LP-BM5 infection impairs spatial working memory in C57BL/6 mice in the Morris water maze

Multisensory body representation in autoimmune diseases

Body representation has been linked to the processing and integration of multisensory signals. An outstanding example of the pivotal role played by multisensory mechanisms in body representation is the Rubber Hand Illusion (RHI). In this paradigm, multisensory stimulation induces a sense of ownership over a fake limb. Previous work has shown high interindividual differences in the susceptibility to the RHI. The origin of this variability remains largely unknown. Given the tight and bidirectional communication between the brain and the immune system, we predicted that the origin of this variability could be traced, in part, to the immune system’s functioning, which is altered by several clinical conditions, including Coeliac Disease (CD). Consistent with this prediction, we found that the Rubber Hand Illusion is stronger in CD patients as compared to healthy controls. We propose a biochemical mechanism accounting for the dependency of multisensory body representation upon the Immune system. Our finding has direct implications for a range of neurological, psychiatric and immunological conditions where alterations of multisensory integration, body representation and dysfunction of the immune system co-exist.

Cytokines induced by long-term potentiation (LTP) recording: a potential explanation for the lack of correspondence between learning/memory performance and LTP

The relationship between learning/memory performance and long-term potentiation (LTP) induction is ambiguous. Although a large body of data supports a strong correspondence between learning/memory performance and LTP, many studies have also provided evidence to the contrary. In this study, we found that 2-month-old senescence-accelerated mice/prone 8 (SAMP8 mice) displayed both impaired performance in a Morris Water Maze (MWM) and enhanced LTP compared to senescence-accelerated mice/resistance 1 (SAMR1). BALB/c mice challenged with Complete Freund's Adjuvant (CFA) performed better in the shuttle-box test but displayed impaired LTP compared to intact animals. It is interesting that BALB/c mice challenged with Incomplete Freund's Adjuvant (IFA) performed better than intact animals, with no LTP impairment. Cytokine analysis showed no significant differences between the interleukin-6 (IL-6), interleukin-10 (IL-10) or TNF-α content in the intact hippocampal tissues of either the SAMR1 and SAMP8 mice or the immune-challenged BALB/c and intact animals. Further analysis demonstrated that the increase in cytokine content was higher in the hippocampal tissues used for LTP recording in the SAMR1 and CFA-challenged animals compared to the SAMP8 and intact BALB/c mice. A correlation analysis demonstrated that pro-inflammatory cytokines (IL-6 and TNF-α) displayed a negative correlation with LTP, while an anti-inflammatory cytokine (IL-10) displayed a positive correlation with LTP. These results suggest that pro-inflammatory cytokines induced by LTP manipulation in experiments (e.g., via tissue injury caused by electrode insertion) may be one of the factors contributing to the observed lack of correspondence between memory/learning ability and LTP.

Dose-dependent effects of endotoxin on neurobehavioral functions in humans

Clinical and experimental evidence document that inflammation and increased peripheral cytokine levels are associated with depression-like symptoms and neuropsychological disturbances in humans. However, it remains unclear whether and to what extent cognitive functions like memory and attention are affected by and related to the dose of the inflammatory stimulus. Thus, in a cross-over, double-blind, experimental approach, healthy male volunteers were administered with either placebo or bacterial lipopolysaccharide (LPS) at doses of 0.4 (n = 18) or 0.8 ng/kg of body weight (n = 16). Pro- and anti-inflammatory cytokines, norephinephrine and cortisol concentrations were analyzed before and 1, 1.75, 3, 4, 6, and 24 h after injection. In addition, changes in mood and anxiety levels were determined together with working memory (n-back task) and long term memory performance (recall of emotional and neutral pictures of the International Affective Picture System). Endotoxin administration caused a profound transient physiological response with dose-related elevations in body temperature and heart rate, increases in plasma interleukin (IL)-6, IL-10, tumor necrosis factor (TNF)-α and IL-1 receptor antagonist (IL-1ra), salivary and plasma cortisol, and plasma norepinephrine. These changes were accompanied by dose-related decreased mood and increased anxiety levels. LPS administration did not affect accuracy in working memory performance but improved reaction time in the high-dose LPS condition compared to the control conditon. In contrast, long-term memory performance was impaired selectively for emotional stimuli after administration of the lower but not of the higher dose of LPS. These data suggest the existence of at least two counter-acting mechanisms, one promoting and one inhibiting cognitive performance during acute systemic inflammation.

