Immediate and delayed anxiety- and depression-like profiles in the adolescent Wistar-Kyoto rat model of endogenous depression following postweaning social isolation
Introduction
Adolescent depression affects 4.7% of the teenage population with etiologies including genetic predisposition, isolation from parents/familial environment, stress associated with academic performance, peer pressure, humiliating experiences, ragging etc. Some of these very commonly occurring causes can lead to juvenile/adolescent stress that, if prolonged, leads to depression [1]. Adolescent depression increases with age and is a strong predictor of adult depression. Other major neuropsychiatric disorders [2], including schizophrenia, ADHD and drug abuse also become evident during puberty and adolescence [3].
Though the classical clinical features of co-morbid human depression and anxiety disorders are of the subjective order, a series of objective readouts or a coding of symptoms has been developed in animal models as per the DSM-V [4]. These include anxiety- and depression-like behaviours, chronic restraint stress, anhedonia, olfactory bulbectomy and others [5], which can be employed to satisfy one or more of the three validities in determining the usefulness of a model, namely face, predictive and construct [6]. However, there is no one animal model that can mimic all the biopsychosocial characteristics of depression. Many animal models reproduce some important aspects of the disorder, such as in chronic/acute stress models that are used to research new therapeutic targets for depression. Most are able to satisfy only one of the above validities. This is where inbred animal models are useful and there is a great need for developing a specialized model which will allow assessment of comorbidity in animals, one example being the Wistar-Kyoto rat [7], [8].
Much of our understanding of depression has come from studies using adult animals. However, studies have established neurochemical [9], and behavioural differences between adult and juveniles after antidepressant treatment [10]. Moreover, juveniles have differences compared to adults [11], in the maturation of serotonergic and noradrenergic systems, continued formation of the dopaminergic systems, development of brain areas such as the prefrontal cortex [12] and the dose of antidepressants needed to achieve similar levels in the brain, all of which make studies using juveniles imperative to better understand adolescent depression. Furthermore, neural, behavioural and hormonal [13] changes that occur during adolescence are conserved across species, so a study of this critical, sensitive period in an animal model can, with caution and reservations, be extrapolated to the human condition, particularly with regard to etiologies and constructs. Also, due to the major brain maturational processes that occur during adolescence within neural networks that mediate emotion processing, adolescents should be examined separately [14], [15]. However, such research has been scarce.
The pathophysiology of depression involves both external/social stressors and internal/genetic vulnerability. The Wistar-Kyoto rat (WKY) represents an endogenous model of depression [16], [17], [18], [19], showing consistency with a classic childhood depressive profile [20], [21] and exhibiting abnormal behavioural patterns and neurochemistry [18]. It was initially bred from the Wistar rat as a control for the spontaneously hypertensive rat (SHR), and demonstrates consistently exaggerated behavioural and physiological responses to stress [22], [18] across a variety of situations when compared to other strains [23], which emphasises its use as an animal model of depressive behaviour [24] and of vulnerability to anxiety [18], [25]. It could probably also constitute a model for separation of anxiety- and depressive-like profiles [26] as indicated by specific neuropeptides emerging as biomarkers that distinguish anxiety from depression [27], though in human adolescents, distress and fear become associative [28].
It is well established that social and environmental influences play a very vital role during adolescence: social isolation leads to drastic changes in a stress-vulnerable, still-maturing brain circuitry and monoaminergic signalling that moulds behaviour accordingly [29], [30], [31], [32], [12]. Chronic, acute, predictable, unpredictable stressors, including maternal separation and social isolation stress have been successfully used to induce a diathesis model or to test out the double-hit hypothesis, particularly in the WKY [16], [17], [18], [33], [34], [35], not specifically however during the juvenile stage. Particularly, adolescents reared in social isolation for four weeks demonstrated reduced social interaction, prepulse inhibition of acoustic startle, enhancement in ethanol self-administration and defensive shock probe burying; effects not observed in adults [36]. We asked whether short bouts of social isolation of a few hours each day during this critical period would induce immediate effects on anxiety- and depression-like behaviours or delayed effects on social interaction and response to hedonic stimuli in an endogenous model of adolescent depression.
In rats, adolescence has been defined as 28pnd (postnatal day) to 42pnd [37], [38], though others call this the pre-pubertal period [39]. Here, we investigate the immediate effects of brief periods of isolation during the pre-pubertal period on novelty-induced activity, emission of ultrasonic vocalizations, and anxiety- and depression-like behaviours during early adolescence. Behavioural analysis was carried out at two time points in different sets of animals, namely during early- (∼30pnd) and mid-adolescence (∼40pnd). The second major aim of the study was to observe whether interventions (social/group housing) during mid adolescence of the previously isolated animals had an effect on hedonic behaviour and social interaction during late adolescence/early adulthood (60pnd). Tests that code for more than one behavioural phenotype were conducted at early, mid and late adolescence.
