PROJECT SUMMARY
Brain development is a complex process that requires the production and differentiation of numerous cells and
cell types, with the additional challenge of spatial and temporal precision in the neural circuitry that connects
these cells. Improper formation of neural circuitry leads to impaired control over brain activity patterns and is
broadly thought to contribute to a number of childhood neurological disorders. Multiple lines of research suggest
that inhibitory GABAergic circuitry in particular contributes to the pathophysiology of neurodevelopmental disor-
ders, yet these disorders remain poorly treated. This project is focused on the GABAergic synapse formed be-
tween a chandelier cell and a specialized neuronal compartment called the axon initial segment (AIS), forming
an axo-axonic synapse. Chandelier cells exert powerful control over neural activity patterns exerting shunting
inhibition at the AIS of large groups of principal cells, which impacts their probability of generating an electrical
signal. Axo-axonic synapses are characterized by GABAA receptors containing the a2 subunit and collybistin, a
specific interacting partner we have recently identified. We have developed and characterized a mouse model
with a substitution mutation in the GABAA receptor a2 subunit (Gabra2-1) that diminishes interaction with colly-
bistin, causing reduced numbers of axo-axonic synapses and spontaneous seizures during development. On
this premise, we hypothesize that the a2 subunit contributes to the organization of the AIS in order to facilitate
the formation of axo-axonic synapses. In this proposal we will examine axo-axonic synapse development and
AIS organization using immunohistochemistry and expansion microscopy, as well as circuit dysfunction using
cortical field recordings. We will examine how these changes correlate with symptom onset in the Gabra2-1
mouse and also evaluate novel methods to replace lost control by using a novel light activated cation channel
targeted to the AIS. Relevance to human health: The proposed project is expected to yield detailed information
about how the AIS organizes during development, as well as the formation of axo-axonic synapses in both typical
and pathological conditions, providing both basic knowledge about brain development and translational insights
for neurodevelopmental disorders. This proposal also offers a novel means of actively manipulating the AIS, a
site known for its potential to control cortical activity patterns. Outcomes: This work will be conducted entirely
by undergraduate and graduate students at UNLV, which is one of the nation’s most diverse campuses. Thus,
this project will provide instrumental training opportunities for the diversification of the biomedical workforce, as
well as enhance the research environment of our institution.
