Depression represents one of the most common comorbidities in patients with epilepsy. However, the mechanisms of depression in epilepsy patients are poorly understood. Establishment of animal models of this comorbidity is critical for both understanding the mechanisms of the condition, and for preclinical development of effective therapies. The current study examined whether a commonly used animal model of temporal lobe epilepsy (TLE) is characterized by behavioral and biochemical alterations involved in depression. Male Wistar rats were subjected to LiCl and pilocarpine status epilepticus (SE). The development of chronic epileptic state was confirmed by the presence of spontaneous seizures and by enhanced brain excitability. Post-SE animals exhibited increase in immobility time under conditions of forced swim test (FST) which was indicative of despair-like state, and loss of taste preference in saccharin solution consumption test which pointed to the symptomatic equivalence of anhedonia. Biochemical studies revealed compromised serotonergic transmission in the raphe-hippocampal serotonergic pathway: decrease of serotonin (5-HT) concentration and turnover in the hippocampus, measured by high performance liquid chromatography, and decrease of 5-HT release from the hippocampus in response to raphe stimulation, measured by fast cyclic voltammetry. Administration of fluoxetine (FLX, 20 mg/kg/day for 10 days) to naïve animals significantly shortened immobility time under conditions of FST, and inhibited 5-HT turnover in the hippocampus. In post-SE rats FLX treatment led to a further decrease of hippocampal 5-HT turnover; however, performance in FST was not improved. At the same time, FLX reversed SE-induced increase in brain excitability. In summary, our studies provide initial evidence that post-SE model of TLE might serve as a model of the comorbidity of epilepsy and depression. The finding that behavioral equivalents of depression were resistant to an antidepressant medication suggested that depression in epilepsy might have distinct underlying mechanisms beyond alterations in serotonergic pathways.
Comorbidity; depression; epilepsy; hippocampus; serotonin
Depression represents one of the most common comorbidities of temporal lobe epilepsy (TLE), and has profound negative impact on the quality of life of TLE patients. However, causes and mechanisms of depression in TLE remain poorly understood, and its effective therapies are lacking. We examined whether a commonly used model of TLE in rats can be used as a model of comorbidity between epilepsy and depression suitable for both mechanistic studies and for the development mechanism-based antidepressant therapies. We established that animals which had been subjected to LiCl and pilocarpine status epilepticus (SE) and developed spontaneous recurrent seizures, exhibited set of impairments congruent with depressive state: behavioral equivalents of anhedonia and despair; dysregulation of the hypothalamo-pituitary adrenocortical (HPA) axis; compromised raphe-hippocampal serotonergic transmission. Pharmacological studies suggested that depressive impairments following SE develop as a result of the enhanced interleukin-1β signaling in the hippocampus, which leads to depression via inducing perturbations in the HPA axis and subsequent deficit in the raphe-hippocampal serotonergic transmission.
Temporal lobe epilepsy; depression; comorbidity; serotonin; hypothalamo-pituitary-adrenocortical axis; interleukin-1β
Depression is a frequent comorbidity of temporal lobe epilepsy (TLE); however its mechanisms remain poorly understood and effective therapies are lacking. Augmentation of hippocampal interleukin-1β (IL-1β) signaling may be a mechanistic factor of both TLE and clinical depression. We examined whether pharmacological blockade of hippocampal interleukin-1 receptor exerts antidepressant effects in an animal model of comorbidity between TLE and depression, which developed in Wistar rats following pilocarpine status epilepticus (SE). In post-SE animals, depression-like state was characterized by behavioral equivalents of anhedonia and despair; dysregulation of the hypothalamo-pituitary-adrenocortical axis; compromised raphe-hippocampal serotonergic transmission. Two-week long bilateral intrahippocampal infusion of human recombinant Interleukin-1 Receptor antagonist (IL-1ra) improved all of the examined depressive impairments, without modifying spontaneous seizure frequency and without affecting normal parameters in naïve rats. These findings implicate hippocampal IL-1β in epilepsy-associated depression, and provide a rationale for the introduction of IL-1β blockers in the treatment of depression in TLE.
Temporal lobe epilepsy; depression; comorbidity; brain inflammation; Interleukin-1β; hippocampus
Depression is a common comorbidity of temporal lobe epilepsy and has highly negative impact on patients’ quality of life. We previously established that pilocarpine-induced status epilepticus (SE) in rats, concurrently with chronic epilepsy leads to depressive impairments, and that the latter may stem from the dysregulation of hypothalamo-pituitary-adrenocortical (HPA) axis and/or diminished raphe-hippocampal serotonergic transmission. We examined possible involvement of presynaptic and postsynaptic serotonin-1A (5-HT1A) receptors in epilepsy-associated depression. Based on their performance in the forced swim test (FST), post-SE animals were classified as those with moderate and severe depressive impairments. In moderately impaired rats, the activity of the HPA axis (examined using plasma corticosterone radioimmunoassay) was higher than in naïve subjects, but the functional capacity of presynaptic 5-HT1A receptors (measured in raphe using autoradiography) remained unaltered. In severely depressed animals, both the activity of the HPA axis and the function of presynaptic 5-HT1A receptors were increased as compared with naïve and moderately depressed rats. Pharmacological uncoupling of the HPA axis from raphe nucleus exerted antidepressant effects in severely impaired rats, but did not modify behavior in both naïve and moderately depressed animals. Further, the function of postsynaptic 5-HT1A receptors was diminished in the hippocampus of post-SE rats. Pharmacological activation of postsynaptic 5-HT1A receptors improved depressive deficits in epileptic animals. We suggest that under conditions of chronic epilepsy, excessively hyperactive HPA axis activates presynaptic 5-HT1A receptors, thus shifting the regulation of serotonin release in favor of autoinhibition. Downregulation of postsynaptic 5-HT1A receptors may further exacerbate the severity of epilepsy-associated depression.
