Effect of Long-Term Sodium Salicylate Administration on Learning, Memory, and Neurogenesis in the Rat Hippocampus

Exploring the effects of naringenin on cell functioning and energy synthesis in the hippocampus of male Wistar rats with chronic tinnitus, by examining genetic indicators such as Bax, Bcl-2, Tfam, and Pgc-1α

BACKGROUND

The pivotal factors, including neural plasticity, oxidative stress, neuronal inflammation, and apoptosis, play a significant role in the pathogenesis of tinnitus. The balance between Bax/Bcl-2 genes is an important factor in determining the rate of apoptosis. Pgc-1α and Tfam genes are fundamental regulators of mitochondrial biogenesis. Naringenin possesses significant antioxidant, neuroprotective, anti-inflammatory, anti-apoptotic, and antiviral properties, and its compounds are effective on cell signaling pathways.

AIMS

In light of the aforementioned information, we endeavored to evaluate the impact of naringenin on the expression levels of Bax, Bcl-2, Pgc-1α, and Tfam genes in the hippocampus of male Wistar rats with chronic tinnitus.

MATERIAL AND METHODS

To demonstrate the existence of tinnitus, all rats were instructed to complete an "active avoidance test" utilizing a conditioning box. The expression levels of genes mentioned above were assessed using real-time PCR.

RESULTS

The sodium salicylate at a dosage of 350 mg/kg showed an upregulation in the expression level of Bax and a downregulation in the expression level of the Bcl-2 gene (p < 0.001). Furthermore, the sodium salicylate displayed significantly higher expression levels of Tfam and Pgc-1α (p < 0.001) genes. The naringenin, at a dose of 100 mg/kg, led to a decrease in Bax gene expression (p < 0.05) and an increase in Bcl-2 gene expression (p < 0.05). On the other hand, naringenin restored the expression level of both Tfam (p < 0.001) and Pgc-1α (p < 0.01) genes.

CONCLUSIONS

Our research findings demonstrate that sodium salicylate-induced tinnitus leads to enhanced apoptosis and mitochondrial biogenesis within the hippocampus. Additionally, our evidence recommends that naringenin can reduce apoptosis effectively and maintain a balanced mitochondrial state.

Molecular and behavioral effects of Acamprosate in male rats with sodium salicylate-induced tinnitus

BACKGROUND

Imbalance in inhibitory and excitatory neurotransmitters have been reported in tinnitus. Acamprosate modulates the excitatory and inhibitory neurotransmission in the nucleus accumbens (NAc). This study aims to assess the effect of Acamprosate on tinnitus, anxiety, depression, and molecular changes in nucleus accumbens (NAc), in Sodium-Salisylate (S-salicylate) model of tinnitus.

METHODS

Forty-four adult male wistar rats were used in this study. The study included Control, Saline, and S-salicylate groups during the first week, which then subdivided into five groups as Control, Saline, S-salicylate, Acamprosate, and S-salicylate+Acamprosate. Gap-in Noise (GIN) and pre-pulse inhibition (PPI) were used to assessment of tinnitus at baseline, day7 and day14. Anxiety and depression were evaluated on day 14, by elevated plus maze (EPM), open field (OF), and tail suspension (TST) tests. The protein expression of GABAAR-δ, NR1 and NR2B in NAc were also measured using western blot technique.

RESULTS

After seven days GIN reduced in S-salicylate compare to Control and Saline groups (P < 0.5), while PPI unchanged. After 14 days, GIN reduced in S-salicylate and S-salicylate+Acamprosate groups compare to Control; Saline; and Acamprosate groups (P < 0.5). Additionally, GIN was higher in S-salicylate+Acamprosate compare to S-salicylate group (P < 0.5). PPI was not changed after 14 days. Open arm time in EPM test was decreased in S-salicylate and S-salicylate+Acamprosate groups compare to Control; Saline; and Acamprosate groups (P < 0.5). Central Zone time in OF test was reduced in S-salicylate group compare to Control, Saline, Acamprosate, and S-salicylate+Acamprosate groups (P < 0.5). Immobility Time in TST was increased in S-salicylate group compare to Control, Saline, Acamprosate, and S-salicylate+Acamprosate groups (P < 0.5). GABAAR-δ was decreased in S-salicylate groups compare to Control, Saline, Acamprosate; and S-salicylate+Acamprosate groups (P < 0.5). NR1 and NR2B in NAc were increased in S-salicylate group compare to Control, Saline, Acamprosate, and S-salicylate+Acamprosate groups (P < 0.5).

