Correlations between behaviours in the elevated plus-maze and sensitivity to unpredictable subchronic mild stress: evidence from inbred strains of mice

This study aimed at investigating the relationship between anxiety-like and depressive-like behaviour in mice. Therefore, we assessed the behaviour of mice from eight different strains (FVB/NA, BALB/c, C57BL/6, DBA/2, 129/Sv, C3H/He, CBA and BA) confronted first to anxiety models (the elevated plus-maze and the free exploratory test) and then to tests of depressive-like behaviours (forced swim test and unpredictable subchronic mild stress). In the forced swim test, mice from the DBA/2, the BA and the C3H/He strains displayed higher immobility than mice from the 129/Sv, the BALB/c, the C57BL/6 and the CBA strains. In the subchronic mild stress, mice from the C57BL/6 and the CBA strains displayed low sensitivity when compared with mice from all the others strains. A stepwise multiple regression analysis suggests that behaviour in the elevated plus-maze is associated with the time of immobility in the forced swim test (20%) and with the susceptibility to the unpredictable subchronic stress procedure (31%). The behaviour in the free exploratory paradigm is slightly associated with behaviours in the two tests of depression. These results suggest that anxiety may be a factor contributing, among others, to the susceptibility to depressive-like behaviours.     

Omission of the habituation procedure in the acquisition of a working memory task - evidence from Balb/c, C57/BL6J, and CD-1 mice

Training animals in spatial mazes have always been preceded by prior habituation to the test apparatus and testing conditions with the main goal to reduce fear and anxiety from exposure to the unfamiliar maze environment. This approach makes assumptions about the baseline level of emotionality in animals without actual objective measurements. It also ignores that genetic factors and experimental manipulations can reduce or prolong fear and anxiety from novelty, hence affecting the acquisition of a memory task. In the present study, C57, CD-1 and Balb/c mice were introduced to a working memory task in a radial-arm maze without habituation. Fear-induced anxiety from exposure to the novelty in this maze is demonstrated by a very low number of arm entries. Animals have to climb onto a bridge in order to reach an arm of the maze. In the first session block, Bab/c mice made very few arm entries and made more arm repeats than CD-1 and C57 mice, and CD-1 made few arm entries and made more arm repeats than C57/BL6J mice. In the second session block, all three strains of mice did make 8 arm entries. Balb/c mice seem to perform better than C57 and CD-1 mice as shown by a low number of arm repeats in the second session block, a high number of correct choices before first errors in the third session block, and low number of errors and sessions to criterion. In the present case, a high baseline level of emotionality did not prevent Balb/c mice to perform better than C57 and CD-1 mice.     

Comparison of nicotine oral consumption and baseline anxiety measures in adolescent and adult C57BL/6J and C3H/Ibg mice

Approximately 80% of smokers initiate tobacco use during adolescence, suggesting that nicotine initiation and nicotine dependence have a substantial age component. There also is a substantial genetic influence on smoking behaviors such as age of initiation and the development of nicotine dependence. The goal of this study was to examine both genetic background and age dependent effects on oral nicotine self-administration and anxiety-like behaviors in mice. Two inbred mouse strains (C3H/Ibg and C57BL/6J) were assessed for oral nicotine preference during early adolescence (postnatal day 24-35), middle adolescence (postnatal day 36-47), late adolescence (postnatal day 48-59), adulthood (postnatal day 60+) and 2 months following their initial exposure to nicotine. Mice also were assessed for innate anxiety using an elevated zero maze to determine if age and/or genetic background influenced anxiety-like behaviors. Results indicated that initial nicotine preference and nicotine preference two months after an initial exposure are both strain and age dependent. Age also had an effect on some baseline anxiety measures but strain differences for most zero maze measures were present throughout all age groups. In general, early adolescent C3H mice exhibited greater nicotine preference while C57 mice displayed greater preference during middle adolescence and upon a second exposure to nicotine. In contrast, C57 mice exhibited reduced anxiety across all ages tested. These studies indicate that genetic background should be considered when evaluating age-dependent effects of drugs of abuse and baseline anxiety-like behaviors.     

