Neonatal clomipramine induced endogenous depression in rats is associated with learning impairment in adulthood

Towards zebrafish models to unravel translational insights of obsessive-compulsive disorder: A neurobehavioral perspective

Obsessive-compulsive disorder (OCD) is a chronic and debilitating illness that has been considered a polygenic and multifactorial disorder, challenging effective therapeutic interventions. Although invaluable advances have been obtained from human and rodent studies, several molecular and mechanistic aspects of OCD etiology are still obscure. Thus, the use of non-traditional animal models may foster innovative approaches in this field, aiming to elucidate the underlying mechanisms of disease from an evolutionary perspective. The zebrafish (Danio rerio) has been increasingly considered a powerful organism in translational neuroscience research, especially due to the intrinsic features of the species. Here, we outline target mechanisms of OCD for translational research, and discuss how zebrafish-based models can contribute to explore neurobehavioral aspects resembling those found in OCD. We also identify possible advantages and limitations of potential zebrafish-based models, as well as highlight future directions in both etiological and therapeutic research. Lastly, we reinforce the use of zebrafish as a promising tool to unravel the biological basis of OCD, as well as novel pharmacological therapies in the field.

Alterations of learning and memory are accompanied by alterations in the expression of 5-HT receptors, glucocorticoid receptor and brain-derived neurotrophic factor in different brain regions of an animal model of depression generated by neonatally male treatment with clomipramine in male rats

Depressive illness has been associated with impaired cognitive processes accompanied by reduced neurotrophin levels, especially brain-derived neurotrophic factor (BDNF), and dysfunctions in the hypothalamic-pituitary-adrenal (HPA) axis. In addition, depression is characterized by a decreased functioning of the serotonergic system due to changes in the activity or expression of its receptors including, most significantly, 5-HT1A, 5-HT2A, and 5-HT3 in brain regions that regulate mood, emotions, and memory, such as the prefrontal cortex, hippocampus, and amygdala. In this regard, rats treated with clomipramine (CMI) in the neonatal stage show depression-like behaviors that persist into adulthood; hence, this constitutes an adequate model of depression for exploring various molecular aspects associated with the etiology of this disorder. This, study, then, was designed to analyze the long-term effects of early postnatal exposure to CMI on the expression of 5-HT1A, 5-HT2A, and 5-HT3 receptors, as well as BDNF and GR in the following brain regions: PFC, amygdala, hippocampus, and hypothalamus, which could be related to alterations in memory and learning, as evaluated using the novel object recognition (NOR) and Morris water maze (MWM). Expression of the 5-HT1A, 5-HT2A, and 5-HT3 receptors, BDNF, and the glucocorticoid receptor (GR) was assessed by RT-qPCR in the four aforementioned brain regions, all of which play important roles in the control of memory and mood. Findings show that neonatal treatment with CMI causes alterations in memory and learning, as indicated by alterations in the results of the MWM and NOR tests. Expression of the 5-HT1A receptor increased in the hippocampus, amygdala, and hypothalamus, but decreased in the PFC, while the 5-HT2A and BDNF receptors decreased their expression in the PFC, amygdala, and hippocampus. There was no change in the expression of the 5-HT3 receptor. In addition, expression of GR in the hippocampus and PFC was low, but increased in the hypothalamus. Taken together, these data show that neonatal CMI treatment produces permanent molecular changes in brain regions related to learning and memory that could contribute to explaining the behavioral alterations observed in this model.

Mifepristone blocks the anxiolytic- and antidepressant-like effects of allopregnanolone in male rats

BACKGROUND

Allopregnanolone (3α, 5α-tetrahydroprogesterone) is an inhibitory neurosteroid synthesized from progesterone via 5α-reductase activity in the brain and has anxiolytic, antidepressant, sedative, anticonvulsant, and analgesic activity. Altered levels of allopregnanolone cause anxiety, depression, premenstrual syndrome, and psychiatric disorders. Although allopregnanolone exerts most of its actions by modulating GABAA receptor, NMDA receptor, BDNF expression, and PXR activity, a recent study showed its effects are blocked by mifepristone on lordosis behavior which indicates the involvement of progestin or glucocorticoid receptors in the effects of allopregnanolone since mifepristone blocks both these receptors. However, whether these receptors are involved in acute anxiolytic or antidepressant-like effects is unknown.

METHODS

Adult male Wistar rats were used to study whether the prior administration of mifepristone would alter the effects of allopregnanolone in the elevated plus maze (EPM) and forced swim test (FST) was evaluated.

