Bacillus Calmette-Guérin vaccine induces a selective serotonin reuptake inhibitor (SSRI)-resistant depression like phenotype in mice

Lycopene alleviates BCG-induced depressive phenotypes in mice by disrupting 5-HT3 receptor - IDO1 interplay in the brain

The 5-HT3 receptor and indoleamine 2,3-dioxygenase 1 (IDO1) enzyme play a crucial role in the pathogenesis of depression as their activation reduces serotonin contents in the brain. Since molecular docking analysis revealed lycopene as a potent 5-HT3 receptor antagonist and IDO1 inhibitor, we hypothesized that lycopene might disrupt the interplay between the 5-HT3 receptor and IDO1 to mitigate depression. In mice, the depression-like phenotypes were induced by inoculating Bacillus Calmette-Guerin (BCG). Lycopene (intraperitoneal; i.p.) was administered alone or in combination with 5-HT3 receptor antagonist ondansetron (i.p.) or IDO1 inhibitor minocycline (i.p.), and the behavioral screening was performed by the sucrose preference test, open field test, tail suspension test, and splash test which are based on the different principles. Further, the brains were subjected to the biochemical analysis of serotonin and its precursor tryptophan by the HPLC. The results showed depression-like behavior in BCG-inoculated mice, which was reversed by lycopene administration. Moreover, prior treatment with ondansetron or minocycline potentiated the antidepressant action of lycopene. Minocycline pretreatment also enhanced the antidepressant effect of ondansetron indicating the regulation of IDO1 activity by 5-HT3 receptor-triggered signaling. Biochemical analysis of brain samples revealed a drastic reduction in the levels of tryptophan and serotonin in depressed animals, which were restored following treatment with lycopene and its combination with ondansetron or minocycline. Taken together, the data from molecular docking, behavioral experiments, and biochemical estimation suggest that lycopene might block the 5-HT3 receptor and consequently inhibit the activity of IDO1 to ameliorate BCG-induced depression in mice.

Bacillus calmette gaurine vaccine ameliorates the neurotoxicity of quinolinic acid in rats via the modulation of antioxidant, inflammatory and apoptotic markers

A mutation in the Huntingtin gene causes 'Huntington's disease, which presents as a motor and behavioral impairment. Due to the limited drug therapy for this disease, scientists are constantly searching for newer and alternative drugs that may either retard or prevent the progress of the disease. This study aims to explore the neuroprotective potential of Bacillus Calmette Gaurine (BCG) vaccine against quinolinic acid-induced (QA) neurotoxicity in rats. QA (200 nmol/2 µl, i.s) was injected bilaterally into the rat striatum, after which a single dose of BCG (2 × 10^7, cfu) was given to the rats. Animals were assessed for behavioral parameters on the 14th and 21st days. On the 22nd day, animals were sacrificed, brains were harvested, and striatum was separated to evaluate biochemical, inflammatory, and apoptotic mediators. Histopathological studies were performed using Hematoxyline and Eosin staining to assess neuronal morphology. BCG treatment reversed motor abnormalities, reduced oxidative stress and neuroinflammatory markers, apoptotic mediators and striatal lesions induced by QA treatment. In conclusion, treat' 'ing rats with BCG vaccine (2 × 10^7, cfu) mitigated the quinolinic acid-induced Huntington's disease-like symptoms. Hence, BCG vaccine (2 ×10^7, cfu) could be used as an adjuvant in managing HD.

