Gestational stress induces depressive-like and anxiety-like phenotypes through epigenetic regulation of BDNF expression in offspring hippocampus

Prenatal Dexamethasone Exposure Induced Alterations in Neurobehavior and Hippocampal Glutamatergic System Balance in Female Rat Offspring

Epidemiological investigations have suggested that periodic use of dexamethasone during pregnancy is a risk factor for abnormal behavior in offspring, but the potential mechanism remains unclear. In this study, we investigated the changes in the glutamatergic system and neurobehavior in female offspring with prenatal dexamethasone exposure (PDE) to explore intrauterine programing mechanisms. Compared with the control group, rat offspring with PDE exhibited spatial memory deficits and anxiety-like behavior. The expression of hippocampal glucocorticoid receptors (GR) and histone deacetylase 2 (HDAC2) increased, whereas histone H3 lysine 14 acetylation (H3K14ac) of brain-derived neurotrophic factor (BDNF) exon IV (BDNF IV) and expression of BDNF decreased. The glutamatergic system also changed. We further observed that changes in the fetal hippocampus were consistent with those in adult offspring. In vitro, the administration of 0.5 μM dexamethasone to the H19-7 fetal hippocampal neuron cells directly led to a cascade of changes in the GR/HDAC2/BDNF pathway, whereas the GR antagonist RU486 and the HDAC2 inhibitor romidepsin (Rom) reversed changes caused by dexamethasone to the H3K14ac level of BDNF IV and to the expression of BDNF. The increase in HDAC2 can be reversed by RU486, and the changes in the glutamatergic system can be partially reversed after supplementation with BDNF. It is suggested that PDE increases the expression of HDAC2 by activating GR, reducing the H3K14ac level of BDNF IV, inducing alterations in neurobehavior and hippocampal glutamatergic system balance. The findings suggest that BDNF supplementation and glutamatergic system improvement are potential therapeutic targets for the fetal origins of abnormal neurobehavior.

Prenatal maternal depressive symptoms and infant DNA methylation: a longitudinal epigenome-wide study

Background: Prenatal maternal stress increases the risk of offspring developmental and psychological difficulties. The biological mechanisms behind these associations are mostly unknown. One explanation suggests that exposure of the fetus to maternal stress may influence DNA methylation. However, this hypothesis is largely based on animal studies, and human studies of candidate genes from single timepoints. Aim: The aim of this study was to investigate if prenatal maternal stress, in the form of maternal depressive symptoms, was associated with variation in genome-wide DNA methylation at two timepoints. Methods: One-hundred and eighty-four mother-child dyads were selected from a population of pregnant women in the Little-in-Norway study. The Edinburgh Postnatal Depression Scale (EPDS) measured maternal depressive symptoms. It was completed by the pregnant mothers between weeks 17 and 32 of gestation. DNA was obtained from infant saliva cells at two timepoints (age 6 weeks and 12 months). DNA methylation was measured in 274 samples from 6 weeks (n = 146) and 12 months (n = 128) using the Illumina Infinium HumanMethylation 450 BeadChip. Linear regression analyses of prenatal maternal depressive symptoms and infant methylation were performed at 6 weeks and 12 months separately, and for both timepoints together using a mixed model. Results: The analyses revealed no significant genome-wide association between maternal depressive symptoms and infant DNA methylation in the separate analyses and for both timepoints together. Conclusions: This sample of pregnant women and their infants living in Norway did not reveal associations between maternal depressive symptoms and infant DNA methylation.

