Social isolation effects on the "behavioral despair" forced swimming test: effect of age and duration of testing

Social loss is considered to be one of the major precipitants of depression. Prior work with the Porsolt forced swimming test (FST) has failed to demonstrate increases in despair-like immobility as a result of prior social isolation in adult animals. In the present work, increased immobility was observed in young Swiss Webster mice that had been socially isolated for 24 h prior to a 15-minute FST. The effect was not apparent until after the first five minutes of testing. The increase in immobility as a result of social isolation was apparent in 17-21-day-old animals but not in 26-30-day-old ones. Control experiments indicated that the increase in immobility was not due to the slightly higher weight loss of the socially isolated animals. Administration of reserpine (0.25 mg/kg) induced a marginal increase in immobility in the youngest animals but decreased immobility at later ages. These data suggest that the mouse only exhibits a short period of time during early development where social isolation can promote despair-like immobility in the FST and suggest that analyses of depressive processes which result from social variables may be best studied during a limited age range in this species.     

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.     

Immobility and Hyperthermia in the Tail Suspension Test: Association with the Porsolt Test and the Reflex Startle Reaction in 11 Inbred Mouse Strains and the Effects of Genetic Knockout of MAO A

Immobility and hyperthermia induced by unavoidable stress imposed by the tail suspension test (TST) and the acoustic startle reaction were assessed in mice of 11 inbred strains and in Tg8 mice, which have genetic knockout of MAO A. Sharp genotypic differences in immobility were seen, while there was no correlation with the hyperthermic response to the TST. A correlation was found between the extent of immobility in the TST and the startle reaction. Studies of 11 strains of mice revealed a positive correlation between the duration of immobility in the TST and the Porsolt “despair test.” Genetic knockout of MAO A, one of the key enzymes in catecholamine and serotonin metabolism in the brain, weakened the startle reaction and TST-induced hyperthermia but had no significant effect on the immobility of Tg8 mice, which provides evidence of differences in the neurochemical regulation of these reactions. These data provide grounds for using the TST as a “dry” Porsolt test and identify TST-induced hyperthermia as a model for reactions to unavoidable stress.     

"Behavioral despair" test predicts stress ulcer in WKY rats

Spontaneously hypertensive rats (SHR), Wistar Kyoto (WKY) and Wistar rats were exposed to Porsolt's forced-swimming test of "behavioral despair." In addition to floating time, which was the measure of despair, headshakes, bobbing, diving and struggling time were also recorded. Rats were subsequently exposed to the activity stress (A-S) ulcer procedure. Wistar rats had the highest struggling time scores and the fewest A-S ulcers. WKY rats were judged as more depressed and their ulcer severity scores were significantly greater as compared to SHR and Wistar rats. In addition, a within strains analysis revealed that WKY rats with high despair scores also had the most severe stress-ulcer scores. These data suggested that stress-ulcer disease may be more prevalent in animals which are prone to depression as defined by the Porsolt test. The value of WKY rats as an animal model to study the relationship between depression and stress ulcer is discussed.     

Does the behavioral "despair" test measure "despair"?

The behavioral "despair" test is widely used to study antidepressants, mainly on the theoretical assumption that the test animal becomes desperate. In view of the above, we compared behavior of animals subjected to various experimental conditions (4, 15, 30 cm of water), in order to assess whether or not "despair" was the cause of immobility. Our results indicate that the animal's behavior in response to exposure to a dangerous situation, such as that represented by 15 or 30 cm water, depends upon previous knowledge of the environment rather than "despair." We concluded that this test is far from reproducing behavioral changes which characterize depressive illness in humans.     

Interaction between behavioral despair and addictive behaviors in rats

It has been suggested that depression can be either a cause or a consequence of drug abuse, providing a possible explanation for the fact that the prevalence of depression is almost 3-fold higher in drug abusers than in the general population. However, the interaction between depression and drug abuse has not been fully elucidated. To examine the interaction between behavioral despair and addictive behaviors, we used the Porsolt's forced swim test (FST) as a model of behavioral despair, and we used morphine conditioned place preference (CPP) and repeated morphine exposure as models of addictive behaviors. We found that rats exposed to a standard FST (15 min on day 0 training) rather than a weak FST (10 min on day 0 training) exhibited behavioral despair, which selectively potentiated morphine CPP (mCPP) but not food CPP (fCPP). The antidepressant imipramine (15 mg/kg, i.p.), which blocked the behavioral despair, prevented the standard FST potentiated morphine CPP. Conversely, repeated exposure to morphine (10 mg/kg, s.c.) for 6, 12 or 20 days decreased, had no effect on, or increased the immobility time, respectively, in the subsequent standard FST. Furthermore, repeated morphine exposure for 20 days exacerbated the pre-existing behavioral despair. Thus, our findings suggest that behavioral despair may increase the vulnerability of individuals to opiate abuse, which may in turn enhance behavioral despair.     

