PERSISTENCE OF THE INTERICTAL EMOTIONALITY PRODUCED BY LONG-TERM AMYGDALA KINDLING IN RATS

Long-term amygdala kindling in rats results in large and reliable incr eases in emotional behaviour that model the interictal emotionality of ten observed in temporal lobe epileptics [Kalynchuk L. E. et al. (1997 ) Biol. Psychiat. 41, 438-451; Pinel J. P. J. er nl. (1977) Science 19 7, 1088-1089]. These experiments investigated the persistence of these kindling-induced increases in emotional behaviour after the cessation of the kindling stimulations. In Experiment 1, rats received 99 amygd ala or sham stimulations. Then, they were tested on three tests of emo tionality (i.e. activity in an unfamiliar open field, resistance to ca pture from the open field, and activity in an elevated-plus maze) eith er one day, one week, or one month after the final stimulation. The ra ts tested one day after the last stimulation displayed substantial dec reases in open-held activity, increases in resistance to capture and i ncreases in open-arm activity on the elevated-plus maze; these effects decreased, but not to control levels, in the rats tested one month af ter the final stimulation. In Experiment 2, rats received 99 amygdala or sham stimulations, and their resistance to capture was assessed one day later. Then, after a 60-day stimulation-free period, the rats rec eived another zero, one, 10, or 30 amygdala stimulations and their res istance to capture was reassessed one day later. The high levels of re sistance to capture observed in the rats tested one day after the 99 s timulations declined significantly during the 60-day stimulation-free period, but it remained significantly above control levels. However, t he administration of 30 additional stimulations reinstated asymptotic levels of resistance to capture. These results provide the first syste matic evidence that kindling-induced increases in emotional behaviour persist at significant levels for at least two months following the te rmination of kindling stimulations. Thus, they suggest that the neural changes underlying the genesis of interictal emotionality may be clos ely related to those mediating epileptogenesis itself. (C) 1998 IBRO. Published by Elsevier Science Ltd.