Animal models of depression: are there any?

Behavioral Animal Models and Neural-Circuit Framework of Depressive Disorder

Depressive disorder is a chronic, recurring, and potentially life-endangering neuropsychiatric disease. According to a report by the World Health Organization, the global population suffering from depression is experiencing a significant annual increase. Despite its prevalence and considerable impact on people, little is known about its pathogenesis. One major reason is the scarcity of reliable animal models due to the absence of consensus on the pathology and etiology of depression. Furthermore, the neural circuit mechanism of depression induced by various factors is particularly complex. Considering the variability in depressive behavior patterns and neurobiological mechanisms among different animal models of depression, a comparison between the neural circuits of depression induced by various factors is essential for its treatment. In this review, we mainly summarize the most widely used behavioral animal models and neural circuits under different triggers of depression, aiming to provide a theoretical basis for depression prevention.

Reserpine-induced rat model for depression: Behavioral, physiological and PET-based dopamine receptor availability validation

BACKGROUND

Reserpine (RES), a Vesicular Monoamine Transporter 2 (VMAT2) inhibitor agent, has been used in preclinical research for many years to create animal models for depression and to test experimental antidepressant strategies. Nevertheless, evidence of the potential use and validity of RES as a chronic pharmacological model for depression is lacking, and there are no comprehensive studies of the behavioral effects in conjunction with molecular outcomes.

METHODS

Experiment 1. Following baseline behavior testing sensitive to depression-like phenotype and locomotion (Phase 1), 27 Sprague-Dawley (SD) rats received i.p. either vehicle solution (0.0 mg/kg), low (0.2 mg/kg) or high (0.8 mg/kg) RES dose for 20 days using a pre-determined schedule and reassessed for behavioral phenotypes (Phase 2). After 10 days washout period, and a final behavioral assessment (Phase 3), the brains were collected 16 days after the last injection for mRNA-expression assessment. Experiment 2. In a similar timetable as in Experiment 1 but without the behavioral testing, 12 SD rats underwent repetitive dopamine D2/3 receptor PET scanning with [18F]DMFP following each Phase. The binding potential (BPND) of [18F]DMFP was quantified by kinetic analysis as a marker of striatal D2/3R availability. Weight and welfare were monitored throughout the study.

RESULTS

Significant, dose-dependent weight loss and behavioral deficits including both motor (hypo-locomotion) and non-motor behavior (anhedonia, mild anxiety and reduced exploration) were found for both the low and high dose groups with significant decrease in D2R mRNA expression in the accumbal region for the low RES group after Phase 3. Both RES treated groups showed substantial increase in [18F]DMFP BPND (in line with dopamine depletion) during Phase 2 and 3 compared to baseline and Controls.

CONCLUSIONS

The longitudinal design of the study demonstrated that chronic RES administration induced striatal dopamine depletion that persisted even after the wash-out period. However, the behavior phenotype observed were transient. The data suggest that RES administration can induce a rodent model for depression with mild face validity.

Modulation of serotonin transporter expression by escitalopram under inflammation

Selective serotonin reuptake inhibitors (SSRIs) are widely used for depression based on the monoamine deficiency hypothesis. However, the clinical use of these agents is controversial, in part because of their variable clinical efficacy and in part because of their delayed onset of action. Because of the complexities involved in replicating human disease and clinical dosing in animal models, the scientific community has not reached a consensus on the reasons for these phenomena. In this work, we create a theoretical hippocampal model incorporating escitalopram's pharmacokinetics, pharmacodynamics (competitive and non-competitive inhibition, and serotonin transporter (SERT) internalization), inflammation, and receptor dynamics. With this model, we simulate chronic oral escitalopram in mice showing that days to weeks are needed for serotonin levels to reach steady-state. We show escitalopram's chemical efficacy is diminished under inflammation. Our model thus offers mechanisms for how chronic escitalopram affects brain serotonin, emphasizing the importance of optimized dose and time for future antidepressant discoveries.

Assessment of commonly used tests in experimental depression studies according to behavioral patterns of rodents

Considering the main factor that causes or triggers depression in humans is stress. Several stress factors are applied to form depression-like symptoms in rodents. Depression tests are used to analyze the nature and patterns of depression. Well-founded modeling and versatile evaluation of tests are necessary to investigate a hypothesis that is related to depression. It is impossible to model or test all aspects of depression in humans by using experimental animals. As a result, the aims of the study should be determined specifically in depression models. The correct interpretation of the tests that are suitable for these aims is indispensable for the reliability of the data. To achieve this goal, the biological basis of the depression-related behaviors of animals should be well known. In this review, model and test concepts related to depression are discussed and behavioral patterns of rodents are explained with several examples.

The effect of curcumin on reserpine-induced depression-like behaviour in rats

The aim of this study was to construct an animal model of depression that reproduces the human clinical manifestation, to evaluate the possible benefits of curcumin (CUR) in the treatment of depression and to compare its effect with the effect of a classic antidepressant, escitalopram (ESC). The behavior of depressive-like animals induced by administration of 1.5 mg/kg i. p. reserpine (R), during 10 days (n = 24) was evaluated via the open field test (OFT) and elevated plus maze (EPM) compared to control animals (n = 24) treated with carboxymethylcellulose (CMC) used as a vehicle. On the 11th day, each group was divided into 3 subgroups (n = 8): control (CMC), CMC+CUR, CMC+ESC for group without depression and CMC+R, CMC+R+CUR, CMC+R+ESC for group with depression. CUR (150 mg/kg i.p.) and ESC (20 mg/kg i.p.) were intraperitoneally administrated for 21 days. The improvement in depressive behaviour was assessed by OFT, EPM and biochemical analysis on the 32nd day. The results demonstrated that R induced hypomotility and increased oxidative stress in the brain, but also in the serum of rats. CUR had an antioxidant effect in the brain without significant effect on depressive-like behaviour while ESC improved the hypomotility of the depressive rats.

Electroconvulsive Therapy: Mechanisms of Action, Clinical Considerations, and Future Directions

LEARNING OBJECTIVES

• Outline and discuss the fundamental physiologic, cellular, and molecular mechanisms of ECT to devise strategies to optimize therapeutic outcomes• Summarize the overview of ECT, its efficacy in treating depression, the known effects on cognition, evidence of mechanisms, and future directions.

ABSTRACT

Electroconvulsive therapy (ECT) is the most effective treatment for a variety of psychiatric illnesses, including treatment-resistant depression, bipolar depression, mania, catatonia, and clozapine-resistant schizophrenia. ECT is a medical and psychiatric procedure whereby electrical current is delivered to the brain under general anesthesia to induce a generalized seizure. ECT has evolved a great deal since the 1930s. Though it has been optimized for safety and to reduce adverse effects on cognition, issues persist. There is a need to understand fundamental physiologic, cellular, and molecular mechanisms of ECT to devise strategies to optimize therapeutic outcomes. Clinical trials that set out to adjust parameters, electrode placement, adjunctive medications, and patient selection are critical steps towards the goal of improving outcomes with ECT. This narrative review provides an overview of ECT, its efficacy in treating depression, its known effects on cognition, evidence of its mechanisms, and future directions.

