotonin availability in autism spectrum disorder

A variety of human and animal studies support the hypothesis that serotonin (5-hydroxytryptamine or 5-HT) system dysfunction is a contributing factor to the development of autism in some patients. However, many questions remain about how developmental manipulation of various components that influence 5-HT signaling (5-HT synthesis, transport, metabolism) persistently impair social behaviors. This review will summarize key aspects of central 5-HT function important for normal brain development, and review evidence implicating perinatal disruptions in 5-HT signaling in the pathophysiology of autism spectrum disorder. We discuss the importance, and relative dearth, of studies that explore the possible correlation to autism in the interactions between important intrinsic and extrinsic factors that may disrupt 5-HT homeostasis during development. In particular, we focus on exposure to 5-HT transport altering mechanisms such as selective serotonin-reuptake inhibitors or genetic polymorphisms in primary or auxiliary transporters of 5-HT, and how they relate to neurological stores of serotonin and its precursors. A deeper understanding of the many mechanisms by which 5-HT signaling can be disrupted, alone and in concert, may contribute to an improved understanding of the etiologies and heterogeneous nature of this disorder. We postulate that extreme bidirectional perturbations of these factors during development likely compound or synergize to facilitate enduring neurochemical changes resulting in insufficient or excessive 5-HT signaling, that could underlie the persistent behavioral characteristics of autism spectrum disorder.

Low empathy-like behaviour in male mice associates with impaired sociability, emotional memory, physiological stress reactivity and variations in neurobiological regulations

Deficits in empathy have been proposed to constitute a hallmark of several psychiatric disturbances like conduct disorder, antisocial and narcissistic personality disorders. Limited sensitivity to punishment, shallow or deficient affect and reduced physiological reactivity to environmental stressors have been often reported to co-occur with limited empathy and contribute to the onset of antisocial phenotypes. Empathy in its simplest form (i.e. emotional contagion) is addressed in preclinical models through the evaluation of the social transmission of emotional states: mice exposed to a painful stimulus display a higher response if in the presence of a familiar individual experiencing a higher degree of discomfort, than in isolation. In the present study, we investigated whether a reduction of emotional contagion can be considered a predictor of reduced sociality, sensitivity to punishment and physiological stress reactivity. To this aim, we first evaluated emotional contagion in a group of Balb/cJ mice and then discretised their values in four quartiles. The upper (i.e. Emotional Contagion Prone, ECP) and the lower (i.e. Emotional Contagion Resistant, ECR) quartiles constituted the experimental groups. Our results indicate that mice in the lower quartile are characterized by reduced sociability, impaired memory of negative events and dampened hypothalamic-pituitary-adrenocortical reactivity to external stressors. Furthermore, in the absence of changes in oxytocin receptor density, we show that these mice exhibit elevated concentrations of oxytocin and vasopressin and reduced density of BDNF receptors in behaviourally-relevant brain areas. Thus, not only do present results translate to the preclinical investigation of psychiatric disturbances, but also they can contribute to the study of emotional contagion in terms of its adaptive significance.

Neonatal corticosterone administration in rodents as a tool to investigate the maternal programming of emotional and immune domains

Neonatal experiences exert persistent influences on individual development. These influences encompass numerous domains including emotion, cognition, reactivity to external stressors and immunity. The comprehensive nature of the neonatal programming of individual phenotype is reverberated in the large amount of experimental data collected by many authors in several scientific fields: biomedicine, evolutionary and molecular biology. These data support the view that variations in precocious environmental conditions may calibrate the individual phenotype at many different levels. Environmental influences have been traditionally addressed through experimental paradigms entailing the modification of the neonatal environment and the multifactorial (e.g. behaviour, endocrinology, cellular and molecular biology) analysis of the developing individual's phenotype. These protocols suggested that the role of the mother in mediating the offspring's phenotype is often associated with the short-term effects of environmental manipulations on dam's physiology. Specifically, environmental manipulations may induce fluctuations in maternal corticosteroids (corticosterone in rodents) which, in turn, are translated to the offspring through lactation. Herein, I propose that this mother-offspring transfer mechanism can be leveraged to devise experimental protocols based on the exogenous administration of corticosterone during lactation. To support this proposition, I refer to a series of studies in which these protocols have been adopted to investigate the neonatal programming of individual phenotype at the level of emotional and immune regulations. While these paradigms cannot replace traditional studies, I suggest that they can be considered a valid complement.

