Altered expression of glial and synaptic markers in the anterior hippocampus of behaviorally depressed female monkeys

Emerging role of microglia and astrocyte in the affective-motivational response induced by a rat model of persistent orofacial pain

Few studies are approaching the neural basis underlying the aggregation of emotional disorders in orofacial pain despite the stress, depression, and anxiety are some of the most commonly reported risk factors. Using a persistent orofacial pain rat model induced by complete Freund's adjuvant (CFA) injection into the temporomandibular joint, we have investigated the plasticity astrocytes and microglia key brain regions for the affective-emotional component of pain. We measured the expression and morphologic pattern of reactivation of glial fibrillary acidic protein (GFAP, astrocyte marker) and Iba-1 (microglial marker) by western blotting and immunohistochemistry analysis. The results showed no alterations on motor activity during inflammatory pain, indicating an exclusive effect of nociceptive behavior on the plasticity of limbic regions. CFA-induced temporomandibular inflammation changed GFAP and Iba-1 expression in distinct regions related to emotional behavior in a time-dependent manner. A significant increase in GFAP and Iba-1 expression was observed in the central nucleus of the amygdala, hippocampus and periaqueductal grey matter from day 3 to day 10 post-CFA injection. Moreover, a positive correlation between GFAP and Iba-1 upregulation and an increased mechanical hypersensitivity was observed. Conversely, no change on GFAP and Iba-1 expression was observed in the hypothalamus and colliculus during orofacial inflammatory pain. Our data suggest an important role for glial cells in the affective-motivational dimension of orofacial pain beyond their well-explored role in the traditional nociceptive transmission circuits.

Chronic haloperidol administration downregulates select BDNF transcript and protein levels in the dorsolateral prefrontal cortex of rhesus monkeys

Post-mortem studies in the prefrontal cortex and hippocampal formation from schizophrenia patients have revealed significant disruptions in the expression molecules associated with cytoarchitecture, synaptic structure, function, and plasticity, known to be regulated in part by brain derived neurotrophic factor (BDNF). Interestingly, several studies using postmortem brain tissue from individuals diagnosed with schizophrenia have revealed a significant reduction in BDNF mRNA and protein levels in the dorsolateral prefrontal cortex (DLPFC), hippocampus and related areas; however, differentiating the effects of illness from antipsychotic history has remained difficult. We hypothesized that chronic antipsychotic treatment may contribute to the altered BDNF mRNA and protein expression observed in post-mortem brains of individuals diagnosed with schizophrenia. To address the influence of antipsychotic administration on BDNF expression in the primate brain, rhesus monkeys orally administered haloperidol, clozapine, or vehicle twice daily for 180 days. We found BDNF splice variants 4 and 5 in the DLPFC and variant 2 in the EC were significantly down-regulated following chronic administration of haloperidol. In addition, proBDNF and mature BDNF expression in the DLPFC, but not the EC, were significantly reduced. Based on the known regulation of BDNF expression by BDNF-AS, we assessed the expression of this lncRNA and found expression was significantly upregulated in the DLPFC, but not EC. The results of the present study provide evidence of haloperidol-induced regulation of BDNF mRNA and protein expression in the DLFPC and suggest an important role for BDNF-AS in this regulation. Given the role of BDNF in synaptic plasticity, neuronal survival and maintenance, aberrant expression induced by haloperidol likely has significant ramifications for neuronal populations and circuits in primate cortex.

Sleep deprivation leads to further impairment of hippocampal synaptic plasticity by suppressing melatonin secretion in the pineal gland of chronically unpredictable stress rats