Role of Quercetin in Depressive-Like Behaviors: Findings from Animal Models

Depressive-like behavior is a highly prevalent worldwide neuropsychiatric disorder that owns a complex pathophysiologic mechanism. The available pharmacotherapy is ineffective for most patients and shown several adverse effects. Therefore, it is important to find efficacy and safe antidepressive compounds. Some phytochemicals compounds regulate the same genes and pathways targeted by drugs; therefore, diets rich in fruits and vegetables could be considered novel treatment approaches. Currently, the functional properties of quercetin acquired great interest, due to its beneficial effects on health. Quercetin is a flavonoid ubiquitously present in vegetables and fruits, interestingly for its strong antioxidant properties. The purpose of this review is to summarize the preclinical studies present in the literature, in the last ten years, aimed at illustrating the effects of quercetin pre-treatment in depressive-like behaviors. Quercetin resulted in antidepressant-like actions due to its antioxidant, anti-inflammatory, and neuroprotective effects. This pointed out the usefulness of this flavonoid as a nutraceutical compound against the development of psychological stress-induced behavioral perturbation. Therefore, quercetin or a diet containing it may become a prospective supplementation or an efficient adjuvant therapy for preventing stress-mediated depressive-like behavior.

Chronic immobilization stress induces anxiety-related behaviors and affects brain essential minerals in male rats

Alterations of essential elements in the brain are associated with the pathophysiology of many neuropsychiatric disorders. It is known that chronic/overwhelming stress may cause some anxiety and/or depression. We aimed to investigate the effects of two different chronic immobilization stress protocols on anxiety-related behaviors and brain minerals. Adult male Wistar rats were divided into 3 groups as follows (n = 10/group): control, immobilization stress-1 (45 minutes daily for 7-day) and immobilization stress-2 (45 minutes twice a day for 7-day). Stress-related behaviors were evaluated by open field test and forced swimming test. In the immobilization stress-1 and immobilization stress-2 groups, percentage of time spent in the central area (6.38 ± 0.41% and 6.28 ± 1.03% respectively, p < 0.05) and rearing frequency (2.75 ± 0.41 and 3.85 ± 0.46, p < 0.01 and p < 0.05, respectively) were lower, latency to center area (49.11 ± 5.87 s and 44.92 ± 8.04 s, p < 0.01 and p < 0.01, respectively), were higher than the control group (8.65 ± 0.49%, 5.37 ± 0.44 and 15.3 ± 3.32 s, respectively). In the immobilization stress-1 group, zinc (12.65 ± 0.1 ppm, p < 0.001), magnesium (170.4 ± 1.7 ppm, p < 0.005) and phosphate (2.76 ± 0.1 ppm, p < 0.05) levels were lower than the control group (13.87 ± 0.16 ppm, 179.31 ± 1.87 ppm and 3.11 ± 0.06 ppm, respectively). In the immobilization stress-2 group, magnesium (171.56 ± 1.87 ppm, p < 0.05), phosphate (2.44 ± 0.07 ppm, p < 0.001) levels were lower, and manganese (373.68 ± 5.76 ppb, p < 0.001) and copper (2.79 ± 0.15 ppm, p < 0.05) levels were higher than the control group (179.31 ± 1.87 ppm, 3.11 ± 0.06 ppm, 327.25 ± 8.35 ppb and 2.45 ± 0.05 ppm, respectively). Our results indicated that 7-day chronic immobilization stress increased anxiety-related behaviors in both stress groups. Zinc, magnesium, phosphate, copper and manganese levels were affected in the brain.

Stressor during Early Adolescence in Hyperreactive Female Wistar Kyoto Rats Induces a 'Double Hit' Manifested by Variation in Neurobehaviors and Brain Monoamines

Stress is an additive factor in the development of depressive-like profiles that mainly onsets during adolescence. However, effects of early post-weaning stress on developing brain neurochemical pathways in inducing anxiety- and depressive-like profiles in vulnerable females have not been extensively studied. The Wistar Kyoto (WKY) rat, a putative model of adolescent depression and stress-sensitivity could elucidate the pathophysiology of stress-related depression in vulnerability. Through such an approach, links between inherent risk for predisposition to depression and homotypic stress, as in a 'double hit' would unravel endocrine regulation, interference in developing neural pathways and neurobehaviors. Here, early adolescent WKY female rats were subjected to 1-h physical restraint over 7 days followed by neurobehavioral testing in the elevated plus maze (EPM) and forced swim test (FST). The stressor's effectiveness was assayed by plasma corticosterone (CORT) and altered functioning in depression-implicated brain areas by assaying monoamines/metabolites. Homotypic stress induced an anxiolytic-like response in the EPM with learned helplessness and reduced struggling behavior in FST. Significant elevation in CORT levels (p < 0.05) indicated an upregulated HPA axis. Medial prefrontal cortex, a still maturing brain area, exhibited increased serotonin (5-HT) metabolite (p < 0.01) and turnover rates (p < 0.01) indicative of altered/maladaptive serotonergic functioning. Nucleus accumbens (p < 0.05) and dorsal striatum (p < 0.01) also depicted increased 5-HT metabolite, with the latter also demonstrating reduced Dopamine turnover (p < 0.01) as a result of homotypic stress. Hence, female WKY rats could constitute a diathesis-stress model to study underlying mechanisms of stress-related depression.

Animal models of depression: pros and cons

Animal models of depression are certainly needed but the question in the title has been raised owing to the controversies in the interpretation of the readout in a number of tests, to the perceived lack of progress in the development of novel treatments and to the expressed doubts in whether animal models can offer anything to make a true breakthrough in understanding the neurobiology of depression and producing novel drugs against depression. Herewith, it is argued that if anything is wrong with animal models, including those for depression, it is not about the principle of modelling complex human disorder in animals but in the way the tests are selected, conducted and interpreted. Further progress in the study of depression and in developing new treatments, will be supported by animal models of depression if these were more critically targeted to drug screening vs. studies of underlying neurobiology, clearly stratified to vulnerability and pathogenetic models, focused on well-defined endophenotypes and validated for each setting while bearing the existing limits to validation in mind. Animal models of depression need not to rely merely on behavioural readouts but increasingly incorporate neurobiological measures as the understanding of depression as human brain disorder advances. Further developments would be fostered by cross-fertilizinga translational approach that is bidirectional, research on humans making more use of neurobiological findings in animals.

Estrous Cycle Phase-Dependent Changes in Anxiety- and Depression-Like Profiles in the Late Adolescent Wistar-Kyoto Rat

BACKGROUND

Depression often manifests during adolescence when the development and networking of social and emotional brain areas is being influenced by hormones. The Wistar Kyoto (WKY) rat has been proposed as an animal model of adolescent depression with various face, construct, and predictive validities for clinical depression having been established.

PURPOSE

The influence of the estrous cycle on anxiety- and depression-like behaviors in female adolescents may be tested out further using this model.

METHODS

Female adolescent WKY rats were tested for anxiety- and depression-like behaviors in the elevated plus maze and forced swim test (FST) during different phases of the estrous cycle with inbred, age-, and phase-matched Wistar rats as controls.

RESULTS

Wistars in proestrus-estrus demonstrated reduced anxiety levels. WKY also demonstrated increased open arm time and entries and closed arm time, but less than Wistars, and as closed arm entries remained unaffected, it did not translate into a lowering of the anxiety levels. Risk taking and risk assessment behaviors were not affected by estrous phases in WKY, though exploratory behavior was reduced in proestrus-estrus. In Wistars, increased risk taking and decreased risk assessment behaviors were observed during proestrus-estrus. Increased immobility in the FST, indicative of learned helplessness was not influenced by phase in the WKY, which was at variance with Wistars that demonstrated phase-specific differences.

