Elsevier

Neuroscience

Volume 172, 13 January 2011, Pages 129-138
Neuroscience

Cellular and Molecular Neuroscience
β-pompilidotoxin modulates spontaneous activity and persistent sodium currents in spinal networks

https://doi.org/10.1016/j.neuroscience.2010.10.034Get rights and content

Abstract

The origin of rhythm generation in mammalian spinal cord networks is still poorly understood. In a previous study, we showed that spontaneous activity in spinal networks takes its origin in the properties of certain intrinsically spiking interneurons based on the persistent sodium current (INaP). We also showed that depolarization block caused by a fast inactivation of the transient sodium current (INaT) contributes to the generation of oscillatory activity in spinal cord cultures. Recently, a toxin called beta-pompilidotoxin (β-PMTX) that slows the inactivation process of tetrodotoxin (TTX) -sensitive sodium channels has been extracted from the solitary wasp venom. In the present study, we therefore investigated the effect of β-PMTX on rhythm generation and on sodium currents in spinal networks. Using intracellular recordings and multielectrode array (MEA) recordings in dissociated spinal cord cultures from embryonic (E14) rats, we found that β-PMTX reduces the number of population bursts and increases the background asynchronous activity. We then uncoupled the network by blocking all synaptic transmission (APV, CNQX, bicuculline and strychnine) and observed that β-PMTX increases both the intrinsic activity at individual channels and the number of intrinsically activated channels. At the cellular level, we found that β-PMTX has two effects: it switches 58% of the silent interneurons into spontaneously active interneurons and increases the firing rate of intrinsically spiking cells. Finally, we investigated the effect of β-PMTX on sodium currents. We found that this toxin not only affects the inactivation of INaT but also increases the peak amplitude of the persistent sodium current (INaP). Altogether, theses findings suggest that β-PMTX acting on INaP and INaT enhances intrinsic activity leading to a profound modulation of spontaneous rhythmic activity in spinal networks.

Research Highlights

▶β-PMTX increases persistent sodium currents (INaP) in spinal neurons. ▶β-PMTX increases intrinsic spiking activity via an up-regulation of INaP. ▶An increase of intrinsic activity suppresses network activity in spinal networks.

Section snippets

Cultures

Cultures were made from the spinal cord of Wistar rats (Janvier, Le Genest St. Isle, France) at embryonic age 14. The cultures were prepared as described previously (Streit et al., 2001). The embryos were delivered by caesarean section from deeply anaesthetized animals (0.4 ml pentobarbital i.m., Streuli Pharma AG, Uznach, Switzerland) and killed by decapitation. Following the delivery of the embryos, the mother was killed by intracardiac injection of pentobarbital. This procedure guarantees a

Results

In the present study, experimental data were obtained from 37 cultures of dissociated spinal cord. From these, 16 were used to study the effect of β-PMTX on network activity with multi site extracellular recordings on MEAs and 21 were investigated with the whole cell patch clamp technique to study sodium currents.

Discussion

In the present study, our experimental results provide three main findings. First, we show that β-PMTX known to act on INaT has an additional effect on INaP. Second, β-PMTX up-regulates the expression of INaP mainly in a specific group of silent spinal cells and turns them into spontaneously spiking interneurons. Third, an enhancement of spontaneously active neurons increases the general intrinsic activity leading to a suppression of the network activity.

Conclusion

In summary, our findings indicate that β-PMTX affects both INaP and the fast inactivation of INaT leading to an increase of the intrinsic activity by switching silent into intrinsically spiking cells and by increasing the firing rate of spiking neurons. At the network level, the consequences are a suppression of the synaptic network activity by the increased intrinsic activity.

Acknowledgments

We thank R. Rubli for doing the culture work and D. de Limoges, H. Ruchti and J. Burkhalter for technical support for the recording setup. We are grateful to H. P. Clamann for critical comments on the manuscript. This work was supported by Swiss National Science Foundation Grants 31-59080.99 and 3100-067048.0

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    Present address: CNRS UMR 7224, Physiopathologie des Maladies du Système Nerveux Central, Paris, France INSERM U952, Paris, France UPMC, University Paris 06, Paris, France.

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