Mice repeatedly exposed to Group-A β-Haemolytic Streptococcus show perseverative behaviors, impaired sensorimotor gating, and immune activation in rostral diencephalon

Repeated exposure to Group-A β-Haemolytic Streptococcus (GAS) may constitute a vulnerability factor in the onset and course of pediatric motor disturbances. GAS infections/colonization can stimulate the production of antibodies, which may cross the blood brain barrier, target selected brain areas (e.g. basal ganglia), and exacerbate motor alterations. Here, we exposed developing SJL male mice to four injections with a GAS homogenate and evaluated the following domains: motor coordination; general locomotion; repetitive behaviors; perseverative responses; and sensorimotor gating (pre-pulse inhibition, PPI). To demonstrate that behavioral changes were associated with immune-mediated brain alterations, we analyzed, in selected brain areas, the presence of infiltrates and microglial activation (immunohistochemistry), monoamines (HPLC), and brain metabolites (in vivo Magnetic Resonance Spectroscopy). GAS-exposed mice showed increased repetitive and perseverative behaviors, impaired PPI, and reduced concentrations of serotonin in prefrontal cortex, a brain area linked to the behavioral domains investigated, wherein they also showed remarkable elevations in lactate. Active inflammatory processes were substantiated by the observation of infiltrates and microglial activation in the white matter of the anterior diencephalon. These data support the hypothesis that repeated GAS exposure may elicit inflammatory responses in brain areas involved in motor control and perseverative behavior, and result in phenotypic abnormalities.

The Snark was a Boojum - reloaded

In this article, we refer to an original opinion paper written by Prof. Frank Beach in 1950 ("The Snark was a Boojum"). In his manuscript, Beach explicitly criticised the field of comparative psychology because of the disparity between the original understanding of comparativeness and its practical overly specialised implementation. Specialisation encompassed both experimental species (rats accounted for 70% of all subjects) and test paradigms (dominated by conditioning/learning experiments). Herein, we attempt to evaluate the extent to which these considerations apply to current behavioural neuroscience. Such evaluation is particularly interesting in the context of "translational research" that has recently gained growing attention. As a community, we believe that preclinical findings are intended to inform clinical practice at the level of therapies and knowledge advancements. Yet, limited reproducibility of experimental results and failures to translate preclinical research into clinical trial sindicate that these expectations are not entirely fulfilled. Theoretical considerations suggest that, before concluding that a given phenomenon is of relevance to our species, it should be observed in more than a single experimental model (be it an animal strain or species) and tested in more than a single standardized test battery. Yet, current approaches appear limited in terms of variability and overspecialised in terms of operative procedures. Specifically, as in 1950, rodents (mice instead of rats) still constitute the vast majority of animal species investigated. Additionally, the scientific community strives to homogenise experimental test strategies, thereby not only limiting the generalizability of the findings, but also working against the design of innovative approaches. Finally, we discuss the importance of evolutionary-adaptive considerations within the field of laboratory research. Specifically, resting upon empirical evidence indicating that developing individuals adjust their long-term phenotype according to early environmental demands, we propose that current rearing and housing standards do not adequately prepare experimental subjects to their actual adult environments. Specifically, while the adult life of a laboratory animal is characterized by frequent stimulations and challenges, the neonatal life is dominated by quietness and stability. We suggest that such form of mismatch may remarkably influence the reproducibility and reliability of experimental findings.

Prenatal corticosterone and adolescent URB597 administration modulate emotionality and CB1 receptor expression in mice

RATIONALE

The central endocannabinoid system (eCB system) sustains the activity of the hypothalamus-pituitary-adrenal (HPA) axis in mediating individual emotional responses. Deviation in maturational trajectories of these two physiological systems, may persistently adjust individual behavioral phenotype.

