Trans-Anethole Alleviates Trimethyltin Chloride-Induced Impairments in Long-Term Potentiation

Abstract

Trans-anethole is an aromatic compound that has been studied for its anti-inflammation, anticonvulsant, antinociceptive, and anticancer effects. A recent report found that trans-anethole exerted neuroprotective effects on the brain via multiple pathways. Since noxious stimuli may both induce neuronal cell injury and affect synaptic functions (e.g., synaptic transmission or plasticity), it is important to understand whether the neuroprotective effect of trans-anethole extends to synaptic plasticity. Here, the effects of trimethyltin (TMT), which is a neurotoxic organotin compound, was investigated using the field recording method on hippocampal slice of mice. The influence of trans-anethole on long-term potentiation (LTP) was also studied for both NMDA receptor-dependent and NMDA receptor-independent cases. The action of trans-anethole on TMT-induced LTP impairment was examined, too. These results revealed that trans-anethole enhances NMDA receptor-dependent and -independent LTP and alleviates TMT-induced LTP impairment. These results suggest that trans-anethole modulates hippocampal LTP induction, prompting us to speculate that it may be helpful for improving cognitive impairment arising from neurodegenerative diseases, including Alzheimer's disease.

Keywords: hippocampus; long-term potentiation (LTP); synaptic plasticity; trans-anethole; trimethyltin chloride.

Figure 1

Chemical structural formula of cis- and trans-anethole.

Figure 2

Trans-anethole enhances NMDA receptor-dependent LTP. (A) NMDA receptor-dependent LTP was induced by 1 TBS. Trans-anethole was applied during the time period indicated by the bar. The numbers of studied mice and slices, respectively, are presented in parenthesis. The filled circles, open circles, filled triangles, open squares, and open triangles indicate the Vehicle group, 10 µM Trans-anethole group, 25 µM Trans-anethole group, 50 µM Trans-anethole group, and 100 µM Trans-anethole group, respectively. (B) Values represent the percent change observed in the fEPSP slope at 58–60 min after 1 TBS. Statistical significance (* p < 0.05 vs. Vehicle) was calculated by one-way ANOVA followed by Tukey HSD test. Examples of responses recorded 1 min before (thin traces) or 60 min after (thick traces) TBS are shown above. * p < 0.05 vs. the corresponding Vehicle group. T-aneth, Trans-anethole; fEPSP, field excitatory synaptic potential.

Figure 3

Trans-anethole (25 µM) enhances NMDA receptor-independent LTP. (A) NMDA receptor-independent LTP was induced by TEA (25 mM), which was applied during the time period indicated by the bar and then washed out. The numbers of mice and slices, respectively, are shown in parentheses. Filled circles, open circles, open triangles, filled triangles, and open squares indicate the Vehicle group, 10 µM Trans-anethole group, 17.5 µM Trans-anethole group, 25 µM Trans-anethole group, and 50 µM Trans-anethole group, respectively. (B) Values represent percent changes in the fEPSP slope observed at 58–60 min after TEA exposure. Statistical significance (* p < 0.05 vs. Vehicle) was calculated by one-way ANOVA followed by Tukey HSD test. Typical traces of fEPSPs recorded 1 min before (thin traces) or 60 min after (thick traces) TBS are shown above. T-aneth, Trans-anethole; fEPSP, field excitatory synaptic potential.

Figure 4

An NMDA receptor antagonist does not affect TEA-induced LTP induction. (A) NMDA receptor-independent LTP was induced by TEA. APV (50 µM) and TEA (25 mM) were applied during the time periods indicated by the bars, and then washed out. (B) Values represent percent changes observed in the fEPSP slope at 58–60 min after TEA exposure. The numbers of mice and slices, respectively, are shown in parentheses. Filled circles, open circles, open triangles, and filled triangles indicate the Vehicle group, 25 µM Trans-anethole group, 50 µM APV + 25 µM Trans-anethole group, and 50 µM APV group, respectively. Statistical significance (* p < 0.05 vs. Vehicle) was calculated by one-way ANOVA followed by Tukey HSD test. T-aneth, Trans-anethole; APV, DL-APV; fEPSP, field excitatory synaptic potential.

