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Preserved number of entorhinal cortex layer II neurons in aged macaque monkeys
A H Gazzaley1, M M Thakker, P R Hof
1Neurobiology of Aging Laboratories, Fishberg Research Center for Neurobiology, Mount Sinai School of Medicine, New York, NY 10029, USA.
Abstract:
The perforant path, which consists of the projection from the layer II neurons of the entorhinal cortex to the outer molecular layer of the dentate gyrus, is a critical circuit involved in learning and memory formation. Accordingly, disturbances in this circuit may contribute to age-related cognitive deficits. In a previous study, we demonstrated a decrease in N-methyl-D-aspartate receptor subunit 1 immunofluorescence intensity in the outer molecular layer of aged macaque monkeys. In this study, we used the optical fractionator, a stereological method, to determine if a loss of layer II neurons occurred in the same animals in which the N-methyl-D-aspartate receptor subunit 1 alteration was observed. Our results revealed no significant differences in the number of layer II neurons between juvenile, young adult, and aged macaque monkeys. These results suggest that the circuit-specific decrease in N-methyl-D-aspartate receptor subunit 1 reported previously occurs in the absence of structural compromise of the perforant path, and thus may be linked to an age-related change in the physiological properties of this circuit.
Insights
Aging does not reduce the number of entorhinal cortex neurons in macaque monkeys. This suggests that changes in N-methyl-D-aspartate receptor 1 function, not neuron loss, underlie age-related memory deficits.
Area of Science:
- Neuroscience
- Aging Research
- Cognitive Function
Background:
- The perforant path is crucial for learning and memory.
- Age-related cognitive decline may involve disturbances in this circuit.
- Previous work showed reduced N-methyl-D-aspartate receptor subunit 1 in aged macaques.
Purpose of the Study:
- To investigate if age-related changes in the perforant path involve a loss of layer II entorhinal cortex neurons.
- To correlate neuronal counts with previously observed N-methyl-D-aspartate receptor subunit 1 alterations.
Main Methods:
- Stereological analysis using the optical fractionator.
- Quantification of layer II neurons in the entorhinal cortex of macaque monkeys across different age groups (juvenile, young adult, aged).
Main Results:
- No significant differences in the number of layer II neurons were found between age groups.
- The observed decrease in N-methyl-D-aspartate receptor subunit 1 in aged macaques was not associated with neuronal loss.
Conclusions:
- Structural integrity of the perforant path (in terms of neuron number) is maintained in aging macaques.
- Age-related alterations in N-methyl-D-aspartate receptor subunit 1 likely reflect changes in physiological properties rather than neuronal loss.