Changes in plasma levels of BDNF and NGF reveal a gender-selective vulnerability to early adversity in rhesus macaques

Neurotrophic basis to the pathogenesis of depression and phytotherapy

Depression is a major neuropsychiatric disease that considerably impacts individuals’ psychosocial function and life quality. Neurotrophic factors are now connected to the pathogenesis of depression, while the definitive neurotrophic basis remains elusive. Besides, phytotherapy is alternative to conventional antidepressants that may minimize undesirable adverse reactions. Thus, further research into the interaction between neurotrophic factors and depression and phytochemicals that repair neurotrophic factors deficit is highly required. This review highlighted the implication of neurotrophic factors in depression, with a focus on the brain-derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF), vascular endothelial growth factor (VEGF), and nerve growth factor (NGF), and detailed the antidepressant activities of various phytochemicals targeting neurotrophic factors. Additionally, we presented future opportunities for novel diagnostic and therapeutic strategies for depression and provided solutions to challenges in this area to accelerate the clinical translation of neurotrophic factors for the treatment of depression.

Effect of combination fluoxetine and exercise on prefrontal BDNF, anxiety-like behavior and fear extinction in a female rat model of post-traumatic stress disorder (PTSD): a comparison with male animals

Despite significant differences between men and women in the symptoms of PTSD and the response to therapeutic interventions, most PTSD studies have been done on male subjects. Continuing our previous study in male rats, this study aimed at better understanding the effect of a combination therapy of exercise with fluoxetine on female PTSD rats. The results were then compared with our past findings in male animals. Female adult Wistar rats subjected to PTSD were treated with moderate treadmill exercise or fluoxetine, or a combination of both. PTSD was induced by the single prolonged stress (SPS) model. Elevated plus-maze (EPM), serum and prefrontal BDNF, and fear extinctions were evaluated. The results showed that exercise plus fluoxetine decreased anxiety-like behavior, improved fear extinction, and increased BDNF changes in female rats. The effects of exercise alone were comparable with those of combination therapy except that combination therapy was more effective on OAT (open arm entry). The majority of results in female rats, except for those of prefrontal BDNF, 4th extinction, and OAT, were similar to those of male rats as shown in our previous study. According to our findings, exercise as a safe and cost-effective intervention can be considered as a complementary efficient option for PTSD treatment in both sexes. To achieve better treatment outcomes in PTSD patient, considering sex differences is recommended.

Sex difference in cognitive behavioral alterations and barrel cortex neuronal responses in rats exposed prenatally to valproic acid under continuous environmental enrichment

Autism spectrum disorder is a developmental disorder that can affect social interactions and sensory-motor behaviors. The present study investigates the effect of environmental enrichment (EE) on behavioral alterations and neuron responses associated with the barrel cortex of young adult female and male rats exposed prenatally to valproic acid (VPA). Pregnant female rats were pretreated with either saline or VPA (500 mg/kg, IP) on day 12.5 of gestation. Male and female pups were exposed to either EE or standard-setting (non-enrichment) conditions for 1 month (between postnatal day [PND] 30 and 63-65) and were divided into non-EE (control), EE, VPA, and VPA + EE groups. Three-chamber sociability and social novelty, acoustic startle reflex, and texture discrimination tests were conducted on PND 62. Responses of barrel cortex neurons of male pups were evaluated using the extracellular single-unit recording technique on PND 63-65. Results showed that the performance of rats of both sexes in social interactions, texture discrimination tasks, and acoustic startle reflex significantly decreased in the VPA groups compared with the control rats (P < 0.05). In this regard, EE attenuated the altered deficit performance observed in the VPA animals compared with the VPA-EE animals (P < 0.05). The performance of females was better than males in the discrimination tasks and acoustic startle reflex. In contrast, males were better than females in the three-chamber social interaction test. Additionally, the excitatory receptive field response magnitude of the barrel cortex neurons in the VPA + EE group increased compared with the VPA group (P < 0.05). The results suggest that continuous EE can attenuate cognitive function disturbances in autistic-like rats and, at least at the behavioral level, the effects depend on sex.

Dual Profile of Environmental Enrichment and Autistic-Like Behaviors in the Maternal Separated Model in Rats

BACKGROUND

Environmental Enrichment (EE) has been suggested as a possible therapeutic intervention for neurodevelopmental disorders such as autism. Although the benefits of this therapeutic method have been reported in some animal models and human studies, the unknown pathophysiology of autism as well as number of conflicting results, urge for further examination of the therapeutic potential of EE in autism. Therefore, the aim of this study was to examine the effects of environmental enrichment on autism-related behaviors which were induced in the maternal separation (MS) animal model.

MATERIAL AND METHODS

Maternally separated (post-natal day (PND) 1-14, 3h/day) and control male rats were at weaning (PND21) age equally divided into rats housed in enriched environment and normal environment. At adolescence (PND42-50), the four groups were behaviorally tested for direct social interaction, sociability, repetitive behaviors, anxiety behavior, and locomotion. Following completion of the behavioral tests, the blood and brain tissue samples were harvested in order to assess plasma level of brain derived neurotrophic factor (BDNF) and structural plasticity of brain using ELISA and stereological methods respectively.

RESULTS

We found that environmental enrichment reduced repetitive behaviors but failed to improve the impaired sociability and anxiety behaviors which were induced by maternal separation. Indeed, EE exacerbated anxiety and social behaviors deficits in association with increased plasma BDNF level, larger volume of the hippocampus and infra-limbic region and higher number of neurons in the infra-limbic area (p < 0.05). Conclusion: We conclude that environmental enrichment has a significant improvement effect on the repetitive behavior as one of the core autistic-like behaviors induced by maternal separation but has negative effect on the anxiety and social behaviors which might have been modulated by BDNF.

Combination of dextromethorphan and memantine in treating bipolar spectrum disorder: a 12-week double-blind randomized clinical trial

Background

The aim of this study is to determine whether adding combination of agents with anti-inflammatory and neurotrophic effects is more efficacious than mood stabilizer alone in improving clinical symptoms, plasma brain-derived neurotrophic factor (BDNF), cytokine levels, and metabolic profiles in patients with bipolar spectrum disorder.

Methods

In a randomized, double-blind, controlled 12-week clinical trial, patients with moderate mood symptoms (HDRS ≥ 18 or YMRS ≥ 14) were recruited. The patients were randomly assigned to a group while still undergoing regular valproate (VPA) treatments: VPA + dextromethorphan (DM) (30 mg/day) + memantine (MM) (5 mg/day) (DM30 + MM5) (n = 66), VPA + DM (30 mg/day) (DM30) (n = 69), VPA + MM (5 mg/day) (MM5) (n = 66), or VPA + Placebo (Placebo) (n = 69). Symptom severity, immunological parameters [plasma tumor necrosis factor (TNF)-α and C-reactive protein (CRP)] and plasma brain-derived neurotrophic factor (BDNF) were regularly examined. Metabolic profiles [cholesterol, triglycerides, glycosylated hemoglobin (HbA1C), fasting serum glucose, body mass index (BMI)] were measured at baseline and at 2, 8, and 12 weeks.

