Facilitatory Effect of IL-6 Deficiency on Long-Term Spatial Memory in Young Adult Mice

Cannabidiol improves memory and decreases IL-1β serum levels in rats with lipopolysaccharide-induced inflammation

AIM

Memory improving and anti-inflammatory properties of cannabidiol (CBD) were investigated in an experimental model of lipopolysaccharide (LPS)-induced inflammation.

Prenatal exposure to concentrated ambient PM2.5 results in spatial memory defects regulated by DNA methylation in male mice offspring

Ambient fine particulate matter (PM_2.5) exposures during pregnancy could lead to adverse birth outcomes, including neurobehavioral development defects. However, limited studies explored the effects and potential epigenetic mechanisms of maternal PM_2.5 exposure on offspring spatial memory defects. This study aims to explore the effects and underlying epigenetic mechanisms of maternal concentrated ambient PM_2.5 exposure in male mice offspring with spatial memory defects. Pregnant female C57BL/6 mice were exposed daily to concentrated ambient PM_2.5 (CAP) or filtered air (FA) throughout gestation, with the concentration of particulates (102.99 ± 78.74 μg/m³) and (2.78 ± 1.19 μg/m³), respectively. Adult male mice offspring were subsequently assessed for spatial learning and memory ability using Morris Water Maze tests and locomotor activities in open field tests. The hippocampus of the male mice offspring was harvested to test mRNA expression and DNA methylation. Results from the probe test of Morris Water Maze showed that the mice offspring in the CAP group had shorter swimming distance travelled in the target quadrant, shorter duration in the target quadrant, and less number of entries into the target quadrant (p < 0.05), suggesting spatial memory impairments. The acquisition trials of Morris Water Maze did not show a significant difference in learning ability between the groups. The mRNA level of interleukin 6 (IL-6) in the CAP group hippocampus (10.80 ± 7.03) increased significantly compared to the FA group (1.08 ± 0.43). Interestingly, the methylation levels of the CpG sites in the IL-6 promoter region declined significantly in the CAP group, (5.66 ± 0.83)% vs. (4.79 ± 0.48)%. Prenatal exposure to concentrated ambient PM_2.5 induced long-lasting spatial memory defects in male mice offspring. The underlying biological mechanism might be mediated by an inflammatory reaction which is regulated by DNA methylation.

Stress while lacking of control induces ventral hippocampal autophagic flux hyperactivity and a depression-like behavior

BACKGROUND

Stressed animals may perform depression-like behavior insomuch as stress-provoking blood-brain barrier (BBB) disruption, central immune activation, and autophagic flux changes. This study was undertaken to assess whether adult mice having (executive) vs. lacking (yoke) of behavioral control in otherwise equivalent stress magnitude condition, may display differences in their BBB integrity, ventral hippocampal (VH) interleukin-6 (IL-6) and autophagic flux level and VH-related depression-like behavior. To further understand the causative relation of enhanced autophagic flux and stress-primed depression-like behavior, we assessed the effects of bilateral intra-VH 3-methyladenine (3-MA), an autophagic flux inhibitor, infusion in stressed mice.

METHODS

Adult mice used had comparable genetic background and housing condition. Executive/yoke pairs of mice received a 10-day (1 h/day) footshock stressor regimen. Throughout the regimen, the ongoing footshock was terminated immediately contingent on the executive mouse', while irrelevant to the respective yoke mouse' voluntary behavior, or lasting for 7 s. Each dyad's cage-mate receiving no such regimen served as no stressor controls.

RESULTS

Yoke mice displayed disrupted BBB integrity (escalated Evans blue extravasation and decreased VH ZO-1, claudin-5 expression), increases in VH autophagic flux (increased LC3II/LC3I and decreased p62) and immobility duration in forced swimming test. Most of these indices remained unaltered in executive mice. Administration of 3-MA did not affect immobility duration in control mice, while prevented the increases in immobility duration in yoke mice.

CONCLUSIONS

(1) stress susceptibility may be determined by their differences in stress-coping results; (2) VH autophagic flux increase plays a permissive role in priming the stressed animals susceptible to exhibit depression-like behavior.

