The effect of variable duration one hertz interference on kindling

Experiments were conducted to evaluate the effect of various durations of 1-Hz brain stimulation on kindling behaviour induced by 60-Hz sine wave stimulation. In two experiments the effective threshold intensity (ETI) to elicit a convulsion was determined on four separate occasions with 5 days of daily trials interspersed between determinations. On each day experimental rats were stimulated with 1-Hz current on the first and third trials for 5, 15, 30, 60, 120, 180, or 600 seconds duration and with 60-Hz current for 30 seconds on the second trial. A steady increase in the intensity required to elicit a convulsion with 60-Hz current from ETI2 to ETI4 resulted for all rats with durations of 15 seconds or greater. Rats stimulated only with 60-Hz sine waves, and those in the 5 second group, maintained relatively stable values from ETI1 to ET4, with a slight decline occurring. Suppression of convulsive behavior on daily trials was modest in the 15 second group, pronounced with the 30 second group, and drastic with the other groups. The 600 second group had the greatest suppressive effect operating. The suppression effect did not appear to be due to tissue damage inasmuch as most of the experimental rats (except the 600 seconds one) convulsed again at previous low ETI levels following a 15 or 16 day rest at the end of the experiment. This result suggests that the suppression effect is a relatively transient event.