CONCLUSION

Results indicate a masking effect of indicative hormones in this putative model of adolescent depression, with implications for an unravelling of the steroid milieu in predisposed adolescent depression and for taking phase-specific time windows into account for therapeutic interventions.

The need for new approaches in CNS drug discovery: Why drugs have failed, and what can be done to improve outcomes

An important goal of biomedical research is to translate basic research findings into useful medical advances. In the field of neuropharmacology this requires understanding disease mechanisms as well as the effects of drugs and other compounds on neuronal function. Our hope is that this information will result in new or improved treatment for CNS disease. Despite great progress in our understanding of the structure and functions of the CNS, the discovery of new drugs and their clinical development for many CNS disorders has been problematic. As a result, CNS drug discovery and development programs have been subjected to significant cutbacks and eliminations over the last decade. While there has been recent resurgence of interest in CNS targets, these past changes in priority of the pharmaceutical and biotech industries reflect several well-documented realities. CNS drugs in general have higher failure rates than non-CNS drugs, both preclinically and clinically, and in some areas, such as the major neurodegenerative diseases, the clinical failure rate for disease-modifying treatments has been 100%. The development times for CNS drugs are significantly longer for those drugs that are approved, and post-development regulatory review is longer. In this introduction we review some of the reasons for failure, delineating both scientific and technical realities, some unique to the CNS, that have contributed to this. We will focus on major neurodegenerative disorders, which affect millions, attract most of the headlines, and yet have witnessed the fewest successes. We will suggest some changes that, when coupled with the approaches discussed in the rest of this special volume, may improve outcomes in future CNS-targeted drug discovery and development efforts. This article is part of the Special Issue entitled "Beyond small molecules for neurological disorders".

Anxiety- and depressive-like profiles during early- and mid-adolescence in the female Wistar Kyoto rat

Approaches for the development of preclinical models of depression extensively use adult and male animals owing to the discrepancies arising out of the hormonal flux in adult females and adolescents during attainment of puberty. Thus the increased vulnerability of females towards clinical depression and anxiety-related disorders remains incompletely understood. Development of clinical models of depression in adolescent females is essential in order to evolve effective treatment strategies for adolescent depression. In the present study, we have examined the anxiety and depressive-like profiles in a putative animal model of childhood depression, the Wistar Kyoto (WKY) rat, during early adolescence (∼postnatal day 30) and mid-adolescence (∼postnatal day 40). Female adolescent WKY rats, tested on a series of behavioural tests modelling anxiety- and depressive-like behaviours with age-matched Wistars as controls, demonstrated marked differences during early adolescence in a strain- and age-specific manner. Anxiety indices were obtained from exposure to the elevated plus maze, where social communication vide 50-kHz ultrasonic vocalizations was also assessed, while immobility and other parameters in the forced swim test were screened for depressive-like profiles. Sucrose preference, used as a measure of anhedonia in animals, was lower in WKYs at both ages tested and decreased with age. Anxiety-related behaviours were prominent in WKY rats only during early adolescence. WKY female rats are anxious during early adolescence and exhibit anhedonia as a core symptom of depression during early- and mid-adolescence, thus indicating that inclusion of female animals in preclinical trials is essential and will contribute to gender-based approaches to diagnosis and treatment of adolescent depression in females.

Ovariectomy results in inbred strain-specific increases in anxiety-like behavior in mice

Women are at an increased risk for developing affective disorders during times of hormonal flux, including menopause when the ovaries cease production of estrogen. However, while all women undergo menopause, not all develop an affective disorder. Increased vulnerability can result from genetic predisposition, environmental factors and gene by environment interactions. In order to investigate interactions between genetic background and estrogen depletion, we performed bilateral ovariectomy, a surgical procedure that results in estrogen depletion and is thought to model the post-menopausal state, in a genetically defined panel of 37 inbred mouse strains. Seventeen days post-ovariectomy, we assessed behavior in two standard rodent assays of anxiety- and depressive-like behavior, the open field and forced swim tests. We detected a significant interaction between ovariectomy and genetic background on anxiety-like behavior in the open field. No strain specific effects of ovariectomy were observed in the forced swim assay. However, we did observe significant strain effects for all behaviors in both the open field and forced swim tests. This study is the largest to date to look at the effects of ovariectomy on behavior and provides evidence that ovariectomy interacts with genetic background to alter anxiety-like behavior in an animal model of menopause.

Antidepressant activity of nociceptin/orphanin FQ receptor antagonists in the mouse learned helplessness

RATIONALE

Pharmacological and genetic evidence support antidepressant-like effects elicited by the blockade of the NOP receptor. The learned helplessness (LH) model employs uncontrollable and unpredictable electric footshocks as a stressor stimulus to induce a depressive-like phenotype that can be reversed by classical antidepressants.

OBJECTIVES

The present study aimed to evaluate the action of NOP receptor antagonists in helpless mice.

METHODS

Male Swiss mice were subjected to the three steps of the LH paradigm (i.e., (1) induction, (2) screening, and (3) test). Only helpless animals were subjected to the test session. During the test session, animals were placed in the electrified chamber and the latency to escape after the footshock and the frequency of escape failures were recorded. The effect of the following treatments administered before the test session were evaluated: nortriptyline (30 mg/kg, ip, 60 min), fluoxetine (30 mg/kg, ip, four consecutive days of treatment), and NOP antagonists SB-612111 (1-10 mg/kg, ip, 30 min) and UFP-101 (1-10 nmol, icv, 5 min). To rule out possible biases, the effects of treatments on controllable stressful and non stressful situations were assessed.

RESULTS

In helpless mice, nortriptyline, fluoxetine, UFP-101 (3-10 nmol), and SB-612111 (3-10 mg/kg) significantly reduced escape latencies and escape failures. No effects of drug treatments were observed in mice subjected to the controllable electric footshocks and non stressful situations.

CONCLUSIONS

Acute treatment with NOP antagonists reversed helplessness similarly to the classical antidepressants. These findings support the proposal that NOP receptor antagonists are worthy of development as innovative antidepressant drugs.

Gamma oscillation in functional brain networks is involved in the spontaneous remission of depressive behavior induced by chronic restraint stress in mice

BACKGROUND

Depression is one of the most prevalent mood disorders, and is known to be associated with abnormal functional connectivity in neural networks of the brain. Interestingly, a significant proportion of patients with depression experience spontaneous remission without any treatment. However, the relationship between electroencephalographic (EEG) functional connectivity and the spontaneous remission in depression remains poorly understood. Here, we investigated regional and network brain activity using EEG signals from a chronic restraint stress (CRS)-induced mouse model of depression. After 1 (CRS1W) or 3 weeks (CRS3W) following the cessation of a 4-week-long CRS, mice were subjected to depression-associated behavioral tasks. EEG signals were obtained from eight cortical regions (frontal, somatosensory, parietal, and visual cortices in each hemisphere).