The Hole-Board Test in Mutant Mice

First described by Boissier and Simon in (Ther Recreat J 17:1225-1232, 1962), the hole-board has become a recognized test of anxiety and spatial memory. Benzodiazepines acting at the GABA_A-BZD site increase hole-pokes in rats and mice, indicating a loss in behavioral inhibition concordant with the behavior of mutant mice deficient in the GABA transporter. Hole-poking also depends on arousal mechanisms dependent on dopaminergic transmission, as indicated by drug and null mutant studies. In addition, the behavior is modified in natural and null mutants affecting the cerebellum as well as null mutants affecting neuropeptides, growth factors, cell adhesion, and inflammation. Further research is required to determine convergences between genetic and pharmacological effects.

Effects of long-term infliximab and tocilizumab treatment on anxiety-like behavior and cognitive function in naive rats

BACKGROUND

Circulating cytokines have been proposed to be implicated in the development of mood disorders and cognitive impairment. This study aims to examine the effect of chronic treatment with infliximab, a tumor necrosis factor-alpha (TNF-alpha) inhibitor, and tocilizumab, an antibody against interleukin-6 (IL-6) receptor on anxiety-like behavior and cognitive function.

METHODS

Twenty-eight male, Wistar rats were randomly allocated into negative control, vehicle, infliximab and tocilizumab groups. After 8 weeks of intraperitoneal drug administration, rats performed the elevated-plus maze, the elevated-zero maze, the olfactory social memory and the passive avoidance tests. Brain sections at the level of the hippocampus, the amygdala and the prefrontal cortex were histologically examined. Finally, hippocampal and amygdaloid brain-derived neurotrophic factor (BDNF) expression was determined by reverse transcription-quantitative polymerase chain reaction (RT-qPCR).

RESULTS

Infliximab group exhibited a significantly higher number of entries and time spent into the open arms of the mazes, showing a lower level of anxiety. In the olfactory social memory test, tocilizumab significantly increased the ratio of interaction. Both infliximab- and tocilizumab-treated animals had a significantly lower latency time in the passive avoidance test that suggests an improved memory. Histological examination revealed similar morphology and neuronal density between groups. BDNF expression levels were significantly increased in the groups receiving anti-cytokine treatment.

CONCLUSIONS

Our findings suggest that long-term peripheral TNF-alpha and IL-6 inhibition improves anxiety and cognitive function in rats and leads to an increased BDNF expression in the brain.

The 4-Hole-Board Test for Assessment of Long-Term Spatial Memory in Mice

The hole-board test has been used in rodents since the early 60s to measure exploratory behavior, locomotor activity and cognitive function. The test is based on rodents' natural curiosity and attraction for novelty. Basically, the hole-board consists of a small square arena with an extractable platform as floor, which has a set of equally spaced circular holes on its surface. In this article, we describe the protocol of a 4-hole-board test allowing the assessment of long-term spatial memory in mice without the employment of water or food restriction, painful stimuli (as electrical shocks) or any aversive condition (as forced swimming or exposure to intense light). Four holes are present on the floor of the square arena (one for each of its four quadrants). Mice released in the arena spontaneously approach the holes and explore them by briefly inserting the snout inside, a behavior defined as nose-poking (or head-dipping). If, after 24 hr, rodents are re-exposed to the hole-board, the novelty of the holes decreases. Animals with an intact long-term memory will show a reduction of the frequency of nose-poking into the holes. The total number of nose-pokes on day 1 is an index of exploration, while the percentage of decrease in nose-poking on day 2 represents an index of long-term spatial memory. Number of quadrant crossings is scored as a control measure for locomotor activity, which with the present protocol should remain stable across the days of testing. Indeed, the 4-hole-board test represents a stress-free and animal-friendly option to evaluate long-term spatial memory. In the present paper, we provide detailed description of the hole-board apparatus and step-by-step protocol for assessment of spatial memory in mice. © 2021 Wiley Periodicals LLC. Basic Protocol 1: Validation of the 4-hole-board Basic Protocol 2: Evaluation of long-term spatial memory through the 4-hole-board test.

