Early maternal deprivation reduces the expression of BDNF and NMDA receptor subunits in rat hippocampus

Methamphetamine reversed maternal separation-induced decrease in nerve growth factor in the ventral hippocampus

Stress has been suggested to predispose individuals to drug abuse. The early life stress of maternal separation (MS) is known to alter the response to drugs of abuse later in life. Exposure to either stress or methamphetamine has been shown to alter neurotrophic factors in the brain. Changes in neurotrophin levels may contribute to the underlying molecular mechanisms responsible for drug use- and stress-induced behaviours. The purpose of the present study was to investigate the individual effects of MS and methamphetamine administration during adolescence and the combined effects of both stressors on brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) levels in the dorsal and ventral hippocampus (HC) in adulthood. Methamphetamine administration (1 mg/kg, daily from postnatal day (PND) 33 to 36 and from PND 39 to 42), MS and the combination of the two stressors resulted in decreased BDNF levels in both the dorsal and ventral HC. MS decreased NGF levels in the ventral HC which was restored by methamphetamine administration in adolescence. In the dorsal HC, NGF remained unaltered by either stressor alone or in combination. We propose that the restoration of NGF levels in the ventral HC may reflect a possible compensatory mechanism in response to methamphetamine exposure in adolescence following the early life stress of MS.

Delayed BDNF alterations in the prefrontal cortex of rats exposed to prenatal stress: preventive effect of lurasidone treatment during adolescence

Psychiatric diseases may often represent the consequence of exposure to adverse events early in life. Accordingly, exposure to stress during gestation in rats has a strong impact on development and can cause long-term abnormalities in adult behavior. Considering that neuronal plasticity has emerged as a major vulnerability element in psychiatric disorders, we investigated the postnatal developmental profile of Brain-Derived Neurotrophic Factor expression (BDNF), an important mediator for long-term functional deterioration associated to mental illness, in male and female rats following exposure to prenatal stress (PNS). Since we found that the majority of alterations became fully manifest at early adulthood, we tried to prevent these abnormalities with an early pharmacological intervention. To address this point, we treated rats during adolescence with the multi-receptor antipsychotic lurasidone, which was proven to be effective in animal models of schizophrenia. Interestingly, we show that lurasidone treatment was able to prevent the reduction of BDNF expression in adult rats that were exposed to PNS. Collectively, our results provide further support to the notion that exposure to early life stress has a negative impact on neuronal plasticity and that pharmacological intervention during critical time windows may prove effective in preventing neuroplastic dysfunction, leading to long-term beneficial effects on brain function.

Exposure to dim light at night during early development increases adult anxiety-like responses

Early experiences produce effects that may persist throughout life. Therefore, to understand adult phenotype, it is important to investigate the role of early environmental stimuli in adult behavior and health. Artificial light at night (LAN) is an increasingly common phenomenon throughout the world. However, animals, including humans, evolved under dark night conditions. Many studies have revealed affective, immune, and metabolic alterations provoked by aberrant light exposure and subsequent circadian disruption. Pups are receptive to entraining cues from the mother and then light early during development, raising the possibility that the early life light environment may influence subsequent behavior. Thus, to investigate potential influences of early life exposure to LAN on adult phenotype, we exposed mice to dim (~5 lux; full spectrum white light) or dark (~0 lux) nights pre- and/or postnatally. After weaning at 3 weeks of age, all mice were maintained in dark nights until adulthood (9 weeks of age) when behavior was assessed. Mice exposed to dim light in early life increased anxiety-like behavior and fearful responses on the elevated plus maze and passive avoidance tests. These mice also displayed reduced growth rates, which ultimately normalized during adolescence. mRNA expression of brain derived neurotrophic factor (BDNF), a neurotrophin previously linked to early life environment and adult phenotype, was not altered in the prefrontal cortex or hippocampus by early life LAN exposure. Serum corticosterone concentrations were similar between groups at weaning, suggesting that early life LAN does not elicit a long-term physiologic stress response. Dim light exposure did not influence behavior on the open field, novel object, sucrose anhedonia, or forced swim tests. Our data highlight the potential deleterious consequences of low levels of light during early life to development and subsequent behavior. Whether these changes are due to altered maternal behavior or persistent circadian abnormalities incurred by LAN remains to be determined.

Sex-specific disruptions in spatial memory and anhedonia in a "two hit" rat model correspond with alterations in hippocampal brain-derived neurotrophic factor expression and signaling

Post-mortem studies have demonstrated reduced expression of brain-derived neurotrophic factor (BDNF) in the hippocampus of schizophrenia and major depression patients. The "two hit" hypothesis proposes that two or more major disruptions at specific time points during development are involved in the pathophysiology of these mental illnesses. However, the role of BDNF in these "two hit" effects is unclear. Our aim was to behaviorally characterize a "two hit" rat model of developmental stress accompanied by an in-depth assessment of BDNF expression and signalling. Wistar rats were exposed to neonatal maternal separation (MS) stress and/or adolescent/young-adult corticosterone (CORT) treatment. In adulthood, models of cognitive and negative symptoms of mental illness were analyzed. The hippocampus was then dissected into dorsal (DHP) and ventral (VHP) regions and analyzed by qPCR for exon-specific BDNF gene expression or by Western blot for BDNF protein expression and downstream signaling. Male "two hit" rats showed marked disruptions in short-term spatial memory (Y-maze) which were absent in females. However, female "two hit" rats showed signs of anhedonia (sucrose preference test), which were absent in males. Novel object recognition and anxiety (elevated plus maze) were unchanged by either of the two "hits". In the DHP, MS caused a male-specific increase in BDNF Exons I, II, IV, VII, and IX mRNA but a decrease in mature BDNF and phosphorylated TrkB (pTrkB) protein expression in adulthood. In the VHP, BDNF transcript expression was unchanged; however, in female rats only, MS significantly decreased mature BDNF and pTrkB protein expression in adulthood. These data demonstrate that MS causes region-specific and sex-specific long-term effects on BDNF expression and signaling and, importantly, mRNA expression does not always infer protein expression. Alterations to BDNF signaling may mediate the sex-specific effects of developmental stress on anhedonic behaviors.

