Early maternal deprivation and neonatal single administration with a cannabinoid agonist induce long-term sex-dependent psychoimmunoendocrine effects in adolescent rats

The long-term effects of maternal deprivation on the number and size of inhibitory interneurons in the rat amygdala and nucleus accumbens

Introduction

There is an increasing evidence supporting the hypothesis that traumatic experiences during early developmental periods might be associated with psychopathology later in life. Maternal deprivation (MD) in rodents has been proposed as an animal model for certain aspects of neuropsychiatric disorders.

Methods

To determine whether early-life stress leads to changes in GABAergic, inhibitory interneurons in the limbic system structures, specifically the amygdala and nucleus accumbens, 9-day-old Wistar rats were exposed to a 24 h MD. On postnatal day 60 (P60), the rats were sacrificed for morphometric analysis and their brains were compared to the control group.

Results

Results show that MD affect GABAergic interneurons, leading to the decrease in density and size of the calcium-binding proteins parvalbumin-, calbindin-, and calretinin-expressing interneurons in the amygdala and nucleus accumbens.

Discussion

This study indicates that early stress in life leads to changes in the number and morphology of the GABAergic, inhibitory interneurons in the amygdala and nucleus accumbens, most probably due to the loss of neurons during postnatal development and it further contributes to understanding the effects of maternal deprivation on brain development.

One day away from mum has lifelong consequences on brain and behaviour

This chapter presents a brief overview of attachment theory and discusses the importance of the neonatal period in shaping an individual's physiological and behavioural responses to stress later in life, with a focus on the role of the parent-infant relationship, particularly in rodents. In rodents, the role of maternal behaviours goes far beyond nutrition, thermoregulation and excretion, acting as hidden regulators of the pup's physiology and development. In this review, we will discuss the inhibitory role of specific maternal behaviours on the ACTH and corticosterone (CORT) stress response. The interest of our group to explore the long-term consequences of maternal deprivation for 24 h (DEP) at different ages (3 days and 11 days) in rats was sparked by its opposite effects on ACTH and CORT levels. In early adulthood, DEP3 animals (males and females alike) show greater negative impact on affective behaviours and stress related parameters than DEP11, indicating that the latter is more resilient in tests of anxiety-like behaviour. These findings create an opportunity to explore the neurobiological underpinnings of vulnerability and resilience to stress-related disorders. The chapter also provides a brief historical overview and highlights the relevance of attachment theory, and how DEP helps to understand the effects of childhood parental loss as a risk factor for depression, schizophrenia, and PTSD in both childhood and adulthood. Furthermore, we present the concept of environmental enrichment (EE), its effects on stress responses and related behavioural changes and its benefits for rats previously subjected to DEP, along with the clinical implications of DEP and EE.

Neurobiological mechanisms involved in maternal deprivation-induced behaviours relevant to psychiatric disorders

Parental care is essential for proper development of stress response and emotion-related behaviours. Epidemiological studies show that parental loss in childhood represents a major risk factor for the development of mental disorders throughout the lifespan, including schizophrenia, depression, and anxiety. In most mammalian species, the mother is the main source of care and maternal behaviours regulate several physiological systems. Maternal deprivation (DEP) for 24 h is a paradigm widely used to disinhibit the hypothalamic-pituitary-adrenal axis response to stress during the stress hyporesponsive period. In this mini-review we will highlight the main DEP-induced neurobiological and behavioural outcomes, including alterations on stress-related hormones, neurogenesis, neurotransmitter/neuromodulatory systems and neuroinflammation. These neurobiological changes may be reflected by aberrant behaviours, which are relevant to the study of mental disorders. The evidence indicates that DEP consequences depend on the sex, the age when the DEP takes place and the age when the animals are evaluated, reflecting dynamic plasticity and individual variability. Individual variability and sex differences have a great relevance for the study of biological factors of stress resilience and vulnerability and the DEP paradigm is a suitable model for evaluation of phenotypes of stress- and emotion-related psychopathologies.

Sex-dependence and comorbidities of the early-life adversity induced mental and metabolic disease risks: Where are we at?

Early-life adversity (ELA) is a major risk factor for developing later-life mental and metabolic disorders. However, if and to what extent ELA contributes to the comorbidity and sex-dependent prevalence/presentation of these disorders remains unclear. We here comprehensively review and integrate human and rodent ELA (pre- and postnatal) studies examining mental or metabolic health in both sexes and discuss the role of the placenta and maternal milk, key in transferring maternal effects to the offspring. We conclude that ELA impacts mental and metabolic health with sex-specific presentations that depend on timing of exposure, and that human and rodent studies largely converge in their findings. ELA is more often reported to impact cognitive and externalizing domains in males, internalizing behaviors in both sexes and concerning the metabolic dimension, adiposity in females and insulin sensitivity in males. Thus, ELA seems to be involved in the origin of the comorbidity and sex-specific prevalence/presentation of some of the most common disorders in our society. Therefore, ELA-induced disease states deserve specific preventive and intervention strategies.

Wisket rat model of schizophrenia: Impaired motivation and, altered brain structure, but no anhedonia

It is well-known that the poor cognition in schizophrenia is strongly linked to negative symptoms, including motivational deficit, which due to, at least partially, anhedonia. The goal of this study was to explore whether the schizophrenia-like Wisket animals with impaired motivation (obtained in the reward-based hole-board test), also show decreased hedonic behavior (investigated with the sucrose preference test). While neurochemical alterations of different neurotransmitter systems have been detected in the Wisket rats, no research has been performed on structural changes. Therefore, our additional aim was to reveal potential neuroanatomical and structural alterations in different brain regions in these rats. The rats showed decreased general motor activity (locomotion, rearing and exploration) and impaired task performance in the hole-board test compared to the controls, whereas no significant difference was observed in the sucrose preference test between the groups. The Wisket rats exhibited a significant decrease in the frontal cortical thickness and the hippocampal area, and moderate increases in the lateral ventricles and cell disarray in the CA3 subfield of hippocampus. To our knowledge, this is the first study to investigate the hedonic behavior and neuroanatomical alterations in a multi-hit animal model of schizophrenia. The results obtained in the sucrose preference test suggest that anhedonic behavior might not be involved in the impaired motivation obtained in the hole-board test. The neuropathological changes agree with findings obtained in patients with schizophrenia, which refine the high face validity of the Wisket model.

Increased negative affect when combining early-life maternal deprivation with adolescent, but not adult, cocaine exposure in male rats: regulation of hippocampal FADD

RATIONALE

Besides early drug initiation during adolescence, another vulnerability factor associated with increased risk for substance abuse later in life is early-life stress. One way of assessing such combined risk is by evaluating the emergence of increased negative affect during withdrawal (i.e., linked to persistence in drug seeking).

OBJECTIVES

To compare the impact of maternal deprivation with cocaine exposure at different ages on affective-like behavior and hippocampal neuroplasticity regulation.

METHODS

Maternal deprivation was performed in whole-litters of Sprague-Dawley rats (24 h, PND 9-10). Cocaine (15 mg/kg, 7 days, i.p.) was administered in adolescence (PND 33-39) or adulthood (PND 64-70). Changes in affective-like behavior were assessed by diverse tests across time (forced-swim, open field, novelty-suppressed feeding, sucrose preference). Hippocampal multifunctional FADD protein (balance between cell death and plasticity) was evaluated by Western blot.

