Animal models of depression
Animal models of depression are research tools used to investigate depression and action of antidepressants as a simulation to investigate the symptomatology and pathophysiology of depressive illness or used to screen novel antidepressants.
Major depressive disorder, also called "clinical depression" or often simply "depression", is a common, long-lasting and diverse psychiatric syndrome that significantly affects a person's thoughts, behavior, feelings and sense of well-being. Symptoms include low mood and aversion to activity. Depressed people may also feel sad, anxious, empty, hopeless, worried, helpless, worthless, guilty, irritable, hurt, or restless. They may lose interest in activities that once were pleasurable, experience loss of appetite or overeating, have problems concentrating, remembering details, or making decisions, and may contemplate or attempt suicide. Insomnia, excessive sleeping, fatigue, loss of energy, or aches, pains, or digestive problems that are resistant to treatment may also be present.
About one in six people in the U.S will succumb to depression at some point during their life span, and according to the World Health Organization, depression is projected to reach second place as leading contributor to the global burden of disease by the year 2020. The effects of current antidepressant drugs are often significantly delayed, with improvements beginning around 3–6 weeks after treatment is started. Despite the clinical success of many antidepressant drugs, such as tricyclic antidepressants (TCAs), monoamine oxidase inhibitors (MAOIs), and serotonin reuptake inhibitors (SRIs), many individuals' symptoms are not adequately alleviated by medication alone, and other methods of treatment may be recommended.
Modeling depression in animalsEdit
It is difficult to develop an animal model that perfectly reproduces the symptoms of depression in patients. Many animals lack self-consciousness, self-reflection, and consideration; moreover, hallmarks of the disorder such as depressed mood, low self-esteem or suicidality are hardly accessible in non-humans. However, depression, as other mental disorders, consists of endophenotypes that can be reproduced independently and evaluated in animals. An ideal animal model offers an opportunity to understand molecular, genetic, and epigenetic factors that may lead to depression. By using animal models, the underlying molecular alterations and the causal relationship between genetic or environmental alterations and depression can be examined, which would afford a better insight into pathology of depression. In addition, animal models of depression are indispensable for identifying novel therapies for depression.
Endophenotypes in animal model of depressionEdit
- Anhedonia: The loss of interest is a core symptom of depression. Anhedonia in rodents can be assessed by sucrose preference or by intracranial self-stimulation.
- Behavioral despair: Behavioral despair might be assessed with tests such as the forced-swimming test or the tail suspension test.
- Changes in appetite or weight gain: Depression is often associated with changes in appetite or weight gain, which is easily measured in rodents.
- Neuroanatomy: Depressed subjects display decreased hippocampal volume and rodents exposed to chronic stress or excess glucocorticoids exhibit similar signs of hippocampal loss of neurons and dendritic atrophy.
- Neuroendocrine disturbances: Disturbances of the hypothalamic–pituitary–adrenal axis (HPA) are one of the most consistent symptoms in major depression. The functionality of the HPA can be assessed by dexamethasone suppression test .
- Alterations in sleep architecture: Disturbances in the circadian rhythm and especially in the sleep architecture are often observed in depressed. In rodents, it is accessible via electroencephalography (EEG).
- Anxiety-related behavior: Anxiety is a symptom with high prevalence in depression. Therefore, animal models of depression often display altered anxiety-related behavior.
Criteria for valid animal models of depressionEdit
An appropriate animal model of human depression should fulfill the following criteria as much as possible: strong phenomenological similarities and similar pathophysiology (face validity), comparable etiology (construct validity), and common treatment (predictive validity). Again, depression is a heterogeneous disorder and its many symptoms are hard to be produced in laboratory animals. The question therefore remains whether we can know the animal is "depressed". Actually, few models of depression fully fit these validating criteria, and most models currently used rely on either actions of known antidepressants or responses to stress. It is not necessary for an "ideal" animal model of depression to exhibit all the abnormalities of depression-relevant behaviors, just as not all patients manifest every possible symptom of depression.
