Acoustic startle-evoked potentials in the rat amygdala: effect of kindling

The electroencephalogram (EEG) of the basolateral nucleus of the amygdala (BLA) was recorded during presentation of acoustic stimuli (70-110 dB SPL) in rats. EEG recordings were performed by chronically implanted bipolar electrodes in the BLA. The auditory evoked response consisted of a broad negative wave followed by a slow positive wave. A characteristic pattern of 1 to 3 negative peaks with a latency of about 12 ms and an increased amplitude of the slow positive wave at about 30 ms was observed when an acoustic startle response (ASR) occurred. These findings suggest that the BLA is involved in the processing of adverse auditory stimuli. These ASR-correlated potentials in the BLA were used to characterize changes of the physiological state of the amygdala that occur after chronic epileptogenesis. To achieve this aim, the rats were subsequently partially or fully kindled by daily electrical stimulation via the recording electrode. The negative peak was depressed in the partially kindled rats, but not in fully kindled rats. These changes in the characteristic EEG pattern of the BLA during the ASR indicate alteration of the physiological response of the amygdala after limbic epileptogenesis.