Long-term effects of maternal deprivation on the neuronal soma area in the rat neocortex

Early separation of rat pups from their mothers (separatio a matrem) is considered and accepted as an animal model of perinatal stress. Adult rats, separated early postnatally from their mothers, are developing long-lasting changes in the brain and neuroendocrine system, corresponding to the findings observed in schizophrenia and affective disorders. With the aim to investigate the morphological changes in this animal model we exposed 9-day-old (P9) Wistar rats to a 24 h maternal deprivation (MD). At young adult age rats were sacrificed for morphometric analysis and their brains were compared with the control group bred under the same conditions, but without MD. Rats exposed to MD had a 28% smaller cell soma area in the prefrontal cortex (PFCX), 30% in retrosplenial cortex (RSCX), and 15% in motor cortex (MCX) compared to the controls. No difference was observed in the expression of glial fibrillary acidic protein in the neocortex of MD rats compared to the control group. The results of this study demonstrate that stress in early life has a long-term effect on neuronal soma size in cingulate and retrosplenial cortex and is potentially interesting as these structures play an important role in cognition.

Sleep and protein synthesis-dependent synaptic plasticity: impacts of sleep loss and stress

Sleep has been ascribed a critical role in cognitive functioning. Several lines of evidence implicate sleep in the consolidation of synaptic plasticity and long-term memory. Stress disrupts sleep while impairing synaptic plasticity and cognitive performance. Here, we discuss evidence linking sleep to mechanisms of protein synthesis-dependent synaptic plasticity and synaptic scaling. We then consider how disruption of sleep by acute and chronic stress may impair these mechanisms and degrade sleep function.

A role for hippocampal PSA-NCAM and NMDA-NR2B receptor function in flavonoid-induced spatial memory improvements in young rats

The increase in incidence and prevalence of neurodegenerative diseases highlights the need for a more comprehensive understanding of how food components may affect neural systems. In particular, flavonoids have been recognized as promising agents capable of influencing different aspects of synaptic plasticity resulting in improvements in memory and learning in both animals and humans. Our previous studies highlight the efficacy of flavonoids in reversing memory impairments in aged rats, yet little is known about the effects of these compounds in healthy animals, particularly with respect to the molecular mechanisms by which flavonoids might alter the underlying synaptic modifications responsible for behavioral changes. We demonstrate that a 3-week intervention with two dietary doses of flavonoids (Dose I: 8.7 mg/day and Dose II: 17.4 mg/day) facilitates spatial memory acquisition and consolidation (24 recall) (p < 0.05) in young healthy rats. We show for the first time that these behavioral improvements are linked to increased levels in the polysialylated form of the neural adhesion molecule (PSA-NCAM) in the dentate gyrus (DG) of the hippocampus, which is known to be required for the establishment of durable memories. We observed parallel increases in hippocampal NMDA receptors containing the NR2B subunit for both 8.7 mg/day (p < 0.05) and 17.4 mg/day (p < 0.001) doses, suggesting an enhancement of glutamate signaling following flavonoid intervention. This is further strengthened by the simultaneous modulation of hippocampal ERK/CREB/BDNF signaling and the activation of the Akt/mTOR/Arc pathway, which are crucial in inducing changes in the strength of hippocampal synaptic connections that underlie learning. Collectively, the present data supports a new role for PSA-NCAM and NMDA-NR2B receptor on flavonoid-induced improvements in learning and memory, contributing further to the growing body of evidence suggesting beneficial effects of flavonoids in cognition and brain health.

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We have identified novel targets for the flavonoid actions in the brain.

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Flavonoid ingestion facilitates hippocampal-dependent learning in healthy animals.

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Flavonoids regulate hippocampal PSA-NCAM in the Dentate Gyrus of the hippocampus.

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Flavonoids modulate the levels of hippocampal glutamate receptors (NMDA-NR2B).

Repeated aripiprazole treatment regulates Bdnf, Arc and Npas4 expression under basal condition as well as after an acute swim stress in the rat brain

Despite the rapid control of schizophrenic symptoms is due to the ability of antipsychotic drugs (APDs) to block D2 receptors in the mesolimbic pathway, it is now well-established that the therapeutic effects rely on adaptive mechanisms set in motion by their long-term administration. Such neuroplastic mechanisms depend on the pharmacological profile of the drug employed, with marked differences existing between first and second generation APDs. On these bases, the major accomplishment of this work was to investigate neuroadaptive changes set in motion by repeated treatment with aripiprazole, a novel APD that is unique for being a partial agonist at dopamine D2 receptors. Moreover, given that stress plays a critical role in the exacerbation of disease symptoms, we also investigated whether aripiprazole could influence the dynamic response of the brain to an acute challenge. We found that repeated aripiprazole treatment in rats regulates the expression of different markers of neuroplasticity such as Bdnf, Arc and Npas4 in a brain-region specific fashion; more importantly, the expression of these molecules was significantly up-regulated by an acute swim stress only in aripiprazole-treated animals, which is suggestive of increased ability to cope with the adverse event. We indeed found an overall facilitation of Bdnf expression, an effect that is mainly evident in the prefrontal cortex on the pool of transcripts undergoing dendritic localization. Overall, our results provide novel information regarding the mechanisms through which aripiprazole may regulate brain function and could contribute to improve neuroplastic defects that are associated with schizophrenia symptomatology.

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.

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.

The effects of brain serotonin deficiency on behavioural disinhibition and anxiety-like behaviour following mild early life stress

Aberrant serotonin (5-HT) signalling and exposure to early life stress have both been suggested to play a role in anxiety- and impulsivity-related behaviours. However, whether congenital 5-HT deficiency × early life stress interactions influence the development of anxiety- or impulsivity-like behaviour has not been established. Here, we examined the effects of early life maternal separation (MS) stress on anxiety-like behaviour and behavioural disinhibition, a type of impulsivity-like behaviour, in wild-type (WT) and tryptophan hydroxylase 2 (Tph2) knock-in (Tph2KI) mice, which exhibit ~60-80% reductions in the levels of brain 5-HT due to a R439H mutation in Tph2. We also investigated the effects of 5-HT deficiency and early life stress on adult hippocampal neurogenesis, plasma corticosterone levels and several signal transduction pathways in the amygdala. We demonstrate that MS slightly increases anxiety-like behaviour in WT mice and induces behavioural disinhibition in Tph2KI animals. We also demonstrate that MS leads to a slight decrease in cell proliferation within the hippocampus and potentiates corticosterone responses to acute stress, but these effects are not affected by brain 5-HT deficiency. However, we show that 5-HT deficiency leads to significant alterations in SGK-1 and GSK3β signalling and NMDA receptor expression in the amygdala in response to MS. Together, these findings support a potential role for 5-HT-dependent signalling in the amygdala in regulating the long-term effects of early life stress on anxiety-like behaviour and behavioural disinhibition.

