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Memory impaired aged rats: no loss of principal hippocampal and subicular neurons
T Rasmussen1, T Schliemann, J C Sørensen
1PharmaBiotec, Department of Anatomy and Cell Biology, University of Odense, Denmark.
Abstract:
A group of 52 male, 2-year-old Ico:WIST rats were tested on the spatial reference memory version of the Morris water maze. Their performance was rated by comparisons with the performance of 2.5-month-old control rats. Unbiased stereological estimates were made of the number of neurons in the major subdivisions of the hippocampus proper and the subiculum of the 5 aged rats with the most impaired performance, the 5 aged rats with the best performance, and 5 young control rats. There were no significant differences between the mean numbers of neurons in the various subdivisions of the hippocampal region of the impaired and nonimpaired aged groups and similarly no decreases in neuron numbers in the pooled group of aged rats relative to the control rats. The results indicate that, in rats, the structural correlates of age-related deficits in spatial memory are to be found in parameters other than the number of neurons in the hippocampus proper and the subiculum.
Insights
Aging rats show spatial memory decline, but neuron counts in the hippocampus and subiculum remain unchanged. This suggests other factors, not neuron loss, cause age-related memory impairments in rats.
Area of Science:
- Neuroscience
- Gerontology
- Cognitive Psychology
Background:
- Age-related cognitive decline is a significant concern.
- Spatial memory deficits are common in aging populations.
- The hippocampus and subiculum are critical for spatial memory.
Purpose of the Study:
- To investigate the relationship between aging, spatial memory performance, and neuronal numbers in specific brain regions.
- To determine if age-related spatial memory impairment in rats is associated with a loss of neurons in the hippocampus and subiculum.
Main Methods:
- Utilized the Morris water maze to assess spatial reference memory in aged (2-year-old) and young (2.5-month-old) male Ico:WIST rats.
- Employed unbiased stereology to quantify neuron numbers in hippocampal and subicular subdivisions.
- Compared neuronal counts between aged rats with impaired and unimpaired spatial memory, and young controls.
Main Results:
- No significant differences in mean neuron numbers were found in hippocampal or subicular subdivisions between aged impaired, aged unimpaired, and young control rats.
- Pooled analysis of aged rats also showed no decrease in neuron numbers compared to young controls.
Conclusions:
- Neuronal number in the hippocampus proper and subiculum is not the structural correlate of age-related spatial memory deficits in rats.
- The findings suggest that other neural parameters or brain regions are responsible for age-related spatial memory decline.