Tumor necrosis factor alpha and its receptors in behaviour and neurobiology of adult mice, in the absence of an immune challenge.

Tumor necrosis factor alpha (TNF-α) is a vital component of the immune system and CNS. We previously showed that 3-month-old TNF-α and TNF-α receptor knockout mice had impaired cognition, whilst at 12-months-old mice had better cognition. To extend these findings on possible age-dependent TNF-α effects in the brain, we investigated the behaviour of 6-month-old TNF-α knockout mice and their neurobiological correlates. 6-month-old TNF(-/-), TNF-R1(-/-) and TNF-R2(-/-) mice were compared to age-matched WT mice and tested for various behaviours. ELISA hippocampal levels of nerve growth factor (NGF) and brain derived neurotrophic factor (BDNF) and qPCR mRNA levels of Tnfa, Tnfr1, Tnfr2, Il10 and Il1ß were measured. TNF-R1(-/-) and TNF(-/-) mice were found to have lesser exploratory behaviour than WT mice, while TNF-R1(-/-) mice displayed better memory than WT and TNF-R2(-/-) mice. Both TNF(-/-) and TNF-R2(-/-) mice exhibited significantly lower immobility on the depression test than WT mice. Additionally, TNF(-/-) mice expressed significantly lower levels of BDNF than WT mice in the hippocampus while TNF-R1(-/-) mice displayed significantly lower BDNF levels compared to both WT and TNF-R2(-/-) mice. TNF-R2(-/-) mice also displayed significantly higher levels of NGF compared to TNF-R1(-/-) mice. These results illustrate that TNF-α and its receptors mediate several behavioural phenotypes. Finally, BDNF and NGF levels appear to be regulated by TNF-α and its receptors even under immunologically unchallenged conditions.

Effects of centrally administered etanercept on behavior, microglia, and astrocytes in mice following a peripheral immune challenge.

Peripheral cytokines affect central nervous system (CNS) function, manifesting in symptoms of anxiety and cognitive decline. Although the peripheral blockage of tumor necrosis factor (TNF)-α has been effective in alleviating depression and rheumatoid arthritis, it is yet unknown whether central blockade of TNF-α is beneficial for immune-challenged CNS function. This study investigated the effects of central etanercept administration following a peripheral immune challenge on anxiety-like and cognition-like behaviors and microglia and astrocyte numbers. Twelve-week-old C57BL/6 mice (n=40) were treated with either LPS or saline administered peripherally 24 h before being treated with either etanercept or artificial CSF (aCSF) by intracerebroventricular injection. Mice underwent behavioral analyses for locomotion, memory, and anxiety-like behavior 24 h post-etanercept/aCSF treatment, and tissue was collected to estimate the numbers of hippocampal microglia and astrocytes. Following peripheral immune challenge with LPS, mice showed increased anxiety-like behavior, which was significantly improved following treatment with etanercept (two-way ANOVA: Interaction: F(1,30)=0.60, P=0.44; Saline/LPS challenge: F(1,30)=23.92, P<0.0001, etanercept vs aCSF: F(1,30)=11.09, P=0.0023). For cognition, a significant interaction effect found by two-way ANOVA (Interaction: F(1,20)=4.96, P=0.037, Saline/LPS challenge: F(1,20)=4.966, P=0.31, aCSF/etanercept treatment: F(1,20)=0.06, P=0.80) and post-hoc analysis revealed a significant decrease in cognition in LPS-aCSF compared with Sal-aCSF mice (P=0.038), but no significant difference was noted between LPS-aCSF and LPS-Etan mice (P>0.9). A significant reduction in the number of microglia within the hippocampus of these mice was noted (two-way ANOVA: Interaction: F(1,15)=11.41, P=0.0041; Saline/LPS challenge: F(1,15)=50.13, P<0.0001, etanercept vs aCSF: F(1,15)=3.36, P=0.08). Centrally administered etanercept improved anxiety-like behavior but not spatial memory under a peripheral immune challenge and was associated with a decrease in the hippocampal microglia numbers. This suggests that etanercept recovers anxiety-like behavior possibly mediated by a reduction of TNF-α-related central inflammation.

TNF-α and its receptors modulate complex behaviours and neurotrophins in transgenic mice.

UNLABELLED: Tumour necrosis factor-α (TNF-α) plays an important role not only in immunity but also in the normal functioning of the central nervous system (CNS). At physiological levels, studies have shown TNF-α is essential to maintain synaptic scaling and thus influence learning and memory formation while also playing a role in modulating pathological states of anxiety and depression. TNF-α signals mainly through its two receptors, TNF-R1 and TNF-R2, however the exact role that these receptors play in TNF-α mediated behavioural phenotypes is yet to be determined. METHODS: We have assessed TNF(-/-), TNF-R1(-/-) and TNF-R2(-/-) mice against C57BL/6 wild-type (WT) mice from 12 weeks of age in order to evaluate measures of spatial memory and learning in the Barnes maze (BM) and Y-maze, as well as other behaviours such as exploration, social interaction, anxiety and depression-like behaviour in a battery of tests. We have also measured hippocampal and prefrontal cortex levels of the neurotrophins nerve growth factor (NGF) and brain derived neurotrophic factor (BDNF) as well as used immunohistochemical analyses to measure number of proliferating cells (Ki67) and immature neurons (DCX) within the dentate gyrus. RESULTS: We have shown that young adult TNF(-/-) and TNF-R1(-/-) mice displayed impairments in learning and memory in the BM and Y-maze, while TNF-R2(-/-) mice showed good memory but slow learning in these tests. TNF(-/-)and TNF-R2(-/-) mice also demonstrated a decrease in anxiety like behaviour compared to WT mice. ELISA analyses showed TNF(-/-) and TNF-R2(-/-) mice had lower levels of NGF compared to WT mice. CONCLUSION: These results indicate that while lack of TNF-α can decrease anxiety-like behaviour in mice, certain basal levels of TNF-α are required for the development of normal cognition. Furthermore our results suggest that both TNF-R1 and TNF-R2 signalling play a role in normal CNS function, with knockout of either receptor impairing cognition on the Barnes maze.