Journals of Gerontology Series A: Biological Sciences and Medical Sciences, Vol 51, Issue 1 B17-B20, Copyright © 1996 by The Gerontological Society of America
Prior instrumental conditioning improves spatial cognition and attenuates changes in hippocampal function in aged rats
RL Port, HA Murphy, RA Magee and KS Seybold
Department of Psychology, Slippery Rock University, Pennsylvania, USA.
These experiments examined the effects of long-term instrumental training
on subsequent radial arm maze performance and synaptic transmission within
the hippocampal formation. In the first experiment, young (3 mo) and aged
(18 mo) male rats underwent 12 weeks of appetitive instrumental
conditioning; half were continually reinforced and the other half
alternated between reinforcement and extinction. Afterward, spatial
cognition was evaluated using an eight-arm radial maze. Subjects undergoing
instrumental training performed at rates superior to untrained (control)
animals regardless of age or training condition; age-related differences
did not exist in the trained groups. In the second experiment, subjects
underwent 12 weeks of instrumental training with continuous reinforcement,
and excitability of the hippocampus was examined by paired-impulse
stimulation of the perforant path. Training enhanced maximal facilitation
of population spikes evoked in the granule cell layer of the dentate gyrus
of aged subjects to the degree that no statistical difference existed
between young and aged animals. Data from untrained control animals
indicated a robust decline in paired-impulse excitability in aged subjects.
These findings suggest that learning-induced plasticity may attenuate both
behavioral and neurobiological changes observed in aged subjects. It is
postulated that disuse may underlie some of the cognitive changes exhibited
across the life span.