CONCLUSION

S-salicylate can induce tinnitus-like behaviors in rat. Furthermore, S-salicylate induced depression/anxiety like behaviors, and changed the expression of GABAR and NMDAR subunits in NAc. Acamprosate partially reversed these changes. In conclusion, NAc may be involved in the pathophysiologic mechanisms of tinnitus.

Modulations of resting-static functional connectivity on insular by electroacupuncture in subjective tinnitus

Objective

To explore the modulations of electroacupuncture in subjective tinnitus (ST) by comparing the difference of functional connectivity (FC) in ST patients and healthy volunteers between the insular (INS) and the whole brain region.

Methods

A total of 34 ST patients were selected into electroacupuncture group (EG) and 34 age- and sex-matched normal subjects were recruited into control group (CG). The EG received acupuncture at SI19 (Tinggong), GB11 (Touqiaoyin), TE17 (Yifeng), GV20 (Baihui), GV15 (Yamen), GV14 (Dazhui), SJ13 (Zhongzhu), among which the points of SI19 and GB11 were connected to the electroacupuncture instrument with the density wave of 2/50 Hz, and 3 treatments per week for 10 sessions in total. The severity of tinnitus was evaluated by Tinnitus Handicap Inventory (THI), the hearing status was recorded using pure tone audiometry, and resting-state functional magnetic resonance imaging (rs-fMRI) was performed on the brain before and after treatment, the CG received no intervention yet only rs-fMRI data were collected.

Results

With the electroacupuncture treatment, the total THI score, average air conduction threshold of patients of EG were significantly lower than before (p < 0.01), and the total effective rate was 88.24%. Compared with CG, FC of ST patients between INS and left superior temporal gyrus and right hippocampal significantly decreased before treatment, while FC of ST patients between INS and right superior frontal gyrus, left middle frontal gyrus and right anterior cuneus significantly decreased after treatment (voxel p < 0.001, cluster p < 0.05, corrected with GRF). FC of ST patients between the INS and right middle frontal gyrus, left superior frontal gyrus and right paracentral lobule showed a significant decrease after treatment (voxel p < 0.001, cluster p < 0.05, corrected with GRF). In addition, THI score in EG was negatively correlated with the reduction of FC value in INS-left superior frontal gyrus before treatment (r = -0.41, p = 0.017). Therefore, this study suggests that abnormal FC of INS may be one of the significant central mechanisms of ST patients and can be modulated by electroacupuncture.

Discussion

Electroacupuncture treatment can effectively reduce or eliminate tinnitus symptoms in ST patients and improve the hearing by decreasing FC between the INS and the frontal and temporal brain regions.

Endoplasmic reticulum stress and mitochondrial injury are critical molecular drivers of AlCl3-induced testicular and epididymal distortion and dysfunction: protective role of taurine

Aluminum, the third most plentiful metal in the Earth's crust, has potential for human exposure and harm. Oxidative stress plays an essential role in producing male infertility by inducing defects in sperm functions. We aimed to investigate the role of endoplasmic reticulum (ER) stress and mitochondrial injury in the pathogenesis of aluminum chloride (AlCl3)-induced testicular and epididymal damage at the histological, biochemical, and molecular levels, and to assess the potential protective role of taurine. Forty-eight adult male albino rats were separated into four groups (12 in each): negative control, positive control, AlCl3, and AlCl3 plus taurine groups. Testes and epididymis were dissected. Histological and immunohistochemical (Bax and vimentin) studies were carried out. Gene expression of vimentin, PCNA, CHOP, Bcl-2, Bax, and XBP1 were investigated via quantitative real-time polymerase chain reaction (qRT-PCR), besides estimation of malondialdehyde (MDA) and total antioxidant capacity (TAC). Light and electron microscopic examinations of the testes and epididymis revealed pathological changes emphasizing both mitochondrial injury and ER stress in the AlCl3 group. Taurine-treated rats showed a noticeable improvement in the testicular and epididymal ultrastructure. Moreover, they exhibited increased gene expression of vimentin, Bcl-2, and PNCA accompanied by decreased CHOP, Bax, and XBP1 gene expression. In conclusion, male reproductive impairment is a significant hazard associated with AlCl3 exposure. Both ER stress and mitochondrial impairment are critical mechanisms of the deterioration in the testes and epididymis induced by AlCl3, but taurine can amend this.