Increased water temperature renders single-housed C57BL/6J mice susceptible to antidepressant treatment in the forced swim test

To investigate genotype x environment interactions in the forced swim test, we tested the influence of water temperature (20 degrees C, 25 degrees C, 30 degrees C) on floating behaviour in single-housed male C57BL/6J and BALB/c mice. We observed a contrasting relationship between floating and water temperature between the two strains, with C57BL/6J floating more and BALB/c floating less with increasing water temperature, independent of the lightening conditions and the time point of testing during the animals' circadian rhythm. Both strains showed an inverse relationship between plasma corticosterone concentration and water temperature, indicating that the differences in stress coping are unrelated to different perception of the aversive encounter. Treatment with desipramine (20mg/kg, i.p.) caused a reduction in immobility time in C57BL/6J mice if the animals were tested at 30 degrees C water temperature, with no effect at 25 degrees C and no effects on forced swim stress-induced corticosterone secretion. The same treatment failed to affect floating behaviour in BALB/c at any temperature, but caused a decrease in plasma corticosterone levels. Taken together we demonstrate that an increase in water temperature in the forced swim test exerts opposite effects on floating behaviour in C57BL/6J and BALB/c and renders single-housed C57BL/6J mice, but not BALB/c mice, susceptible to antidepressant-like behavioral effects of desipramine.     

C1473G polymorphism in mouse tph2 gene is linked to tryptophan hydroxylase‐2 activity in the brain,intermale aggression,and depressive‐like behavior in the forced swim test

Tryptophan hydroxylase‐2 (TPH2) is the rate‐limiting enzyme of brain serotonin synthesis. The C1473G polymorphism in the mouse tryptophan hydroxylase‐2 gene affects the enzyme's activity. In the present study, we investigated the linkage between the C1473G polymorphism, enzyme activity in the brain, and behavior in the forced swim, intermale aggression, and open field tests using mice of the C57BL/6 (C/C) and CC57BR/Mv (G/G) strains and the B6‐1473C (C/C) and B6‐1473G (G/G) lines created by three successive backcrossings on C57BL/6. Mice of the CC57BR/Mv strain had decreased brain enzyme activity, aggression intensity, and immobility in the forced swim test, but increased locomotor activity and time spent in the central part of the open field arena compared with animals of the C57BL/6 strain. Mice of the B6‐1473G line homozygous for the 1473G allele had lower TPH2 activity in the brain, aggression intensity, and immobility time in the forced swim test compared with animals of the B6‐1473C line homozygous for the 1473C allele. No differences were found between the B6‐1473G and B6‐1473C mice in locomotor activity and time spent in the central part of the arena in the open field test. Thus, the C1473G polymorphism is involved in the determination of TPH2 activity and is linked to aggression intensity and forced‐swim immobility in mice. At the same time, the polymorphism does not affect locomotion and anxiety‐related behavior in the open field test. The B6‐1473C and B6‐1473G mice represent a valuable experimental model for investigating molecular mechanisms of serotonin‐related behavior. © 2008 Wiley‐Liss, Inc.     

Dose- and time-related effects of acute diisopropylfluorophosphate intoxication on forced swim behavior and sucrose preference in rats