Is immobility of rats in the forced swim test "behavioral despair"?

Rats were forced to swim in a cistern until sinking in order to examine the possible relationship between sinking and immobility which has been reported to reflect "behavioral despair" in the forced swim test. Rats were classified into sinking and non-sinking groups, according to the appearance of sinking behavior over a 2 hr test. The sinking rats showed significantly shorter immobility times during the first 15 min as compared to the non-sinking rats. Therefore, sinking behavior seems to be a sign of emotional behavior such as fear and/or anxiety accompanied by defecation. Discriminant analysis showed that the immobility time during the first 15 min was a prediction of sinking. These findings suggest that the rapidly induced immobility in this forced swim test reflects the possibility of floating behavior in connection with the emotional reaction.     

Nucleus accumbens muscarinic receptors in the control of behavioral depression: antidepressant-like effects of local M1 antagonist in the Porsolt swim test.

Systemically administered cholinomimetics or cholinesterase inhibitors can depress behavior in humans and animals, whereas antimuscarinic agents reverse this effect or even produce euphoria. Although these effects have been well documented, the specific brain regions that mediate them remain largely unknown. In the present experiments, muscarinic agonists and antagonists were locally injected into the nucleus accumbens of female Sprague-Dawley rats to test for their effects on behavioral depression in the Porsolt swim test and locomotor activity. Local, microinjections of the drugs in the accumbens elicited behaviors that were similar to the systemic effects reported in other studies. Injection of the non-specific agonist arecoline (40 and 80 microg) dose-dependently inhibited swimming and escape behavior. This may be mediated in part by accumbens M1 receptors because blocking these receptors with the specific antagonist pirenzepine (17.5 and 35.0 microg) did the opposite by increasing swimming. Gallamine (0.13, 0.44, and 0.88 microg), an antagonist at M2 receptors, dose-dependently decreased swimming. Two-way microdialysis suggested that this was in part due to the release of ACh by blocking M2 autoreceptors. Scopolamine, a mixed M1/M2 receptor antagonist, also released ACh but did not decrease swimming, probably because the M1 receptors were blocked; the drug (1.0 microg) increased swimming time, much like pirenzepine. With the exception of arecoline, none of the drugs significantly affected locomotor activity in a photocell cage. Arecoline (40 microg), which had decreased swimming, reduced activity.The present study suggests that muscarinic receptors in the nucleus accumbens can control immobility in the Porsolt swim test. The onset of immobility may depend on the activation of post-synaptic M1 receptors.     

Identification of multiple genetic loci linked to the propensity for "behavioral despair" in mice

The forced swim test (FST) and tail suspension test (TST) are widely used and well established screening paradigms for antidepressants. A variety of antidepressive agents are known to reduce immobility time in both FST and TST. To identify genetic determinants of immobility duration in both tests, we analyzed 560 F2 mice from an intercross between C57BL/6 (B6) and C3H/He (C3) strains. Composite interval mapping revealed five major loci (suggestive and significant linkage) affecting immobility in the FST, and four loci for the TST. The quantitative trait loci (QTL) on chromosomes 8 and 11 overlap between the two behavioral measures. Genome-wide interaction analysis, which was developed to identify locus pairs that may contribute epistatically to a phenotype, detected two pairs of chromosomal loci for the TST. The QTL on chromosome 11 and its associated epistatic TST-QTL on chromosome X encode gamma-aminobutyric acid type A (GABA(A)) receptor subunits as candidates. Sequence and expression analyses of these genes from the two parental strains revealed a significantly lower expression of the alpha1 subunit gene in the frontal cortex of B6 mice compared to C3 mice. The present quantitative trait study should open up avenues for identifying novel molecular targets for antidepressants and unraveling the complex genetic mechanisms of depressive and anxiety disorders.     

