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Signal transduction mechanisms underlying group I mGluR-mediated increase in frequency and amplitude of spontaneous EPSCs in the spinal trigeminal subnucleus oralis of the rat.

Song JH, Park ES, Han SM, Han SR, Ahn DK, Youn DH - Mol Pain (2009)

Bottom Line: The DHPG-induced increase in the frequency of sEPSCs, the presynaptic effect being further confirmed by the DHPG effect on paired-pulse ratio of trigeminal tract-evoked EPSCs, an index of presynaptic modulation, was significantly but partially reduced by blockades of voltage-dependent sodium channel, mGluR1 or mGluR5.Further study of signal transduction mechanisms revealed that PLC and CaMKII mediated the increases of sEPSC in both frequency and amplitude by DHPG, while IP3 receptor, NO and ERK only that of amplitude during DHPG application.Altogether, these results indicate that the activation of group I mGluRs and their signal transduction pathways differentially regulate glutamate release and synaptic responses in Vo, thereby contributing to the processing of somatosensory signals from orofacial region.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Oral Physiology, School of Dentistry and Brain Korea 21, Brain Science and Engineering Institute, Kyungpook National University, 188-1 Samduk-2-ga, Chung-gu, Daegu 700-412, Korea. thdwlgus09@hanmail.net

ABSTRACT
Group I mGluRs (mGluR1 and 5) pre- and/or postsynaptically regulate synaptic transmission at glutamatergic synapses. By recording spontaneous EPSCs (sEPSCs) in the spinal trigeminal subnucleus oralis (Vo), we here investigated the regulation of glutamatergic transmission through the activation of group I mGluRs. Bath-applied DHPG (10 microM/5 min), activating the group I mGluRs, increased sEPSCs both in frequency and amplitude; particularly, the increased amplitude was long-lasting. The DHPG-induced increases of sEPSC frequency and amplitude were not NMDA receptor-dependent. The DHPG-induced increase in the frequency of sEPSCs, the presynaptic effect being further confirmed by the DHPG effect on paired-pulse ratio of trigeminal tract-evoked EPSCs, an index of presynaptic modulation, was significantly but partially reduced by blockades of voltage-dependent sodium channel, mGluR1 or mGluR5. Interestingly, PKC inhibition markedly enhanced the DHPG-induced increase of sEPSC frequency, which was mainly accomplished through mGluR1, indicating an inhibitory role of PKC. In contrast, the DHPG-induced increase of sEPSC amplitude was not affected by mGluR1 or mGluR5 antagonists although the long-lasting property of the increase was disappeared; however, the increase was completely inhibited by blocking both mGluR1 and mGluR5. Further study of signal transduction mechanisms revealed that PLC and CaMKII mediated the increases of sEPSC in both frequency and amplitude by DHPG, while IP3 receptor, NO and ERK only that of amplitude during DHPG application. Altogether, these results indicate that the activation of group I mGluRs and their signal transduction pathways differentially regulate glutamate release and synaptic responses in Vo, thereby contributing to the processing of somatosensory signals from orofacial region.

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Increase of sEPSC frequency and amplitude and change of Vt stimulation-evoked EPSC amplitude by bath application of DHPG in Vo. A diagram (A) demonstrates the recording site of the Vo area within the spinal trigeminal nucleus and the electrical stimulation site in the Vt. sEPSCs recorded at holding potential of -70 mV in the Vo area were blocked by 10 μM NBQX (B). Representative sEPSC traces at -70 mV, recorded from Vo neurons with Cs-based internal solution, before and during DHPG (10 μM, 5 min), the group I mGluR agonist, and after washout of the drug (Ca). Time-course graphs demonstrate DHPG-induced increases of sEPSC frequency (Cb) and amplitude (Cc) in Krebs's solution containing 5 μM BMI and 1 μM strychnine (n = 13). Each point with error bar represents mean ± SEM. Numbers on the graphs (Cb) indicate the corresponding time of the traces sampled. Representative EPSCs evoked by two pulses (interval, 50 ms) of Vt stimulation (Da). During DHPG, the amplitude of the first EPSC was slightly decreased, whereas that of the second EPSC increased (upper traces), resulting in an increase of paired pulse ratio (PPR, the second/the first EPSC). In traces (Da), the EPSC before DHPG was normalized to the amplitude of the first EPSCs during DHPG or after washout of DHPG (dotted line, normalized EPSCs). Histograms summarized the amplitude of the first EPSC (Db) and the PPR (Dc) before, during and after DHPG. The mean amplitude of EPSC was significantly increased after washout of DHPG, (Db, *P < 0.05, n = 5), whereas the mean PPR was significantly increased during DHPG (Dc, *P < 0.05, n = 8).
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Figure 1: Increase of sEPSC frequency and amplitude and change of Vt stimulation-evoked EPSC amplitude by bath application of DHPG in Vo. A diagram (A) demonstrates the recording site of the Vo area within the spinal trigeminal nucleus and the electrical stimulation site in the Vt. sEPSCs recorded at holding potential of -70 mV in the Vo area were blocked by 10 μM NBQX (B). Representative sEPSC traces at -70 mV, recorded from Vo neurons with Cs-based internal solution, before and during DHPG (10 μM, 5 min), the group I mGluR agonist, and after washout of the drug (Ca). Time-course graphs demonstrate DHPG-induced increases of sEPSC frequency (Cb) and amplitude (Cc) in Krebs's solution containing 5 μM BMI and 1 μM strychnine (n = 13). Each point with error bar represents mean ± SEM. Numbers on the graphs (Cb) indicate the corresponding time of the traces sampled. Representative EPSCs evoked by two pulses (interval, 50 ms) of Vt stimulation (Da). During DHPG, the amplitude of the first EPSC was slightly decreased, whereas that of the second EPSC increased (upper traces), resulting in an increase of paired pulse ratio (PPR, the second/the first EPSC). In traces (Da), the EPSC before DHPG was normalized to the amplitude of the first EPSCs during DHPG or after washout of DHPG (dotted line, normalized EPSCs). Histograms summarized the amplitude of the first EPSC (Db) and the PPR (Dc) before, during and after DHPG. The mean amplitude of EPSC was significantly increased after washout of DHPG, (Db, *P < 0.05, n = 5), whereas the mean PPR was significantly increased during DHPG (Dc, *P < 0.05, n = 8).