There has been ample research showing that insomnia is a potential trigger of depression as well as a symptom of depression. These two factors contribute to behavioral problems and are closely related to the plasticity of hippocampal synapses. Although depression and insomnia impair hippocampal synaptic plasticity, the mechanism by which this happens remains a mystery. This study aimed to investigate the pathogenesis of insomnia comorbidity in depression and the regulatory effect of venlafaxine combined with melatonin on hippocampal synaptic plasticity in chronic unpredictable mild stress (CUMS) with sleep deprivation (SD) rats. Thus, rats were subjected to 14 days of chronic mild unpredictable stress, gradually acclimated to sleep deprivation on days 12-14. Followed by 21 consecutive days of sleep deprivation, 18 hours per day, with daily gavage of venlafaxine (13.5 mg/kg) + melatonin (72 mg/kg) on days 15-36. Venlafaxine + melatonin treatment improves depression-like behavior, pentobarbital sodium experimental sleep latency, and sleep duration in CUMS +SD rats. In addition to improving depressive-like behaviors, sleep deprivation also upregulates the expression of caspase-specific cysteine protein 3 (Caspase 3) in the pineal glial cells of chronic mild rats, as well as in hippocampal microglia. Expression of ionic calcium-binding adaptor 1 (iba-1), downregulates the secretion of several synaptic plasticity-related proteins, notably cAMP response element binding protein (CREB), glial cell line-derived neurotrophic factor (GDNF), and the synaptic scaffolding protein Spinophiline (Spinophiline). Hematoxylin-eosin staining showed that the structure of the pineal gland and hippocampus was damaged, and Golgi staining showed that the dendrites and spines in the DG area of ​​the hippocampus were destroyed, vaguely aggregated or even disappeared, and the connection network could not be established. Western blot analysis further revealed a positive correlation between low melatonin levels and reduced Spinophiline protein. Interestingly, venlafaxine + melatonin reversed these events by promoting hippocampal synaptic plasticity by regulating melatonin secretion from the pineal gland. Therefore, it exerted an antidepressant effect in sleep deprivation combined with CUMS model rats. Overall, the results of this study suggest that the pathophysiology of depressive insomnia comorbidity is mediated by impaired pineal melatonin secretion and impaired hippocampal synaptic plasticity. In addition, these responses are associated with melatonin secretion from the pineal gland.

Lack of the peroxiredoxin 6 gene causes impaired spatial memory and abnormal synaptic plasticity

Peroxiredoxin 6 (PRDX6) is expressed dominantly in the astrocytes and exerts either neuroprotective or neurotoxic effects in the brain. Although PRDX6 can modulate several signaling cascades involving cognitive functions, its physiological role in spatial memory has not been investigated yet. This study aims to explore the function of the Prdx6 gene in spatial memory formation and synaptic plasticity. We first tested Prdx6-/- mice on a Morris water maze task and found that their memory performance was defective, along with reduced long-term potentiation (LTP) in CA3-CA1 hippocampal synapses recorded from hippocampal sections of home-caged mice. Surprisingly, after the probe test, these knockout mice exhibited elevated hippocampal LTP, higher phosphorylated ERK1/2 level, and decreased reactive astrocyte markers. We further reduced ERK1/2 phosphorylation by administering MEK inhibitor, U0126, into Prdx6-/- mice before the probe test, which reversed their spatial memory deficit. This study is the first one to report the role of PRDX6 in spatial memory and synaptic plasticity. Our results revealed that PRDX6 is necessary for maintaining spatial memory by modulating ERK1/2 phosphorylation and astrocyte activation.

Serotonin modulation of hippocampal functions: From anatomy to neurotherapeutics

The hippocampal region receives a dense serotoninergic innervation originating from both medial and dorsal raphe nuclei. This innervation regulates hippocampal activity through the activation of distinct receptor families that are expressed in excitatory and inhibitory neurons, terminals of several afferent neurotransmitter systems, and glial cells. Preclinical and clinical studies indicate that hippocampal dysfunctions are involved in learning and memory deficits, dementia, Alzheimer's disease, epilepsy and mood disorders such as anxiety, depression and post-traumatic syndrome disorder, whereas the hippocampus participates also in the therapeutic mechanisms of numerous medicines. Not surprisingly, several drugs acting via 5-HT mechanisms are efficacious to some extent in some diseases and the link between 5-HT and the hippocampus although clear remains difficult to untangle. For this reason, we review reported data concerning the distribution and the functional roles of the 5-HT receptors in the hippocampal region in health and disease. The impact of the 5-HT systems on the hippocampal function is such that the research of new 5-HT mechanisms and drugs is still very active. It concerns notably drugs acting at the 5-HT_1A,_2A,_2C,_4,6 receptor subtypes, in addition to the already existing drugs including the selective serotonin reuptake inhibitors.

