Morphometric analysis of phrenic motoneurons in the cat during postnatal development

Abstract

The dendritic geometry of 20 phrenic motoneurons from four postnatal ages (2 weeks, 1 and 2 months, and adult) was examined by using intracellular injection of horseradish peroxidase. The number of primary dendrites (approximately 11-12) remained constant throughout postnatal development. In general, postnatal growth of the dendrites resulted from an increase in the branching and in the length and diameter of segments at all orders of the dendritic tree. There was one exception. Between 2 weeks and 1 month, the maximum extent of the dendrites increased in parallel with the growth of the spinal cord; however, there was no increase in either combined dendritic length or total membrane surface area. In addition, there was a significant decrease in the number of dendritic terminals per cell (59.8 +/- 9.3 vs. 46.4 +/- 7.4 for 2 weeks and 1 month, respectively). The distance from the soma, where the peak number of dendritic terminals per cell occurred, ranged from 700-900 microns at 2 weeks and 2 months to 1,300-1,700 microns in the adult. The diameter of dendrites as a function of distance from the soma along the dendritic path increased with age. The process of maturation tended to increase the distance from the soma over which the surface area and dendritic trunk parameter (sigma d1.5/D1.5) remained constant. The three-dimensional distribution of dendrites was analyzed by dividing space into six equal volumes or hexants. This analysis revealed that the postnatal growth in surface area in the rostral and caudal hexants was proportionately larger than that in either the medial, lateral, dorsal, or ventral hexants. Strong linear correlations were found between the diameter of the primary dendrite and the combined length, surface area, volume, and number of terminals of the dendrite at all ages studied.

Developmental changes in spinal motoneuron dendrites in neonatal mice

“…complexity in P11 dendrites , contrasts with the developmental pattern found in some other studies. For example, in cat phrenic MNs Cameron et al (1991a) reported a considerable decrease of the number of bifurcations per tree that paralleled dendritic elongation between the second and fourth week of age, such that the combined surface area during this period remained nearly constant. A similar phenomenon was found in rat hypoglossal (genioglossus) MNs between birth and the end of the second week of age (Nuñ ez-Abades et al, 1994).…”

Effect of Spinal Cord Injury on the Respiratory System: Basic Research and Current Clinical Treatment Options

“…Numerous studies have shown that neuronal pathways grow extensively during fetal development and that nonfunctional neural projections are eliminated (94,95), even in the respiratory system (96)(97)(98). Because the CPP is latent in adult rats, but remains intact, it was hypothesized that this pathway must have been active during development.…”

Key aspects of phrenic motoneuron and diaphragm muscle development during the perinatal period

“…The morphology of motoneurons within a pool, including the phrenic pool, varies considerably (16,17,73). Differences in soma morphology and dendritic arborization correspond to the diverse intrinsic electrophysiological properties of motoneurons.…”

“…Phrenic motoneurons exhibit significant postnatal growth (16,17). For example, rat phrenic motoneurons increase in both soma and dendrite dimensions between postnatal day 21 (P21) and adulthood (Fig.…”