Advance in Stress for Depressive Disorder

Stress is an adaptive response to environment aversive stimuli and a common life experience of one's daily life. Chronic or excessive stress especially that happened in early life is found to be deleterious to individual's physical and mental health, which is highly related to depressive disorders onset. Stressful life events are consistently considered to be the high-risk factors of environment for predisposing depressive disorders. In linking stressful life events with depressive disorder onset, dysregulated HPA axis activity is supposed to play an important role in mediating aversive impacts of life stress on brain structure and function. Increasing evidence have indicated the strong association of stress, especially the chronic stress and early life stress, with depressive disorders development, while the association of stress with depression is moderated by genetic risk factors, including polymorphism of SERT, BDNF, GR, FKBP5, MR, and CRHR1. Meanwhile, stressful life experience particularly early life stress will exert epigenetic modification in these risk genes via DNA methylation and miRNA regulation to generate long-lasting effects on these genes expression, which in turn cause brain structural and functional alteration, and finally increase the vulnerability to depressive disorders. Therefore, the interaction of environment with gene, in which stressful life exposure interplay with genetic risk factors and epigenetic modification, is essential in predicting depressive disorders development. As the mediator of environmental risk factors, stress will function together with genetic and epigenetic mechanism to influence brain structure and function, physiology and psychology, and finally the vulnerability to depressive disorders.

Gestational stress induced differential expression of HDAC2 in male rat offspring hippocampus during development

Accumulating evidence from preclinical and clinical studies indicates prenatal exposure to stress or excess glucocorticoids can affect offspring brain. HDAC2 is an important target of glucocorticoid. Here we detected HDAC2 expression in male offspring hippocampus from gestational restraint stressed rat during development and the relationship between HDAC2 expression and behaviors and neurogenesis in male offspring. Pregnant rats received restrained stress during the last week of pregnancy. Expressions of HDAC2 in offspring hippocampus were detected on postnatal 0 day (P0) and 60 days (P60). Neurogenesis was evaluated by Doublecortin (DCX) staining on P60. Anxiety-like behavior and cognition were detected in open field, elevated plus maze, novel object recognition test, and Barnes maze. We found that HDAC2 expression in the hippocampus of male prenatally stressed offspring (MPSO) was similar to the male control offspring on P0, but significantly lower on P60. Corresponding to the decreased expression of HDAC2 in MPSO hippocampus at P60, neurogenesis in the dentate gyrus of MPSO was significantly lower than the control male offspring. And MPSO also showed greater anxiety and poorer learning and memories abilities than control male offspring. These showed that HDAC2 could partly explain the effects of gestational stress on male offspring behaviors.

Epigenetic Inheritance: Concepts, Mechanisms and Perspectives

Parents’ stressful experiences can influence an offspring’s vulnerability to many pathological conditions, including psychopathologies, and their effects may even endure for several generations. Nevertheless, the cause of this phenomenon has not been determined, and only recently have scientists turned to epigenetics to answer this question. There is extensive literature on epigenetics, but no consensus exists with regard to how and what can (and must) be considered to study and define epigenetics processes and their inheritance. In this work, we aimed to clarify and systematize these concepts. To this end, we analyzed the dynamics of epigenetic changes over time in detail and defined three types of epigenetics: a direct form of epigenetics (DE) and two indirect epigenetic processes—within (WIE) and across (AIE). DE refers to changes that occur in the lifespan of an individual, due to direct experiences with his environment. WIE concerns changes that occur inside of the womb, due to events during gestation. Finally, AIE defines changes that affect the individual’s predecessors (parents, grandparents, etc.), due to events that occur even long before conception and that are somehow (e.g., through gametes, the intrauterine environment setting) transmitted across generations. This distinction allows us to organize the main body of epigenetic evidence according to these categories and then focus on the latter (AIE), referring to it as a faster route of informational transmission across generations—compared with genetic inheritance—that guides human evolution in a Lamarckian (i.e., experience-dependent) manner. Of the molecular processes that are implicated in this phenomenon, well-known (methylation) and novel (non-coding RNA, ncRNA) regulatory mechanisms are converging. Our discussion of the chief methods that are used to study epigenetic inheritance highlights the most compelling technical and theoretical problems of this discipline. Experimental suggestions to expand this field are provided, and their practical and ethical implications are discussed extensively.