Section snippets
Subjects
Adult male and female WKY rats were procured from NIN-Hyderabad, India for breeding and housed in pairs under standard laboratory conditions with artificial 12 h light/dark cycle (lights on at 7:00 a.m.) at an ambient temperature of 25–27 °C with free access to food and water. When the females of the breeding pairs were clearly pregnant (on 21st day), the males were removed from the cages. The day of parturition was designated as 0pnd. Pups were weaned on 21 ± 1pnd. Sexing of pups was carried out
Results
Social isolation for 6 h per day from 22pnd to 29pnd (Fig. 1) had no effect on the body weight, neither did the longer isolation period from 22pnd to 39pnd induce any changes in body weight (Fig. 2).
Discussion
The first goal here was to observe immediate effects on anxiety- and depression-like profiles at 30 and 40pnd in the WKY rat, a putative model of adolescent depression after social isolation during two time windows in the critical period of brain and behavioural development, that is from 22 to 30 or 40pnd (post-weaning social isolation). Secondly, to observe whether daily 6 h periods of post-weaning social isolation, despite subsequent interventions (group/social housing from 41 to 55pnd) have
Acknowledgements
This work was supported by the Department of Biotechnology, Govt. of India [Grant No. BT/PR4676/MED/30/735/2012]; and the Department of Science and Technology, Govt. of India [Grant No. CSI/05/2009].
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2023, Progress in Neuro-Psychopharmacology and Biological PsychiatryUsing zebrafish (Danio rerio) models to understand the critical role of social interactions in mental health and wellbeing
2022, Progress in NeurobiologyCitation Excerpt :However, various brain areas linked to social behavior (dorsal caudal hypothalamus and preoptic area), social cue processing (optic tectum), and the control of anxiety/stress (posterior tuberal nucleus), differentially express the immediate early marker gene c-fos in socially isolated vs. antisocial ‘loner’ fish (Tunbak et al., 2020). These functional changes caused by social deprivation in the former are consistent with increased anxiety resulting from hyper-sensitization to social stimuli, similar to the effects of social isolation on humans (Butler et al., 2016; Tunbak et al., 2020) and rodents (Lukkes et al., 2009; Shetty and Sadananda, 2017). Thus, using zebrafish to probe the impact of social isolation on brain function represents an alternative model of how pharmacological and/or non-pharmacological therapies may circumvent negative impacts of social deprivation.
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2020, Progress in Neuro-Psychopharmacology and Biological PsychiatryCitation Excerpt :This finding again demonstrates that WKY rats may exhibit a predictive adaptive response when subjected to early life stress or handling (Bateson et al., 2014). There is some evidence to suggest that the predictive adaptive response to early stress on social behaviours might be timeline dependant with one study showing that social isolation (6 h/day) at a later age (PN22–40), reduces social interactions in WKY male rats at PN60 (Shetty and Sadananda, 2017). The increased anxiety- and depressive-like phenotype of the WKY strain is largely maintained across both sexes (D'Souza and Sadananda, 2017; Millard et al., 2019, Millard et al., 2018); however, subtle differences in some behaviours have been observed.
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2019, NeuropharmacologyCitation Excerpt :Taken together, these findings suggest that emission of USVs may be measured in longitudinal studies to evaluate how stressful events in early life influence the manifestation of anxious-like and/or depressive-like phenotypes in juvenile and adult rats. In this regard, it is also noteworthy that sex and basal affectivity of rats may heavily influence the effects that aversive stimuli have on USV emissions (Kõiv et al., 2016; Mällo et al., 2009; Shetty and Sadananda, 2017; Vares et al., 2018). Besides, it has been demonstrated that the number of 50-kHz USVs emitted in response to tickling, which is a measure of positive affect (Burgdorf et al., 2011), may predict rats’ behavior in tests used to evaluate the presence of anxious-like and depressive-like phenotypes (i.e., EPM, FST) (Mällo et al., 2007).
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2019, Neuroscience and Biobehavioral ReviewsCitation Excerpt :In addition, subjecting WKY rats to CMS under a two-hit model exacerbates their depression- and anxiety- like phenotypes (Luo et al., 2015; Tejani-Butt et al., 1994; Willner et al., 2018). Interestingly, early-life stress, such as neonatal handling or maternal separation, do not generally enhance the WKY phenotype, indicating a strong genetic component (Nam et al., 2014; Van Zyl et al., 2014; Zalsman et al., 2015), although some exceptions exist in the literature (Shetty and Sadananda, 2017b). Importantly, as is the case of clinical depression, WKY rats display various cognitive deficits.
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2019, Seminars in Cell and Developmental BiologyCitation Excerpt :These changes in microglial phenotype are associated with an altered transcriptomic signature in the hippocampus –mainly mediated by CREB1, SP1, ReIA, c-Jun and STAT1 transcription factors– both at P14 and P28, suggesting that maternal separation compromises microglial maturation and function into adolescence [188]. At adulthood, exposure to stress, which could trigger the onset of pathology as a second hit [190], differentially affects male and female rats. Indeed, Bollinger et al. observe that exposure to acute or chronic restraint stress at adulthood increases the prevalence of ramified microglia and disrupts the expression of Cx3cl1 and Cx3cr1 in the prefrontal cortex of female rats only [20].