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. 1970 Dec;211(3):571–584. doi: 10.1113/jphysiol.1970.sp009294

Calcium, magnesium and the electrical activity of guinea-pig olfactory cortex in vitro

C D Richards, R Sercombe
PMCID: PMC1396076  PMID: 5501052

Abstract

1. Evoked electrical activity was observed in slices from guinea-pig olfactory cortex maintained in vitro. This evoked activity was studied in saline solutions containing various concentrations of Ca2+ and Mg2+.

2. The evoked potentials recorded from the surface of the prepiriform cortex comprised a negative wave (N-wave) of about 10-15 msec duration upon which a variable number of short duration positive notches were superimposed. The N-wave was identified as a population excitatory post-synaptic potential (EPSP) of the olfactory cortex neurones and the positive notches were identified with synchronous discharge of cortical neurones.

3. The relation between the EPSP amplitude and saline Ca2+ concentration was sigmoid. The N-wave amplitude (EPSP) was proportional to [Ca2+]on. When saline Ca2+ was between 0·4 and 1 mM n averaged 2·5 (range 1·5-4·3).

4. The EPSP amplitude was reduced by increasing saline [Mg2+]. High Mg2+ salines (about 10 mM) abolished the EPSP.

5. Both Ca2+ and Mg2+ in high concentrations depressed the positive notches.

6. Salines containing little or no Ca2+ and Mg2+ caused the preparation to show signs of hyperexcitability. Under these conditions the evoked potentials were very variable and unstable. `Ca2+-free' salines caused a reversible loss of excitability.

7. The results indicated that Ca2+ and Mg2+ had antagonistic effects on the release of the transmitter substance(s). Increased Ca2+ concentrations increased the output of transmitter, increased Mg2+ concentrations reduced the output of transmitter. Both Ca2+ and Mg2+ in increasing concentration increased the threshold for action potential generation.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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