Epilepsy; depression; comorbidity; serotonin 1A receptors; dorsal raphe; hypothalamo-pituitary-adrenocortical axis
Depression is a common comorbidity of temporal lobe epilepsy and has highly negative impact on patients' quality of life. We previously established that pilocarpine-induced status epilepticus (SE) in rats, concurrently with chronic epilepsy leads to depressive impairments, and that the latter may stem from the dysregulation of hypothalamo–pituitary–adrenocortical (HPA) axis and/or diminished raphe–hippocampal serotonergic transmission. We examined possible involvement of presynaptic and postsynaptic serotonin 1A (5-HT1A) receptors in epilepsy-associated depression. Based on their performance in the forced swim test (FST), post-SE animals were classified as those with moderate and severe depressive impairments. In moderately impaired rats, the activity of the HPA axis (examined using plasma corticosterone radioimmunoassay) was higher than in naive subjects, but the functional capacity of presynaptic 5-HT1A receptors (measured in raphe using autoradiography) remained unaltered. In severely depressed animals, both the activity of the HPA axis and the function of presynaptic 5-HT1A receptors were increased as compared with naive and moderately depressed rats. Pharmacological uncoupling of the HPA axis from raphe nucleus exerted antidepressant effects in severely impaired rats, but did not modify behavior in both naive and moderately depressed animals. Further, the function of postsynaptic 5-HT1A receptors was diminished in the hippocampus of post-SE rats. Pharmacological activation of postsynaptic 5-HT1A receptors improved depressive deficits in epileptic animals. We suggest that under the conditions of chronic epilepsy, excessively hyperactive HPA axis activates presynaptic 5-HT1A receptors, thus shifting the regulation of serotonin release in favor of autoinhibition. Downregulation of postsynaptic 5-HT1A receptors may further exacerbate the severity of epilepsy-associated depression.
epilepsy; depression; comorbidity; serotonin 1A receptors; dorsal raphe; hypothalamo–pituitary–adrenocortical axis; mood / anxiety / stress disorders; serotonin; animal models; neurology; epilepsy; comorbidity; dorsal aphe; hippocampus; serotonin 1A receptors
Affective symptoms such as anxiety and depression are frequently observed in patients with epilepsy. The mechanisms of comorbidity of epilepsy and affective disorders, however, remain unclear. Diverse models are traditionally used in epilepsy research, including the status epilepticus (SE) model in rats, which are aimed at generating chronic epileptic animals; however, the implications of different SE models and rat strains in emotional behaviors has not been reported. To address this issue, we examined the emotional sequelae of two SE models of temporal lobe epilepsy (TLE) – the lithium-pilocarpine (LIP) model and the kainic acid (KA) model – in two different rat strains (Wistar and Sprague-Dawley), which differ significantly in the pattern and extent of TLE-associated brain lesions. We found differences between LIP- and KA-treated animals in tests for depression-like and anxiety-like behaviors, as well as differences in plasma corticosterone levels. Whereas only LIP-treated rats displayed increased motivation to consume saccharin, both SE models led to reduced motivation for social contact, with LIP-treated animals being particularly affected. Evaluation of behavior in the open field test indicated very low levels of anxiety in LIP-treated rats and a mild decrease in KA-treated rats compared to controls. After exposure to a battery of behavioral tests, plasma corticosterone levels were increased only in LIP-treated animals. This hyperactivity in the hypothalamus-pituitary-adrenocortical (HPA) axis was highly correlated with performance in the open field test and the social interaction test, suggesting that comorbidity of epilepsy and emotional behaviors might also be related to other factors such as HPA axis function. Our results indicate that altered emotional behaviors are not inherent to the epileptic condition in experimental TLE; instead, they likely reflect alterations in anxiety levels related to model-dependent dysregulation of the HPA axis.
This is the first metabolic mapping study of the effects of fluoxetine after learned helplessness training. Antidepressants are the most commonly prescribed medications, but the regions underlying treatment effects in affectively disordered brains are poorly understood. We hypothesized the antidepressant action of fluoxetine would produce adaptations in mesolimbic regions after two weeks of treatment. We used Holtzman rats, a genetic strain showing susceptibility to novelty-evoked hyperactivity and stress-evoked helplessness, to map regional brain metabolic effects caused by fluoxetine treatment. Animals underwent learned helplessness, and subsequently immobility time was scored in the forced swim test (FST). On the next day, animals began receiving two weeks of fluoxetine (5 mg/kg/day) or vehicle and were retested in the FST at the end of drug treatment. Antidepressant behavioral effects of fluoxetine were analyzed using a ratio of immobility during pre- and post-treatment FST sessions. Brains were analyzed for regional metabolic activity using quantitative cytochrome oxidase histochemistry as in our previous study using congenitally helpless rats. Fluoxetine exerted a protective effect against FST-induced immobility behavior in Holtzman rats. Fluoxetine also caused a significant reduction in the mean regional metabolism of the nucleus accumbens shell and the ventral hippocampus as compared to vehicle-treated subjects. Additional networks affected by fluoxetine treatment included the prefrontal-cingulate cortex and brainstem nuclei linked to depression (e.g. habenula, dorsal raphe and interpeduncular nucleus). We concluded that corticolimbic regions such as the prefrontal-cingulate cortex, nucleus accumbens, ventral hippocampus and key brainstem nuclei represent important contributors to the neural network mediating fluoxetine antidepressant action.
