The effect of 5- and 14-day intertrial intervals on the 1-Hz suppression effect

Abstract

Experiments were conducted to evaluate the effect of 5-day and 14-day intertrial intervals of 1-Hz brain stimulation on kindling behavior induced by 60-Hz sine-wave stimulation. The effective threshold intensity (ETI) to elicit a kindled response with 60-Hz stimulation was determined on two separate occasions with 15 brain-stimulation trials between determinations. In Experiment 1, experimental rats were stimulated with 1-Hz sine waves before and after a 60-Hz brain-stimulation trial, with a 14-day interval between each stimulation session (Group 1- 60-1). A second group (Group X-60-X) received only the 60-Hz stimulation on the same trials as those on which Group 1-60-1 was stimulated with 60-Hz current. Experiment 2 was similar to Experiment 1, but the interval was 5 days. In previous experiments with 1, 3, or 24 h between trials, Group 1-60-1 had had a gradual increase in the intensity required to elicit a kindled response with 60-Hz current from ETI1 to ETI4 (the suppression effect). However, with a 72-h interval, a decline similar to that of Group X-60-X occurred in ETI values. The results with 14-day and 5-day intervals were similar to those with a 72-h interval. Suppression of kindled behavior on daily trials was not present in Group 1-60-1, in contrast to the results with 1, 3, and 24 h. Apparently, intervals of 3 days or greater allow much of the suppression effect to dissipate.