S. Matsutani et N. Yamamoto, Differentiation of mitral cell dendrites in the developing main olfactory bulbs of normal and naris-occluded rats, J COMP NEUR, 418(4), 2000, pp. 402-410
The morphological differentiation of mitral cell dendrites during embryonic
and early postnatal development was examined in the main olfactory bulb of
rats to determine a possible role of afferent activity in the development
of the dendrites. Mitral cells and olfactory nerve fibers were labeled with
1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) a
nd fluorescein-conjugated lectin (Ulex europeus agglutinin-I), respectively
. Morphogenesis of mitral cell dendrites proceeded as previously described
(Malun and Brunjes [1996] J. Comp. Neurol. 368:1-16); that is, undifferenti
ated dendrites with radial orientation were transformed into a single prima
ry dendrite having a glomerular tuft and secondary dendrites extending tang
entially into the external plexiform layer. Quantitative examinations in bo
th pre- and postnatal rats revealed that the differentiation of primary den
drites, including tuft formation, increases in diameter and decreases in br
anching, started before birth, whereas differentiated secondary dendrites w
ere only observed in postnatal animals. Mitral cells with more than two pri
mary dendrites were found after embryonic day 21. The proportion of the mit
ral cells with differentiated dendrites increased postnatally. At postnatal
day 10, almost all mitral cells had fully differentiated dendrites, and mi
tral cells with multiple primary dendrites were no longer seen. No signific
ant change was found during development in the number of stem dendrites tha
t arose directly from the cell body. Unilateral naris occlusion started on
postnatal day 1 retarded differentiation of primary and secondary dendrites
, and increased the proportion of mitral cells with multiple primary dendri
tes. These finding revealed that differentiation of mitral cell primary den
drites precedes that of secondary dendrites, and suggested that the differe
ntiation of secondary dendrites proceeds in an activity-dependent manner. (
C) 2000 Wiley-Liss, Inc.