Journal of Neuroscience, Vol 13, 2391-2404, Copyright © 1993 by Society for Neuroscience
Basal versus apical dendritic long-term potentiation of commissural afferents to hippocampal CA1: a current-source density study
T Kaibara and LS Leung
Department of Physiology, University of Western Ontario, London, Canada.
Current-source density analysis was used to estimate the magnitude of the
synaptic excitation at the basal and apical dendritic synapses of CA1
following commissural stimulation in the urethane-anesthetized rat, before
and after a theta-frequency patterned primed burst tetanus. Stimulation of
the contralateral CA3 or the contralateral CA1 stratum oriens excited both
the basal and apical dendrites in CA1 about equally. However, primed burst
tetanization of the contralateral CA3 or CA1 stratum oriens resulted in
significant long-term potentiation (LTP) only at the basal dendrites and
not at the apical dendrites. Stimulation of the contralateral CA1 stratum
radiatum excited the apical dendrites more than the basal dendrites of CA1,
but tetanization of this contralateral site gave little change in the
apical or basal dendritic excitation. Tetanization of the contralateral CA1
stratum radiatum after an intraventricular administration of bicuculline, a
GABAA antagonist, however, resulted in significant LTP at both the apical
and basal dendrites. It was concluded that, in the intact hippocampus in
vivo, the threshold for LTP at the commissural apical dendritic synapse was
high in comparison to that at the basal dendritic synapse and this high
threshold may be partly caused by inhibitory interneurons that
predominantly synapsed on the apical dendrites. Thus, the basal and apical
dendrites of the CA1 pyramidal cells are not equal in their propensity for
long-term plasticity.
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