Cytochrome oxidase; Brain mapping; Depression; Fluoxetine; Antidepressant effect; Animal model
While translational evidence suggests that long-chain omega-3 fatty acid status is positively associated with the efficacy of selective serotonin reuptake inhibitor drugs, the neurochemical mechanisms mediating this interaction are not known. Here we investigated the effects of dietary omega-3 (n-3) fatty acid insufficiency on the neurochemical and behavioral effects of chronic fluoxetine (FLX) treatment. Female rats were fed diets with (CON, n=56) or without (DEF, n=40) the n-3 fatty acids during peri-adolescent development (P21-P90), and one half of each group were administered FLX (10 mg/kg/d) for 30 d (P60-P90) prior to testing. In adulthood (P90), regional brain serotonin (5-HT) and 5-hydroxyindoleacetic (5-HIAA) concentrations, presynaptic markers of 5-HT neurotransmission, behavioral responses in the forced swim test (FST), and plasma FLX and norfluoxetine (NFLX) concentrations were investigated. Peri-adolescent n-3 insufficiency led to significant reductions in cortical docosahexaenoic acid (DHA, 22:6n-3) composition in DEF (−25%, p≤0.0001) and DEF+FLX (−28%, p≤0.0001) rats. Untreated DEF rats exhibited significantly lower regional 5-HIAA/5-HT ratios compared with untreated CON rats, but exhibited similar behavioral responses in the FST. In both CON and DEF rats, chronic FLX treatment similarly and significantly decreased 5-HIAA concentrations and the 5-HIAA/5-HT ratio in the hypothalamus, hippocampus, and nucleus accumbens, brainstem tryptophan hydroxylase-2 mRNA expression, and immobility in the FST. While the FLX-induced reduction in 5-HIAA concentrations in the prefrontal cortex was significantly blunted in DEF rats, the reduction in the 5-HIAA/5-HT ratio was similar to CON rats. Although plasma FLX and NFLX levels were not significantly different in DEF and CON rats, the NFLX/FLX ratio was significantly lower in DEF+FLX rats. These preclinical data demonstrate that n-3 fatty acid deficiency does not significantly reduce the effects of chronic FLX treatment on central 5-HT turnover or behavior in the FST in female rats.
Omega-3 fatty acid; Docosahexaenoic acid; Fluoxetine; Serotonin; Female; Forced swim test
In Cameroonian traditional medicine various extracts of Gladiolus dalenii Van Geel (Iridaceae) have been used as a cure for various ailments that include headaches, digestive problems, muscle and joint aches, and some central nervous system disorders such as epilepsy, schizophrenia and mood disorders. Owning to this background, the aim of the study was to investigate whether an aqueous macerate of the bulb of Gladiolus dalenii has any antidepressant activity focusing specifically on depression-like behaviours associated with epilepsy.
We used the combined administration of atropine and pilocarpine to rats as our animal model of epilepsy. The forced swim test and spontaneous locomotor activity in the open field test were the two tools used to assess the presence of depression-like behaviour in epileptic and control animals. The following depression-related parameters were determined: plasma ACTH, plasma corticosterone, adrenal gland weight and hippocampal levels of brain-derived neurotrophic factor (BDNF). The effects of Gladiolus dalenii were compared to that of fluoxetine.
Our results showed that we had a valid animal model of epilepsy-induced depression as all 3 measures of construct, predictive and face validity were satisfied. The data indicated that Gladiolus dalenii significantly reduced the immobility times in the forced swim test and the locomotor activity as assessed in the open field. A similar pattern was observed when the HPA axis parameters were analysed. Gladiolus dalenii significantly reduced the levels of ACTH, corticosterone, but not the adrenal gland weight. Gladiolus dalenii significantly increased the level of BDNF in the hippocampus. In all parameters measured the effects of Gladiolus dalenii were significantly greater than those of fluoxetine.
The results show that Gladiolus dalenii has antidepressant-like properties similar to those of fluoxetine in epilepsy-associated depressive states. The antidepressant activity of Gladiolus dalenii is likely to be mediated by restoring the activity of the HPA axis and increasing the levels of BDNF in the hippocampus.
Depression; Epilepsy; HPA axis; BDNF; Gladiolus dalenii
Forced swimming test (FST) is an animal model which evaluates behavioral despair and the effect of antidepressants such as the selective serotonin reuptake inhibitors; the FST modifies the expression of some receptors related to antidepressant response, but it is not known whether serotonin transporter (SERT), their main target, is affected by this test in animals of different ages. Antidepressant response has shown age-dependent variations which could be associated with SERT expression. The aim of the present study was to analyze changes in the SERT immunoreactivity (SERT-IR) in dorsal raphe and lateral septum of male rats from different age groups with or without behavioral despair induced by their exposure to the FST, since these two structures are related to the expression of this behavior.