RESULTS

Exposing rats to either maternal deprivation or adolescent cocaine did not modulate affective-like behavior immediately during adolescence, but increased negative affect in adulthood. Maternal deprivation combined with adolescent cocaine advanced the negative impact to adolescence. Adult cocaine exposure alone and/or in combination with maternal deprivation did not induce any behavioral changes at the time-points analyzed. FADD regulation might participate in the neural adaptations taking place in the hippocampus in relation to the observed behavioral changes.

CONCLUSIONS

Adolescence is a more vulnerable period, as compared to adulthood, to the combined impact of cocaine and early maternal deprivation, thus suggesting that the accumulation of stress early in life can anticipate the negative behavioral outcome associated with drug consumption.

Do Adolescent Exposure to Cannabinoids and Early Adverse Experience Interact to Increase the Risk of Psychiatric Disorders: Evidence from Rodent Models

There have been growing concerns about the protracted effects of cannabis use in adolescents on emotion and cognition outcomes, motivated by evidence of growing cannabis use in adolescents, evidence linking cannabis use to various psychiatric disorders, and the increasingly perceived notion that cannabis is harmless. At the same time, studies suggest that cannabinoids may have therapeutic potential against the impacts of stress on the brain and behavior, and that young people sometimes use cannabinoids to alleviate feelings of depression and anxiety (i.e., “self-medication”). Exposure to early adverse life events may predispose individuals to developing psychopathology in adulthood, leading researchers to study the causality between early life factors and cognitive and emotional outcomes in rodent models and to probe the underlying mechanisms. In this review, we aim to better understand the long-term effects of cannabinoids administered in sensitive developmental periods (mainly adolescence) in rodent models of early life stress. We suggest that the effects of cannabinoids on emotional and cognitive function may vary between different sensitive developmental periods. This could potentially affect decisions regarding the use of cannabinoids in clinical settings during the early stages of development and could raise questions regarding educating the public as to potential risks associated with cannabis use.

Long term effects of stress on hippocampal function: Emphasis on early life stress paradigms and potential involvement of neuropeptide Y

The brain is both central in orchestrating the response to stress, and, a very sensitive target when such response is not controlled. In fact, stress has long been associated with the onset and/or exacerbation of several neuropsychiatric disorders such as anxiety, depression, and drug addiction. The hippocampus is a key brain region involved in the response to stress, not only due to its anatomical connections with the hypothalamic-pituitary-adrenal axis but also as a major target of stress mediators. The hippocampal dentate gyrus (DG)-CA3 circuit, composed of DG granule cells axons (mossy fibers) synapsing onto CA3 pyramidal cells, plays an essential role in memory encoding and retrieval, functions that are vulnerable to stress. Although naturally excitatory, this circuit is under the inhibitory control of GABAergic interneurons that maintain the excitation/inhibition balance. One subgroup of such interneurons produces neuropeptide Y (NPY), which has emerged as a promising endogenous stress "resilience molecule" due to its anxiolytic and anti-epileptic properties. Here we examine existing evidence that reveals a potential role for hilar NPY+ interneurons in mediating stress-induced changes in hippocampal function. We will focus specifically on rodent models of early life stress (ELS), defined as adverse conditions during the early postnatal period that can have profound consequences for neurodevelopment. Collectively, these findings suggest that the long-lasting effects of ELS might stem from the loss of GABAergic NPY+ cells, which then can lead to reduced inhibition in the DG-CA3 pathway. Such change might then lead to hyperexcitability and concomitant hippocampal-dependent behavioral deficits.

Kolaviron protects against cognitive deficits and cortico-hippocampal perturbations associated with maternal deprivation in rats

Prolonged separation of pups from their mother in early postnatal period can interfere with normal growth and development, resulting in different behavioral changes similar to features of schizophrenia in man. This study explored the cytoprotective action of kolaviron, a biflavonoid, on the prefrontal cortex and hippocampus of maternally deprived Wistar rats. Eight months old female rats were time-mated, and after delivery their pups were randomly assigned into four groups; group A received 0.5 ml of normal saline, group B received kolaviron orally (200 mg/kg/bw) on postnatal days (PND) 21–35, group C were maternally deprived on PND 9 for 24 hours, while group D were also maternally deprived on PND 9 for 24 hours, and then received kolaviron orally (200 mg/kg/bw) on PND 21–35. Behavioral studies (open field test, Morris water test, and Y-maze test) were conducted after the experiment prior to sacrifice. Some of the rats were anesthetized with ketamine and perfusion-fixed with 0.1 M phosphate buffered saline and 4% paraformaldehyde, while others were sacrificed by cervical dislocation for enzyme studies. The hippocampus and prefrontal cortex were excised from the brain and processed for tissue histology, histochemistry, and enzymatic analysis. Results revealed behavioral deficits, oxidative stress, degenerative changes, and astrocytosis in the prefrontal cortex and hippocampus of maternally deprived rats, but intervention with kolaviron caused significant improvement in neurobehavior, morphology, and neurochemistry in these brain areas. We concluded that kolaviron could protect the brain against neurological consequences of nutritional and environmental insults arising from maternal separation in early postnatal period.

Maternal regulation of the infant's hypothalamic-pituitary-adrenal axis stress response: Seymour 'Gig' Levine's legacy to neuroendocrinology

Thirty years ago, Seymour 'Gig' Levine published a serendipitous, yet, seminal finding with respect to the regulatory role of maternal presence on the corticosterone stress response of neonatal rats during the developmental period known as the stress hyporesponsive period. At the same time, his group of students also investigated the stress response of infant monkeys with respect to maternal separation, as a means of understanding the stress to the primary caregiver resulting from disruptions of attachment. Gig and his group of students and collaborators, mainly in the USA and the Netherlands, investigated how initial social relationships buffer the stress response of nonhuman primates and rodent infants. His work in rodents involved determining how prolonged deprivation of maternal care disinhibits the stress response of neonates and how maternal behaviours regulate specific aspects of the hypothalamic-pituitary-adrenal axis. Maternal deprivation for 24 hours was useful for determining the importance of nutrition in suppressing the corticosterone stress response, whereas anogenital licking and grooming inhibited stress-induced adrenocortoctrophic hormone release, with the combination of both behaviours preventing the effects of maternal deprivation on the central hypothalamic stress response. Levine's group also studied the consequences of maternal deprivation on basal and stress-induced activity of the hypothalamic-pituitary-adrenal axis in juveniles and the persistent effects of the replacement of maternal behaviours on these parameters. Gig's legacy allowed many groups around the world to use the 24-hour maternal deprivation paradigm as an animal model of vulnerability and resilience to stress-related psychiatric disorders, as well as in studies of the neurobiological underpinnings of disruption of the mother-infant relationship and loss of parental care, a highly prevalent condition in humans. This review pays homage to a great scientist and mentor, whose discoveries paved the way for the understanding of how early social relationsships build resilience or lead to susceptibility to emotional disorders later in life.

