Related Experiment Videos
An overview of phrenic nerve and diaphragm muscle development in the perinatal rat
J J Greer1, D W Allan, M Martin-Caraballo
1Department of Physiology, University of Alberta, Edmonton, Canada T6G 2S2. john.greer@ualberta.ca
Insights
This study details the development of the phrenic nerve and diaphragm in fetal rats, tracing axon growth, muscle formation, and neural connections from embryonic day 11 to birth.
Area of Science:
- Developmental biology
- Neuroscience
- Anatomy
Background:
- The formation of the diaphragm and its innervation by the phrenic nerve are critical for respiration.
- Understanding these developmental processes is essential for diagnosing and treating congenital respiratory disorders.
Purpose of the Study:
- To provide a comprehensive overview of the key developmental stages of phrenic nerve and diaphragm formation in perinatal rats.
- To detail the timeline of axonal growth, muscle development, and neural maturation.
Main Methods:
- Review of existing literature on perinatal rat development.
- Chronological outlining of key developmental events based on embryonic (E) days.
Main Results:
- Phrenic axons emerge from the spinal cord around E11 and reach the primordial diaphragm by E13.5.
- Diaphragm muscle development involves myoblast fusion and myotube formation, guided by nerve branching from E14 to E17.
- Maturation of phrenic motoneurons (PMNs), including dendritic rearrangement and changes in electrical properties, occurs from E17 to birth.
Conclusions:
- The development of the phrenic nerve and diaphragm is a complex, coordinated process involving precise axonal guidance and muscle differentiation.
- Significant neural and morphological changes in phrenic motoneurons occur late in gestation, preparing for postnatal respiratory function.
Abstract:
In this overview, we outline what is known regarding the key developmental stages of phrenic nerve and diaphragm formation in perinatal rats. These developmental events include the following. Cervical axons emerge from the spinal cord during embryonic (E) day 11. At approximately E12.5, phrenic and brachial axons from the cervical segments merge at the brachial plexi. Subsequently, the two populations diverge as phrenic axons continue to grow ventrally toward the diaphragmatic primordium and brachial axons turn laterally to grow into the limb bud. A few pioneer axons extend ahead of the majority of the phrenic axonal population and migrate along a well-defined track toward the primordial diaphragm, which they reach by E13.5. The primordial diaphragmatic muscle arises from the pleuroperitoneal fold, a triangular protrusion of the body wall composed of the fusion of the primordial pleuroperitoneal and pleuropericardial tissues. The phrenic nerve initiates branching within the diaphragm at approximately E14, when myoblasts in the region of contact with the phrenic nerve begin to fuse and form distinct primary myotubes. As the nerve migrates through the various sectors of the diaphragm, myoblasts along the nerve's path begin to fuse and form additional myotubes. The phrenic nerve intramuscular branching and concomitant diaphragmatic myotube formation continue to progress up until E17, at which time the mature pattern of innervation and muscle architecture are approximated. E17 is also the time of the commencement of inspiratory drive transmission to phrenic motoneurons (PMNs) and the arrival of phrenic afferents to the motoneuron pool. During the period spanning from E17 to birth (gestation period of approximately 21 days), there is dramatic change in PMN morphology as the dendritic branching is rearranged into the rostrocaudal bundling characteristic of mature PMNs. This period is also a time of significant changes in PMN passive membrane properties, action-potential characteristics, and firing properties.