Artur H. Swiergiel

Effects of Interleukin-1β and Lipopolysaccharide on Behavior of Mice in the Elevated Plus-Maze and Open Field Tests

It has been postulated that infections, inflammatory processes and resulting cytokines may be causative factors in emotional disorders, including depression and anxiety. Support for this possibility has been sought in studies of animal behavior following administration of interleukin-1 (IL-1) and lipopolysaccharide (LPS). However, such treatments induce a variety of behavioral responses, collectively known as sickness behavior, some of which could affect the performance in tests used to assess anxiety and depression. Thus the effects of peripheral administration of IL-1beta and LPS on the behavior of mice were studied in the elevated plus-maze (EPM) and the open field (OF). Mouse IL-1beta (30, 100, 300, and 1000 ng) was injected intraperitoneally 30 or 60 min, and LPS (0.5, 1 and 5 microg) 120 min before the tests. IL-1beta and LPS induced dose-dependent decreases in open arm entries and the time spent on the open arms in the EPM, effects considered to reflect anxiety-like behavior. However, entries to all arms were also reduced in a dose-dependent manner, indicating a decrease in general activity. In the OF, IL-1beta and LPS decreased the number of line crossings in the center of the field, that can also be considered to reflect anxiety-like behavior. However, this effect was accompanied by a similar decrease in line crossings in the periphery, as well as in rears and climbs. Thus the doses of IL-1beta and LPS necessary to induce these effects also decreased locomotor activity in the EPM and OF. Therefore, the behavioral responses induced by IL-1beta and LPS in the EPM and the OF considered to reflect anxiety must be interpreted in the light of this reduction in overall activity. Thus the results do not provide unequivocal support for the suggestion that LPS or IL-1 mediate anxiety. Nevertheless, because infections, endotoxins, and the ensuing cytokines cause alterations in CNS norepinephrine and serotonin, they may contribute to emotionality, and perhaps to anxiety.

Brain Circuits Involved in Corticotropin‐Releasing Factor‐Norepinephrine Interactions during Stress

Abstract: Corticotropin‐releasing factor (CRF)‐ and norepinephrine (NE)‐containing neurons in the brain are activated during stress, and both have been implicated in the behavioral responses. NE neurons in the brain stem can stimulate CRF neurons in the hypothalamic paraventricular nucleus (PVN) to activate the hypothalamic‐pituitary‐adrenocortical axis and may affect other CRF neurons. CRF‐containing neurons in the PVN, the amygdala, and other brain areas project to the area of the locus coeruleus (LC), and CRF injected into the LC alters the electrophysiologic activity of LC‐NE neurons. Neurochemical studies have indicated that CRF applied intracerebroventricularly or locally activates the LC‐NE system, and microdialysis and chronoamperometric measurements indicate increased NE release in LC‐NE terminal fields. However, chronoamperometric studies indicated a significant delay in the increase in NE release, suggesting that the CRF input to LC‐NE neurons is indirect. The reciprocal interactions between cerebral NE and CRF systems have been proposed to create a “feed‐forward” loop. It has been postulated that a sensitization of such a feed‐forward loop may underlie clinical depression. However, in the majority of studies, repeated or chronic stress has been shown to decrease the behavioral and the neurochemical responsivity to acute stressors. Repeated stress also seems to decrease the responsivity of LC neurons to CRF. These results do not provide support for a feed‐forward hypothesis. However, a few studies using certain tasks have indicated sensitization, and some other studies have suggested that the effect of CRF may be dose dependent. Further investigations are necessary to establish the validity or otherwise of the feed‐forward hypothesis.

The role of corticotropin-releasing factor and noradrenaline in stress-related responses, and the inter-relationships between the two systems

Substantial evidence indicates that brain neurons containing and secreting noradrenaline and corticotropin-releasing factor (CRF) are activated during stress, and that physiological and behavioural responses observed during stress can be induced by exogenous administration of CRF and adrenoceptor agonists. This review focusses on the evidence for the involvement of these two factors in stress-related responses, and the inter-relationships between them. The possible abnormalities of these two systems in depressive illness are also discussed.