Alcohol, psychomotor-stimulants and behaviour: methodological considerations in preclinical models of early-life stress

BACKGROUND

In order to assess the risk associated with early-life stress, there has been an increase in the amount of preclinical studies investigating early-life stress. There are many challenges associated with investigating early-life stress in animal models and ensuring that such models are appropriate and clinically relevant.

OBJECTIVES

The purpose of this review is to highlight the methodological considerations in the design of preclinical studies investigating the effects of early-life stress on alcohol and psychomotor-stimulant intake and behaviour.

METHODS

The protocols employed for exploring early-life stress were investigated and summarised. Experimental variables include animals, stress models, and endpoints employed.

RESULTS

The findings in this paper suggest that there is little consistency among these studies and so the interpretation of these results may not be as clinically relevant as previously thought.

CONCLUSION

The standardisation of these simple stress procedures means that results will be more comparable between studies and that results generated will give us a more robust understanding of what can and may be happening in the human and veterinary clinic.

Multimodal early-life stress induces biological changes associated to psychopathologies

Evidences suggest the contributive role of early-life stress (ELS) to affective and anxiety disorders. Chronic exposure to the same stressor may generate habituation, while the exposure to different and repeated stressors gradually promotes maladaptive plasticity. Therefore, to further understand the effects of heterotypic stressors during early life period, male Wistar rat pups (P1-P21) were exposed to Multimodal ELS paradigm. Results indicate pups did not habituate to multimodal ELS and neonates respond to both physical and psychogenic stressors. Adult rats that underwent ELS protocol showed significant lower sucrose intake, decreased latency to immobility in the forced swim test and increased latency to light compartment in the light-dark test when compared to control group. Although it has been shown that ELS-induced changes in hippocampus can be used as biomarkers, multimodal ELS did not significantly alter BDNF, Tyrosine Kinase B (TrkB) receptor expression or neurogenesis in the hippocampus. Taken together, these findings indicate that multimodal ELS protocol can be an interesting experimental model for understanding long-term psychiatric disorders associated with stress. Indeed, our data with neurogenesis, BDNF and TrkB, and conflicting data from the literature, suggest that additional studies on synaptic plasticity/intracellular cascades would help to detect the underlying mechanisms.

Maternal deprivation induces alterations in cognitive and cortical function in adulthood

Early life trauma is a risk factor for a number of neuropsychiatric disorders, including schizophrenia (SZ). The current study assessed how an early life traumatic event, maternal deprivation (MD), alters cognition and brain function in rodents. Rats were maternally deprived in the early postnatal period and then recognition memory (RM) was tested in adulthood using the novel object recognition task. The expression of catechol-o-methyl transferase (COMT) and glutamic acid decarboxylase (GAD67) were quantified in the medial prefrontal cortex (mPFC), ventral striatum, and temporal cortex (TC). In addition, depth EEG recordings were obtained from the mPFC, vertex, and TC during a paired-click paradigm to assess the effects of MD on sensory gating. MD animals exhibited impaired RM, lower expression of COMT in the mPFC and TC, and lower expression of GAD67 in the TC. Increased bioelectric noise was observed at each recording site of MD animals. MD animals also exhibited altered information theoretic measures of stimulus encoding. These data indicate that a neurodevelopmental perturbation yields persistent alterations in cognition and brain function, and are consistent with human studies that identified relationships between allelic differences in COMT and GAD67 and bioelectric noise. These changes evoked by MD also lead to alterations in shared information between cognitive and primary sensory processing areas, which provides insight into how early life trauma confers a risk for neurodevelopmental disorders, such as SZ, later in life.

Phenotypic outcomes in adolescence and adulthood in the scarcity-adversity model of low nesting resources outside the home cage

Early life adversity is known to disrupt behavioral trajectories and many rodent models have been developed to characterize these stress-induced outcomes. One example is the scarcity-adversity model of low nesting resources. This model employs resource scarcity (i.e., low nesting materials) to elicit adverse caregiving conditions (including maltreatment) toward rodent neonates. Our lab utilizes a version of this model wherein caregiving exposures occur outside the home cage during the first postnatal week. The aim of this study was to determine adolescent and adult phenotypic outcomes associated with this model, including assessment of depressive- and anxiety-like behaviors and performance in different cognitive domains. Exposure to adverse caregiving had no effect on adolescent behavioral performance whereas exposure significantly impaired adult behavioral performance. Further, adult behavioral assays revealed substantial differences between sexes. Overall, data demonstrate the ability of repeated exposure to brief bouts of maltreatment outside the home cage in infancy to impact the development of several behavioral domains later in life.

Interaction between neonatal maternal deprivation and serum leptin levels on metabolism, pubertal development, and sexual behavior in male and female rats

BACKGROUND

Maternal deprivation (MD) during neonatal life can have long-term effects on metabolism and behavior, with males and females responding differently. We previously reported that MD during 24 h at postnatal day (PND) 9 blocks the physiological neonatal leptin surge in both sexes. It is known that modifications in neonatal leptin levels can affect metabolism in adulthood. Thus, we hypothesized that at least some of the long-term metabolic changes that occur in response to MD are due to the decline in serum leptin during this critical period of development. Hence, we predicted that treatment with leptin during MD would normalize these metabolic changes, with this response also differing between the sexes.

METHODS

MD was carried-out in Wistar rats for 24 h on PND9. Control and MD rats of both sexes were treated from PND 9 to 13 with leptin (3 mg/kg/day sc) or vehicle. Weight gain, food intake, glucose tolerance, and pubertal onset were monitored. Sexual behavior was analyzed in males. Rats were killed at PND90, and serum hormones and hypothalamic neuropeptides involved in metabolic control and reproduction were measured. Results were analyzed by three-way analysis of covariance using sex, MD, and leptin treatment as factors and litter as the covariate and employing repeated measures where appropriate.

RESULTS

In males, MD advanced the external signs of puberty and increased serum insulin and triglyceride levels and hypothalamic proopiomelanocortin mRNA levels at PND90. Neonatal leptin treatment normalized these effects. In contrast, MD decreased circulating triglycerides, as well as estradiol levels, in females at PND90 and these changes were also normalized by neonatal leptin treatment. Neonatal leptin treatment also had long-term effects in control rats as it advanced the external signs of puberty in control males, but delayed them in females. Neonatal leptin treatment increased serum insulin and hypothalamic mRNA levels of the leptin receptor and cocaine- and amphetamine-regulated transcript in control males and increased orexin mRNA levels in controls of both sexes. Although pubertal onset in males was advanced by either MD or neonatal leptin treatment in males and delayed by leptin treatment in females, the mRNA levels of hypothalamic neuropeptides and receptors related to reproduction were not affected by MD or neonatal leptin treatment in either sex at PND90.

CONCLUSIONS

These findings indicate that some of the long-term changes in metabolic and reproductive parameters induced by MD, such as advanced pubertal onset and increased hypothalamic proopiomelanocortin (POMC) expression, hyperinsulinemia, and hypertriglyceridemia in adult males and decreased serum triglyceride and estradiol levels in females, are most likely due to the decrease in leptin levels during the period of MD.

