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Title

Electrophysiologically Distinct Subpopulations of Murine Nociceptive Neurons as Revealed by a Genetic RET Reporter

Date of Award

Spring 5-15-2012

Author's School

Graduate School of Arts and Sciences

Author's Department

Biology & Biomedical Sciences (Neurosciences)

Degree Name

Doctor of Philosophy (PhD)

Degree Type

Dissertation

Abstract

The neurons of the dorsal root ganglia (DRG) are the initial detectors of somatic and visceral stimuli. The diversity of neurons of the DRG has long been recognized as distinct subpopulations have been identified by soma size and degree of axonal myelination. More recently, biochemical markers of specific subtypes have been used to segregate analysis of these cells and to study the function of individual cells in vitro. One particular subtype, small-diameter DRG neurons, has been identified as the primary detectors of noxious stimuli. These nociceptive neurons are identified not only by their small size, but also by the particular biomarkers and functional profiles they exhibit. Patch clamp recording of dissociated DRG neurons is a method frequently used in studies of nociception to assess the function of primary sensory afferents in vitro. One can use the characteristic markers of nociceptive neurons of the DRG in order to target specific subpopulations for study.

Here, a genetic RET reporter mouse was used to guide electrophysiological targeting of different subsets of nociceptive neurons of the DRG based on a direct marker of nociceptive neurons. Immunocytochemistry was employed to identify the distributions of known DRG nociceptive subtypes within the preparation. Experiments demonstrate distinct subpopulations of nociceptive neurons as identified by the presence or absence of RET. A comparison of the two groups demonstrates that RET-negative neurons exhibit lower intrinsic excitability than do RET-positive neurons. Further, the two groups exhibit action potentials of differing waveforms, most notably distinguished by more hyperpolarized afterhyperpolarization minima in RET-negative DRG neurons compared to the RET-positive population. Lastly, cluster analysis of nociceptive DRG neurons agnostic to RET profile revealed four clusters, or types, of neurons based on membrane and excitability properties. The RET-positive and RET-negative profiles map well to two of these clusters, however there are two clusters of nociceptive DRG neurons that are functionally distinct yet comprise both RET-positive and -negative members.

Together, these studies demonstrate the presence of distinct subtypes of nociceptive DRG neurons based on function, morphology, and protein expression profile. Clusters of neurons within the nociceptive population stratify based on membrane properties and excitability parameters. We further demonstrate the heterogenous nature of nociceptive neurons of the DRG.

Language

English (en)

Chair and Committee

Robert W Gereau

Committee Members

Yu-Qing Cao, Steven Mennerick, Jeanne Nerbonne, Joe Henry Steinbach, Gina Story

Comments

Permanent URL: https://doi.org/10.7936/K7XG9P21

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