Prepubertal (24 PN), pubertal (40 PN), young adult (3–5 months) and middle-aged (12 months) male rats were assigned to a control group (non-FST) or depressed group (FST, two sessions separated by 24 h). Changes in SERT-IR in dorsal raphe and lateral septum were determined with immunofluorescence.
Pubertal and middle-aged rats showed higher levels of immobility behavior compared to prepubertal rats on the FST. SERT-IR showed an age-dependent increase followed by a moderate decrease in middle-aged rats in both structures; a decreased in SERT-IR in lateral septum and dorsal raphe of pubertal rats was observed after the FST.
Age differences were observed in the SERT-IR of structures related to behavioral despair; SERT expression was modified by the FST in lateral septum and dorsal raphe of pubertal rats.
Despair; Forced swimming test; Rats; Serotonin transporter; Age differences
Depression represents a common comorbidity of epilepsy and is frequently resistant to selective serotonin reuptake inhibitors (SSRI). We tested the hypothesis that the SSRI resistance in epilepsy associated depression may be a result of a pathologically enhanced interleukin-1β (IL1-β) signaling, and consequently that the blockade of IL1-β may restore the effectiveness of SSRI. Epilepsy and concurrent depression-like impairments were induced in Wistar rats by pilocarpine status epilepticus (SE). The effects of the 2-week long treatment with fluoxetine, interleukin-1 receptor antagonist (IL-1ra), and their combination were examined using behavioral, biochemical, neuroendocrine, and autoradiographic assays. In post-SE rats, depression-like impairments included behavioral deficits indicative of hopelessness and anhedonia; the hyperactivity of the hypothalamo-pituitary-adrenocortical axis; the diminished serotonin output from raphe nucleus; and the upregulation of presynaptic serotonin 1-A (5-HT1A) receptors. Fluoxetine monotherapy exerted no antidepressant effects, whereas the treatment with IL-1ra led to the complete reversal of anhedonia and to a partial improvement of all other depressive impairments. Combined administration of fluoxetine and IL-1ra completely abolished all hallmarks of epilepsy-associated depressive abnormalities, with the exception of the hyperactivity of the hypothalamo-pituitary-adrenocortical axis, the latter remaining only partially improved. We propose that in certain forms of depression, including but not limited to depression associated with epilepsy, the resistance to SSRI may be driven by the pathologically enhanced interleukin-1β signaling and by the subsequent upregulation of presynaptic 5-HT1A receptors. In such forms of depression, the use of interleukin-1β blockers in conjunction with SSRI may represent an effective therapeutic approach.
Electronic supplementary material
The online version of this article (doi:10.1007/s13311-012-0110-4) contains supplementary material, which is available to authorized users.
Epilepsy; depression; comorbidity; cytokines; selective serotonin reuptake inhibitors
Serotonin reuptake inhibitor (SRI) antidepressants such as fluoxetine (Prozac), promote hippocampal neurogenesis. They also increase the levels of the bcl-2 protein, whose overexpression in transgenic mice enhances adult hippocampal neurogenesis. However, the mechanisms underlying SRI-mediated neurogenesis are unclear. Recently, we identified the microRNA miR-16 as an important effector of SRI antidepressant action in serotonergic raphe and noradrenergic locus coeruleus (LC). We show here that miR-16 mediates adult neurogenesis in the mouse hippocampus. Fluoxetine, acting on serotonergic raphe neurons, decreases the amount of miR-16 in the hippocampus, which in turn increases the levels of the serotonin transporter (SERT), the target of SRI, and that of bcl-2 and the number of cells positive for Doublecortin, a marker of neuronal maturation. Neutralization of miR-16 in the hippocampus further exerts an antidepressant-like effect in behavioral tests. The fluoxetine-induced hippocampal response is relayed, in part, by the neurotrophic factor S100β, secreted by raphe and acting via the LC. Fluoxetine-exposed serotonergic neurons also secrete brain-derived neurotrophic factor, Wnt2 and 15-Deoxy-delta12,14-prostaglandin J2. These molecules are unable to mimic on their own the action of fluoxetine and we show that they act synergistically to regulate miR-16 at the hippocampus. Of note, these signaling molecules are increased in the cerebrospinal fluid of depressed patients upon fluoxetine treatment. Thus, our results demonstrate that miR-16 mediates the action of fluoxetine by acting as a micromanager of hippocampal neurogenesis. They further clarify the signals and the pathways involved in the hippocampal response to fluoxetine, which may help refine therapeutic strategies to alleviate depressive disorders.
antidepressant; hippocampus; locus coeruleus; microRNA; neurogenesis; raphe
Depression is the most common psychiatric disorder in Huntington's disease (HD) patients. In the general population, women are more prone to develop depression and such susceptibility might be related to serotonergic dysregulation. There is yet to be a study of sexual dimorphism in the development and presentation of depression in HD patients. We investigated whether 8-week-old male and female R6/1 transgenic HD mice display depressive-like endophenotypes associated with serotonergic impairments. We also studied the behavioral effects of acute treatment with sertraline. We found that only female HD mice exhibited a decreased preference for saccharin as well as impaired emotionality-related behaviors when assessed on the novelty-suppressed feeding test (NSFT) and the forced-swimming test (FST). The exaggerated immobility time displayed by female HD in the FST was reduced by acute administration of sertraline. We also report an increased response to the 5-HT1A receptor agonist 8-OH-DPAT in inducing hypothermia and a decreased 5-HT2A receptor function in HD animals. While tissue levels of serotonin were reduced in both male and female HD mice, we found that serotonin concentration and hydroxylase-2 (TPH2) mRNA levels were higher in the hippocampus of males compared to female animals. Finally, the antidepressant-like effects of sertraline in the FST were blunted in male HD animals. This study reveals sex-specific depressive-related behaviors during an early stage of HD prior to any cognitive and motor deficits. Our data suggest a crucial role for disrupted serotonin signaling in mediating the sexually dimorphic depression-like phenotype in HD mice.
