E169 (5 mg) produced a significant memory-enhancing effect on MK801-induced short- and long-term memory impairments in NORT. Keywords: H3R antagonists, MK801-induced amnesia in mice, PI3K/AKT/GSK-3β signaling pathway, novel object recognition test, memory, cognition,.
Introduction
Overview
Statement of the problem
Research objectives
Memory
- Types of memory
- Stages of memory formation
Information must be translated into a form that our memory system can understand in order to be stored, so when new information is received (via sensory input), our memory system begins to encode this information using one of three methods: auditory (sound). visual (picture) and semantic (meaning) (Frankland et al., 2019; Josselyn et al., 2015). As a result, restoring the internal physiological state may be sufficient to restore the affected memory (Gisquet-Verrier et al., 2015).
Role of sleep in memory
Primate amnesia modeling is much more difficult than the previous two modeling approaches, takes considerably longer and costs much more money, but it models human global amnesia better and makes more sense to investigate amnesia processes and therapies (Morgan et al., 1982), and genetics, where rodents have been genetically modified by researchers to lack functionally or behaviorally significant alleles or to have missing or altered gene sequences (Blundell et al., 2010; Mouri et al., 2010). Recent memories are thought to be transferred from short-term memory storage sites in the hippocampus to long-term memory storage sites during this slow-wave sleep (Diekelmann & Born, 2010).
Role of hippocampus in memory
Several studies showed that selective damage to the hippocampus has a significant impact on recognition memory retrieval (Gaskin et al., 2010). As a result, CA3 functions as a buffer, helping to retrieve information from short-term memory, which is common in cognitive tasks used in an experimental setting, such as recall tests (Lee et al., 2017). CA1 appears to become more salient when the delay is extended beyond the short-term interval of 5 min to 24 h (Hunsaker & Kesner, 2018).
PI3K/AKT/GSK-3β signaling pathway
- PI3K/AKT/GSK-3β signaling pathway and cognition
- PI3K/AKT/GSK-3β signaling pathway and neuroinflammation
Glycogen synthase kinase-3 (GSK-3β) was the first protein identified as a substrate in the activation of AKT (Xu et al., 2020) and its role in the propagation of apoptotic signals has been well established in several studies. by increasing the . Activated AKT leads to phosphorylation of GSK-3β at Ser9, making it more susceptible to degradation (Yea & Fruman, 2013). In the absence of GSK-3β, the apoptotic signal in the cells would be dampened and thus neural stem cells (NSCs) would have a better survival rate and have a neuroprotective effect due to the absence of GSK-3β (Watanabe et al., 2006).
Neuroinflammation and memory
Microglia have also been implicated in causing injury by apparently switching from a benign anti-inflammatory state (known as M2) to a harmful pro-inflammatory state (known as M1) which generates and releases cytokines and chemokines (Bilbo & Schwarz, 2012). Microglia play a key role in modulating synaptic plasticity, including LTP, LTD (Hansen et al., 2018), memory enhancement, better sensory-motor function, and. This persistent activation of microglia causes an increase in the release of proinflammatory cytokines and decreases phagocytic activity, all of which lead to decreased synaptic plasticity and impairment of learning and memory (Cornell et al., 2022).
Activation of microglia causes the release of various pro-inflammatory cytokines such as interferon and interleukins. Under completely natural conditions it results in microglia switching to an anti-inflammatory phenotype (M2) and starting to release anti-inflammatory cytokines such as brain-derived neurotrophic factor, nerve growth factor and interleukin which help restore synaptic function. On the other hand, under pathological circumstances, microglia cells will not return to their resting position, resulting in inflammation characterized by an excess of pro-inflammatory cytokines and a decrease in neuroprotective factors.
Consequently, continuous activation of the innate and adaptive immune system is a key factor in the development of various dementias and Alzheimer's disease (Bagyinszky et al., 2017; Obulesu & Jhansilakshmi, 2014; Tournier et al., 2020).
Neuroinflammation and cognitive disorders
- Neuroinflammation and dementia
- Neuroinflammation and Alzheimer’s disease (AD)
- Neuroinflammation and Parkinson's disease (PD)
These variables worsen synaptic excitation and brain network connectivity, which accelerates synaptic dysfunction and neurodegeneration (Giacobbo et al., 2019). Although there is no known etiology for Alzheimer's disease, persistent inflammatory processes are known to play a role in the development of amyloid plaques, resulting in additional accumulation and inflammatory processes that affect neuronal connections because it is a pro-inflammatory causing a response in which microglia increase. the release of cytokines (Interleukins and TNF-α), chemokines (NF-kB) and peptides (bradykinin) (Gorlovoy et al., 2009). The release of various proteases involved in amyloid degradation also promotes amyloid plaque clearance (Hickman et al., 2018; Simard et al., 2006; Wang & Colonna, 2019).
Despite the benefits of early microglia cell activation, persistent activation by amyloid plaques is harmful and causes chronic inflammation and excessive amyloid plaque accumulation that accelerates neurodegeneration ( Simard et al., 2006 ). In addition, microglia's usual phagocytic activity decreased, leading to neuroinflammation and neurodegeneration (Businaro et al., 2018; Ledo et al., 2016). The activity of amyloid precursor protein-cleaving enzyme 1 is reduced as a result of this activation leading to reduced amyloid plaque formation (Deardorff & Grossberg, 2017; Rawat et al., 2019).
Minocycline protects the brain by reducing levels of inflammatory markers including IL-6 as well as microglial activation (Cheng et al., 2015).