Figure 5

Anethole (25 µM) treatment does not affect the PPF ratio. (A) Paired-pulse facilitation (PPF) ratios were similar before and after perfusion of anethole (25 µM). Filled circles and open circles indicate the Pre-25 µM Trans-anethole group and Post-25 µM Trans-anethole group, respectively. (B) The areas under the curve (AUCs) for the PPF ratio did not significantly differ. Statistical significance (Post-Trans-anethole group vs. Pre-Trans-anethole group) was calculated by Student’s t-test. ISI: interstimulus interval, AUC: area under the curve. T-aneth: Trans-anethole.

Figure 6

TMT reduces NMDA receptor-dependent LTP in a dose-dependent manner. (A) The responses represent LTP induction over 1 h after NMDA receptor-dependent LTP was induced by 1 TBS. TMT in aCSF solution was applied at the beginning of the recording and perfused throughout the time period indicated by the bar. The numbers of mice and slices, respectively, are expressed in parentheses. Filled circles, open circles, open triangles, and filled triangles indicate the Vehicle group, 100 nM TMT group, 200 nM TMT group, and 500 nM TMT group, respectively. (B) Values represent percent changes in the fEPSP slope observed at 58–60 min. Statistical significance (* p < 0.05 vs. Vehicle) was calculated by one-way ANOVA followed by Tukey HSD test.; fEPSP: field excitatory synaptic potential.

Figure 7

TMT (500 nM) does not affect the PPF ratio. (A) PPF ratios were similar before and after TMT (500 nM) perfusion. Filled circles and open circles indicate the Pre-500 nM TMT group and Post-500 nM TMT group, respectively. (B) The AUCs for the PPF ratio were not significantly different. Statistical significance (Post-TMT group vs. Pre-TMT group) was calculated by Student’s t-test. ISI: interstimulus interval, AUC: area under the curve.

Figure 8

Trans-anethole (25 µM) attenuates TMT-induced impairment in NMDA receptor-dependent LTP. (A) The responses represent LTP induction over 1 h after NMDA receptor-dependent LTP was induced by 1 TBS. Trans-anethole (25 µM) was applied 10 min before the addition of TMT (500 nM), which was perfused in aCSF during the time period indicated by the bar. The numbers of mice and slices, respectively, are shown in parentheses. Filled circles, open circles, and open triangles indicate the Vehicle group, 500 nM TMT group, and 25 µM Trans-anethole + 500 nM TMT group, respectively. (B) Values represent percent changes in the EPSP slope observed at 58–60 min. Statistical significance (* p < 0.05 vs. 500 nM TMT) was calculated by one-way ANOVA followed by Tukey HSD test. T-aneth: Trans-anethole; fEPSP: field excitatory synaptic potential.

Figure 9

Trans-anethole (25 µM) modulates the TMT-induced impairment of NMDA receptor-independent LTP. The responses represent LTP induction at 1 h after 1 TBS (A). NMDA receptor-independent LTP was induced by TEA. Trans-anethole (25 µM) was applied 10 min before TMT (500 nM). Each drug was exposed during the time period indicated by the corresponding bar (B). Values represent percent changes in the fEPSP slope observed at 58–60 min (B). The numbers of mice and slices, respectively, are expressed in parentheses. Filled circles, open circles, and open triangles indicate the Vehicle group, 500 nM TMT group, and 25 µM anethole + 500 nM TMT group, respectively. Statistical significance (* p < 0.05 vs. 500 nM TMT) was calculated by one-way ANOVA followed by Tukey HSD test. T-aneth: Trans-anethole; fEPSP: field excitatory synaptic potential.