ELSEVIER Epilepsy Research 21 (1995) 171-182 EPILEPSY RESEARCH Persistence of kindling: Effect of partial kindling, retention interval, kindling site, and stimulation parameters Zoe Dennison a,1, G. Campbell Teskey a,2, Donald P. Cain b,. a Department of Psychology, University of Western Ontario, London, Ontario N6A 5C2, Canada b Graduate Program in Neuroscience, University of Western Ontario, London, Ontario N6A 5C2, Canada Received 14 September 1994; accepted 10 March 1995 Abstract The kindling effect is generally thought to be highly persistent and possibly permanent, but little direct evidence is available to support this idea. Retention of amygdala kindling was examined after a 12-wk interval in groups of rats that had been electrically kindled to different seizure stages (stages 1, 3, or 5), or kindled by high intensity or low frequency (3 pulses per second) stimulation, or fully kindled and allowed a rest of 1-24 wk. The retention of hippocampal kindling after a 12-wk interval was also examined. Rekindling after a 12-wk rest in the groups initially kindled to different seizure stages indicated that although there was evidence of erosion of the kindling effect in all groups, there were savings in all groups. There was also evidence of greater erosion in the aflerdischarge response than in the convulsive response to the first stimulation after the interval. Although there was evidence of erosion of kindling during the 1-24-wk intervals, there was evidence of savings in all groups, none of which required more than a mean of 2.2 afterdischarges to rekindle to stage 5. Seizures kindled in the hippocampus were retained as well as those kindled in the amygdala, and seizures kindled using low frequency stimulation were retained as well as those kindled using conventional 60 pulses per second stimulation. We conclude that the effects of kindling the amygdala a:ad hippocampus are highly persistent, and that the effects of kindling with low frequency stimulation are as persistent as kindling with conventional stimulation. Keywords: Kindling;Seizures;Amygdala;Hippocampus 1. Introduction An important aspect of kindling, a neuroplastic model of temporal lobe epilepsy [11,20], is its appar- * Corresponding author. Tel.: (519) 679-2111 ext. 4628; Fax: (519) 661-3961; email: cai:a@vaxr.sscl.uwo.ca. 1To whom reprint requests should be addressed. Present ad- dress: Departmentof Psychology,University College of the Fraser Valley, 33844 Marshall Rd., Abbotsford, British Columbia V2S 4N2, Canada. z Present address: Department of Psychology, University of Calgary, Calgary, Alberta T2N 1N4, Canada. ent permanence. Although the kindling effect is thought to be permanent [4,10,23], relatively little direct evidence has been gathered in support of this idea. Goddard et al. [11] measured the permanence of kindling after an interval of 12 weeks, but they did not record afterdischarge (AD), a critical factor in kindling [18], or report the nature of the convul- sive response after the interval. Other studies used intervals as long as 868 days, but reported few details of the rekindled response or studied only a few animals [17,22,23]. Retention of kindling has been demonstrated in 0920-1211/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 0920-121 1(95)00025-9