RT Journal Article
SR Electronic
T1 Loss of Presynaptic and Postsynaptic Structures Is Accompanied by Compensatory Increase in Action Potential-Dependent Synaptic Input to Layer V Neocortical Pyramidal Neurons in Aged Rats
JF The Journal of Neuroscience
JO J. Neurosci.
FD Society for Neuroscience
SP 8596
OP 8606
DO 10.1523/JNEUROSCI.20-22-08596.2000
VO 20
IS 22
A1 Tak Pan Wong
A1 Giorgio Marchese
A1 Maria Antonietta Casu
A1 Alfredo Ribeiro-da-Silva
A1 A. Claudio Cuello
A1 Yves De Koninck
YR 2000
UL http://www.jneurosci.org/content/20/22/8596.abstract
AB Reduction in both presynaptic and postsynaptic structures in the aging neocortex may significantly affect functional synaptic properties in this area. To directly address this issue, we combined whole-cell patch-clamp recording of spontaneously occurring postsynaptic currents (PSCs) with morphological analysis of layer V pyramidal neurons in the parietal cortex of young adult (1- to 2-month-old) and aged (28- to 37-month-old) BNxF344 F1 hybrid rats. Analysis of spontaneous PSCs was used to contrast functional properties of basal synaptic input with structural alterations in the dendritic tree of pyramidal neurons and density of terminals in contact with these cells.We observed significant changes in a number of morphological parameters of pyramidal neurons in aged rats. These include smaller cell body size and fewer basal dendritic branches (but not of oblique dendrites and dendritic tufts) and spines. Ultrastructural analysis also revealed a lower density of presynaptic terminals per unit length of postsynaptic membrane of labeled pyramidal neurons in the aged brain. This reduction in both presynaptic and postsynaptic elements was paralleled by a significant decrease in frequency of tetrodotoxin-insensitive miniature (action potential-independent) PSCs (mPSCs). The frequency of excitatory and inhibitory mPSCs was reduced to the same extent. In contrast, no significant change was observed in the frequency of spontaneous PSCs recorded in absence of tetrodotoxin (sPSCs), indicating an increase in action potential-dependent (frequencysPSCs − frequencymPSCs) input to pyramidal neurons in the aged group. This functional compensation may explain the lack of drastic loss of spontaneous neuronal activity in normal aging.