There is a fundamental gap in understanding how changes in frontal lobe function that emerge in middle age contribute to aging-related deficits in cognitive flexibility. Continued existence of this gap represents an important problem because, until it is filled, understanding how functional and structural changes that occur during normal aging contribute to deficits in cognitive decline will remain unclear. The long-term goal is to determine how neurobiological changes in the frontal lobe contribute to cognitive decline during normal aging. The objective of this proposal is to investigate aging-related neuronal changes in discrete sub-regions of medial prefrontal cortex (mPFC) to better understand how they impact cognitive decline during normal aging. Extinction of trace fear conditioning is an excellent model for these studies because middle-aged and aged rats exhibit pronounced deficits that parallel distinct aging-related changes within the infra-limbic (IL) and pre-limbic (PL) sub-regions of mPFC. The central hypothesis is that aging-related extinction deficits correlate with differential expression of activity and plasticity markers in IL and PL, and that region-specific modulation of plasticity mechanisms will alleviate these extinction deficits. This hypothesis has been formulated based on preliminary data produced in the applicant's laboratory. The rationale for the proposed research is that knowledge of the underlying plasticity deficits that accompany aging-related extinction impairments will provide critical data necessary for determining the underlying mechanisms of aging-related frontal lobe dysfunction and the development of targeted strategies to improve cognitive function in the elderly. Guided by strong preliminary data, this hypothesis will be tested by pursuing two specific aims: 1) Identify plasticity mechanisms underlying aging- related extinction deficits;and 2) Identify a candidate mechanism that ameliorates aging-related extinction deficits. Under the first aim, proven western blot and patch-clamp recording approaches, which have been established as feasible in the applicants'hands, will be used to study changes in immediate-early gene expression and intrinsic excitability in mPFC of behaviorally characterized adult, middle-aged, and aged rats. Under the second aim, a proven mPFC cannulation approach, established as feasible in the applicant's hands, will be used to specifically increase the excitability of IL neurons, and thus explore candidate mechanisms for aging- related extinction deficits. The approach is innovative because it combines aging-related deficits in extinction learning with immediate-early gene and intrinsic excitability measurements to investigate early, aging-related changes in mPFC function. The proposed research is significant because it is expected to vertically advance and expand understanding of how aging-related changes in activity-dependent gene expression can interact with intrinsic neuronal excitability to produce measurable deficits in extinction learning that emerge in middle age. Ultimately, such knowledge has the potential to inform the development of neurobiologically-based strategies for treating aging-related frontal lobe dysfunction and improving quality of life for the elderly.

Public Health Relevance

The proposed research is relevant to public health because the discovery of underlying causes for aging-related frontal lobe dysfunction is ultimately expected to increase understanding of how the early emergence of mPFC dysfunction relates to an aging-related development of cognitive flexibility deficits. Thus, the proposed research is relevant to the part of NIH's mission that pertains to developing and advancing fundamental knowledge in the field of aging that will help to alleviate aging-related cognitive decline.

National Institute of Health (NIH)
National Institute on Aging (NIA)
Small Research Grants (R03)
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Aging Systems and Geriatrics Study Section (ASG)
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Wagster, Molly V
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University of Wisconsin Milwaukee
Schools of Arts and Sciences
United States
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Song, Chenghui; Ehlers, Vanessa L; Moyer Jr, James R (2015) Trace Fear Conditioning Differentially Modulates Intrinsic Excitability of Medial Prefrontal Cortex-Basolateral Complex of Amygdala Projection Neurons in Infralimbic and Prelimbic Cortices. J Neurosci 35:13511-24
Sehgal, Megha; Ehlers, Vanessa L; Moyer Jr, James R (2014) Learning enhances intrinsic excitability in a subset of lateral amygdala neurons. Learn Mem 21:161-70
Sehgal, Megha; Song, Chenghui; Ehlers, Vanessa L et al. (2013) Learning to learn - intrinsic plasticity as a metaplasticity mechanism for memory formation. Neurobiol Learn Mem 105:186-99