The relationship between audiogenic seizure (AGS) susceptibility and forebrain tone-responsiveness in genetically AGS-prone Wistar rats

The present study characterized the intensity-response functions of extrace llular field responsiveness of different cortical/subcortical structures of the forebrain following the free-field presentation of tone stimuli, withi n a population of genetically audiogenic seizure (AGS)-prone KM-Wistar rats . The neural response properties of each case were compared to its propensi ty to exhibit AGSs during the continuous tone stimulation (15 kHz, 90 s at max.). The amplitudes or slope components of the evoked responses and their peak latencies showed significant positive (amplitude and slope) and negat ive (peak latency) Bolzmann's sigmoid relationships with the onset-latency of AGS. These relationships, with areal differences in the slopes of satura tion functions, applied for the three different data sets recorded simultan eously from the stratum radiatum dendritic layer of the hippocampal CA1 are a, primary auditory cortex layers II-IV, and frontal cortex surface. In add ition, the similar type of functions between the evoked response variables and AGS onset latency held when all the areas were considered together. The se data suggest that the neural responsiveness to acoustic stimulation of t he primary sensory, multimodal and association cortices of the forebrain ma y altogether contribute to the seizure initiation by that modality in the g enetically AGS-prone rats. It has been previously shown that there exist ab undant and dispersed auditory projections from these forebrain areas to the brain stem and spinal cord, structures that are generally considered to be the key predisposing factors in the generation of AGS. Hence, the types of correlation found reflect the subject-specific stage of forebrain responsi veness, being either related or unrelated to genetic AGS-specific changes, and possibly its triggering impact upon the lower brain AGS network. Accord ingly, the mere comparison of forebrain response measures of these AGS-pron e animals with those of the AGS-resistant ones could not reveal the result presented. (C) 2000 Elsevier Science Inc. All rights reserved.