The aging hippocampus: Neural mechanisms underlying learning and memory deficits in old rats
AuthorShen, Jiemin, 1968-
AdvisorBarnes, Carol A.
MetadataShow full item record
PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractThis dissertation focuses on the effect of aging on two functional aspects of rat hippocampus: cholinergic synaptic transmission and place specific firing of CA1 pyramidal cells. The effect of age on the cholinergic slow EPSP was studied in hippocampal slices of young, adult and old rats. The old rats were impaired on the spatial version of the Morris water task. The amplitude of the slow EPSP was significantly reduced in old rats in all hippocampal subregions (CA1 59%; CA3 55%; and DG 56%). Few statistically significant correlations, however, were found between the age-related deficit in spatial learning and the cholinergic deficit. In the subsequent study, effects of selective neurotoxic lesions of cholinergic afferents to the hippocampus on performance on two versions (spatial working memory and spatial reference memory) of the radial-8-arm maze task were examined. The lesioned rats were impaired in acquisition, but not retention, of the working memory task. There was no treatment effect, however, on acquisition of the reference memory task. The results suggest that the age-related deficits in hippocampal cholinergic function may contribute to behavioral deficits of old rats in working memory situations, but may not be primarily responsible for the spatial reference memory problem in the Morris water task. The spatial and temporal firing characteristics of CA1 neurons were studied in young and old rats performing a simple spatial task on a rectangular track. The average place fields of young rats were larger than those of old rats. Precession of spike discharge relative to the theta rhythm proceeded faster in old rats, while the total phase change remained constant. These age-related changes were apparently due to a loss of experience dependent place field expansion of old rats during the first few laps around the track for a given recording session. The field sizes were not different between groups on lap 1. Because experience-dependent place field expansion is a prediction of two recent theories which invoke asymmetric Hebbian LTP, the present observations point towards a substantial deficit in an LTP-like process in old rats.
Degree ProgramGraduate College