Chronic Mycobacterium avium infection differentially affects the cytokine expression profile of three mouse strains, but has no effect on behavior

One of the most remarkable findings in the immunology and neuroscience fields was the discovery of the bidirectional interaction between the immune and the central nervous systems. This interplay is tightly regulated to maintain homeostasis in physiological conditions. Disruption in this interplay has been suggested to be associated with several neuropsychiatric disorders. Most studies addressing the impact of an immune system disruption on behavioral alterations focus on acute pro-inflammatory responses. However, chronic infections are highly prevalent and associated with an altered cytokine milieu that persists over time. Studies addressing the potential effect of mycobacterial infections on mood behavior originated discordant results and this relationship needs to be further addressed. To increase our understanding on the effect of chronic infections on the central nervous system, we evaluated the role of Mycobacterium avium infection. A model of peripheral chronic infection with M. avium in female from three mouse strains (Balb/c, C57BL/6, and CD-1) was used. The effect of the infection was evaluated in the cytokine expression profile (spleen and hippocampus), hippocampal cell proliferation, neuronal plasticity, serum corticosterone production and mood behavior. The results show that M. avium peripheral chronic infection induces alterations not just in the peripheral immune system but also in the central nervous system, namely in the hippocampus. Interestingly, the cytokine expression profile alterations vary between mouse strains, and are not accompanied by hippocampal cell proliferation or neuronal plasticity changes. Accordingly, no differences were observed in locomotor, anxious and depressive-like behaviors, in any of the mouse strains used. We conclude that the M. avium 2447 infection-induced alterations in the cytokine expression profile, both in the periphery and the hippocampus, are insufficient to alter hippocampal plasticity and behavior.

The Potential Antidepressant Action of Duloxetine Co-Administered with the TAAR1 Receptor Agonist SEP-363856 in Mice

Here, we explored the possible interaction between duloxetine and SEP-363856 (SEP-856) in depression-related reactions. The results showed that oral administration of duloxetine showed powerful antidepressant-like effects in both the forced swimming test (FST) and the suspension tail test (TST). SEP-856 orally administered alone also exerted an antidepressant-like effect in FST and TST, especially at doses of 0.3, 1, and 10 mg/kg. In addition, duloxetine (15 mg/kg) and SEP-856 (15 mg/kg) both showed antidepressant-like effects in the sucrose preference test (SPT). Most importantly, in the above experiments, compared with duloxetine alone, the simultaneous use of duloxetine and SEP-856 caused a more significant antidepressant-like effect. It is worth noting that doses of drug combination in FST and TST did not change the motor activities of mice in the open-field test (OFT). Thus, duloxetine and SEP-856 seem to play a synergistic role in regulating depression-related behaviors and might be beneficial for refractory depression.

Efficacy of BCG vaccine in animal models of neurological disorders

The Bacillus Calmette-Guerin (BCG) vaccine can modulate the immune response via antigen-specific immune response, but also it can confer nonspecific protection and therapeutic benefits in several neurological conditions through different heterologous effects of vaccination. However, the precise mechanism of action of BCG remains unclear. In this review, different mechanisms underlying BCG-mediated immunity will be explained in animal models that reflects characteristic feature of neuroinflammatory and neurodegenerative disorders such as multiple sclerosis, Alzheimer's and Parkinson's diseases. Furthermore, evidence for a beneficial effect of the BCG on neuropsychiatric disorders, will be also discussed.

Immunoregulation and antidepressant effect of ketamine

Major depressive disorder (MDD) is a common mental health disorder that brings severe disease burden worldwide. Traditional antidepressants are mainly targeted at monoamine neurotransmitters, with low remission rates and high recurrence rates. Ketamine is a noncompetitive glutamate N-methyl-d-aspartate receptor (NMDAR) antagonist, and its rapid and powerful antidepressant effects have come to light. Its antidepressant mechanism is still unclarified. Research found that ketamine had not only antagonistic effect on NMDAR but also strong immunomodulatory effect, both of which were closely related to the pathophysiology of MDD. Although there are many related studies, they are relatively heterogeneous. Therefore, this review mainly describes the immune mechanisms involved in MDD and how ketamine plays an antidepressant role by regulating peripheral and central immune system, including peripheral inflammatory cytokines, central microglia, and astrocytes. This review summarizes the related research, finds out the deficiencies of current research, and provides ideas for future research and the development of novel antidepressants.