RESULTS

The CRS1W group exhibited behavioral dysfunctions in the open field and forced swim tasks, whereas the CRS3W group displayed normal levels of behaviors in those tasks. In a linear correlation analysis, the CRS1W group exhibited increased correlation coefficient values at all frequency bands (delta, 1.5-4; theta, 4-8; alpha, 8-12; beta, 12-30; gamma, 30-80 Hz) compared with the control group. However, the differences in delta- and gamma-frequency bands between the control and CRS1W groups were no longer observed in the CRS3W group. Persistent brain network homology revealed significantly different functional connectivity between the control and CRS1W groups, and it demonstrated a huge restoration of the decreased distances in the gamma-frequency band for the CRS3W group. Moreover, the CRS3W group displayed a similar strength of connectivity among somatosensory and frontal cortices as the control group.

CONCLUSION

A mouse model of CRS-induced depression showed spontaneous behavioral remission of depressive behavior. Using persistent brain network homology analysis of EEG signals from eight cortical regions, we found that restoration of gamma activity at the network level is associated with behavioral remission.

Animal models of major depression and their clinical implications

Major depressive disorder is a common, complex, and potentially life-threatening mental disorder that imposes a severe social and economic burden worldwide. Over the years, numerous animal models have been established to elucidate pathophysiology that underlies depression and to test novel antidepressant treatment strategies. Despite these substantial efforts, the animal models available currently are of limited utility for these purposes, probably because none of the models mimics this complex disorder fully. It is presumable that psychiatric illnesses, such as affective disorders, are related to the complexity of the human brain. Here, we summarize the animal models that are used most commonly for depression, and discuss their advantages and limitations. We discuss genetic models, including the recently developed optogenetic tools and the stress models, such as the social stress, chronic mild stress, learned helplessness, and early-life stress paradigms. Moreover, we summarize briefly the olfactory bulbectomy model, as well as models that are based on pharmacological manipulations and disruption of the circadian rhythm. Finally, we highlight common misinterpretations and often-neglected important issues in this field.

Ondansetron, a 5HT3 receptor antagonist reverses depression and anxiety-like behavior in streptozotocin-induced diabetic mice: possible implication of serotonergic system

Increased prevalence and high comorbidity of depression-like mood disorders and diabetes have prompted investigation of new targets and potential contributing agents. There is considerable evidence supporting the inconsistent clinical efficacy and persistent undesirable effects of existing antidepressant therapy for depression associated with diabetes. Therefore, the present study was aimed at investigating the effect of ondansetron, a selective 5HT3 receptor antagonist in attenuating depression and anxiety-like behavior comorbid with diabetes. Experimentally, Swiss albino mice were rendered diabetic by a single intraperitoneal (i.p.) injection of streptozotocin (STZ, 200 mg/kg). After 8 weeks, diabetic mice received a single dose of vehicle/ondansetron (0.5 and 1 mg/kg, p.o.)/fluoxetine (the positive control, 10 mg/kg p.o.) for 28 days. Thereafter, behavioral studies were conducted to test depression-like behavior using forced swim test (FST) and anxiety-like deficits using hole-board and light-dark tests, followed by biochemical estimation of serotonin content in discrete brain regions. The results demonstrated that, STZ-induced diabetic mice exhibited increased duration of immobility and decreased swimming behavior in FST, reduced exploratory behavior during hole-board test and increased aversion to brightly illuminated light area in light-dark test as compared to non-diabetic mice, while ondansetron (similar to fluoxetine) treatment significantly reversed the same. Biochemical assay revealed that ondansetron administration attenuated diabetes-induced neurochemical impairment of serotonin function, indicated by elevated serotonin levels in discrete brain regions of diabetic mice. Collectively, the data indicate that ondansetron may reverse depression and anxiety-like behavioral deficits associated with diabetes in mice and modulation of serotonergic activity may be a key mechanism of the compound.

Neurobehavioral evaluation of adolescent male rats following repeated exposure to chlorpyrifos

Chlorpyrifos (CPF), a highly effective organophosphate pesticide (OP), is extensively used worldwide. However, its agricultural use was extensively reduced in 2001. Several studies have suggested an association between mood disorders and CPF exposure in humans, especially in children, a subgroup that is highly susceptible to xenobiotics. We investigated the hypothesis that repeated CPF exposure in animals would elicit depressive-like behavioral alterations that reflected depression-related symptoms. Adolescent male rats were subcutaneously injected with either olive oil or 2.5, 5, 10, or 20mg/kg CPF from postnatal day 27 to 36, then were followed by a series of neurobehavioral evaluation. Our studies revealed depressive-like alterations that were manifested by increased despair behavior in the forced swimming test, increased escape failure in the learned helplessness test, and altered approach-avoidance conflict in the novelty-suppressed feeding test. There was no effect on locomotor activity in the open-field activity test. This study indicates that repeated exposure to CPF elicits depressive-like behavioral alterations in adolescent male rats.

Depressive-like behavioral profiles in captive-bred single- and socially-housed rhesus and cynomolgus macaques: a species comparison

BACKGROUND

To unravel the causes of major depressive disorder (MDD), the third leading cause of disease burden around the world, ethological animal models have recently been proposed. Our previous studies highlighted a depressive-like profile among single- and socially-housed farm-bred cynomolgus macaques. Although phylogenetically close, cynomolgus and rhesus macaques, the two most commonly used macaque species in biomedical research, differ on several levels such as patterns of aggression, reconciliation, temperament, or dominance styles. The question of whether one captive macaque species was more vulnerable than another in the development of a pathological profile reminiscent of MDD symptoms was explored.

METHODS

Behavioral data (including body postures, orientations, gaze directions, inter-individual distances, and locations in the cage) were collected in farming conditions. Using an unbiased validated ethological scan-sampling method, followed by multiple correspondence and hierarchical clustering analyses, 40 single- and 35 socially-housed rhesus macaques were assessed. Independently, for each housing condition, inter-species comparisons were made with previously acquired data on farm-bred cynomolgus monkeys.

RESULTS

Consistent with our previous studies, we found depressive-like characteristics (e.g., inactivity, low level of investigation and maintenance, long time spent inactive while facing the wall) among single- and socially-housed rhesus macaques. Species-specificities were reported in non-depressive time budgets and in the prevalence of the pathological profiles.

CONCLUSIONS

Our results suggest that rhesus may be more vulnerable to developing a despair-like state than cynomolgus macaques, both in single- and in social-housing conditions. Therefore, rhesus macaques are more suitable for use as a "spontaneous" model of depressive disorders.

Reduction in ultrasonic vocalizations in pups born to rapid eye movement sleep restricted mothers in rat model

The effects of rapid eye movement sleep restriction (REMSR) in rats during late pregnancy were studied on the ultrasonic vocalizations (USVs) made by the pups. USVs are distress calls inaudible to human ears. Rapid eye movement (REM) sleep was restricted in one group of pregnant rats for 22 hours, starting from gestational day 14 to 20, using standard single platform method. The USVs of male pups were recorded after a brief isolation from their mother for two minutes on alternate post-natal days, from day one till weaning. The USVs were recorded using microphones and were analysed qualitatively and quantitatively using SASPro software. Control pups produced maximum vocalization on post-natal days 9 to 11. In comparison, the pups born to REMSR mothers showed not only a reduction in vocalization but also a delay in peak call making days. The experimental group showed variations in the types and characteristics of call types, and alteration in temporal profile. The blunting of distress call making response in these pups indicates that maternal sleep plays a role in regulating the neural development involved in vocalizations and possibly in shaping the emotional behaviour in neonates. It is suggested that the reduced ultrasonic vocalizations can be utilized as a reliable early marker for affective state in rat pups. Such impaired vocalization responses could provide an important lead in understanding mother-child bonding for an optimal cognitive development during post-partum life. This is the first report showing a potential link between maternal REM sleep deprivation and the vocalization in neonates and infants.

