The cannabinoid receptors, CB1 and CB2, and endogenous ligands for these receptors, anandamide (AEA), 2-arachidonoyl glycerol (2-AG) and 2-arachidonoyl glyceryl ether (noladin), together form the ?endocannabinoid system?. AEA interacts not only with CB1 and CB2 receptors but also with vanilloid VR1 receptors on sensory neurons. We propose to use analogs obtained from Drs. Martin and Razdan to look for differences in the structure-activity relationships of AEA analogs at CB1 and VR1 receptors and for evidence of ?cross-talk? between CB1 and VR1 receptors. The possibility that AEA or other endocannabinoids act on neuronal receptor types other than CB1, CB2 and VR1 will also be investigated. Some of these experiments will build on pilot data that we have recently obtained with an analog of (-)-cannabidiol. These data point to the existence of an as yet uncharacterized SR141716A-sensitive non-CB1, non-CB2 receptor in the mouse vas deferens. It is also proposed to characterize the pharmacology of the endocannabinoids, 2-AG and noladin, more fully by investigating their pharmacological actions in vitro. We also intend to investigate the presence of tonic activity of the endocannabinoid system in the peripheral nervous system and to establish the extent to which this arises from tonic endocannabinoid release or from the presence of constitutively active CB1 receptors. This will involve the development and/or characterization of inhibitors of processes responsible for terminating the actions of added or endogenously released endocannabinoids: (a) tissue uptake and (b) intracellular enzymic hydrolysis by fatty acid amide hydrolase. Both these processes are potential targets for drugs that by inhibiting endocannabinoid uptake or metabolism could be used to explore the physiological and pathophysiological role(s) of the endocannabinoid system. Such drugs might also come to be exploited clinically. Experiments in this part of the project will also be performed with a silent CB1 receptor antagonist if such a compound becomes available (from the projects of Drs. Razdan and Martin). Whilst some of our experiments will be carried out with isolated tissue preparations containing functional neuronal cannabinoid or vanilloid receptors (or other ?anandamide receptors?), we shall conduct other experiments (a) with brain membranes or CB1, CB2 or VR1-transfected cells that will be used for binding or functional assays or (b) with cells that express an AEA membrane transporter. Many of these experiments will be carried out with novel compounds provided by other members of this group.