Swim test immobility in a genetic rat model of depression is modified by maternal environment: a cross-foster study

The Flinders sensitive line (FSL) genetic animal model of depression exhibits marked immobility during forced swimming, an accepted index of depressive like behavior in rodent depression models. The present experiment tested the hypothesis that swim test behavior in the FSL rats is influenced in part by early experience, specifically maternal environment. Male FSL and control Flinders resistant line (FRL) pups were cross fostered onto dams of the same or complementary strain. Nest quality and dam behavior during pup retrieval were measured on PN5 and PN8, and swim test behavior assessed in the adult males on PN60. FSL rats reared by foster FRL dams were significantly less immobile than FSL rats raised by FSL dams, but still significantly more immobile that the two FRL groups, which did not differ from each other. FSL dams took significantly longer to retrieve their pups and dropped them more often than the FRL control dams. Moreover, strain differences in maternal retrieval behavior significantly predicted later swim test immobility in the FSL animals. These findings suggest that swim test immobility in the FSL rats is modified by maternal environment. In contrast, the FRL control rats were relatively insensitive to the influence of maternal environment. The FSL model offers promise for understanding the interactions of genetic vulnerabilities and environmental influences in the etiology of clinical depression.     

Ovarian hormone withdrawal-induced "depression" in female rats

Approximately 15% of child-bearing women develop postpartum depression (PPD), and many women with PPD experience anxious symptoms. It has been proposed that PPD is precipitated by the dramatic decline in reproductive hormones that occurs just after childbirth. To examine this hypothesis, ovariectomized female Sprague-Dawley rats underwent a hormone-simulated pregnancy (HSP) regimen; during the subsequent hormone withdrawal period, rats were tested in the forced swim test or elevated plus-maze, animal models of depression and anxiety, respectively. The HSP regimen consisted of injections with progesterone and escalating doses of estradiol benzoate for 22 days; control rats received daily vehicle injections. One, two, four or seven days after the last hormone injection, separate groups of rats were tested once on either the forced swim test or the elevated plus-maze. To examine any hormone withdrawal-induced changes in activity levels, spontaneous locomotor activity was measured at the same time points. At 2 and 4 days after the last hormone injection, HSP-treated females displayed significant increases in immobility relative to vehicle-treated females in the forced swim test. Behavior on the elevated plus-maze did not differ between the HSP and control groups at any of the withdrawal time points. There were also no differences in spontaneous locomotor activity between the HSP and control females at any of the withdrawal time points. The results of this study suggest that postpartum hormone withdrawal may contribute to depressive symptoms experienced after giving birth, and that the HSP-hormone withdrawal protocol may provide a useful animal model of PPD.     

The Fawn-Hooded (FH/Wjd) rat: a genetic animal model of comorbid depression and alcoholism

The Fawn-Hooded (FH/Wjd) rat is an inbred strain of rat that has been reported to exhibit both high immobility in the forced swim test and high voluntary ethanol intake, measures that have been periodically linked with depression and alcoholism in humans. The present paper will first present a survey of the literature and previously unpublished findings that bear on the question of whether FH/Wjd rats should be considered genetic animal models of depression and alcoholism. Subsequently, behavioral studies of the FH/Wjd rats, the non-drinking ACI/N strain, and their F1 and F2 intercrosses will be described. Under free choice conditions, the FH/Wjd rat drinks up to 6 g/kg 10% ethanol per day. This intake was sufficient to render the rats tolerant to the hypothermic effects of injected ethanol (2.5 g/kg). Rats that had been voluntarily drinking for at least 6 weeks also exhibited withdrawal-induced anxiety in the social interaction, elevated plus maze, and ultrasonic vocalization tasks. The FH/Wjd rat exhibits a 25-30% increase in alcohol intake when the alcohol is returned after a 24-h period of deprivation. It responds to drugs that are effective in humans with a reduction in alcohol intake. Therefore, the FH/Wjd rat meets most of the criteria for an animal model of alcoholism. Chronic antidepressant treatments correct several of the abnormalities exhibited by the FH/Wjd rats, including the exaggerated immobility in the forced swim test. Therefore, the FH/Wjd rats also fulfill some of the criteria for an animal model of depression. On the contrary, inbred ACI/N rats do not drink much alcohol voluntarily and are quite active in the forced swim test. The FH/Wjd and ACI/N rats were intercrossed to obtain the F1 and F2 progenies, which were then tested for alcohol intake and immobility. Alcohol intake and immobility were distributed in different patterns in the F1 and F2 progenies. Alcohol intake was intermediate in the F1 progeny, while immobility was closer to the FH/Wjd parents. In the F2 progeny, chi-square analyses indicated that the distributions were significantly different. In addition, there were no significant litter effects, indicating that maternal effects did not appear to occur. There were also no significant differences among rats with different coat colors, suggesting that the Fawn-Hooded phenotype can be separated from the measures of alcohol intake and immobility. We conclude that the FH/Wjd rat is a genetic animal model of depression and alcoholism, but that the two measures reflective of these states are under separate genetic controls.     

