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Neonatal Brain Injury and Calcium Homeostasis

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title
Neonatal Brain Injury and Calcium Homeostasis
author
Lema Tomé, Carla Maria
abstract
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.
subject
calcium binding proteins
calcium homeostasis
development
MK801
neonatal brain injury
NMDA
rat
contributor
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)
creator
Lema Tomé, Carla Maria
date
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)
degree
null (defenseDate)
Neurobiology & Anatomy (discipline)
Wake Forest University (grantor)
PHD/MBA (level)
identifier
lematomecm_08_08.pdf
http://hdl.handle.net/10339/14921 (uri)
migration
etd-09052008-162118 (oldETDId)
rights
Release the entire work for access only to the Wake Forest University system for one year from the date of approval. After one year, release the entire work for access worldwide, unless I send notification to delay release. (accessRights)
I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to Wake Forest University or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. (license)

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