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KLLB94c
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Literature
38 records
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maturation of axon targeting, dendritic morphology, and electrophysiological
properties.
pyramidal neurons in layer 5 of the rat visual cortex in relation to the
targets chosen by their axons. Cells were prelabeled by retrograde transport
from the superior colliculus or the contralateral visual cortex and
intracellularly injected either in fixed slices or after recording in living
slices. In the adult, corticotectal cells have thick apical dendrites with an
extensive terminal arborization extending into layer 1, and fire
characteristic bursts of action potentials when injected with a depolarizing
current; interhemispheric cells have slender apical dendrites that terminate
without a terminal tuft, usually in layer 2/3, and they display a more regular
firing pattern (Kasper et al.: J Comp Neurol, this issue, 339:459-474). At
embryonic day E18 (when axons of the two classes of cells are already taking
different routes towards their targets) and E21, pyramidal-like cells
throughout the cortical plate all have similar soma-dendritic morphology, with
spindle-shaped cell bodies and few, short basal dendrites but apical dendrites
that all end in distinct tufts in the marginal zone. At postnatal day P3,
after the axons of both cell classes have reached their targets, all pyramidal
neurons in layer 5 still have distinct terminal arborizations in layer 1,
though they vary in complexity and extent. The somata are now more mature
(round to ovoid in shape), and the basal dendritic tree has extended. As early
as P5, all cells studied could be clearly classified as tufted or untufted
(considerably earlier than previously reported; Koester and O'Leary: J
Neurosci 12:1382, '92), and these features correlated precisely with the
projection target, as in the adult. Measurement showed that although
interhemispheric cells lose their terminal tufts, in general the trunks of
their apical dendrites do not withdraw but continue to grow, at roughly the
same rate as those of corticotectal cells. The two classes of layer 5
pyramidal neurons differentiate from each other in three distinct phases:
pathway selection by axons precedes the loss of the apical tuft by
interhemispheric cells, and these morphological characteristics are
established 10 days before the onset of burst-firing in corticotectal cells.
These three steps may be guided by different molecular signals.
REF:Larkman & Mason (J Neurosci. 1990 May;10(5), 2 papers) or Larkman (J Comp
Neurol. 1991 Apr 8;306(2)) 3 papers.