RESULTS

10 mg/Kg dose of allopregnanolone increased percent open arm entries in the EPM, whereas 3 mg/Kg dose of allopregnanolone decreased percent immobility in the FST. Mifepristone administration resulted in a U-shaped response in the FST (with 1 mg/Kg, s.c., decreasing the immobility time) without significantly impacting the behavior in the EPM. In combination studies, mifepristone blocked the anxiolytic and antidepressant effects of allopregnanolone.

CONCLUSION

The current study provides evidence for the first time that progestin or glucocorticoid receptors are involved in the acute anxiolytic and antidepressant effects of allopregnanolone. Understanding the mechanism of action of allopregnanolone will help us design better therapeutic strategies to treat neuropsychiatric diseases such as depression and anxiety.

Chronic clomipramine treatment reverses depressogenic-like effects of a chronic treatment with dexamethasone in rats

Corticosteroids are widely used in medicine, for their anti-inflammatory and immunosuppressive actions, but can lead to troubling psychiatric side-effects. In fact, corticosteroids can induce many symptoms and syndromes, for example, mood disorders, anxiety and panic disorder, suicidal thinking and behavior. Furthermore, chronic stress and the administration of exogenous glucocorticoids are reported to induce affective changes in humans and rodents that relate to depressive state. Animal models are highly useful tools for studying the depression etiology. Face validity, construct validity, and predictive validity are the main criteria to evaluate animal depression models. The present study aimed to investigate the behavioral, cognitive, and biochemical effects of a chronic administration of DEX on Wistar rats. Wistar rats were administered daily with DEX (1.5 mg/kg, i.p., 21 days) or saline, the clomipramine treatment (2 mg/kg, i.p.) was realized just after the DEX injections for 21 days. DEX induced changes were evaluated by: forced swimming, novelty suppressed feeding, saccharin preference, open field, Morris water maze, and oxidative stress state in the brain. Results showed that chronic DEX administration conduct to a range of depression-related behavioral traits, including anhedonia, despair, weight loss, anxiety-like behavior, and cognitive impairments, which fill the face validity criterion. The DEX induced behavioral changes may result from the massive production of oxidative stress agents. This sustains the etiological hypothesis claiming that hyper-circulating glucocorticoid resulting from HPA dysfunction induces damage in certain neural structures related to depressive disorder, essentially the hippocampus. The antidepressant treatment has restored the behavioral state of rats which fills the predictive validity criterion.

The potential involvement of cholinergic system in finasteride induced cognitive dysfunction

OBJECTIVE

Neurosteroids are known to exert diverse functions in the brain. 5α-reductase (5α-R), a rate-limiting enzyme involved in the biosynthesis of neurosteroids is inhibited by finasteride. Clinical studies suggest that administration of finasteride causes the emergence of affective symptoms and cognitive dysfunction. Modeling this in rats would provide an opportunity to understand the mechanisms. Accordingly, in the present study, we evaluated the effects of repeated finasteride administration on spatial learning and memory in the partially baited radial arm maze task (RAM) and social cognitive behavior in the social interaction test. Further, to initiate the quest to understand the mechanisms underlying the effects of finasteride, in a separate group of animals, acetylcholinesterase (AChE) activity in the frontal cortex, hippocampus, septum and striatum was estimated.

METHODS

2 months old male Wistar rats were trained to learn a partially baited radial arm maze task (four trials per day till they reach a choice accuracy of 80 %). Following this, rats were administered with either vehicle (HPβCD) or finasteride (30 or 100 mg/Kg, s.c.) for 7 days and then subjected to retention test on the eighth day. To evaluate the social cognition, finasteride was administered for 7 days, followed by social interaction test on the eighth day. All the sessions were video-recorded and analyzed using Noldus Ethovision XT™ software. Following finasteride administration, on the eighth day, rats were euthanized, and AChE activity was estimated by modified Ellman's method.

RESULTS

Finasteride (100 mg/Kg, s.c.) administration decreased the percent correct choice during the retention trial of the RAM task. This was paralleled by an increase in the number of total number of errors and reference memory errors. In the social interaction test, finasteride (100 mg/Kg, s.c.) administration decreased the time spent with the rat compared to the object, implying decreased sociability and diminished social preference evidenced by similar time spent with the novel and familiar rat. Reduced AChE activity was observed in the frontal cortex, hippocampus and septum.

CONCLUSION

Our study provides evidence that repeated administration of finasteride decreases social interaction and results in cognitive deficits, potentially through a cholinergic mechanism. Further studies are required to understand the exact link between the cognitive effects and the cholinergic system. A deeper probe of the current findings holds promise for the development of novel neurosteroid-based therapeutics to treat affective and cognitive disorders.

