Further characterization of kindling antagonism.

Alternating stimulation of two sites in the forebrain culminates in typical kindling of generalized seizures from one site (dominant), whereas the other site (suppressed) supports only nongeneralized seizures for as long as stimulation of the dominant site continues, a phenomenon referred to as kindling antagonism. With the termination of stimulation of the dominant site, however, seizures provoked from the suppressed site eventually generalize, a progression thought to reflect the resumption of kindling from a previous point of arrest. To further assess the nature of kindling antagonism, we established antagonism between the amygdala and the septal area and subsequently evaluated the development of seizures provoked by stimulation of sites distal to the dominant site (always the amygdala). In Experiment 1, a 30-d stimulation-free period imposed after the establishment of antagonism failed to result in immediate generalization of seizures provoked from the suppressed site (septal area) in seven of eight rats. Although these results suggest that antagonism reflects an actual arrest of kindling rather than a transient inhibition of seizures, they are not entirely unambiguous: Rats exposed to the prolonged stimulation-free period required only half the number of septal stimulations for the expression of a generalized seizure as compared to rats receiving septal stimulation immediately after the establishment of antagonism. The latter finding is suggestive of a transient component of antagonism. In Experiment 2, development of generalized seizures from the previously naive right amygdala was virtually identical in rats previously kindled from the left amygdala and in rats expressing antagonism between the septal area and left amygdala. Development of generalized seizures from the right amygdala was faster than from the left amygdala in both groups of rats, however, suggesting that the expression of seizures provoked from the suppressed site after the establishment of antagonism does not involve a general impairment or enhancement of transfer. Experiment 3 revealed that radio-frequency lesions of the dominant site (amygdala) after the establishment of antagonism did not alter the subsequent development of generalized seizures from the suppressed site (septal area). This suggests that the expression of generalized seizures from the suppressed site after the establishment of kindling antagonism is not dictated by the functional state of the dominant site.