Exposure to aversive stimuli triggers an adaptive balance between defensive and appetitive behaviors, which,
for survival, needs to be acquired rapidly, stored over time, and must be flexible to accommodate modifications
in the organism’s internal and/or external state. A detailed characterization of the mechanisms underlying the
formation, storage and flexibility of the balance is critical to understand how this fundamental process operates
to help organisms survive in a changing environment. In the model organism Aplysia, exposure to aversive
stimuli induces a balance that manifests as concurrent enhancement of defensive reflexes (an elementary form
of learning known as sensitization) and suppression of the appetitive behavior of feeding. This balance is stored
in short-term (minutes to hours) and long-term (days) timeframes depending on the amount of aversive
exposure. The balance is sustained, at least in part, by changes at key sites within the corresponding neural
circuits: decreased excitability of feeding decision-making neuron B51 co-expressed with increased excitability
of the sensory neurons controlling defensive reflexes. The PI’s lab has begun to analyze the cellular and
biochemical mechanism of the balance. Short-term sensitization and feeding suppression are mediated by
distinct modulators, serotonin (5-HT) and nitric oxide (NO), respectively. Conversely, long-term sensitization
and feeding suppression share the requirement of NO. Although sensitization and feeding suppression are
concurrently induced following aversive experience, the long-term storage of sensitization following multiple
days of repeated exposures to aversive stimuli has been found to outlast the suppression of feeding, suggesting
the presence of constraints that may limit the maintenance of the balance over time.
Using a combination of in vivo and in vitro procedures, this R15 AREA grant will: 1) determine whether
common plasticity rules govern changes in feeding and defensive circuits; 2) further characterize the
modulatory systems underlying the storage of the balance and 3) examine flexibility and constraints in the
storage of the balance.
The outcomes will contribute to the fundamental understanding of how the balance between defensive and
appetitive behaviors in generated and stored in the normal nervous system. The acquired knowledge may
ultimately provide important insights into those neurological disorders caused by deficits in the correct
formation, storage and flexibility of this balance, thus aligning with the mission of the National Institute of
Neurological Disorders & Stroke. The proposed experiments will be performed primarily by undergraduate
students, under the supervision of the PI, research associate and/or a senior graduate student(s). This project
represents a unique opportunity for Texas A&M University – Corpus Christi, a Hispanic-Serving Institution, to
increase its visibility in biomedical research, and for its undergraduate students to conduct research in the field
of neuroscience, which is underrepresented at this institution.