Repeated finasteride administration induces depression-like behavior in adult male rats

The enzyme 5α-Reductase (5α-R) catalyzes the formation of dihydrotestosterone, which is involved in male pattern hair loss and benign prostatic hyperplasia. Finasteride inhibits 5α-R and is used to treat both these conditions. Several clinical studies show that chronic finasteride treatment induces persistent depression, suicidal thoughts, and cognitive impairment. The neural mechanisms underlying these effects of finasteride are not known and it is imperative that an animal model that mimics the clinical neuropsychiatric effects of finasteride is developed. Accordingly, we evaluated the behavioral effects of acute and repeated finasteride administration. Two months old male Wistar rats were administered with either vehicle (hydroxypropyl-β-cyclodextrin) or different doses of finasteride, subcutaneously, either acutely (30 min or 2 h) or for 1, 3, and 6 days (one dose per day). Behavioral despair and motivational behavior were evaluated in the forced swim test (FST) and splash test, respectively. FST and splash test were video-recorded and analyzed offline. Finasteride did not show any effects in the acute, one day or three days studies in the FST. However, repeated finasteride administration for 6 days significantly increased the immobility time. In the splash test, finasteride (100 mg/kg) administration increased the latency to groom and decreased the grooming duration implying lack of motivation in the three-day study. In the six-day study, latency to groom was significantly increased by the 100 mg/Kg dose. Further, a significant dose dependent decrease in the grooming duration was observed. In summary, our results indicate that repeated finasteride administration induces depression-like behavior in rats. This study provides the evidence that an animal model of finasteride-induced depression is feasible to investigate the cellular and molecular mechanisms, and the pharmacology underlying the neuropsychiatric effects of finasteride. Further, these results provide insights into the potential involvement of neurosteroids in depression and will lead to the development of novel therapeutics for its treatment.

Chronic brain stimulation rewarding experience ameliorates depression-induced cognitive deficits and restores aberrant plasticity in the prefrontal cortex

BACKGROUND

Major depressive disorder (MDD) is a multifactorial disease which often coexists with cognitive deficits. Depression-induced cognitive deficits are known to be associated with aberrant reward processing, neurochemical and structural alterations. Recent studies have shown that chronic electrical stimulation of brain reward areas induces a robust antidepressant effect. However, the effects of repeated electrical self-stimulation of lateral hypothalamus - medial forebrain bundle (LH-MFB) on depression-induced cognitive deficits and associated neurochemical and structural alterations in the prefrontal cortex (PFC) are unknown.

OBJECTIVES

We investigated the effect of chronic rewarding self-stimulation of LH-MFB in neonatal clomipramine (CLI) model of depression. During adulthood, neonatal CLI and saline administered rats were implanted with bilateral electrodes stereotaxically in the LH-MFB and trained to receive intracranial self-stimulation (ICSS) for 14 days. The rats were tested for depressive-like behaviors, learning and memory followed by estimation of PFC volumes, levels of monoamines and its metabolites in the PFC.

RESULTS

We found that chronic ICSS of LH-MFB reverses CLI-induced behavioral despair and anhedonia. Interestingly, self-stimulation normalizes the impaired novel object and location recognition memory in CLI rats. The amelioration of learning impairments in CLI rats was associated with the reversal of volume loss and restoration of monoamine metabolism in the PFC.

CONCLUSION

We demonstrated that repeated intracranial self-stimulation of LH-MFB ameliorates CLI-induced learning deficits, reverses altered monoamine metabolism and the atrophy of PFC. Our results support the hypothesis that chronic brain stimulation rewarding experience might be evolved as a potential treatment strategy for reversal of learning deficits in depression and associated disorders.

Contrasting effects of pre-training on acquisition of operant and radial arm maze tasks in rats

Performing multiple tasks either simultaneously, in rapid alternation or in succession, is routine in daily life. Further, testing rodents in a battery of tests is common both in drug discovery and behavioral phenotyping research. However, learning of new tasks can be influenced by prior experience(s). There has been some research on 'switching cost' involved in the transition from one behavior to another. However, there has been no specific assessment of the effect of learning an operant paradigm on performance in a spatial memory task and vice versa. Accordingly, we evaluated task switching between two forms of learning paradigms, operant conditioning and radial arm maze (RAM) tasks. In experiment 1, rats were trained for operant conditioning with food reward followed by a partially baited RAM task. In experiment 2, rats were trained first on a RAM task followed by operant learning. Pre-training on the operant task, impaired the acquisition of the RAM. On the contrary, pre-training on the RAM enhanced operant performance. Our study reveals significant effects of the test order on task-switching in rats. This knowledge can be useful when framing test sequences in test batteries for drug discovery research and screening genetically modified mice.

