Regionally selective decline in hippocampal somatostatin-immunoreactive neuron number in aged rhesus monkeys with memory impairment

Monday, September 22, 2014 — Poster Session I
12:00 p.m. – 2:00 p.m.	FAES Academic Center	NIA	NEURO-28

Authors

• A.M. Spiegel
• E.J. Perez
• J.M. Long
• P. Park
• P.R. Rapp

Abstract

Evidence indicates that the integrity of hilar somatostain-expressing interneurons is compromised in aged rats with memory deficits (Spiegel et al., 2013). The decline in hilar interneuron integrity may represent a marker of hippocampal circuitry change related to cognitive decline in older individuals. To better understand how interneuron integrity contributes to cognitive impairment in normal aging, we determined the total number of somatostatin-immunoreactive neurons in the hippocampus of young and aged monkeys behaviorally characterized for medial temporal lobe memory function. Aged monkeys were classified as memory-impaired or unimpaired relative to young adults based on their delayed nonmatching-to-sample task scores. Total neuron numbers were estimated using design-based stereological quantification. Independent of age and cognitive status, the total number of somatostatin-immunoreactive neurons averaged 194,488. Group-wise comparisons revealed a significant decrease in somatostatin-positive neuron number in the CA1 hippocampal subregion in aged monkeys with memory deficits compared to both young adults and aged animals with preserved memory function. The number of somatostatin-expressing neurons was unchanged across all other hippocampal subregions in relation to age and cognitive status. Together these data highlight an age-related vulnerability among somatostatin interneurons that is circuit specific in the primate hippocampus and linked to individual differences in cognitive outcome.

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