ASSOCIATION OF CALCIUM BUFFERING CAPACITY AND LOCAL INFLAMMATORY REACTIONS IN INJURY OF MOTOR NEURONS Ph.D. Thesis

Motor neurons that exhibit differences in vulnerability to degeneration have been identified in motor neuron disease and in its animal models. The oculomotor andhypoglossal neurons are regarded as the prototypes of the resistant and susceptible cell types, respectively.Because an increase in the level of intracellular calciumhas been proposed as a feature amplifying degenerative processes, we earlier studied the calcium increase inthese motor neurons after axotomy in Balb/c mice anddemonstrated a correlation between the susceptibility to degeneration and the intracellular calcium increase,with an inverse relation with the calcium bufferingcapacity, characterized by the parvalbumin or calbindin-D28k content. Because the differential susceptibility ofthe cells might also be attributed to their different cel-lular environments, in the present experiments, with theaim of verifying directly that a higher calcium bufferingcapacity is indeed responsible for the enhanced resistance, motor neurons were studied in their original milieu in mice with a genetically increased parvalbumin level. The changes in intracellular calcium level of thehypoglossal and oculomotor neurons after axotomywere studied electron microscopically at a 21-day interval after axotomy, during which time no significant cal-cium increase was detected in the hypoglossal motorneurons, the response being similar to that of the oculomotor neurons. The hypoglossal motor neurons of theparental mice, used as positive controls, exhibited atransient, significant elevation of calcium. These data provide more direct evidence of the protective role ofparvalbumin against the degeneration mediated by acalcium increase in the acute injury of motor neurons. J. Comp. Neurol. 518:1946–1961, 2010. VC 2009 Wiley-Liss, Inc. INDEXING TERMS: calcium; calcium buffering; parvalbumin; axotomy; neuroprotection Motor neuron disease (or amyotrophic lateral sclerosis[ALS]) is a fatal degenerative disorder of the nervous sys-tem that affects primarily the upper and lower motor neurons (Rowland and Shneider, 2001). Its etiology is basi-cally unknown, although several mechanisms have beenproposed, which probably contribute synergistically to the destruction of the motor neurons (Boillée et al., 2006;Bendotti and Carri, 2009; Rothstein, 2009). The sequenceof events during these pathologic processes is mostly known, and some aspects of their reciprocal contributionto the propagation of the injury cascade have been welldescribed (Mattson, 1998). Our research focuses on the role of the increase in the intracellular calcium level of the motor neurons during degeneration. We hypothesize that the inability of themotor neurons to cope successfully with a nonphysiologiccalcium load after or during injury may be one of the key events maintaining the complex destructive machinerythrough a positive feedback of the elementary steps, and an elevated calcium buffering capacity may attenuate the degree of the lesion during stress conditions (Appel et al.,2001; Siklós and Appel, 2005). Support for this hypothesis has emerged from clinical observations and experimental studies. Patients with ALS present an increased Grant sponsor: the Hungarian Scientific Research Fund; Grant number:OTKA-T 048718; Grant sponsor: the Hungarian National Office forResearch and Technology; Grant number: GVOP-3.2.1. 2004-04-0052/3.0;Grant number: TÁMOP-4.2.2/08/1/2008-0002. *CORRESPONDENCE TO: László Siklós, Ph.D., Laboratory of MolecularNeurobiology, Institute of Biophysics, Biological Research Center, P.O. Box521, H-6701 Szeged, Hungary. E-mail: [email protected] VC 2009 Wiley-Liss, Inc.Received July 3, 2009; Revised November 24, 2009; Accepted November24, 2009DOI 10.1002/cne.22312Published online December 17, 2009 in Wiley InterScience (www.interscience.wiley.com) 1946 The Journal of Comparative Neurology | Research in Systems Neuroscience 518:1946–1961 (2010)RESEARCH ARTICLE