Sex-dependence of anxiety-like behavior in cannabinoid receptor 1 (Cnr1) knockout mice

Epidemiological data suggest women are at increased risk for developing anxiety and depression, although the mechanisms for this sex/gender difference remain incompletely understood. Pre-clinical studies have begun to investigate sex-dependent emotional learning and behavior in rodents, particularly as it relates to psychopathology; however, information about how gonadal hormones interact with the central nervous system is limited. We observe greater anxiety-like behavior in male mice with global knockout of the cannabinoid 1 receptor (Cnr1) compared to male, wild-type controls as measured by percent open arm entries on an elevated plus maze test. A similar increase in anxiety-like behavior, however, is not observed when comparing female Cnr1 knockouts to female wild-type subjects. Although, ovariectomy in female mice did not reverse this effect, both male and female adult mice with normative development were sensitive to Cnr1 antagonist-mediated increases in anxiety-like behavior. Together, these data support an interaction between sex, potentially mediated by gonadal hormones, and the endocannabinoid system at an early stage of development that is critical for establishing adult anxiety-like behavior.

Physical exercise prevents short and long-term deficits on aversive and recognition memory and attenuates brain oxidative damage induced by maternal deprivation

It is known from previous research that physical exercise prevents long-term memory deficits induced by maternal deprivation in rats. But we could not assume similar effects of physical exercise on short-term memory, as short- and long-term memories are known to result from some different memory consolidation processes. Here we demonstrated that, in addition to long-term memory deficit, the short-term memory deficit resultant from maternal deprivation in object recognition and aversive memory tasks is also prevented by physical exercise. Additionally, one of the mechanisms by which the physical exercise influences the memory processes involves its effects attenuating the oxidative damage in the maternal deprived rats' hippocampus and prefrontal cortex.

Long Term Hippocampal and Cortical Changes Induced by Maternal Deprivation and Neonatal Leptin Treatment in Male and Female Rats

Maternal deprivation (MD) during neonatal life has diverse long-term behavioral effects and alters the development of the hippocampus and frontal cortex, with several of these effects being sexually dimorphic. MD animals show a marked reduction in their circulating leptin levels, not only during the MD period, but also several days later (PND 13). A neonatal leptin surge occurs in rodents (beginning around PND 5 and peaking between PND 9 and 10) that has an important neurotrophic role. We hypothesized that the deficient neonatal leptin signaling of MD rats could be involved in the altered development of their hippocampus and frontal cortex. Accordingly, a neonatal leptin treatment in MD rats would at least in part counteract their neurobehavioural alterations. MD was carried out in Wistar rats for 24 h on PND 9. Male and female MD and control rats were treated from PND 9 to 13 with rat leptin (3 mg/kg/day sc) or vehicle. In adulthood, the animals were submitted to the open field, novel object memory test and the elevated plus maze test of anxiety. Neuronal and glial population markers, components of the glutamatergic and cannabinoid systems and diverse synaptic plasticity markers were evaluated by PCR and/or western blotting. Main results include: 1) In some of the parameters analyzed, neonatal leptin treatment reversed the effects of MD (eg., mRNA expression of hippocampal IGF1 and protein expression of GFAP and vimentin) partially confirming our hypothesis; 2) The neonatal leptin treatment, per se, exerted a number of behavioral (increased anxiety) and neural effects (eg., expression of the following proteins: NG2, NeuN, PSD95, NCAM, synaptophysin). Most of these effects were sex dependent. An adequate neonatal leptin level (avoiding excess and deficiency) appears to be necessary for its correct neuro-programing effect.

Environmental enrichment does not reverse the effects of maternal deprivation on NMDAR and Balb/c mice behaviors

Early adverse life experiences have been associated with anxiety-like behavior and memory impairment. N-methyl-d-aspartate receptors (NMDARs) play an important role in brain development. Enriched environments are known to positively influence emotional and cognitive functions in the brain. We examined the effects of maternal deprivation (MD) on NMDAR subunits in the hippocampus, locomotor activity, anxiety behaviors, and learning-memory performance of Balb/c mice. We also examined whether these effects could be reversed by raising the offspring in an enriched environment. The mice were separated from their mothers for a single 24h episode on postnatal day (PND) 9. The mice were weaned on day 21 and were housed under either standard (SE) or enriched (EE) environmental conditions. Emotional behaviors and cognitive processes of mice were evaluated using an open field (OF) test, an elevated plus maze (EPM) test, and a Morris water-maze (MWM). NMDAR subunits (GluN1, GluN2A, and GluN2B) mRNA expression levels in the hippocampus were examined by real-time PCR. In OF, MD had no effect on horizontal locomotor activity. MD increased anxiety-like behaviors in the EPM and decreased spatial learning performance in MWM; however, these effects were not reversed by EE. MD (in SE and EE conditions) increased GluN1, GluN2A, and GluN2B mRNA expressions in the hippocampus. In conclusion, MD led to the deterioration of the emotional and cognitive processes during adulthood. Moreover, environmental enrichment did not reverse the deleterious effects of the MD on emotional and cognitive functions and increased the NMDAR levels.

Early maternal deprivation enhances voluntary alcohol intake induced by exposure to stressful events later in life

In the present study, we aimed to assess the impact of early life stress, in the form of early maternal deprivation (MD, 24 h on postnatal day, pnd, 9), on voluntary alcohol intake in adolescent male and female Wistar rats. During adolescence, from pnd 28 to pnd 50, voluntary ethanol intake (20%, v/v) was investigated using the two-bottle free choice paradigm. To better understand the relationship between stress and alcohol consumption, voluntary alcohol intake was also evaluated following additional stressful events later in life, that is, a week of alcohol cessation and a week of alcohol cessation combined with exposure to restraint stress. Female animals consumed more alcohol than males only after a second episode of alcohol cessation combined with restraint stress. MD did not affect baseline voluntary alcohol intake but increased voluntary alcohol intake after stress exposure, indicating that MD may render animals more vulnerable to the effects of stress on alcohol intake. During adolescence, when animals had free access to alcohol, MD animals showed lower body weight gain but a higher growth rate than control animals. Moreover, the higher growth rate was accompanied by a decrease in food intake, suggesting an altered metabolic regulation in MD animals that may interact with alcohol intake.

The maternal deprivation animal model revisited

Early life stress, in the form of MD (24h at pnd 9), interferes with brain developmental trajectories modifying both behavioral and neurobiochemical parameters. MD has been reported to enhance neuroendocrine responses to stress, to affect emotional behavior and to impair cognitive function. More recently, changes in body weight gain, metabolic parameters and immunological responding have also been described. Present data give support to the fact that neuronal degeneration and/or astrocyte proliferation are present in specific brain regions, mainly hippocampus, prefrontal cortex and hypothalamus, which are particularly vulnerable to the effects of neonatal stress. The MD animal model arises as a valuable tool for the investigation of the brain processes occurring at the narrow time window comprised between pnd 9 and 10 that are critical for the establishment of brain circuitries critical for the regulation of behavior, metabolism and energy homeostasis. In the present review we will discuss three possible mechanisms that might be crucial for the effects of MD, namely, the rapid increase in glucocorticoids, the lack of the neonatal leptin surge, and the enhanced endocannabinoid signaling during the specific critical period of MD. A better understanding of the mechanisms underlying the detrimental consequences of MD is a concern for public health and may provide new insights into mental health prevention strategies and into novel therapeutic approaches in neuropsychiatry.

