As mentioned before, complex I and complex IV functions are impaired in aging and AD. Thus, the possible efficacy of piracetam to protect individual complexes of the mitochondrial respiratory chain after treatment with specific complex inhibitors was also investigated. Complexes I, II, and III were already protected at concentrations as low as 500 μM piracetam, while a significant protection of complexes IV and V was observed at a concentration of 1000 μM piracetam (Keil et al., 2006). This broad activity of piracetam is in line with the assumptions that improvement of complex activity might be due rather to its fluidity enhancing properties at mitochondrial membranes rather than by specific effects at the individual complexes. This is also supported by the data of Zhang et al. (2010) indicating enhanced activity of complexes I–IV in mice after induction of mitochondrial dysfunction with d-galactose. It is very important to note that the beneficial effects of piracetam have not only been seen at the level of MMP but also in using several other measures of mitochondrial function since MMP alterations are not always directly connected with changes of mitochondrial function (Cao et al., 2007; Kahlert et al., 2008).