Sodium salicylate enhances neural excitation via reducing GABAergic transmission in the dentate gyrus area of rat hippocampus in vivo

Repeated injections of isovaline lead to analgesic tolerance and cross-tolerance to salicylate but not to morphine in male mice

Tolerance to the antinociceptive effects of opioids is a major concern. Studies have shown that chronic use of non-steroidal anti-inflammatory (NSAIDs) causes significant tolerance and cross-tolerance to morphine. Chronic NSAIDs use can increase the risk of certain diseases, such as peptic ulcers, and exacerbate others, like heart failure. Therefore, developing novel pharmacological approaches could provide considerable benefits for chronic therapeutic procedures. Isovaline with a chemical structure similar to glycine and GABA induce a significant analgesic effect through GABA-B receptors. In this study, we investigated the impact of both short-term and long-term use of isovaline on the immediate response to pain, as well as the development of analgesic tolerance through daily injection (i.p.) of isovaline (100 mg/kg) for 5 days in male Balb/c mice. Additionally, on day 6, we examined the potential for cross-tolerance between isovaline and sodium salicylate (300 mg/kg) or morphine (5 mg/kg). The findings showed that isovaline injection resulted in a delayed onset of analgesic effect, a lowered peak effect, and less cumulative pain relief compared with sodium salicylate and morphine. This analgesic effect gradually decreased over the five days of isovaline injection. When sodium salicylate was injected into isovaline-tolerant mice, the antinociceptive effect decreased, suggesting cross-tolerance to sodium salicylate. However, no such tolerance was observed following morphine injection. Accordingly, it seems that chronic isovaline may interact with the sodium salicylate analgesic pathway but not with morphine.

Long-term maintenance of synaptic plasticity by Fullerenol Ameliorates lead-induced-impaired learning and memory in vivo

Fullerenol, a functional and water-soluble fullerene derivative, plays an important role in antioxidant, antitumor and antivirus, implying its enormous potential in biomedical applications. However, the in vivo performance of fullerenol remains largely unclear. We aimed to investigate the effect of fullerenol (i.p., 5 mg/kg) on the impaired hippocampus in a rat model of lead exposure. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) is a kind of newly developed soft-ionization mass spectrometry technology. In the present study, an innovative strategy for biological distribution analysis using MALDI-TOF-MS confirmed that fullerenol could across the blood-brain barrier and accumulate in the brain. Results from behavioral tests showed that a low dose of fullerenol could improve the impaired learning and memory induced by lead. Furthermore, electrophysiology examinations indicated that this potential repair effect of fullerenol was mainly due to the long-term changes in hippocampal synaptic plasticity, with enhancement lasting for more than 2-3 h. In addition, morphological observations and biochemistry analyses manifested that the long-term change in synaptic efficacy was accompanied by some structural alteration in synaptic connection. Our study demonstrates the therapeutic feature of fullerenol will be beneficial to the discovery and development as a new drug and lays a solid foundation for further biomedical applications of nanomedicines.

Salicylate Induced GABAAR Internalization by Dopamine D1-Like Receptors Involving Protein Kinase C (PKC) in Spiral Ganglion Neurons

BACKGROUND Sodium salicylate (SS) induces excitotoxicity of spiral ganglion neurons (SGNs) by inhibiting the response of γ-aminobutyric acid type A receptors (GABAARs). Our previous studies have shown that SS can increase the internalization of GABAARs on SGNs, which involves dopamine D1-like receptors (D1Rs) and related signaling pathways. In this study, we aimed to explore the role of D1Rs and their downstream molecule protein kinase C (PKC) in the process of SS inhibiting GABAARs. MATERIAL AND METHODS The expression of D1Rs and GABARγ2 on rat cochlear SGNs cultured in vitro was tested by immunofluorescence. Then, the SGNs were exposed to SS, D1R agonist (SKF38393), D1R antagonist (SCH23390), clathrin/dynamin-mediated endocytosis inhibitor (dynasore), and PKC inhibitor (Bisindolylmaleimide I). Western blotting and whole-cell patch clamp technique were used to assess the changes of surface and total protein of GABARγ2 and GABA-activated currents. RESULTS Immunofluorescence showed that D1 receptors (DRD1) were expressed on SGNs. Data from western blotting showed that SS promoted the internalization of cell surface GABAARs, and activating D1Rs had the same result. Inhibiting D1Rs and PKC decreased the internalization of GABAARs. Meanwhile, the phosphorylation level of GABAARγ2 S327 affected by PKC was positively correlated with the degree of internalization of GABAARs. Moreover, whole-cell patch clamp recording showed that inhibition of D1Rs or co-inhibition of D1Rs and PKC attenuated the inhibitory effect of SS on GABA-activated currents. CONCLUSIONS D1Rs mediate the GABAAR internalization induced by SS via a PKC-dependent manner and participate in the excitotoxic process of SGNs.