Type II pyrethroid deltamethrin produces antidepressant-like effects in mice

Pyrethroids, which are widely used insecticides with low acute toxicity in mammals, affect sodium channels in neurons. In primary culture of rat cortical neurons, the type II pyrethroid deltamethrin (DM) markedly enhances the expression of the mRNA of brain-derived neurotrophic factor (BDNF) and exerts neurotrophic effects. In this study, we investigated the antidepressant-like effect of DM in mice. The effects of DM were assessed using the forced swimming test (FST) and were compared with those of type I pyrethroid permethrin (PM). Intraperitoneal administration of DM (5 and 10mg/kg), but not of PM (10mg/kg), increased the expression of BDNF mRNA in the hippocampus. DM, but not PM, significantly decreased the immobility time in the FST, and did not affect locomotor activity and motor coordination, suggesting that DM has an antidepressant-like effect. This effect of DM was inhibited by intracerebroventricular injection of K252a, which is an inhibitor of the BDNF receptor TrkB, indicating that the antidepressant-like effects of DM are mediated by BDNF/TrkB signaling pathways. Repeated administration of DM, but not of PM, also exerted antidepressant-like effects, which were long lasting. The results of the present study suggest that DM possesses antidepressant-like properties, and may be a possible source for the development of drugs to treat neurodegenerative and psychiatric disorders including depression.

Enriched early life experiences reduce adult anxiety-like behavior in rats: a role for insulin-like growth factor 1

Early life experiences can affect brain development, contributing to shape interindividual differences in stress vulnerability and anxiety-like behavior. In rodents, high levels of maternal care have long-lasting positive effects on the behavior of the offspring and stress response; post-weaning rearing in an enriched environment (EE) or massage counteract the negative effects of maternal separation or prenatal stressors. We recently found that insulin-like growth factor 1 (IGF-1) is a key mediator of early EE or massage on brain development. Whether early enrichment of experience can induce long-lasting effects on anxiety-like behavior and whether IGF-1 is involved in these effects is not known. We assessed anxiety-like behavior by means of the elevated plus maze in control adult rats and in adult rats subjected to early EE or to massage. We found that both EE and massage reduced adult anxiety-like behavior. Early IGF-1 systemic injections in rat pups reared in standard condition mimic the effects of EE and massage, reducing anxiety-like behavior in the adult; blocking early IGF-1 action in massaged and EE animals prevents massage and EE effects. In EE and IGF-1-treated animals, we assessed the hippocampal expression of glucocorticoid receptors (GRs) at postnatal day 12 (P12) and P60, finding a significantly higher GR expression at P60 for both treatments. These results suggest that IGF-1 could be involved in mediating the long-lasting effects of early life experiences on vulnerability/resilience to stress in adults.

Prenatal stress changes the glycoprotein GPM6A gene expression and induces epigenetic changes in rat offspring brain

Prenatal stress (PS) exerts strong impact on fetal brain development and on adult offspring brain functions. Previous work demonstrated that chronic stress alters the mRNA expression of GPM6A, a neuronal glycoprotein involved in filopodium extension. In this work, we analyzed the effect of PS on gpm6a expression and the epigenetic mechanisms involved. Pregnant Wistar rats received restraint stress during the last week of gestation. Male offspring were sacrificed on postnatal days 28 and 60. Hippocampus and prefrontal cortex samples were analyzed for gene expression (qPCR for mRNAs and microRNAs), methylation status (bisulfite conversion) and protein levels. Hippocampal neurons in culture were used to analyze microRNA overexpression effects. Prenatal stress induced changes in gpm6a levels in both tissues and at both ages analyzed, indicating a persistent effect. Two CpG islands in the gpm6a gene were identified. Variations in the methylation pattern at three specific CpGs were found in hippocampus, but not in PFC samples from PS offspring. microRNAs predicted to target gpm6a were identified in silico. qPCR measurements showed that PS modified the expression of several microRNAs in both tissues, being microRNA-133b the most significantly altered. Further studies overexpressing this microRNA in neuronal cultures showed a reduction in gmp6a mRNA and protein level. Moreover filopodium density was also reduced, suggesting that GPM6A function was affected. Gestational stress affected gpm6a gene expression in offspring likely through changes in methylation status and in posttranscriptional regulation by microRNAs. Thus, our findings propose gpm6a as a novel target for epigenetic regulation during prenatal stress.

Neonatal allopregnanolone levels alteration: effects on behavior and role of the hippocampus

Several works have pointed out the importance of the neurosteroid allopregnanolone for the maturation of the central nervous system and for adult behavior. The alteration of neonatal allopregnanolone levels in the first weeks of life alters emotional adult behavior and sensory gating processes. Without ruling out brain structures, some of these behavioral alterations seem to be related to a different functioning of the hippocampus in adult age. We focus here on the different behavioral studies that have revealed the importance of neonatal allopregnanolone levels for the adult response to novel environmental stimuli, anxiety-related behaviors and processing of sensory inputs (prepulse inhibition). An increase in neonatal physiological allopregnanolone levels decreases anxiety and increases novelty responses in adult age, thus affecting the individual response to environmental cues. These effects are also accompanied by a decrease in prepulse inhibition, indicating alterations in sensory gating that have been related to that present in disorders, such as schizophrenia. Moreover, behavioral studies have shown that some of these effects are related to a different functioning of the dorsal hippocampus, as the behavioral effects (decrease in anxiety and locomotion or increase in prepulse inhibition) of intrahippocampal allopregnanolone infusions in adult age are not present in those subjects in whom neonatal allopregnanolone levels were altered. Recent data indicated that this hippocampal involvement may be related to alterations in the expression of gamma-aminobutyric-acid receptors containing α4 and δ subunits, molecular alterations that can persist into adult age and that can, in part, explain the reported behavioral disturbances.

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.