Interleukin-10/Ceftriaxone prevents E. coli-induced delays in sensorimotor task learning and spatial memory in neonatal and adult Sprague-Dawley rats

Intrauterine infection during pregnancy is associated with early activation of the fetal immune system and poor neurodevelopmental outcomes. Immune activation can lead to alterations in sensorimotor skills, changes in learning and memory and neural plasticity. Both interleukin-10 (IL-10) and Ceftriaxone have been shown to decrease immune system activation and increase memory capacity, respectively. Using a rodent model of intrauterine infection, we examined sensorimotor development in pups, learning and memory, via the Morris water maze, and long-term potentiation in adult rats. Pregnant rats at gestational day 17 were inoculated with 1 x 10(5) colony forming units of Escherichia coli (E. coli) or saline. Animals in the treatment group received IL-10/Ceftriaxone for 3 days following E. coli administration. Intrauterine infection delayed surface righting, negative geotaxis, startle response and eye opening. Treatment with IL-10/Ceftriaxone reduced the delay in these tests. Intrauterine infection impaired performance in the probe trial in the Morris water maze (saline 25.13+/-1.01; E. coli 20.75+/-1.01; E. coli+IL-10/Ceftriaxone 20.2+/-1.62) and reduced the induction of long-term potentiation (saline 141.5+/-4.3; E. coli 128.7+/-3.9; E. coli+IL-10/Ceftriaxone 140.0+/-10). In summary, the results of this study indicate that E. coli induced intrauterine infection delays sensorimotor and learning and memory, while IL-10/Ceftriaxone rescues some of these behaviors. These delays were also accompanied by an increase in interleukin-1beta levels, which indicates immune activation. IL-10/Ceftriaxone prevents these delays as well as decreases E. coli-induced interleukin-1beta activation and may offer a window of time in which suitable treatment could be administered.

A murine model of retroviral encephalopathy

This unit delineates the steps for production of a murine model of retroviral encephalopathy. The LP-BM5 infected mouse develops a chronic inflammation of the brain secondary to profound immune deficiency. The model is robust, develops rapidly and does not require the use of human pathogens. In addition, the behavioral and neurochemical characteristics of this model is reviewed.

Immune-based regulation of adult neurogenesis: implications for learning and memory

Neurogenesis, the formation of new neurons from stem/progenitor cells, occurs in the hippocampal dentate gyrus throughout life. Although the exact function of adult hippocampal neurogenesis is currently unknown, recent studies suggest that the newly formed neuronal population plays an important role in hippocampal-dependent cognitive abilities, including declarative memory. The process of adult neurogenesis is greatly influenced by the interaction between cells of the adaptive immune system and CNS-resident immune cells. Our laboratory has recently demonstrated that immune cells contribute to maintaining life-long hippocampal neurogenesis. The regulation of such immune-cell activity is crucial: too little immune activity (as in immune deficiency syndromes) or too much immune activity (as in severe inflammatory diseases) can lead to impaired hippocampal neurogenesis, which could then result in impaired hippocampal-dependent cognitive abilities. From these converging discoveries arise a mechanism that can explain one route by which our body affects our mind.

Reconsolidation of a long-term spatial memory is impaired by cycloheximide when reactivated with a contextual latent learning trial in male and female rats

Reconsolidation of long-term memory has become a topic of great interest in recent years, and has the potential to provide important information regarding memory processes and the treatment of memory-related disorders. The present study examined the role of systemic protein synthesis inhibition in reconsolidation of a long-term spatial memory reactivated by a contextual latent learning trial in male and female rats. Using the Morris water maze, we demonstrate that: 1) a contextual latent reactivation treatment enhances memory, 2) systemic protein synthesis inhibition selectively impairs test performance when administered in conjunction with a memory reactivation treatment, and 3) that these effects are more pronounced in female rats. These findings indicate a role for protein synthesis in the reconsolidation of a contextually reactivated long-term spatial memory using the water maze, and a potential differential effect of sex in this apparatus. The role of the strength of the memory trace is discussed and the relevance of these findings to theories of reconsolidation and therapeutic treatment of post-traumatic stress disorder is discussed.

