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Postnatal growth of genioglossal motoneurons
B S Brozanski1, R D Guthrie, E A Volk
1Department of Pediatrics, Magee-Womens Hospital, Pittsburgh, Pennsylvania 15213.
Insights
Kitten genioglossal motoneuron growth primarily occurs along the major axis until 8 weeks. Cell body surface area increases linearly during this period, with no further growth in dimensions or surface area in adulthood.
Area of Science:
- Neuroscience
- Developmental Biology
- Anatomy
Background:
- The genioglossus muscle is crucial for tongue protrusion and airway patency.
- Understanding the development of genioglossal motoneurons is important for respiratory control.
- Previous studies have not fully characterized the postnatal morphological development of these neurons.
Purpose of the Study:
- To investigate the postnatal morphological development of kitten genioglossal motoneurons.
- To quantify changes in cell body size, shape, and dendritic structure during development.
- To establish baseline morphological data for future functional studies.
Main Methods:
- Used retrograde transport of horseradish peroxidase (HRP) in six age groups of kittens (newborn to adult).
- Analyzed 100-150 motoneurons per group in transverse sections.
- Measured somatic dimensions, form factor, primary dendrites, and calculated surface area.
Main Results:
- Somal major axis length increased significantly from birth to 8 weeks (25.2 to 41.3 microns).
- Cell body eccentricity increased (form factor decreased from 0.94 to 0.80) from birth to adulthood.
- Somal surface area increased linearly until 8 weeks, then plateaued; growth rate differed from body weight and surface area growth rates.
Conclusions:
- Genioglossal motoneuron somatic growth is largely complete by 8 weeks of postnatal age.
- The observed morphological development suggests potential functional maturation during this period.
- Further research is needed to correlate these structural changes with genioglossal muscle function, especially in conditions like infant apnea.
Abstract:
The postnatal growth of kitten genioglossal motoneurons were examined in six different age groups (newborn, 2, 4, 8, and 12 weeks and adult) using the technique of retrograde transport of horseradish peroxidase (HRP). The cell bodies of 100-150 motoneurons in each age group were analyzed in a transverse plane of section using standard techniques. Somatic genioglossal motoneuron growth occurred primarily along the major axis, which increased from 25.2 microns to 41.3 microns between birth and 8 weeks of postnatal age, after which time there was no further increase in either major or minor dimension of the cell body. The form factor decreased from 0.94 to 0.80 from birth to adulthood indicating an increased eccentricity of the cell body. The number of primary dendrites visible with this technique remained constant throughout the postnatal period. Calculated somal surface area increased in a linear fashion from birth through 8 weeks of postnatal life. There was no further increase in surface area beyond this age. The rate of increase in somal surface area with age was significantly different from both the rate of increase of animal weight and animal surface area with age. The correlations between the demonstrated immature genioglossal morphology and its cellular electrophysiology or integrated respiratory function remain unknown. The recent demonstration of decreased activation of the genioglossus muscle following airway occlusion in premature infants with apnea suggests that the relationships between developing genioglossal motoneuron structure and function warrant further investigation.