The interplay of early-life stress, nutrition, and immune activation programs adult hippocampal structure and function

Early-life adversity increases the vulnerability to develop psychopathologies and cognitive decline later in life. This association is supported by clinical and preclinical studies. Remarkably, experiences of stress during this sensitive period, in the form of abuse or neglect but also early malnutrition or an early immune challenge elicit very similar long-term effects on brain structure and function. During early-life, both exogenous factors like nutrition and maternal care, as well as endogenous modulators, including stress hormones and mediator of immunological activity affect brain development. The interplay of these key elements and their underlying molecular mechanisms are not fully understood. We discuss here the hypothesis that exposure to early-life adversity (specifically stress, under/malnutrition and infection) leads to life-long alterations in hippocampal-related cognitive functions, at least partly via changes in hippocampal neurogenesis. We further discuss how these different key elements of the early-life environment interact and affect one another and suggest that it is a synergistic action of these elements that shapes cognition throughout life. Finally, we consider different intervention studies aiming to prevent these early-life adversity induced consequences. The emerging evidence for the intriguing interplay of stress, nutrition, and immune activity in the early-life programming calls for a more in depth understanding of the interaction of these elements and the underlying mechanisms. This knowledge will help to develop intervention strategies that will converge on a more complete set of changes induced by early-life adversity.

Modulation of early stress-induced neurobiological changes: a review of behavioural and pharmacological interventions in animal models

Childhood adversity alters the predisposition to psychiatric disorders later in life. Those with psychiatric conditions and a history of early adversity exhibit a higher incidence of treatment resistance compared with individuals with no such history. Modulation of the influence early stress exerts over neurobiology may help to prevent the development of psychiatric disorders in some cases, while attenuating the extent of treatment resistance in those with established psychiatric disorders. This review aims to critically evaluate the ability of behavioural, environmental and pharmacologic interventions to modulate neurobiological changes induced by early stress in animal models. Databases were systematically searched to locate literature relevant to this review. Early adversity was defined as stress that resulted from manipulation of the mother-infant relationship. Analysis was restricted to animal models to enable characterisation of how a given intervention altered specific neurobiological changes induced by early stress. A wide variety of changes in neurobiology due to early stress are amenable to intervention. Behavioural interventions in childhood, exercise in adolescence and administration of epigenetic-modifying drugs throughout life appear to best modulate cellar and behavioural alterations induced by childhood adversity. Other pharmacotherapies, such as endocannabinoid system modulators, anti-inflammatories and antidepressants can also influence these neurobiological and behavioural changes that result from early stress, although findings are less consistent at present and require further investigation. Further work is required to examine the influence that behavioural interventions, exercise and epigenetic-modifying drugs exert over alterations that occur following childhood stress in human studies, before possible translational into clinical practice is possible.

Sex-dependent long-term effects of adolescent exposure to THC and/or MDMA on neuroinflammation and serotoninergic and cannabinoid systems in rats

BACKGROUND AND PURPOSE

Many young people consume ecstasy as a recreational drug and often in combination with cannabis. In this study, we aimed to mimic human consumption patterns and investigated, in male and female animals, the long-term effects of Δ(9) -tetrahydrocannabinol (THC) and 3,4-methylenedioxymethamphetamine (MDMA) on diverse neuroinflammation and neurotoxic markers.

EXPERIMENTAL APPROACH

Male and female Wistar rats were chronically treated with increasing doses of THC and/or MDMA during adolescence. The effects of THC and/or MDMA on glial reactivity and on serotoninergic and cannabinoid systems were assessed by immunohistochemistry in the hippocampus and parietal cortex.

KEY RESULTS

THC increased the area staining for glial fibrilar acidic protein in both sexes. In males, both drugs, either separately or in combination, increased the proportion of reactive microglia cells [ionized calcium binding adaptor molecule 1 (Iba-1)]. In contrast, in females, each drug, administered alone, decreased of this proportion, whereas the combination of both drugs resulted in a 'normalization' to control values. In males, MDMA reduced the number of SERT positive fibres, THC induced the opposite effect and the group receiving both drugs did not significantly differ from the controls. In females, MDMA reduced the number of SERT positive fibres and the combination of both drugs counteracted this effect. THC also reduced immunostaining for CB1 receptors in females and this effect was aggravated by the combination with MDMA.

CONCLUSIONS AND IMPLICATIONS

Adolescent exposure of rats to THC and/or MDMA induced long-term, sex-dependent neurochemical and glial alterations, and revealed interactions between the two drugs.

LINKED ARTICLES

This article is part of a themed section on Cannabinoids 2013. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2014.171.issue-6.

Early maternal deprivation immunologically primes hippocampal synapses by redistributing interleukin-1 receptor type I in a sex dependent manner

Challenges experienced in early life cause an enduring phenotypical shift of immune cells towards a sensitised state that may lead to an exacerbated reaction later in life and contribute to increased vulnerability to neurological diseases. Peripheral and central inflammation may affect neuronal function through cytokines such as IL-1. The extent to which an early life challenge induces long-term alteration of immune receptors organization in neurons has not been shown. We investigated whether a single episode of maternal deprivation (MD) on post-natal day (PND) 9 affects: (i) the synapse distribution of IL-1RI together with subunits of NMDA and AMPA receptors; and (ii) the interactions between IL-1RI and the GluN2B subunit of the NMDAR in the long-term, at PND 45. MD increased IL-1RI levels and IL-1RI interactions with GluN2B at the synapse of male hippocampal neurons, without affecting the total number of IL-1RI or NMDAR subunits. Although GluN2B and GluN2A were slightly but not significantly changed at the synapse, their ratio was significantly decreased in the hippocampus of the male rats who had experienced MD; the levels of the GluA1 and GluA2 subunits of the AMPAR were also decreased. These changes were not observed immediately after the MD episode. None of the observed alterations occurred in the hippocampus of the females or in the prefrontal cortex of either sex. These data reveal a long-term, sex-dependent modification in receptor organisation at the hippocampal post-synapses following MD. We suggest that this effect might contribute to priming hippocampal synapses to the action of IL-1β.

Postnatal maternal separation enhances tonic GABA current of cortical layer 5 pyramidal neurons in juvenile rats and promotes genesis of GABAergic neurons in neocortical molecular layer and subventricular zone in adult rats

Postnatal maternal separation (PMS) has been shown to be associated with an increased vulnerability to psychiatric illnesses in adulthood. However, the underlying neurological mechanisms are not well understood. Here we evaluated its effects on neurogenesis and tonic GABA currents of cortical layer 5 (L5) pyramidal neurons. PMS not only increased cell proliferation in the subventricular zone, cortical layer 1 and hippocampal dentate gyrus in the adult brain, but also promoted the newly generated cells to differentiate into GABAergic neurons, and PMS adult brain maintained higher ratios of GABAergic neurons in the survival of newly generated cells within 5 days immediately post PMS. Additionally, PMS increased the tonic currents at P7-10 and P30-35 in cortical L5 pyramidal cells. Our results suggest that the newly generated GABAergic neurons and the low GABA concentration-activated tonic currents may be involved in the development of psychiatric disorders after PMS.