Prenatal stress leads to chromatin and synaptic remodeling and excessive alcohol intake comorbid with anxiety-like behaviors in adult offspring

Epidemiologic evidence suggests that individuals during their prenatal development may be especially vulnerable to the effects of environmental factors such as stress that predisposes them to psychiatric disorders including alcohol use disorder (AUD) later in life. Currently, the epigenetic mechanisms of anxiety comorbid with AUD induced by prenatal stress (PRS) remain to be elucidated. Here, we examined anxiety-like and alcohol drinking behaviors in adult offspring of prenatally stressed dam (PRS-mice) using elevated plus maze, light/dark box and two-bottle free-choice paradigm. It was found that PRS-mice exhibit heightened anxiety-like behaviors and increased alcohol intake in adulthood and these behavioral deficits were associated with a significant decrease in dendritic spine density (DSD) in medial prefrontal cortex (mPFC) relative to non-stressed mice (NS mice). To determine the mechanisms by which PRS reduces DSD, we examined the expressions of key genes associated with synaptic plasticity, including activity regulated cytoskeleton associated protein (Arc), spinophilin (Spn), postsynaptic density 95 (Psd95), tropomyosin receptor kinase B (TrkB), protein kinase B (Akt), mammalian target of rapamycin (mTOR) and period 2 (Per2) in mPFC of PRS and NS mice. The mRNA levels of these genes were significantly decreased in PRS mice. Methylated DNA and chromatin immunoprecipitation studies revealed hyper DNA methylation or reduced histone H3K14 acetylation on promoters of above genes suggesting that epigenetic dysregulation may be responsible for the deficits in their expression. Findings from this study suggest that prenatal stress induced abnormal epigenetic mechanisms and synaptic plasticity-related events may be associated with anxiety-like and alcohol drinking behaviors in adulthood.

Developmental Lead Exposure and Prenatal Stress Result in Sex-Specific Reprograming of Adult Stress Physiology and Epigenetic Profiles in Brain

Developmental exposure to lead (Pb) and prenatal stress (PS) both impair cognition, which could derive from their joint targeting of the hypothalamic-pituitary-adrenal axis and the brain mesocorticolimbic (MESO) system, including frontal cortex (FC) and hippocampus (HIPP). Glucocorticoids modulate both FC and HIPP function and associated mediation of cognitive and other behavioral functions. This study sought to determine whether developmental Pb ± PS exposures altered glucocorticoid-related epigenetic profiles in brain MESO regions in offspring of female mice exposed to 0 or 100 ppm Pb acetate drinking water from 2 mos prior to breeding until weaning, with half further exposed to prenatal restraint stress from gestational day 11-18. Overall, changes in females occured in response to Pb exposure. In males, however, Pb-induced neurotoxicity was modulated by PS. Changes in serum corticosterone levels were seen in males, while glucocorticoid receptor changes were seen in both sexes. In contrast, both Pb and PS broadly impacted brain DNA methyltransferases and binding proteins, particularly DNMT1, DNMT3a and methyl-CpG-binding protein 2, with patterns that differed by sex and brain regions. Specifically, in males, effects on FC epigenetic modifiers were primarily influenced by Pb, whereas extensive changes in HIPP were produced by PS. In females, Pb exposure and not PS primarily altered epigenetic modifiers in both FC and HIPP. Collectively, these findings indicate that epigenetic mechanisms may underlie associated neurotoxicity of Pb and of PS, particularly associated cognitive deficits. However, mechanisms by which this may occur will be different in males versus females.

Genipin normalizes depression-like behavior induced by prenatal stress through inhibiting DNMT1

Synthetic antidepressants in current use for the complex etiopathogeneses of depression have slow response and remission as well as various unpleasant side effects. As a result, it is imperative to develop new antidepressants with more effectiveness and less severe side effects. Recent studies demonstrated that genipin, the aglycon of geniposide, extracted from Gardenia jasminoides Ellis has antidepressive effects. However, knowledge regarding the molecular mechanisms of its antidepressant effects remains limited. Employing a depression-like mouse model, we confirmed that genipin is capable of correcting depressions-like behaviors induced by prenatal stress in offspring from prenatally stressed dams (defined as PRS mice). In further experiments, we found that the effect of genipin on PRS mice occurs through DNA demethylation by inhibiting DNA methyltransferase 1 (DNMT1), normalizing the expression of reduced brain-derived neurotrophic factor (BDNF) in the hippocampus.