Astroglial correlates of neuropsychiatric disease: From astrocytopathy to astrogliosis

Complex roles for astrocytes in health and disease continue to emerge, highlighting this class of cells as integral to function and dysfunction of the nervous system. In particular, escalating evidence strongly implicates a range of changes in astrocyte structure and function associated with neuropsychiatric diseases including major depressive disorder, schizophrenia, and addiction. These changes can range from astrocytopathy, degeneration, and loss of function, to astrogliosis and hypertrophy, and can be either adaptive or maladaptive. Evidence from the literature indicates a myriad of changes observed in astrocytes from both human postmortem studies as well as preclinical animal models, including changes in expression of glial fibrillary protein, as well as changes in astrocyte morphology and astrocyte-mediated regulation of synaptic function. In this review, we seek to provide a comprehensive assessment of these findings and consequently evidence for common themes regarding adaptations in astrocytes associated with neuropsychiatric disease. While results are mixed across conditions and models, general findings indicate decreased astrocyte cellular features and gene expression in depression, chronic stress and anxiety, but increased inflammation in schizophrenia. Changes also vary widely in response to different drugs of abuse, with evidence reflective of features of astrocytopathy to astrogliosis, varying across drug classes, route of administration and length of withdrawal.

Pacing stereotypies in laboratory rhesus macaques: Implications for animal welfare and the validity of neuroscientific findings

Stereotypic behaviours are commonly observed in captive animals and are usually interpreted as a sign of poor welfare. Stereotypies have also been linked with brain abnormalities. However, stereotypies are a heterogeneous class of behaviours and mounting evidence indicates that different stereotypies can have different causes, and can be linked to different affective states. As a consequence, the implications of a specific stereotypy in a specific species cannot be safely inferred from evidence on other stereotypies or species. Here we review what is known about pacing behaviour in laboratory rhesus macaques, a common stereotypy in this species. Our review highlights the current lack of understanding of the causal factors underlying pacing behaviour. According to current knowledge, the welfare of pacing macaques could be either better, worse or equivalent to that of non-pacing individuals. It is also unclear whether pacing results from brain abnormalities. Since rhesus macaques are widely used as a model of healthy humans in neuroscience research, determining if pacing behaviour reflects an abnormal brain and/or poor welfare is urgent.

The impact of treatment with selective serotonin reuptake inhibitors on primate cardiovascular disease, behavior, and neuroanatomy

Selective serotonin reuptake inhibitor (SSRI) use is ubiquitous because they are widely prescribed for a number of disorders in addition to depression. Depression increases the risk of coronary heart disease (CHD). Hence, treating depression with SSRIs could reduce CHD risk. However, the effects of long term antidepressant treatment on CHD risk, as well as other aspects of health, remain poorly understood. Thus, we undertook an investigation of multisystem effects of SSRI treatment with a physiologically relevant dose in middle-aged adult female cynomolgus monkeys, a primate species shown to be a useful model of both depression and coronary and carotid artery atherosclerosis. Sertraline had no effect on depressive behavior, reduced anxious behavior, increased affiliation, reduced aggression, changed serotonin neurotransmission and volumes of neural areas critical to mood disorders, and exacerbated coronary and carotid atherosclerosis. These data suggest that a conservative approach to prescribing SSRIs for cardiovascular or other disorders for long periods may be warranted, and that further study is critical given the widespread use of these medications.

Reduced marker of vascularization in the anterior hippocampus in a female monkey model of depression

Depression is a common and debilitating mood disorder that impacts women more often than men. The mechanisms that result in depressive behaviors are not fully understood; however, the hippocampus has been noted as a key structure in the pathophysiology of depression. In addition to neural implications of depression, the cardiovascular system is impacted. Although not as commonly considered, the cerebrovasculature is critical to brain function, impacted by environmental stimuli, and is capable of altering neural function and thereby behavior. In the current study, we assessed the relationship between depressive behavior and a marker of vascularization of the hippocampus in adult female cynomolgus macaques (Macaca fascicularis). Similar to previously noted impacts on neuropil and glia, the depressed phenotype predicts a reduction in a marker of vascular length in the anterior hippocampus. These data reinforce the growing recognition of the effects of depression on vasculature and support further consideration of vascular endpoints in studies aimed at the elucidation of the mechanisms underlying depression.

Long term sertraline effects on neural structures in depressed and nondepressed adult female nonhuman primates

BACKGROUND

Selective serotonin reuptake inhibitors (SSRIs) are widely prescribed for mood and other disorders. However, their neural effects are difficult to study due to patient compliance and drug history variability, and rarely studied in those prescribed SSRIs for non-mood disorders. Here we evaluated SSRI effects on neural volumetrics in depressed and nondepressed monkeys.