Puberty and adolescence as a time of vulnerability to stressors that alter neurobehavioral processes

Puberty and adolescence are major life transitions during which an individual's physiology and behavior changes from that of a juvenile to that of an adult. Here we review studies documenting the effects of stressors during pubertal and adolescent development on the adult brain and behavior. The experience of complex or compound stressors during puberty/adolescence generally increases stress reactivity, increases anxiety and depression, and decreases cognitive performance in adulthood. These behavioral changes correlate with decreased hippocampal volumes and alterations in neural plasticity. Moreover, stressful experiences during puberty disrupt behavioral responses to gonadal hormones both in sexual performance and on cognition and emotionality. These behavioral changes correlate with altered estrogen receptor densities in some estrogen-concentrating brain areas, suggesting a remodeling of the brain's response to hormones. A hypothesis is presented that activation of the immune system results in chronic neuroinflammation that may mediate the alterations of hormone-modulated behaviors in adulthood.

Antidepressant- and anticompulsive-like effects of purinergic receptor blockade: involvement of nitric oxide

Activation of purinergic receptors by ATP (P2R) modulates glutamate release and the activation of post-synaptic P2R is speculated to induce nitric oxide (NO) synthesis. Increased glutamatergic and nitrergic signaling have been involved in the neurobiology of stress-related psychiatric disorders such as anxiety and depression. Therefore, the aim of this study was to test the effects of two P2R antagonists (PPADS and iso-PPADS) in animals submitted to models predictive of antidepressant-, anxiolytic- and anticompulsive-like effects. Swiss mice receiving PPADS at 12.5mg/kg showed reduced immobility time in the forced swimming test (FST) similarly to the prototype antidepressant imipramine (30mg/kg). This dose was also able to decrease the number of buried marbles in the marble-burying test (MBT), an anticompulsive-like effect. However, no effect was observed in animals submitted to the elevated plus maze (EPM) and to the open field test. The systemic administration of iso-PPADS, a preferential P2XR antagonist, also reduced the immobility time in FST, which was associated to a decrease in NOx levels in the prefrontal cortex. In addition, P2X7 receptor was found co-immunoprecipitated with neuronal nitric oxide synthase (NOS1) in the prefrontal cortex. These results suggest that P2X7, possibly coupled to NOS1, could modulate behavioral responses associated to stress-related disorders and it could be a new target for the development of more effective treatments for affective disorders.

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.

Individual differences in pre-carcinogen cytokine and corticosterone concentrations and depressive-like behavior predict tumor onset in rats exposed to a carcinogen

Individual variation in the susceptibility to chronic disease can be attributed to both genetic and environmental factors. Measures of the immune, nervous, and endocrine systems are predictive of survival outcomes after a chronic disease is diagnosed. However, determining biomarkers or "traits" that predict risk before chronic disease development remains elusive. In this study, natural individual variation in circulating cytokines, corticosterone, and depressive-like behaviors (using the Porsolt forced swim test) were measured in female rats before induction of mammary tumors using a chemical carcinogen (N-nitroso-N-methylurea). Early tumor onset was associated with relatively high (but within the physiologically typical range) circulating cytokine concentrations (IL-1α, IL-1β, TNFα) and depressive-like behavior and with relatively low corticosterone concentrations, all of which were assessed at baseline before carcinogen treatment. Multiple regression analyses indicated that IL-1β was primarily responsible for the variation in tumor onset when controlling for corticosterone concentration. These results suggest that the susceptibility to tumor initiation and/or growth may be related to individual differences in baseline immune and endocrine physiology and emotional tone present at the time of carcinogen exposure. Investigation of the mechanistic relevance of these individual differences may lead to prophylactic approaches to cancer treatment in the context of carcinogen exposure.

The discovery of 071031B, a novel serotonin and noradrenaline reuptake inhibitor

Depression is a severe mood disorder with increasing morbidity and suicidality, while the current therapy is not satisfactory. Serotonin and noradrenaline reuptake inhibitors (SNRIs) have been reported to have higher efficacy and/or faster acting rate than commonly used antidepressants. The present study was designed to screen the potential SNRIs, using in vitro radioligand receptor binding assays and in vivo animal tests, and introduced the discovery of 071031B. In the tail suspension test and forced swimming test in mice, six compounds (071017S, 071026W, 071031A, 071031B, 080307A and 080307B) showed robust antidepressant activity, without stimulant effect on the locomotor activity or other side effects, and the minimal effective dose of 071017S, 071026W, 071031A and 071031B was less than that of duloxetine; in vitro binding tests indicated that 071031B had high affinity to both serotonin transporter and noradrenaline transporter with similar inhibitory rates to duloxetine at 1 and 100 nM; acute toxicity test indicated that the LD50 value of 071031B was similar to that of duloxetine. These findings demonstrated that this integrated system, combining high throughput screening technology and in vivo animal tests, is effective to screen potential monoamine reuptake inhibitors fast and accurately; 071031B is expected to be a novel serotonin and noradrenaline reuptake inhibitor for its robust antidepressant activity and transporter affinity.

Depression-like behavior is dependent on age in male SAMP8 mice

Aging is associated with an increased risk of depression in humans. To elucidate the underlying mechanisms of depression and its dependence on aging, here we study signs of depression in male SAMP8 mice. For this purpose, we used the forced swimming test (FST). The total floating time in the FST was greater in SAMP8 than in SAMR1 mice at 9 months of age; however, this difference was not observed in 12-month-old mice, when both strains are considered elderly. Of the two strains, only the SAMP8 animals responded to imipramine treatment. We also applied the dexamethasone suppression test (DST) and studied changes in the dopamine and serotonin (5-HT) uptake systems, the 5-HT2a/2c receptor density in the cortex, and levels of TPH2. The DST showed a significant difference between SAMR1 and SAMP8 mice at old age. SAMP8 exhibits an increase in 5-HT transporter density, with slight changes in 5-HT2a/2c receptor density. In conclusion, SAMP8 mice presented depression-like behavior that is dependent on senescence process, because it differs from SAMR1, senescence resistant strain.

Comparative study of efficacy of l-5-hydroxytryptophan and fluoxetine in patients presenting with first depressive episode

INTRODUCTION

Role of l-5-hydroxytryptophan (l-5-HTP) in depression is relatively less studied but the literature has shown its robust role in depression. The present randomized double blind study was undertaken to assess the role of l-5-HTP as an antidepressant and to compare its antidepressant efficacy with fluoxetine in first depressive episode patients of Indian population.

METHODS

A total of 70 patients of first depressive episode, all of whom were diagnosed with ICD-10 criteria, were recruited but only 60 patients completed the study and were randomly divided into two groups, receiving l-5-HTP and fluoxetine, respectively, for a period of 8weeks. All patients were administered Hamilton Rating Scale for Depression (HAM-D) to assess severity of depression at baseline, 2weeks, 4weeks and 8weeks. The efficacy of treatment was assessed by comparing HAM-D scores obtained at these examinations with the baseline examination; final evaluation of both efficacy and tolerance was assessed using the Clinical Global Impression (CGI) scale at the end of study.