A Review on Potential Footprints of Ferulic Acid for Treatment of Neurological Disorders

Ferulic acid is being screened in preclinical settings to combat various neurological disorders. It is a naturally occurring dietary flavonoid commonly found in grains, fruits, and vegetables such as rice, wheat, oats, tomatoes, sweet corn etc., which exhibits protective effects against a number of neurological diseases such as epilepsy, depression, ischemia-reperfusion injury, Alzheimer's disease, and Parkinson's disease. Ferulic acid prevents and treats different neurological diseases pertaining to its potent anti-oxidative and anti-inflammatory effects, beside modulating unique neuro-signaling pathways. It stays in the bloodstream for longer periods than other dietary polyphenols and antioxidants and easily crosses blood brain barrier. The use of novel drug delivery systems such as solid-lipid nanoparticles (SLNs) or its salt forms (sodium ferulate, ethyl ferulate, and isopentyl ferulate) further enhance its bioavailability and cerebral penetration. Based on reported studies, ferulic acid appears to be a promising molecule for treatment of neurological disorders; however, more preclinical (in vitro and in vivo) mechanism-based studies should be planned and conceived followed by its testing in clinical settings.

Protective Effect of Sphaerococcus coronopifolius Crude Extract in Combination with Bacillus Calmette-Guerin on Ligature-Induced Depression in Female Wistar Rats

OBJECTIVE

Immunomodulation is a therapeutic technique that modulates the balance of cytokines in the body. In this regard, our experiment was conducted to investigate the potential effect of S. coronopifolius crude extract in combination with low dose of Bacillus Calmette-Guerin (BCG) on depression-like behaviors in female Wistar rats.

METHODS

Sciatic nerve injury was employed to induce depression and intradermal injection of 0.02 mL of BCG per rat was administered to lead an activation of innate immune system. Daily intra-peritoneal injections of 25 mg algae extract kg-1 body weight were performed for 14 continuous days. Forced Swimming (FS) and Open Field (OF) tests were conducted to assess despairing and spontaneous behaviors. At the end of the experiment, brain was removed to determine the activities of catalase (CAT) and glutathione-S-transferase (GST), whereas spleen and adrenals were used for the histopathological study.

RESULTS

The combined treatment exhibited antidepressant-like activity in FST by reducing immobility time, without inducing any significant change in ambulatory behavior in OFT. The histological analyses of spleen and adrenal structure showed a conserved architecture.

CONCLUSION

The results suggested that algae extract produce an antidepressant-like effect in combination with low dose of BCG, which is possibly trigged by its anti-oxidant and anti-inflammatory properties.

Diminished responses to monoaminergic antidepressants but not ketamine in a mouse model for neuropsychiatric lupus

BACKGROUND

A significant proportion of patients suffering from major depression fail to remit following treatment and develop treatment-resistant depression. Developing novel treatments requires animal models with good predictive validity. MRL/lpr mice, an established model of systemic lupus erythematosus, show depression-like behavior.

AIMS

We evaluated responses to classical antidepressants, and associated immunological and biochemical changes in MRL/lpr mice.

METHODS AND RESULTS

MRL/lpr mice showed increased immobility in the forced swim test, decreased wheel running and sucrose preference when compared with the controls, MRL/MpJ mice. In MRL/lpr mice, acute fluoxetine (30 mg/kg, intraperitoneally (i.p.)), imipramine (10 mg/kg, i.p.) or duloxetine (10 mg/kg, i.p.) did not decrease the immobility time in the Forced Swim Test. Interestingly, acute administration of combinations of olanzapine (0.03 mg/kg, subcutaneously)+fluoxetine (30 mg/kg, i.p.) or bupropion (10 mg/kg, i.p.)+fluoxetine (30 mg/kg, i.p.) retained efficacy. A single dose of ketamine but not three weeks of imipramine (10 mg/kg, i.p.) or escitalopram (5 mg/kg, i.p.) treatment in MRL/lpr mice restored sucrose preference. Further, we evaluated inflammatory, immune-mediated and neuronal mechanisms. In MRL/lpr mice, there was an increase in autoantibodies' titers, [3H]PK11195 binding and immune complex deposition. There was a significant infiltration of the brain by macrophages, neutrophils and T-lymphocytes. p11 mRNA expression was decreased in the prefrontal cortex. Further, there was an increase in the 5-HT_2aR expression, plasma corticosterone and indoleamine 2,3-dioxygenase activity.