Early postnatal treatment with clomipramine induces female sexual behavior and estrous cycle impairment

Administration of clomipramine (CMI), a tricyclic antidepressant, in early stages of development in rats, is considered an animal model for the study of depression. This pharmacological manipulation has induced behavioral and physiological alterations, i.e., less pleasure-seeking behaviors, despair, hyperactivity, cognitive dysfunction, alterations in neurotransmitter systems and in HPA axis. These abnormalities in adult male rats are similar to the symptoms observed in major depressive disorders. One of the main pleasure-seeking behaviors affected in male rats treated with CMI is sexual behavior. However, to date, no effects of early postnatal CMI treatment have been reported on female reproductive cyclicity and sexual behavior. Therefore, we explored CMI administration in early life (8-21 PN) on the estrous cycle and sexual behavior of adult female rats. Compared to the rats in the early postnatal saline treatment (CTRL group), the CMI rats had fewer estrous cycles, fewer days in the estrous stage, and longer cycles during a 20-day period of vaginal cytology analysis. On the behavioral test, the CMI rats displayed fewer proceptive behaviors (hopping, darting) and had lower lordosis quotients. Also, they usually failed to display lordosis and only rarely manifested marginal or normal lordosis. In contrast, the CTRL rats tended to display normal lordosis. These results suggest that early postnatal CMI treatment caused long-term disruptions of the estrous cycle and female sexual behavior, perhaps by alteration in the hypothalamic-pituitary-gonadal (HPG) axes and in neuronal circuits involved in the regulation of the performance and motivational of sexual behavior as the noradrenergic and serotonergic systems.

Chronic treatment with estradiol restores depressive-like behaviors in female Wistar rats treated neonatally with clomipramine

Neonatal administration of clomipramine (CMI) induces diverse behavioral and neurochemical alterations in adult male rats that resemble major depression disorder. However, the possible behavioral alterations in adult female rats subjected to neonatal treatment with clomipramine are unknown. Therefore, the aim of this study was to explore the effect of neonatal treatment with CMI on adult female rats in relation to locomotion and behavioral despair during the estrus cycle. Also evaluated was the effect of chronic treatment with E2 on these female CMI rats. We found no effects on spontaneous locomotor activity due to neonatal treatment with CMI, or after 21days of E2 administration. In the FST, neonatal treatment with CMI increased immobility and decreased active swimming and climbing behaviors. Influence of the ovarian cycle was detected only in relation to climbing behavior, as the rats in the MD phase displayed less climbing activity. Chronic E2 administration decreased immobility but increased only swimming in CMI rats. These results suggest that neonatal treatment with CMI induces despair-like behavior in female rats, but that chronic E2 administration generates antidepressant-like behavior by decreasing immobility and increasing swimming, perhaps through interaction with the serotonergic system.

Environmental enrichment ameliorates chronic immobilisation stress-induced spatial learning deficits and restores the expression of BDNF, VEGF, GFAP and glucocorticoid receptors

Severe and prolonged stress is the main environmental factor that precipitates depression, anxiety and cognitive dysfunctions. On the other hand, exposure to environmental enrichment (EE) has been shown to induce progressive plasticity in the brain and improve learning and memory in various neurological and psychiatric disorders. It is not known whether exposure to enriched environment could ameliorate chronic immobilisation stress-induced cognitive deficits and altered molecular markers. Hence, in the present study we aimed to evaluate the effect of enriched environment on chronic immobilisation stress (CIS) associated changes in spatial learning and memory, behavioural measures of anxiety, depression and molecular markers as well as structural alterations. Male Wistar rats were subjected to chronic immobilisation stress for 2h/day/10days followed by 2weeks of exposure to EE. CIS resulted in weight loss, anhedonia, increased immobility, spatial learning and memory impairment, enhanced anxiety, and reduced expression of BDNF, VEGF, GFAP and glucocorticoid receptors (GR) in discrete brain regions. Interestingly, stressed rats exposed to enrichment ameliorated behavioural depression, spatial learning and memory impairment and reduced anxiety behaviour. In addition, EE restored BDNF, VEGF, GFAP and GR expression and normalized hypotrophy of dentate gyrus and hippocampus in CIS rats. In contrast, EE did not restore hypertrophy of the amygdalar complex. Thus, EE ameliorates stress-induced cognitive deficits by modulating the neurotrophic factors, astrocytes and glucocorticoid receptors in the hippocampus, frontal cortex and amygdala.

Enriched environment attenuates behavioral seizures and depression in chronic temporal lobe epilepsy

OBJECTIVE

Temporal lobe epilepsy (TLE) is commonly associated with depression, anxiety, and cognitive impairment. Despite significant progress in our understanding of the pathophysiology of TLE, it remains the most common form of refractory epilepsy. Enriched environment (EE) has a beneficial effect in many neuropsychiatric disorders. However, the effect of EE on cognitive changes in chronic TLE has not been evaluated. Accordingly, the present study evaluated the effects of EE on chronic epilepsy-induced alterations in cognitive functions, electrophysiology, and cellular changes in the hippocampus.

