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Neonatal Brain Injury and Calcium Homeostasis

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During development, the neonatal brain undergoes a period of synaptogenesis known as the brain growth spurt period. During this time, developing neurons are susceptible to injury due to environmental factors, including agents commonly used in obstetric and pediatric medicine. Previous studies have shown that during this critical time period, agents that alter intracellular calcium homeostasis lead to pathological cell death, as explained by the “calcium set-point hypothesis”. Indeed, reductions in intracellular calcium ([Ca2+]i) using N-methyl-D-aspartate receptor (NMDAR) antagonists lead to widespread neuronal degeneration in the rat brain at postnatal day (P) 7 but not at P21. We investigated the role of calcium binding proteins (CaBPs), calbindin (CB), calretinin (CR) and parvalbumin (PV) in apoptotic cell death in the developing rat brain following blockade of the NMDAR ion channel pore. Single treatment with MK801 led to widespread activated caspase-3 mediated apoptotic cell death in cortical and subcortical regions in the P7 rat brain but not at P21. Caspase- 3 activation at P7 was found in cells that lacked CaBP expression. Moreover, the number of CaBP-expressing cells at the early age was found to be low, in particular that of PV-expressing cells, whereas CaBP expression was highly increased at P21. Thus, we concluded that an inverse relationship between activated caspase-3 and CaBP expression exists in the neonatal rat brain. We further characterized expression of CaBP across the developmental period in the rat brain. We investigated CB, CR and PV expression in several brain regions, including the cingulate (Cg2), retrosplenial (Rsgb), somatosensory (S1), and motor (M1/M2) cortex, from P0 to P21 and in adults. Expression of CB and in particular PV was found to increase significantly as development progressed, in contrast with CR expression which was variable. Thus, we concluded that CaBP expression may be critical in facilitating survival in the face of calcium deregulation, and that PV may have a decisive role. To further understand PV’s role in maintenance of calcium homeostasis, we used in vitro primary cortical neurons transfected with a PV expression vector. Cultures were exposed to agents that alter [Ca2+]i, including BAPTA-AM, Nimodipine and MK801. We found that PV-expressing cells maintained intracellular calcium levels when exposed to the different agents and that apoptotic cell death was reduced in transfected cultures in contrast to controls. Thus, PV may play a critical role in mediating neuronal survival by regulating [Ca2+]i so that it is maintained within a “set point”. Overall, these data illustrate the important role that CaBPs play during development. We show that CaBPs may confer protection when calcium deviates from the “set point” at which neuronal survival is supported. Our data indicate that new therapeutic avenues in which calcium homeostasis is maintained should be investigated to prevent pathological apoptosis in early development, which may be a factor affecting development of psychological and psychiatric illness later in life.
calcium binding proteins
calcium homeostasis
neonatal brain injury
Lema Tomé, Carla Maria (author)
cltome@wfubmc.edu (authorEmail)
Robert E Hampson (committee chair)
Christopher P Turner (committee member)
Qiang Gu (committee member)
Dwayne W Godwin (committee member)
Ronald W Oppenheim (committee member)
Lema Tomé, Carla Maria
2008-09-28T10:50:44Z (accessioned)
2010-06-18T19:00:05Z (accessioned)
null (available)
2008-09-28T10:50:44Z (available)
2010-06-18T19:00:05Z (available)
2008-08-01 (issued)
null (defenseDate)
Neurobiology & Anatomy (discipline)
Wake Forest University (grantor)
PHD/MBA (level)
http://hdl.handle.net/10339/14921 (uri)
etd-09052008-162118 (oldETDId)
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Neonatal Brain Injury and Calcium Homeostasis

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