Effects of chronic and acute stressors and CRF on depression-like behavior in mice

The effects of chronic footshock (CFS) on behavioral responses of CD1 mice to acute footshock and restraint were studied in tests commonly used to assess antidepressant treatments. Adult male mice were subjected to 20 min of footshock daily for 14-16 days, and then tested in the tail suspension test (TST) and the forced swim test (FST). CFS treatment did not alter immobility in the TST when mice were tested before the footshock on that day. However, when the TST was performed after the footshock, immobility decreased in both control and CFS mice. In the FST, chronic footshock significantly increased the time spent floating when mice were tested before footshock on that day. However, when the FST was performed immediately after the footshock, floating decreased in the CFS mice, but not in previously unshocked mice. Restraint, shortly before the FST, decreased floating in both CFS and unshocked mice. Thus, CFS induced depression-like activity in the FST, but not in the TST, whereas acute footshock or restraint immediately before testing induced antidepressant-like effects in both the TST and the FST. In unshocked mice, intracerebroventricular corticotropin-releasing factor (CRF) consistently decreased immobility in the TST and the FST, with significant effects at the 100ng dose. The same dose of CRF depressed activity in the open field, so that these changes in immobility are unlikely to reflect a change in overall activity. CRF thus mimicked the effects of the acute stressors in the TST and the FST. Responses to icv CRF were attenuated by chronic footshock suggesting that CFS desensitizes the brain to CRF. CFS treatment did not alter basal concentrations of ACTH and corticosterone in blood plasma. Acute footshock increased the plasma concentrations of the hormones but in CFS mice these responses were attenuated, significantly for plasma ACTH. Acute footshock activated brain dopamine, norepinephrine and serotonin metabolism, and increased tryptophan concentrations in the brain. In CFS mice, these responses were attenuated, significantly for hypothalamic NE.

The Reductions in Sweetened Milk Intake Induced by Interleukin-1 and Endotoxin Are Not Prevented by Chronic Antidepressant Treatment

Administration of interleukin-1 (IL-1) and endotoxin (lipopolysaccharide, LPS) to rodents can decrease food intake, a behavioral response resembling the diminution of appetite observed in human depression. IL-1 and LPS are known to affect cerebral neurotransmission involving norepinephrine and serotonin, both of which have been implicated in feeding behavior and in the pharmacotherapy of depression in man. The ability of chronic antidepressant treatment to attenuate LPS-induced depressed feeding in rats has been cited as evidence that cytokines may be involved in human depression. Thus, we studied the effects of chronic treatment with the tricyclic antidepressant, imipramine, and the novel antidepressant, venlafaxine, on the sweetened milk intake challenged with intraperitoneally injected IL-1β and LPS. Chronic (from 2 to 8 weeks) treatment of the mice with imipramine (10 mg/kg once or twice daily) or venlafaxine (10 and 20 mg/kg/day) did not significantly alter the decreases in milk intake in response to mIL-1β or LPS. In some experiments, chronic imipramine slightly decreased body weight and slightly increased milk intake, but not food pellet intake. Venlafaxine had none of these effects. Analysis of variance did not indicate any significant interactions between the antidepressant and IL-1 or LPS treatments. These results indicate that chronic treatment with antidepressants does not significantly alter the responses to IL-1 or LPS in the mouse sweetened milk model of sickness behavior.

Effects of acute and chronic stressors and CRF in rat and mouse tests for depression.