Influence of ovariectomy, estradiol and progesterone on the behavior of mice in an experimental model of depression

In the tail suspension test (an animal model of depression) the duration of immobility during the 6 min of observation was 56.84 +/- 6.54 sec in sham-ovariectomized mice and 113.11 +/- 7.86 sec 30-32 days after ovariectomy. Estradiol (10, 100 or 1,000 micrograms/kg) and progesterone (50, 1,000 or 10,000 micrograms/kg), subcutaneously injected daily 4 times before the test, restored the duration of immobility in ovariectomized mice to normal, while having no effect on sham-operated animals. On the other hand, desipramine (20 mg/kg IP 1 hr before testing) significantly reduced the duration of immobility both in ovariectomized and in sham-operated mice. These data indicate that ovarian sex hormones, while having no "antidepressant," desipramine-like, effect on the behavior of intact adult female mice, have such an effect in ovariectomized mice, and enable the animal to cope in a "normal" way with adverse environmental situations.     

The effects of inositol treatment in animal models of psychiatric disorders

Clinical trials indicate that inositol may be effective in the treatment of patients with depression, panic disorder and obsessive compulsive disorder (OCD), but not in the treatment of patients with schizophrenia, Alzheimer's disease, ADHD or autism. This spectrum of clinical action parallels that of serotonin selective reuptake inhibitors (SSRIs), but inositol is a precursor in the phosphatidylinositol cycle, a second messenger system distal to the receptor for 5HT-2. To study its mechanism of therapeutic action there is a need to test inositol's activity in animal models of psychopathology. In rats, chronic inositol was demonstrated to increase activity levels, reduce immobility time in the forced swim test and in the reserpine-induced hypoactivity models of depression, and reduce anxiety-like behaviors in the elevated plus-maze. The reduction in anxiety-like behaviors appears to be related to baseline levels of activity. Inositol treatment was not observed to have any effect on amphetamine-induced hyperactivity, apomorphine-induced stereotypy, or on the performance of memory tasks by monkeys. Clinical controlled trials of inositol in patients with depression, panic disorder, and OCD were small, and positive psychoactive effects in animals clearly strengthen the case for further clinical trials and potential for general therapeutic use in humans.     

Opposite behaviours in the forced swimming test are linked to differences in spatial working memory performances in the rat

Despite consistent evidence of an association between depression and impaired memory performance, only a few studies have investigated memory processes in animal models of depression. The aim of the present study was to determine if rats selected for marked differences in their immobility response in the forced swimming test (FST, i.e. high-immobility, [HI] and low-immobility [LI] rats) exhibit differences in spatial and non-spatial memory performances. In a classic radial maze elimination task, we observed that HI rats made significantly more errors than LI rats, and their first error appeared significantly earlier. In a delayed spatial win-shift procedure where rats have to hold spatially relevant information in working memory across a 30 min delay, HI rats tended initially to perform more poorly than LI rats. HI rats made more across-phase errors, the occurrence of the first error was earlier and by the end of the experiment the differences between the two groups disappeared. Thus, HI rats present more difficulties to learn the rules in a spatial task and show weaker performances in spatial working memory in comparison to LI rats. On the other hand, performances in the two groups of animals were similar in a non-spatial task, the object recognition task. Complementary behavioral data indicate that the differences observed between the two groups are not attributable to opposite locomotor activities or to different levels of anxiety. Overall we can conclude that opposite swimming behavior in the FST could parallel some differences in cognitive performances, more specifically linked to spatial working memory.     

Sex differences in behavioral, neurochemical and neuroendocrine effects induced by the forced swim test in rats

The forced swim test (FST) has been considered as a pharmacologically valid test of the depressive syndrome in rodents. However, few studies have focused on neurochemical and behavioral responses during FST in both male and female rats. Thus, we investigated certain behavioral and neuroendocrine responses as well as the serotonergic activity after the application of FST in both sexes. Our data show that the duration of immobility was increased in both male and female rats during the 2nd session of the FST. Sex differences are observed in some behavioral responses, such as head swinging that is mostly present in male rats. In female rats FST induced a decrease in serotonergic activity in hippocampus and hypothalamus while in male rats it induced an increase in serotonergic activity in hypothalamus. Corticosterone serum levels were elevated in both sexes. However, hippocampal GR mRNA levels tended to be increased in males and females respectively. Moreover, hypothalamic serotonin (5-HT)1A mRNA levels were decreased in female rats while in male rats hippocampal 5-HT1A mRNA levels were increased. These data have shown that FST induces "depressive like symptoms" in both sexes and provide evidence that sex differences characterize certain behavioral aspects in the FST. Notably, hippocampal and hypothalamic serotonergic activity has been differentially modified in male rats compared with female rats and these neurochemical findings could be relevant to the differentiated expression of 5-HT1A receptor. Hypothalamic-pituitary-adrenal axis activity was also affected by FST application in a sex specific manner. The present results support that FST induced behavioral, neurochemical and neurobiological alterations, which are sex dependent.     