Results

Depression scores were significantly (P = 0.03) decreases and BDNF levels significantly (P = 0.04) increased in the DM30 + MM5 group than in the Placebo group. However, neither depressive scores nor BDNF levels were significantly different between the DM30, MM5, and Placebo groups. Changes in certain plasma cytokine and BDNF levels were significantly correlated with metabolic parameters.

Conclusion

We concluded that add-on DM30 + MM5 was significantly more effective than placebo for clinical symptoms and plasma BDNF levels. Additional studies with larger samples and mechanistic studies are necessary to confirm our findings.

Trial registration NCT03039842 (https://register.clinicaltrials.gov/). Trial date was from 1 Jan 2013 to 31 December 2016 in National Cheng Kung University Hospital. Registered 28 February 1 2017-Retrospectively registered, https://clinicaltrials.gov/ct2/show/NCT03039842?term=NCT03039842&rank=1.

Altered Plasma Levels of Glial Cell Line-Derived Neurotrophic Factor in Patients with Internet Gaming Disorder: A Case-Control, Pilot Study

Glial cell line-derived neurotrophic factor (GDNF) has been reported to be involved in negatively regulating the effects of addictive disorders. The objective of this study was to investigate alterations in the levels of GDNF in patients with Internet gaming disorder (IGD) and to assess the relationship between GDNF levels and the severity of IGD indices. Nineteen male patients with IGD and 19 sexmatched control subjects were evaluated for alteration of plasma GDNF levels and for relationship between GDNF levels and clinical characteristics of Internet gaming, including the Young's Internet Addiction Test (Y-IAT). The GDNF levels were found to be significantly low in patients with IGD (103.2±62.0 pg/mL) compared with the levels of controls (245.2±101.6 pg/mL, p<0.001). GDNF levels were negatively correlated with Y-IAT scores (Spearman's rho=-0.645, p=<0.001) and this negative correlation remained even after controlling for multiple variables (r=-0.370, p=0.048). These findings support the assumed role of GDNF in the regulation of IGD.

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.

The correlation between plasma brain-derived neurotrophic factor and cognitive function in bipolar disorder is modulated by the BDNF Val66Met polymorphism

We explored the effect of the Brain-derived neurotrophic factor (BDNF) Val66Met polymorphism (rs6265) on correlation between changes in plasma BDNF levels with cognitive function and quality of life (QoL) after 12 weeks of treatment in bipolar disorder (BD). Symptom severity and plasma BDNF levels were assessed upon recruitment and during weeks 1, 2, 4, 8 and 12. QoL, the Wisconsin Card Sorting Test (WCST), and the Conners’ Continuous Performance Test (CPT) were assessed at baseline and endpoint. The BDNF Val66Met polymorphism was genotyped. Changes in cognitive function and QoL over 12 weeks were reduced using factor analysis for the evaluation of their correlations with changes in plasma BDNF. Five hundred forty-one BD patients were recruited and 65.6% of them completed the 12-week follow-up. Changes in plasma BDNF levels with factor 1 (WCST) were significantly negatively correlated (r = −0.25, p = 0.00037). After stratification of BD subtypes and BDNF genotypes, this correlation was significant only in BP-I and the Val/Met genotype (r = −0.54, p = 0.008). We concluded that changes in plasma BDNF levels significantly correlated with changes in WCST scores in BD and is moderated by the BDNF Val66Met polymorphism and the subtype of BD.

Stress Response and Perinatal Reprogramming: Unraveling (Mal)adaptive Strategies

Environmental stressors induce coping strategies in the majority of individuals. The stress response, involving the activation of the hypothalamic-pituitary-adrenocortical axis and the consequent release of corticosteroid hormones, is indeed aimed at promoting metabolic, functional, and behavioral adaptations. However, behavioral stress is also associated with fast and long-lasting neurochemical, structural, and behavioral changes, leading to long-term remodeling of glutamate transmission, and increased susceptibility to neuropsychiatric disorders. Of note, early-life events, both in utero and during the early postnatal life, trigger reprogramming of the stress response, which is often associated with loss of stress resilience and ensuing neurobehavioral (mal)adaptations. Indeed, adverse experiences in early life are known to induce long-term stress-related neuropsychiatric disorders in vulnerable individuals. Here, we discuss recent findings about stress remodeling of excitatory neurotransmission and brain morphology in animal models of behavioral stress. These changes are likely driven by epigenetic factors that lie at the core of the stress-response reprogramming in individuals with a history of perinatal stress. We propose that reprogramming mechanisms may underlie the reorganization of excitatory neurotransmission in the short- and long-term response to stressful stimuli.

Brain-derived neurotrophic factor serum levels in heroin-dependent patients after 26weeks of withdrawal

BACKGROUND

Brain-derived neurotrophic factor (BDNF) has been implicated in the pathophysiology of heroin dependence. BDNF expression is dramatically changed during drug withdrawal, and is associated with drug withdrawal syndrome. This study aimed to explore (1) alterations of BDNF serum levels in heroin-dependent patients after long term abstinence; and (2) the association between BDNF serum levels and protracted withdrawal syndrome.

METHOD

Fifty-three male heroin-dependent patients and fifty-two gender-matched healthy controls were enrolled in this study. We measured BDNF serum levels at baseline and 26 weeks after heroin abstinence. Moreover, protracted withdrawal symptoms, depression and anxiety symptoms were measured by Protracted Withdrawal Symptoms of Heroin-dependent patients (PWSHA), Self-rating Depression Scale (SDS) and Self-rating Anxiety Scale (SAS), respectively.

RESULT

We found that baseline BDNF serum levels were significantly lower in heroin-dependent patients compared to controls (p<0.01). There was also a significantly difference in BDNF serum levels among heroin-dependent patients at baseline and 26-week follow-up (p<0.01). The BDNF serum levels were not associated with age, BMI, years of education, age of initial use, or duration of use. Of the clinical symptoms measured, the change in BDNF serum levels from baseline to 26-week follow-up was negatively associated with the change in PWSHA scores (r = -0.44, p<0.01, see Table 2 and Figure 2 for details).

CONCLUSION

The results show that the BDNF serum levels in heroin-dependent patients are lower than those of healthy controls at baseline and increased after 26 weeks of abstinence, although the BDNF serum levels are still lower than those of the healthy controls. A negative correlation between the change in BDNF serum levels and protracted withdrawal symptoms was found but needs to be confirmed in further study. The results revealed that BDNF serum level is worth paying attention to in order to further investigate the possibility of it being a biomarker of treatment outcome for opiate dependence.