CONCLUSION

In summary, the MRL/lpr mice could be a useful model for Treatment Resistant Depression associated with immune dysfunction with potential to expedite antidepressant drug discovery.

Chronic infection with Mycobacterium lepraemurium induces alterations in the hippocampus associated with memory loss

Murine leprosy, caused by Mycobacterium lepraemurium (MLM), is a chronic disease that closely resembles human leprosy. Even though this disease does not directly involve the nervous system, we investigated a possible effect on working memory during this chronic infection in Balb/c mice. We evaluated alterations in the dorsal region of the hippocampus and measured peripheral levels of cytokines at 40, 80, and 120 days post-infection. To evaluate working memory, we used the T-maze while a morphometric analysis was conducted in the hippocampus regions CA1, CA2, CA3, and dentate gyrus (DG) to measure morphological changes. In addition, a neurochemical analysis was performed by HPLC. Our results show that, at 40 days post-infection, there was an increase in the bacillary load in the liver and spleen associated to increased levels of IL-4, working memory deterioration, and changes in hippocampal morphology, including degeneration in the four subregions analyzed. Also, we found a decrease in neurotransmitter levels at the same time of infection. Although MLM does not directly infect the nervous system, these findings suggest a possible functional link between the immune system and the central nervous system.

Time of Administration of Acute or Chronic Doses of Imipramine Affects its Antidepressant Action in Rats

The pathogenesis and therapeutics of depression are linked to the operation of the circadian system. Here, we studied the chronopharmacological action of a tricyclic antidepressant, imipramine. Male adult Wistar–Hannover rats were administered imipramine acutely or chronically in the morning or in the evening. The antidepressant action of imipramine was analyzed using the forced swim test (FST). A single dose of imipramine (30 mg/kg) in the morning, but not in the evening, reduced immobility and increased climbing in the FST. The plasma concentrations of imipramine and its metabolite, desipramine, were slightly higher in the morning than in the evening, which might explain the dosing time-dependent action of imipramine. Next, we analyzed the effect of chronic imipramine treatment. Rats received imipramine in the morning or in the evening for 2 weeks. The morning treatment resulted in larger effects in the FST than the evening treatment, and was effective at a dose that was ineffective when administered acutely. The levels of brain α-adrenergic receptors tended to decrease after chronic imipramine treatment. Imipramine might interact with noradrenergic neurons, and this interaction might chronically alter receptor expression. This alteration seemed greater in the morning than in the evening, which might explain the dosing time-dependent action of imipramine.

Desipramine decreases expression of human and murine indoleamine-2,3-dioxygenases

Abundant evidence connects depression symptomology with immune system activation, stress and subsequently elevated levels of kynurenine. Anti-depressants, such as the tricyclic norepinephrine/serotonin reuptake inhibitor desipramine (Desip), were developed under the premise that increasing extracellular neurotransmitter level was the sole mechanism by which they alleviate depressive symptomologies. However, evidence suggests that anti-depressants have additional actions that contribute to their therapeutic potential. The Kynurenine Pathway produces tryptophan metabolites that modulate neurotransmitter activity. This recognition identified another putative pathway for anti-depressant targeting. Considering a recognized role of the Kynurenine Pathway in depression, we investigated the potential for Desip to alter expression of rate-limiting enzymes of this pathway: indoleamine-2,3-dioxygenases (Ido1 and Ido2). Mice were administered lipopolysaccharide (LPS) or synthetic glucocorticoid dexamethasone (Dex) with Desip to determine if Desip alters indoleamine-dioxygenase (DO) expression in vivo following a modeled immune and stress response. This work was followed by treating murine and human peripheral blood mononuclear cells (PBMCs) with interferon-gamma (IFNγ) and Desip. In vivo: Desip blocked LPS-induced Ido1 expression in hippocampi, astrocytes, microglia and PBMCs and Ido2 expression by PBMCs. Ex vivo: Desip decreased IFNγ-induced Ido1 and Ido2 expression in murine PBMCs. This effect was directly translatable to the human system as Desip decreased IDO1 and IDO2 expression by human PBMCs. These data demonstrate for the first time that an anti-depressant alters expression of Ido1 and Ido2, identifying a possible new mechanism behind anti-depressant activity. Furthermore, we propose the assessment of PBMCs for anti-depressant responsiveness using IDO expression as a biomarker.

