Neural Circuitry of Conditioned and Unconditioned Fear: Effects of lesions of the Bed Nucleus of the Stria Terminalis

Agostini, Andrew
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University of Delaware
The bed nucleus of the stria terminalis (BNST) is suggested to play a role in certain types of fear, such as unconditioned fear and conditioned fear to long duration stimuli, but not others such as short duration conditioned fear stimuli. The main goal of the present research is to better understand the role the BNST plays in conditioned fear and unconditioned fear behavior. To study conditioned fear, a conditioned fear-potentiated startle paradigm was used where a light previously paired with a shock potentiates the acoustic startle reflex. For unconditioned fear, rats were exposed to a predator odor, trimethylthiazoline, to elicit unconditioned freezing behavior. Adult male Sprague-Dawley rats were first conditioned to a light. The rats were then subjected to neurotoxic lesions of the posterior division of the BNST. Following a week of recovery, the rats were tested for fear-potentiated startle. Several days later, they were tested for unconditioned freezing to TMT. Results demonstrate that lesions of the posterior division of the BNST significantly reduce cue-specific fear-potentiated startle, without affecting startle when the light was not present. This indicates that the BNST lesions interfered with expression of learned fear, but not the ability to startle, nor background anxiety, which is an increase in “baseline” startle after fear conditioning compared to pre-fear conditioned startle. Freezing to TMT was also reduced slightly in BNST lesioned animals, but this reduction was not statistically significant. Our data is contrary to previous research focused on the anterior nuclei of BNST, and suggests that the BNST has a heterogeneous collection of nuclei or cells that can affect both conditioned and unconditioned fear.