A comprehensive review of genetic and epigenetic mechanisms that regulate BDNF expression and function with relevance to major depressive disorder

Major depressive disorder (MDD) is a mood disorder that affects behavior and impairs cognition. A gene potentially important to this disorder is the brain derived neurotrophic factor (BDNF) as it is involved in processes controlling neuroplasticity. Various mechanisms exist to regulate BDNF's expression level, subcellular localization, and sorting to appropriate secretory pathways. Alterations to these processes by genetic factors and negative stressors can dysregulate its expression, with possible implications for MDD. Here, we review the mechanisms governing the regulation of BDNF expression, and discuss how disease-associated single nucleotide polymorphisms (SNPs) can alter these mechanisms, and influence MDD. As negative stressors increase the likelihood of MDD, we will also discuss the impact of these stressors on BDNF expression, the cellular effect of such a change, and its impact on behavior in animal models of stress. We will also describe epigenetic processes that mediate this change in BDNF expression. Similarities in BDNF expression between animal models of stress and those in MDD will be highlighted. We will also contrast epigenetic patterns at the BDNF locus between animal models of stress, and MDD patients, and address limitations to current clinical studies. Future work should focus on validating current genetic and epigenetic findings in tightly controlled clinical studies. Regions outside of BDNF promoters should also be explored, as should other epigenetic marks, to improve identification of biomarkers for MDD.

Involvement of Epigenetic Modifications of GABAergic Interneurons in Basolateral Amygdala in Anxiety-like Phenotype of Prenatally Stressed Mice

BACKGROUND

Prenatal stress is considered a risk factor for anxiety disorder. Downregulation in the expression of GABAergic gene, that is, glutamic acid decarboxylase 67, associated with DNA methyltransferase overexpression in GABAergic neurons has been regarded as a characteristic component of anxiety disorder. Prenatal stress has an adverse effect on the development of the basolateral amygdala, which is a key region in anxiety regulation. The aim of this study is to analyze the possibility of epigenetic alterations of GABAergic neurons in the basolateral amygdala participating in prenatal stress-induced anxiety.

METHODS

Behavioral tests were used to explore the prenatal stress-induced anxiety behaviors of female adult mice. Real-time RT-PCR, western blot, chromatin immunoprecipitation, and electrophysiological analysis were employed to detect epigenetic changes of GABAergic system in the basolateral amygdala.

RESULTS

Prenatal stress mice developed an anxiety-like phenotype accompanied by a significant increase of DNA methyltransferase 1 and a reduced expression of glutamic acid decarboxylase 67 in the basolateral amygdala. Prenatal stress mice also showed the increased binding of DNA methyltransferase 1 and methyl CpG binding protein 2 to glutamic acid decarboxylase 67 promoter region. The decrease of glutamic acid decarboxylase 67 transcript was paralleled by an enrichment of 5-methylcytosine in glutamic acid decarboxylase 67 promoter regions. Electrophysiological study revealed the increase of postsynaptic neuronal excitability in the cortical-basolateral amygdala synaptic transmission of prenatal stress mice. 5-Aza-deoxycytidine treatment restored the increased synaptic transmission and anxiety-like behaviors in prenatal stress mice via improving GABAergic system.

CONCLUSION

The above results suggest that DNA epigenetic modifications of GABAergic interneurons in the basolateral amygdala participate in the etiology of anxiety-like phenotype in prenatal stress mice.

