Abstract
Introduction
Epilepsy is a common neurological disorder that presents with challenging mechanisms and treatment strategies. This study investigated the neuroprotective effects of quinpirole on lithium chloride pilocarpine-induced epileptic rats and explored its potential mechanisms.
Methods
Lithium chloride pilocarpine was used to induce an epileptic model in rats, and the effects of quinpirole on seizure symptoms and cognitive function were evaluated. The Racine scoring method, electroencephalography, and Morris water maze test were used to assess seizure severity and learning and memory functions in rats in the epileptic group. Additionally, immunohistochemistry and Western blot techniques were used to analyze the protein expression levels and morphological changes in glutamate receptor 2 (GluR2; GRIA2), BAX, and BCL2 in the hippocampi of rats in the epileptic group.
Results
First, it was confirmed that the symptoms in rats in the epileptic group were consistent with features of epilepsy. Furthermore, these rats demonstrated decreased learning and memory function in the Morris water maze test. Additionally, gene and protein levels of GluR2 in the hippocampi of rats in the epileptic group were significantly reduced.
Quinpirole treatment significantly delayed seizure onset and decreased the mortality rate after the induction of a seizure. Furthermore, electroencephalography showed a significant decrease in the frequency of the spike waves. In the Morris water maze test, rats from the quinpirole treatment group demonstrated a shorter latency period to reach the platform and an increased number of crossings through the target quadrant. Network pharmacology analysis revealed a close association between quinpirole and GluR2 as well as its involvement in the cAMP signaling pathway, cocaine addiction, and dopaminergic synapses.
Furthermore, immunohistochemistry and Western blot analysis showed that quinpirole treatment resulted in a denser arrangement and a more regular morphology of the granule cells in the hippocampi of rats in the epileptic group. Additionally, quinpirole treatment decreased the protein expression of BAX and increased the protein expression of BCL2.
Conclusion
The current study demonstrated that quinpirole exerted neuroprotective effects in the epileptic rat model induced by lithium chloride pilocarpine. Additionally, it was found that the treatment not only alleviated the rats' seizure symptoms, but also improved their learning and memory abilities. This improvement was linked to the modulation of protein expression levels of GLUR2, BAX, and BCL2. These findings provided clues that would be important for further investigation of the therapeutic potential of quinpirole and its underlying mechanisms for epilepsy treatment.
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Introduction
Epilepsy is a common neurological disorder characterized by recurrent seizures and cognitive impairments. However, significant challenges persist in understanding its underlying mechanisms and develo** effective treatment strategies. Despite extensive research on the aforementioned topic, an optimal therapeutic approach for epilepsy remains elusive [1]. Therefore, it is critical to investigate new potential treatments that can provide neuroprotective effects and improve seizure symptoms and cognitive function.
In the present study, the researchers investigated the effects of quinpirole, which is a compound known for its potential neuroprotective properties, in an epileptic rat model induced by lithium chloride pilocarpine [2]. Understanding the mechanisms underlying the neuroprotective effects of quinpirole is essential for the development of improved therapeutic strategies for epilepsy.
To evaluate the effects of quinpirole on the symptoms of seizures and cognitive function, an epileptic rat model induced by lithium chloride pilocarpine was utilized. Manifestation of seizures was assessed using the Racine scoring method, and learning and memory functions were evaluated using the Morris water maze test [3]. In addition, electroencephalography (EEG) and immunohistochemistry techniques were used to analyze the protein expression levels of GluR2, BAX, and BCL2 and morphological changes in the hippocampi, which is a key brain region involved in epilepsy [4].
The results of the current study confirmed that the rat model displayed features that were consistent with those of epilepsy. Furthermore, the rats exhibited impaired learning and memory functions, as indicated by the Morris water maze test. The hippocampi of rats in the epileptic group exhibited significantly reduced gene and protein levels of GluR2, suggesting its involvement in the pathogenesis of epilepsy [5].
Quinpirole treatment demonstrated promising results in alleviating symptoms of seizures and improving cognitive function. Notably, quinpirole delayed the onset of seizure and resulted in a decreased frequency of spike waves, as observed by EEG. Moreover, the rats in the quinpirole treatment group exhibited improved performance in the Morris water maze test, with a shorter latency period to reach the platform and an increased number of crossings through the target quadrant.
Furthermore, network pharmacology analysis revealed an intriguing association between quinpirole and GluR2, suggesting its involvement in various signaling pathways associated with epilepsy, such as the cAMP signaling pathway and those related to cocaine addiction and dopaminergic synapses [6,7,8].
Immunohistochemistry and Western blot analysis further corroborated the neuroprotective effects of quinpirole. Notably, quinpirole treatment resulted in a denser arrangement and more regular morphology of granule cells in the hippocampus, indicating potential structural improvements [9]. Additionally, quinpirole treatment decreased the protein expression of pro-apoptotic BAX and increased the protein expression of anti-apoptotic BCL2 [10.11].
In conclusion, this study demonstrated the neuroprotective effects of quinpirole in a rat model of epilepsy. Improvements were observed in symptoms of seizures and cognitive function, which were associated with the modulation of the protein expression levels of GluR2, BAX, and BCL2. These findings provided valuable insights into the potential therapeutic role of quinpirole in epilepsy treatment and established a foundation for further investigation into the underlying mechanisms. Ultimately, the findings of the current research may contribute to the development of novel treatment strategies for epilepsy.