Transgenerational Social Stress, Immune Factors, Hormones, and Social Behavior

A social signal transduction theory of depression has been proposed that states that exposure to social adversity alters the immune response and these changes mediate symptoms of depression such as anhedonia and impairments in social behavior The exposure of maternal rats to the chronic social stress (CSS) of a male intruder depresses maternal care and impairs social behavior in the F1 and F2 offspring of these dams. The objective of the present study was to characterize basal peripheral levels of several immune factors and related hormone levels in the adult F2 offspring of CSS exposed dams and assess whether changes in these factors are associated with previously reported deficits in allogrooming behavior. CSS decreased acid glycoprotein (α1AGP) and intercellular adhesion molecule-1 (ICAM-1) in F2 females, and increased granulocyte macrophage-colony stimulating factor (GM-CSF) in F2 males. There were also sex dependent changes in IL-18, tissue inhibitors of metalloproteinases 1 (TIMP-1), and vascular endothelial growth factor (VEGF). Progesterone was decreased and alpha melanocyte stimulating hormone (α-MSH) was increased in F2 males, and brain-derived neurotrophic factor (BDNF) was decreased in F2 females. Changes in α1AGP, GM-CSF, progesterone, and α-MSH were correlated with decreased allogrooming in the F2 offspring of stressed dams. These results support the hypothesis that transgenerational social stress affects both the immune system and social behavior, and also support previous studies on the adverse effects of early life stress on immune functioning and stress associated immunological disorders, including the increasing prevalence of asthma. The immune system may represent an important transgenerational etiological factor in disorders which involve social and/or early life stress associated changes in social behavior, such as depression, anxiety, and autism, as well as comorbid immune disorders. Future studies involving immune and/or endocrine assessments and manipulations will address specific questions of function and causation, and may identify novel preventative measures and treatments for the growing number of immune mediated disorders.

Correlation of plasma brain-derived neurotrophic factor and metabolic profiles in drug-naïve patients with bipolar II disorder after a twelve-week pharmacological intervention

OBJECTIVE

Brain-derived neurotrophic factor (BDNF) is thought to be involved in the pathophysiology of bipolar disorder (BD) and metabolic syndrome. We investigated the correlation between plasma BDNF with mood symptoms and metabolic indices in patients with BD-II over a 12-week pharmacological intervention.

METHOD

Drug-naïve patients with BD-II (n=117) were recruited. Metabolic profiles [cholesterol, triglyceride, HbA1C, fasting serum glucose, body mass index (BMI)] and plasma BDNF wtrun "tblautotrun "tblsctrun "tbl_contere measured at baseline and 2, 8, and 12 weeks after beginning medication. To adjust within-subject dependence over repeated assessments, multiple linear regressions with generalized estimating equation methods were used.

RESULTS

Seventy-six (65.0%) patients completed the intervention. Plasma BDNF levels were significantly associated with BMI (P=9.6E-5), low-density lipoprotein (P=0.034) and total (P=0.001) cholesterol, but not with the Hamilton Depression Rating Scale-17 and Young Mania Rating Scale scores over the 12-week treatment.

CONCLUSION

We found initial evidence of a positive correlation between plasma BDNF levels and BMI, low-density lipoprotein and total cholesterol in drug-naïve patients with BD-II. The specific function of BDNF in regulating and maintaining peripheral metabolic health requires additional investigation.

Social deprivation and the HPA axis in early development

Growing evidence suggests that early social deprivation impacts the activity of the hypothalamic-pituitary-adrenocortical axis. Early adverse care in the form of institutional or orphanage care provides a human model for early social deprivation. The present study examined changes in diurnal cortisol during the transition to family care in the first 2 years post-adoption. Children adopted between 15 and 36 months from institutional care were examined four times during their first 2 years post-adoption (N=58). Comparison groups included same-aged peers reared in their birth families (N=50) and children adopted during their first year from overseas foster care (N=47). Children provided daily cortisol samples at roughly 2, 9, 17, and 25 months post-adoption. Post-institutionalized and post-foster care children exhibited less steep diurnal cortisol compared to non-adopted same-aged peers; these differences did not diminish across the 2 year period. For post-institutionalized children, lower social care quality in institutions was associated with less steep cortisol slopes. Lastly, shallower diurnal cortisol was a mediator between adoption status and increased behavioral problems 2 years post-adoption. Consistent with the non-human primate literature, early social deprivation may contribute to early programming of the HPA axis.

Therapeutic effects of add-on low-dose dextromethorphan plus valproic acid in bipolar disorder

Changes in inflammatory cytokines and dysfunction of the neurotrophic system are thought to be involved in the pathology of bipolar disorder (BP). We investigated whether inflammatory and neurotrophic factors were changed in BP. We also investigated whether treating BP with valproic acid (VPA) plus low-dose (30 or 60 mg/day) dextromethorphan (DM) is more effective than treating it with VPA only, and whether DM affects plasma cytokines and brain derived neurotrophic factor (BDNF) levels. In a 12-week, randomized, double-blind study, patients were randomly assigned to the VPA+DM30, VPA+DM60, or VPA+Placebo groups. The Young Mania Rating Scale (YMRS) and Hamilton Depression Rating Scale (HDRS) were used to evaluate symptom severity, and ELISA to analyze plasma cytokine and BDNF levels. We recruited 309 patients with BP and 123 healthy controls. Before treatment, patients with BP had significantly higher plasma cytokine and lower plasma BDNF levels than did healthy controls. After treatment, HDRS and YMRS scores in each group showed significant improvement. Plasma cytokine levels tended to decline in all groups. Changes in plasma BDNF levels were significantly greater in the VPA+DM60 group than in the VPA+Placebo group.

CONCLUSION

patients with BP have a certain degree of systemic inflammation and BDNF dysfunction. Treatment with VPA plus DM (60 mg/day) provided patients with BP significantly more neurotrophic benefit than did VPA treatment alone.

Sex differences in Alzheimer's disease risk: are we looking at the wrong hormones?

Two-thirds of individuals with Alzheimer's disease (AD) are women, owing largely to the fact that women outlive men (https://www.alz.org/downloads/facts_figures_2012.pdf). Women's increased longevity, however, is not sufficient to explain the fact that women are 1.5 times more likely than men to develop the disease (Gao et al., 1998). After age 80, the incidence of AD is much higher in women than in men, such that the proportion of women with AD is almost twice the proportion of men with the disease (e.g., Zandi et al., 2002; Plassman et al., 2007). Moreover, once diagnosed with AD, women decline more rapidly, both cognitively and functionally, compared to men (Ito et al., 2011; Tschanz et al., 2011).

The BDNF Val66Met polymorphism and plasma brain-derived neurotrophic factor levels in Han Chinese patients with bipolar disorder and schizophrenia

OBJECTIVE

Brain-derived neurotropic factor (BDNF) is widely distributed in the peripheral and central nervous systems. BDNF and its gene polymorphism may be important in synaptic plasticity and neuron survival, and may become a key target in the physiopathology of several mental illnesses. To elucidate the role of BDNF, we compared the plasma BDNF levels and the BDNF Val66Met gene variants effect in several mental disorders.

METHOD

We enrolled 644 participants: 177 patients with bipolar I disorder (BP-I), 190 with bipolar II disorder (BP-II), 151 with schizophrenia, and 126 healthy controls. Their plasma BDNF levels and BDNF Val66Met single nucleotide polymorphisms (SNP) were checked before pharmacological treatment.

RESULTS

Plasma levels of BDNF were significantly lower in patients with schizophrenia than in healthy controls and patients with bipolar disorder (F = 37.667, p<0.001); the distribution of the BDNF Val66Met SNP was not different between groups (χ(2) = 5.289, p = 0.507). Nor were plasma BDNF levels significantly different between Met/Met, Met/Val, and Val/Val carriers in each group, which indicated that the BDNF Val66Met SNP did not influence plasma BDNF levels in our participants. Plasma BDNF levels were, however, significantly negatively correlated with depression scores in patients with bipolar disorder and with negative symptoms in patients with schizophrenia.