Acute intoxication by organophosphorus anticholinesterases (OPs) has been associated with depression and other neuropsychiatric disorders. We previously reported that adult male rats treated with diisopropylfluorophosphate (2.5 mg/kg, sc) showed acute cholinergic signs followed by changes (increased immobility/decreased swimming) in the forced swim test (a measure of behavioral despair) for at least one month. This study was conducted to evaluate the further persistence of changes in the forced swim test out to 4 months and to compare responses in a sucrose preference test, a measure of anhedonia. Adult male rats were treated with vehicle (peanut oil, 1 mL/kg, sc) or DFP (2.0, 2.25 or 2.5 mg/kg) followed by sacrifice 4 h later for measurement of OP-sensitive serine hydrolases (cholinesterase [ChE], fatty acid amide hydrolase [FAAH], and monoacylglycerol lipase [MAGL]) in hippocampus. Additional rats were treated similarly and evaluated for functional signs of acute toxicity from 30 min to 6 days, and then motor activity, forced swim behavior and sucrose preference at approximately 1 week, 1 month and 4 months after dosing. All dosages of DFP elicited serine hydrolase inhibition (ChE, 92–96 %; FAAH, 46–63 %; MAGL, 26–33 %). Body weight was reduced in all DFP-treated groups during the first two weeks, and lethality was noted with the higher dosages. Involuntary movements were elicited in all DFP treatment groups during the first week, but both time of onset and rate of recovery were dose-related. There was a significant reduction in ambulation at one week after the highest dosage (2.5 mg/kg), but no other significant locomotor changes were noted. Immobility was increased and swimming was decreased in the forced swim test at all three time-points by 2.25 mg/kg DFP, and at 2 of 3 time-points by the other dosages. While length of water deprivation and time after DFP dosing affected sucrose preference, DFP treatment had no main effect. We conclude that the forced swim test (a measure of behavioral despair/coping mechanism for inescapable stress) is a robust and persistent neurobehavioral consequence of acute DFP intoxication while sucrose preference, a measure of anhedonia and a common symptom of major clinical depression, is not affected.     

Kainate-induced epileptogenesis alters circular hole board learning strategy but not the performance of C57BL/6J mice

Patients with mesial temporal lobe epilepsy (mTLE) frequently show cognitive deficits. However, the relation between mTLE and cognitive impairment is poorly understood. To gain more insight into epilepsy-associated alterations in cognitive performance, we studied the spatial learning of C57BL/6J mice five weeks after kainate-induced status epilepticus (SE). Typically, structural hippocampal rearrangements take place within five weeks after SE. Mice were monitored by exposing them to four tasks with a focus on spatial memory and anxiety: the circular hole board, modified hole board, novel object-placement task, and elevated plus maze. On the circular hole board, animals showed a higher preference for hippocampus-independent strategies after SE. In contrast, no change in strategy was seen on the modified hole board, but animals with SE were able to finish the task more often. Animals did not have an increased preference for a relocated object in the novel object-placement task but showed an increased locomotion after SE. No indications for altered anxiety were found when tested on the elevated plus maze following SE. These data suggest that the circular hole board is a well-suited paradigm to detect subtle SE-induced hippocampal deficits.     

A single day of constant light (L/L) provides immunity to behavioral despair in female rats maintained on an L/D cycle

The present experiment investigated the potentially ameliorative effect of exposure to light in the dark phase of an 12:12 h daily lighting schedule (12L/12D cycle) on behavioral despair, an animal model of depression based on two forced swim tests separated by 24 h. Experimental groups of female Wistar rats were maintained on the 12L/12D cycle except for a single exposure to 12 h of light treatment in the dark phase of the 12L/12D cycle. Control animals were treated similarly except for light treatment. Animals then underwent one of two sets of behavioral tests starting on either the day light (or control) treatment ended (No Delay groups) or 24 h thereafter (Delay groups). The treatment for subgroups of light-treated and control animals tested with or without delay consisted of either two forced swim tests separated by 24 h or testing in the open field and elevated plus maze. Results indicated that a single exposure to a 12-h light treatment has protective effect on behavioral despair in groups tested with or without delay as measured by shorter duration of immobility in the second swim test compared to the controls. Light-treated and control animals behaved similarly in the open field and elevated plus-maze tests.     

