Assessment of anxiety-like behaviors in female rats bred for differences in kindling susceptibility and amygdala excitability

Two rat lines bred for kindling susceptibility were previously observed to engage in different behavioral strategies in tests of emotionality. In order to extend past research on defensive behaviors in these strains which largely used males, Fast- and Slow-kindling females were assessed for anxiety-like behaviors in a number of aversive paradigms. Fast rats entered and spent more time in the open arms and spent less time in the closed arms of the elevated plus-maze (EPM) compared to Slow animals. Fast rats had higher conditioned suppression ratios across testing days, defecated less often during conditioning, and successfully disinhibited suppression during extinction in the conditioned emotional response (CER) paradigm compared to Slow-kindlers. In order to pursue these differences in emotional reactivity between the strains and differentiate negative affect from motivational, learning, and impulsive explanations, a separate group of animals were assessed in the light-enhanced acoustic startle chamber, a test of anxiety. When initially exposed to a bright-light, Slow rats significantly increased their startle response while this was not observed in the Fast strain. In combination with previous research on these strains, the present data tentatively suggest that Fast and Slow animals utilize different neural systems in tests of fear and anxiety which may have been co-selected with the direct selection of amygdala-kindling susceptibility.