CONCLUSION

We conclude that plasma BDNF profiles in different mental disorders are not affected by BDNF Val66Met gene variants, but by the process and progression of the illness itself.

Nerve growth factor variations in patients with mood disorders: no changes in eight weeks of clinical treatment

BACKGROUND

Nerve growth factor (NGF) has received much attention for its role in mood disorders. The primary objective of the present study was to examine serum NGF levels in Chinese inpatients with depressive or manic episodes in the acute phase and to explore the changes in NGF levels after effective clinical treatments.

METHODS

One hundred and seven consecutive inpatients and outpatients with mood disorders (30 with unipolar depression, 23 with bipolar depression, and 54 with bipolar mania), and 50 healthy controls were recruited. The serum NGF levels were detected by enzyme-linked immunosorbent assay.

RESULTS

Patients with bipolar mania presented higher serum NGF levels compared to those of healthy controls. After 8 weeks of medical treatment, there were significant improvements in symptoms in patients, but no significant changes in NGF levels.

CONCLUSION

The present findings may help to strengthen and expand the understanding of the role of NGF in the acute stages of mood disorders.

Salivary nerve growth factor reactivity to acute psychosocial stress: a new frontier for stress research

OBJECTIVE

Neurotrophins such as nerve growth factor (NGF) may represent a stress-responsive system complementing the better known neuroendocrine (hypothalamic-pituitary-adrenal axis) and autonomic nervous system, but there is little evidence for NGF response to acute stress in humans because noninvasive measures have not been available. We investigated salivary NGF (sNGF) in 40 healthy young adults confronting a romantic conflict stressor.

METHODS

Five saliva samples-two collected before and three after the conflict-were assayed for sNGF, cortisol (hypothalamic-pituitary-adrenal marker), and α-amylase (sAA; ANS marker). In addition, a control group (n = 20) gave saliva samples at the same time intervals to determine whether sNGF changes were specific to the conflict stressor.

RESULTS

sNGF showed significant reactivity from entry to the first poststress sample among study participants (β = .13, p = .001), with nonsignificant change across poststress samples. Control participants showed no change in sNGF across the same period. Within-person changes in sNGF were generally aligned with both cortisol (β = .17, p = .003) and sAA (β = .17, p = .021) responses. Preconflict negative emotion predicted lower sNGF reactivity (β = -.08, p = .009) and less alignment with sAA (β = -.09, p = .040), whereas positive emotion predicted less alignment with cortisol (β = -.10, p = .019).

CONCLUSIONS

This study is the first to document sNGF as a marker that responds to stress in humans.

Nerve growth factor: basic studies and possible therapeutic applications

The nerve growth factor (NGF) belongs to a family of neurotrophic factors called neurotrophins. It was discovered as a molecule that stimulates the survival and maturation of developing neurons in the peripheral nervous system and has later been shown to protect adult neurons in the degenerating mammalian brain. Basic and clinical studies have been undertaken to use NGF as a therapeutic agent aimed at restoring and maintaining neuronal function in the central nervous system and to determine the mechanisms to safely deliver the molecule into the brain. Recent studies have also recognized that the role of NGF extends far beyond the horizon of nerve cells and even beyond the peripheral and central nervous system. Studies published from our laboratory have shown that topical application of NGF possesses a protective action on human pressure ulcer, corneal ulcer and glaucoma. Here, we will review these studies, supporting the therapeutic potential of NGF.

Peripheral biomarkers in animal models of major depressive disorder

Investigations of preclinical biomarkers for major depressive disorder (MDD) encompass the quantification of proteins, peptides, mRNAs, or small molecules in blood or urine of animal models. Most studies aim at characterising the animal model by including the assessment of analytes or hormones affected in depressive patients. The ultimate objective is to validate the model to better understand the neurobiological basis of MDD. Stress hormones or inflammation-related analytes associated with MDD are frequently measured. In contrast, other investigators evaluate peripheral analytes in preclinical models to translate the results in clinical settings afterwards. Large-scale, hypothesis-free studies are performed in MDD models to identify candidate biomarkers. Other studies wish to propose new targets for drug discovery. Animal models endowed with predictive validity are investigated, and the assessment of peripheral analytes, such as stress hormones or immune molecules, is comprised to increase the confidence in the target. Finally, since the mechanism of action of antidepressants is incompletely understood, studies investigating molecular alterations associated with antidepressant treatment may include peripheral analyte levels. In conclusion, preclinical biomarker studies aid the identification of new candidate analytes to be tested in clinical trials. They also increase our understanding of MDD pathophysiology and help to identify new pharmacological targets.

Hand rearing affects emotional responses but not basic cognitive performance in European starlings

Hand rearing is a common procedure in behavioural research on birds. While likely to produce tamer experimental animals, there is a risk that it could induce pathological changes in brain and behaviour similar to those seen in mammals that have experienced maternal separation. We explored the effects of hand rearing on the cognitive and behavioural development of European starlings, Sturnus vulgaris, to assess the generality of results obtained from hand-reared animals. Two groups of age-matched birds were created from the same wild population: one hand-reared from 10 days posthatch and one brought into the laboratory as independent juveniles. These groups were compared on a battery of neuropsychological tasks designed to probe different aspects of cognitive function including learning, perseverative cognition, interval timing, neophobia and impulsivity. There was no evidence for cognitive impairment in the hand-reared birds. They did not have reduced learning speed, impairments in accuracy or precision of interval timing or pathological perseverative cognition compared to the wild-caught birds. Additionally, there was no evidence that birds that developed stereotypies in laboratory cages (predominantly the wild-caught birds) had any cognitive impairments, although this may be because no birds had severe, crystallized stereotypies. There was some evidence that hand-reared birds were less neophobic and less impulsive than wild-caught birds, suggesting that hand rearing might alter emotionally mediated decision making in a direction usually associated with reduced developmental stress in mammals. This study therefore supports the use of hand rearing as an experimental procedure in behavioural research on passerine birds.

Cortisol responses to social evaluation in 10- to 15-year-old boys and girls

This study investigated Cortisol responses and perceived stress of 10-15-year-olds to a computerized paradigm including elements of social evaluation, unpredictability, and uncontrollability. Both age and sex differences were examined. Participants were 52 children and adolescents (23 boys, mean age = 12.5 years). Over the course of an approximately 2-h testing session participants were exposed to a computerized testing paradigm, the social evaluative stress test (SEST), that lasted for 50 min and includes elements of social evaluation, unpredictability and uncontrollability. Seven saliva samples were obtained to measure cortisol concentrations before, during and after the SEST, to provide pre-stress values, cortisol reactivity to the stressor and recovery after stress. In addition, subjective emotional stress experiences were recorded. The results showed no effect of age on cortisol responses. Furthermore, although both sexes reported experiencing the paradigm as (equally) stressful, only boys reacted with significant cortisol increases (M = 163%). To our knowledge, this is the first computerized stressor that induces cortisol responses in 10- to 15-year-old boys. Whether the girls' perceived stress results in the activation of other biological systems, such as the sympathetic nervous system as well as in differential activation of brain regions, remains to be determined. Future studies investigating sex differences in stress reactivity during adolescence should include neuroimaging, as well as psychophysiological measures, to unveil some of the mechanisms behind the current findings.