RESULTS

Both treatment groups showed significant and nearly equal reduction in HAM-D scores beginning at week two and continuing through week eight. Twenty-two patients (73.33%) in the l-5-HTP group and 24 patients (80%) in the fluoxetine group showed positive response at the end of the study.

CONCLUSION

l-5-HTP has definitely got antidepressant effect in patients of depression. Antidepressant effect was seen within 2weeks of treatment and was apparent in all degrees of depression. The therapeutic efficacy of l-5-HTP was considered as equal to that of fluoxetine.

From the stressed adolescent to the anxious and depressed adult: investigations in rodent models

Anxiety and depression are the most prevalent of the psychiatric disorders. The average age of onset of these disorders is in adolescence, and stressful experiences are recognized as an important pathway to such dysfunction. Until recently, however, most animal models of these disorders involved adult males. We provide a brief overview of anxiety and depression and the extent to which adolescent rodents are a valid model for their investigation, and briefly review the main measures of anxiety-like and depressive behaviour in rodents. The focus of the review is investigations in which adolescent rodents were exposed to chronic stressors, describing our research using social instability stress and that of other researchers using various social and non-social stressors. The evidence to date suggests stress in adolescence alters the trajectory of brain development, and particularly that of the hippocampus, increasing anxiety and depressive behaviour in adulthood.

Rosmarinus officinalis L. hydroalcoholic extract, similar to fluoxetine, reverses depressive-like behavior without altering learning deficit in olfactory bulbectomized mice

ETHNOPHARMACOLOGICAL RELEVANCE

Rosemary, Rosmarinus officinalis L., has several therapeutic applications in folk medicine for the treatment of a wide range of diseases, including depression.

AIM OF THE STUDY

To evaluate the ability of Rosmarinus officinalis hydroalcoholic extract (ROHE), as compared to the positive control fluoxetine, to reverse behavioral (hyperactivity, anhedonic behavior and learning deficit in water maze) and biochemical alterations (serum glucose level and acetylcholinesterase, AChE, activity) induced by an animal model of depression, the olfactory bulbectomy (OB) in mice.

MATERIALS AND METHODS

Locomotor and exploratory behavior was assessed in the open-field, novel object and novel cage tests, anhedonic behavior was assessed in the splash test; cognitive deficits were evaluated in the water maze task. For the first set of experiments, ROHE (10-300 mg/kg) or fluoxetine (10mg/kg) was administered once daily (p.o.) for 14 days after OB and the behavioral tests were performed. For the second set of experiments, serum glucose and hippocampal and cerebrocortical AChE activity were determined in OB and SHAM-operated mice treated orally with ROHE (10mg/kg), fluoxetine (10mg/kg) or vehicle.

RESULTS

ROHE (10-300 mg/kg), similar to fluoxetine, reversed OB-induced hyperactivity, increased exploratory and anhedonic behavior. OB needed significantly more trials in the training session to acquire the spatial information, but they displayed a similar profile to that of SHAM mice in the test session (24h later), demonstrating a selective deficit in spatial learning, which was not reversed by ROHE or fluoxetine. A reduced serum glucose level and an increased hippocampal AChE activity were observed in bulbectomized mice; only the latter effect was reversed by fluoxetine, while both effects were reversed by ROHE.

CONCLUSIONS

ROHE exerted an antidepressant-like effect in bulbectomized mice and was able to abolish AchE alterations and hypoglycemia, but not spatial learning deficit induced by OB. Overall, results suggest the potential of Rosmarinus officinalis for the treatment of depression, validating the traditional use of this plant.

Towards an ethological animal model of depression? A study on horses

BACKGROUND

Recent reviews question current animal models of depression and emphasise the need for ethological models of mood disorders based on animals living under natural conditions. Domestic horses encounter chronic stress, including potential stress at work, which can induce behavioural disorders (e.g. "apathy"). Our pioneering study evaluated the potential of domestic horses in their usual environment to become an ethological model of depression by testing this models' face validity (i.e. behavioural similarity with descriptions of human depressive states).

METHODOLOGY/PRINCIPAL FINDINGS

We observed the spontaneous behaviour of 59 working horses in their home environment, focusing on immobility bouts of apparent unresponsiveness when horses displayed an atypical posture (termed withdrawn hereafter), evaluated their responsiveness to their environment and their anxiety levels, and analysed cortisol levels. Twenty-four percent of the horses presented the withdrawn posture, also characterized by gaze, head and ears fixity, a profile that suggests a spontaneous expression of "behavioural despair". When compared with control "non-withdrawn" horses from the same stable, withdrawn horses appeared more indifferent to environmental stimuli in their home environment but reacted more emotionally in more challenging situations. They exhibited lower plasma cortisol levels. Withdrawn horses all belonged to the same breed and females were over-represented.

CONCLUSIONS/SIGNIFICANCE

Horse might be a useful potential candidate for an animal model of depression. Face validity of this model appeared good, and potential genetic input and high prevalence of these disorders in females add to the convergence. At a time when current animal models of depression are questioned and the need for novel models is expressed, this study suggests that novel models and biomarkers could emerge from ethological approaches in home environments.

Licking and Liking: The Assessment of Hedonic Responses in Rodents

Affective processes are a key determinant of behaviour: At its simplest, liked stimuli are approached while disliked stimuli are avoided. Although assessing hedonic responses in nonverbal animals can be difficult, one relatively tractable approach relies on detailed analyses of rodents' consummatory behaviour. Rodents typically produce rhythmic sets of licks that can be grouped into clusters on the basis of the intervals between licks. The mean number of licks in a cluster (cluster size) is directly related to the concentration of palatable and unpalatable solutions. These relationships suggest that lick cluster size might be a useful index of an animal's hedonic reaction to the solution being consumed. I begin by reviewing studies of conditioned flavour preference and aversion that support the idea that lick cluster size can provide useful information about rats' hedonic reactions. I then describe how this methodology has been used to address previously intractable issues in the investigation of contrast effects as well as revealing an analogue of effort justification effects that, in humans, are commonly explained in terms of cognitive dissonance reduction. Finally, I consider how lick analysis might provide information about hedonic responses in animal models of human psychiatric disorders. In all these cases, how an animal did something was particularly informative about why it was doing it.

Antidepressant-like properties of oral riluzole and utility of incentive disengagement models of depression in mice

RATIONALE

The neuroprotective agent riluzole has antidepressant-like properties in humans, but its mechanisms of action are unclear. Despite the increasing utility of transgenic and knockout mice in addressing such issues, previous studies aimed at characterizing biochemical mechanisms have been conducted in rats.

OBJECTIVES

We sought to optimize an oral riluzole administration protocol with antidepressant-like consequences in C57BL/6 mice, a common background strain in genetically modified mice.

METHODS

Riluzole (6-60 μg/ml) was dissolved in tap water and replaced regular drinking water for up to 3 weeks; sensitivity to tail suspension, forced swimming, and the locomotor response to extinction training in a model of "incentive disengagement" were tested. Peripheral and central effects of long-term 60-μg/ml treatment were also evaluated.

RESULTS

Riluzole had dose-dependent antidepressant-like effects in the forced swim test, and like chronic fluoxetine, exerted antidepressant-like actions in an adaptation of the "incentive disengagement" model at the highest concentration tested. This 60-μg/ml concentration also restored hippocampal brain-derived neuroptrophic factor (BDNF) expression after chronic corticosteroid exposure and increased glutamate glial transporter 1 (GLT-1, or EAAT2) expression without significantly affecting baseline locomotor activity, thymus and adrenal gland weights, or blood serum corticosterone. The lowest 6-μg/ml concentration increased locomotor activity, potentially consistent with an anxiolytic-like effect.