Saraswatarishta (SA) is a herbo-mineral formulation consisting of 18 plants some of which are Medhyarasayanas. It has been claimed to be useful in treating central nervous system disorders.
To evaluate antidepressant effect of ‘Saraswatarishta’(SA) alone and in combination with imipramine and fluoxetine in animal models of depression.
Materials and Methods:
After obtaining IAEC permission, 144 rats (n = 36/part) were randomized into 6 groups- Group 1: Distilled water (1 mL), Group 2: Imipramine (30 mg/kg), Group 3: Fluoxetine (10 mg/kg), Group 4: SA (1.8 mL/kg), Group 5: Imipramine + SA, Group 6: Fluoxetine + SA. Effects of study drugs were evaluated in forced swim test (FST) with single exposure to FST (Part 1) and repeated exposure for 14 days (Part 2). In Part 3, reserpine was used with FST and effects of study drugs were evaluated against single exposure to FST. Same model was used with repeated exposures to FST (Part 4). In each part, rats were subjected to open field test (OFT) for 5 min prior to final FST. The variables measured: Immobility time in FST; line crossing, rearing and defecation in the OFT.
In all four parts, individual drugs and combinations thereof produced significant decrease in immobility time as compared to control, and extent of decrease was comparable amongst these groups. However, values for combination of fluoxetine with SA group were found to be lesser than that for individual agents in Parts 2 and 3. Combination of SA with imipramine did not enhance its anti-depressant effect in any of the parts. OFT findings did not vary significantly amongst the study groups.
Decreased immobility in FST and absence of generalized stimulation or depression of motor activity in OFT point towards potential antidepressant effect of Saraswatarishta. Its co-administration with fluoxetine showed more promising effects.
Depression; forced swimming test; reserpine; saraswatarishta
This study was to investigate antidepressant activities of Shuyusan (a Chinese herb), using a rats model of depression induced by unpredictable chronic mild stress (UCMS). The administration groups were treated with Shuyusan decoction for 3 weeks and compared with fluoxetine treatment. In order to understand the potential antidepressant-like activities of Shuyusan, tail suspension test (TST) and forced swimming test (FST) were used as behavioral despair study. The level of corticotropin-releasing factor (CRH), adrenocorticotropic hormone (ACTH), corticosterone (CORT) and hippocampus glucocorticoid receptor expression were examined. After modeling, there was a significant prolongation of immobility time in administration groups with the TST and FST. High-dose Shuyusan could reduce the immobility time measured with the TST and FST. The immobility time in high-dose herbs group and fluoxetine group was increased significantly compared with the model group. After 3 weeks herbs fed, the serum contents level of CRH, ACTH, and CORT in high-dose herb group was significantly decreased compared to the model group. The result indicated that Shuyusan had antidepressant activity effects on UCMS model rats. The potential antidepressant effect may be related to decreasing glucocorticoid levels activity, regulating the function of HPA axis, and inhibiting glucocorticoid receptor expression in hippocampus.
Antidepressant medications are effective only in a subpopulation of patients with depression, and some patients respond to certain drugs but not others. The biological bases for these clinical observations remain unexplained. To investigate individual differences in response to antidepressants, we have examined the effects of the norepinephrine reuptake inhibitor desipramine (DMI) and the selective serotonin reutake inhibitor fluoxetine (FLU) in the forced swim test (FST) in rats that differ for their emotional behavior. After FST, animals with higher locomotor activity in a novel environment (HR) showed higher c-fos mRNA levels than their counterpart (LR) in the locus coeruleus (LC). No group differences in c-fos mRNA expression were present in the dorsal raphe nucleus or nucleus of the solitary tract (NTS). When behavioral effects of DMI or FLU were compared in HR vs. LR animals in the FST, DMI caused a significant decrease in immobility in LR animals only, while FLU caused a significant reduction in immobility regardless of the animals’ phenotype. Moreover, our results showed a decrease in FST-induced c-fos mRNA levels in prefrontal cortex (PFC) and paraventricular nucleus of the hypothalamus (PVN) in LR but not HR animals after DMI treatment, and a significant decrease in FST-induced corticosterone secretion in DMI-treated LR but not HR rats. Taken together, our results suggest that the HR-LR model is a useful tool to investigate individual differences in responses to norepinephrine reutake inhibitors (NRIs) and that a diffential activation of PFC and/or PVN could underlie some of the inter-individual differences in NRIs efficacy.
