Effects of elevated magnesium on discharge of myenteric neurons of cat small bowel

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Abstract
Electrical discharge of single units in myenteric ganglia of cat intestine was recorded extracellularly, and the effects on the electrical discharge of elevating the concentration of Mg++ in the Tyrode solution from 0.2 to 10.2 mM were determined. The ongoing discharge of 83% of the burst-type units was blocked by elevation of Mg++. The remainder of the burst-type units and all of the single-spike units tested continued to discharge in elevated Mg++. Frequency distribution histograms of interburst intervals of burst units that were unaffected by elevated Mg++ showed low variance of interburst interval, and multimodes on the histograms were multiples of the first mode. The variance of interburst intervals of burst-type neurons that were blocked by elevated Mg++ was greater than variance of the burst-type neurons that were unaffected by increased Mg++. If it is assumed that the action of elevated Mg++ is blockade of synaptic transmission, then the results indicated that the ongoing discharge of the neurons that were blocked by elevated Mg++ was dependent on synaptic input to the cell. The burst-type units that were unaffected by elevated Mg++ may be endogenous oscillators that do not receive synaptic input. The burst-type units that were blocked by elevated Mg++ may be driven by synaptic input from the burst-type oscillators.

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