Prenatal nicotine and maternal deprivation stress de-regulate the development of CA1, CA3, and dentate gyrus neurons in hippocampus of infant rats

Adverse experiences by the developing fetus and in early childhood are associated with profound effects on learning, emotional behavior, and cognition as a whole. In this study we investigated the effects of prenatal nicotine exposure (NIC), postnatal maternal deprivation (MD) or the combination of the two (NIC+MD) to determine if hippocampal neuron development is modulated by exposure to drugs of abuse and/or stress. Growth of rat offspring exposed to MD alone or NIC+MD was repressed until after weaning. In CA1 but not CA3 of postnatal day 14 (P14) pups, MD increased pyramidal neurons, however, in dentate gyrus (DG), decreased granule neurons. NIC had no effect on neuron number in CA1, CA3 or DG. Unexpectedly, NIC plus MD combined caused a synergistic increase in the number of CA1 or CA3 neurons. Neuron density in CA regions was unaffected by treatment, but in the DG, granule neurons had a looser packing density after NIC, MD or NIC+MD exposure. When septotemporal axes were analyzed, the synergism of stress and drug exposure in CA1 and CA3 was associated with rostral, whereas MD effects were predominantly associated with caudal neurons. TUNEL labeling suggests no active apoptosis at P14, and doublecortin positive neurons and mossy fibers were diminished in NIC+MD relative to controls. The laterality of the effect of nicotine and/or maternal deprivation in right versus left hippocampus was also analyzed and found to be insiginificant. We report for the first time that early life stressors such as postnatal MD and prenatal NIC exposure, when combined, may exhibit synergistic consequences for CA1 and CA3 pyramidal neuron development, and a potential antagonistic influence on developing DG neurons. These results suggest that early stressors may modulate neurogenesis, apoptosis, or maturation of glutamatergic neurons in the hippocampus in a region-specific manner during critical periods of neurodevelopment.

The brain-derived neurotrophic factor Val66Met polymorphism moderates early deprivation effects on attention problems

Adverse early care is associated with attention regulatory problems, but not all so exposed develop attention problems. In a sample of 612 youth (girls = 432, M = 11.82 years, SD = 1.5) adopted from institutions (e.g., orphanages) in 25 countries, we examined whether the Val66Met polymorphism of the brain-derived neurotrophic factor gene moderates attention problems associated with the duration of institutional care. Parent-reported attention problem symptoms were collected using the MacArthur Health and Behavior Questionnaire. DNA was genotyped for the brain-derived neurotrophic factor Val66Met (rs6265) single nucleotide polymorphism. Among youth from Southeast (SE) Asia, the predominant genotype was valine/methionine (Val/Met), whereas among youth from Russia/Europe and Caribbean/South America, the predominant genotype was Val/Val. For analysis, youth were grouped as carrying Val/Val or Met/Met alleles. Being female, being from SE Asia, and being younger when adopted were associated with fewer attention regulatory problem symptoms. Youth carrying at least one copy of the Met allele were more sensitive to the duration of deprivation, yielding an interaction that followed a differential susceptibility pattern. Thus, youth with Val/Met or Met/Met genotypes exhibited fewer symptoms than Val/Val genotypes when adoption was very early and more symptoms when adoption occurred later in development. Similar patterns were observed when SE Asian youth and youth from other parts of the world were analyzed separately.

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.

Sex and litter effects on anxiety and DNA methylation levels of stress and neurotrophin genes in adolescent rats

Maternal care variations associate with DNA methylation of the glucocorticoid receptor gene, Nr3c1, in hippocampus at a nerve-growth factor-inducible protein 1 binding site. Epigenetic regulation of brain-derived neurotrophin factor is affected by early stress. These systems contribute to anxiety and fear. Early stress has sex-dependent effects perhaps reflecting sex differences in maternal care. Altering litter gender composition affects maternal behavior and DNA methylation levels of another gene in hippocampus and nucleus accumbens (NAc). We now test if DNA methylation levels of Nr3c1, Egr1, and Bdnf differ by litter composition or sex. Rats from mixed- or single-sex litters were tested for anxiety and fear on postnatal day 35. Brain tissues were collected and analyzed using direct sequencing methods. Females showed hypermethylation of Nr3c1 of hippocampal DNA and litter composition modified sex effects on methylation of Egr1 in NAc. Few differences were seen for Bdnf. LGC modified some sex differences in behavior.

Companions reverse stressor-induced decreases in neurogenesis and cocaine conditioning possibly by restoring BDNF and NGF levels in dentate gyrus

The presence of companions can reverse the stressor-induced decrease in neurogenesis in mouse dentate gyrus (DG). In this study, we decided to study the underlying mechanisms of the companions' protective effect and to assess whether two DG neurogenesis-related memories, cocaine-induced conditioned place preference (CPP) and spatial memory, can be affected by our stressor and companions. Neurotrophin levels in DG were measured, in this regard, to reveal their roles in mediating the stressors' and companions' effect. We found that the stressor did not affect NT-3 but acutely decreased NGF and BDNF levels in DG. The presence of companions abolished these stressor-decreased NGF and BDNF levels. Neither the stressor nor the presence of companions affected TrkA, TrkB or TrkC expression in DG. Pre-exposure to the stressor rendered deficits in cocaine-induced CPP and spatial memory, while companions reversed the stressor-decreased cocaine-induced CPP. Intra-ventricular infusion with K252a, a mixed TrkA and TrkB antagonist, did not affect the protective effects of companions on local NGF, BDNF levels in DG, but abolished the companions' protective effects against the stressor-decreased DG neurogenesis and cocaine-induced CPP. Systemic pretreatment with 7,8-dihydroxyflavone (DHF), a selective TrkB agonist, did not affect baseline, the stressor-stimulated corticosterone (CORT) secretion or local NGF, BDNF levels in DG, but in part mimicked companions' protective effects. These results, taken together, indicate that stressor-decreased NGF and BDNF levels in DG could be involved in the stressor-decreased DG neurogenesis and cocaine conditioning. The presence of companions reverses the stressor-decreased DG neurogenesis and cocaine conditioning possibly by restoring BDNF and NGF levels in DG.