Antidepressant screening testsEdit
Antidepressant screening tests, not like the models which can be defined as an [organism] or a particular state of an organism that reproduces aspects of human pathology, provide only an end-point behavioral or physiological measure designed to assess the effect of the genetic, pharmacological, or environmental manipulation.
- Forced-swimming test: The forced-swimming test (FST) is based on the observation that animals develop an immobile posture in an inescapable cylinder filled with water. In this test, immobility is interpreted as a passive stress-coping strategy or depression-like behavior (behavioral despair). After antidepressant administration, the animals will actively perform escape-directed behaviors with longer duration than animals with control saline treatment. FST is the most widely used tool in depression research, more specifically as a screen for acute antidepressants.
- The advantages of FST are that it is low-costing and is a fast and reliable tool, easy to handle and has proven its reliability across laboratories, for testing potential antidepressants activities with a strong predictive validity. Besides, it allows rapid screening of large numbers of drugs. The major disadvantages of FST are that it has poor face and construct validities. The test is sensitive to acute treatment only, and its validity for non-monoamine antidepressants is uncertain
- Tail suspension test: The TST, also known as tail suspension test, shares a common theoretical basis and behavioral measure with the FST. In the TST, mice are suspended by their tails using adhesive tape to a horizontal bar for a certain couple of minutes, and the time of immobility is recorded. Typically, the suspended rodents perform immediately escape-like behaviors, followed by developing an immobile posture. If antidepressants are given prior to the test, the subjects will be engaged in escape-directed behaviors for longer periods of time than after saline treatment, exhibiting a decrease in duration of immobility.
- A major advantage of the TST is that it is simple and inexpensive. A major disadvantage of the TST is that it is restricted to mice and limited to strains that do not tend to climb their tail. Besides, like FST, TST is sensitive to acute treatment only, and its validity for non-monoamine antidepressants is uncertain.
- Sucrose preference: Rodents are born with an interest in sweet foods or solutions. Reduced preference for sweet solution in sucrose preference test represents anhedonia, while this reduction can be reversed by treatment with chronic antidepressants. This test can measure the affective state and motivation of subject rodents; however, further validation is needed for working as a model of depression.
- Intracranial self-stimulation: Intracranial self-stimulation (ICSS) can be utilized in rodents to understand how drugs affect the function of brain reward system. In this paradigm, in which the animal is trained to spin a wheel to receive a current through electrodes implanted in its own brain for rewarding hypothalamic stimulation. ICSS shares a common theoretical basis with the sucrose preference. Reduced preference for self-stimulating for reward cognition represents a loss of interest, fatigue and a loss of energy during depressive episodes, while this reduction can be reversed by treatment with antidepressants. Like sucrose preference test, ICSS can measure the affective state and motivation of subject rodents, and again, further validation is needed for working as a model of depression.
- Novelty-induced hypophagia: Hypophagia, one of the anxiety symptoms in rodents, is defined as the reduction in feeding in response to novelty, and it can be evoked by various novel features of the environment, including novel food, novel testing environment and novel food containers. Novelty-induced hypophagia (NIH) is a very recently developed test, which measures the latency and consumption of food in a novel unfamiliar environment. The test rather reflects the anxiolytic effects of antidepressants, and the response is seen only after chronic treatment with antidepressants rather than acute.
- Open field: Rodents tend to avoid brightly illuminated areas, and this avoidance is interpreted as a symptom of anxiety. Open field is a bright enclosure and during the test rodents are placed in this arena thus forced to interact with a novel and bright environment. The movement of the experimental subject will be recorded in distance and pathway.
- Elevated plus maze: For the elevated plus maze test, the rodents are placed at the intersection of the four arms of the maze (two open, two closed), facing an open arm. The number of entries and time spent in each arm is recorded and valid results are obtained in a single 5-minute testing session. An increase in the open-arm time is an index of anti-anxiety behavior of rodents.