METHODS

42 socially-housed cynomolgus monkeys were randomized to treatment balanced on pretreatment depressive behavior and body weight. Monkeys were trained for oral administration of placebo or 20 mg/kg sertraline HCl daily for 18 months and depressive and anxious behavior recorded. Volumes of neural regions of interest in depression were measured in magnetic resonance images and analyzed by 2 (depressed, nondepressed)×2 (placebo, sertraline) ANOVA.

RESULTS

Sertraline reduced anxiety (p=0.04) but not depressive behavior (p=0.43). Left Brodmann's Area (BA) 32 was smaller in depressed than nondepressed monkeys (main effect of depression: p<0.05). Sertraline and depression status interacted to affect volumes of left Anterior Cingulate Cortex (ACC), left BA24, right hippocampus (HC), and right anterior HC (sertraline×depression interactions: all p's<0.05). In the Placebo group, depressed monkeys had smaller right anterior HC and left ACC than nondepressed monkeys. In nondepressed monkeys, sertraline reduced right HC volume, especially right anterior HC volume. In depressed monkeys sertraline increased left ACC volume. In nondepressed monkeys, sertraline reduced left BA24 volumes resulting in smaller BA24 volumes in nondepressed than sertraline-treated depressed monkeys.

CONCLUSIONS

These observations suggest that SSRIs may differentially affect neural structures in depressed and nondepressed individuals.

Propofol prevents electroconvulsive-shock-induced memory impairment through regulation of hippocampal synaptic plasticity in a rat model of depression

BACKGROUND

Although a rapid and efficient psychiatric treatment, electroconvulsive therapy (ECT) induces memory impairment. Modified ECT requires anesthesia for safety purposes. Although traditionally found to exert amnesic effects in general anesthesia, which is an inherent part of modified ECT, some anesthetics have been found to protect against ECT-induced cognitive impairment. However, the mechanisms remain unclear. We investigated the effects of propofol (2,6-diisopropylphenol) on memory in depressed rats undergoing electroconvulsive shock (ECS), the analog of ECT in animals, under anesthesia as well as its mechanisms.

METHODS

Chronic unpredictable mild stresses were adopted to reproduce depression in a rodent model. Rats underwent ECS (or sham ECS) with anesthesia with propofol or normal saline. Behavior was assessed in sucrose preference, open field and Morris water maze tests. Hippocampal long-term potentiation (LTP) was measured using electrophysiological techniques. PSD-95, CREB, and p-CREB protein expression was assayed with Western blotting.

RESULTS

Depression induced memory damage, and downregulated LTP, PSD-95, CREB, and p-CREB; these effects were exacerbated in depressed rats by ECS; propofol did not reverse the depression-induced changes, but when administered in modified ECS, propofol improved memory and reversed the downregulation of LTP and the proteins.

CONCLUSION

These findings suggest that propofol prevents ECS-induced memory impairment, and modified ECS under anesthesia with propofol improves memory in depressed rats, possibly by reversing the excessive changes in hippocampal synaptic plasticity. These observations provide a novel insight into potential targets for optimizing the clinical use of ECT for psychiatric disorders.

Nonhuman primate models of depression: effects of early experience and stress

Depression causes significant morbidity in the human population. The Diathesis-Stress/Two-Hit model of depression hypothesizes that stress interacts with underlying (probably genetic) predispositions to produce a central nervous system that is primed to express psychopathology when confronted with stressful experiences later in life. Nonhuman primate (NHP) studies have been extensively utilized to test this model. NHPs are especially useful for studying effects of early experience, because many aspects of NHP infancy are similar to humans, whereas development occurs at an accelerated rate and therefore allows for more rapid assessment of experimental variables. In addition, the ability to manipulate putative risk factors, including introducing experimental stress during development, allows inference of causality not possible with human studies. This manuscript reviews experimental paradigms that have been utilized to model early adverse experience in NHPs, including peer-rearing, maternal separation, and variable foraging. It also provides examples of how this model has been used to investigate the effects of early experience on later neurobiology, physiology, and behavior associated with depression. We conclude that the NHP offers an excellent model to research mechanisms contributing to the Diathesis-Stress/Two-Hit model of depression.