Facilitation of fear extinction by the 5-HT(1A) receptor agonist tandospirone: possible involvement of dopaminergic modulation

Fear extinction-based exposure treatment is an important component of psychotherapy for anxiety disorders such as posttraumatic stress disorder (PTSD). Recent studies have focused on pharmacological approaches combined with exposure therapy to augment extinction. In this study, we elucidated the therapeutic potential of the serotonin 1A (5-HT(1A) ) receptor agonist tandospirone compared with the effects of the N-methyl-D-aspartate partial agonist D-cycloserine (DCS), focusing on the possible involvement of dopaminergic mechanisms. We used a rat model of juvenile stress [aversive footshock (FS)] exposure during the third postnatal week (3wFS). The 3wFS group exhibited extinction deficit reflected in sustained fear-related behavior and synaptic dysfunction in the hippocampal CA1 field and medial prefrontal cortex (mPFC), which are responsible for extinction processes. Tandospirone administration (5 mg/kg, i.p.) before and after the extinction trials ameliorated both the behavioral deficit and synaptic dysfunction, i.e., synaptic efficacy in the CA1 field and mPFC associated with extinction training and retrieval, respectively, was potentiated in the tandospirone-treated 3wFS group. Extracellular dopamine release in the mPFC was increased by extinction retrieval in the non-FS control group. This facilitation was not observed in the 3wFS group; however, tandospirone treatment increased cortical dopamine levels after extinction retrieval. DCS (15 mg/kg, i.p.) also ameliorated the extinction deficit in the 3wFS group, but impaired extinction in the non-FS control group. These results suggest that tandospirone has therapeutic potential for enhancing synaptic efficacy associated with extinction processes by involving dopaminergic mechanisms. Pharmacological agents that target cortical dopaminergic systems may provide new insights into the development of therapeutic treatments of anxiety disorders, including PTSD.

Have studies of the developmental regulation of behavioral phenotypes revealed the mechanisms of gene-environment interactions?

This review addresses the recent convergence of our long-standing knowledge of the regulation of behavioral phenotypes by developmental experience with recent advances in our understanding of mechanisms regulating gene expression. This review supports a particular perspective on the developmental regulation of behavioral phenotypes: That the role of common developmental experiences (e.g. maternal interactions, peer interactions, exposure to a complex environment, etc.) is to fit individuals to the circumstances of their lives within bounds determined by long-standing (evolutionary) mechanisms that have shaped responses to critical and fundamental types of experience via those aspects of gene structure that regulate gene expression. The phenotype of a given species is not absolute for a given genotype but rather variable within bounds that is determined by mechanisms regulated by experience (e.g. epigenetic mechanisms). This phenotypic variation is not necessarily random, or evenly distributed along a continuum of description or measurement, but often highly disjointed, producing distinct, even opposing, phenotypes. The potentiality for these varying phenotypes is itself the product of evolution, the potential for alternative phenotypes itself conveying evolutionary advantage. Examples of such phenotypic variation, resulting from environmental or experiential influences, have a long history of study in neurobiology, and a number of these will be discussed in this review: neurodevelopmental experiences that produce phenotypic variation in visual perception, cognitive function, and emotional behavior. Although other examples will be discussed, particular emphasis will be made on the role of social behavior on neurodevelopment and phenotypic determination. It will be argued that an important purpose of some aspects of social behavior is regulation of neurobehavioral phenotypes by experience via genetic regulatory mechanisms.

Upregulated mRNA levels of SERT, NET, MAOB, and BDNF in various brain regions of ovariectomized rats exposed to chronic aversive stimuli

Estrogen deficiency increases the risk of anxiety and mood disorders, presumably by deranging metabolism of the monoamine neurotransmitters and the expression of their reuptake transporters in the brain. Although estrogen-deficient individuals were also susceptible to stress, little was known regarding the effect of stress on the levels of transcripts related to brain monoamine metabolism. Herein, we used quantitative real-time PCR to quantify the mRNA levels of serotonin reuptake transporter (SERT), norepinephrine transporter (NET), monoamine oxidase-B (MAOB), tryptophan hydroxylase (TPH), and tyrosine hydroxylase (TH) in various brain regions of ovariectomized (OVX) rats which had been exposed for 4 weeks to chronic aversive stimuli (CAS), such as water deprivation, cage tilt, and illumination. We found that CAS induced stress responses in OVX rats as indicated by increases in the adrenal gland weight and sucrose intake. After CAS exposure, mRNA levels of SERT and NET were upregulated in the frontal cortex, hippocampus, amygdala, and periaqueductal gray. In addition, CAS also increased the mRNA levels of MAOB, an enzyme for dopamine degradation, in the same brain regions. However, CAS did not alter the mRNA levels of TPH or TH, both of which are rate-limiting enzymes for the synthesis of serotonin and norepinephrine in the dorsal raphé and locus coeruleus, respectively. Interestingly, mRNA expression of brain-derived neurotrophic factor precursor was upregulated in the hippocampus of CAS-exposed OVX rats, suggesting a compensatory mechanism which might counteract the stress-induced depression. Therefore, the present data have provided evidence to explain how stress affected brain monoamine metabolism in estrogen-deficient stressed patients.

Fluoxetine prevents development of an early stress-related molecular signature in the rat infralimbic medial prefrontal cortex. Implications for depression?

Background

Psychological stress, particularly in chronic form, can lead to mood and cognitive dysfunction and is a major risk factor in the development of depressive states. How stress affects the brain to cause psychopathologies is incompletely understood. We sought to characterise potential depression related mechanisms by analysing gene expression and molecular pathways in the infralimbic medial prefrontal cortex (ILmPFC), following a repeated psychological stress paradigm. The ILmPFC is thought to be involved in the processing of emotionally contextual information and in orchestrating the related autonomic responses, and it is one of the brain regions implicated in both stress responses and depression.

Results

Genome-wide microarray analysis of gene expression showed sub-chronic restraint stress resulted predominantly in a reduction in transcripts 24 hours after the last stress episode, with 239 genes significantly decreased, while just 24 genes had increased transcript abundance. Molecular pathway analysis using DAVID identified 8 pathways that were significantly enriched in the differentially expressed gene list, with genes belonging to the brain-derived neurotrophic factor – neurotrophin receptor tyrosine kinase 2 (BDNF-Ntrk2) pathway most enriched. Of the three intracellular signalling pathways that are downstream of Ntrk2, real-time quantitative PCR confirmed that only the PI3K-AKT-GSK3B and MAPK/ERK pathways were affected by sub-chronic stress, with the PLCγ pathway unaffected. Interestingly, chronic antidepressant treatment with the selective serotonin reuptake inhibitor, fluoxetine, prevented the stress-induced Ntrk2 and PI3K pathway changes, but it had no effect on the MAPK/ERK pathway.

