Blood cells themselves are, however, a significant source of endocannabi noids and this, together with the CB1-receptor expression measured on these cells indicates differences in stress-induced activation of the ECS in blood cells between individuals with and without motion sickness. An activation of the peripheral ECS by physical and emotional stress has recently been demonstrated. Within this context it is of interest to note that volunteers who later developed motion Schizandrin-A sickness had, albeit not significantly, lower endocannabinoid blood levels in-flight Magnoflorine during the pre-parabola phase of the experiment when kinetic stimulation was low but stress exposure may have been already high. This suggests differences in the endocannabinoid response to stress between individuals prone to develop motion sickness and those who are not. The observation that lower endocannabinoid levels in participants with motion sickness were accompanied by a lower expression of CB1-receptors may appear counterintuitive but could point to a failure of upregulation in endocannabinoid signaling during stress exposure. There is also preliminary evidence that alterations of the ECS in blood cells mirrors dysfunctions of central endocannabinoid signaling and that peripheral blood may serve as a reservoir of anandamide for the brain. Thus, lower peripheral endocannabinoid activity in individuals with motion sickness may indicate central ECS dysfunction which could help to explain many central symptoms of motion sickness including N&V. Another interesting observation from our study is that anandamide and 2-AG seem to play different roles in the adaptation to parabolic flight stress and motion sickness. Changes in anandamide blood levels are seen earlier and seem more associated with nausea and the stress reaction during the parabolic maneuvers, whereas changes in 2-AG blood levels appear later and seem more closely related to stress recovery immediately after the parabolas. 2-AG is known to be more selective for CB1 receptors which play an important role in stress recovery reactions.