Dissertation Defense: Catherine Elorette
Candidate Name: Catherine Elorette
Advisors: Ludise Malkova, Ph.D. and Patrick Forcelli, Ph.D.
Title: The Basolateral Amygdala and Superior Colliculus Regulate Physiological and Behavioral Measures of Avoidance and Approach
The superior colliculus (SC) and amygdala are central components of the defensive system within the brain. The SC processes both conscious and non-conscious visual information and in turn, directs orienting and defensive behavioral responses. The amygdala exerts “top down” control over SC and may interact with the SC to regulate emotional response to visual stimuli.
To determine the anatomical connectivity between the SC and the amygdala, I injected retrograde tracers into the amygdala and anterograde tracers into the SC and examined regions of colocalization within the pulvinar nucleus of the thalamus. Anterograde tracers labeled axonal projections that colocalized with cell bodies labeled by the retrograde tracer, concentrated in the medial portions of the medial (PM), oral (PO) and inferior pulvinar (PI). These data support the existence of a "bottom up” pathway mediating fast processing of emotionally salient information projecting from the SC to the pulvinar to the amygdala.
To determine the causal association of activity in the amygdala on (1) autonomic activity, (2) emotional reactivity to social and threatening stimuli, and (3) social dominance, I used a pharmacological microinjection approach. I inhibited the amygdala via GABA A agonist muscimol (MUS) and activated it with GABA A antagonist bicuculline methiodide (BMI). Saline was injected as a control. Following drug infusion, animals were tested in each of the behavioral domains listed above. Activity in the amygdala was associated with bradycardia, decreased fearful reaction and increased interest in social stimuli, and decreased dominance. Inhibition of the amygdala was associated with bradycardia, increased passive behavior, fearful reactions, and decreased dominance.
To determine if activity within the SC regulated autonomic responses, I microinjected BMI into the SC and measured heart rate and blood pressure. Consistent with its laminar structure and segregated zones of anatomical inputs and outputs, subregions of the SC showed a diversity of responses, primarily bradycardia and depressor response, localized in intermediate and deep layers. I have shown that BLA and SC separably regulate autonomic outputs. BLA regulates behavioral response to threats and challenges to established behavioral patterns, reflecting alterations in larger networks involved in recognizing and responding appropriately to environmental cues.
Monday, June 10 at 1:00pm to 3:00pm
New Research Building, Auditorium
3800 Reservoir Road, N.W., Washington
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