Control of arthritis pain with anti-nerve-growth factor: risk and benefit

Arthritis is characterized by pain and inflammation. Recently, attention has been focused on nerve-growth factor (NGF), a neurotrophin that is a key regulator of peripheral nociception because it mediates overexpression of proinflammatory neuron-derived molecules such as substance P, serotonin, and calcitonin gene-related peptide. Antibodies have been generated for NGF and its receptor that are effective in reducing pain in preclinical pain models, and clinical trials in patients with advanced knee and hip osteoarthritis and low-back pain. Results show pain reduction is rapid and sustained. Adverse events with anti-NGF included transient paraesthesia and edema, rapidly progressive OA, and, in a small number of patients treated with both anti-NGF and nonsteroidal anti-inflammatory drugs, osteonecrosis. Inhibition of the NGF-stimulated nociceptive pathway seems to be effective; however, the adverse effects require further investigation.

Not all stressors are equal: early social enrichment favors resilience to social but not physical stress in male mice

Early experiences profoundly affect the adult coping response to stress and, consequently, adult vulnerability to psychopathologies triggered by stressing conditions, such as major depression. Though studies in animal models have demonstrated that individuals reared in different conditions are differently vulnerable to a stressor of a specific quality, no information is available as to whether such vulnerability differs when facing stressors of different qualities. To this purpose, we reared C57BL/6 male mice either in standard laboratory rearing condition (SN) or in Communal Nest (CN) condition, the latter consisting of a single nest where three mothers keep their pups together and share care-giving behavior until weaning. We scored the amount of interactions with the mother and with peers and found that CN is a form of social enrichment because both these components are significantly increased. At adulthood, we exposed SN and CN mice, for 4 weeks, to either a physical (forced swim) or a social stress (social instability). Immediately before, at week 1 and at week 4 of the stress procedure, corticosterone levels and the hedonic profile were measured. The results show that CN mice are more resilient to social stress than SN mice since they displayed no anhedonia and lower corticosterone levels. By contrast, both experimental groups were similarly vulnerable to physical stress. Overall, our results show that, in male mice, the adult vulnerability to stress changes according to the quality of the stressor, as a function of early experiences. In addition, the stressor to which CN mice are resilient is qualitatively similar to the stimuli they have experienced early on, both concerning the social domain.

Serum brain-derived neurotrophic factor and nerve growth factor concentrations change after alcohol withdrawal: preliminary data of a case-control comparison

BACKGROUND

Brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) are involved in neuroadaptation and foster survival of central and peripheral neurons. In this study, we addressed the question whether BDNF and NGF serum concentrations change during subacute alcohol withdrawal in patients with alcohol dependence compared to healthy controls.

METHODS

Fifteen patients (age 48.6 ± 7 years) and 15 healthy age-matched controls (age 48.8 ± 7 years) participated consecutively in a 2-week withdrawal study.

RESULTS

Mean BDNF levels (7.8 ng/ml, IQR = 4.4-10.7 vs. 16.5 ng/ml, IQR = 13.9-25.6; Z = -3.8, p < 0.0001) and NGF levels (5.8 pg/ml, IQR = 3.8-13.0 vs. 18.4 pg/ml, IQR = 10.9-25.1; Z = -2.5, p = 0.012) were significantly decreased in alcohol-dependent subjects when compared to healthy matched controls. NGF concentrations decreased significantly from day 3 to day 14 (Z = -2.36; p = 0.019). Mean BDNF concentrations showed a tendency to increase after withdrawal from day 3 to day 14 (Z = 1.7; p = 0.078).

CONCLUSION

Decreased NGF and BDNF concentrations in patients suffering from alcohol dependence, which stabilize after physical withdrawal, are in line with withdrawal symptoms and neurological risk factors. In turn, increase of BDNF after acute withdrawal might be connected to neurobiological and behavioral stabilization.

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

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

Gestational or acute restraint in adulthood reduces levels of 5α-reduced testosterone metabolites in the hippocampus and produces behavioral inhibition of adult male rats

Stressors, during early life or adulthood, can alter steroid-sensitive behaviors, such as exploration, anxiety, and/or cognitive processes. We investigated if exposure to acute stressors in adulthood may alter behavioral and neuroendocrine responses of male rats that were exposed to gestational stress or not. We hypothesized that rats exposed to gestational and acute stress may show behavioral inhibition, increased corticosterone, and altered androgen levels in the hippocampus. Subjects were adult, male offspring of rat dams that were restrained daily on gestational days 14–20, or did not experience this manipulation. Immediately before testing, rats were restraint stressed for 20 min or not. During week 1, rats were tested in a battery of tasks, including the open field, elevated plus maze, social interaction, tailflick, pawlick, and defensive burying tasks. During week 2, rats were trained and tested 24 h later in the inhibitory avoidance task. Plasma corticosterone and androgen levels, and hippocampal androgen levels, were measured in all subjects. Gestational and acute restraint stress increased plasma levels of corticosterone, and reduced levels of testosterone's 5α-reduced metabolites, dihydrotestosterone (DHT) and 3α-androstanediol (3α-diol), but not the aromatized metabolite, estradiol (E₂), in plasma or the hippocampus. Gestational and acute restraint stress reduced central entries made in the open field, and latencies to enter the shock-associated side of the inhibitory avoidance chamber during testing. Gestational stress reduced time spent interacting with a conspecific. These data suggest that gestational and acute restraint stress can have actions to produce behavioral inhibition coincident with increased corticosterone and decreased 5α-reduced androgens of adult male rats. Thus, gestational stress altered neural circuits involved in the neuroendocrine response to acute stress in early adulthood.

Inflammation in patients with schizophrenia: the therapeutic benefits of risperidone plus add-on dextromethorphan

Increasing evidence suggests that inflammation contributes to the etiology and progression of schizophrenia. Molecules that initiate inflammation, such as virus- and toxin-induced cytokines, are implicated in neuronal degeneration and schizophrenia-like behavior. Using therapeutic agents with anti-inflammatory or neurotrophic effects may be beneficial for treating schizophrenia. One hundred healthy controls and 95 Han Chinese patients with schizophrenia were tested in this double-blind study. Their PANSS scores, plasma interleukin (IL)-1β, tumor necrosis factor-α (TNF-α) and brain-derived neurotrophic factor (BDNF) levels were measured before and after pharmacological treatment. Pretreatment, plasma levels of IL-1β and TNF-α were significantly higher in patients with schizophrenia than in controls, but plasma BDNF levels were significantly lower. Patients were treated with the atypical antipsychotic risperidone (Risp) only or with Risp+ dextromethorphan (DM). PANSS scores and plasma IL-1β levels significantly decreased, but plasma TNF-α and BDNF levels significantly increased after 11 weeks of Risp treatment. Patients in the Risp+ DM group showed a greater and earlier reduction of symptoms than did those in the Risp-only group. Moreover, Risp+ DM treatment attenuated Risp-induced plasma increases in TNF-α. Patients with schizophrenia had a high level of peripheral inflammation and a low level of peripheral BDNF. Long-term Risp treatment attenuated inflammation and potentiated the neurotrophic function but also produced a certain degree of toxicity. Risp+ DM was more beneficial and less toxic than Risp-only treatment.

