Influence of hippocampal kindling on avoidance learning in cats

Abstract

The formation of avoidance response and differentiation was studied in 13 control and 7 kindled cats with developed hippocampal epileptic focus and complex partial or secondary generalized tonic-clonic seizures. Conditioning sessions lasted from 15 to 20 min in a period following afterdischarges and seizures resulting from electrical stimulation of the hippocampal formation. In two out of seven kindled cats the conditioned reflex was established within time limits (9 and 20 days) comparable to the control cats. These two animals had relatively short-lasting afterdischarges (mean values: 17 and 19 s). In cats with longer-lasting afterdischarges and complex partial seizures (mean duration: 32 to 65 s, in different animals) criterion was not reached during parallel kindling-conditioning stage of 10 to 30 days. The level of correct responses was low and variable (0-70 percent), despite typical reactions to the unconditioned stimuli and clear orienting responses to the conditioning stimuli on more advanced stages of training. Four kindled animals entered the stage of secondary generalization of seizures after hippocampal stimulation. Reflex performance after tonic-clonic seizures was practically abolished. The termination of kindling resulted in acquisition of the conditioned reflex in all the animals. The results indicate, that in animals with long-lasting complex partial seizures the learning of the avoidance response is impaired. In contrast to the effects exerted by afterdischarges and complex partial seizures, intensive interictal hippocampal spiking did not seem to have a direct negative influence on, this particular type of learning.