Histamine and memory
- Histamine receptors
- Effect of histamine on microglia
Endogenous histamine mediates a variety of physiological processes through four different subtypes (H1, H2, H3, and H4) that are all G protein-coupled receptors ( Alexander et al., 2007 ). The role of histaminergic neurotransmission via central H1Rs was highlighted by recent findings (Dai et al., 2007; Mobarakeh et al., 2000). H4 receptors are bound to the Gi/o protein in the same way as H3Rs, but unlike H3Rs they are mainly expressed in the periphery (Zhu et al., 2001).
Humans have high levels of H3R expression in the hippocampus, frontal cortex, hypothalamus and cortex (MARTINEZ-MIR et al., 1990). While the H3R in mice is most abundant in the cerebral cortex, hippocampal formations, and hypothalamus (Drutel et al., 2001), all of these brain locations are involved in cognition. In a normal state, histamine increases microglia cell motility, phagocytosis activity, NADPH oxidase (Nox) activation and increased ROS generation ( Barata-Antunes et al., 2017 ).
Histamine has both positive and negative effects on microglial activity (Biber et al., 2007; Zhang et al., 2020).
Materials and Methods
- Animals
- Drugs
- Reagents and antibodies
- Behavioral tests
- Novel object recognition test
- Open Field Test (OFT)
- Biochemicals assessment
- Brain collection and tissue processing
- Western blotting
- Data analysis
During the test session (T2), each mouse was left in the test arena for 5 minutes with one of the old objects and another new object and observed for 5 minutes. Vehicle (DMSO) was injected to remove any biasing effect of the injection procedure or the vehicle itself on memory. After each mouse's completion of the test, the open field test area was carefully wiped with 70%.
Usually, excessive anxiety causes experimental mice to spend less time in the center of the arena and more time closer to the walls (in the periphery). On the other hand, higher time spent in the center of the test arena suggests lower anxiety and more exploratory behavior in tested animals (Walsh & Cummins, 1976). Following the previously reported protocol (Eissa et al., 2020), the animals were euthanized at the end of the behavioral tests.
Evacuation of blood was confirmed by the pale color of the liver, heart, and kidneys, confirming that they were bloodless.
Results
- Overview of the main findings
- NORT
- STM in naïve and MK801- treated mice
- DI for STM in naïve and MK801-treated mice
- LTM in naïve and MK801-treated mice
- DI for LTM in naïve and MK801-treated mice
- Open Field Test (OFT)
- Results in OFT for naive mice following STM experiment
- Results in OFT for naive mice following LTM experiment
- Results in OFT for MK801- treated mice following STM experiment
- Results in OFT for MK801- treated mice following LTM experiment
- Western blot
Compared to the MK801-treated group, Figure (9-B) shows that the group injected only with MK801 showed memory impairment due to the amnesic effect of MK801 and showed a significantly lower percentage of time spent exploring the novel objects compared to time spent exploring the novel objects in naïve mice (F P<0.05). While systemic administration of the 5 mg/kg dose produced a significant increase in time spent exploring the novel objects (F P<0.01) compared to the MK801-treated mice, indicating that there was an improved effect on memory, and similar results were. Experimental mice injected with the PI3K inhibitor (LY mg/kg i.p) showed a significant increase in time spent exploring the novel objects compared to MK801-treated mice (F P<0.05), demonstrating that LY294002 has a positive effect on memory impairment induced with MK801 in mice.
However, the group co-injected with E169 (5 mg/kg) and LY mg/kg) showed significantly more time spent exploring novel objects when. Similarly, the RAMH-treated group significantly decreased the time spent exploring novel objects compared to naïve rats (F P<0.05). Compared to the MK801-treated group, Figure (11-B) shows that the group injected with MK801 alone exhibited memory impairment due to the amnesic effect of MK801 and demonstrated a significantly lower percentage of time spent exploring objects novel compared to time spent exploring novel objects in naïve control mice (F P<0.05).
However, mice treated with (5 mg/kg) showed a significant increase in the time spent exploring novel objects (F P<0.01) compared to MK801-treated mice, indicating a memory-enhancing effect of E169 at this dose level.
Discussion
The latest findings are consistent with a previous study in which RAMH abolished the memory-enhancing effects of the H3R antagonist ciproxifan on LTM in experimental rodents (Pascoli et al., 2009). Accordingly, hyperphosphorylation of pathogen tau was found to increase β-amyloid synthesis and that memory impairments are all caused by unphosphorylated GSK-3β (Giacobini & Becker, 2007; Hooper et al., 2008; Jaworski et al., 2011). It has also been suggested that H3R antagonists may improve cognitive functions in a variety of cognitive disorders by increasing ACh release and inducing pGSK-3β (Bitner et al., 2011; Passani & Blandina, 2011).
MK801, and these results were consistent with previous preclinical experiments performed in experimental rodents (Svenningsson et al., 2003). Surprisingly, (Kitagawa et al., 2002) found that only Ser473-Akt phosphorylation became overactive when neurons in rat culture were exposed to glutamate, but not overactivated phosphorylation of Ser473-Akt. However, and contrary to the latter results, our observations showed that the NMDA receptor antagonist MK801 was able to overactivate Ser473-Akt phosphorylation (Kitagawa et al., 2002).
The observed results showed that LY294002 impaired performance in NORT in control mice, and the impairments obtained in our experiments were similar to those reported in several previous rodent preclinical studies (Barros et al., 2001; Chen et al., 2005; Slouzkey et al al., 2013).
Conclusion
Limitations and future directions of the study
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