Sex-dependent psychoneuroendocrine effects of THC and MDMA in an animal model of adolescent drug consumption

Ecstasy is a drug that is usually consumed by young people at the weekends and frequently, in combination with cannabis. In the present study we have investigated the long-term effects of administering increasing doses of delta-9-tetrahydrocannabinol [THC; 2.5, 5, 10 mg/kg; i.p.] from postnatal day (pnd) 28 to 45, alone and/or in conjunction with 3,4-methylenedioxymethamphetamine [MDMA; two daily doses of 10 mg/kg every 5 days; s.c.] from pnd 30 to 45, in both male and female Wistar rats. When tested one day after the end of the pharmacological treatment (pnd 46), MDMA administration induced a reduction in directed exploration in the holeboard test and an increase in open-arm exploration in an elevated plus maze. In the long-term, cognitive functions in the novel object test were seen to be disrupted by THC administration to female but not male rats. In the prepulse inhibition test, MDMA-treated animals showed a decrease in prepulse inhibition at the most intense prepulse studied (80 dB), whereas in combination with THC it induced a similar decrease at 75 dB. THC decreased hippocampal Arc expression in both sexes, while in the frontal cortex this reduction was only evident in females. MDMA induced a reduction in ERK1/2 immunoreactivity in the frontal cortex of male but not female animals, and THC decreased prepro-orexin mRNA levels in the hypothalamus of males, although this effect was prevented when the animals also received MDMA. The results presented indicate that adolescent exposure to THC and/or MDMA induces long-term, sex-dependent psychophysiological alterations and they reveal functional interactions between the two drugs.

Maternal deprivation is associated with sex-dependent alterations in nociceptive behavior and neuroinflammatory mediators in the rat following peripheral nerve injury

Early-life stress is associated with an increased risk of developing affective disorders and chronic pain conditions. This study examined the effect of maternal deprivation (MD) on nociceptive responding prior to and following peripheral nerve injury (L5-L6 spinal nerve ligation [SNL]). Because neuroimmune signaling plays an important role in pain and affective disorders, associated alterations in glial and cytokine expression were assessed in key brain regions associated with emotional and nociceptive responding, the hippocampus and prefrontal cortex. MD female, but not male, rats exhibited thermal hypoalgesia and mechanical allodynia compared with control (non-MD) counterparts. SNL resulted in mechanical and cold allodynia in MD and control rats of both sexes. However, MD females exhibited enhanced SNL-induced allodynic responding compared with non-MD counterparts. Interleukin 6 (IL-6) expression was reduced in the prefrontal cortex of MD-SNL males when compared with non-SNL counterparts. Glial fibrillary acidic protein and IL-1β expression in the hippocampus of MD-SNL males was increased compared with non-MD controls. MD-SNL females exhibited reduced tumor necrosis factor alpha in the prefrontal cortex with a concomitant increase in IL-6 and tumor necrosis factor alpha expression in the hippocampus, compared with either MD or SNL alone. In conclusion, MD female, but not male, rats exhibit enhanced nociceptive responding following peripheral nerve injury, effects that may relate to the distinct neuroinflammatory profile observed in female versus male rats.

PERSPECTIVE

This study demonstrates that females rats exposed to early-life stress exhibit enhanced neuropathic pain responding, effects that are associated with alterations in neuroinflammatory mediators. Increased understanding of the interactions among early-life stress, gender, and pain may lead to the identification of novel therapeutic targets for the treatment of chronic pain disorders.

Behavioral deficits, abnormal corticosterone, and reduced prefrontal metabolites of adolescent rats subject to early life stress

The present study investigated the effect of early life stress in adolescent rats on brain metabolites, serum corticosterone, and depressive-like behavior. A group of rats was subject to early life stress from postnatal day (PND) 1 to 14. A matched control group was studied. Behavioral tests, serum corticosterone and high-resolution proton magnetic resonance spectroscopy were conducted between PND 30 and 40. In this study, adolescent rats exposed to early life stress demonstrated depressive-like behavior and increased serum corticosterone during adolescence. They also showed reduced glutamate, glutamine, and N-acetylaspartate (NAA) levels in the prefrontal cortex. A reduced myo-inositol level, consistent with astroglial deficits, was observed but was not statistically significant. Together, these findings characterize the effect of early life stress on adolescent animals and underscore the long-lasting and detrimental effects of childhood adversities.

Sex-dependent changes in brain CB1R expression and functionality and immune CB2R expression as a consequence of maternal deprivation and adolescent cocaine exposure

Early life stress has been associated with several psychiatric disorders, including drug addiction. Actually, maternal deprivation (MD) alters the endocannabinoid system, which participates in motivation and reward for drugs, including cocaine. At youth, the rate of cocaine abuse is alarmingly increasing. Herein, we have investigated the consequences of MD and/or adolescent cocaine exposure in brain CB1Rs and CB2Rs in immune tissues. Control and maternally deprived (24h on postnatal day, pnd, 9) male and female Wistar rats were administered cocaine (8mg/kg/day) or saline during adolescence (pnd 28-42). At adulthood, [(3)H]-CP-55,940 autoradiographic binding was employed for the analysis of CB1R density and CP-55,940-stimulated [(35)S]-GTPgammaS binding for CB1R functionality; CB2R expression was analyzed by Western blotting. Sex differences in CB1R expression and functionality were found, and MD induced important and enduring sex-dependent changes. In addition, the plastic changes induced by adolescent cocaine administration in brain CB1Rs were differentially influenced by early life events. MD increased spleen CB2R expression while adolescent cocaine administration attenuated this effect; cocaine exposure also diminished CB2R expression in bone marrow. Present findings provide evidence for changes in brain CB1R expression and functionality and immune CB2R expression as a consequence of early life stress and adolescent cocaine exposure, and indicate functional interactions between both treatments, which in many regions differ between males and females.

Interaction between neonatal allopregnanolone administration and early maternal separation: effects on adolescent and adult behaviors in male rat

Endogenous neurosteroid level fluctuations are related to several emotional and behavioral alterations. Neurosteroids also have important roles during neurodevelopment, with there being a relationship between modification of their levels in neurodevelopmental periods and behavioral alterations in adolescence and adulthood. Early maternal separation (EMS) is a stressful event that also alters neurodevelopment and adolescent and adult behaviors. The aim of the present study is to analyze the interaction between the effects of the neonatal alteration of allopregnanolone (AlloP), neurosteroid that increase its levels after acute stress presentation, and EMS on adolescent exploration and adult anxiety and sensorimotor gating in male rats. AlloP (10 mg/kg s.c.) was administrated between postnatal day 5 (PN5) and PN9, and a single 24-hour period of EMS was carried out on PN9. Exploration was analyzed at PN40 and PN60. At adult age (PN85), anxiety was tested by means of the elevated plus-maze test (EPM), and sensorimotor gating by means of prepulse inhibition test (PPI). PPI deterioration has been considered as a reliable indicator of diseases such as schizophrenia. Results showed that the previous neonatal AlloP administration neutralized the effects of EMS in the adolescent exploration (increase of traveled distance and decrease of head-dips). In adult age, an anxiolytic-like profile was observed as a consequence of EMS. Finally, EMS and neonatal AlloP disrupted PPI. Taken together, these data show the important role that physiological neonatal AlloP levels and stressful events play in neural development, adult behavior and vulnerability to neurodevelopmental disorders such as schizophrenia.

