PROJECT SUMMARY
The lateral septum (LS) is an inhibitory limbic brain structure long thought to be essential for threat processing
and defensive behavior. In part due to its anatomical and molecular heterogeneity, the precise means by which
the LS mediates these processes remains elusive. To this end, I have focused my graduate work on LS neurons
expressing the stress-related Corticotropin releasing hormone type II receptor (LS-Crhr2). CRH-family G-protein
coupled receptors (GPCRs) are critical for behavioral and physiological stress responses and are implicated in
mood and anxiety disorders, providing a direct link between this subset of LS neurons and a central stress
system. Moreover, LS-Crhr2 neurons are activated by innate threats, and its activity modulates concomitant
defensive responses, evokes physiological arousal, and elicits aversion. The overall goal of these studies is to
determine the molecular and functional organization of LS-Crhr2 neurons in threat processing. Threat
processing, however, is multifaceted and largely involves the ability to rapidly detect and evaluate sensory stimuli
as potential threats in order to respond with the appropriate behavioral defenses. To capture this complexity, I
use two-way signaled active avoidance, a behavioral paradigm in which mice learn to perform goal-directed
avoidance behaviors in response to punishment-predictive cues. Using microendoscopic calcium imaging,
optogenetics, and single-nuclei RNA sequencing, I have thus far established the following: 1) LS-Crhr2
population activity is required for executing learned avoidance; 2) LS-Crhr2 population activity dynamically codes
threat cues in a manner predicting defense decisions and upcoming action initiation; 3) LS-Crhr2 comprises of
ten functional subclasses (defined by calcium dynamics) specialized in distinct threat-related processes; and 4)
LS-Crhr2 comprises of ten molecular subclasses (defined by transcriptomics) with unique anatomical
organization. Building on these observations, the central goal of this study is to identify how these molecular LS-
Crhr2 subsets mediate specific threat-related processes and how they are dynamically recruited. In the following
aims, we will use viral-genetic strategies to monitor and manipulate the activity of these molecularly-defined
subclasses, which together comprise of roughly 84% of the total LS-Crhr2 population. Aim 1 will use
microendoscopic calcium imaging of single neurons to determine whether each molecular subclass maps to
functional LS-Crhr2 clusters whose neural activity dynamics resemble discrete threat-related processes during
active avoidance. Aim 2 will use optogenetics to directly inhibit the activity of each subset to test their role in
these distinct processes. The successful completion of these aims will capture how the molecular diversity of
LS-Crhr2 neurons maps to function, thereby providing a framework for understanding the role of LS in threat
processing and, more generally, for studying the role of discrete functional units of cells that express druggable
GPCRs of interest.