Alzheimer’s disease (AD) and epilepsy are separated in the medical community, but seizures occur in some patients with AD, and AD is a risk factor for epilepsy. Furthermore, memory impairment is common in patients with epilepsy. The relationship between AD and epilepsy remains an important question because ideas for therapeutic approaches could be shared between AD and epilepsy research laboratories if AD and epilepsy were related. Here we focus on one of the many types of epilepsy, temporal lobe epilepsy (TLE), because patients with TLE often exhibit memory impairment, depression and other comorbidities that occur in AD. Moreover, the seizures that occur in patients with AD may be nonconvulsive, which occur in patients with TLE. Here we first compare neuropathology in TLE and AD with an emphasis on the hippocampus, which is central to both AD and TLE research. Then we compare animal models of AD pathology with animal models of TLE. Although many aspects of the comparisons are still controversial, there is one conclusion that we suggest is clear: some animal models of TLE could be used to help address questions in AD research, and some animal models of AD pathology are bona fide animal models of epilepsy.
amyloid precursor protein; dentate gyrus; hilus; mossy fiber sprouting; neurodegeneration; presenilin-1; seizure; temporal lobe
Clinical evidence shows a strong, bidirectional comorbidity between depression and epilepsy that is associated with decreased quality of life and responsivity to pharmacotherapies. At present, the neurobiological underpinnings of this comorbidity remain hazy. To complicate matters, anticonvulsant drugs can cause mood disturbances, while antidepressant drugs can lower seizure threshold, making it difficult to treat patients suffering from both depression and epilepsy. Animal models have been created to untangle the mechanisms behind the relationship between these disorders and to serve as screening tools for new therapies targeted to treat both simultaneously. These animal models are based on chemical interventions (e.g. pentylenetetrazol, kainic acid, pilocarpine), electrical stimulations (e.g. kindling, electroshock), and genetic/selective breeding paradigms (e.g. Genetically Epilepsy-Prone Rats (GEPRs), Genetic Absence Epilepsy Rat from Strasbourg (GAERS), WAG/Rij rats, Swim Lo-Active rats (SwLo)). Studies on these animal models point to some potential mechanisms that could explain epilepsy and depression comorbidity, such as various components of the dopaminergic, noradrenergic, serotonergic, and GABAergic systems, as well as key brain regions, like the amygdala and hippocampus. These models have also been used to screen possible therapies. The purpose of the present review is to highlight the importance of animal models in research on comorbid epilepsy and depression and to explore the contributions of these models to our understanding of the mechanisms and potential treatments for these disorders.
Epilepsy; Depression; Animal Model; Comorbidity
The aim of the study was to evaluate a novel 5 HT3 receptor antagonist (6g) on chronic stress induced changes in behavioural and brain oxidative stress parameter in mice. A complicated relationship exists among stressful stimuli, body's reaction to stress and the onset of clinical depression. Chronic unpredictable stressors can produce a situation similar to human depression, and such animal models can be used for the preclinical evaluation of antidepressants.
Materials and Methods:
In the present study, a novel and potential 5-HT3 receptor antagonist (4-benzylpiperazin-1-yl)(3-methoxyquinoxalin-2-yl) methanone (6g) with good Log P (3.08) value and pA2(7.5) values, synthesized in our laboratory was investigated to study the effects on chronic unpredictable mild stress (CUMS)-induced behavioural and biochemical alterations in mice. Mice were subjected to different stress paradigms daily for a period of 28 days to induce depressive-like behaviour.
The results showed that CUMS caused depression-like behaviour in mice, as indicated by the significant (P < 0.05) decrease in sucrose consumption and locomotor activity and increase in immobility the forced swim test. In addition, it was found that lipid peroxidation and nitrite levels were significantly (P < 0.05) increased, whereas glutathione levels, superoxide dismutase and catalase activities decreased in brain tissue of CUMS-treated mice. ‘6g’ (1 and 2 mg/kg, p.o., 21 days) and fluoxetine treatment (20 mg/kg, p.o., 21 days) significantly (P < 0.05) reversed the CUMS-induced behavioural (increased immobility period, reduced sucrose preference and decreased locomotor activity) and biochemical (increased lipid peroxidation; decreased glutathione levels, superoxide dismutase and catalase activities). However fluoxetine treatment (20 mg/kg, p.o., 21 days) significantly decreased the nitrite level in the brain while ‘6g’ (1 and 2 mg/kg, p.o., 21 days) did not show significant (P < 0.05) effect on the nitrite levels in brain.
Compound ‘6g’ exerted antidepressant-like effects in behavioural despair paradigm in chronically stressed mice by restoring antioxidant mechanisms.
5-HT3 receptor antagonist; chronic unpredictable mild stress; depression; oxidative stress
Opiate abuse is a chronic relapsing disorder and maintaining prolonged abstinence remains a major challenge. Protracted abstinence is characterized by lowered mood and clinical studies show elevated co-morbidity between addiction and depressive disorders. At present, their relationship remains unclear and has been little studied in animal models. Here we investigated emotional alterations during protracted abstinence, in mice with a history of chronic morphine exposure.
C57BL6J mice were exposed to a chronic intermittent escalating morphine regimen (20-100mg/kg). Physical dependence (naloxone-precipitated withdrawal), despair-related (tail suspension test) and social behaviors were examined after 1 or 4 weeks of abstinence. Stress hormones and forebrain bioamine levels were analyzed at the end of morphine regimen and after 4 weeks abstinence. Finally, we examined the effects of chronic fluoxetine during abstinence on morphine-induced behavioral deficits.
