Kindling-related changes in afterdischarge "thresholds"

Amygdaloid stimulations were applied to rats at gradually increasing current intensities once every 60 sec until and afterdischarge (AD) was recorded through the stimulation electrode. These initial AD "thresholds" (x = 75 muA) were reduced over a 4-day period by a series of 12 subthreshold stimulations. In contrast, stimulations administered on the same regimen but at a higher intensity (400 muA) had raised the AD threshold. The decreases in the AD threshold were relatively permanent, whereas the elevated thresholds were subsequently reduced to control levels by a series of subthreshold stimulations or by a 7-day stimulation-free period. Two days following the completion of Experiment 1, all of the rats were injected with a low dose of pentylenetetrazol. The incidence of pentylenetetrazol-induced epileptic symptoms was much higher in the experimental animals than in the control subjects previously subjected only to the threshold estimation procedure.