Maternal deprivation exacerbates the response to a high fat diet in a sexually dimorphic manner

Maternal deprivation (MD) during neonatal life has diverse long-term effects, including affectation of metabolism. Indeed, MD for 24 hours during the neonatal period reduces body weight throughout life when the animals are maintained on a normal diet. However, little information is available regarding how this early stress affects the response to increased metabolic challenges during postnatal life. We hypothesized that MD modifies the response to a high fat diet (HFD) and that this response differs between males and females. To address this question, both male and female Wistar rats were maternally deprived for 24 hours starting on the morning of postnatal day (PND) 9. Upon weaning on PND22 half of each group received a control diet (CD) and the other half HFD. MD rats of both sexes had significantly reduced accumulated food intake and weight gain compared to controls when raised on the CD. In contrast, when maintained on a HFD energy intake and weight gain did not differ between control and MD rats of either sex. However, high fat intake induced hyperleptinemia in MD rats as early as PND35, but not until PND85 in control males and control females did not become hyperleptinemic on the HFD even at PND102. High fat intake stimulated hypothalamic inflammatory markers in both male and female rats that had been exposed to MD, but not in controls. Reduced insulin sensitivity was observed only in MD males on the HFD. These results indicate that MD modifies the metabolic response to HFD intake, with this response being different between males and females. Thus, the development of obesity and secondary complications in response to high fat intake depends on numerous factors.

Maternal deprivation effects on brain plasticity and recognition memory in adolescent male and female rats

Data from both human and animal studies suggest that exposure to stressful life events at neonatal stages may increase the risk of psychopathology at adulthood. In particular, early maternal deprivation, 24 h at postnatal day (pnd) 9, has been associated with persistent neurobehavioural changes similar to those present in developmental psychopathologies such as depression and schizophrenic-related disorders. Most neuropsychiatric disorders first appear during adolescence, however, the effects of MD on adolescent animals' brain and behaviour have been scarcely explored. In the present study, we aimed to investigate the emotional and cognitive consequences of MD in adolescent male and female rats, as well as possible underlying neurobiological mechanisms within frontal cortex and hippocampus. Animals were exposed to a battery of behavioural tasks, from pnd 35 to 42, to evaluate cognitive [spontaneous alternation task (SAT) and novel object test (NOT)] and anxiety-related responses [elevated plus maze (EPM)] during adolescence. Changes in neuronal and glial cells, alterations in synaptic plasticity as well as modifications in cannabinoid receptor expression were investigated in a parallel group of control and adolescent (pnd 40) male and female animals. Notably, MD induced a significant impairment in recognition memory exclusively among females. A generalized decrease in NeuN expression was found in MD animals, together with an increase in hippocampal glial fibrillar acidic protein (GFAP) expression exclusively among MD adolescent males. In addition, MD induced in the frontal cortex and hippocampus of male and female adolescent rats a significant reduction in brain derived neurotrophic factor (BDNF) and postsynaptic density (PSD95) levels, together with a decrease in synaptophysin in frontal cortex and neural cell adhesion molecule (NCAM) in hippocampus. MD induced, in animals of both sexes, a significant reduction in CB1R expression, but an increase in CB2R that was statistically significant only for the frontal cortex. Taken together, these results indicate that adolescent females are more vulnerable than males to the cognitive deficits derived from MD despite the changes in neural cells, cannabinoid receptors, as well as the reduction in neural plasticity seem to be similar in both sexes. Further investigation is needed to understand the neurobiological mechanisms underlying the sexual dimorphisms associated to the MD effects, and thus, for a better understanding of the specific sex-dependent vulnerabilities to early life stress. This article is part of the Special Issue entitled 'Neurodevelopmental Disorders'.

A comparative, developmental, and clinical perspective of neurobehavioral sexual dimorphisms

Women and men differ in a wide variety of behavioral traits and in their vulnerability to developing certain mental disorders. This review endeavors to explore how recent preclinical and clinical research findings have enhanced our understanding of the factors that underlie these disparities. We start with a brief overview of some of the important genetic, molecular, and hormonal determinants that contribute to the process of sexual differentiation. We then discuss the importance of animal models in studying the mechanisms responsible for sex differences in neuropsychiatric disorders (e.g., drug dependence) - with a special emphasis on experimental models based on the neurodevelopmental and "three hits" hypotheses. Next, we describe the most common brain phenotypes observed in vivo with magnetic resonance imaging. We discuss the challenges in interpreting these phenotypes vis-à-vis the underlying neurobiology and revisit the known sex differences in brain structure from birth, through adolescence, and into adulthood. This is followed by a presentation of pertinent clinical and epidemiological data that point to important sex differences in the prevalence, course, and expression of psychopathologies such as schizophrenia, and mood disorders including major depression and posttraumatic stress disorder. Recent evidence implies that mood disorders and psychosis share some common genetic predispositions and neurobiological bases. Therefore, modern research is emphasizing dimensional representation of mental disorders and conceptualization of schizophrenia and major depression as a continuum of cognitive deficits and neurobiological abnormalities. Herein, we examine available evidence on cerebral sexual dimorphism to verify if sex differences vary quantitatively and/or qualitatively along the psychoses-depression continuum. Finally, sex differences in the prevalence of posttraumatic disorder and drug abuse have been described, and we consider the genomic and molecular data supporting these differences.

Maternal deprivation and adolescent cannabinoid exposure impact hippocampal astrocytes, CB1 receptors and brain-derived neurotrophic factor in a sexually dimorphic fashion

We have recently reported that early maternal deprivation (MD) for 24 h [postnatal day (PND) 9-10] and/or an adolescent chronic treatment with the cannabinoid agonist CP-55,940 (CP) [0.4 mg/kg, PND 28-42] in Wistar rats induced, in adulthood, diverse sex-dependent long-term behavioral and physiological modifications. Here we show the results obtained from investigating the immunohistochemical analysis of CB1 cannabinoid receptors, glial fibrillary acidic protein (GFAP) positive (+) cells and brain-derived neurotrophic factor (BDNF) expression in the hippocampus of the same animals. MD induced, in males, a significant increase in the number of GFAP+ cells in CA1 and CA3 areas and in the polymorphic layer of the dentate gyrus (DG), an effect that was attenuated by CP in the two latter regions. Adolescent cannabinoid exposure induced, in control non-deprived males, a significant increase in the number of GFAP+ cells in the polymorphic layer of the DG. MD induced a decrease in CB1 expression in both sexes, and this effect was reversed in males by the cannabinoid treatment. In turn, the drug "per se" induced, in males, a general decrease in CB1 immunoreactivity, and the opposite effect was observed in females. Cannabinoid exposure tended to reduce BDNF expression in CA1 and CA3 of females, whereas MD counteracted this trend and induced an increase of BDNF in females. As a whole, the present results show sex-dependent long-term effects of both MD and juvenile cannabinoid exposure as well as functional interactions between the two treatments.

