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Stress-Induced Pathophysiology 253accommodation of the response with repeated presentation. The fact that both thebasolateral and central amygdala respond to footshock in the same direction afterchronic stress suggests that these regions both receive direct input from regionsmediating this response. In summary, chronic cold stress strongly augmented thesignal-to-noise ratio of central amygdala responses by causing a decrease in baselineactivity but an augmentation of stimulus-evoked responses.Prefrontal Cortical Modulatory Effectsin Chronically Stressed SubjectsThe studies reviewed above show that chronic stress alters the baseline populationactivity and responsivity of neurons within the amygdala. In particular, therewas a substantial effect on the autonomic output region, the central medial nucleus.It is clear from our studies that the central medial nucleus is strongly controlledby the intercalated cell masses, and studies by Quirk et al. (2003) provide evidencesuggesting that the intercalated cell masses may receive input from the prefrontalcortex. Given the evidence that the prefrontal cortex modulates responsesto stress, we examined whether the responses observed in the central medialnucleus following chronic stress may be due to a regulatory influence of the prefrontalcortex.As reviewed above, central medial amygdala neurons in chronic cold-stressedrats exhibited significantly decreased baseline activity. Following prefrontal corticallesions, the average baseline activity exhibited a small decrease with respectto poststress baseline activity; however, the decrease was substantially less thanthat observed with a prefrontal cortical lesion in control rats (Correll et al., 2005).Similarly, lesion of the prefrontal cortex also revealed a substantially augmentedfootshock-induced activation of central medial neurons. However, as with baselineactivity, the percent increase above the elevated baseline response was significantlydiminished compared to that in the nonstressed rats. Therefore, the effectsof chronic cold on central medial neuron activity were similar in direction as thoseproduced by prefrontal cortical lesions. However, the effects of prefrontal lesionsand cold stress were not additive. Indeed, chronically stressed rats exhibited activityand responsivity levels similar to what would be expected in a rat with decreasedprefrontal cortical function.Relevance of Stress Effects in Amygdalato the Pathophysiology of SchizophreniaWe believe that the apparent decreased prefrontal cortical function in chronicallystressed rats has relevance for the onset of schizophrenia symptoms (Grace, 2004;