Conclusions

These findings indicate that abnormal BDNF-Ntrk2 signalling may manifest at a relatively early time point, and is consistent with a molecular signature of depression developing well before depression-like behaviours occur. Targeting this pathway prophylactically, particularly in depression-susceptible individuals, may be of therapeutic benefit.

Effects of repeated deep brain stimulation on depressive- and anxiety-like behavior in rats: comparing entopeduncular and subthalamic nuclei

BACKGROUND

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) or internal globus pallidus (GPi) has been routinely used for the treatment of some movement disorders. However, DBS may be associated with adverse psychiatric effects, such as depression, anxiety and impulsivity.

OBJECTIVE

To compare DBS applied to the entopeduncular nucleus (EPN; the rodent homolog of the GPi) and STN in terms of their effects on depressive- and anxiety-like behavior in rats.

METHODS

DBS was applied for 21 days (4 h a day) to either the STN or EPN. Rats then underwent behavioral testing on learned helplessness and elevated plus maze tasks before being sacrificed for brain analyses of zif268, BDNF and trkB mRNA as well as BDNF protein levels.

RESULTS

Repeated DBS of the STN, but not of the EPN, led to impaired performance in the learned helplessness task, suggesting that STN-DBS induces or potentiates depressive-like behavior. There was no effect of DBS on elevated plus maze or on open field behavior. Repeated STN-DBS, but not EPN-DBS, led to decreased levels of BDNF and trkB mRNA in hippocampus. Acute stimulation of the STN or EPN resulted in similar changes in zif268 levels in several brain areas, except for the raphe where decreases were seen only after STB-DBS.

CONCLUSIONS

Together these results indicate that the effects of STN- and EPN-DBS differ in behavioral and neurochemical respects. Results further suggest that the EPN may be a preferable target for clinical DBS when psychiatric side effects are considered insofar as it may be associated with a lower incidence of depressive-like behavior than the STN.

Effects of fluoxetine, tianeptine and olanzapine on unpredictable chronic mild stress-induced depression-like behavior in mice

AIMS

Tianeptine is an atypical antidepressant drug that has a different mechanism of action than other antidepressants. Olanzapine is an atypical antipsychotic drug used for the treatment of schizophrenia. The present study was undertaken to investigate effects of chronic administration of tianeptine or olanzapine on unpredictable chronic mild stress (UCMS)-induced depression-like behavior in mice compared to a widely used SSRI antidepressant, fluoxetine.

MAIN METHODS

Male inbred BALB/c mice were subjected to different kinds of stressors several times a day for 7weeks and were treated intraperitoneally with tianeptine (5mg/kg), olanzapine (2.5mg/kg), fluoxetine (15mg/kg) or vehicle for 5weeks (n=7-8 per group).

KEY FINDINGS

All the drugs tested prevented stress-induced deficit in coat state during UCMS procedure, in grooming behavior in the splash test, decreased the attack frequency in the resident intruder test and decreased the immobility time in the tail suspension test. In the open field test olanzapine had anxiolytic-like effects in both stressed and non-stressed mice. Tianeptine, olanzapine and fluoxetine decreased the enhanced levels of plasma ACTH and IL-6. Chronic treatment with tianeptine resulted in a significant increase in both total number and density of BrdU-labeled cells in stressed animals, while fluoxetine and olanzapine had a partial effect.

SIGNIFICANCE

The results of this study support the hypothesis that tianeptine can be as effective as fluoxetine for the treatment of depression in spite of the differences in the mechanism of action of these drugs. Moreover, olanzapine could be used effectively in psychotic patients with depression.

Children under stress - COMT genotype and stressful life events predict cortisol increase in an acute social stress paradigm

Dopamine and norepinephrine are key regulators of cognitive and affective processes. The enzyme catechol-O-methyltransferase (COMT) catabolizes catecholamines and the COMT Val158Met polymorphism has been linked to several neuropsychiatric variables. Additionally, stressful life events (SLEs) contribute substantially to affective processes. We used the stress-induced activation of the hypothalamic-pituitary-adrenal axis to investigate the effects of COMT and SLEs on the cortisol response in 119 healthy children (8-12 yr). Saliva cortisol was measured during and after the Trier Social Stress Test for Children. SLEs were assessed with a standardized interview with one of the children's parents. Linear regression analysis revealed a significant effect for COMT, with Met allele carriers showing a higher cortisol response (β=0.300, p=0.001). In turn, more SLEs lead to a less pronounced cortisol increase (β=-0.192, p=0.029) probably indicating increased resilience. Our results further underscore the essential and differential role of genetic variation and environmental factors on stress responsivity.

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'.

Neurotrophins role in depression neurobiology: a review of basic and clinical evidence

Depression is a neuropsychiatric disorder affecting a huge percentage of the active population especially in developed countries. Research has devoted much of its attention to this problematic and many drugs have been developed and are currently prescribed to treat this pathology. Yet, many patients are refractory to the available therapeutic drugs, which mainly act by increasing the levels of the monoamines serotonin and noradrenaline in the synaptic cleft. Even in the cases antidepressants are effective, it is usually observed a delay of a few weeks between the onset of treatment and remission of the clinical symptoms. Additionally, many of these patients who show remission with antidepressant therapy present a relapse of depression upon treatment cessation. Thus research has focused on other possible molecular targets, besides monoamines, underlying depression. Both basic and clinical evidence indicates that depression is associated with several structural and neurochemical changes where the levels of neurotrophins, particularly of brain-derived neurotrophic factor (BDNF), are altered. Antidepressants, as well as other therapeutic strategies, seem to restore these levels. Neuronal atrophy, mostly detected in limbic structures that regulate mood and cognition, like the hippocampus, is observed in depressed patients and in animal behavioural paradigms for depression. Moreover, chronic antidepressant treatment enhances adult hippocampal neurogenesis, supporting the notion that this event underlies antidepressants effects. Here we review some of the preclinical and clinical studies, aimed at disclosing the role of neurotrophins in the pathophysiological mechanisms of depression and the mode of action of antidepressants, which favour the neurotrophic/neurogenic hypothesis.

