2013 |
Griffin, Amy L. |
P20Activity Code Description: To support planning for new programs, expansion or modification of existing resources, and feasibility studies to explore various approaches to the development of interdisciplinary programs that offer potential solutions to problems of special significance to the mission of the NIH. These exploratory studies may lead to specialized or comprehensive centers. |
Udel Subproject 2 @ Delaware State University
The external cues that guide the migration of developing neurons and outgrowth of neurons upon differentiation have been intensely studied for decades. CXCR4, a chemokine receptor, has been implicated in the regulation of chemotaxis, neuronal migration, and axonal guidance. Neuroblastoma cells, which are of neural crest origin, are capable of differentiating into more mature sympathetic neurons in culture, and insulin-like growth factor I (IGF-1), has been shown to promote both migration and neurite outgrowth in these cells. In addition, neuroblastoma cells often express high levels of CXCR4, are responsive to CXCLI 2 and, depending upon the level of differentiation, are capable of producing fully extended axons. The mediator of the cytoskeletal changes seen in during process extension is actin polymerization. We have shown that in the neuroblastoma cell line, SHSY-5Y, both CXCR4 and IGF I receptors are involved in neuronal outgrowth, however, treatment with ligands for these receptors results in different cellular morphologies. CXCR4 stimulation stimulated the cells to take on a more differentiated neuronal form and directly involved actin, while IGF-IR stimulation resulted in a very immature neuronal morphology with shorter, broader processes. Based on these results, our overall hypothesis is that CXCR4 promotes neuronal migration and neurite extension through direct regulation of actin dynamics. Our preliminary data suggest that activation of CXCR4 by CXCL12 in cultured neuroblastoma cells promotes the elongation of neurites, and we have found CXCR4 along these projections. In this work we will be testing three specific hypotheses: 1) Cellular context, including the extracellular matrix present and the concentration of CXCL12 ligand to which the cells are exposed play a large role in determining the signaling pathways that are activated, and thereby the ability of the cells to migrate; 2) CXCR4 activation by CXCL12 promotes an increase in neurite length in neuroblastoma cells; 3) CXCR4 regulates elongation of neuronal processes through interaction with actin using the actin binding protein Dbn; We will use immunocytochemistry/confocal microscopy, neurite analysis, and immunoprecipitation with cultured neuroblastoma and sympathetic neurons to test these hypotheses. Posttranslational modification of CXCR4 will be analyzed using Mass Spectroscopy.
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0.92 |
2014 — 2018 |
Griffin, Amy L. |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Hippocampal-Prefrontal Synchrony in Working Memory
DESCRIPTION (provided by applicant): Despite decades of research, the neural mechanisms of working memory, the ability to hold information over a temporal delay to guide goal-directed behavior, remain poorly understood. Although oscillatory synchrony between the hippocampus (HC) and the prefrontal cortex (PFC) is known to increase in situations of high working memory demand, the mechanisms and circuitry supporting HC-PFC interactions during working memory is unknown. The midline thalamic nucleus reuniens (RE) is reciprocally connected to both the HC and the PFC and has been shown to be critical for working memory tasks. Therefore, the guiding hypothesis of the current proposal is that HC-PFC oscillatory synchrony is regulated by the RE. If this hypothesis is true, when working memory demand is high, RE should drive HC-PFC oscillatory synchrony, giving rise to relatively higher HC-PFC theta coherence and stronger PFC phase-locking to the hippocampal theta rhythm. Similarly, suppression of RE activity should yield reduced HC-PFC oscillatory synchrony and lead to working memory impairments. We have shown that hippocampal neurons exhibit different patterns of spatial coding in response to manipulation of working memory demand. New published data from our lab demonstrate that RE inactivation selectively impairs a working memory task, leaving a very similar, but non-working memory, task unchanged. Additional preliminary data show that HC-PFC oscillatory synchrony is also modulated by working memory demand. The proposed studies will use a combination of electrophysiological methods, bidirectional optogenetic manipulation