Limits...
Impact of single-site axonal GABAergic synaptic events on cerebellar interneuron activity.

de San Martin JZ, Jalil A, Trigo FF - J. Gen. Physiol. (2015)

Bottom Line: Axonal ionotropic receptors are present in a variety of neuronal types, and their function has largely been associated with the modulation of axonal activity and synaptic release.The frequency of presynaptic, autoR-mediated miniature currents is twice that of their somatodendritic counterparts, suggesting that autoR-mediated responses have an important effect on interneuron activity.Finally, we show that single-site activation of presynaptic GABA(A) autoRs leads to an increase in MLI excitability and thus conveys a strong feedback signal that contributes to spiking activity.

View Article: PubMed Central - HTML - PubMed

Affiliation: Laboratoire de Physiologie Cérébrale, Université Paris Descartes and Centre National de la Recherche Scientifique, CNRS UMR8118, 75794 Paris, France.

No MeSH data available.


Related in: MedlinePlus

Subthreshold ASPs from single release sites backpropagate to the soma. (A) Representative current-clamp recordings of six consecutive ASPs (black) and their average (gray) evoked by local Ca2+ photolysis in an individual varicosity; the cell was recorded at physiological [Cl−]i (15 mM) and kept at a −70-mV holding potential; the dotted gray line indicates timing of the laser pulse. The reconstruction on the left shows the location of the photolysis spot (arrowhead). (B) Average traces of ASPs evoked in four different release sites from different cells located at 36, 45, 54, and 87 µm from the soma (amplitudes were 6.3, 4.9, 2.8, and 2 mV, respectively; n = 2–10 events per site). (C) Plot of ASP amplitude as a function of the distance between the soma and the release site. Individual points correspond to average amplitudes made from 2 to 26 individual sweeps from single release sites. Continuous line is the exponential fit (D37 = 91 ± 66 µm; n = 21 sites). (D) Plot of ASP amplitude as a function of τRise (continuous line is the linear fit; P > 0.05; Pearson’s coefficient = 0.61; n = 21 sites). (E) Plot of τDecay as a function of τRise (continuous line is the linear fit; P > 0.05; Pearson’s coefficient = −0.24; n = 21 sites).
© Copyright Policy - openaccess
Related In: Results  -  Collection

License 1 - License 2
getmorefigures.php?uid=PMC4664828&req=5

fig6: Subthreshold ASPs from single release sites backpropagate to the soma. (A) Representative current-clamp recordings of six consecutive ASPs (black) and their average (gray) evoked by local Ca2+ photolysis in an individual varicosity; the cell was recorded at physiological [Cl−]i (15 mM) and kept at a −70-mV holding potential; the dotted gray line indicates timing of the laser pulse. The reconstruction on the left shows the location of the photolysis spot (arrowhead). (B) Average traces of ASPs evoked in four different release sites from different cells located at 36, 45, 54, and 87 µm from the soma (amplitudes were 6.3, 4.9, 2.8, and 2 mV, respectively; n = 2–10 events per site). (C) Plot of ASP amplitude as a function of the distance between the soma and the release site. Individual points correspond to average amplitudes made from 2 to 26 individual sweeps from single release sites. Continuous line is the exponential fit (D37 = 91 ± 66 µm; n = 21 sites). (D) Plot of ASP amplitude as a function of τRise (continuous line is the linear fit; P > 0.05; Pearson’s coefficient = 0.61; n = 21 sites). (E) Plot of τDecay as a function of τRise (continuous line is the linear fit; P > 0.05; Pearson’s coefficient = −0.24; n = 21 sites).