IL-6 deficiency attenuates p53 protein accumulation in aged male mouse hippocampus

Our earlier studies demonstrated slower age-related memory decline in IL-6-deficient than in control mice. Therefore, in the present study we evaluated the effect of IL-6 deficiency and aging on expression of p53, connected with accumulation of age-related cellular damages, in hippocampus of 4- and 24-month-old IL-6-deficient C57BL/6J (IL-6KO) and wild type control (WT) mice. The accumulation of p53 protein in hippocampus of aged IL-6KO mice was significantly lower than in aged WT ones, while p53 mRNA level was significantly higher in IL-6-deficient mice, what indicates that the effect was independent on p53 transcription. Presence of few apoptotic cells in hippocampal dentate gyrus and lack of changes in levels of pro-apoptotic Bax, antiapoptotic Bcl-2, as well as in p21 protein in aged animals of both genotypes, points to low transcriptional activity of p53, especially in aged WT mice. Because the amount of p53 protein did not correlate with the level of Mdm2 protein, its main negative regulator, other than Mdm2-dependent mechanism was involved in p53 build-up. Significantly higher mRNA levels of autophagy-associated genes: Pten, Tsc2, and Dram1 in IL-6KO mice, in conjunction with significantly lower amount of Bcl-2 protein in 4-month-old IL-6KO mice, suggests that lack of IL-6/STAT3/Bcl-2 signaling could account for better autophagy performance in these mice, preventing excessive accumulation of proteins. Taken together, attenuated p53 protein build-up, absence of enhanced apoptosis, and transcriptional up-regulation of autophagy-associated genes imply that IL-6 deficiency may protect hippocampus from age-related accumulation of cellular damages.

Differential role of interleukin-1β in neuroinflammation-induced impairment of spatial and nonspatial memory in hyperammonemic rats

Activated microglia and increased brain IL-1β play a main role in cognitive impairment in much pathology. We studied the role of IL-1β in neuroinflammation-induced impairment of the following different types of learning and memory: novel object recognition (NOR), novel object location (NOL), spatial learning, reference memory (RM), and working memory (WM). All these processes are impaired in hyperammonemic rats. We assessed which of these types of learning and memory are restored by blocking the IL-1 receptor in vivo in hyperammonemic rats and the possible mechanisms involved. Blocking the IL-1 receptor reversed microglial activation in the hippocampus, perirhinal cortex, and prefrontal cortex but not in the postrhinal cortex. This was associated with the restoration of NOR and WM but not of tasks involving a spatial component (NOL and RM). This suggests that IL-1β would be involved in neuroinflammation-induced nonspatial memory impairment, whereas spatial memory impairment would be IL-1β-independent and would be mediated by other proinflammatory factors.-Taoro-González, L., Cabrera-Pastor, A., Sancho-Alonso, M., Arenas, Y. M., Meseguer-Estornell, F., Balzano, T., ElMlili, N., Felipo, V. Differential role of interleukin-1β in neuroinflammation-induced impairment of spatial and nonspatial memory in hyperammonemic rats.

Significance of IL-6 Deficiency in Recognition Memory in Young Adult and Aged Mice

Chronic peripheral elevation of interleukin 6 (IL-6) in humans is associated with cognitive deficits. 4- and 24-month-old IL-6-deficient C57BL/6J (IL-6KO) and reference wild-type (WT) mice were tested in an object recognition test. Discrimination ratios and recognition indexes were significantly lower in 4-month-old IL-6KO and in 24-month-old WT mice vs 4-month-old WT animals. Their discrimination ratios had negative values and recognition indexes were below 50% indicating inability to differentiate the novel from the familiar object after 1-hour delay. In 24-month-old IL-6KO mice recognition index reached 53.17% indicating that their recognition memory was not worsened with age in comparison with younger IL-6-deficient animals. Results of holeboard and elevated plus maze indicated that this effect was memory specific. Inborn IL-6 deficiency attenuated recognition memory in 4-month-old mice and did not altered recognition memory in aged animals. IL-6 signalling may constitute a target for development of the protection against memory disturbances connected with IL-6 overexpression.