Student Theses and Dissertations


Michael Riad

Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)

RU Laboratory

Heintz Laboratory


The cerebral cortex is composed primarily of two neuronal cell types: excitatory pyramidal cells and inhibitory interneurons. Their neurochemical diversity and complex organization into interconnected laminar and columnar circuits imbues the cortex with countless computational and functional possibilities. At the behavioral level, changes in the molecular profile and electrophysiological activity of cortical neurons produce noticeable changes in perception, learning and memory, motor skills, and executive cognitive functions. In the initial chapter of this thesis, I briefly cover the history and progress of cell type studies in cerebral cortex and provide frameworks for understanding and interrogating interneuron diversity. We next apply modern molecular tools to test the validity of a proposed circuit model for cortical serotonin receptor 3 (5-HT3AR) interneurons enriched with corticotropin-releasing hormone (CRH), generated using these established frameworks. Molecular profiling using Translating Ribosome Affinity Purification (TRAP-seq) predicted an elegant, bimodal postsynaptic mechanism for CRH neuron modulation of both pyramidal cells and interneurons. In mouse prefrontal cortex (mPFC), we initiate a host of molecular, anatomical, and electrophysiological studies in this less understood subpopulation and validate that cortical CRH cells are interneurons (CrhINs). Further characterization revealed CrhINs express vasoactive intestinal peptide (VIP), a marker for the disinhibitory class of interneurons. These preliminary findings predict an elegant and multi-layered mechanism for CrhIN activation of prefrontal cortex, achieved through complementary GABAergic signaling and CRH release. In chapter two, we use transgenic mouse lines, RNA sequencing, gene excision, cell type-specific viral approaches, and electrophysiological whole cell patch clamp recordings, in combination with optogenetics and pharmacology, to probe the validity of this proposed circuit. Oxytocin receptor interneurons (OxtR-INs), a subset of somatostatin interneurons first discovered and characterized by Drs. Miho Nakajima, Kun Li, Ines Ibañez-Tallon, and Nathaniel Heintz, were found to mediate prosocial and anxiolytic effects through the release of corticotropin-releasing hormone binding protein (CRHBP). CRHBP, the endogenous antagonist to CRH, sequesters unbound CRH and blocks CRH – CRHR1 signaling, ultimately reducing the excitability of CRHR1 L2/3 pyramidal cells. A critical insight revealed in these initial studies is the identification of CRH peptide expression in VIP interneurons and, in contrast, CRHBP expression in SST interneurons. To test the prediction that CRH/VIP interneurons both inhibit OxtR/SST/CRHBP interneurons and release CRH onto CRHR1 expressing neurons, we applied optogenetic stimulation at both low and high frequency, in parallel with pharmacology, to isolate dual cell type-specific GABA and CRH-mediated currents in mPFC.


A Thesis Presented to the Faculty of The Rockefeller University in Partial Fulfillment of the Requirements for the degree of Doctor of Philosophy

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