Acute naloxone-induced withdrawal was clearly measurable after 1 week, and became undetectable after 4 weeks. In contrast, social and despair-related were unchanged after 1 week, but low sociability and despair-like behavior became significant after 4 weeks. Chronic morphine regimen increased both corticosterone levels and forebrain serotonin turnover, but only serotonergic activity in the dorsal raphe remained impaired after 4 weeks. Remarkably, chronic fluoxetine prevented depressive-like behavioral deficits in 4-week abstinent mice.
During protracted abstinence, the immediate consequences of morphine exposure attenuate while fluoxetine-sensitive emotional alterations strengthen with time. Our study establishes a direct link between morphine abstinence and depressive-like symptoms, and strongly suggests that serotonin dysfunction represents a main mechanism contributing to mood disorders in opiate abstinence.
Opiates; incubation; depression; serotonin; fluoxetine; dorsal raphe
Many neuropsychiatric disorders, including stress-related mood disorders, are complex multi-parametric syndromes. Susceptibility to stress and depression is individually different. The best animal model of individual differences that can be used to study the neurobiology of affect regards spontaneous reactions to novelty. Experimentally, when naive rats are exposed to the stress of a novel environment, they display a highly variable exploratory activity and are classified as high or low responders (HR or LR, respectively). Importantly, HR and LR rats do not seem to exhibit a substantial differentiation in relation to their ‘depressive-like’ status in the forced swim test (FST), a widely used animal model of ‘behavioral despair’. In the present study, we investigated whether FST exposure would be accompanied by phenotype-dependent differences in hippocampal gene expression in HR and LR rats.
HR and LR rats present a distinct behavioral pattern in the pre-test session but develop comparable depressive-like status in the second FST session. At 24 h following the second FST session, HR and LR rats (stressed and unstressed controls) were sacrificed and hippocampal samples were independently analyzed on whole rat genome Illumina arrays. Functional analysis into pathways and networks was performed using Ingenuity Pathway Analysis (IPA) software. Notably, hippocampal gene expression signatures between HR and LR rats were markedly divergent, despite their comparable depressive-like status in the FST. These molecular differences are reflected in both the extent of transcriptional remodeling (number of significantly changed genes) and the types of molecular pathways affected following FST exposure. A markedly higher number of genes (i.e., 2.28-fold) were statistically significantly changed following FST in LR rats, as compared to their HR counterparts. Notably, genes associated with neurogenesis and synaptic plasticity were induced in the hippocampus of LR rats in response to FST, whereas in HR rats, FST induced pathways directly or indirectly associated with induction of apoptotic mechanisms.
The markedly divergent gene expression signatures exposed herein support the notion that the hippocampus of HR and LR rats undergoes distinct transcriptional remodeling in response to the same stress regimen, thus yielding a different FST-related ‘endophenotype’, despite the seemingly similar depressive-like phenotype.
Stress; Gene expression; Rats; Depression; Individual differences; Hippocampus; FST; Neurogenesis; Neuroplasticity; Apoptosis
To study agomelatine (S 20098), a potent agonist at melatonin receptors and antagonist at serotonin-2C (5-HT2C) receptors, in an animal model of depression, namely, the rodent forced swimming test (FST).
The effects of acute and repeated administration of S 20098 were compared with those of melatonin (4, 8, 16, 32, 64 mg/kg intraperitoneally [IP] for mice), imipramine (64 mg/kg orally for rats, 8 mg/kg IP for mice) and fluoxetine (16 mg/kg IP for mice). The influence of the pretreatments with 5-HT1A or 5-HT1B receptor agonists (8-OH-DPAT, anpirtoline) and 5-HT1A/1B, 5-HT2A/2C or 5-HT3 antagonists (pindolol, ritanserin, ondansetron) on the effects of S 20098 or melatonin were compared with imipramine and fluoxetine in mice.
Acute or repeated (13 days) administration of S 20098 or imipramine in rats significantly decreased the duration of immobility during the FST at all doses. A dose-dependent effect was observed after the repeated treatment with S 20098. When given for 10 days to mice in the evening, S 20098 was active on the FST at doses of 4, 16 and 32 mg/kg, whereas the acute administration of S 20098 (in the morning and evening) was without any significant effect. Acute or repeated administration of S 20098 did not modify the locomotor activity of mice. The combination of S 20098 with the above-mentioned pretreatments enhanced the effects of S 20098, given alone, on the duration of immobility. By comparison, acute melatonin was inactive in the FST and only pretreatment with 8-OH-DPAT or pindolol revealed an anti-immobility effect. A pretreatment with 8-OH-DPAT also induced anti-immobility effects with imipramine, but not fluoxetine, whereas pindolol exerted additive effects with fluoxetine but not imipramine.
