Decline in reactive fiber growth in the dentate gyrus of aged rats compared to young adult rats following entorhinal cortex removal.
The reaction of septal and commissural-associational afferents in the dentate gyrus was examined at various times following a unilateral entorhinal lesion in 2- and 3-month-old, 12- to 18-month-old and 25--30-month-old rats. The response of septo-hippocampal fibers was examined histochemically by staining for acetylcholinesterase (AChE) activity; and that of commissural-associational fibers by the Holmes' fiber stain. In 2- and 3-month-old rats, AChE staining fibers, which project to the outer three-fourths of the molecular layer of the dentate gyrus, increased their staining intensity within 5--6 days following lesion of the entorhinal cortex. The rate of the response and the eventual magnitude declined progressively with the age of the subject. In 2- and 3-month-old rats, the commissural-associational fiber plexus appeared to expand partially into the entorhinal zone within 6 days following the lesion. This response also decreased progressively in rate and magnitude with age. Animals in the oldest age group showed at 12 days after the lesion a greater variability in the expansion of the commissural-associational fiber plexus than all younger groups. Astrocytes in the dentate molecular layer appeared to become more abundant and more hypertrophied in unoperated animals with age. The appearance of astrocytes in 25- to 30-month-old rats was similar to that seen in 2- and 3-month-old animals following an entorhinal lesion. An entorhinal lesion in the aged animals did not appear to cause a marked change in the appearance of astrocytes.
D000375:Aging; D000818:Animals; D001253:Astrocytes / Q000648:ultrastructure; D003714:Denervation; D004292:Dominance, Cerebral / Q000502:physiology; D006624:Hippocampus / Q000033:anatomy & histology*; D008032:Limbic System / Q000033:anatomy & histology*; D008297:Male; D009412:Nerve Fibers / Q000648:ultrastructure*; D009416:Nerve Regeneration; D009434:Neural Pathways / Q000033:anatomy & histology; D009474:Neurons / Q000648:ultrastructure; D051381:Rats; D012686:Septal Nuclei / Q000033:anatomy & histology