Mentions: sEPSCs were recorded in Vo neurons (Fig. 1A), voltage-clamped at -70 mV in the presence of 5 μM bicuculline methiodide (BMI) and 1-2 μM strychnine to block inhibitory synaptic responses (see Methods). The sEPSCs were predominantly mediated by AMPA receptors because most of them were disappeared by 10 μM 2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo [f]quinoxaline-7-sulfonamide (NBQX), an AMPA/kainate receptor blocker (Fig. 1B). Bath application of (S)-3,5-dihydroxyphenylglycine (DHPG; 10 μM, 5 min), a selective group I mGluR agonist, rapidly and significantly increased both the frequency (230.7 ± 42.9% of baseline) and the amplitude (124.6 ± 6.8% of baseline) of sEPSC (n = 13; Fig. 1C; P < 0.01 vs. baseline) at 2.5 min from the start of the application. The increased frequency of sEPSC was recovered to the baseline period (107.1 ± 41.9% of baseline at 13-14 min; Fig. 1Cb), whereas the increased amplitude was only partially recovered (114.3 ± 6.0% of baseline at 7-9 min; Fig. 1Cc), indicating that the DHPG-induced increase of sEPSC amplitude is long-lasting.


Signal transduction mechanisms underlying group I mGluR-mediated increase in frequency and amplitude of spontaneous EPSCs in the spinal trigeminal subnucleus oralis of the rat.

Song JH, Park ES, Han SM, Han SR, Ahn DK, Youn DH - Mol Pain (2009)

Increase of sEPSC frequency and amplitude and change of Vt stimulation-evoked EPSC amplitude by bath application of DHPG in Vo. A diagram (A) demonstrates the recording site of the Vo area within the spinal trigeminal nucleus and the electrical stimulation site in the Vt. sEPSCs recorded at holding potential of -70 mV in the Vo area were blocked by 10 μM NBQX (B). Representative sEPSC traces at -70 mV, recorded from Vo neurons with Cs-based internal solution, before and during DHPG (10 μM, 5 min), the group I mGluR agonist, and after washout of the drug (Ca). Time-course graphs demonstrate DHPG-induced increases of sEPSC frequency (Cb) and amplitude (Cc) in Krebs's solution containing 5 μM BMI and 1 μM strychnine (n = 13). Each point with error bar represents mean ± SEM. Numbers on the graphs (Cb) indicate the corresponding time of the traces sampled. Representative EPSCs evoked by two pulses (interval, 50 ms) of Vt stimulation (Da). During DHPG, the amplitude of the first EPSC was slightly decreased, whereas that of the second EPSC increased (upper traces), resulting in an increase of paired pulse ratio (PPR, the second/the first EPSC). In traces (Da), the EPSC before DHPG was normalized to the amplitude of the first EPSCs during DHPG or after washout of DHPG (dotted line, normalized EPSCs). Histograms summarized the amplitude of the first EPSC (Db) and the PPR (Dc) before, during and after DHPG. The mean amplitude of EPSC was significantly increased after washout of DHPG, (Db, *P < 0.05, n = 5), whereas the mean PPR was significantly increased during DHPG (Dc, *P < 0.05, n = 8).
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC2743647&req=5