OBJECTIVE

We investigated, in outbred CD1 male mice, whether exposure to prenatal stress may influence short- and long-term emotional and neurochemical responses to a pharmacological stimulation of the eCB system during adolescence.

METHODS

To mimic prenatal stress, pregnant mice were supplemented with corticosterone in the drinking water (33.3 mg/l); their adolescent male offspring received daily injections of the fatty acid amide hydrolase inhibitor, URB597 (0.4 mg/kg), in order to enhance eCB signaling. Mice were then tested for: locomotor activity during adolescence and locomotor activity, anxiogenic, and anhedonic profiles in adulthood. We analyzed the expression of CB1 receptors (CB1Rs) in prefrontal cortex, hippocampus, striatum, and cerebellum in adulthood.

RESULTS

Corticosterone administration (PC group) resulted, in adolescence, in a reduction in body weight and locomotion, while in adulthood, in increased anxiety-related behavior and reduced CB1Rs expression in cerebellum. URB597 exposure reduced locomotor activity and increased anhedonia in adulthood. CB1Rs were up-regulated in striatum and hippocampus and down-regulated in the cerebellum. PC-URB597 mice failed to show reductions in locomotion; exhibited increased risk assessment behavior; and showed reduced CB1Rs expression within the prefrontal cortex.

CONCLUSIONS

Present results provide support to the hypothesis that precocious manipulations mapping onto the HPA axis and eCB system may persistently adjust individual emotional responses and eCB system plasticity.

Endocannabinoid receptor deficiency affects maternal care and alters the dam's hippocampal oxytocin receptor and brain-derived neurotrophic factor expression

Maternal care is the newborn's first experience of social interaction, and this influences infant survival, development and social competences throughout life. We recently found that postpartum blocking of the endocannabinoid receptor-1 (CB1R) altered maternal behaviour. In the present study, maternal care was assessed by the time taken to retrieve pups, pups' ultrasonic vocalisations (USVs) and pup body weight, comparing CB1R deleted (CB1R KO) versus wild-type (WT) mice. After culling on postpartum day 8, hippocampal expression of oxytocin receptor (OXTR), brain-derived neurotrophic factor (BDNF) and stress-mediating factors were evaluated in CB1R KO and WT dams. Comparisons were also performed with nulliparous (NP) CB1R KO and WT mice. Compared to WT, CB1R KO dams were slower to retrieve their pups. Although the body weight of the KO pups did not differ from the weight of WT pups, they emitted fewer USVs. This impairment of the dam-pup relationship correlated with a significant reduction of OXTR mRNA and protein levels among CB1R KO dams compared to WT dams. Furthermore, WT dams exhibited elevated OXTR mRNA expression, as well as increased levels of mineralocorticoid and glucocorticoid receptors, compared to WT NP mice. By contrast, CB1R KO dams showed no such elevation of OXTR expression, alongside lower BDNF and mineralocorticoid receptors, as well as elevated corticotrophin-releasing hormone mRNA levels, when compared to CB1R KO NP. Thus, it appears that the disruption of endocannabinoid signalling by CB1R deletion alters expression of the OXTR, apparently leading to deleterious effects upon maternal behaviour.

Emotional, endocrine and brain anandamide response to social challenge in infant male rats

Individual response to stress is orchestrated by hypothalamus-pituitary axis corticosteroids, although critically modulated by the central endocannabinoid (eCB) system. Whilst the role of the eCB system in stress response and emotional homeostasis in adult animals has been extensively studied, it has only been scarcely investigated in developing animals. Herein, we aimed to investigate the participation of eCB ligands in the stress responses of neonate rats. Twelve days-old Wistar male rats were exposed to a social challenge (repeated brief isolations from dam and littermates), which resulted in a significant increase in serum corticosterone levels. This stressful social challenge also decreased spontaneous rat pups' behaviours and augmented isolation-induced ultrasonic vocalizations. Notably, a specific decrease in anandamide content (not 2-AG) was observed within the hippocampus (not in the striatum). However, the enhancement of eCB signalling by URB597 administration (0.1mg/kg) did not affect the adrenocortical and behavioural responses to this postnatal social challenge. The influence of gestational stress was also evaluated in the infant offspring of rats dams exposed to restraint stress (PRS, three episodes/day, on gestation days 14 till delivery); however, PRS did not modify neonate responses to this postnatal challenge. Present findings provide evidence for the participation of the eCB system in the acute response to a social challenge in infant male rats. However, the lack of evidences from the pharmacological study encourages the investigation of alternative and/or indirect mechanisms that may participate in the behavioural and endocrine response to stress in developing animals. Further experiments are still needed to clarify the interactions between the HPA axis and the eCB system in stress reactivity at early postnatal stages.