A preclinical perspective on the enhanced vulnerability to Alzheimer's disease after early-life stress

Stress experienced early in life (ES), in the form of childhood maltreatment, maternal neglect or trauma, enhances the risk for cognitive decline in later life. Several epidemiological studies have now shown that environmental and adult life style factors influence AD incidence or age-of-onset and early-life environmental conditions have attracted attention in this respect. There is now emerging interest in understanding whether ES impacts the risk to develop age-related neurodegenerative disorders, and their severity, such as in Alzheimer's disease (AD), which is characterized by cognitive decline and extensive (hippocampal) neuropathology. While this might be relevant for the identification of individuals at risk and preventive strategies, this topic and its possible underlying mechanisms have been poorly studied to date. In this review, we discuss the role of ES in modulating AD risk and progression, primarily from a preclinical perspective. We focus on the possible involvement of stress-related, neuro-inflammatory and metabolic factors in mediating ES-induced effects on later neuropathology and the associated impairments in neuroplasticity. The available studies suggest that the age of onset and progression of AD-related neuropathology and cognitive decline can be affected by ES, and may aggravate the progression of AD neuropathology. These relevant changes in AD pathology after ES exposure in animal models call for future clinical studies to elucidate whether stress exposure during the early-life period in humans modulates later vulnerability for AD.

Neurodevelopmental theory of depression

The aim of research studies in the field of psychiatry conducted in recent years is to formulate a consistent theory that would exhaustively explain the aetiology of depression. So far, biochemical, genetic, anatomical and environmental factors, which may play a role in the occurrence of the first symptoms of depressive disorders, have been sought. The authors of this paper present a theory that combines the previously mentioned elements into one whole and links them to one another. We have called our theory "neurodevelopmental" to underline the importance and impact of earlier stages of human life, including the prenatal period, on the occurrence of depressive disorders. We will make an attempt to find an answer to why this time in the life of a human being is so important, what kind of biological mechanisms are activated then, and what aspects of our later functioning are affected by them.

Insights into neuroepigenetics through human histone deacetylase PET imaging

Epigenetic dysfunction is implicated in many neurological and psychiatric diseases, including Alzheimer's disease and schizophrenia. Consequently, histone deacetylases (HDACs) are being aggressively pursued as therapeutic targets. However, a fundamental knowledge gap exists regarding the expression and distribution of HDACs in healthy individuals for comparison to disease states. Here, we report the first-in-human evaluation of neuroepigenetic regulation in vivo. Using positron emission tomography with [(11)C]Martinostat, an imaging probe selective for class I HDACs (isoforms 1, 2, and 3), we found that HDAC expression is higher in cortical gray matter than in white matter, with conserved regional distribution patterns within and between healthy individuals. Among gray matter regions, HDAC expression was lowest in the hippocampus and amygdala. Through biochemical profiling of postmortem human brain tissue, we confirmed that [(11)C]Martinostat selectively binds HDAC isoforms 1, 2, and 3, the HDAC subtypes most implicated in regulating neuroplasticity and cognitive function. In human stem cell-derived neural progenitor cells, pharmacologic-level doses of Martinostat induced changes in genes closely associated with synaptic plasticity, including BDNF (brain-derived neurotrophic factor) and SYP (synaptophysin), as well as genes implicated in neurodegeneration, including GRN (progranulin), at the transcript level, in concert with increased acetylation at both histone H3 lysine 9 and histone H4 lysine 12. This study quantifies HDAC expression in the living human brain and provides the foundation for gaining unprecedented in vivo epigenetic information in health and disease.