- Dark/light box: The dark/light box test is also based on the rodents' innate aversion to brightly illuminated areas and on the spontaneous exploratory behaviour of the animals. A natural conflict situation occurs when an animal is exposed to an unfamiliar environment or novel objects. The conflict is between the tendency to explore and the initial tendency to avoid the unfamiliar. The exploratory activity reflects the combined result of these tendencies in novel situations. The test apparatus of dark/light box consists of a dark compartment and an illuminated compartment. Drug-induced increases in behaviors in the white part of a two-compartment box are suggested as an index of anxiolytic activity.
- Open field test, elevated plus maze test, and dark/light box test can work as an antidepressant screen by measuring anxiety-related behavior as an accompanying endophenotype of depression. It is known that some antidepressants administration will cause a decrease behavior in these tests just like anxiolytics. However, the response to some antidepressants couldn't be detected. Besides, these tests each have their own problems. It is difficult to discriminate decreased anxiety-related avoidance from increased novelty-seeking in these tests.
Certain types of human depression are precipitated by stressful life events, and vulnerable individuals experiencing these stressors may develop clinical depression. Consequently, the majority of animal models of depression are based on the exposure to various types of acute or chronic stressors.
Adult stress modelsEdit
- Learned helplessness: The learned helplessness model (LH), one of the well validated animal models, is the best replicated one. The rationale is that exposure to uncontrollable and stressful life events makes people feel like they are losing control, and this sometimes leads to depressive like behaviors. The model is based on the observation that animals also develop deficits in escape, cognitive and rewarded behaviors when they have been subjected to repeated unavoidable and uncontrollable shocks. LH is induced in one day or over several days of repeated inescapable stress by the treating of tail shock or foot shock in shuttle boxes. Helpless behavior is evaluated by analyzing the performance in an active escape test, such as the latency to press a lever or cross a door.
- An advantage of LH is that the cognitive and other behavioral outcomes seem to be correlated, thus helping to understand the depressive symptomatology in humans. Besides, this model can also be generally used to measure the escape performance of mice with different mutations, in which target genes of depression may affect the vulnerability to develop a depressive-like state. These excellent face and predictive validities make LH an interesting model to explore the pathophysiology of depression. The biggest disadvantage of LH is it requires very strong stressors to induce the behavioral phenotypes, which does raise ethical problems. Also, most of the symptoms do not persist long enough following cessation of the uncontrollable shock.
- Chronic mild stress: The chronic mild stress (CMS) model is probably the most valid animal model of depression. It aims to model a chronic depressive-like state that develops gradually over time in response to stress, and they can provide more natural induction. CMS involves the exposure of animals to a series of mild and unpredictable stressors (periods of food and water deprivation, small temperature reductions, changes of cage mates, and other similar individually innocuous manipulations) during at least 2 weeks. The model has been reported to result in long lasting changes of behavioral, neurochemical, neuroimmune, and neuroendocrinological variables resembling reward functions including decreased intracranial self-stimulation, reflecting anhedonia that is reversed by chronic but not acute antidepressant treatment. Of note, this CMS model can be used to screen and test potential antidepressant compounds and to develop new treatment strategies.
- The advantages of this model are its good predictive validity (behavioral changes are reversed by chronic treatment with a wide variety of antidepressants), face validity (almost all demonstrable symptoms of depression have been reproduced), and construct validity (CMS causes a generalized decrease in responsiveness to rewards). However, there is a common practical difficulty in carrying out CMS experiments, which are labor intensive, demanding of space, and of long duration. Besides, the procedure can be difficult to be established and data can be hardly replicated.
- Social defeat stress: Social defeat stress (SDS) is a chronic and recurring factor in the lives of virtually all higher animal species. Humans experiencing social defeat show increased symptoms of depression, loneliness, anxiety, social withdrawal and a loss of self-esteem. Since the majority of stress stimuli in humans that lead to psychopathological changes are of social nature, SDS model have gained increasing attention as they might render useful to study certain endophenotypes of depression. During the stress period, the male rodent will be introduced into a different territory of other cospecific males for each day as an intruder, that cause it to be investigated, attacked and defeated by the residents. The consequent behavior changes in the subject caused by SDS, like decreased social interaction or lack of interest, are similar to some parts of human depression, and behavioral treatment and antidepressants can reverse these changes in SDS model.