CONCLUSIONS

Riluzole's therapeutic potential for treating mood disorders may involve GLT-1 and BDNF, and we suggest this protocol could be used to further characterize its precise long-term biochemical mechanisms of action in animal models of depression.

Animal models of depression vulnerability

The rapid increase in the number of proposed animal models of depression reflects the dissatisfaction with our current state of knowledge on neurobiology of depression and unsuccessful drug development. Results obtained with even the best validated models can be difficult to compare. Because evidence from epidemiological studies suggests that depression occurs in biologically predisposed subjects under the impact of adverse life events, increasing attempts have been made to use the diathesis-stress concept in animal models. In this way, factors underpinning vulnerability to depression have been identified by measuring behavioural traits analogous to facets of human personality, or created by inducing neurochemical lesions. Stressful interventions administered prenatally, in early life or in adulthood have been combined with other vulnerability factors including genetic changes. As a result, several putative animal models of endophenotypes of depression or depression vulnerability have been proposed. Diathesis-stress models may aid in separating adaptive and maladaptive strategies in coping with stress, and understanding the relevant neurobiology. Studies comparing effects of stress on males and females should reveal to which extent the pathogenetic processes leading to depression can be specific to sex/gender.

Animal model and neurobiology of suicide

Animal models are formidable tools to investigate the etiology, the course and the potential treatment of an illness. No convincing animal model of suicide has been produced to date, and despite the intensive study of thousands of animal species naturalists have not identified suicide in nonhuman species in field situations. When modeling suicidal behavior in the animal, the greatest challenge is reproducing the role of will and intention in suicide mechanics. To overcome this limitation, current investigations on animals focus on every single step leading to suicide in humans. The most promising endophenotypes worth investigating in animals are the cortisol social-stress response and the aggression/impulsivity trait, involving the serotonergic system. Astroglia, neurotrophic factors and neurotrophins are implied in suicide, too. The prevention of suicide rests on the identification and treatment of every element increasing the risk.

Behavioral animal models of depression

Depression is a chronic, recurring and potentially life-threatening illness that affects up to 20% of the population across the world. Despite its prevalence and considerable impact on human, little is known about its pathogenesis. One of the major reasons is the restricted availability of validated animal models due to the absence of consensus on the pathology and etiology of depression. Besides, some core symptoms such as depressed mood, feeling of worthlessness, and recurring thoughts of death or suicide, are impossible to be modeled on laboratory animals. Currently, the criteria for identifying animal models of depression rely on either of the 2 principles: actions of known antidepressants and responses to stress. This review mainly focuses on the most widely used animal models of depression, including learned helplessness, chronic mild stress, and social defeat paradigms. Also, the behavioral tests for screening antidepressants, such as forced swimming test and tail suspension test, are also discussed. The advantages and major drawbacks of each model are evaluated. In prospective, new techniques that will be beneficial for developing novel animal models or detecting depression are discussed.

Shaping brain development: mouse communal nesting blunts adult neuroendocrine and behavioral response to social stress and modifies chronic antidepressant treatment outcome

Early experiences shape brain function and behavior and, consequently, vulnerability to psychopathology at adulthood. Here we exploited the mouse communal nest (CN) paradigm in order to investigate the effect of the early social environment on the emergence of endophenotypes of depression and on antidepressant efficacy at adulthood. CN, which consists in a single nest where three mothers keep their pups together and share care-giving behavior until weaning, is characterized by high levels of maternal behavior and peer interactions, thus representing an highly stimulating environment. Our results show that, when compared to mice reared in standard laboratory conditions (SN), adult CN mice exhibited greater sucrose preference on the first days of the test, displayed reduced anhedonia during social stress and had lower corticosterone levels after acute and prolonged social stress. Furthermore, in line with previous work, CN displayed longer immobility than SN mice in the forced swim test. Here we show that such behavioral response is differently affected by antidepressants according to early experiences. A 3-week fluoxetine treatment affected only SN mice, leading to an increase of immobility duration up to the levels showed by CN mice, while acute fluoxetine administration decreased immobility duration in both groups. These results show that being reared in a CN profoundly changes developmental trajectories, reducing the adult display of endophenotypes of depression and modifying response to antidepressants. The present findings suggest that early experiences represent one of those factors to be taken into account to identify the appropriate individual pharmacological strategy to treat depression in patients.

Depressant-like effects of parthenolide in a rodent behavioural antidepressant test battery

The anti-serotonergic effects of parthenolide (PTL) demonstrated in platelets inspired the present psychopharmacological investigation, which employs a battery of rodent behavioural assays of depression. In mice, PTL (0.5-2 mg kg−1) exhibited dose-dependent depressant-like effects in a forced swim test and a tail suspension test, without affecting the baseline locomotor status. The doses (1 and 2 mg kg−1) that induced depressant-like effects were found to significantly reduce 5-hydroxytrypto-phan-induced head twitch response. Interaction studies revealed that the depressant-like effects of PTL (1 mg kg−1) were reversed more efficiently by serotonergic antidepressants (venlafaxine, escitalopram, citalopram, fluoxetine) than by others (desipramine, bupropion) tested. Chronic treatment of PTL (1 and 2 mg kg−1) augmented the hyper-emotionality of olfactory bulbectomized rats, when compared with sham rats, as observed in modified open field, elevated plus maze and social interaction paradigms. This study depicts the severe depressogenic potential of PTL (in its pure form) plausibly mediated by platelet/neuronal hypo-serotonergic effects.

New approaches to the pharmacological management of major depressive disorder

Despite effective and safe therapies for major depressive disorder (MDD), the current arsenal of antidepressant therapies does not fully satisfy the needs of patients or physicians. Many patients are only partial responders or are treatment resistant and side effects interfere with compliance. The majority of antidepressants directly affect monoamine neurotransmission within the central nervous system. Moving beyond this mechanism has been a challenge because of the lack of knowledge about the underlying etiology and pathophysiology of MDD. Provided in this report is a review of some of the major new advances in MDD research that suggest the possibility of novel and improved future therapeutic options. Emphasis is placed on studies of unipolar, but not bipolar, depression. New therapies include dual and triple monoamine uptake inhibitors, non-conventional antidepressants such as tianeptine, and a number of augmentation strategies. In addition, studies are underway on a number of mechanisms of action that might yield the next therapeutic advance. These include agents that interact with endocannabiniod systems, examination of natural products, and compounds that influence neuropeptide systems such as galanin and melanin-concentrating hormone, and growth and neurotrophic factors. Epigenetic mechanisms involving histone modification are also being explored. An area of intensive investigation is glutamate neurotransmission. Data support the hypothesis that NMDA receptor antagonists are effective in MDD individuals resistant to conventional therapies. The potential of metabotropic glutamate receptors as novel targets is also discussed. Accumulating evidence supports the idea that amplification of AMPA receptor function is a critical link in the transduction processes involved antidepressant effects.

