Extracellular sodium modulates the excitability of cultured hippocampal pyramidal cells.

Abstract

Recent studies demonstrated a photophobia mechanism with modulation of nociceptive, cortico-thalamic neurons by retinal ganglion cell projections; however, little is known about how their neuronal homeostasis is disrupted. Since we have found that lumbar cerebrospinal fluid (CSF) sodium increases during migraine and that cranial sodium increases in a rat migraine model, the purpose of this study was to examine the effects of extracellular sodium ([Na(+)](o)) on the intrinsic excitability of hippocampal pyramidal neurons. We monitored excitability by whole cell patch using a multiplex micropipette with a common outlet to change artificial CSF (ACSF) [Na(+)](o) at cultured neurons accurately (SD<7 mM) and rapidly (<5s) as determined by a sodium-selective micro-electrode of the same size and at the same location as a neuronal soma. Changing [Na(+)](o) in ACSF from 100 to 160 mM, choline-balanced at 310-320 mOsm, increased the action potential (AP) amplitude, decreased AP width, and augmented firing rate by 28%. These effects were reversed on returning the ACSF [Na(+)](o) to 100mM. Testing up to 180 mM [Na(+)](o) required ACSF with higher osmolarity (345-355 mOsm), at which the firing rate increased by 36% between 100 and 180 mM [Na(+)](o), with higher amplitude and narrower APs. In voltage clamp mode, the sodium and potassium currents increased significantly at higher [Na(+)](o). These results demonstrate that fluctuations in [Na(+)](o) modulate neuronal excitability by a sodium current mechanism and that excessively altered neuronal excitability may contribute to hypersensitivity symptoms.

• Authors: Xianghong Arakaki, Hailey Foster, Lei Su, Huy Do, Andrew J Wain, Alfred N Fonteh, Feimeng Zhou, Michael G Harrington
• Journal: Brain research (Brain Res) Vol. 1401 Pg. 85-94 (Jul 15 2011) ISSN: 1872-6240 [Electronic] Netherlands
• PMID: 21679932 (Publication Type: Comparative Study, Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)
• Copyright: Copyright © 2011 Elsevier B.V. All rights reserved.

Chemical References

• Sodium

Topics

• Action Potentials (physiology)
• Animals
• Animals, Newborn
• Cells, Cultured
• Extracellular Fluid (physiology)
• Hippocampus (cytology, physiology)
• Pyramidal Cells (physiology)
• Rats
• Rats, Sprague-Dawley
• Sodium (physiology)