Failure of neonatal clomipramine treatment to alter forced swim immobility: chronic treadmill or activity-wheel running and imipramine

We examined whether chronic running on a treadmill or activity wheel would attenuate the increased swim immobility that has been reported after neonatal clomipramine (CLI) treatment. Male Sprague-Dawley pups (N = 60) were injected with the monoamine reuptake inhibitor clomipramine hydrochloride (40 mg/kg per day i.p.) from 8 to 21 days of age. Another group (N = 12) received saline vehicle. At age 4 weeks, the CLI pups were randomly assigned to experimental conditions: (1) sedentary; (2) 24-h access to an activity wheel; (3) sedentary that received the antidepressant drug imipramine hydrochloride (10 mg/kg twice daily) during the last 10 days of the experiment; (4) activity wheel + imipramine; (5) treadmill running (30 m/min for 1 h at 0 degrees incline, 6 days/week). At age 16 weeks, rats underwent the Porsolt swim test 48 h after the last imipramine injection and/or the last exercise session. The increase in swim immobility among CLI-treated rats was small (one quarter of SD) and not statistically significant (p>0.10). The results are not consistent with our previous finding of antidepressant-like effects of activity-wheel running based on brain noradrenergic adaptations and enhanced male copulatory performance after neonatal CLI treatment. The lack of change in swim performance after clomipramine questions the generalizability of the CLI model of depression and the validity of the forced swim test as a behavioral measure of depression when it is used after neonatal CLI injection or chronic activity-wheel running.     

Effect of enterosorbent noolith on behavior and serotonin (1A) receptors in mouse brain

Protective properties of a new enterosorbent noolith (lithium ions immobilized on mineral matrix) were studied in C57Bl/6J mice predisposed to depression caused by intermale confrontations. The drug was administered daily for 15 days after the 5th confrontation and then the animals were tested in the forced swimming test. The number of specific ³H-8-OH-DPAT binding sites in 3 brain regions was determined. It is shown that noolith produced an antidepressive effect manifested in decreased immobility time in the Porsolt test. Moreover, noolith reduced the number of 1A-serotonin receptors in the frontal cortex and hypothalamus. It is concluded that noolith possesses protective properties.     

抑郁症动物模型的评价及认知行为变化

目的研究抑郁症动物模型的评价方法及认知行为变化。方法造模前后分别测量摄食量和体重,使用Y型电迷宫评价抑郁症动物模型的认知,强迫游泳试验评价抗抑郁药物作用后动物行为的变化。结果造模前后动物的体重增加量,造模后的动物摄食量,药物干预后动物强迫游泳实验中的静止时间在两组之间有显著差异。结论体重增加量,摄食量,电迷宫实验可以作为抑郁症动物模型的评价方法。强迫游泳试验可以评价抗抑郁药物干预后动物行为的变化。慢性应激抑郁动物模型存在认知行为的变化。     

Effects of chronic social defeat stress on MAP kinase cascade

Chronic psychological and social stress can cause psychiatric disorders in humans. In this study, we analyzed the mitogen-activated protein kinase (MAPK) cascade in the hippocampus of chronically socially defeated rats. The rats that were subjected to social defeat every day for 5 weeks showed physiological and behavioral changes, including a reduced rate of weight gain, enlarged adrenal glands, and increased immobility in the forced swim test without concomitant changes in locomotor activity in the open field test. Altered body weight and enlarged adrenal glands are typical symptoms of human depression. Prolonged immobility in the forced swim test indicates behavioral despair, a well-established index of depression. Because the MAPK cascade plays a pivotal role in depression, we quantified the expression of these molecules in the hippocampus of chronically defeated rats using western blot analysis. We found that phospho-MAPK kinases 1/2 (MEK1/2) and phospho-extracellular signal-regulated kinases 1/2 (ERK1/2) were decreased, whereas MAPK phosphatase-1 (MKP-1) was increased in the hippocampus of chronically defeated rats compared to the control group. These results were consistent with findings in depressed patients and other animal models of depression. In conclusion, our findings suggest that chronic psychosocial stress in Wistar rats induced depression-like behavior and downregulated the MAPK cascade in the hippocampus.