CLINICAL TRIAL REGISTRATION

Protocol Record: HR-93-50;

TRIAL REGISTRATION NUMBER

NCT01189006; URL: http://www.clinicaltrials.gov.

Neuroprotective and neurogenesis agent for treating bipolar II disorder: add-on memantine to mood stabilizer works

Bipolar disorder, characterized by a dysregulation of mood, impulsivity, risky behavior and interpersonal problems, is a recurrent and often becomes chronic psychiatric illness. However, bipolar subtypes are not often recognized in psychiatric settings, especially bipolar II subtype, until Akiskal and Angst made clear definition to bipolar I (BP-I) and bipolar II (BP-II) disorder in 1999. More and more studies, not only on family inheritance, diagnosis, but also on disease process have been reported that BP-I and BP-II are two different disorders with distinct pathological mechanisms. In general, patients with BP-II express less symptoms and have shorter hypomania stages than BP-I. According to a longitudinal research, patients with BP-II have poor recovery than do BP-I patients. Memantine used to be recognized as a noncompetitive N-methyl-d-aspartate receptor antagonist. However, it was found to have neuroprotective and neurogenesis effect in several neurodegenerative diseases in the past years. We found that memantine could inhibit brain inflammatory response through its action on neuroglial cells and provide neurotrophic effect. The above evidences of benefit on auto-immune system with memantine would support that memantine as add-on therapy to valproate might be more effective than valproate alone on improvement of the neuron degeneration in bipolar disorders. Review articles indicate that not only the mood stabilizers provide with good neuroprotection, but the memantine also have conspicuous anti-autoimmune and neurogenesis effect. Therefore, we propose that drugs with neuroprotective effect and neurotrophic effect may treat neurodegenerative diseases including BP-II. The combination treatment of mood stabilizers memantine may not only augment and improve the remedy for bipolar disorders, but also repair the damaged neurons and neurogenesis through activation of astroglial cell and release of neurotrophic factors.

Social deprivation stress is a triggering factor for the emergence of anxiety- and depression-like behaviours and leads to reduced brain BDNF levels in C57BL/6J mice

Stress is a main risk factor that can trigger psychiatric disorders, including anxiety and major depression. Neurotrophins, such as Brain-Derived Neurotrophic Factor (BDNF), have been identified as neuroendocrine effectors involved in the response to stress and in the neurobehavioural changes associated with depression. Aim of this paper was to study the relationship between neuroendocrine activation (circulating corticosterone and brain BDNF levels) and a wide array of depression- and anxiety-like behaviours (anhedonia, behavioural despair, generalised and social anxiety) resulting from exposure to chronic stress. To this end, 3-month-old C57BL/6J male mice were exposed to either chronic disruption of the social structure (SS), to a stable social structure (SG) or to social deprivation (SD), a condition lacking social stimuli. Results show that, despite not developing anhedonia (decreased preference for a sucrose solution), SD mice were characterised by increased emotionality and hypothalamic-pituitary-adrenal axis reactivity in addition to reduced BDNF levels. By contrast, SG and SS mice showed increased anhedonia accompanied by no alterations in the behavioural and neuroendocrine profile. The results here reported indicate that mice exposed to different social housing conditions use different behavioural strategies to cope with external challenges. In addition they suggest that social deprivation might represent a stressful condition triggering the emergence of both anxiety- and depression-like behaviours and clearly indicate BDNF as a main neurobiological variable mediating these responses.

Low-dose memantine attenuated morphine addictive behavior through its anti-inflammation and neurotrophic effects in rats

Opioid abuse and dependency are international problems. Studies have shown that neuronal inflammation and degeneration might be related to the development of opioid addiction. Thus, using neuroprotective agents might be beneficial for treating opioid addiction. Memantine, an Alzheimer's disease medication, has neuroprotective effects in vitro and in vivo. In this study, we evaluated whether a low dose of memantine prevents opioid-induced drug-seeking behavior in rats and analyzed its mechanism. A conditioned-place-preference test was used to investigate the morphine-induced drug-seeking behaviors in rats. We found that a low-dose (0.2-1 mg/kg) of subcutaneous memantine significantly attenuated the chronic morphine-induced place-preference in rats. To clarify the effects of chronic morphine and low-dose memantine, serum and brain levels of cytokines and brain-derived neurotrophic factor (BDNF) were measured. After 6 days of morphine treatment, cytokine (IL-1β, IL-6) levels had significantly increased in serum; IL-1β and IL-6 mRNA levels had significantly increased in the nucleus accumbens and medial prefrontal cortex, both addiction-related brain areas; and BDNF levels had significantly decreased, both in serum and in addiction-related brain areas. Pretreatment with low-dose memantine significantly attenuated chronic morphine-induced increases in serum and brain cytokines. Low-dose memantine also significantly potentiated serum and brain BDNF levels. We hypothesize that neuronal inflammation and BDNF downregulation are related to the progression of opioid addiction. We hypothesize that the mechanism low-dose memantine uses to attenuate morphine-induced addiction behavior is its anti-inflammatory and neurotrophic effects.

Neurotrophic gene polymorphisms and response to psychological therapy

Therapygenetics, the study of genetic determinants of response to psychological therapies, is in its infancy. Here, we investigate whether single-nucleotide polymorphisms in nerve growth factor (NGF) (rs6330) and brain-derived neutrotrophic factor (BDNF) (rs6265) genes predict the response to cognitive behaviour therapy (CBT). Neurotrophic genes represent plausible candidate genes: they are implicated in synaptic plasticity, response to stress, and are widely expressed in brain areas involved in mood and cognition. Allelic variation at both loci has shown associations with anxiety-related phenotypes. A sample of 374 anxiety-disordered children with white European ancestry was recruited from clinics in Reading, UK, and in Sydney, Australia. Participants received manualised CBT treatment and DNA was collected from buccal cells using cheek swabs. Treatment response was assessed at post-treatment and follow-up time points. We report first evidence that children with one or more copies of the T allele of NGF rs6330 were significantly more likely to be free of their primary anxiety diagnosis at follow-up (OR = 0.60 (0.42-0.85), P = 0.005). These effects remained even when other clinically relevant covariates were accounted for (OR = 0.62 (0.41-0.92), P = 0.019). No significant associations were observed between BDNF rs6265 and response to psychological therapy. These findings demonstrate that knowledge of genetic markers has the potential to inform clinical treatment decisions for psychotherapeutic interventions.

NGF, brain and behavioral plasticity

Nerve Growth Factor (NGF) was initially studied for its role as a key player in the regulation of peripheral innervations. However, the successive finding of its release in the bloodstream of male mice following aggressive encounters and its presence in the central nervous system led to the hypothesis that variations in brain NGF levels, caused by psychosocial stressor, and the related alterations in emotionality, could be functional to the development of proper strategies to cope with the stressor itself and thus to survive. Years later this vision is still relevant, and the body of evidence on the role of NGF has been strengthened and expanded from trophic factor playing a role in brain growth and differentiation to a much more complex messenger, involved in psychoneuroendocrine plasticity.