Mentions: In young MLIs, EGABA is more depolarized than in other cerebellar cell types and is highly variable as a result of heterogeneity in [Cl−]i (estimated to be 15 mM on average; Chavas and Marty, 2003). Here, we examine the changes in the neuronal membrane potential produced by the activation of GABAA autoRs in physiological conditions. For this purpose, we recorded the cells in current clamp with a physiological intracellular solution containing 15 mM Cl− and evoked local GABA release using caged-Ca2+ photolysis. As mentioned before, in MLIs subthreshold somatodendritic depolarizations are transmitted to presynaptic terminals and induce an increase in the frequency of spontaneous axonal events or preminis (Trigo et al., 2010), all in an AP-independent manner. To study the impact of evoked, single-site responses and avoid any possible contribution of spontaneous events, membrane potential was kept near −70 mV by injection of negative current (−30 ± 4 pA; n = 12 cells). In these conditions, local caged-Ca2+ photolysis in the axon produced subthreshold depolarizing responses (Fig. 6 A; black traces are individual sweeps, and the gray trace is the average); we called the laser-evoked responses “autoR-mediated synaptic potentials” (ASPs), in analogy to the ASCs. ASP amplitudes were relatively big, and their timing clearly indicated the pairing with the laser pulse. The depolarizations shown in Fig. 6 A had an average amplitude of 5.0 mV and a decay time constant of 47 ms. Averaged traces revealed clear depolarizing responses with a mean amplitude among all the sites of 3.4 ± 0.4 mV (ranging from 1.2 to 6.4 mV), mean τrise of 9.2 ± 1.0 ms, and mean τdecay of 92 ± 16 ms (21 sites; 17 cells; holding potential was between −67 and −76 mV). As expected for filtered signals, the ASP amplitude decreased as a function of the distance between the stimulated release site and the soma. Representative traces of ASPs evoked at 36, 45, 54, and 87 µm from the soma are shown in Fig. 6 B. A fit of the amplitudes plotted as a function of the distance between the release site and the soma with an exponential function gave a D37 value of 91 ± 66 µm (n = 21 sites; Fig. 6 C). Extrapolation of the ASP amplitude versus distance plot predicts nonfiltered (in situ) local amplitudes of ∼6 mV. Interestingly, contrary to predictions for a passive filter (Rall, 1967) and to the results obtained in voltage clamp (Fig. 4 E), there was no significant negative correlation between the ASP amplitude and τrise (Fig. 6 D), and no correlation between τdecay and τrise (Fig. 6 E). These results show for the first time that, in physiological conditions, axonal depolarizations from individual release sites can backpropagate and produce substantial somatic depolarizations.


Impact of single-site axonal GABAergic synaptic events on cerebellar interneuron activity.

de San Martin JZ, Jalil A, Trigo FF - J. Gen. Physiol. (2015)

Subthreshold ASPs from single release sites backpropagate to the soma. (A) Representative current-clamp recordings of six consecutive ASPs (black) and their average (gray) evoked by local Ca2+ photolysis in an individual varicosity; the cell was recorded at physiological [Cl−]i (15 mM) and kept at a −70-mV holding potential; the dotted gray line indicates timing of the laser pulse. The reconstruction on the left shows the location of the photolysis spot (arrowhead). (B) Average traces of ASPs evoked in four different release sites from different cells located at 36, 45, 54, and 87 µm from the soma (amplitudes were 6.3, 4.9, 2.8, and 2 mV, respectively; n = 2–10 events per site). (C) Plot of ASP amplitude as a function of the distance between the soma and the release site. Individual points correspond to average amplitudes made from 2 to 26 individual sweeps from single release sites. Continuous line is the exponential fit (D37 = 91 ± 66 µm; n = 21 sites). (D) Plot of ASP amplitude as a function of τRise (continuous line is the linear fit; P > 0.05; Pearson’s coefficient = 0.61; n = 21 sites). (E) Plot of τDecay as a function of τRise (continuous line is the linear fit; P > 0.05; Pearson’s coefficient = −0.24; n = 21 sites).
© Copyright Policy - openaccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4664828&req=5