Serotonin transporter, 5‐HT1A receptor,and behavior in DBA/2J mice in comparison with four inbred mouse strains

Prepulse inhibition (PPI), the reduction in acoustic startle produced when it is preceded by a weak prepulse stimulus, is impaired in schizophrenic patients. The DBA/2J mouse strain displayed deficient PPI and is therefore suggested as an experimental animal model for the loss of sensorimotor gating in schizophrenia. Brain serotonin (5‐HT) has been implicated in the pathophysiology of several psychiatric disorders, including major depressive disorder and schizophrenia. In the present study, behavior, 5‐HT transporter (5‐HTT) mRNA level, 5‐HT_1A receptor mRNA level, and 5‐HT_1A receptor density in the brain regions were studied in DBA/2J mice in comparison with four inbred mouse strains (CBA/Lac, C57BL/6, BALB/c, and ICR). A decrease in 5‐HTT mRNA level in the midbrain and a reduced density of 5‐HT_1A receptors in the frontal cortex without significant changes in 5‐HT_1A receptor mRNA level in DBA/2J mice were found. It was shown that, along with decreased PPI, DBA/2J mice demonstrated considerably reduced immobility in the tail suspension test and in the forced swim test. No significant interstrain differences in intermale aggression, or in light‐dark box and elevated plus‐maze tests, were found. The results suggested the involvement of decreased 5‐HTT gene expression and 5‐HT_1A receptor density in genetically defined PPI deficiency and showed a lack of any association between PPI deficiency and predisposition to aggressive, anxiety, and depressive‐like behaviors. © 2009 Wiley‐Liss, Inc.     

Ontogeny of fear-, anxiety- and depression-related behavior across adolescence in C57BL/6J mice

Adolescence is characterized by behavioral traits such as emotional lability and impulsivity that are associated with increased vulnerability to affective illness and addictions. Research in rodents has found that adolescent rats and mice differ from adults on measures of anxiety-like behavior, novelty seeking and stress-responsivity. The present study sought to extend these data by evaluating fear-, anxiety- and depression-related behaviors in male C57BL/6J mice aged four (early adolescent), six (peri-adolescent) or eight (early adult) weeks of age. Age groups were compared on: Pavlovian fear conditioning and extinction, anxiety-like behavior and exploratory locomotion (using elevated plus-maze and novel open field), and depression-related behavior (via forced swim test). Results showed that early adolescent mice exhibited enhanced fear conditioning, but extinguished at a similar rate as adults. There were no major differences in anxiety-like behavior across age groups, although early adolescent and peri-adolescent mice exhibited less exploratory locomotion than adults. Depression-related immobility behavior in the forced swim test was lower in early adolescents than adult mice across three test exposures. Present findings in the C57BL/6J inbred strain add to growing evidence of changes in rodent fear- and stress-related behaviors across the developmental transition from juvenility through adulthood. Understanding the neural basis of these ontogenic changes could provide insight into the pathogenesis and treatment of affective disorders that have their origins in adolescence.     

Short-term and long-term effects of postnatal exposure to an adult male in C57BL/6J mice

Rodent models provide a valuable approach to elucidating the pathophysiological mechanisms underlying the deleterious effects of childhood trauma and stress. Neonatal rats and mice emit ultrasonic vocalizations (USVs) when separated from the dam and litter. USVs are suppressed in rat pups by exposure to the putatively infanticidal threat of an adult male. In the present study, C57BL/6J mouse pups were exposed to an anaesthetized (non-sire) adult C57BL/6J male for 3-min/day from postnatal days 2-14, and subsequently tested for anxiety-related behaviors (using the novel open field, elevated plus-maze, light/dark exploration tests) and depression-related behavior (using the forced swim test) at 11 weeks of age. In a separate cohort, hypothalamic-pituitary-adrenal-axis activation was measured via plasma corticosterone levels following either a single male-exposure or separation episode. Results showed that pups exposed to an adult male emitted significantly fewer USVs than separation-only counterparts. Corticosterone levels were significantly lower following single exposure to the adult male than separation alone. Repeated neonatal male-exposure did not lead to significant alterations in anxiety- or depression-related behaviors in adulthood. Taken together, present data suggest that the form of adult male-exposure employed did not act as a significant stressor, at least in this mouse strain. Further studies will be needed to determine whether alternative mouse strains, exposure protocols or adult behavioral assays will produce a different pattern of short-term and long-term effects.     