Association of nerve growth factor and vascular endothelial growth factor A with psychometric measurements of opiate dependence: results of a pilot study in patients participating in a structured diamorphine maintenance program

Preclinical study results suggest that neurotrophic peptides like nerve growth factor (NGF) and vascular endothelial growth factor A (VEGF-A) may be associated with symptoms of addictive behavior like withdrawal symptoms and rewarding effects. We investigated alterations in NGF and VEGF-A serum levels in opiate-dependent patients (25 male patients), who received diamorphine (DAM, heroin) treatment within a structured opiate maintenance program, and compared the results with the NGF and VEGF-A serum levels of healthy controls (23 male controls). NGF and VEGF-A serum levels were assessed before and after DAM administration twice a day (in the morning (16 h after last application--t1) and in the afternoon (7 h after last application--t3)) in order to detect a possible immediate or summative (in the afternoon) heroin effect on these two neuropeptides. Moreover, we investigated possible associations between the serum levels of these neurotrophic growth factors and psychometric dimensions of addictive behavior, e.g. craving, withdrawal, depression. Whereas there was no direct effect of DAM application on the serum levels of both neurotrophic growth factors neither in the morning nor in the afternoon, the NGF serum levels of the patient group were found to be significantly increased at all four time points of investigation compared with the healthy controls. In contrast, VEGF-A serum levels did not differ significantly in the patient and control groups. We found a significant positive association between the NGF serum levels and several items of the short opiate withdrawal scale as well as a negative association between self-reported mood (measured by visual analogue scale) and mood before heroin application (in the morning as in the afternoon). Moreover, we found a significant positive association between the NGF serum levels (t1 and t3) and the self-reported craving for methadone. In contrast, we found a negative association between the VEGF-A serum levels and avoidance, anxiety, suicide intentions of the SCL-90 as well as a positive association between the VEGF-A serum levels and the subscales of the heroin craving questionnaire measuring the rewarding effects of heroin. In conclusion, the results of this pilot study show that there might be an association between symptoms of opiate dependence and withdrawal and serum levels of VEGF-A and NGF.

Risk, resilience, and gene-environment interplay in primates

OBJECTIVES

The primary objectives of the body of research reported here was to demonstrate significant interactions between genetic and social environmental factors that clearly influenced both the biological and behavioral responses of rhesus monkeys to social stressors such as separation from familial and/or familiar conspecifics throughout development and to investigate possible mechanisms underlying such interactions.

METHODS

Prospective longitudinal studies of rhesus monkeys reared in both captive and naturalistic settings have examined individual differences in biological and behavioral responses to stress throughout the lifespan.

RESULTS

Approximately 20% of monkeys in both settings consistently display unusually fearful and anxious-like behavioral reactions to novel, mildly stressful social situations and depressive-like symptoms following repeated separations from familial and/or familiar conspecifics during their infant and juvenile years, as well as profound and prolonged activation of the hypothalamic-pituitary-adrenal (HPA) axis in both situations. Both genetic and experiential factors - as well as their interaction -- are implicated in these reactions to social stress. For example, a specific polymorphism in the serotonin transporter gene is associated with deficits in neonatal neurobehavioral functioning and in extreme behavioral and adreno-cortical responses to social separation among infant and juvenile monkeys who experienced insecure early attachments but not in monkeys who developed secure attachment relationships with their mothers during infancy (maternal "buffering"). Similar instances of maternal "buffering" have been demonstrated in significant gene-environment interplay involving several other "candidate" gene polymorphisms. Moreover, because the attachment style of a monkey mother is typically "copied" by her daughters when they become mothers themselves, similar "buffering" is likely to occur for the next generation of infants carrying so-called "risk" alleles.

CONCLUSIONS

Specific gene-environment interactions can influence behavioral and biological reactions to social stress not only throughout development but also across successive generations of rhesus monkey families.

Early-life stress produces muscle hyperalgesia and nociceptor sensitization in the adult rat

Chronic pain in adults has been associated with early-life stress. To examine the pronociceptive effect of early-life stress, we evaluated cutaneous and muscle nociception and activity in muscle nociceptors in an animal model of neonatal stress, limited bedding, in the rat. In this neonatal limited bedding (NLB) model, litters are exposed to limited bedding between postnatal days 2 and 9, and controls to standard bedding. In adult NLB-treated rats, mechanical nociceptive threshold in skeletal muscle was significantly lower (~22%) than in controls. Furthermore, administration of prostaglandin E(2) in skin as well as muscle produced markedly prolonged hyperalgesia, an effect prevented by spinal intrathecal injection of oligodeoxynucleotide antisense to protein kinase Cε (PKCε), a second messenger in nociceptors that has been implicated in the induction and maintenance of chronic pain. In electrophysiological studies, mechanical threshold of muscle nociceptors was reduced by ~31% and conduction velocity significantly increased (~28%). These findings indicate that neonatal stress induces a persistent hyperalgesia and nociceptor sensitization manifest in the adult and that the second messenger PKCε may be a target against which therapies might be directed to treat a chronic pain syndrome that is associated with early-life traumatic stress.

The richness of social stimuli shapes developmental trajectories: Are laboratory mouse pups impoverished?

The early environment is crucial for brain and behavior development. In particular, social experiences involving the mother and the peers are critical in shaping the adult individual. Though animal models of psychiatric disorders have widely investigated the relevance of the mother-offspring interaction, the peer interaction has so far been rarely studied. The communal nest (CN) is an innovative experimental strategy that favors a more comprehensive investigation of the long-term effects of both components. CN is a rearing condition employed by up to 90% of mouse females in naturalistic settings and consists of a single nest where two or more mothers keep their pups together and share care-giving. In a CN, the developing pup is exposed to high levels of both maternal care and interaction with peers. At adulthood, these mice display relevant changes in bran function and behavior, including high levels of neural plasticity markers, such as BDNF, and elaborate adult social competences. Overall, on the one hand, CN is an experimental approach complementary to the ones currently used that allows to investigate how the early environment determines developmental trajectories. On the other, it may represent a strategy to improve the study of animal models of psychiatric disorders characterized by social dysfunction, such as major depression, autism and attention deficit hyperactivity disorder. Indeed, the more elaborate social competences shown by these mice at adulthood may allow to better characterize deficits in the social domain induced by genetic and/or environmental manipulations.

Variation in NGFB is associated with primary affective disorders in women

Affective disorders (AFDs) are highly comorbid with substance dependence (SD) and both are genetically influenced. However, the specific etiology of the comorbidity is not well understood. We genotyped an array of 1,350 single nucleotide polymorphisms (SNPs) in or near 130 genes in 868 European-Americans (EAs), including 182 individuals with primary AFDs (PAFDs), 214 with SD comorbid with AFD (CAFD), and 472 screened controls. NGFB, which encodes nerve growth factor β and was represented in the array by 15 SNPs, showed the strongest evidence of association, but only among women with PAFDs. Six of the SNPs showed nominally significant association with PAFDs in women (P's = 0.0007-0.01); three (rs2856813, rs4332358, and rs10776799) were empirically significant based on 1,000,000 permutations (P's = 0.008-0.015). Seven haplotypes were significantly associated with PAFDs in women (P's = 0.0014-0.01), of which six were significant based on empirical permutation analysis (minimal P = 0.0045). Four diplotypes were significantly associated with PAFDs in women (global P's = 0.001-0.01). The specific diplotype GG-TC, reconstructed from rs2856813 and rs6678788, showed the strongest evidence of association with PAFDs in women (OR = 4.07, P = 4.2E-05). No SNPs or haplotypes were associated with PAFDs in men or with CAFDs in either sex. We conclude that variation in NGFB is a risk factor for PAFDs in women, but not for CAFD.