Depressive illness is frequently associated with life stress. Corticotropin‐releasing factor (CRF) is believed to be a key brain mediator of behaviors associated with stress, and abnormalities in the function of CRF have been associated with depression. Therefore, we have studied the effects of acute and chronic footshock and restraint in tests used in rodents to assess depression‐like activity and antidepressant effects: the forced swim test in rats and mice, and the tail suspension test in mice. We also tested the effect of intracerebroventricular (icv) CRF administration. The results were complex. In the forced swim test in rats, acute footshock and restraint reduced floating, whereas chronic footshock increased floating as did icv CRF. However, chronic restraint induced opposite effects, decreasing floating in the forced swim test. The results from mice were significantly different. In the forced swim test, acute footshock and restraint decreased floating, while chronic footshock increased floating, and chronic restraint decreased floating as it did in rats. However, icv CRF decreased floating. The results from the tail‐suspension test paralleled those from the forced swim test except that chronic footshock tended to decrease the time spent immobile. Thus in rats, the behavioral effects of the chronic footshock in the forced swim test could be explained by a desensitization of the CRF systems, either decreased activation of CRF, or desensitization of its receptors. However, such an effect cannot explain the responses to restraint, nor the behavioral effects of chronic footshock and restraint in mice.

The usage of video analysis system for detection of immobility in the tail suspension test in mice.

The Tail Suspension Test (TST) is a commonly used screening method for antidepressants properties of drugs in mice. To date, immobility in the TST was scored live, by an observer, or automatically, using devices in which mouse movements were detected by a strain gauge. In this study we tested whether the EthoVision video analysis system can be used reliably and accurately for automatic recording and scoring of duration of immobility in the TST. First, the duration of immobility in two mouse lines was assessed. Different mobility thresholds of the video analysis system were applied and the results compared with the duration of immobility scored manually. Next, the selected immobility threshold was applied to determine the dose-response curves for the drug venlafaxine. Finally, scores from the video analysis system were compared with scores generated by an electromechanical strain gauge device (Med Associates) and a human rater. It was found that the EthoVision system could reliably and accurately quantify the duration of immobility in the TST. The best setup was an immobility threshold ranging from 2 to 3 percentage change in the object area. The EthoVision system was effective in detecting the differences between the mouse lines and the dose response to venlafaxine. The results obtained using the video analysis system were similar to the scores yielded by a human rater and the strain gauge device.

Reduced Ingestion of Sweetened Milk Induced by Interleukin-1 and Lipopolysaccharide Is Associated with Induction of Cyclooxygenase-2 in Brain Endothelia

Previous studies have shown that interleukin-1 (IL-1) and lipopolysaccharide (LPS) administration to animals induces behavioral changes, including a reduction in feeding. These effects of IL-1 and LPS have been shown to be sensitive to inhibitors of cyclooxygenase (COX). Objectives: To determine the relationships between induction of COX-2 in the brain with IL-1β- and LPS-induced changes in body temperature, plasma corticosterone and feeding. Methods: Mice were injected with intraperitoneal doses of IL-1β and LPS that decreased feeding. The induction of COX-2 was studied immunocytochemically in the brain, in parallel with core body temperature, the drinking of sweetened milk, and plasma concentrations of corticosterone. Results: COX-2 immunoreactivity (ir) was sparse in the brains of the untreated mice, but IL-1β and LPS both increased its expression. This COX-2 induction appeared to be confined to blood vessels, and was not markedly region specific. Induction was evident 30 min after IL-1 or LPS, and was greater at 90 than at 30 min. COX-2-ir in the parenchyma did not change significantly. Thus induction of COX-2 occurred in brain endothelia in parallel with the reduction in feeding. This is consistent with the previously determined sensitivity of IL-1-induced changes in feeding to selective COX-2 inhibitors, and the responses to IL-1 in COX-2-deficient mice. The time courses of the IL-1- and LPS-induced increases in plasma corticosterone paralleled those in the reduction in milk drinking, however, the changes in body temperature appeared later. Conclusions: Endothelial COX-2 may be involved in IL-1- and LPS-induced decreases in milk drinking, and possibly in the HPA axis activation. The decreased milk drinking may occur when IL-1 and LPS bind to receptors on brain endothelial cells subsequently inducing COX-2 and the production of prostanoids which elicit the reductions in milk drinking. Thus the behavioral effects of peripherally administered IL-1 and LPS appear to be mediated by multiple mechanisms, including endothelial COX-2, and vagal afferents.