Early life manipulations alter learning and memory in rats

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

Acupuncture stimulation at HT7 alleviates depression-induced behavioral changes via regulation of the serotonin system in the prefrontal cortex of maternally-separated rat pups

A possible application of acupuncture in alleviating depression-like behavioral changes and regulating serotonin signaling in the prefrontal cortex (PFC) of maternally-separated rat pups was investigated in this study. On postnatal day 15, rat pups were maternally-separated and received acupuncture stimulation at acupoint HT7 or ST36 once a day for 7 days. On postnatal day 21, the tail suspension test was performed and the PFC was harvested. Tissue levels of serotonin (5-HT) and 5-hydroxyindole-3-acetic acid (5-HIAA) were then measured by high-performance liquid chromatography and expression of serotonin transporter (5-HTT) and brain-derived neurotrophic factor (BDNF) were assessed by western blotting. Levels of 5-HT and 5-HIAA were not significantly changed, but the 5-HIAA/5-HT ratio was significantly increased by maternal separation. The immobility time of maternally-separated rat pups was increased, and increased 5-HTT expression and reduced BDNF level were observed in the PFC. But acupuncture stimulation at HT7 alleviated the behavioral change and regulated the changes of 5-HIAA/5-HT ratio, 5-HTT, and BDNF. In conclusion, acupuncture stimulation at HT7 can relieve maternal separation-induced changes, and we propose that regulation of the 5-HIAA/5-HT ratio and of 5-HTT expression by acupuncture stimulation are important acupuncture-induced benefits in this animal model of depression.

Childhood trauma and platelet brain-derived neurotrophic factor (BDNF) after a three month follow-up in patients with major depressive disorder

A large amount of brain-derived neurotrophic factor (BDNF) is stored in the human platelets and only small amounts of it circulate in the plasma. However, a few studies have focused on platelet BDNF in patients with major depressive disorder (MDD) and childhood trauma. Our study population consisted of 105 MDD patients and 50 healthy controls. We used the mini-international neuropsychiatric interview (M.I.N.I.), the early trauma inventory self report-short form (ETISR-SF), as well as measured serum, plasma, and platelet BDNF at baseline, 1 month, and 3 month periods. There was a significant association between childhood trauma and platelet BDNF at baseline, 1 month, and 3 months, after adjusting for age, gender, education, body mass index, severity of depression, anxiety, alcohol consumption, and current stress. Conversely, plasma and serum BDNF did not have a significant association with childhood trauma. MDD patients revealed significantly higher levels of platelet BDNF in those with childhood trauma than in those without (t = 2.4, p = 0.018), and platelet BDNF was significantly higher in cases with sexual abuse on post-hoc analysis (p = 0.042). However, no significant differences were found in healthy controls, according to whether or not they had experienced childhood trauma. Platelet BDNF showed a significant correlation with severity of childhood trauma at baseline (r = 0.25, p = 0.012) and at 3 months (r = 0.38, p = 0.003) in MDD. In conclusion, platelet BDNF was significantly higher in MDD patients with childhood trauma than in those without, and it was correlated with severity of trauma.

Environmental regulation of the neural epigenome

There are numerous examples of enduring effects of early experience on gene transcription and neural function. We review the emerging evidence for epigenetics as a candidate mechanism for such effects. There is now evidence that intracellular signals activated by environmental events can directly modify the epigenetic state of the genome, including CpG methylation, histone modifications and microRNAs. We suggest that this process reflects an activity-dependent epigenetic plasticity at the level of the genome, comparable with that observed at the synapse. This epigenetic plasticity mediates neuronal differentiation and phenotypic plasticity, including that associated with learning and memory. Altered epigenetic states are also associated with the risk for and expression of mental disorders. In a broader context, these studies define a biological basis for the interplay between environmental signals and the genome in the regulation of individual differences in behavior, cognition and physiology, as well as the risk for psychopathology.

Selective DNA methylation of BDNF promoter in bipolar disorder: differences among patients with BDI and BDII

The etiology of bipolar disorder (BD) is still poorly understood, involving genetic and epigenetic mechanisms as well as environmental contributions. This study aimed to investigate the degree of DNA methylation at the promoter region of the brain-derived neurotrophic factor (BDNF) gene, as one of the candidate genes associated with major psychoses, in peripheral blood mononuclear cells isolated from 94 patients with BD (BD I=49, BD II=45) and 52 healthy controls. A significant BDNF gene expression downregulation was observed in BD II 0.53±0.11%; P<0.05), but not in BD I (1.13±0.19%) patients compared with controls (CONT: 1±0.2%). Consistently, an hypermethylation of the BDNF promoter region was specifically found in BD II patients (CONT: 24.0±2.1%; BDI: 20.4±1.7%; BDII: 33.3±3.5%, P<0.05). Of note, higher levels of DNA methylation were observed in BD subjects on pharmacological treatment with mood stabilizers plus antidepressants (34.6±4.2%, predominantly BD II) compared with those exclusively on mood-stabilizing agents (21.7±1.8%; P<0.01, predominantly BD I). Moreover, among the different pharmacological therapies, lithium (20.1±3.8%, P<0.05) and valproate (23.6±2.9%, P<0.05) were associated with a significant reduction of DNA methylation compared with other drugs (35.6±4.6%). Present findings suggest selective changes in DNA methylation of BDNF promoter in subjects with BD type II and highlight the importance of epigenetic factors in mediating the onset and/or susceptibility to BD, providing new insight into the mechanisms of gene expression. Moreover, they shed light on possible mechanisms of action of mood-stabilizing compounds vs antidepressants in the treatment of BD, pointing out that BDNF regulation might be a key target for their effects.

