The effects of glial cells inhibition on spatial reference, reversal and working memory deficits in a rat model of traumatic brain injury (TBI)

S100B Secretion in Astrocytes, Unlike C6 Glioma Cells, Is Downregulated by Lactate

S100B is a calcium-binding protein produced and secreted by astrocytes in response to various extracellular stimuli. C6 glioma cells are a lineage commonly employed for astroglial studies due to the expression of astrocyte specific markers and behavior. However, in high-glucose medium, C6 S100B secretion increases, in contrast to the trend in primary astrocyte cultures. Additionally, S100B secretion decreases due to fluorocitrate (FC), a Krebs cycle inhibitor, highlighting a connection between S100B and metabolism. Herein, we investigate the impact of FC on S100B secretion in primary astrocyte cultures, acute hippocampal slices and C6 glioma cells, as well as lactate mediation. Our results demonstrated that C6 responded similarly to astrocytes in various parameters, despite the decrease in S100B secretion, which was inversely observed in astrocytes and slices. Furthermore, FC inversely altered extracellular lactate in both models, suggesting a role for lactate in S100B secretion. This was reinforced by a decrease in S100B secretion in hippocampal slices treated with lactate and its agonist, but not in C6 cells, despite HCAR1 expression. Our findings indicate that extracellular lactate mediates the decrease in S100B secretion in astrocytes exposed to FC. They also emphasize the differences in C6 glioma cells regarding energetic metabolism. The proposed mechanism via HCAR1 provides further compelling evidence of the relationship between S100B and glucose metabolism.

Spatial working memory is disparately interrelated with social status through different developmental stages in rats

Social life necessitates cognitive competence to meet the dynamic demands of social development. The formation of dominance hierarchy is a general phenomenon in social groups. As an essential element of executive and cognitive function, working memory could influence and be influenced by social status in a dominance hierarchy. However, the direction and degree of the association between them through different developmental stages remain unclear. To address this issue and clarify the "cause or consequence" problem, we investigated the spatial working memory performance in a Y-maze and Morris water maze in home-caged sibling Wistar rats (N = 26 cages, three rats/cage) through three stages of their life: before (week 7), during (week 10), and after (week 20) assumed timings of the social dominance hierarchy formation (SDHF). We used the social dominance tube test during the assumed time of hierarchy formation (weeks 9-11) to measure the relative dominance status in each cage. Here, we found that higher working memory index before SDHF could be predictive of later acquisition of higher social status. Working memory performance declined for all animals during SDHF, in which agonistic conflicts are increased. However, living within an established hierarchical social network for several weeks deteriorated the working memory performance of dominant and middle-ranked animals, while the performance of subordinates improved and got significantly better than higher-ranked animals. In conclusion, while working memory and social status were correlated positively before dominance hierarchy formation, there was a trade-off between them after the formation of it. In contrast to the common view, these results highlight the adverse effect of higher social status on cognitive behavior.

Sex differences in spatial learning and memory and hippocampal long-term potentiation at perforant pathway-dentate gyrus (PP-DG) synapses in Wistar rats

BACKGROUND

Recent studies show that gender may have a significant impact on brain functions. However, the reports of sex effects on spatial ability and synaptic plasticity in rodents are divergent and controversial. Here spatial learning and memory was measured in male and female rats by using Morris water maze (MWM) task. Moreover, to assess sex difference in hippocampal synaptic plasticity we examined hippocampal long-term potentiation (LTP) at perforant pathway-dentate gyrus (PP-DG) synapses.

RESULTS

In MWM task, male rats outperformed female rats, as they had significantly shorter swim distance and escape latency to find the hidden platform during training days. During spatial reference memory test, female rats spent less time and traveled less distance in the target zone. Male rats also had larger LTP at PP-DG synapses, which was evident in the high magnitude of population spike (PS) potentiation and the field excitatory post synaptic potentials (fEPSP) slope.

CONCLUSIONS

Taken together, our results suggest that sex differences in the LTP at PP-DG synapses, possibly contribute to the observed sex difference in spatial learning and memory.

Effects of post-training administration of LY341495, as an mGluR2/3 antagonist on spatial memory deficit in rats fed with high-fat diet

High-fat diets (HFDs) adversely influence glutamate metabolism and neurotransmission. The precise role of the group II metabotropic glutamate receptors (mGluR2/3) antagonist on spatial memory deficit following consumption of HFD has not yet been clarified. Therefore, in this study, we examined the effects of post-training administration of mGluR2/3 antagonism; LY341495 on spatial memory in rats fed with HFD (for 10 weeks) by using Morris Water Maze (MWM) task. The training session for testing memory acquisition in MWM consisted of 4 trials per day for 4 consecutive days. Twenty-four hours after the last training session the spatial probe test (retention) was given. Intraperitoneal injection (i.p) injection of LY341495 was done 30 min before probe test. Our results showed that 10 weeks consumption of HFD had no significant effect on escape latency and swimming distance in memory acquisition. Our finding showed that consumption of a HFD leads to reference memory impairment in the probe test. HFD animals spent less time in the target zone in compare with control animals. Also, LY341495 improved HFD-induced reference memory (retention) impairment. HFD animals treated with LY341495 spent more time in the target zone in compare with HFD animals. Escape latencies to find the visible platform during visual task were same in all experimental groups, indicating no visual impairment in the animals. We propose that a HFD may act through mGluR2/3 within the brain to reduce synaptic plasticity, which impairs memory retrieval, and post-training administration of LY341495 can reduce HFD-induced reference memory impairment.

Chronic NaHS treatment improves spatial and passive avoidance learning and memory and anxiety-like behavior and decreases oxidative stress in rats fed with a high-fat diet

Cognitive function is impaired by increased consumption of a high-fat diet (HFD). Also, HFD consumption can alter hydrogen sulfide (H₂S) metabolism. H₂S is an important signaling molecule with antioxidant effects that regulates multiple functions in the brain. In the present study, we investigated the effect of sodium hydrosulfide (NaHS, an H₂S donor) on cognitive impairment and oxidative stress changes induced by HFD consumption. Following 11 weeks of HFD regimes in Wistar rats, elevated plus-maze (EPM), Morris water maze (MWM), and passive avoidance learning (PAL) tasks were used to evaluate the anxiety-like behavior and spatial and passive learning and memory, respectively. Daily intraperitoneal injection of NaHS was done during the dietary regimen. Serum and hippocampal oxidative stress biomarkers (malondialdehyde (MDA), total antioxidant capacity (TAC), and total oxidant status (TOS)) were measured. We demonstrated that treatment with NaHS ameliorated the impairment in the retrieval of reference memory and passive avoidance learning. Moreover, HFD increased anxiety-like behavior, which was reversed by the administration of NaHS. Additionally, the increase in MDA and TOS and the decrease in TAC induced by HFD in the serum and hippocampus were significantly reduced following administration of NaHS. These results indicate that NaHS could significantly ameliorate HFD-induced spatial and passive learning and memory impairment and anxiety-like behavior, at least in part, via its antioxidant activities. Therefore, the administration of NaHS can provide a therapeutic approach for HFD-induced memory impairment.