- Like CMS, SDS has good predictive validity (behavioral changes are reversed by chronic treatment with a wide variety of antidepressants), face validity (many symptoms of depression have been reproduced), and construct validity (causing a generalized decrease in responsiveness to rewards) and gives another validity that only chronic but not acute antidepressant administration can reverse the social aversion. One disadvantage of SDS model is the long duration. To apply SDS model for studying human depression, the period of it should last at least 20 days otherwise only anxiety symptoms could be induced. Worthy of note, only male rodents can be used for this model, since female rodents do not fight each other in a resident–intruder confrontation.
Early life stress modelsEdit
Early adverse experiences such as traumatic life events in childhood result in an increased sensitivity to the effects of stress later in life and influence the individual vulnerability to depression. Suitable animal models could provide a basis for understanding potential mechanisms of environmental and developmental factors of individual differences in stress reactivity and vulnerability to disorders. Models of early life stress involve prenatal stress, early postnatal handling and maternal separation. All these treatments have been demonstrated to produce significant effects that last until adulthood.
- Maternal deprivation: The maternal deprivation model is the most widely used early life stress model. This model manipulates the maternal separation of early life deprivation, in which pups are separated from the dam for 1–24 h per day during the first two postnatal weeks. Maternal separation results in increased anxiety- and depression-like behaviors and increased HPA response in adulthood.
- Olfactory bulbectomy: The olfactory bulbectomy in rodents results in a disruption of the limbic-hypothalamic axis with the consequence of behavioral, neurochemical, neuroendocrine and neuroimmune changes, of which many resemble changes seen in depressed patients. It is still not clear how bulbectomy in animals actually relates to depression in humans. It might simply result from a high intensity of chronic stressor caused by chronic sensory deprivation. This model shows high predictive validity as it mimics the slow onset of antidepressant action reported in clinical studies, responding chronic but not subchronic antidepressant treatment with no response to other drugs. It is worth to be mentioned that, unlike stress-related models, the rat in lesion model represents an agitated, hyposerotonergic depression-related phenotype, rather than a retarded depression.
- Psychostimulant withdrawal (amphetamine, cocaine): In humans, withdrawal from chronic psychostimulants generates symptoms that have strong behavioral and physiological parallels to depression. Therefore, the examination of the behavioral effects of drug withdrawal in rodents may provide insights into the underlying neurobiological mechanisms and aid in the development of animal models of depression that are sensitive to antidepressant agents. Following withdrawal from drugs such as amphetamine or cocaine, rodents display behavioral changes that are highly similar to some aspects of depression in humans, such as anhedonia, and behaviors opposite to those seen after treatment with antidepressant drugs.
- Genetically engineered mice: Only few generated mutant lines can be regarded as depression models, for example, α2A adrenergic receptor knockout mice, glucocorticoid receptor heterozygous mice, and cAMP response element-binding protein overexpressing mice.
- Forward genetics: Forward genetics allows identifying relevant genes without any prior knowledge of genetic to the phenotype. Large scale random mutagenesis screens, like ENU, have resulted in a great number of mutants displaying depression or antidepressant-like behavior.
- "Depression Basics". National Institute of Mental Health.
- Kessler, Ronald C.; Berglund, Patricia; Demler, Olga; Jin, Robert; Merikangas, Kathleen R.; Walters, Ellen E. (2005-06-01). "Lifetime Prevalence and Age-of-Onset Distributions of DSM-IV Disorders in the National Comorbidity Survey Replication" (PDF). Archives of General Psychiatry. 62 (6): 593–602. doi:10.1001/archpsyc.62.6.593. ISSN 0003-990X. PMID 15939837.
