Age-related decline of presumptive inhibitory synapses in the sensorimotor cortex as revealed by the physical disector.
The synapse, as the site of functional neural interaction, has been suggested as a possible substrate for age-related impairment of cognitive ability. Using the physical disector probe with tissue prepared for ultrastructural analysis, we find an age-related decline in the numerical density of presumptive inhibitory synapses in layer 2 of the sensorimotor cortex of the Brown Norway x Fisher 344 rat. This age-related decline in presumptive inhibitory synapses is maintained when the density of synapses is combined with the numerical density of neurons quantified from the same anatomical space to arrive at a ratio of synapses per neuron. The numerical density of these synapses declines between middle-aged (18 months) and old (29 months) animals by 36% whereas numerical density of neurons does not change between these ages, resulting in a decline in the ratio of presumptive inhibitory synapses per neuron in this cortical area. This study demonstrates a deficit in the intrinsic inhibitory circuitry of the aging neocortex, which suggests an anatomical substrate for age-related cognitive impairment.
Poe
B H
BH
Neuroscience Program, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27157-1010, USA. bpoe@Raven.Brand.com
Linville
C
C
Brunso-Bechtold
J
J
D000375:Aging / Q000502:physiology*; D000818:Animals; D002452:Cell Count; D008297:Male; D009433:Neural Inhibition / Q000502:physiology*; D009474:Neurons / Q000166:cytology; D051381:Rats; D013003:Somatosensory Cortex / Q000502:physiology* / Q000648:ultrastructure; D013569:Synapses / Q000502:physiology* / Q000648:ultrastructure