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Calcium, magnesium and the electrical activity of guinea‐pig olfactory cortex in vitro
Author(s) -
Richards C. D.,
Sercombe R.
Publication year - 1970
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1970.sp009294
Subject(s) - excitatory postsynaptic potential , chemistry , saline , guinea pig , endocrinology , magnesium , population , calcium , medicine , cortex (anatomy) , inhibitory postsynaptic potential , neuroscience , biology , environmental health , organic chemistry
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 Ca 2+ and Mg 2+ . 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 Ca 2+ concentration was sigmoid. The N‐wave amplitude (EPSP) was proportional to [Ca 2+ ] o n . When saline Ca 2+ was between 0·4 and 1 m M n averaged 2·5 (range 1·5–4·3). 4. The EPSP amplitude was reduced by increasing saline [Mg 2+ ]. High Mg 2+ salines (about 10 m M ) abolished the EPSP. 5. Both Ca 2+ and Mg 2+ in high concentrations depressed the positive notches. 6. Salines containing little or no Ca 2+ and Mg 2+ caused the preparation to show signs of hyperexcitability. Under these conditions the evoked potentials were very variable and unstable. ‘Ca 2+ ‐free’ salines caused a reversible loss of excitability. 7. The results indicated that Ca 2+ and Mg 2+ had antagonistic effects on the release of the transmitter substance(s). Increased Ca 2+ concentrations increased the output of transmitter, increased Mg 2+ concentrations reduced the output of transmitter. Both Ca 2+ and Mg 2+ in increasing concentration increased the threshold for action potential generation.