of neuronal excitation, and behavior to address the following questions (1) Does RE inactivation reduce hippocampal-PFC synchrony and concomitantly impair working memory? (2) Does RE activation increase HC-PFC synchrony and concomitantly improve working memory? (3) Does RE show increased oscillatory synchrony with the HC and PFC during working memory task performance? If funded, the proposed work will have a significant impact on memory research and on the field of neuroscience by advancing the basic understanding of the circuit-level interactions between the HC, RE and PFC. More broadly, the proposal will advance the understanding of the neural mechanisms underlying working memory by uncovering the mechanisms underlying HC-PFC oscillatory synchrony. Moreover, by pioneering RE recordings during memory-guided behavior, we will not only characterize RE behavioral correlates for the first time, but also identify the role of the RE in regulating functinal interactions between the HC and the PFC. Finally, we will be the first to use optogenetic methods to manipulate the activity of the RE and measure the effects on memory-guided behavior as well as on HC-PFC synchrony. Although optogenetic methods are becoming more widely used, the studies proposed here will advance the use of this state-of-the-art technique as a tool for understanding circuits and mechanisms underlying higher cognitive functions.
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1 |
2019 — 2020 |
Griffin, Amy L. |
R21Activity Code Description: To encourage the development of new research activities in categorical program areas. (Support generally is restricted in level of support and in time.) |
Using Hippocampal-Prefrontal Theta Synchrony to Enhance Spatial Working Memory
PROJECT SUMMARY Efforts to improve cognitive function by harnessing endogenous brain rhythms have yielded promising results in both humans and experimental animals. However, this approach has not yet been extended to use interregional oscillatory synchrony for cognitive enhancement. Rodent neurophysiology studies have shown that oscillations within the theta band coordinate interactions between the hippocampus (HC) and the medial prefrontal cortex (mPFC) during the performance of spatial working memory (SWM) tasks. These tasks require the rat to use the memory of a previous traversal to guide an upcoming behavioral choice. Although recent work shows that disruptions of HC-mPFC theta synchrony result in SWM deficits, it is not yet known if HC- mPFC theta synchrony can be used to enhance SWM. Recently, new tools have been developed that not only allow real-time monitoring of neural synchrony, but also are capable of driving interregional synchrony with millisecond precision. Therefore, the goal of the current project is to facilitate SWM by first harnessing (Aim 1), then manipulating (Aim 2) HC-mPFC theta synchrony using a combination of in vivo recording and optogenetic techniques in freely moving rats during SWM task performance. The scientific premise of the proposed project is based on published work that shows a strong link between HC-mPFC synchrony and SWM. The overarching hypothesis is that SWM can be enhanced by ensuring that memory-guided decisions are accompanied by high HC-mPFC theta synchrony. For Aim 1, HC-mPFC theta coherence will be monitored in real time while rats perform a SWM-dependent delayed alternation (DA) task. A trial will be initiated when coherence exceeds or falls below values that have been shown previously to be associated with good or poor SWM performance. It is predicted that choice accuracy on the DA task will be highest for sessions in which trials were initiated based on high HC-mPFC theta coherence. This finding would be the first to demonstrate a working memory improvement simply by timing trials to coincide with strong HC-mPFC theta synchrony. For Aim 2, theta frequency optical stimulation using the excitatory opsin, channelrhodopsin (ChR2) will be delivered to mPFC triggered by real-time detection of HC theta. It is predicted that choice accuracy will be higher on stimulation trials compared to light-off trials. These results would demonstrate for the first time that SWM can be improved through direct induction of HC-mPFC theta synchrony. The success of this exploratory grant will direct future work by setting the stage for experiments that will (1) use HC-mPFC theta synchrony to rescue cognitive deficits in animal models of developmental insults and neuropsychiatric disorders, and (2) explore the specific mechanisms that drive synchrony within the extended HC-mPFC circuit.
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1 |