METHODS

Status epilepticus (SE) was induced in 2-month-old male Wistar rats with lithium and pilocarpine. Six weeks' post SE, epileptic rats were either housed in their respective home cages or in an enrichment cage (6 h/day) for 14 days. Seizure behavior was video-monitored 2 weeks before and during exposure to EE. Depression-like behavior, anxiety-like behavior, and spatial learning and memory were assessed using the sucrose preference test (SPT), elevated plus maze (EPM), and Morris water maze (MWM), respectively. Delta and theta power in the CA1 region of hippocampus was assessed from recordings of local field potentials (LFPs). Cellular changes in hippocampus were assessed by histochemistry followed by unbiased stereologic analysis.

RESULTS

EE significantly reduced seizure episodes and seizure duration in epileptic rats. In addition, EE alleviated depression and hyperactivity, and restored delta and theta power of LFP in the hippocampal CA1 region. However, EE neither ameliorated epilepsy-induced spatial learning and memory deficits nor restored cell density in hippocampus.

SIGNIFICANCE

This is the first study that evaluates the role of EE in a chronic TLE model, where rats were exposed to EE after occurrence of spontaneous recurrent seizures (SRS). Given that 30% of TLE patients are refractory to drug treatment, therapeutic strategies that utilize components of EE could be designed to alleviate seizures and psychiatric comorbidities associated with TLE.

Sleep and Behavior in Cross-Fostering Rats: Developmental and Sex Aspects

STUDY OBJECTIVE

Adverse early-life events induce behavioral psychopathologies and sleep changes in adulthood. In order to understand the molecular level mechanisms by which the maltreatment modifies sleep, valid animal models are needed. Changing pups between mothers at early age (cross-fostering) may satisfyingly model adverse events in human childhood.

METHODS

Cross-fostering (CF) was used to model mild early-life stress in male and female Wistar rats. Behavior and BDNF gene expression in the basal forebrain (BF), cortex, and hypothalamus were assessed during adolescence and adulthood. Spontaneous sleep, sleep homeostasis, and BF extracellular adenosine levels were assessed in adulthood.

RESULTS

CF rats demonstrated increased number of REM sleep onsets in light and dark periods of the day. Total REM and NREM sleep duration was also increased during the light period. While sleep homeostasis was not severely affected, basal level of adenosine in the BF of both male and female CF rats was lower than in controls. CF did not lead to considerable changes in behavior.

CONCLUSIONS

Even when the consequences of adverse early-life events are not observed in tests for anxiety and depression, they leave a molecular mark in the brain, which can act as a vulnerability factor for psychopathologies in later life. Sleep is a sensitive indicator for even mild early-life stress.

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.

Substance P receptor antagonist in lateral habenula improves rat depression-like behavior

Substance P (SP) levels are closely related with the pathogenesis of depression. Recent work has focused on antidepressive effect of substance P receptor antagonist (SPA), however, its action site and mechanism remain largely unresolved. Our previous results showed that the lateral habenula (LHb) plays a key role in the pathogenesis of depression. The current study investigated the effects of SPA microinjected into LHb on the behavioral responses of two rat models that exhibit depression-like behavior. To produce adult rats that exhibit depression-like behavior, rats were either exposed to chronic mild stress (CMS), or chronically administered clomipramine (CLI), a tricyclic antidepressant, during the neonatal state of life. The forced-swimming test (FST) was used to evaluate behavioral responses. Furthermore, we measured serotonin (5-HT) levels in dorsal raphe nucleus (DRN) using microdialysis. The FST showed a decreased immobility time and an increased climbing time after SPA injection into the LHb of depression-like behavior rats. In addition, 5-HT levels in DRN increased after SPA was microinjected into LHb of the rats that exhibited depression-like behavior. This study demonstrates that LHb mediates antidepressive effect of SPA by increasing 5-HT levels in the DRN, suggesting that the LHb may be a potential target of antidepressant.

