“…Various studies reported increased sympathetic activity in depressed and anxious subjects compared with healthy controls, measured by different indices like spillover of norepinephrine (NE) and epinephrine (EPI), skin conductance responses, QT interval variability (QTvi), or the pre-ejection period (PEP) (Light et al, 1998;Esler et al, 1982;Guinjoan et al, 1995;Gold et al, 2005;Koschke et al, 2009;Barton et al, 2007). However, other studies reported no association between psychopathology and SNS activity or reported decreased SNS activity in subjects with depressive or anxiety disorders (Wilkinson et al, 1998;Esler et al, 2004;Roth et al, 2008;Ahrens et al, 2008), so findings remain inconclusive. A first major source of confounding in studies comparing SNS activity between depressed/anxious subjects and controls might be the different SNS indices used, with some measuring true NE release whereas others measure organ responsivity, which may also be influence by changes in clearance, re-uptake, or adrenoceptor sensitivity.…”