Behavioural analysis of four mouse strains in an anxiety test battery

Differences in locomotor activity, exploratory activity and anxiety-like behaviour of C57BL/6ChR,C57BL/6J, Swiss Webster/J and A/J strain were investigated in an anxiety battery. The battery consisted of paradigms studying spontaneous behaviour after a mild stressor, tasks of innate anxiety (light-dark box, elevated plus maze, novel object exploration), response to a conflict situation (Vogel conflict), conditioned fear and response to inescapable swim stress. Locomotor activity was studied in an open field and compared with locomotion in the other tests. Exploratory behaviour was studied in a 16-hole board task. The data confirm previous studies suggesting that A/J mice are a relatively anxious strain. Also, the data indicated that locomotor activity was independent of the paradigm employed, while the rank order of strain-dependent effects on anxiety-related behaviour changed as a function of the task under study. Our data provide further support for the notion that choice of strain is essential in studies of anxiety-related behaviour. Influence of strain should be considered in pharmacological and lesion studies, as well as in studies with mutant mice. In addition, the data indicate that different anxiety paradigms tax different aspects of anxiety, suggesting that a battery of different tests should be used in studies of anxiety-related behaviour.     

Impaired learning in a spatial working memory version and in a cued version of the water maze in rats with MPTP-induced mesencephalic dopaminergic lesions

The inbred strain FVB/N is becoming increasingly popular to generate transgenic animals. We compared animals from this strain with well-characterized C57BL/6J animals on four different behavioral tests: the elevated plus maze test of anxiety, a standard opponent aggression test, the open-field test, and spatial learning in a radial maze. Our results indicate that FVB/N animals have slightly higher levels of anxiety and aggression, are hyperactive, and have a clear learning deficit. The latter finding seems to be related to an exceptionally small intrapyramidal and infrapyramidal mossy fiber projection. It is recommended that transgenic experiments employing this strain use F1 crosses between FVB/N and C57BL/6J as much as possible for behavioral experiments intended to evaluate spatial learning.     

Exaggerated responses to stress in the BTBR T+tf/J mouse: an unusual behavioral phenotype

This study shows that the BTBR T+tf/J mouse, a model for autism spectrum disorder (ASD), has increased levels of the stress hormone corticosterone, when compared to C57BL/6J mice. In addition, we have shown that tail suspension of the BTBR produces a heightened anxiety response in the elevated plus maze. These results suggest that the BTBR mouse is stressor-reactive exhibiting hormone responses that might predispose it to ASD.     

Antidepressant-like effects of ceftriaxone in male C57BL/6J mice.

BACKGROUND: Excessive glutamatergic neurotransmission is hypothesized to be associated with depressive-like behaviors and possibly major depressive disorder (MDD). Recent evidence that beta-lactam antibiotic agents stimulate uptake of glutamate suggests that this class of compounds might possess antidepressant-like activity. METHODS: Three-month old, male, C57BL/6J mice were administered ceftriaxone (200 mg/kg IP) for 14-18 days, then tested in the tail-suspension, forced swim, and novelty-suppressed feeding tests to determine whether ceftriaxone had similar effects to classical antidepressant compounds in these models. RESULTS: Ceftriaxone treatment had an antidepressant-like effect across models. Reduced immobility and decreased freezing were observed in the forced swim and tail suspension tests. The same trend was seen in novelty-suppressed feeding, but the effect was not statistically significant. CONCLUSION: Ceftriaxone demonstrates antidepressant-like effects in several mouse models. This is consistent with the hypothesis that enhanced uptake of glutamate might have antidepressant-like effects.     