Adjuvant quercetin therapy for combined treatment of epilepsy and comorbid depression

Epilepsy is one of the major neurological disorders frequently associated with psychiatric disorders such as depression. The predisposition of tryptophan metabolism towards kynurenine pathway has been reported as one of the plausible reasons for association of depression in epilepsy. Hence, this study was envisaged to evaluate the dose dependent inhibition of indoleamine 2,3-dioxygenase (IDO) enzyme employing quercetin (screened employing in vitro method) with levetiracetam for combined management of epilepsy and comorbid depression. Kindling was induced in male swiss albino mice by administration of pentylenetetrazole subconvulsive doses (35 mg/kg, i.p.) at an interval of 48 ± 2 h. Kindled animals were treated with vehicle, levetiracetam (40 mg/kg/day i.p.) levetiracetam in combination with different doses of quercetin (10 mg/kg; 20 mg/kg; 40 mg/kg)/day/p.o. for 15 days. Except naïve, all the groups were challenged with pentylenetetrazole (35 mg/kg i.p.) on day 5, 10, and 15 to evaluate the seizure severity score. Depression was evaluated in all experimental groups using the tail suspension and sucrose preference test on days 1, 5, 10 and 15, 2 h after pentylenetetrazole challenge. Results suggested that vehicle treated kindled animals were significantly associated with depression. Chronic levetiracetam treatment significantly reduced seizure severity score, but further worsened the associated depression. Quercetin supplementation with levetiracetam dose dependently ameliorated depression associated with epilepsy. Neurochemical and biochemical findings also supported the behavioural findings of the study. Thus, our results suggested that supplementation of quercetin with levetiracetam could be explored further for combined treatment of epilepsy and comorbid depression.

Adjuvant neuronal nitric oxide synthase inhibition for combined treatment of epilepsy and comorbid depression

BACKGROUND

Elevated nitric oxide (NO) levels in the brain have been apparently associated with depression in kindled animals. Owing to the major role of neuronal nitric oxide synthase (nNOS) in brain and ineffectiveness of antiepileptic drugs (AEDs) in restoring nitrosative stress, the present study was envisaged to evaluate the adjuvant nNOS inhibitor, 7-nitroindazole (7-NI) with valproic acid for combined treatment of epilepsy and associated depression.

METHODS

Pentylenetetrazole kindled animals associated with depression were treated with vehicle, valproate (300mg/kg/day ip), valproate with 7-NI (10mg/kg; 20mg/kg; 40mg/kg)/day ip and 7-NI (40mg/kg/day ip) for 15days. Except naïve, all groups were challenged with pentylenetetrazole (35mg/kg ip) on days 5, 10, and 15 to evaluate seizure severity. Depression was evaluated in all experimental groups using the tail suspension and forced swim test on days 1, 5, 10 and 15. On day 15, biochemical (corticosterone levels) and neurochemical (serotonin, kynurenine, tryptophan, glutamate, GABA, nitrite levels) estimations were carried out in cortical and hippocampal area of mice brain.

RESULTS

Vehicle treated kindled animals were significantly associated with depression. Chronic valproate treatment in kindled animals significantly reduced seizure severity, but could not reverse associated depression. 7-NI per se treatment in kindled animals was also reported unable to restore the associated depression completely. However, 7-NI supplementation with valproate significantly reduced seizure severity score and completely ameliorated depression with restoration of altered biochemical and neurochemical milieu.

