Biomedical subjects

Michelle L Monje

Publications and source records attributed to Michelle L Monje.

3 recordsLinked to original sources

PubMed2003

Extreme sensitivity of adult neurogenesis to low doses of X-irradiation.

Therapeutic irradiation of the brain is associated with a number of adverse effects, including cognitive impairment. Although the pathogenesis of radiation-induced cognitive injury is unknown, it may involve loss of neural precursor cells from the subgranular zone (SGZ) of the hippocampal dentate gyrus and alterations in new cell production (neurogenesis). Young adult male C57BL mice received whole brain irradiation, and 6-48 h later, hippocampal tissue was assessed using immunohistochemistry for detection of apoptosis and numbers of proliferating cells and immature neurons. Apoptosis peaked 12 h after irradiation, and its extent was dose dependent. Forty-eight h after irradiation, proliferating SGZ cells were reduced by 93-96%; immature neurons were decreased from 40 to 60% in a dose-dependent fashion. To determine whether acute cell sensitivity translated into long-term changes, we quantified neurogenesis 2 months after irradiation with 0, 2, 5, or 10 Gy. Multiple injections of BrdUrd were given to label proliferating cells, and 3 weeks later, confocal microscopy was used to determine the percentage of BrdUrd-labeled cells that showed mature cell phenotypes. The production of new neurons was significantly reduced by X-rays; that change was dose dependent. In contrast, there were no apparent effects on the production of new astrocytes or oligodendrocytes. Measures of activated microglia indicated that changes in neurogenesis were associated with a significant inflammatory response. Given the known effects of radiation on cognitive function and the relationship between hippocampal neurogenesis and associated memory formation, our data suggest that precursor cell radiation response and altered neurogenesis may play a contributory if not causative role in radiation-induced cognitive impairment.

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PubMed2003

Radiation injury and neurogenesis.

PURPOSE OF REVIEW: For many cancers, survival depends on aggressive combined therapies, but treatment comes at a price. Children and adults who receive radiotherapy involving the brain frequently experience a progressive cognitive decline. The overt pathologies of radiation injury such as white matter necrosis or vasculopathy are the obvious "smoking guns" of dysfunction. However, many patients exhibit severe learning and memory deficits with no overt pathologic changes. This is especially true when the radiation field involves the temporal lobes. The cause of this debilitating dysfunction is currently unknown and untreatable. RECENT FINDINGS: Within the temporal lobe, the hippocampal formation plays a central role in short-term learning and memory--the functions most notably affected by radiation. Recent work has also shown that hippocampus-dependent learning and memory are strongly influenced by the activity of neural stem cells and their proliferative progeny. The hippocampal granule cell layer undergoes continuous renewal and restructuring by the addition of new neurons. Radiation at much lower doses than that needed to injure the more resistant post-mitotic neurons and glia of the brain has been found to affect these highly proliferative progenitors severely. The stem/progenitor cell is so sensitive to radiation that a single low dose to the cranium of a mature rat is sufficient to ablate hippocampal neurogenesis. SUMMARY: Progressive learning and memory deficits following irradiation may be caused by the accumulating hippocampal dysfunction that results from a long-term absence of normal stem/progenitor activity. Here, the authors describe the nature of this stem cell dysfunction and contemplate how restoration of stem/progenitor cell activity might be approached in experimental models and, eventually, the clinic.

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PubMed2002

Irradiation induces neural precursor-cell dysfunction.

In both pediatric and adult patients, cranial radiation therapy causes a debilitating cognitive decline that is poorly understood and currently untreatable. This decline is characterized by hippocampal dysfunction, and seems to involve a radiation-induced decrease in postnatal hippocampal neurogenesis. Here we show that the deficit in neurogenesis reflects alterations in the microenvironment that regulates progenitor-cell fate, as well as a defect in the proliferative capacity of the neural progenitor-cell population. Not only is hippocampal neurogenesis ablated, but the remaining neural precursors adopt glial fates and transplants of non-irradiated neural precursor cells fail to differentiate into neurons in the irradiated hippocampus. The inhibition of neurogenesis is accompanied by marked alterations in the neurogenic microenvironment, including disruption of the microvascular angiogenesis associated with adult neurogenesis and a marked increase in the number and activation status of microglia within the neurogenic zone. These findings provide clear targets for future therapeutic interventions.

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