Reduced saccharin preference in CXBK (opioid receptor-deficient) mice

The preference for sweet solutions in opioid receptor-deficient (CXBK) and control (C57BL/6By) mice was compared. CXBK and C57BL/6By (C57) mice were presented for 2 h/day with 2 tubes, one always containing water and the other containing either water or various concentrations of saccharin solution. Fifteen minutes before the drinking session, half of the mice in each strain were injected with naltrexone (0.2 mg/kg) and the other half with saline. Compared to C57 mice, CXBK mice had significantly lower saccharin preference. Naltrexone reduced the saccharin preference in both strains, almost completely abolishing preference in CXBK mice. The results support the hypothesis that brain opioid receptors are involved in mediating sweet palatability and suggest that genetic differences in opioid receptor density contribute to differences in the palatability of sweet solutions.     

Central effects of a local inflammation in three commonly used mouse strains with a different anxious phenotype

As in humans, genetic background in rodents may influence a peculiar set of behavioural traits such as sensitivity to pain and stressors or anxiety-related behaviours. Therefore, we tested the hypothesis that mice with different genetic backgrounds [outbred (CD1), inbred (C57BL/6J) and hybrid (B6C3F1) adult male mice] display altered reactivity to pain, stress and anxiety related behaviours.We demonstrated that B6C3F1 mice displayed the more anxious phenotype with respect to C57BL/6J or CD1 animals, with the latter being the less anxious strain when tested in an open field and on an elevated plus maze. No difference was observed across strains in thermal sensitivity to a radiant heat source. Mice were then treated with a sub-plantar injection of the inflammatory agent Complete Freund's Adjuvant (CFA), 24 h later they were hyperalgesic with respect to saline exposed animals, irrespective of strain. We then measured intra-strain differences and CFA-induced inter-strain effects on the expression of various genes with a recognized role in pain and anxiety: BDNF, IL-6, IL-1β, IL-18 and NMDA receptor subunits in the mouse thalamus, hippocampus and hypothalamus. The more anxious phenotype observed in B6C3F1 hybrid mice displayed lower levels of BDNF mRNA in the hippocampus and hypothalamus when compared to outbred CD1 and C57BL/6J inbred mice. CFA led to a general decrease in central gene expression of the evaluated targets especially in CD1 mice, while BDNF hypothalamic downregulation stands out as a common effect of CFA in all three strains evaluated.     

Lowering barometric pressure aggravates depression-like behavior in rats

Weather change has been known to influence the condition of patients with mood disorder. However, no animal studies have tested the influence of climatic factor on emotional impairment. In this study, we examined the effect of lowering barometric pressure (LP) in a climate-controlled room on immobility time in the forced swim test in rats, which is considered to be an index of behavioral despair (helplessness). When the rats were exposed to daily repeated forced swim, the immobility time gradually increased. This increment was inhibited by repeated administration of the antidepressant imipramine, suggesting that the immobility is an anxiety/depression-like behavior. LP exposure (20 hPa below the natural atmospheric pressure) further increased immobility time in rats submitted to repeated forced swim. In another series of experiments, we examined the effect of daily repeated LP exposure on the maintenance of immobility after withdrawal from 6-day repeated forced swim. When the rats were challenged with forced swim under natural atmospheric pressure on day 14 after the withdrawal, immobility time was significantly longer than in non-conditioned rats. These findings demonstrated that LP in the range of natural weather change augmented the depression-like behavior in rats.     

MHC-congenic mice (C57BL/6J and B6-H-2K) show differences in speed but not accuracy in learning the Hebb-Williams Maze

We compared spatial learning and memory in male and female mice of two MHC-congenic strains (C57BL/6J and B6-H-2K) in two versions of the Hebb-Williams Maze. In the food-reward paradigm, males required fewer sessions to learn than females, but there were no strain differences in acquisition. There were no strain or sex differences in the number of errors during the test phase, but the B6-H-2K mice reached the goal box faster than the C57BL/6J mice. In the water-escape paradigm, the C57BL/6J mice required more sessions than the B6-H-2K mice during acquisition. There were no strain or sex differences in the number of errors or in the latency to swim to the goal box in the test phase of the water-escape task. There were no significant correlations between the number of sessions to learn the two mazes; the number of errors made or the latencies to reach the goal box in each maze. These results indicate that these two strains show differences in performance in the Hebb-Williams Maze, but do not differ in cognitive ability.