Quantitative analysis of the dendritic architectures of cat hypoglossal motoneurons stained intracellularly with horseradish peroxidase

Little is known about the dendritic architecture of cat hypoglossal motoneu rons. Thus, the present study was done to provide quantitative descriptions of hypoglossal motoneurons and to determine correlations between dendritic size parameters by using the intracellular horseradish peroxidase (HRP) in jection technique in the cat. Twelve hypoglossal motoneurons stained with H RP were antidromically activated by stimulation applied to the medial branc h of hypoglossal nerve. Eight (type I) and four (type II) of the 12 motoneu rons were located in the ventral and dorsal parts of the ventromedial subnu cleus of hypoglossal nucleus, respectively. The somatodendritic morphology of the two types of neurons was remarkably different, especially in the den dritic arborization pattern. The type I neurons established an egg-shaped d endritic tree that was distributed through the nucleus to the reticular for mation; the type II dendritic tree was confined within the nucleus and pres ented a rostrocaudally oriented, mirror-image, fan-shape appearance. The to tal dendritic area and length and the number of terminations and branch poi nts were significantly larger for type I than for type II neurons. For the two types of neuron, there was a positive correlation between stem dendriti c diameter and several dendritic size parameters. Although the slopes of th e regression lines were slightly different between the two, these were not statistically significant. The present study provides evidence that hypoglo ssal motoneurons located in the ventromedial subnucleus could be divided in to two types according to the dendritic arborization pattern and quantitati ve analysis of the dendritic tree and according to neuronal location and su ggests that the two types of hypoglossal motoneurons can be viewed as intri nsically distinct cell types: type I and type II, which innervate extrinsic and intrinsic muscles, respectively. In addition, the morphometric analysi s made it possible to estimate the size of the dendritic tree by measuring the stem dendritic diameter. (C) 1999 Wiley-Liss, Inc.