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FSPRA98
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Literature
38 records
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characteristics in layer V pyramidal neurons of the sensorimotor cortex.
neurons of rat sensorimotor cortex, injected with biocytin for morphological
reconstruction, was analysed by means of intracellular recordings made between
postnatal day (P)3 and 22. Starting from the onset of the second postnatal
week, the pyramidal neurons could be differentiated as adapting or
non-adapting regular spiking on the basis of the presence or absence of spike
frequency adaptation. The percentage of non-adapting regular spiking neurons
was very high during the second postnatal week (53%) and progressively
decreased with age, concurrently with the appearance of the new class of
intrinsically bursting neurons (beginning of the third week) whose percentage
progressively increased from 23%, found in P14-P16 rats, to 46% in adult rats.
Non-adapting regular spiking neurons were found to share with intrinsically
bursting neurons several physiological characteristics comprehending faster
action potentials, more prominent effect of anomalous rectification and
consistent depolarizing afterpotentials, that differentiated them from the
adapting regular spiking neurons. Moreover, intrinsically bursting and
non-adapting regular spiking neurons were characterized by a round-shaped
distribution of basal dendrites and expanded apical dendritic arborization,
that differentiated them from the adapting regular spiking neurons showing a
simpler dendritic arborization. These morphological hallmarks were seen in
immature intrinsically bursting neurons as soon as they became
distinguishable, and in immature non-adapting regular spiking neurons starting
from the onset of the second postnatal week. These findings suggest that a
significant subpopulation of immature non-adapting regular spiking neurons are
committed to becoming bursters, and that they are converted into intrinsically
bursting neurons during the second postnatal week, as soon as the ionic
current sustaining the burst firing is sufficiently strong. The faster action
potentials in both immature non-adapting regular spiking and intrinsically
bursting neurons suggest a higher density of Na+ channels in these neuronal
classes: the maturational increase in Na+-current, namely of its persistent
fraction, may represent the critical event for the conversion of the
non-adapting regular spiking neurons into the intrinsically bursting ones.