- Murray, Christopher JL; Lopez, Alan D (May 1997). "Alternative projections of mortality and disability by cause 1990–2020: Global Burden of Disease Study" (PDF). The Lancet. 349 (9064): 1498–1504. doi:10.1016/s0140-6736(96)07492-2. ISSN 0140-6736. PMID 9167458. S2CID 10556268.
- Yan, Hua-Cheng; Cao, Xiong; Das, Manas; Zhu, Xin-Hong; Gao, Tian-Ming (August 2010). "Behavioral animal models of depression". Neuroscience Bulletin. 26 (4): 327–337. doi:10.1007/s12264-010-0323-7. ISSN 1673-7067. PMC 5552573. PMID 20651815.
- Hasler, Gregor; Drevets, Wayne C; Manji, Husseini K; Charney, Dennis S (2004-06-23). "Discovering Endophenotypes for Major Depression". Neuropsychopharmacology. 29 (10): 1765–1781. doi:10.1038/sj.npp.1300506. ISSN 0893-133X. PMID 15213704.
- Willner, P.; Mitchell, P. J. (May 2002). "The validity of animal models of predisposition to depression". Behavioural Pharmacology. 13 (3): 169–188. doi:10.1097/00008877-200205000-00001. ISSN 0955-8810. PMID 12122308.
- Anisman, Hymie; Matheson, Kim (January 2005). "Stress, depression, and anhedonia: Caveats concerning animal models". Neuroscience & Biobehavioral Reviews. 29 (4–5): 525–546. doi:10.1016/j.neubiorev.2005.03.007. ISSN 0149-7634. PMID 15925696. S2CID 5904832.
- Vollmayr, Barbara; Mahlstedt, Magdalena M.; Henn, Fritz A. (2007-04-01). "Neurogenesis and depression: what animal models tell us about the link". European Archives of Psychiatry and Clinical Neuroscience. 257 (5): 300–303. doi:10.1007/s00406-007-0734-2. ISSN 0940-1334. PMID 17401725. S2CID 16130112.
- Petit-Demouliere, Benoit; Chenu, Franck; Bourin, Michel (2005). "Forced swimming test in mice: a review of antidepressant activity". Psychopharmacology. 177 (3): 245–255. doi:10.1007/s00213-004-2048-7. PMID 15609067.
- Cryan, John F.; Mombereau, Cedric; Vassout, Annick (January 2005). "The tail suspension test as a model for assessing antidepressant activity: Review of pharmacological and genetic studies in mice". Neuroscience & Biobehavioral Reviews. 29 (4–5): 571–625. doi:10.1016/j.neubiorev.2005.03.009. ISSN 0149-7634. PMID 15890404. S2CID 2758433.
- Nielsen, Christina Kurre; Arnt, Jorn; Sánchez, Connie (January 2000). "Intracranial self-stimulation and sucrose intake differ as hedonic measures following chronic mild stress: interstrain and interindividual differences" (PDF). Behavioural Brain Research. 107 (1–2): 21–33. doi:10.1016/S0166-4328(99)00110-2. ISSN 0166-4328. PMID 10628727. S2CID 4001711.
- Dulawa, Stephanie C.; Hen, Rene (January 2005). "Recent advances in animal models of chronic antidepressant effects: The novelty-induced hypophagia test". Neuroscience & Biobehavioral Reviews. 29 (4–5): 771–783. doi:10.1016/j.neubiorev.2005.03.017. ISSN 0149-7634. PMID 15890403. S2CID 21949826.
- Holmes, A. (May 2001). "Targeted gene mutation approaches to the study of anxiety-like behavior in mice". Neuroscience and Biobehavioral Reviews. 25 (3): 261–273. doi:10.1016/S0149-7634(01)00012-4. ISSN 0149-7634. PMID 11378180. S2CID 7947941.
- Drugan, R. C.; Basile, A. S.; Ha, J. H.; Healy, D.; Ferland, R. J. (1997-12-01). "Analysis of the importance of controllable versus uncontrollable stress on subsequent behavioral and physiological functioning". Brain Research. Brain Research Protocols. 2 (1): 69–74. doi:10.1016/S1385-299X(97)00031-7. ISSN 1385-299X. PMID 9438074.
