We used microdialysis to determine extracellular concentrations of norepinephrine (NE), dopamine (DA) and serotonin (5-HT) before and during a 1-day amygdala kindling paradigm. Subjects were young cats (<1 year old; n=8; 6 female, 2 male). Consecutive 5-min samples (2 μl/min infusion rate) were obtained from left amygdala and ipsilateral locus ceruleus complex (LC) under 3 experimental conditions lasting 1-h each (n=12 samples per cat per condition): (1) just before amygdala stimulation (baseline), (2) during focal afterdischarge (AD) and (3) during generalized AD. ADs were elicited by electrical stimulation applied to establish thresholds immediately before dialysate collection as well as during each sample collected in focal vs. generalized AD conditions. Sample concentrations were time-adjusted to correspond with sleep vs. waking state and/or focal vs. generalized ADs. Seizure activity was indexed by AD threshold (mA) and duration (s) as well as number and duration of specific clinically evident (behavioral) seizure manifestations. Main results were: (1) Lower baseline concentrations (fmoles per sample) of NE, DA and 5-HT correlated with subsequent increases in duration of focal and generalized AD as well as number of behavioral seizure correlates. (2) When compared to baseline levels, NE, DA and 5-HT concentrations significantly increased only in amygdala during focal AD and in both amygdala and LC during generalized AD. (3) NE and 5-HT concentrations were higher than DA at both collection sites and were selectively associated with increased wakefulness throughout the study.