Figure 1: Increase of sEPSC frequency and amplitude and change of Vt stimulation-evoked EPSC amplitude by bath application of DHPG in Vo. A diagram (A) demonstrates the recording site of the Vo area within the spinal trigeminal nucleus and the electrical stimulation site in the Vt. sEPSCs recorded at holding potential of -70 mV in the Vo area were blocked by 10 μM NBQX (B). Representative sEPSC traces at -70 mV, recorded from Vo neurons with Cs-based internal solution, before and during DHPG (10 μM, 5 min), the group I mGluR agonist, and after washout of the drug (Ca). Time-course graphs demonstrate DHPG-induced increases of sEPSC frequency (Cb) and amplitude (Cc) in Krebs's solution containing 5 μM BMI and 1 μM strychnine (n = 13). Each point with error bar represents mean ± SEM. Numbers on the graphs (Cb) indicate the corresponding time of the traces sampled. Representative EPSCs evoked by two pulses (interval, 50 ms) of Vt stimulation (Da). During DHPG, the amplitude of the first EPSC was slightly decreased, whereas that of the second EPSC increased (upper traces), resulting in an increase of paired pulse ratio (PPR, the second/the first EPSC). In traces (Da), the EPSC before DHPG was normalized to the amplitude of the first EPSCs during DHPG or after washout of DHPG (dotted line, normalized EPSCs). Histograms summarized the amplitude of the first EPSC (Db) and the PPR (Dc) before, during and after DHPG. The mean amplitude of EPSC was significantly increased after washout of DHPG, (Db, *P < 0.05, n = 5), whereas the mean PPR was significantly increased during DHPG (Dc, *P < 0.05, n = 8).
Mentions: sEPSCs were recorded in Vo neurons (Fig. 1A), voltage-clamped at -70 mV in the presence of 5 μM bicuculline methiodide (BMI) and 1-2 μM strychnine to block inhibitory synaptic responses (see Methods). The sEPSCs were predominantly mediated by AMPA receptors because most of them were disappeared by 10 μM 2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo [f]quinoxaline-7-sulfonamide (NBQX), an AMPA/kainate receptor blocker (Fig. 1B). Bath application of (S)-3,5-dihydroxyphenylglycine (DHPG; 10 μM, 5 min), a selective group I mGluR agonist, rapidly and significantly increased both the frequency (230.7 ± 42.9% of baseline) and the amplitude (124.6 ± 6.8% of baseline) of sEPSC (n = 13; Fig. 1C; P < 0.01 vs. baseline) at 2.5 min from the start of the application. The increased frequency of sEPSC was recovered to the baseline period (107.1 ± 41.9% of baseline at 13-14 min; Fig. 1Cb), whereas the increased amplitude was only partially recovered (114.3 ± 6.0% of baseline at 7-9 min; Fig. 1Cc), indicating that the DHPG-induced increase of sEPSC amplitude is long-lasting.

Bottom Line: The DHPG-induced increase in the frequency of sEPSCs, the presynaptic effect being further confirmed by the DHPG effect on paired-pulse ratio of trigeminal tract-evoked EPSCs, an index of presynaptic modulation, was significantly but partially reduced by blockades of voltage-dependent sodium channel, mGluR1 or mGluR5.Further study of signal transduction mechanisms revealed that PLC and CaMKII mediated the increases of sEPSC in both frequency and amplitude by DHPG, while IP3 receptor, NO and ERK only that of amplitude during DHPG application.Altogether, these results indicate that the activation of group I mGluRs and their signal transduction pathways differentially regulate glutamate release and synaptic responses in Vo, thereby contributing to the processing of somatosensory signals from orofacial region.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Oral Physiology, School of Dentistry and Brain Korea 21, Brain Science and Engineering Institute, Kyungpook National University, 188-1 Samduk-2-ga, Chung-gu, Daegu 700-412, Korea. thdwlgus09@hanmail.net

ABSTRACT
Group I mGluRs (mGluR1 and 5) pre- and/or postsynaptically regulate synaptic transmission at glutamatergic synapses. By recording spontaneous EPSCs (sEPSCs) in the spinal trigeminal subnucleus oralis (Vo), we here investigated the regulation of glutamatergic transmission through the activation of group I mGluRs. Bath-applied DHPG (10 microM/5 min), activating the group I mGluRs, increased sEPSCs both in frequency and amplitude; particularly, the increased amplitude was long-lasting. The DHPG-induced increases of sEPSC frequency and amplitude were not NMDA receptor-dependent. The DHPG-induced increase in the frequency of sEPSCs, the presynaptic effect being further confirmed by the DHPG effect on paired-pulse ratio of trigeminal tract-evoked EPSCs, an index of presynaptic modulation, was significantly but partially reduced by blockades of voltage-dependent sodium channel, mGluR1 or mGluR5. Interestingly, PKC inhibition markedly enhanced the DHPG-induced increase of sEPSC frequency, which was mainly accomplished through mGluR1, indicating an inhibitory role of PKC. In contrast, the DHPG-induced increase of sEPSC amplitude was not affected by mGluR1 or mGluR5 antagonists although the long-lasting property of the increase was disappeared; however, the increase was completely inhibited by blocking both mGluR1 and mGluR5. Further study of signal transduction mechanisms revealed that PLC and CaMKII mediated the increases of sEPSC in both frequency and amplitude by DHPG, while IP3 receptor, NO and ERK only that of amplitude during DHPG application. Altogether, these results indicate that the activation of group I mGluRs and their signal transduction pathways differentially regulate glutamate release and synaptic responses in Vo, thereby contributing to the processing of somatosensory signals from orofacial region.

Show MeSH
Related in: MedlinePlus