- Grahn, R. E.; Watkins, L. R.; Maier, S. F. (July 2000). "Impaired escape performance and enhanced conditioned fear in rats following exposure to an uncontrollable stressor are mediated by glutamate and nitric oxide in the dorsal raphe nucleus". Behavioural Brain Research. 112 (1–2): 33–41. doi:10.1016/S0166-4328(00)00161-3. ISSN 0166-4328. PMID 10862933. S2CID 33316951.
- Durgam, Robert C. (May 2001). Rodent Models of Depression: Learned Helplessness Using a Triadic Design in Rats. Current Protocols in Neuroscience. Chapter 8. pp. 8.10B.1–8.10B.12. doi:10.1002/0471142301.ns0810bs14. ISBN 978-0471142300. PMID 18428537. S2CID 7360339.
- Chourbaji, S.; Zacher, C.; Sanchis-Segura, C.; Dormann, C.; Vollmayr, B.; Gass, P. (December 2005). "Learned helplessness: Validity and reliability of depressive-like states in mice". Brain Research Protocols. 16 (1–3): 70–78. doi:10.1016/j.brainresprot.2005.09.002. ISSN 1385-299X. PMID 16338640.
- Vollmayr, B.; Henn, F. A. (August 2001). "Learned helplessness in the rat: improvements in validity and reliability". Brain Research. Brain Research Protocols. 8 (1): 1–7. doi:10.1016/S1385-299X(01)00067-8. ISSN 1385-299X. PMID 11522522.
- Willner, Paul (2005). "Chronic Mild Stress (CMS) Revisited: Consistency and Behavioural-Neurobiological Concordance in the Effects of CMS". Neuropsychobiology. 52 (2): 90–110. doi:10.1159/000087097. ISSN 0302-282X. PMID 16037678. S2CID 22504035.
- Willner, P.; Muscat, R.; Papp, M. (1992). "Chronic mild stress-induced anhedonia: a realistic animal model of depression". Neuroscience and Biobehavioral Reviews. 16 (4): 525–534. doi:10.1016/S0149-7634(05)80194-0. ISSN 0149-7634. PMID 1480349. S2CID 9078352.
- Monleon, S.; D'Aquila, P.; Parra, A.; Simon, V. M.; Brain, P. F.; Willner, P. (February 1995). "Attenuation of sucrose consumption in mice by chronic mild stress and its restoration by imipramine". Psychopharmacology. 117 (4): 453–457. doi:10.1007/BF02246218. ISSN 0033-3158. PMID 7604147.
- Stemmelin, Jeanne; Cohen, Caroline; Yalcin, Ipek; Keane, Peter; Griebel, Guy (January 2010). "Implication of β3-adrenoceptors in the antidepressant-like effects of amibegron using Adrb3 knockout mice in the chronic mild stress". Behavioural Brain Research. 206 (2): 310–312. doi:10.1016/j.bbr.2009.09.003. ISSN 0166-4328. PMID 19744528. S2CID 23269414.
- Zhao, Dan; Xu, Xulin; Pan, Linna; Zhu, Wei; Fu, Xiaopei; Guo, Lianjun; Lu, Qing; Wang, Jian (December 2017). "Pharmacologic activation of cholinergic alpha7 nicotinic receptors mitigates depressive-like behavior in a mouse model of chronic stress". Journal of Neuroinflammation. 14 (1): 234. doi:10.1186/s12974-017-1007-2. ISSN 1742-2094. PMC 5712092. PMID 29197398.
- Blanchard, R. J.; McKittrick, C. R.; Blanchard, D. C. (June 2001). "Animal models of social stress: effects on behavior and brain neurochemical systems" (PDF). Physiology & Behavior. 73 (3): 261–271. doi:10.1016/S0031-9384(01)00449-8. ISSN 0031-9384. PMID 11438351. S2CID 26571582.
