Neocortical synaptogenesis, aging, and behavior: lifespan development in the motor-sensory system of the rat

Exp Neurol. 1987 May;96(2):262-78. doi: 10.1016/0014-4886(87)90045-8.


Little evidence presently exists on the development and aging of synaptic contacts and their relationship to behavior, particularly in nonvisual brain areas. To investigate this interrelationship, rats at a series of developmental ages [postnatal day 1 (P1) to P90] were initially examined on a battery of motor tasks. The battery, ranging from simple reflexive tests to tests of complex locomotor capacities, consisted of tactile-induced forelimb placing, chin-induced placing, body righting, climbing an inclined plane, traversing a narrow beam, and keeping up with a revolving wheel. Following completion of the behavioral testing, the animals, together with an additional group of aged (28- to 29-month-old) rats, were killed and their motor-sensory cortex was removed, stained with osmium tetroxide or ethanol phosphotungstic acid (EPTA), and examined under electron microscopy for density of synaptic contacts. Simple motor abilities such as tactile-induced placing was present by the end of the first postnatal week, with locomotor performance reaching a mature level by the end of the third postnatal week, and intermediate task abilities maturing within this range. Paralleling the development of complex locomotor skills was a sharp increase in synaptic density in the molecular layer of the motor-sensory cortex, commencing in the second postnatal week and peaking at P30. After P30 there was a sharp decline in synaptic density as well as a decline in performance on some motor tasks, although these two functions seemed to be occurring independently. There was a continued, but less dramatic synaptic loss evident in the aged rats.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aging / physiology*
  • Animals
  • Behavior, Animal / physiology
  • Body Weight
  • Microscopy, Electron
  • Motor Activity / physiology*
  • Motor Cortex / physiology*
  • Motor Cortex / ultrastructure
  • Organ Size
  • Rats
  • Rats, Inbred Strains
  • Somatosensory Cortex / physiology*
  • Somatosensory Cortex / ultrastructure
  • Synapses / physiology*
  • Synapses / ultrastructure