Stress susceptibility-specific phenotype associated with different hippocampal transcriptomic responses to chronic tricyclic antidepressant treatment in mice.

BackgroundThe effects of chronic treatment with tricyclic antidepressant (desipramine, DMI) on the hippocampal transcriptome in mice displaying high and low swim stress-induced analgesia (HA and LA lines) were studied. These mice displayed different depression-like behavioral responses to DMI: stress-sensitive HA animals responded to DMI, while LA animals did not.ResultsTo investigate the effects of DMI treatment on gene expression profiling, whole-genome Illumina Expression BeadChip arrays and qPCR were used. Total RNA isolated from hippocampi was used. Expression profiling was then performed and data were analyzed bioinformatically to assess the influence of stress susceptibility-specific phenotypes on hippocampal transcriptomic responses to chronic DMI. DMI treatment affected the expression of 71 genes in HA mice and 41 genes in LA mice. We observed the upregulation of Igf2 and the genes involved in neurogenesis (HA: Sema3f, Ntng1, Gbx2, Efna5, and Rora; LA: Otx2, Rarb, and Drd1a) in both mouse lines. In HA mice, we observed the upregulation of genes involved in neurotransmitter transport, the termination of GABA and glycine activity (Slc6a11, Slc6a9), glutamate uptake (Slc17a6), and the downregulation of neuropeptide Y (Npy) and corticotropin releasing hormone-binding protein (Crhbp). In LA mice, we also observed the upregulation of other genes involved in neuroprotection (Ttr, Igfbp2, Prlr) and the downregulation of genes involved in calcium signaling and ion binding (Adcy1, Cckbr, Myl4, Slu7, Scrp1, Zfp330).ConclusionsSeveral antidepressant treatment responses are similar in individuals with different sensitivities to stress, including the upregulation of Igf2 and the genes involved in neurogenesis. However, the findings also reveal that many responses to antidepressant treatments, involving the action of individual genes engaged in neurogenesis, neurotransmitter transport and neuroprotection, depend on constitutive hippocampal transcriptomic profiles and might be genotype dependent. The results suggest that, when and if this becomes feasible, antidepressant treatment should take into consideration individual sensitivity to stress.

Effects of chlordiazepoxide on footshock- and corticotropin-releasing factor-induced increases in cortical and hypothalamic norepinephrine secretion in rats.

Noradrenergic and corticotropin-releasing factor (CRF) neuronal systems within the brain have been implicated in stress and anxiety. Synaptic release of cerebral norepinephrine (NE) is increased during stress, and following intracerebral CRF administration. Benzodiazepines are commonly used anxiolytic drugs but information on their effects on the stress- and CRF-related release of NE is limited. We have used in vivo microdialysis to test the effects of the benzodiazepine, chlordiazepoxide (CDP) on the noradrenergic responses to footshock and intracerebroventricular CRF in the medial hypothalamus and the medial prefrontal cortex (PFM) of freely moving rats. Footshock (60 x 0.1-0.2 mA shocks in 20 min) significantly increased microdialysate concentrations of NE in the first sample collected after initiating the footshock. In the hypothalamus, microdialysate NE was augmented 64% above baseline. A second footshock session (100 min after the first footshock) increased microdialysate NE to 313% of the baseline. Thus the noradrenergic responses to footshock were enhanced by preceding footshocks. CRF (100 ng) administered into the locus coeruleus (LC) almost tripled microdialysate concentrations of NE in the PFM. CDP (5mg/kg, i.p.) had no statistically significant effects on the basal dialysate concentrations of NE, but it significantly attenuated both footshock- and CRF-induced increases in dialysate NE. CDP may exert a direct inhibitory effect on the noradrenergic neurons, alter the input to LC noradrenergic neurons, or alter the ability of CRF to activate the LC noradrenergic system.