Neonatal tryptophan depletion and corticosterone supplementation modify emotional responses in adult male mice

The serotonergic system and the hypothalamic-pituitary-adrenal (HPA) axis are crucially involved in the regulation of emotions. Specifically, spontaneous and/or environmentally mediated modulations of the functionality of these systems early in development may favour the onset of depressive- and anxiety-related phenotypes. While the independent contribution of each of these systems to the emergence of abnormal phenotypes has been detailed in clinical and experimental studies, only rarely has their interaction been systematically investigated. Here, we addressed the effects of reduced serotonin and environmental stress during the early stages of postnatal life on emotional regulations in mice. To this aim, we administered, to outbred CD1 mouse dams, during their first week of lactation, a tryptophan deficient diet (T) and corticosterone via drinking water (C; 80μg/ml). Four groups of dams (animal facility rearing, AFR; T treated, T; C treated, C; T and C treated, TC) and their male offspring were used in the study. Maternal care was scored throughout treatment and adult offspring were tested for: anhedonia (progressive ratio schedule); anxiety-related behaviour (approach-avoidance conflict paradigm); BDNF, dopamine and serotonin concentrations in selected brain areas. T, C and TC treatments reduced active maternal care compared to AFR. Adult TC offspring showed significantly increased anxiety- and anhedonia-related behaviours, reduced striatal and increased hypothalamic BDNF and reduced dopamine and serotonin in the prefrontal cortex and their turnover in the hippocampus. Thus, present findings support the view that neonatal variations in the functionality of the serotonergic system and of HPA axis may jointly contribute to induce emotional disturbances in adulthood.

Prenatal stress and peripubertal stimulation of the endocannabinoid system differentially regulate emotional responses and brain metabolism in mice

The central endocannabinoid system (ECS) and the hypothalamic-pituitary-adrenal-axis mediate individual responses to emotionally salient stimuli. Their altered developmental adjustment may relate to the emergence of emotional disturbances. Although environmental influences regulate the individual phenotype throughout the entire lifespan, their effects may result particularly persistent during plastic developmental stages (e.g. prenatal life and adolescence). Here, we investigated whether prenatal stress – in the form of gestational exposure to corticosterone supplemented in the maternal drinking water (100 mg/l) during the last week of pregnancy – combined with a pharmacological stimulation of the ECS during adolescence (daily fatty acid amide hydrolase URB597 i.p. administration - 0.4 mg/kg - between postnatal days 29–38), influenced adult mouse emotional behaviour and brain metabolism measured through in vivo quantitative magnetic resonance spectroscopy. Compared to control mice, URB597-treated subjects showed, in the short-term, reduced locomotion and, in the long term, reduced motivation to execute operant responses to obtain palatable rewards paralleled by reduced levels of inositol and taurine in the prefrontal cortex. Adult mice exposed to prenatal corticosterone showed increased behavioural anxiety and reduced locomotion in the elevated zero maze, and altered brain metabolism (increased glutamate and reduced taurine in the hippocampus; reduced inositol and N-Acetyl-Aspartate in the hypothalamus). Present data further corroborate the view that prenatal stress and pharmacological ECS stimulation during adolescence persistently regulate emotional responses in adulthood. Yet, whilst we hypothesized these factors to be interactive in nature, we observed that the consequences of prenatal corticosterone administration were independent from those of ECS drug-induced stimulation during adolescence.