**4. Limitations of current research and the path forward**

Sympathetic neurons have been long regarded as an important model system for studying neuronal differentiation. Due to increased recognition of the importance of sympathetic nervous system dysregulation in many diseases, there has been a renewed interest in understanding the mechanisms controlling neuronal differentiation, target innervation and neuronal survival in these neurons. Significant strides have been made in understanding axonal growth over the past 70 years *in vitro and in vivo* but there are still questions that need further exploration. While we understand the importance of individual growth factors for axonal growth, many of the null mutants show some innervation of target tissues. That still leaves the question of how *Signaling Pathways Regulating Axogenesis and Dendritogenesis in Sympathetic Neurons DOI: http://dx.doi.org/10.5772/intechopen.102442*

much each of these growth factors contribute to initiation and elongation of axons during normal development and how their signaling pathways are coordinated to regulate final axonal growth in different paravertebral and prevertebral ganglia.

In comparison to axonal growth, our understanding of dendritic growth in these neurons is much more limited. Most of the studies on sympathetic neurons have been limited to cultured SCG neurons, which leaves the question of whether similar signals are important for regulation of dendritic growth in other paravertebral and prevertebral ganglia. Even in the SCG, many disparate signaling pathways including BMP, NGF, cytokine, ROS, ubiquitin-proteasome, etc. have been shown to control the dendritic tree *in vitro.* However, it is unclear which of these interactions are crucial for dendritic arborization *in vivo* in the SCG and how these pathways coordinately regulate dendritogenesis.

Finally, additional whole genome analysis looking at transcripts, proteins and non-coding RNAs is needed to fully understand the downstream mediators of both axogenesis and dendritogenesis to identify the common regulators controlling neuronal polarity and function in these neurons.

### **Acknowledgements**

This work was supported through Saint Mary's College internal research funding through Faculty Development Fund and Summer Research Fund.

### **Author details**

Vidya Chandrasekaran Saint Mary's College of California, Moraga, CA, USA

\*Address all correspondence to: vc5@stmarys-ca.edu

© 2022 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