CONCLUSION

Adjuvant nNOS inhibition can be previewed as safe therapy with AEDs for the combined management of epilepsy and associated depression.

Neonatal Bacillus Calmette-Guérin vaccination alleviates lipopolysaccharide-induced neurobehavioral impairments and neuroinflammation in adult mice

The Bacillus Calmette-Guérin (BCG) vaccine is routinely administered to human neonates worldwide. BCG has recently been identified as a neuroprotective immune mediator in several neuropathological conditions, exerting neuroprotection in a mouse model of Parkinson's disease and slowing the progression of clinically isolated syndrome in patients with multiple sclerosis. The immune system is significantly involved in brain development, and several types of neonatal immune activations exert influences on the brain and behavior following a secondary immune challenge in adulthood. However, whether the neonatal BCG vaccination affects the brain in adulthood remains to be elucidated. In the present study, newborn C57BL/6 mice were injected subcutaneously with BCG (10⁵ colony forming units) or phosphate-buffered saline (PBS). A total of 12 weeks later, the mice were injected intraperitoneally with 330 µg/kg lipopolysaccharide (LPS) or PBS. The present study reported that the neonatal BCG vaccination alleviated sickness, anxiety and depression-like behavior, lessened the impairments in hippocampal cell proliferation and downregulated the proinflammatory responses in the serum and brain that were induced by the adult LPS challenge. However, BCG vaccination alone had no evident influence on the brain and behavior in adulthood. In conclusion, the neonatal BCG vaccination alleviated the neurobehavioral impairments and neuroinflammation induced by LPS exposure in adult mice, suggesting a potential neuroprotective role of the neonatal BCG vaccination in adulthood.

Role of neuro-immunological factors in the pathophysiology of mood disorders

Mood disorders, despite the widespread availability of monoamine-based antidepressant treatments, are associated with persistently high rates of disability, together with elevated rates of mortality due to suicide, cardiovascular disease, and other causes. The development of more effective treatments has been hindered by the lack of knowledge about the etiology and pathogenesis of mood disorders. An emerging area of science that promises novel pathways to antidepressant and mood stabilizing therapies surrounds evidence that immune cells and their signaling play a major role in the pathophysiology of major depressive disorder (MDD) and bipolar disorder (BD). Here, we review evidence that the release of neuroactive cytokines, particularly interleukins such as IL-1β, IL-6, and TNF-α, is altered in these disorders and discuss mechanisms such as the ATP-gated ion channel P2X7, through which cytokine signaling can influence neuro-glial interactions. Brain P2X7, an emerging target and antagonism of P2X7 holds promise as a novel mechanism for targeting treatment-resistant depression. We further discuss the role of microglia and astroglia in central neuroinflammation and their interaction with the peripheral immune system We present extant clinical evidence that bolsters the role of neuroinflammation and neuroactive cytokines in mood disorders. To that end, the role of clinical imaging by probing neuroinflammatory markers is also discussed briefly. Finally, we present data using preclinical neuroinflammation models that produce depression-like behaviors in experimental animals to identify neuroinflammatory mechanisms which may aid in novel neuroimmune target identification for the development of exciting pharmacological interventions in mood disorders.

Role of the Kynurenine Metabolism Pathway in Inflammation-Induced Depression: Preclinical Approaches

Physically ill patients with chronic inflammation often present with symptoms of depression. Our understanding of the pathophysiology of inflammation-associated depression has benefited from preclinical studies on the mechanisms of sickness and clinical studies on the symptoms of sickness and depression that develop in patients treated with immunotherapy. Sickness behavior develops when the immune system is activated by pathogen- or damage-associated molecular patterns. It is a normal biological response to infection and cell injury. It helps the organism to mobilize its immune and metabolic defenses to fight the danger. Depression emerges on the background of sickness when the inflammatory response is too intense and long lasting or the resolution process is deficient. The transition from sickness to depression is mediated by activation of the kynurenine metabolism pathway that leads to the formation of neurotoxic kynurenine metabolites including quinolinic acid, an agonist of N-methyl-D-aspartate receptors. The neuroimmune processes and molecular factors that have been identified in the studies of inflammation-associated depression represent potential new targets for the development of innovative therapies for the treatment of major depressive disorders.

