Summary
The endocannabinoid anandamide (AEA) has many neurovascular activities. However, it
is not yet clear how AEA can be metabolized at the neurovascular interface, and how
it can move through the vascular and the cerebral compartments. The results reported
in this article show that isolated bovine brain microvessels, an ex vivo model of the blood-brain barrier, have detectable levels of endogenous AEA and possess
the biochemical machinery to bind and metabolize it, i. e. type-1 and type-2 cannabinoid
receptors (CB1R and CB2R), a selective AEA membrane transporter (AMT), an AEA-degrading
fatty acid amide hydrolase, and the AEA-synthesizing enzymes N-acyltransferase and N-acyl-phosphatidylethanolamines-specific phospholipase D. We also show that activation
of CB1R enhances AMT activity through increased nitric oxide synthase (NOS) activity
and subsequent increase of NO production. AMT activity is instead reduced by activation
of CB2R, which inhibits NOS and NO release. In addition, binding experiments and immunoelectronmicroscopy
demonstrate that different endothelial cells vary in the expression of CB1R and CB2R
on the luminal and/or abluminal sides. The different localization of CBRs can lead
to a diverse effect on AMT activity on the luminal and abluminal membranes, suggesting
that the distribution of these receptors may drive AEA directional transport through
the blood-brain barrier and other endothelial cells.
Keywords
Brain - directional uptake - endocannabinoids - endothelial cells - nitric oxide -
receptors - transporters