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    • br Materials and methods br Results

    2021-09-08


    Materials and methods
    Results
    Discussion Nervous system disease is an important signal of AIDS deterioration (Rosca et al., 2012, Yilmaz et al., 2012). It is possible that HIV crosses the blood Sodium salicylate barrier or blood cerebrospinal fluid barrier into the central nervous system freely or via infected immune cells. Studies have shown that gp120 can cause toxicity of rodent hippocampal neurons and human embryonic neurons (Kasyanov et al., 2006, Zheng et al., 1999), and severe brain damage was observed when neonatal rats were given gp120 in vivo and when adult rats were given LV injection of gp120 (Potter et al., 2013, Xiong et al., 2000). Further, gp120 may influence glutamate uptake by astrocytes and block neuron glutamine supply, which affects learning and memory ability, thus causing brain defects (Yu et al., 2007). Throughout our experiments, we observed no difference between control and sham group rats in respect to water maze test performance or P2X7 receptor/P65 protein expression in the hippocampus, indicating that the surgery had no effect on the test rats. In addition, a further test showed that neither naringin nor BBG exerted significant effect on the behavior or P2X7 receptor/P65 protein expression of the control or sham group rats. We also found that LV infusion of gp120 (50, 70, 100ng/day) for three consecutive days significantly prolonged the rats’ escape latency in the water maze, indicating that their learning and memory ability was impaired due to gp120; gp120 infusion also significantly increased their target platform errors, further indicating that gp120 exerted detrimental effect on learning and memory. The P2X family belongs to the ligand gated ion channel receptor. Notably, P2X family receptors (P2X1-7) have been cloned successfully in mammalian cells. The abnormal expression of P2X7 receptors is associated with inflammation (Burnstock et al., 2011, Skaper et al., 2010), and the P2X7 receptor is known to play an important role in microglia activity regulation (Bordt and Polster, 2014, Fang et al., 2009, Monif et al., 2009). ATP may stimulate the P2X7 receptor to activate microglia, which not only promotes the proliferation of microglia but also contributes to the release of inflammatory mediators that lead to chronic nerve cell inflammation and neurotoxicity. In addition to its involvement in inflammation and immune responses, the P2X7 receptor also plays a role in neurodegenerative diseases (Burnstock et al., 2011, Skaper et al., 2010), therefore, P2X7 receptors may be closely associated with ADC. Brilliant Blue G (BBG, a selective P2X7 receptor antagonist) may block the interaction between ATP and P2X7 receptors to suppress microglial activation in the hippocampus (Xu et al., 2015) and alleviate neural injury and consequent functional deficits (Deng et al., 2015). BBG may also decrease P2X7 receptor-related immunoreactivity (Zou et al., 2016). In the present study, we found that spatial memory ability decreased significantly in gp120-treated rats, while there was no difference between the gp120+BBG group and control group, implying that P2X7 receptors made a significant difference in gp120-induced learning and memory deficits—interestingly, we also found that BBG had no effect on the behavior or P2X7 protein/mRNA expression in the hippocampus of naïve rats. The expression of P2X7 protein and mRNA in the hippocampus did increase considerably after LV perfusion of gp120, however. These results altogether indicated that P2X7 receptors were likely involved in the pathogenic processes of gp120-induced learning and memory deficits in rats. P2X7 receptors on microglial cells can be exploited to identify ATP signals and activation of intracellular signaling cascades which trigger the microglia's transition from resting to active state and promote their proliferation (Monif et al., 2010, Shiratori et al., 2010). P2X7 receptors can mediate the lengthy historical response of the cell to extracellular proliferation, differentiation, and death by activating MAPK or other signaling pathways. Nuclear transcription factor kappa B (NF-κB), which has a sequence-specific dimeric structure, is an important transcription factor abundant in mammalian cells that can bind specifically to a variety of cellular gene promoters and enhancer sequences (Byeon et al., 2012, Kwak et al., 2011, Yamanaka et al., 2011); NF-κB plays an important role in immune response, inflammatory reaction, and cell growth regulation by controlling the expression of many important cytokines, adhesion molecules, and chemokines. Its activation is also involved in cell proliferation and apoptosis processes (Byeon et al., 2012, Kwak et al., 2011, Yamanaka et al., 2011), and it is also the main regulator of inflammation and oxidative stress reactions (Goldin et al., 2006, Gratas-Delamarche et al., 2014). In this study, P65 protein expression increased significantly in the hippocampus of gp120-treated rats, implying that NF-κB may play a sizable role in gp120-induced learning and memory deficits mediated by P2X7 receptors. This is also important to consider alongside the fact that BBG had no effect on P65 protein expression in the hippocampus of naïve rats.