, 1998, Vanselow and Keller, 2000 and von INCB024360 ic50 Lewinski and Keller, 2005). In addition, motoneurons depend on neuromodulatory activity acting via the activation of low voltage-gated ion channels such as Cav1.3, further enhancing Ca loads in order to produce spiking activity. The absence of intracellular Ca buffers renders these neurons particularly dependent on mitochondria for regulating cytosolic Ca transients, which predisposes them for excitotoxic vulnerability upon mitochondrial impairments (Rothstein, 1995–1996, Verkhratsky, 2005, von Lewinski and Keller, 2005,

Browne et al., 2006, Spät et al., 2008, Teuling et al., 2007, Atkin et al., 2008 and Urushitani et al., 2008). Taken together, motoneurons affected in ALS are particularly prone to excitotoxicity, cellular damage due to Ca overload, and cell stress. Consistent with a role for these selective vulnerabilities in ALS, elevated persistent inward currents were detected early in corticospinal and in spinal motoneurons DNA Synthesis inhibitor in ALS models and in aging motoneurons, supporting the notion that these are involved in the disease process (Kuo et al., 2005). Mutant SOD1 specifically associates with motoneuron ER and

mitochondria and interferes with their function in ALS; accordingly, ER stress and mitochondrial pathology have been detected early in ALS model mice ( Kong and Xu, 1998, Liu et al., 2004, Pasinelli et al., 2004, Ferri et al., 2006 and Vande Velde et al., 2008). Furthermore, VAPB has a role in the ER stress response, and VAPB mutations associated with familial ALS predispose to ER stress ( Teuling et al., 2007 and Kanekura et al., 2009). Cell stress pathways may also account for how mutations in the RNA-binding proteins TDP-43, FUS and VCP lead to sporadic and familial ALS ( Sreedharan et al., 2008, Kwiatkowski et al., 2009, Gitcho et al., 2009 and Johnson et al., 2010). Thus, the three proteins interact functionally, and VCP is involved in ubiquitin-dependent protein degradation and cell stress. In sum, mutations

associated with familial ALS appear to enhance the sensitivity Parvulin of motoneurons to stressors, supporting the notion that cellular stress has an important role in the etiology of ALS. Interestingly, the most vulnerable, highly phasic, motoneurons exhibit lowest membrane excitability properties, thus rendering them particularly inefficient to produce spiking activity under a regime of reduced synaptic and/or mitochondrial function ( Siklós et al., 1998). This may account for compensatory hyperexcitability, which in a disease setting is particularly prominent in these motoneurons, setting them up for greater cytosolic Ca overloads upon recruitment, and thus enhanced vulnerability to stressors.