Neuroprotective Effect of Valproic Acid on Salicylate-Induced Tinnitus

High-dose salicylate induces temporary moderate hearing loss and the perception of a high-pitched tinnitus in humans and animals. Previous studies demonstrated that high doses of salicylate increase N-methyl-d-aspartate (NMDA) receptor levels, resulting in a rise in Ca²⁺ influx and induction of excitotoxicity. Glutamate excitotoxicity is associated with failure in the maintenance of calcium homeostasis, mitochondrial dysfunction, and production of reactive oxygen species (ROS). Valproic acid (VPA) is widely used for the management of bipolar disorder, epilepsy, and migraine headaches, and is known to regulate NMDA receptor activity. In this study, we examined the beneficial effects of VPA in a salicylate-induced tinnitus model in vitro and in vivo. Cells were pretreated with VPA followed by salicylate treatment. The expression levels of NMDA receptor subunit NR2B, phosphorylated cAMP response element-binding protein—an apoptosis marker, and intracellular levels of ROS were measured using several biochemical techniques. We observed increased expression of NR2B and its related genes TNFα and ARC, increased intracellular ROS levels, and induced expression of cleaved caspase-3. These salicylate-induced changes were attenuated in the neuronal cell line SH-SY5Y and rat cortical neurons after VPA pretreatment. Together, these results provide evidence of the beneficial effects of VPA in a salicylate-induced temporary hearing loss and tinnitus model.

Non-selective COX inhibitors impair memory formation and short-term but not long-term synaptic plasticity

Cyclooxygenase (COX) plays a critical role in synaptic plasticity. Therefore, long-term administration of acetylsalicylic acid (ASA) and its main metabolite, salicylate, as a COX inhibitor may impair synaptic plasticity and subsequently memory formation. Although different studies have tried to explain the effects of ASA and sodium salicylate (SS) on learning and memory, the results are contradictory and the mechanisms are not exactly known. The present study was designed to investigate the effects of long-term low-dose (equivalent to prophylactic dose) and short-term high-dose (equivalent to analgesic dose) administration of ASA and SS respectively, on spatial learning and memory and hippocampal synaptic plasticity. Animals were treated with a low dose of ASA (2 mg/ml solvated in drinking water, 6 weeks) or a high dose of SS, a metabolite of ASA, (300 mg/kg, 3 days, twice-daily, i.p). Spatial memory and synaptic plasticity were assessed by water maze performance and in vivo field potential recording from CA1, respectively. Animals treated with ASA but not SS showed a significant increase in escape latency and distance moved. Furthermore, in the probe test, animals treated with both drugs spent less time in the target quadrant zone. The paired-pulse ratio (PPR) at 20-ms inter-pulse intervals (IPI) as an index of short-term plasticity in both treated groups was significantly higher than of the control group. Interestingly, none of the administered drugs affected long-term potentiation (LTP). These data suggested that long-term inhibition of COX disrupted memory acquisition and retrieval. Interestingly, cognitive impairments happened along with short-term but not long-term synaptic plasticity disturbance.

Hippocampal Subgranular Zone FosB Expression Is Critical for Neurogenesis and Learning

Neural proliferation in the dentate gyrus (DG) is closely linked with learning and memory, but the transcriptional programming that drives adult proliferation remains incompletely understood. Our lab previously elucidated the critical role of the transcription factor ΔFosB in the dorsal hippocampus (dHPC) in learning and memory, and the FosB gene has been suggested to play a role in neuronal proliferation. However, the subregion-specific and potentially cell-autonomous role of dHPC ΔFosB in neurogenesis-dependent learning has not been studied. Here, we crossed neurotensin receptor-2 (NtsR2) Cre mice, which express Cre within the subgranular zone (SGZ) of dHPC DG, with floxed FosB mice to show that knockout of ΔFosB in hippocampal SGZ neurons reduces antidepressant-induced neurogenesis and impedes hippocampus-dependent learning in the novel object recognition task. Taken together, these data indicate that FosB gene expression in SGZ is necessary for both hippocampal neurogenesis and memory formation.