Chronic citalopram treatment elevates serotonin synthesis in flinders sensitive and flinders resistant lines of rats, with no significant effect on Sprague-Dawley rats

The influence of citalopram on regional 5-hydroxytryptamine (serotonin, 5-HT) synthesis, one of the most important presynaptic parameters of serotonergic neurotransmission, was studied. Sprague-Dawley (SPD) rats were used as the controls, and Flinders Resistant Line (FRL) rats were used as auxiliary controls, to hopefully obtain a better understanding of the effects of citalopramon Flinders Sensitive Line (FSL; "depressed") rats. Regional 5-HT synthesis was evaluated using a radiographic method with a labelled tryptophan analog tracer. In each strain of rats, the animals were treated with citalopram (10 mg/(kg day)) or saline for 14 days. The groups consisted of between fourteen and twenty rats. There were six groups of rats with citalopram (CIT) and saline (SAL) groups in each of the strains (SPD-AL, SPD-IT, FRL-AL, FRL-IT, FSL-AL and FSL-IT). A two-factor analysis of variance was used to evaluate the effect of the treatment c., SPD-SAL relative to SPD-CIT) followed by planned comparisons to evaluate the effect in each brain region. In addition, the planned comparison with appropriate contrast was used to evaluate a relative effects in SPD relative to FSL and FRL, and FSL relative to FRL groups. A statistical analysis was first performed in the a priori selected regions, because we had learned, from previous work, that it was possible to select the brain regions in which neurochemical variables had been altered by the disorder and subsequent antidepressant treatments. The results clearly show that citalopram treatment does not have an overall effect on synthesis in the control SPD rats; there was no significant (p > 0.05) difference between the SPD-SAL and SPD-CIT rats. In "depressed" FSL rats, citalopram produced a significant (p < 0.05) elevation of synthesis in seventeen out of thirty-four regions, with a significant (p < 0.05) reduction in the dorsal and median raphe. In the FRL rats, there was a significant (p < 0.05) elevation in the synthesis in twenty-two out of thirty-four brain regions, with a reduction in the dorsal raphe. In addition to these regions magnus raphe was different in the SPD and FSL groups, but it was on the statistical grounds identified as an outlier. There were significant changes produced in the FSL and FRL rats in thirteen out of seventeen a priori selected brain regions, while in the SPD rats, citalopram produced significant changes in only four out of seventeen a priori selected regions. The statistical evaluation also revealed that changes produced by citalopram in the FSL and FRL rats were significantly greater than those in the SPD rats and that there was no significant difference between the effect produced in the FSL and FRL rats. The presented results suggest that in "depressed" FSL rats, the antidepressant citalopram elevates 5-HT synthesis, which probably in part relates to the reported improved in behaviour with citalopram.

Investigations of HPA function and the enduring consequences of stressors in adolescence in animal models

Developmental differences in hypothalamic-pituitary-adrenal (HPA) axis responsiveness to stressors and ongoing development of glucocorticoid-sensitive brain regions in adolescence suggest that similar to the neonatal period of ontogeny, adolescence may also be a sensitive period for programming effects of stressors on the central nervous system. Although research on this period of life is scarce compared to early life and adulthood, the available research indicates that effects of stress exposure during adolescence differ from, and may be longer-lasting than, effects of the same stress exposure in adulthood. Research progress in animal models in this field is reviewed including HPA function and the enduring effects of stress exposures in adolescence on sensitivity to drugs of abuse, learning and memory, and emotional behaviour in adulthood. The effects of adolescent stress depend on a number of factors, including the age, gender, the duration of stress exposure, the type of stressor, and the time between stress exposure and testing.

Both acute and chronic buspirone treatments have different effects on regional 5-HT synthesis in Flinders Sensitive Line rats (a rat model of depression) than in control rats

The main objective of this investigation was to evaluate the effects of buspirone, a 5-HT(1A) agonist with some partial agonist properties and also an antidepressant, on regional 5-HT synthesis in Flinders Sensitive Line (FSL) rats ("depressed"), and to compare the effects to the Flinders Resistant Line (FRL) control rats (not "depressed"). In addition results were compared to those previously reported in normal Sprague-Dawley (SPD) rats (normal control). Serotonin synthesis in both FSL and FRL rats was measured following acute and chronic treatments with buspirone. Both of these strains were derived from the SPD rats. No direct comparison was done between the FSL saline and FRL saline groups, or the FSL buspirone and FRL buspirone groups, because the objective of the studies was to evaluate effects of buspirone in these two strains. The results show that acute treatment with buspirone elevates 5-HT synthesis throughout the brain in the FRL rats. In the FSL rats, there were reductions in some brain regions (e.g., dorsal and median raphe, amygdala, anterior olfactory nucleus, substantia nigra reticulate), while in other regions, there were increases in the synthesis observed (e.g., frontal, parietal, visual and somatosensory cortices, ventral hippocampus). In 20 out of the 30 brain regions investigated in the FSL rats, there was no significant change in the synthesis following acute buspirone treatment. During the chronic treatment, buspirone produced a significant reduction of 5-HT synthesis in 15 out of 30 brain regions in the FRL rats. In the FSL rats, buspirone produced a significant elevation of the synthesis in 10 out of 30 brain regions. In both the FSL and FRL rats, buspirone produced rather different effects than those reported previously for SPD (normal) rats. The acute effect in the FSL rats was somewhat similar to the effect reported previously for the SPD rats, while in the FRL rats, the acute buspirone treatment produced an effect observed previously in treatments with 5-HT(1A) antagonists suggesting an action of buspirone as partial agonist in FRL rats. The data suggest that with respect to 5-HT synthesis, FRL rats differ from SPD rats (a natural control; normal rats) and, as such, indicate that when the effects related to the serotonergic system (e.g., influence of serotonergic drugs) are studied in the FSL rats and compared to those in the FRL rats, any conclusions drawn may not reflect differences relative to a normal rat.

Evaluation of animal models of neurobehavioral disorders

Animal models play a central role in all areas of biomedical research. The process of animal model building, development and evaluation has rarely been addressed systematically, despite the long history of using animal models in the investigation of neuropsychiatric disorders and behavioral dysfunctions. An iterative, multi-stage trajectory for developing animal models and assessing their quality is proposed. The process starts with defining the purpose(s) of the model, preferentially based on hypotheses about brain-behavior relationships. Then, the model is developed and tested. The evaluation of the model takes scientific and ethical criteria into consideration.Model development requires a multidisciplinary approach. Preclinical and clinical experts should establish a set of scientific criteria, which a model must meet. The scientific evaluation consists of assessing the replicability/reliability, predictive, construct and external validity/generalizability, and relevance of the model. We emphasize the role of (systematic and extended) replications in the course of the validation process. One may apply a multiple-tiered 'replication battery' to estimate the reliability/replicability, validity, and generalizability of result.Compromised welfare is inherent in many deficiency models in animals. Unfortunately, 'animal welfare' is a vaguely defined concept, making it difficult to establish exact evaluation criteria. Weighing the animal's welfare and considerations as to whether action is indicated to reduce the discomfort must accompany the scientific evaluation at any stage of the model building and evaluation process. Animal model building should be discontinued if the model does not meet the preset scientific criteria, or when animal welfare is severely compromised. The application of the evaluation procedure is exemplified using the rat with neonatal hippocampal lesion as a proposed model of schizophrenia.In a manner congruent to that for improving animal models, guided by the procedure expounded upon in this paper, the developmental and evaluation procedure itself may be improved by careful definition of the purpose(s) of a model and by defining better evaluation criteria, based on the proposed use of the model.