Impact of varying social experiences during life history on behaviour, gene expression, and vasopressin receptor gene methylation in mice

Both negative and positive social experiences during sensitive life phases profoundly shape brain and behaviour. Current research is therefore increasingly focusing on mechanisms mediating the interaction between varying life experiences and the epigenome. Here, male mice grew up under either adverse or beneficial conditions until adulthood, when they were subdivided into groups exposed to situations that either matched or mismatched previous conditions. It was investigated whether the resulting four life histories were associated with changes in anxiety-like behaviour, gene expression of selected genes involved in anxiety and stress circuits, and arginine vasopressin receptor 1a (Avpr1a) gene methylation. Varying experiences during life significantly modulated (1) anxiety-like behaviour; (2) hippocampal gene expression of Avpr1a, serotonin receptor 1a (Htr1a), monoamine oxidase A (Maoa), myelin basic protein (Mbp), glucocorticoid receptor (Nr3c1), growth hormone (Gh); and (3) hippocampal DNA methylation within the Avpr1a gene. Notably, mice experiencing early beneficial and later adverse conditions showed a most pronounced downregulation of Avpr1a expression, accompanied by low anxiety-like behaviour. This decrease in Avpr1a expression may have been, in part, a consequence of increased methylation in the Avpr1a gene. In summary, this study highlights the impact of interactive social experiences throughout life on the hippocampal epigenotype and associated behaviour.

Paternal spatial training enhances offspring's cognitive performance and synaptic plasticity in wild-type but not improve memory deficit in Alzheimer's mice

Recent studies suggest that spatial training can maintain associative memory capacity in Tg2576 mice, but it is not known whether the beneficial effects can be inherited from the trained fathers to their offspring. Here, we exposed male wild-type and male 3XTg Alzheimer disease (AD) mice (3-m old) respectively to spatial training for one week and assessed the transgenerational effects in the F1 offspring when they were grown to 7-m old. We found that the paternal spatial training significantly enhanced progeny’s spatial cognitive performance and synaptic transmission in wild-type mice. Among several synapse- or memory-associated proteins, we observed that the expression level of synaptotagmin 1 (SYT1) was significantly increased in the hippocampus of the paternally trained-offspring. Paternal training increased histone acetylation at the promoter of SYT1 in both fathers’ and the offspring’s hippocampus, and as well as in the fathers’ sperm. Finally, paternal spatial training for one week did not improve memory and synaptic plasticity in 3XTg AD F1 offspring. Our findings suggest paternal spatial training for one week benefits the offspring’s cognitive performance in wild-type mice with the mechanisms involving an enhanced transgenerational histone acetylation at SYT1 promoter.

Prenatal noise and restraint stress interact to alter exploratory behavior and balance in juvenile rats, and mixed stress reverses these effects

We aimed to investigate in adolescent rats the individual and combined effects of prenatal noise and restraint stress on balance control, exploration, locomotion and anxiety behavior. Three groups of pregnant rats were exposed to daily repeated stress from day 11 to day 19 of pregnancy: 3 min noise (Noise Stress, NS); 10 min restraint (restraint stress, RS); or 3 min noise followed by 10 min restraint (mixed stress, MS). On postnatal days (PND) 44, 45 and 46, four groups of male rats (Control, NS, RS:, MS; 16 rats each), were tested as follows: (1) beam walking (BW), (2) open field (OF) and (3) elevated plus maze (EPM). Our results show that the NS group had significantly impaired balance control, locomotion and both horizontal and vertical exploration (p < .01 for all measures). The RS group showed only a decrease in vertical exploration (p < .05). In contrast, locomotion and balance were not affected in the MS group (OF: crossed squares: p = .34, missteps: p = .18). However, MS rats exhibited significantly higher anxiety levels (less time in EPM open arms: p < .05), and took more time to complete BW: p < .05). Hence, combined prenatal stressors exert non-additive effects on locomotion, exploration and balance control, but induce greater anxiety through additive effects. Terminal plasma ACTH concentration was increased by prenatal stress, especially noise, which group had the largest adrenal glands. Overall, contrary to expectation, combined prenatal stressors can interact to increase anxiety level, but diminish alteration of exploration, locomotion and impaired balance control, which were strongly induced by noise stress. Lay summary: Experience of stress in pregnancy can have negative effects on the offspring that are long-lasting. Here, we used laboratory rats to see whether repeated episodes of exposure to loud noise or preventing free movement, alone or together, during pregnancy had different effects on behaviors of the adolescent offspring. Using standard tests, we found the prenatal stresses caused the offspring to be anxious, and not to balance when moving around as well as normal offspring; the degree of impairment depended on the type of stress - loud noise exposure had the greatest effects, but if the stresses were combined the effects were not worse. The results point to the need to aim to avoid stress in pregnant women.

