Neural plasticity and stress induced changes in defense in the rat.

We investigated the effects of predator stress on behavior and amygdala afferent and efferent neural transmission in rats. Pathways studied were: ventral angular bundle input to the basolateral amygdala; central and basolateral amygdala output to the periaqueductal gray (PAG). Predator stress was 'anxiogenic' in elevated plus maze, light/dark box and acoustic startle tests one week after stress. Lasting changes were also observed in neural transmission. Predator stress appeared to potentiate right and depotentiate left hemisphere afferent amygdala transmission. In contrast, predator stress potentiated amygdala efferent transmission to right and left PAG, depending on the amygdala nucleus stimulated. Paired pulse and intensity series analysis suggests that transmission changes may be postsynaptic or presynaptic, depending on the pathway. Path analysis relating brain and behavioral changes suggests that potentiation and depotentiation in both hemispheres participate jointly in effecting some, but not all, of the behavioral changes produced by predator stress. Potentiation in left hemisphere amygdala afferents and efferents predicts anxiolytic-like effects, while potentiation in the right hemisphere amygdala afferents predicts anxiogenic-like effects. Path analysis also supports the view that changes in different neural systems mediate changes in different behaviors. These findings have their parallel in studies in the cat, but there are species differences.