Table of Contents
Normal Aging of Synapses
Question of Decline in Cognitive Function with Aging
Modern Methods to count Neurons
E.g. Sample every 10th section
Subsample (a) within the x,y areas
Only count cells that just come into focus within height h (depth of focus)
Total N =
Proper counts reveal no neuronal loss in any hippocampal subfield whether or not memory was impaired on the Morris water maze in aged rats.
Similarly no cell loss - CA3/CA2, or CA1
No correlation between cell number and behavioral score
Neuronal cell loss
Main Effects during Aging Across Brain Regions
Compensatory Effects! Of Synapse Loss during Normal Aging
Compare Young and Aged Rats
Rat Parietal (association) Cortex
Biocytin Filled Layer V pyramidal Cells from rat Parietal Cortex
Reconstructions from Biocytin Filled Layer V Pyramidal Cells
Layer V Pyramidal Cell bodies are Smaller in Aged Rats
Basal dendrites decrease in number and total length
Loss primarily of higher order Basal Dendritic Branches
Sholl analysis also reveals less branching of basal dendrites in aged rats.
Apical tuft has more branches in Aged Rats
Dendritic lengths are unchanged in apical dendritic compartments (slightly increased?)
Dendritic Spines on all types of dendrites in the young and aged rats
Fewer Dendritic Spines on all types of Layer V Pyramidal Cell dendrites in Aged Rats
Decrease in number of presynaptic Boutons on remaining CB and Basal Dendrites => further decline in number of inputs
Recording from Layer V Cells to determine whether this dramatic loss in synaptic connectivity results in a functional loss of synaptic input to the neurons
Spontaneous Action Potential Dependent Excitatory Synaptic Currents
Spontaneous AP dependent Inhibitory Synaptic Currents
No change in Frequency of Spontaneous EPSCs in Aged Rats
No change in frequency of spontaneous IPSCs in aged rats
Kinetic properties of sEPSCs
Similarly, little or no change in kinetic parameters of the inhibitory action potential dependent spontaneous events
Recording only miniature postsynaptic currents
Decrease in mEPSCs in Aged Rats consistent with Spine loss
“Matching” decrease in mIPSCs in Aged Rats consistent with smaller CBs
No change in kinetics of mEPSCs or mIPSCs show not due to dendrite filtering from different locations.
Summary
Conclusion
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