These results demonstrate the antidepressant-like activity of repeated administration of S 20098 in the FST. Moreover, the combination of 5-HT agonists and antagonists leads to more powerful effects with S 20098 than with melatonin, thereby emphasizing the contribution of 5-HT receptors to the antidepressant activity of S 20098. Compared with imipramine and fluoxetine, the 5-HT receptor subtypes that may be involved in the antidepressant-like activity of S 20098 are not similar. Indeed, when considering the binding properties of S 20098, the 5-HT2C receptor subtype appears to be the most attractive candidate. It is concluded that the antidepressant-like activity of S 20098 in this model most probably involves a combination of both its melatonin agonist and 5-HT2C receptor antagonist properties.
antidepressive agents; melatonin; mice; models, animal; serotonin; rats
Recent studies indicate that chronic treatment with serotonergic antidepressants upregulates adult neurogenesis of the dentate gyrus (DG). In contrast, some studies claimed that there was very little alteration of neurogenesis in the subventricular zone (SVZ) by the antidepressants. Since almost all of those studies treated animals with drugs for 2 to 4 weeks as chronic treatment models of antidepressants, it is possible that antidepressant treatments for longer periods would affect adult neurogenesis in the SVZ.
In the present study, we examined the effects of long-term (up to 9 weeks) administration of fluoxetine (FLX), a selective serotonin reuptake inhibitor, on cell proliferation and survival in the DG and the SVZ of adult mice. As reported previously, in the DG of mice treated with FLX for 3, 6, or 9 weeks that were also injected with 5-bromodeoxyuridine (BrdU) in the last 3 days before perfusion, the numbers of Ki67- and BrdU-positive cells, which are cell proliferation markers, were significantly upregulated even at 3 weeks after the onset of the FLX treatments, and these increases were sustained in mice treated with FLX for 9 weeks. On the other hand, in the SVZ, we found a small, insignificant decrease in the numbers of Ki67- and BrdU-positive cells at 3 weeks, followed by highly significant decreases in the numbers of Ki67- and BrdU-positive cells at both 6 and 9 weeks. Furthermore, among olfactory newly generated cells that survived for 3 weeks after BrdU injection, the number of new cells was decreased at 9 weeks of FLX treatment.
These results demonstrate that long-term (more than 6 weeks) treatment with FLX has the opposite effect on neurogenesis in the SVZ than it does in the DG. The results also suggest that the decrease in neurogenesis in the SVZ might be involved in some aspects of the drugs' therapeutic effects on depression. In addition, our findings raise the possibility that some of the side effects of antidepressants might be mediated by decreased adult neurogenesis in the SVZ.
Temporal lobe epilepsy (TLE) is a neurological condition associated with neuron loss, axon sprouting, and hippocampal sclerosis, which results in modified synaptic circuitry. Cannabinoids appear to be anti-convulsive in patients and animal models of TLE, but the mechanisms of this effect are not known. A pilocarpine-induced status epilepticus mouse model of TLE was used to study the effect of cannabinoid agonists on recurrent excitatory circuits of the dentate gyrus using electrophysiological recordings in hippocampal slices isolated from control mice and mice with TLE. Cannabinoid agonists WIN 55,212-2, anandamide (AEA), or 2-arachydonoylglycerol (2-AG) reduced the frequency of spontaneous and tetrodotoxin-resistant excitatory postsynaptic currents (EPSCs) in mice with TLE, but not in controls. WIN 55,212-2 also reduced the frequency of EPSCs evoked by glutamate-photolysis activation of other granule cells in epileptic mice. Secondary population discharges evoked after antidromic electrical stimulation of mossy fibers in the hilus were also attenuated by cannabinoid agonists. Agonist effects were blocked by the cannabinoid type 1 receptor (CB1R) antagonist AM251. No change in glutamate release was observed in slices from mice that did not undergo status epilepticus. Western blot analysis suggested an up-regulation of CB1R in the dentate gyrus of animals with TLE. These findings indicate that activation of CB1R present on nerve terminals can suppress recurrent excitation in the dentate gyrus of mice with TLE. This suggests a mechanism for the anti-convulsive role of cannabinoids aimed at modulating receptors on synaptic terminals expressed de novo after epileptogenesis.
The observed high incidence of smoking amongst depressed individuals has led to the hypothesis of ‘self medication” with nicotine in some of these patients. The inbred Wistar-Kyoto (WKY) rats exhibit depressive-like characteristics as evidenced by exaggerated immobility in the forced swim test (FST). One aim of this study was to investigate whether nicotine may have an antidepressant-like effect in these animals. Moreover, because of human postmortem studies indicating a reduction of the hippocampus volume in depressed patients, it was of interest to determine whether such an anatomical anomaly may also be manifested in WKY rats and whether it would be affected by chronic nicotine treatment. Adult female WKY and their control Wistar rats were administered nicotine consecutively (0.2 mg/kg, ip, once or twice daily for 14 days) and their activity in an open field, as well as their immobility in FST were assessed either 15 min or 18 hr after the last injection. Another set of animals was treated twice daily with 0.2 mg/kg nicotine for 14 days and sacrificed on day 15 for stereological evaluation of the hippocampal volume. When tested 15 min after the last injection, once or twice daily nicotine exacerbated the immobility in the FST in WKY rats only. When tested 18 hr after the last injection, only twice daily nicotine treatment resulted in less immobility in the FST in WKY rats. Open field locomotor activity was not affected by any nicotine regimen. WKY rats had significantly less hippocampal volume (approximately 20%) than Wistar rats which was not altered by nicotine. These findings further validate the use of WKY rats as an animal model of human depression and signify the importance of inherent genetic differences in final behavioral outcome of nicotine.
WKY rats; Depression; Hippocampus; Nicotine; Forced Swim Test; Stereology