Limits...
Agrin mediates a rapid switch from electrical coupling to chemical neurotransmission during synaptogenesis.

Martin AO, Alonso G, Guérineau NC - J. Cell Biol. (2005)

Bottom Line: When applied at the developing splanchnic nerve-chromaffin cell cholinergic synapse in rat adrenal acute slices, agrin rapidly modified cell-to-cell communication mechanisms.This developmental switch from predominantly electrical to chemical communication was fully operational within one hour and depended on the activation of Src family-related tyrosine kinases.Hence, agrin may play a pivotal role in synaptogenesis in promoting a rapid switch between electrical coupling and synaptic neurotransmission.

View Article: PubMed Central - PubMed

Affiliation: CNRS UMR5203, INSERM U661, Université Montpellier I, Département d'Endocrinologie, Institut de Génomique Fonctionnelle, 34094 Montpellier Cedex 5, France.

ABSTRACT
In contrast to its well-established actions as an organizer of synaptic differentiation at the neuromuscular junction, the proteoglycan agrin is still in search of a function in the nervous system. Here, we report an entirely unanticipated role for agrin in the dual modulation of electrical and chemical intercellular communication that occurs during the critical period of synapse formation. When applied at the developing splanchnic nerve-chromaffin cell cholinergic synapse in rat adrenal acute slices, agrin rapidly modified cell-to-cell communication mechanisms. Specifically, it led to decreased gap junction-mediated electrical coupling that preceded an increase in nicotinic synaptic transmission. This developmental switch from predominantly electrical to chemical communication was fully operational within one hour and depended on the activation of Src family-related tyrosine kinases. Hence, agrin may play a pivotal role in synaptogenesis in promoting a rapid switch between electrical coupling and synaptic neurotransmission.

Show MeSH

Related in: MedlinePlus

Effect of prolonged agrin treatment on spontaneous excitatory synaptic activity recorded in adult and neonate chromaffin cells (holding potential −80 mV). (A and B) Chart recordings illustrating sEPSCs in control and agrin-treated slices (4–5 h before recordings). (C and D) Summarized effects of agrin on sEPSC frequency and amplitude variance. *, P < 0.01 compared with untreated slices. (E) Plots showing the cumulative probability of sEPSC amplitude.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2171940&req=5

fig2: Effect of prolonged agrin treatment on spontaneous excitatory synaptic activity recorded in adult and neonate chromaffin cells (holding potential −80 mV). (A and B) Chart recordings illustrating sEPSCs in control and agrin-treated slices (4–5 h before recordings). (C and D) Summarized effects of agrin on sEPSC frequency and amplitude variance. *, P < 0.01 compared with untreated slices. (E) Plots showing the cumulative probability of sEPSC amplitude.

Mentions: Excitatory synaptic transmission between splanchnic nerve endings and chromaffin cells is mainly mediated by neuronal-type nAChRs (Barbara and Takeda, 1996). We recorded spontaneous excitatory postsynaptic currents (sEPSCs) in whole-cell voltage-clamped chromaffin cells in acute adrenal slices from adults and neonates (Fig. 2). About 20% of cells recorded in both adults and neonates exhibited sEPSCs. The mean sEPSC amplitude (but not the frequency) was significantly lower in neonates than in adults (51.8 ± 2.6 pA, n = 216 sEPSCs, 17 cells in neonates vs. 126.3 ± 6.6 pA, n = 408 sEPSCs, 20 cells in adults, P < 0.01). Because neonate chromaffin cells are smaller in size than adult cells, the corresponding mean current density was calculated. Given a mean membrane capacitance of 7.50 ± 0.55 pF (n = 16) in neonates and 11.64 pF in adults (Martin et al., 2001), the mean sEPSC amplitude corresponded to a mean current density of 6.91 ± 0.51 pA/pF in neonates and 10.85 ± 0.37 pA/pF in adults (P < 0.01). Prolonged exposure to recombinant rat COOH-terminal agrin (4–5 h, 50 ng/ml) induced a dramatic increase in sEPSC amplitude in neonates (Fig. 2 B; 51.8 ± 2.6 pA, n = 17 cells in control slices vs. 380.4 ± 13.4 pA, n = 438 sEPSCs, 11 cells in agrin-treated slices, P < 0.01) by inducing the appearance of high amplitude events. Consistent with this finding, sEPSC amplitude variance (σ2) displayed a wide distribution range in agrin-treated slices—a change that was statistically significant compared with neonate control slices (Fig. 2 D, P < 0.01). The plots illustrating the cumulative probability of sEPSC amplitude clearly indicate that agrin treatment modified sEPSC amplitude in neonates (Fig. 2 E). sEPSC frequency was not modified by agrin treatment (Fig. 2 C, P > 0.01). Increased synaptic transmission induced by agrin was fully prevented in the presence of an anti–rat agrin-neutralizing pAb (R&D Systems; 100 ng/ml, 4–5 h, mean sEPSC amplitude 61.8 ± 8.4 pA, n = 8 cells, P > 0.01, as compared with untreated neonate slices; unpublished data). In adults, agrin did not have any detectable effects on either sEPSC frequency or σ2 (Fig. 2, B–D; P > 0.01, n = 476 sEPSCs, 14 cells). To ascertain that agrin likely acted postsynaptically, we investigated the effects of agrin on nicotine-triggered inward currents in neonates (100-ms puff, 100 μM). This resulted in a statistically significant increase in the mean current amplitude (68.4 ± 19.1 pA, n = 18 in control slices vs. 175 ± 33 pA, n = 17 in agrin-treated slices, P < 0.01; unpublished data). In addition, the number of cells in which nicotine evoked an inward current was significantly higher after agrin exposure (94.4 vs. 62.1% in untreated slices, P < 0.01).