The endocannabinoid system in critical neurodevelopmental periods: sex differences and neuropsychiatric implications

This review focuses on the endocannabinoid system as a crucial player during critical periods of brain development, and how its disturbance either by early life stressful events or cannabis consumption may lead to important neuropsychiatric signs and symptoms. First we discuss the advantages and limitations of animal models within the framework of neuropsychiatric research and the crucial role of genetic and environmental factors for the establishment of vulnerable phenotypes. We are becoming aware of important sex differences that have emerged in relation to the psychobiology of cannabinoids. We will discuss sexual dimorphisms observed within the endogenous cannabinoid system, as well as those observed with exogenously administered cannabinoids. We start with how the expression of cannabinoid CB(1) receptors is regulated throughout development. Then, we discuss recent results showing how an experimental model of early maternal deprivation, which induces long-term neuropsychiatric symptoms, interacts in a sex-dependent manner with the brain endocannabinoid system during development. This is followed by a discussion of differential vulnerability to the pathological sequelae stemming from cannabinoid exposure during adolescence. Next we talk about sex differences in the interactions between cannabinoids and other drugs of abuse. Finally, we discuss the potential implications that organizational and activational actions of gonadal steroids may have in establishing and maintaining sex dependence in the neurobiological actions of cannabinoids and their interaction with stress.

The endocannabinoid system in the regulation of emotions throughout lifespan: a discussion on therapeutic perspectives

Alterations in emotion regulation processes may form the basis of psychopathologies. The endocannabinoid (eCB) system, composed of endogenous ligands, the enzymatic machinery in charge of their metabolism and the specific metabotropic receptors, has emerged as a major neuromodulatory system critically involved in the control of emotional homeostasis and stress responsiveness. Data from animal models indicate that the eCB system plays a key role in brain development, and is probably involved in the control of emotional states from early developmental stages. The present review summarizes the latest information on the role of the eCB system in emotionality and anxiety-related disorders throughout the lifespan. Putative therapeutic strategies based on the pharmacological modulation of this system will be discussed. Given the fact that the pharmacological modulation of the eCB system has recently arisen as a promising strategy in the management of anxiety and mood disorders, the potential efficacy of this pharmacological approach (i.e. blockers of the catabolic pathway) will be discussed, as well as pharmacological alternatives such as modulators of cannabinoid receptors other than the classical CB1 receptor, or administration of other plant-derived compounds (e.g. cannabidiol).

A single episode of maternal deprivation impairs the motivation for cocaine in adolescent mice

RATIONALE

Early-life adverse events, like maternal deprivation (MD), have been associated with the later development of mood and anxiety disorders. Scarce data are available describing behavioural and endocrine alterations in maternally deprived (DEP) animals during the periadolescent period. We hypothesize that a single episode of MD early in life would alter reward function and lead to a long-lasting behavioural and neuroendocrine changes during adolescence.

OBJECTIVES

Our aim was to evaluate the effects of a single episode of MD in CD1 adolescent mice (postnatal day 35) on a range of tests for anxiety- and depression-related behaviours (open field, elevated plus maze and tail suspension test). We further assess whether these effects could affect cocaine self-administration behaviour. In order to correlate behavioural and neuroendocrine responses to stress, brain-derived neurotrophic factor (BDNF) levels were assessed in brain structures related to emotional and cognitive processes.

RESULTS

During the cocaine self-administration, the time required for achieving the acquisition criteria was significantly increased and the breaking point values in progressive schedule were significantly reduced in DEP adolescent mice, suggesting impairment in rewarding functions. The behavioural tests also confirm an increase in anxiety- and depression-related behaviours in DEP adolescent mice. The results on BDNF level indicated a decrease in response to MD in amygdala and hippocampus, confirming the behavioural data.

CONCLUSIONS

Our findings demonstrated for the first time that a single episode of early MD can impair the motivation for cocaine consumption in adolescent mice and can be associated with anxiety- and depressive-like behaviour.

Timing is everything: evidence for a role of corticolimbic endocannabinoids in modulating hypothalamic-pituitary-adrenal axis activity across developmental periods

Growing evidence suggests that the endocannabinoid system is vital to ensuring normative maturation of the brain into adulthood. Endocannabinoid signaling contributes to guiding pro-neurogenic processes in early life and the development of neurotransmitter systems. Moreover, there is extensive evidence that recruitment of the endocannabinoid system is crucial in the regulation of neuroendocrine responses to stress via the hypothalamic-pituitary-adrenal (HPA) axis, and contributes to subsequent psychopathological consequences associated with emotionality and anxiety. These stress-induced physiological and behavioural sequelae are regulated by neural structures within the corticolimbic circuit, including the amygdala, hypothalamus, hippocampus, and prefrontal cortex. Based on evidence demonstrating endocannabinoid system involvement in both development and stress-induced changes in HPA axis function, it is reasonable to suggest that endocannabinoid signaling is an important mediator of interactions between stress responsivity and maturational stage. In this review, we discuss the ontogeny of the endocannabinoid system in the central nervous system, clinical and rodent models demonstrating short- and long-term effects of stress exposure, regulation of HPA axis responsivity by endocannabinoid signaling, as well as pharmacological and stress models indicating involvement of the endocannabinoid system in early post-natal and adolescent development on stress reactivity of the HPA, the corticolimbic system, and behaviour.

Sex-dependent effects of maternal deprivation and adolescent cannabinoid treatment on adult rat behaviour

Early life experiences such as maternal deprivation (MD) exert long-lasting changes in adult behaviour and reactivity to stressors. Adolescent exposure to cannabinoids is a predisposing factor in developing certain psychiatric disorders. Therefore, the combination of the two factors could exacerbate the negative consequences of each factor when evaluated at adulthood. The objective of this study was to investigate the long-term effects of early MD [24 hours at postnatal day (PND) 9] and/or an adolescent chronic treatment with the cannabinoid agonist CP-55,940 (0.4 mg/kg, PND 28-42) on diverse behavioural and physiological responses of adult male and female Wistar rats. We tested them in the prepulse inhibition (PPI) of the startle response and analysed their exploratory activity (holeboard) and anxiety (elevated plus maze, EPM). In addition, we evaluated their adrenocortical reactivity in response to stress and plasma leptin levels. Maternal behaviour was measured before and after deprivation. MD induced a transient increase of maternal behaviour on reuniting. In adulthood, maternally deprived males showed anxiolytic-like behaviour (or increased risk-taking behaviour) in the EPM. Adolescent exposure to the cannabinoid agonist induced an impairment of the PPI in females and increased adrenocortical responsiveness to the PPI test in males. Both, MD and adolescent cannabinoid exposure also induced sex-dependent changes in plasma leptin levels and body weights. The present results indicate that early MD and adolescent cannabinoid exposure exerted distinct sex-dependent long-term behavioural and physiological modifications that could predispose to the development of certain neuropsychiatric disorders, though no synergistic effects were found.