Neonatal BCG vaccination of mice improves neurogenesis and behavior in early life

Bacillus Calmette-Guérin (BCG) is administered to neonates worldwide, but it is still unknown whether this neonatal vaccination affects brain development during early postnatal life, despite the close association of the immune system with the brain. Newborn C57BL/6 mice were injected subcutaneously with BCG or phosphate-buffered saline (PBS) and their mood status and spatial cognition were observed at four and eight weeks (w) old. The mice were also subjected to tests at 2 and 6 w to examine BCG's effects on neurogenesis, the hippocampal microglia phenotype and number, and the expression of hippocampal neuroimmune molecules and peripheral cytokines. The BCG-injected mice showed better behavioral performances at 4 w. We observed elevated neurogenesis, M2 microglial activation and a neurotrophic profile of neuroimmune molecules [more interferon (IFN)-γ, interleukin (IL)-4, transforming growth factor (TGF)-β, brain-derived neurotrophic factor (BDNF) and insulin-like growth factor (IGF)-1 and less tumor necrosis factor (TNF)-α and IL-1β] in the hippocampus of the 2-w-old BCG-mice. In the periphery, BCG induced a T helper (Th)-1 serum response. At the individual level, there were positive correlations between the serum IFN-γ/IL-4 ratio and the levels of neurotrophins and neurogenesis in the hippocampus. These findings suggest that neonatal BCG vaccination improved neurogenesis and mouse behavior in early life by affecting the neuroimmune milieu in the brain, which may be associated with a systemic Th1 bias.

Advancing the understanding of behaviors associated with Bacille Calmette Guérin infection using multivariate analysis

Behavioral indicators in the murine Bacille Calmette Guérin (BCG) model of inflammation have been studied individually; however, the variability of the behaviors across BCG levels and the mouse-to-mouse variation within BCG-treatment group are only partially understood. The objectives of this study were: (1) to gain a comprehensive understanding of sickness and depression-like behaviors in a BCG model of inflammation using multivariate approaches, and (2) to explore behavioral differences between BCG-treatment groups and among mice within group. Adult mice were challenged with either 0mg (saline), 5mg or 10mg of BCG (BCG-treatment groups: BCG0, BCG5, or BCG10, respectively) at Day 0 of the experiment. Sickness indicators included body weight changes between Day 0 and Day 2 and between Day 2 and Day 5, and horizontal locomotor activity and vertical activity (rearing) measured at Day 6. Depression-like indicators included duration of immobility in the forced swim test and in the tail suspension test at Day 6 and sucrose consumption in the sucrose preference test at Day 7. The simultaneous consideration of complementary sickness and depression-like indicators enabled a more precise characterization of behavioral changes associated with BCG-treatment and of mouse-to-mouse variation, relative to the analysis of indicators individually. Univariate and multivariate analyses confirmed differences between BCG-treatment groups in weight change early on the trial. Significant differences between BCG-treatment groups in depression-like behaviors were still measurable after Day 5. The potential for multivariate models to account for the correlation between behavioral indicators and to augment the analytical precision relative to univariate models was demonstrated both for sickness and for depression-like indicators. Unsupervised learning approaches revealed the complementary information provided by the sickness and depression-like indicators considered. Supervised learning approaches using cross-validation confirmed subtle differences between BCG-treatment groups and among mice within group identified by the consideration of sickness and depression-like indicators. These findings support the recommendation for multivariate and multidimensional analyses of sickness and depression-like indicators to augment the systemic understanding of the behavioral changes associated with infection.