The Epigenetic Link between Prenatal Adverse Environments and Neurodevelopmental Disorders

Prenatal adverse environments, such as maternal stress, toxicological exposures, and viral infections, can disrupt normal brain development and contribute to neurodevelopmental disorders, including schizophrenia, depression, and autism. Increasing evidence shows that these short- and long-term effects of prenatal exposures on brain structure and function are mediated by epigenetic mechanisms. Animal studies demonstrate that prenatal exposure to stress, toxins, viral mimetics, and drugs induces lasting epigenetic changes in the brain, including genes encoding glucocorticoid receptor (Nr3c1) and brain-derived neurotrophic factor (Bdnf). These epigenetic changes have been linked to changes in brain gene expression, stress reactivity, and behavior, and often times, these effects are shown to be dependent on the gestational window of exposure, sex, and exposure level. Although evidence from human studies is more limited, gestational exposure to environmental risks in humans is associated with epigenetic changes in peripheral tissues, and future studies are required to understand whether we can use peripheral biomarkers to predict neurobehavioral outcomes. An extensive research effort combining well-designed human and animal studies, with comprehensive epigenomic analyses of peripheral and brain tissues over time, will be necessary to improve our understanding of the epigenetic basis of neurodevelopmental disorders.

Brain-derived neurotrophic factor and early-life stress: Multifaceted interplay

The brain-derived neurotrophic factor (BDNF) is a key regulator of neural development and plasticity. Longterm changes in the BDNF pathway are associated with childhood adversity and adult depression symptoms. Initially, stress-induced decreases in the BDNF pathway were found in some studies, but subsequent reports indicated the relationship between stress and BDNF to be much more complex, and the concept was significantly revised. In the present mini-review, we focus on the structure and regulation of the Bbnf gene as well as on the stress-BDNF interactions under early-life adverse conditions.

Altered Acoustic Startle Reflex, Prepulse Inhibition, and Peripheral Brain-Derived Neurotrophic Factor in Morphine Self-Administered Rats

BACKGROUND

Previous studies suggested that opiate withdrawal may increase anxiety and disrupt brain-derived neurotrophic factor function, but the effects of i.v. morphine self-administration on these measures remain unclear.

METHODS

Adult male Sprague-Dawley rats were implanted with a catheter in the jugular vein. After 1 week of recovery, the animals were allowed to self-administer either i.v. morphine (0.5 mg/kg per infusion, 4 h/d) or saline in the operant conditioning chambers. The acoustic startle reflex and prepulse inhibition were measured at a baseline and on self-administration days 1, 3, 5, and 7 (1- and 3-hour withdrawal). Blood samples were collected on self-administration days 3, 5, and 7 from separate cohorts of animals, and the levels of brain-derived neurotrophic factor and corticosterone were assayed using the enzyme-linked immunosorbent assay method.

RESULTS

Compared with the saline group, the morphine self-administration group showed hyper-locomotor activity and reduced defecation during the self-administration. The morphine self-administration increased acoustic startle reflex at 1-hour but not 3-hour withdrawal from morphine and disrupted prepulse inhibition at 3-hour but not 1-hour withdrawal. The blood brain-derived neurotrophic factor levels were decreased in the morphine self-administration group at self-administration days 3 and 5, while the corticosterone levels remained unchanged throughout the study.

CONCLUSIONS

The current findings suggest that spontaneous withdrawal from i.v. morphine self-administration may have transient effects on acoustic startle, sensorimotor gating, and peripheral brain-derived neurotrophic factor levels, and these changes may contribute to the adverse effects of opiate withdrawal.