Agrin mediates a rapid switch from electrical coupling to chemical neurotransmission during synaptogenesis.

Martin AO, Alonso G, Guérineau NC - J. Cell Biol. (2005)

Effect of prolonged agrin treatment on spontaneous excitatory synaptic activity recorded in adult and neonate chromaffin cells (holding potential −80 mV). (A and B) Chart recordings illustrating sEPSCs in control and agrin-treated slices (4–5 h before recordings). (C and D) Summarized effects of agrin on sEPSC frequency and amplitude variance. *, P < 0.01 compared with untreated slices. (E) Plots showing the cumulative probability of sEPSC amplitude.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2171940&req=5

fig2: Effect of prolonged agrin treatment on spontaneous excitatory synaptic activity recorded in adult and neonate chromaffin cells (holding potential −80 mV). (A and B) Chart recordings illustrating sEPSCs in control and agrin-treated slices (4–5 h before recordings). (C and D) Summarized effects of agrin on sEPSC frequency and amplitude variance. *, P < 0.01 compared with untreated slices. (E) Plots showing the cumulative probability of sEPSC amplitude.
Mentions: Excitatory synaptic transmission between splanchnic nerve endings and chromaffin cells is mainly mediated by neuronal-type nAChRs (Barbara and Takeda, 1996). We recorded spontaneous excitatory postsynaptic currents (sEPSCs) in whole-cell voltage-clamped chromaffin cells in acute adrenal slices from adults and neonates (Fig. 2). About 20% of cells recorded in both adults and neonates exhibited sEPSCs. The mean sEPSC amplitude (but not the frequency) was significantly lower in neonates than in adults (51.8 ± 2.6 pA, n = 216 sEPSCs, 17 cells in neonates vs. 126.3 ± 6.6 pA, n = 408 sEPSCs, 20 cells in adults, P < 0.01). Because neonate chromaffin cells are smaller in size than adult cells, the corresponding mean current density was calculated. Given a mean membrane capacitance of 7.50 ± 0.55 pF (n = 16) in neonates and 11.64 pF in adults (Martin et al., 2001), the mean sEPSC amplitude corresponded to a mean current density of 6.91 ± 0.51 pA/pF in neonates and 10.85 ± 0.37 pA/pF in adults (P < 0.01). Prolonged exposure to recombinant rat COOH-terminal agrin (4–5 h, 50 ng/ml) induced a dramatic increase in sEPSC amplitude in neonates (Fig. 2 B; 51.8 ± 2.6 pA, n = 17 cells in control slices vs. 380.4 ± 13.4 pA, n = 438 sEPSCs, 11 cells in agrin-treated slices, P < 0.01) by inducing the appearance of high amplitude events. Consistent with this finding, sEPSC amplitude variance (σ2) displayed a wide distribution range in agrin-treated slices—a change that was statistically significant compared with neonate control slices (Fig. 2 D, P < 0.01). The plots illustrating the cumulative probability of sEPSC amplitude clearly indicate that agrin treatment modified sEPSC amplitude in neonates (Fig. 2 E). sEPSC frequency was not modified by agrin treatment (Fig. 2 C, P > 0.01). Increased synaptic transmission induced by agrin was fully prevented in the presence of an anti–rat agrin-neutralizing pAb (R&D Systems; 100 ng/ml, 4–5 h, mean sEPSC amplitude 61.8 ± 8.4 pA, n = 8 cells, P > 0.01, as compared with untreated neonate slices; unpublished data). In adults, agrin did not have any detectable effects on either sEPSC frequency or σ2 (Fig. 2, B–D; P > 0.01, n = 476 sEPSCs, 14 cells). To ascertain that agrin likely acted postsynaptically, we investigated the effects of agrin on nicotine-triggered inward currents in neonates (100-ms puff, 100 μM). This resulted in a statistically significant increase in the mean current amplitude (68.4 ± 19.1 pA, n = 18 in control slices vs. 175 ± 33 pA, n = 17 in agrin-treated slices, P < 0.01; unpublished data). In addition, the number of cells in which nicotine evoked an inward current was significantly higher after agrin exposure (94.4 vs. 62.1% in untreated slices, P < 0.01).

Bottom Line: When applied at the developing splanchnic nerve-chromaffin cell cholinergic synapse in rat adrenal acute slices, agrin rapidly modified cell-to-cell communication mechanisms.This developmental switch from predominantly electrical to chemical communication was fully operational within one hour and depended on the activation of Src family-related tyrosine kinases.Hence, agrin may play a pivotal role in synaptogenesis in promoting a rapid switch between electrical coupling and synaptic neurotransmission.

View Article: PubMed Central - PubMed

Affiliation: CNRS UMR5203, INSERM U661, Université Montpellier I, Département d'Endocrinologie, Institut de Génomique Fonctionnelle, 34094 Montpellier Cedex 5, France.

ABSTRACT
In contrast to its well-established actions as an organizer of synaptic differentiation at the neuromuscular junction, the proteoglycan agrin is still in search of a function in the nervous system. Here, we report an entirely unanticipated role for agrin in the dual modulation of electrical and chemical intercellular communication that occurs during the critical period of synapse formation. When applied at the developing splanchnic nerve-chromaffin cell cholinergic synapse in rat adrenal acute slices, agrin rapidly modified cell-to-cell communication mechanisms. Specifically, it led to decreased gap junction-mediated electrical coupling that preceded an increase in nicotinic synaptic transmission. This developmental switch from predominantly electrical to chemical communication was fully operational within one hour and depended on the activation of Src family-related tyrosine kinases. Hence, agrin may play a pivotal role in synaptogenesis in promoting a rapid switch between electrical coupling and synaptic neurotransmission.

Show MeSH
Related in: MedlinePlus