A novel BDNF polymorphism affects plasma protein levels in interaction with early adversity in rhesus macaques

Early stressful events can increase vulnerability for psychopathology, although knowledge on the effectors is still limited. In this report we describe the characterization of a single nucleotide polymorphism (SNP) in rhesus macaques, which results in a Val to Met transition in the pro-BDNF domain, similar to a well described variant in the human gene. Further, we tested the hypothesis that peripheral levels of BDNF, which is involved in the response to stress and in the pathophysiology of anxiety and depression, might be differentially affected in a non-human primate model of early adverse rearing in a genotype-dependent manner. Males and females rhesus macaques reared either with their mothers (MR), in peer-only groups (PR), or in a "surrogate/peer-reared" (SPR) condition with limited peer interactions, were used as experimental subjects. BDNF levels were determined at baseline on postnatal days (PND) 14, 30 and 60 by means of specific ELISA procedure. Data indicate that BDNF levels were increased as a result of peer-rearing and that this increase was moderated by the presence of the SNP. Overall these data indicate that a SNP, which results in a Val to Met transition in the pro-BDNF domain, is present in rhesus macaques and is able to affect BDNF peripheral levels, thus making this primate model a fundamental tool to study gene by environment interactions involving the BDNF gene.

Early-stress regulates resilience, vulnerability and experimental validity in laboratory rodents through mother-offspring hormonal transfer

The role of early-life stressors in the calibration of individual responses to future challenges has long been investigated in laboratory rodents. Specifically, countless studies show that exposure to early-life stressors - in the form of various periods of maternal separation, administration of exogenous corticosterone and variable feeding conditions - modulate the regulation of defensive responses (e.g. behavioral fearfulness/anxiety and endocrine stress reactivity) in adulthood. Yet, the link between early-life stress and adult defensive responses is not linear. Specifically, while neonatal moderate stress is generally associated with adult subjects characterized by reduced stress reactivity, neonatal elevated stress is often reported to relate to opposite responses. Not only are these findings relevant to the understanding of individual plasticity to contextual features, but also they can have direct implications in the development of rodent models of human disorders. Specifically, these studies demonstrate that the experimental individual responds to early environmental cues with the consequence of adjusting its adaptation to the future environment. If neglected, this aspect may have detrimental consequences in laboratory animal experimentation. For example, neonatal conditions increasing adult responses to moderate stress may result in experimental subjects showing abnormal hypothalamic-pituitary-adrenocortical (HPA) activation to routine husbandry conditions, test environment and general laboratory procedures. The aim of the present review is threefold: (i) propose that neonatal circulating levels of corticosteroids may constitute a potential mediator connecting early and adult defensive systems; (ii) propose that the link between early and adult stress follows a U-shaped curve, with low levels down-regulating individual reactivity to external stressors and high levels exerting opposite effects; (iii) discuss the methodological implications of these considerations in the development of rodent models of human disorders.

BDNF and GDNF serum levels in alcohol-dependent patients during withdrawal

Preclinical study results suggest that brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) modulate addictive behaviour. Therefore we investigated alterations in BDNF (81 male patients) and GDNF serum levels (52 male patients) in alcohol-dependent patients during alcohol withdrawal (day 1, 7 and 14) in comparison to healthy controls (41 male controls). BDNF serum levels were not significantly altered in alcohol-dependent patients compared to healthy controls (p=0.685). GDNF serum levels were significantly reduced in the alcohol-dependent patients (p<0.001). BDNF (p=0.265) and GDNF (p=0.255) serum levels did not change significantly during alcohol withdrawal. BDNF serum levels were significantly negatively associated with alcohol withdrawal severity on day 1 (CIWA-Ar score, p=0.004). GDNF serum levels were significantly negatively associated with individual estimation of alcohol tolerance (SESA-XT score, p=0.028). There was no further association with psychometric dimensions of alcohol withdrawal. In conclusion we found that GDNF serum levels are significantly reduced in alcohol-dependent patients. GDNF serum levels were negatively associated with alcohol tolerance. Moreover BDNF serum levels were found to be associated with withdrawal severity.

Effects of maternal smoking and exposure to methylmercury on brain-derived neurotrophic factor concentrations in umbilical cord serum

Brain-derived neurotrophic factor (BDNF) is a neurotrophin essential for neuronal survival and differentiation. We examined the concentration of BDNF in cord serum from newborns exposed to methylmercury (MeHg) and polychlorinated biphenyls (PCB) in utero by maternal consumption of whale meat. The cohort consisted of 395 singleton births (206 boys and 189 girls), gestational age ranging from 38 to 42 weeks. Serum BDNF was measured by sandwich ELISA. Maternal smoking habits and other relevant factors were obtained by interviewing the mothers. The exposure to MeHg was estimated from Hg concentrations in cord blood, whereas exposure to PCB was estimated based on maternal serum concentrations. Only MeHg exposure affected the serum BDNF, which decreased in a concentration-dependent manner in girls born to nonsmoking mothers. Maternal smoking significantly increased BNDF in girls but not in boys. For further statistical analyses, we used the serum BDNF concentration as a continuous outcome variable in supervised regression models. Serum BDNF concentration increased with gestational age, increased by maternal smoking, decreased slightly with MeHg exposure, and maternal smoking enhanced the decrease in serum BDNF induced by MeHg exposure. Cord blood BDNF has been reported to increase in association with perinatal brain injuries and has been proposed as a possible predictive marker of neurodevelopmental outcomes. The negative effect that MeHg seems to exert on cord blood BDNF concentration could endanger compensatory responses to an adverse impact and therefore deserves attention.

Maternal deprivation induces a rapid decline in circulating leptin levels and sexually dimorphic modifications in hypothalamic trophic factors and cell turnover

Pathological outcomes, including metabolic and endocrine disturbances, of maternal deprivation (MD) in Wistar rats depend on gender and the timing of deprivation during development. We analyzed the effect of MD between postnatal days 9 and 10, a critical period in hypothalamic development, on circulating hormones and local production of trophic factors involved in this process, as well as on markers of cell turnover and maturation. Males and females were studied 12 and 24 h after MD and 12 h (MD36) after returning the dam to her pups. Circulating corticosterone levels were increased and glucose and leptin levels decreased throughout the study in both sexes. Hypothalamic mRNA levels of leptin receptor increased significantly at MD24 in both sexes, normalizing in females at MD36, but not in males. In male rats insulin-like growth factor mRNA levels were significantly decreased at MD24 and brain derived neurotrophic factor mRNA levels decreased at MD12 and MD24, with both trophic factors unaffected in females. In males cell proliferation was significantly decreased at MD36, as were the glial structural proteins, glial fibrillary acidic protein and vimentin. In females, nestin levels decreased significantly at MD24. These results indicate that MD differently affects trophic factors and cell-turnover in the hypothalamus of males and females, which may underlie the sex differences seen in the endocrine and metabolic outcome.