Methods
Animals
Twenty-one-day-old healthy male Wistar rats (weight: 55 ± 3 g) were purchased from the Experimental Animal Center of Shandong University. The rats were randomly divided into the following groups: the control group, the epileptic group, and the quinpirole group. The rats were housed in the animal facility of the Research Centre Laboratory, Tai'an Central Hospital, with a 12-h light/dark cycle and free access to food and water. All the rats were euthanized through an overdose of sodium pentobarbital. Thereafter, they underwent cardiac perfusion with physiological saline for biochemical analysis and were perfused with 4% paraformaldehyde for histological analysis. All the experimental procedures were approved by the Animal Care and Use Committee of the Tai'an Central Hospital and conducted in accordance with the guidelines of the institution. Ethics-related documents are presented in Supplement 1. Lithium chloride (30 mg/kg, Sigma-Aldrich, St. Louis, Missouri, USA) was injected intraperitoneally into the rats, and pilocarpine (30 mg/kg, Sigma-Aldrich) was injected in a similar manner after 24 h. In the control group, an equivalent volume of normal saline was administered as a substitute for pilocarpine. Quinpirole was injected into the lateral ventricle of the rats 60 min before injecting pilocarpine in the quinpirole group. Meanwhile, an equivalent volume of normal saline was injected as a substitute for quinpirole in the epileptic group. After the injection was completed, the syringe was kept at the site of injection for 5 min and then carefully withdrawn. The injection site was 0.7 mm behind the fontanel, 1.3 mm outside the midline, and 3.0 mm in depth [25]. However, rats treated with quinpirole showed improved cognitive performance, as indicated by a reduced latency period to reach the platform and an increased number of crossings of the target quadrant. These results suggested that quinpirole treatment not only reduced seizures, but also preserved cognitive function in rats with epilepsy induced by lithium chloride pilocarpine. Frequent and sustained seizures may cause changes in the variety of amino acids and neurotransmitters in the brain, further resulting in neuronal necrosis in the responding regions [26]. To further understand the underlying mechanisms of the neuroprotective effects of quinpirole, the protein expression levels of GluR2, BAX, and BCL2 in the hippocampus were investigated. GluR2 is a subunit of the AMPA receptor, which plays a critical role in excitatory synaptic transmission [27]. In the current study, a significant decrease in GluR2 expression was observed in the hippocampi of rats with epilepsy. This reduction in GluR2 expression may contribute to the increased permeability for calcium ions and apoptosis of neuronal cells observed in epilepsy [28]. Interestingly, the quinpirole treatment reversed the decrease in GluR2 expression, suggesting that it may regulate glutamate signaling and restore the balance between excitatory and inhibitory neurotransmission [10, 29, 30]. This was consistent with the findings of previous studies, which demonstrated the neuroprotective effects of dopamine receptor agonists on glutamatergic neurotransmission [31].
Moreover, network pharmacology analysis revealed a close relationship between quinpirole and GluR2, further supporting the involvement of glutamate signaling in the therapeutic effects of quinpirole. The decreased expression of GluR2 in a variety of neurological diseases increases the inward flow of calcium ions, which can activate protease, phospholipase, and ATPase, ultimately leading to cellular swelling and apoptosis of neurocytes. Additionally, KEGG pathway analysis suggested the potential involvement of the cAMP signaling pathway and other pathways related to cocaine addiction and dopaminergic synapses [32,33,34]. Furthermore, the protein expression levels of BAX and BCL2 were investigated, which are involved in regulating apoptosis. In the epileptic group, an increase in BAX expression and a decrease in BCL2 expression were observed, indicating an imbalance between pro-apoptotic and anti-apoptotic factors. However, quinpirole treatment reversed these changes, suggesting its potential role in inhibiting apoptosis and promoting neuronal survival [35, 36].
In conclusion, the study highlights promising neuroprotective effects of quinpirole in an epileptic model induced by lithium chloride pilocarpine. Further, quinpirole treatment effectively reduced seizure activity, improved cognitive function, and regulated the protein expression of GLUR2, BAX, and BCL2 in the hippocampus. These findings provided important insights into the potential therapeutic benefits of quinpirole and its underlying mechanisms in the treatment of epilepsy. Further studies are warranted to explore the clinical potential of quinpirole and its optimal dosage and treatment regimen for epilepsy.
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This project was supported by the Tai’an City Science and Technology Innovation Development Project (2018NS0221). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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WH, ZY, and ZD conceived and designed the experiments, performed the experiments, analyzed the data, prepared figures and/or tables, and approved the final draft. LJ and YK conceived and designed the experiments, authored or reviewed drafts of the paper, and approved the final draft. LB and YJ conceived and designed the experiments, authored or reviewed drafts of the paper, and approved the final draft.
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Wang, H., Zhao, Y., Zhang, D. et al. Neuroprotective effects of quinpirole on lithium chloride pilocarpine-induced epilepsy in rats and its underlying mechanisms. Eur J Med Res 29, 121 (2024). https://doi.org/10.1186/s40001-024-01694-x
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DOI: https://doi.org/10.1186/s40001-024-01694-x