Evaluation of animal models of obsessive-compulsive disorder: correlation with phasic dopamine neuron activity

Obsessive compulsive disorder (OCD) is a psychiatric condition defined by intrusive thoughts (obsessions) associated with compensatory and repetitive behaviour (compulsions). However, advancement in our understanding of this disorder has been hampered by the absence of effective animal models and correspondingly analysis of the physiological changes that may be present in these models. To address this, we have evaluated two current rodent models of OCD; repeated injection of dopamine D2 agonist quinpirole and repeated adolescent injection of the tricyclic agent clomipramine in combination with a behavioural paradigm designed to produce compulsive lever pressing. These results were then compared with their relative impact on the state of activity of the mesolimbic dopaminergic system using extracellular recoding of spontaneously active dopamine neurons in the ventral tegmental area (VTA). The clomipramine model failed to exacerbate compulsive lever pressing and VTA dopamine neurons in clomipramine-treated rats had mildly diminished bursting activity. In contrast, quinpirole-treated animals showed significant increases in compulsive lever pressing, which was concurrent with a substantial diminution of bursting activity of VTA dopamine neurons. Therefore, VTA dopamine activity correlated with the behavioural response in these models. Taken together, these data support the view that compulsive behaviours likely reflect, at least in part, a disruption of the dopaminergic system, more specifically by a decrease in baseline phasic dopamine signalling mediated by burst firing of dopamine neurons.

Neonatal tricyclic antidepressant clomipramine treatment reduces the spike-wave discharge activity of the adult WAG/Rij rat

Recently it was revealed that the absence-like epileptic activity of the WAG/Rij (Wistar Albino Glaxo/Rijswijk) rat is associated with depression-like behavioural symptoms. Whether these depressive-like symptoms are accompanying epileptic activity (manifested in spike-wave discharges, SWDs, in the EEG) or whether they are causative for each other are open questions. Neonatally administered tricyclic antidepressant clomipramine is a well characterized animal model of major depression. It evokes behavioural symptoms of depression and changes sleep pattern in normal adult rats. We investigated whether in the WAG/Rij rat the neonatally administered clomipramine would aggravate the depression-like behavioural symptoms and the SWD activity. Male WAG/Rij pups from postnatal day 8 (PD8) to PD21 were treated with clomipramine (20mg/kg) or saline (control animals) twice daily intraperitoneally (i.p.). In the 8 months old rats, sleep parameters and sucrose solution intake (as hedonic index) as well as the SWD activity were measured. While the neonatal clomipramine treatment significantly increased the rapid eye movement sleep (REM) amount and decreased the sucrose preference score, it surprisingly attenuated the adult (8 months old) SWD activity. We concluded that neonatal clomipramine treatment produced aggravation of depression-like symptoms while decreased the SWD activity in the adult (8 months old) WAG/Rij rat.

Inter-tissue networks between the basal forebrain, hippocampus, and prefrontal cortex in a model for depression caused by disturbed sleep

Disturbances in sleep are encountered in the majority of patients with depressive disorder. To elucidate the molecular mechanisms behind this relationship, we examined gene expression changes in a rodent model for disturbed sleep and depression. The animals were treated with daily injections of clomipramine to affect their sleep during early infancy. This early interference with sleep is known to induce depression-like behavior in adult animals. After 2 weeks of treatment, the change in gene expression was examined using the Affymetrix Rat 230.2 chip. We studied the gene expression in the basal forebrain, hippocampus, and frontal cortex and combined the results to reveal the otherwise indissectible networks between and around the tissues. The major disrupted pathways between the three brain areas were related to synaptic transmission, regulation of translation, and ubiquitinylation. The involved pathways were within the cellular components of the axons, growth cones, melanosomes, and pigment granules. A network analysis allowing for additional interactors, in the form of chemicals or gene products, revealed a disturbed communicational network between the different brain areas. This disturbed network is centered around serotonin, Mn(II), and Rhoa. The findings elucidate inter-tissue pathways and networks in the brain that are involved in sleep and mood regulation. The findings are of uttermost interest, some are quite predictable and obvious, but some are novel or have only been proposed by rare theoretical speculations (such as the melanosome and Mn(II) involvement). Equally important as the findings are the methods described in this article. In this study, we present two novel simple ways to perform system biological analysis based on gene expression array data. We used two already existing tools in a new way, and by careful planning of the input data, managed to extrapolate intricate hidden inter-tissue networks to build a molecular picture of disease.

Sleep homeostasis and depression: studies with the rat clomipramine model of depression