Sympathetic nerve destruction in spleen in murine AIDS

In susceptible strains of mice, the LP-BM5 mixture of murine retroviruses induces the fatal immunodeficiency disease known as murine acquired immunodeficiency syndrome (murine AIDS or MAIDS). We have previously reported that murine AIDS produces a profound depletion of splenic norepinephrine (NE). Here, we demonstrate that NE depletion is limited to the spleen, a major site affected by LP-BM5 infection. NE depletion in the spleen is first observed at two weeks following LP-BM5 inoculation, concurrent with the onset of splenomegaly, and continues through 12 weeks post-infection. Neuroanatomical studies revealed that the reduction in NE is due to destruction of splenic sympathetic nerve fibers. Administration of the NE reuptake blocker desipramine did not prevent LP-BM5-induced NE depletion, suggesting that destruction is not caused by excess release and reuptake of NE. Elucidating the mechanism of MAIDS-induced sympathetic nerve destruction may provide insight into autonomic and peripheral neuropathies reported in people with AIDS.

In search of a better mouse test

To elucidate pathways from specific genes to complex behaviors, assays of mouse behavior need to be valid, reliable and replicable across laboratories. Behavioral assays are proving to be as complex as the intricate cellular and molecular pathways that are the main interest of many mouse users. There is no perfect behavioral test, but we propose some aphorisms to stimulate discussion that is necessary for continued progress in task development. For maximal utility, a behavioral test should yield valid data for most of the commonly used inbred mouse strains. Tests of simple, ubiquitous behaviors usually yield meaningful data for most mice, especially when based on automated scoring or on simple physical measures that are likely to be replicable across laboratories. Extreme test scores resulting from non-performance on a task can inflate the apparent reliability of a test, and devious adaptations to a task can undermine its validity. The optimal apparatus configuration for certain genetic or pharmacological analyses might depend on the particular laboratory environment. Despite our best efforts, the mice will continue to win some innings.

Effects of LP-BM5 murine leukemia virus infection on errors and response time in a two-choice serial reaction time task in C57BL/6 mice

Human immunodeficiency virus type 1 (HIV-1) infection is often accompanied by cognitive, motor, and behavioral dysfunction. Cognitive function diminishes in indices of attention, psychomotor speed, and learning and memory. These are collectively termed acquired immunodeficiency syndrome dementia complex (ADC or neuroAIDS). Inoculation with the LP-BM5 murine leukemia virus (MuLV) causes profound immunosuppression (murine acquired immunodeficiency syndrome, or MAIDS) in C57BL/6 mice. Previous studies show that the LP-BM5 MuLV impairs learning and memory without gross motor impairment. Since learning and memory performance deficits can be related to attention deficits, we assessed the effect of LP-BM5 MuLV infection on sustained attention performance using a two-choice serial reaction time task. This task required the animals to detect a visual stimulus presented randomly on the right or the left unit and respond by a nose-poke in the illuminated hole within a 5 s period for water reward. The LP-BM5 MuLV infected group, like the control group, improved sustained attention performance until 7 weeks of virus infection in all measures including choice accuracy, response omission, and correct response time. However, during the late stage of infection, LP-BM5 MuLV infected mice showed selective sustained attention performance deficits. From 8 weeks after LP-BM5 MuLV infection, the virus infected mice started to lose their improved sustained attention performance in response omission and began to make correct responses more slowly than the control mice when the duration of stimulus light was 5 s. Moreover, at 13 and 14 weeks after LP-BM5 MuLV infection, the virus infected group made correct choices significantly less accurately than the control group when duration of stimulus light was shortest (1 s). These data show that LP-BM5 MuLV infection causes not only the previously reported learning and memory deficits but also produces sustained attention performance deficits in mice.

Chemical sympathectomy has no effect on the severity of murine AIDS: murine AIDS alone depletes norepinephrine levels in infected spleen

Numerous studies have shown that alterations in sympathetic nervous system (SNS) function produced by beta-adrenergic receptor blockade or chemical sympathectomy can produce changes in T and B lymphocyte function and both innate and acquired immune responses. However, fewer studies have investigated changes in immune response following SNS alterations in animal models of disease. We tested whether blocking SNS activity using 6-OHDA or the beta-receptor antagonist nadolol alters the typical pattern in production of T helper 1 (Th1) and Th2 cytokines seen in cultures of spleen cells from C57BL/6 mice infected with murine AIDS (MAIDS). We found that neither method of sympathetic blockade affected cytokine response to MAIDS. We also found that the norepinephrine concentration and content of the spleen were reduced dramatically by the MAIDS infection itself at 3 and 6 weeks after LP-BM5 inoculation. This finding has not been previously reported in mice with MAIDS and suggests that the viral infection itself produces a functional sympathectomy in the spleen, a target of that infection.