fig6: Subthreshold ASPs from single release sites backpropagate to the soma. (A) Representative current-clamp recordings of six consecutive ASPs (black) and their average (gray) evoked by local Ca2+ photolysis in an individual varicosity; the cell was recorded at physiological [Cl−]i (15 mM) and kept at a −70-mV holding potential; the dotted gray line indicates timing of the laser pulse. The reconstruction on the left shows the location of the photolysis spot (arrowhead). (B) Average traces of ASPs evoked in four different release sites from different cells located at 36, 45, 54, and 87 µm from the soma (amplitudes were 6.3, 4.9, 2.8, and 2 mV, respectively; n = 2–10 events per site). (C) Plot of ASP amplitude as a function of the distance between the soma and the release site. Individual points correspond to average amplitudes made from 2 to 26 individual sweeps from single release sites. Continuous line is the exponential fit (D37 = 91 ± 66 µm; n = 21 sites). (D) Plot of ASP amplitude as a function of τRise (continuous line is the linear fit; P > 0.05; Pearson’s coefficient = 0.61; n = 21 sites). (E) Plot of τDecay as a function of τRise (continuous line is the linear fit; P > 0.05; Pearson’s coefficient = −0.24; n = 21 sites).
Mentions: In young MLIs, EGABA is more depolarized than in other cerebellar cell types and is highly variable as a result of heterogeneity in [Cl−]i (estimated to be 15 mM on average; Chavas and Marty, 2003). Here, we examine the changes in the neuronal membrane potential produced by the activation of GABAA autoRs in physiological conditions. For this purpose, we recorded the cells in current clamp with a physiological intracellular solution containing 15 mM Cl− and evoked local GABA release using caged-Ca2+ photolysis. As mentioned before, in MLIs subthreshold somatodendritic depolarizations are transmitted to presynaptic terminals and induce an increase in the frequency of spontaneous axonal events or preminis (Trigo et al., 2010), all in an AP-independent manner. To study the impact of evoked, single-site responses and avoid any possible contribution of spontaneous events, membrane potential was kept near −70 mV by injection of negative current (−30 ± 4 pA; n = 12 cells). In these conditions, local caged-Ca2+ photolysis in the axon produced subthreshold depolarizing responses (Fig. 6 A; black traces are individual sweeps, and the gray trace is the average); we called the laser-evoked responses “autoR-mediated synaptic potentials” (ASPs), in analogy to the ASCs. ASP amplitudes were relatively big, and their timing clearly indicated the pairing with the laser pulse. The depolarizations shown in Fig. 6 A had an average amplitude of 5.0 mV and a decay time constant of 47 ms. Averaged traces revealed clear depolarizing responses with a mean amplitude among all the sites of 3.4 ± 0.4 mV (ranging from 1.2 to 6.4 mV), mean τrise of 9.2 ± 1.0 ms, and mean τdecay of 92 ± 16 ms (21 sites; 17 cells; holding potential was between −67 and −76 mV). As expected for filtered signals, the ASP amplitude decreased as a function of the distance between the stimulated release site and the soma. Representative traces of ASPs evoked at 36, 45, 54, and 87 µm from the soma are shown in Fig. 6 B. A fit of the amplitudes plotted as a function of the distance between the release site and the soma with an exponential function gave a D37 value of 91 ± 66 µm (n = 21 sites; Fig. 6 C). Extrapolation of the ASP amplitude versus distance plot predicts nonfiltered (in situ) local amplitudes of ∼6 mV. Interestingly, contrary to predictions for a passive filter (Rall, 1967) and to the results obtained in voltage clamp (Fig. 4 E), there was no significant negative correlation between the ASP amplitude and τrise (Fig. 6 D), and no correlation between τdecay and τrise (Fig. 6 E). These results show for the first time that, in physiological conditions, axonal depolarizations from individual release sites can backpropagate and produce substantial somatic depolarizations.

Bottom Line: Axonal ionotropic receptors are present in a variety of neuronal types, and their function has largely been associated with the modulation of axonal activity and synaptic release.The frequency of presynaptic, autoR-mediated miniature currents is twice that of their somatodendritic counterparts, suggesting that autoR-mediated responses have an important effect on interneuron activity.Finally, we show that single-site activation of presynaptic GABA(A) autoRs leads to an increase in MLI excitability and thus conveys a strong feedback signal that contributes to spiking activity.

View Article: PubMed Central - HTML - PubMed

Affiliation: Laboratoire de Physiologie Cérébrale, Université Paris Descartes and Centre National de la Recherche Scientifique, CNRS UMR8118, 75794 Paris, France.

No MeSH data available.


Related in: MedlinePlus