Neonatal treatment of rat pups with clomipramine (CLI) has been shown to cause long-lasting and persistent depression-related behaviors and changes in sleep architecture and in brain-derived neurotrophic factor (BDNF) signaling in adult animals, producing an animal model of depression. However, the molecular mechanisms which mediate these effects of early-life CLI treatment on adult animals remain largely unknown. In order to characterize these further, we investigated in neonatally CLI-treated rats the sleep architecture as well as the extracellular and cellular levels of sleep regulators (nitric oxide, adenosine) and BDNF, respectively, in the basal forebrain (BF), i.e. the brain area which is implicated in sleep and depression. We found that CLI-treated rats exhibited a disturbed sleep architecture (REM sleep fragmentation was increased and NREM periods preceding REM were shorter) and reduced levels of BDNF and adenosine in the BF, whereas the levels of nitric oxide were elevated. Next, we examined sleep deprivation (SD)-induced homeostatic responses on sleep regulation and brain BDNF levels in CLI-treated rats. Compared to control rats, 3h of SD induced a smaller increase in the amount of NREM sleep during sleep recovery. At the molecular level, the normal homeostatic response was dissociated: the rise in the adenosine level was not accompanied by a rise in the nitric oxide concentration. Moreover, while BF BDNF levels decreased during SD in control rats, such a decline was not observed in CLI rats. Taken together, neonatal CLI treatment produces long-lasting functional changes in the sleep architecture and sleep regulation in adult rats, accompanied by dysregulated BDNF signaling in the BF.

Oxotremorine treatment restores hippocampal neurogenesis and ameliorates depression-like behaviour in chronically stressed rats

RATIONALE

Chronic stress results in cognitive impairment, affects hippocampal neurogenesis and is known to precipitate affective disorders such as depression. In addition to stress, neurotransmitters such as acetylcholine (ACh) modulate adult neurogenesis. Earlier, we have shown that oxotremorine, a cholinergic muscarinic agonist, ameliorates stress-induced cognitive impairment and restores cholinergic function.

OBJECTIVES

In the current study, we have looked into the possible involvement of adult neurogenesis in cognitive restoration by oxotremorine. Further, we have assessed the effect of oxotremorine treatment on depression-like behaviour and hippocampal volumes in stressed animals.

METHODS

Chronic restraint stressed rats were treated with either vehicle or oxotremorine. For neurogenesis studies, proliferation, survival and differentiation of the progenitor cells in the hippocampus were examined using 5'-bromo-2-deoxyuridine immunohistochemistry. Depression-like behaviour was evaluated using forced swim test (FST) and sucrose consumption test (SCT). Volumes were estimated using Cavalieri's estimator.

RESULTS

Hippocampal neurogenesis was severely decreased in stressed rats. Ten days of oxotremorine treatment to stressed animals partially restored proliferation and survival, while it completely restored the differentiation of the newly formed cells. Stressed rats showed increased immobility and decreased sucrose preference in the FST and SCT, respectively, and oxotremorine ameliorated this depression-like behaviour. In addition, oxotremorine treatment recovered the stress-induced decrease in hippocampal volume.

CONCLUSIONS

These results indicate that the restoration of impaired neurogenesis and hippocampal volume could be associated with the behavioural recovery by oxotremorine. Our results imply the muscarinic regulation of adult neurogenesis and incite the potential utility of cholinomimetics in ameliorating cognitive dysfunction in stress-related disorders.

Effect of repeated restraint stress and clomipramine on Na+/K+-ATPase activity and behavior in rats

Activation of the limbic-hypothalamic-pituitary-adrenal axis (LHPA) and the release of glucocorticoids are fundamental for the adaptive response and immediate survival of an organism in reaction to acute stimuli. However, high levels of glucocorticoids in the brain may produce neuronal injury and a decrease of Na(+)/K(+)-ATPase activity, with effects on neurotransmitter signaling, neural activity, as well as the whole animal behavior. Clomipramine is a tricyclic antidepressant that inhibits the reuptake of serotonin and norepinephrine by indirect actions on the dopaminergic system and LHPA axis. Its chronic use increases the body's ability to cope with stress; however, high doses can potentiate its side effects on memory, learning, and sensory motor function. The purpose of the present study was to compare the effect of repeated restraint stress and clomipramine treatment on Na(+)/K(+)-ATPase activity and on the behavior of male rats. Changes in the behavioral response were evaluated by measuring the memory, learning, anxiety, and exploratory responses. Our results showed that exposure to repeated restraint stress reduced levels of Na(+)/K(+)-ATPase in brain structures and changed short and long-term memory, learning, and exploratory response when compared to the control group. Exposure to clomipramine treatment increased anxiety levels and reduced Na(+)/K(+)-ATPase activity in the cerebral cortex as well as short term memory, learning, and exploratory response. In conclusion, the present results provide additional evidence concerning how repeated restraint stress and clomipramine chronically administered at higher dose levels affect the neural activity and behavior of male rats.

