Distribution & Density of 5-HT Fibers in the Lumbar Spinal Cord of the Mouse Public

Abstract

Serotonergic (5-HT) neurons in the raphe nuclei of the brainstem profusely innervate every part of the central nervous system (CNS) to exert a breadth of modulatory functions, including regulating spinal motor circuits. The existing literature has reported complex and sometimes conflicting actions of 5-HT on spinal motor circuits. This has been attributed to methodological differences (species, age, etc.) and a lack of approaches that would enable the specific activation of the 5-HT raphe neurons projecting to the spinal cord (5-HT raphe-spinal neurons) without activation of the non-5-HT raphe-spinal neurons. Now that such a specific approach is possible in the mouse (Giorgi & Perreault, 2021), it is critical that we gather information about the anatomy of the 5-HT raphe-spinal system in this species. Therefore, this study aims to assess the laminar and funicular distribution and density of 5-HT raphe-spinal fibers projecting to the upper lumbar segments of the spinal cord, where core circuits of hindlimb movements are found, both in newborn mice and in young adult mice. We find approximately 53% more 5-HT axon segments in the ventral horn of the neonate compared to the adult mouse. In addition, we report the ventral and lateral funiculi of the neonate mouse having over three times the number of 5-HT axon segments than the adult mouse. One hypothesis for this large drop in fibers with age is proposed by ten Donkelaar, who suggests redundant axons are selectively reduced following collateralization in the spinal cord.

Table of Contents

1) Purpose

2) Background

2) Serotonergic (5-HT) Neurons

4) 5-HT Fiber Development in the Mouse

4) 5-HT Fiber Morphology

5) Methods

5) Perfusion & Tissue Preparation

5) Sectioning

6) Immunohistochemistry

7) Imaging & Analysis

9) Troubleshooting

11) Results

11) 5-HT Fibers in the Gray Matter

14) 5-HT Fibers in the White Matter

15) Other Statistical Analyses

16) Discussion

16) Decrease in 5-HT Fibers in the Ventral Gray Matter

17) Decrease in 5-HT Fibers across the White Matter Funiculi

18) Strengths of Study

18) Limitations of Study

19) Future Directions

21) References

About this Honors Thesis

Rights statement

• Permission granted by the author to include this thesis or dissertation in this repository. All rights reserved by the author. Please contact the author for information regarding the reproduction and use of this thesis or dissertation.

School	Emory College
Department	Neuroscience and Behavioral Biology
Degree	B.S.
Submission	Honors Thesis
Language	English
Research Field	Biology, Neuroscience
Mot-clé	Serotonin Descending Axons Brainstem Motor Control Reticulospinal
Committee Chair / Thesis Advisor	Marie-Claude Perreault, Emory University
Committee Members	Francisco Alvarez, Emory University Astrid Prinz, Emory University

Dernière modification

Primary PDF

Thumbnail	Title	Date Uploaded	Actions
	Distribution & Density of 5-HT Fibers in the Lumbar Spinal Cord of the Mouse ()	2023-04-10 10:12:44 -0400	Press to Select an action Download

Supplemental Files

Thumbnail	Title	Date Uploaded	Actions