Epigenetic regulation of the BDNF gene: implications for psychiatric disorders

Abnormal brain-derived neurotrophic factor (BDNF) signaling seems to have a central role in the course and development of various neurological and psychiatric disorders. In addition, positive effects of psychotropic drugs are known to activate BDNF-mediated signaling. Although the BDNF gene has been associated with several diseases, molecular mechanisms other than functional genetic variations can impact on the regulation of BDNF gene expression and lead to disturbed BDNF signaling and associated pathology. Thus, epigenetic modifications, representing key mechanisms by which environmental factors induce enduring changes in gene expression, are suspected to participate in the onset of various psychiatric disorders. More specifically, various environmental factors, particularly when occurring during development, have been claimed to produce long-lasting epigenetic changes at the BDNF gene, thereby affecting availability and function of the BDNF protein. Such stabile imprints on the BDNF gene might explain, at least in part, the delayed efficacy of treatments as well as the high degree of relapses observed in psychiatric disorders. Moreover, BDNF gene has a complex structure displaying differential exon regulation and usage, suggesting a subcellular- and brain region-specific distribution. As such, developing drugs that modify epigenetic regulation at specific BDNF exons represents a promising strategy for the treatment of psychiatric disorders. Here, we present an overview of the current literature on epigenetic modifications at the BDNF locus in psychiatric disorders and related animal models.

Developmental traumatic brain injury decreased brain derived neurotrophic factor expression late after injury

Pediatric traumatic brain injury (TBI) is a major cause of acquired cognitive dysfunction in children. Hippocampal Brain Derived Neurotrophic Factor (BDNF) is important for normal cognition. Little is known about the effects of TBI on BDNF levels in the developing hippocampus. We used controlled cortical impact (CCI) in the 17 day old rat pup to test the hypothesis that CCI would first increase rat hippocampal BDNF mRNA/protein levels relative to SHAM and Naïve rats by post injury day (PID) 2 and then decrease BDNF mRNA/protein by PID14. Relative to SHAM, CCI did not change BDNF mRNA/protein levels in the injured hippocampus in the first 2 days after injury but did decrease BDNF protein at PID14. Surprisingly, BDNF mRNA decreased at PID 1, 3, 7 and 14, and BDNF protein decreased at PID 2, in SHAM and CCI hippocampi relative to Naïve. In conclusion, TBI decreased BDNF protein in the injured rat pup hippocampus 14 days after injury. BDNF mRNA levels decreased in both CCI and SHAM hippocampi relative to Naïve, suggesting that certain aspects of the experimental paradigm (such as craniotomy, anesthesia, and/or maternal separation) may decrease the expression of BDNF in the developing hippocampus. While BDNF is important for normal cognition, no inferences can be made regarding the cognitive impact of any of these factors. Such findings, however, suggest that meticulous attention to the experimental paradigm, and possible inclusion of a Naïve group, is warranted in studies of BDNF expression in the developing brain after TBI.

Intensification of maternal care by double-mothering boosts cognitive function and hippocampal morphology in the adult offspring

Mice born from high care-giving females show, as adults, low anxiety levels, decreased responsiveness to stress, and substantial improvements in cognitive function and hippocampal plasticity. Given the relevance of this issue for preventing emotional and cognitive abnormalities in high-risk subjects, this study examines the possibility to further enhance the beneficial effects observed in the progeny by augmenting maternal care beyond the highest levels females can display in standard laboratory conditions. This was produced by placing a second female with the dam and its litter in the rearing cage from the partum until pups weaning. Maternal behavior of all females was scored during the first week postpartum, and behavioral indices of emotionality, prestress and poststress corticosterone levels, cognitive performance, and hippocampal morphology were assessed in the adult offspring. We found that pups reared by female dyads received more maternal care than pups reared by dams alone, but as adults, they did not exhibit alterations in emotionality or corticosterone response estimated in basal condition or following restraint stress. Conversely, they showed enhanced performance in hippocampal-dependent tasks including long-term object discrimination, reactivity to spatial change, and fear conditioning together with an increase in dendritic length and spine density in the CA1 region of the hippocampus. In general, the beneficial effects of dyadic maternal care were stronger when both the females were lactating. This study demonstrates that double-mothering exerts a long-term positive control on cognitive function and hippocampal neuronal connectivity. This experimental manipulation, especially if associated with increased feeding, might offer a concrete possibility to limit or reverse the consequences of negative predisposing conditions for normal cognitive development.

Serum brain-derived neurotrophic factor, vascular endothelial growth factor and leptin levels in patients with a diagnosis of severe major depressive disorder with melancholic features

OBJECTIVE

Brain-derived neurotrophic factor (BDNF), vascular endothelial growth factor (VEGF) and leptin have been hypothesized to be involved in the neurobiology of depression. The aim of this study was to investigate BDNF, VEGF and leptin levels in patients with severe melancholic depression.

METHODS

A total of 40 drug-free patients with major depressive disorder (MDD) with melancholic features and 40 healthy controls were included in the study. Demographic information, psychiatric evaluation and physical examination were documented for both groups. Serum BDNF, VEGF levels were determined by enzyme-linked immunosorbent assay and leptin with radioimmunoassay methods. The Hamilton Depression Rating Scale and Hamilton Anxiety Rating Scale were applied to the patients.

RESULTS

There were no significant differences in serum BDNF, VEGF and leptin levels between the patient and control groups. There was a negative correlation between BDNF levels and the number of depressive episodes. It was noted that VEGF levels decreased with increasing severity of depression.

CONCLUSIONS

These findings suggest that BDNF levels might be associated with the recurrence of depression and VEGF levels might be a determinant of the severity of depression.

Modulation of BDNF expression by repeated treatment with the novel antipsychotic lurasidone under basal condition and in response to acute stress

It is known that long-term treatment with antipsychotic drugs (APDs) produces neuroadaptive changes through the modulation of different proteins that, by enhancing neuronal plasticity and cellular resiliency, may improve core disease symptoms. The aim of this study was to investigate the ability of chronic treatment with the novel antipsychotic lurasidone to modulate BDNF expression in hippocampus and prefrontal cortex, under basal conditions or in response to an acute stress, a major precipitating element in psychiatric disorders. By means of real-time PCR, we found that (1) chronic lurasidone treatment increases total BDNF mRNA levels in rat prefrontal cortex and, to less extent, in hippocampus; (2) the modulation of BDNF mRNA levels in response to acute swim stress in lurasidone-treated rats was markedly potentiated in hippocampus, and to less extent in prefrontal cortex, through the selective regulation of different neurotrophin isoforms. The increase of BDNF mRNA levels in prefrontal cortex was paralleled by an enhancement of mature BDNF protein levels. In conclusion, repeated exposure to lurasidone regulates BDNF expression, through a finely tuned modulation of its transcripts. This effect may contribute to the amelioration of functions, such as cognition, closely associated with neuronal plasticity, which are deteriorated in schizophrenia patients.