Sex and age differences in the impact of the forced swimming test on the levels of steroid hormones

Compared with the adult disorder, depression in children exhibits differences in its neurobiology, particularly in the HPA axis regulation. The bases of such differences can be evaluated in animal models of depression. The objective of the present study was to determine age and sex differences of Wistar rats in the forced swimming test (FST). The influence of sex and age on corticosterone, estrogens and testosterone serum levels was also determined. Prepubertal rats showed immobility, swimming and climbing behaviors during the pre-test and test sessions. In addition, in the prepubertal animals, no sex differences were found during the pre-test and test sessions. Age comparisons indicated no differences in the female groups, however adult males exhibited more immobility and less swimming than young males, in both FST sessions. The young and female rats showed less immobility behavior and increased levels of estrogens after the FST. The present results indicate that the FST is an animal model suitable to evaluate depressive-like behaviors in prepubertal subjects and to explore behavioral changes related to neurodevelopment.

Chronic escitalopram treatment restores spatial learning, monoamine levels, and hippocampal long-term potentiation in an animal model of depression

RATIONALE

The neural basis of depression-associated cognitive impairment remains poorly understood, and the effect of antidepressants on learning and synaptic plasticity in animal models of depression is unknown. In our previous study, learning was impaired in the neonatal clomipramine model of endogenous depression. However, it is not known whether the cognitive impairment in this model responds to antidepressant treatment, and the electrophysiological and neurochemical bases remain to be determined.

OBJECTIVES

To address this, we assessed the effects of escitalopram treatment on spatial learning and memory in the partially baited radial arm maze (RAM) task and long-term potentiation (LTP) in the Schaffer collateral-CA1 synapses in neonatal clomipramine-exposed rats. Also, alterations in the levels of biogenic amines and acetylcholinesterase (AChE) activity were estimated.

RESULTS

Fourteen days of escitalopram treatment restored the mobility and preference to sucrose water in the forced swim and sucrose consumption tests, respectively. The learning impairment in the RAM was reversed by escitalopram treatment. Interestingly, CA1-LTP was decreased in the neonatal clomipramine-exposed rats, which was restored by escitalopram treatment. Monoamine levels and AChE activity were decreased in several brain regions, which were restored by chronic escitalopram treatment.

CONCLUSIONS

Thus, we demonstrate that hippocampal LTP is decreased in this animal model of depression, possibly explaining the learning deficits. Further, the reversal of learning and electrophysiological impairments by escitalopram reveals the important therapeutic effects of escitalopram that could benefit patients suffering from depression.

Effect of neonatal clomipramine in the pathogenesis of ligature-induced periodontitis in Lewis rats

OBJECTIVE

The aim of this study was to verify the association between an endogenous depression model and the development of ligature-induced periodontitis in rats.

MATERIAL AND METHODS

Nine male Lewis rats received 30 mg/kg clomipramine from neonatal day 8 to day 21 (depressed group), while 13 control Lewis rats were left untouched (control group). On day 150, ligatures were placed around the 2nd upper molars in both groups, i.e. the contralateral molar of the intra-group control. On day 190, the rats were killed and the maxillae were defleshed. The distance between the cemento-enamel junction and the alveolar bone crest was measured by a blinded examiner using standardized digital photographs.

RESULTS

The depressed rats showed hyperactivity in open field on day 142 and greater attempts to escape on day 143 compared to controls. The other behavioral data did not show statistically significant differences between the groups (Mann-Whitney, p>0.05). In teeth with ligature, mean alveolar bone loss varied from 0.51 to 0.60 and from 0.63 to 0.64 mm for tests and controls, respectively (t-test, p>0.05). In teeth without ligature, these values varied from 0.38 to 0.43 and 0.42 to 0.45 mm in the test and control groups, respectively (t-test, p>0.05).

CONCLUSION

Induced depression did not alter ligature-induced bone loss in Lewis rats.

Lateral habenula lesions improve the behavioral response in depressed rats via increasing the serotonin level in dorsal raphe nucleus

The dorsal raphe nucleus (DRN)-serotonin (5-HT) system plays a key role in stress-related psychiatric disorders such as anxiety and depression. The habenular nucleus (Hb) is closely connected with the DRN both morphologically and functionally. Here, we used two types of depressive animal models by exposing rats to chronic mild stress (CMS) and by chronically administering the tricyclic antidepressant clomipramine (CLI) in the rat during the neonatal state of life to produce adult depressed rats. We investigated the effects of lateral habenular nucleus (LHb) lesions on the behavioral response and on the level of 5-HT in DRN in the depressed rats. Forced-swimming test (FST) showed that the immobility time decreased, and the climbing time increased after lesioning LHb of depressed rats. Microdialysis results indicated that the 5-HT level in DRN in depressed rats was lower than that of the control group. Lesion of the LHb was followed by an increased 5-HT turnover in the DRN. Our results suggested that the lesion of the LHb could improve the behavioral response of the depressed rats and the 5-HT level of the DRN increased by LHb lesions could be involved in the effects.