- Krishnan, Vaishnav; Han, Ming-Hu; Graham, Danielle L.; Berton, Olivier; Renthal, William; Russo, Scott J.; LaPlant, Quincey; Graham, Ami; Lutter, Michael (October 2007). "Molecular Adaptations Underlying Susceptibility and Resistance to Social Defeat in Brain Reward Regions". Cell. 131 (2): 391–404. doi:10.1016/j.cell.2007.09.018. ISSN 0092-8674. PMID 17956738.
- Cryan, John F; Slattery, David A (January 2007). "Animal models of mood disorders: recent developments" (PDF). Current Opinion in Psychiatry. 20 (1): 1–7. doi:10.1097/yco.0b013e3280117733. ISSN 0951-7367. PMID 17143074. S2CID 2320195.
- Kudryavtseva, N. N.; Bakshtanovskaya, I. V.; Koryakina, L. A. (February 1991). "Social model of depression in mice of C57BL/6J strain". Pharmacology Biochemistry and Behavior. 38 (2): 315–320. doi:10.1016/0091-3057(91)90284-9. ISSN 0091-3057. PMID 2057501. S2CID 24450372.
- McEwen, Bruce S. (2003). "Early life influences on life-long patterns of behavior and health". Mental Retardation and Developmental Disabilities Research Reviews. 9 (3): 149–154. doi:10.1002/mrdd.10074. ISSN 1080-4013. PMID 12953293.
- Meaney, Michael J (March 2001). "Maternal Care, Gene Expression, and the Transmission of Individual Differences in Stress Reactivity Across Generations". Annual Review of Neuroscience. 24 (1): 1161–1192. doi:10.1146/annurev.neuro.24.1.1161. ISSN 0147-006X. PMID 11520931.
- Song, Cai; Leonard, Brian E. (2005). "The olfactory bulbectomised rat as a model of depression". Neuroscience & Biobehavioral Reviews. 29 (4–5): 627–647. doi:10.1016/j.neubiorev.2005.03.010. ISSN 0149-7634. PMID 15925697. S2CID 42450349.
- O'Neil, Michael F.; Moore, Nicholas A. (2003). "Animal models of depression: are there any?". Human Psychopharmacology: Clinical and Experimental. 18 (4): 239–254. doi:10.1002/hup.496. ISSN 0885-6222. PMID 12766928. S2CID 21885931.
- Schramm, Nicole L.; McDonald, Michael P.; Limbird, Lee E. (2001-07-01). "The α2A-Adrenergic Receptor Plays a Protective Role in Mouse Behavioral Models of Depression and Anxiety". Journal of Neuroscience. 21 (13): 4875–4882. doi:10.1523/jneurosci.21-13-04875.2001. PMC 6762349. PMID 11425914.
- Ridder, Stephanie; Chourbaji, Sabine; Hellweg, Rainer; Urani, Alexandre; Zacher, Christiane; Schmid, Wolfgang; Zink, Mathias; Hörtnagl, Heide; Flor, Herta (2005-06-29). "Mice with Genetically Altered Glucocorticoid Receptor Expression Show Altered Sensitivity for Stress-Induced Depressive Reactions". Journal of Neuroscience. 25 (26): 6243–6250. doi:10.1523/jneurosci.0736-05.2005. PMC 6725059. PMID 15987954.
- Pliakas, A. M.; Carlson, R. R.; Neve, R. L.; Konradi, C.; Nestler, E. J.; Carlezon, W. A. (2001-09-15). "Altered responsiveness to cocaine and increased immobility in the forced swim test associated with elevated cAMP response element-binding protein expression in nucleus accumbens". The Journal of Neuroscience. 21 (18): 7397–7403. doi:10.1523/JNEUROSCI.21-18-07397.2001. ISSN 1529-2401. PMC 4205577. PMID 11549750.
- Bućan, Maja; Abel, Ted (2002). "The mouse: genetics meets behaviour". Nature Reviews Genetics. 3 (2): 114–123. doi:10.1038/nrg728. ISSN 1471-0056. PMID 11836505. S2CID 5985686.