title: Endocannabinoid modulation by FAAH and monoacylglycerol lipase within the analgesic circuitry of the periaqueductal grey.
abstract: OBJECTIVE
  Endogenous cannabinoids (endocannabinoids) in the periaqueductal grey (PAG) play a vital role in mediating stress-induced analgesia. This analgesic effect of endocannabinoids is enhanced by pharmacological inhibition of their degradative enzymes. However, the specific effects of endocannabinoids and the inhibitors of their degradation are largely unknown within this pain-modulating region.
  
  
  METHODS
  In vitro electrophysiological recordings were conducted from PAG neurons in rat midbrain slices. The effects of the major endocannabinoids and their degradation inhibitors on inhibitory GABAergic synaptic transmission were examined.
  
  
  RESULTS
  Exogenous application of the endocannabinoid, anandamide (AEA), but not 2-arachidonoylglycerol (2-AG), produced a reduction in inhibitory GABAergic transmission in PAG neurons. This AEA-induced suppression of inhibition was enhanced by the fatty acid amide hydrolase (FAAH) inhibitor, URB597, whereas a 2-AG-induced suppression of inhibition was unmasked by the monoacylglycerol lipase (MGL) inhibitor, JZL184. In addition, application of the CB1 receptor antagonist, AM251, facilitated the basal GABAergic transmission in the presence of URB597 and JZL184, which was further enhanced by the dual FAAH/MGL inhibitor, JZL195.
  
  
  CONCLUSIONS
  Our results indicate that AEA and 2-AG act via disinhibition within the PAG, a cellular action consistent with analgesia. These actions of AEA and 2-AG are tightly regulated by their respective degradative enzymes, FAAH and MGL. Furthermore, individual or combined inhibition of FAAH and/or MGL enhanced tonic disinhibition within the PAG. Therefore, the current findings support the therapeutic potential of FAAH and MGL inhibitors as a novel pharmacotherapy for pain.
authors.affiliation: Pain Management Research Institute, Kolling Institute of Medical Research, Northern Clinical School, The University of Sydney at Royal North Shore Hospital, St Leonards, NSW, Australia.
authors.forename: Benjamin K
authors.initials: BK
authors.lastname: Lau
authors.forename: Geoffrey M
authors.initials: GM
authors.lastname: Drew
authors.forename: Vanessa A
authors.initials: VA
authors.lastname: Mitchell
authors.forename: Christopher W
authors.initials: CW
authors.lastname: Vaughan
mesh_terms: D000581:Amidohydrolases / Q000037:antagonists & inhibitors / Q000502:physiology*; D000818:Animals; D001095:Arachidonic Acids / Q000502:physiology*; D001549:Benzamides / Q000494:pharmacology; D052117:Benzodioxoles / Q000494:pharmacology; D002219:Carbamates / Q000494:pharmacology; D063388:Endocannabinoids / Q000502:physiology*; D005260:Female; D005989:Glycerides / Q000502:physiology*; D066298:In Vitro Techniques; D053444:Inhibitory Postsynaptic Potentials; D008297:Male; D008994:Monoacylglycerol Lipases / Q000037:antagonists & inhibitors / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology; D010146:Pain / Q000188:drug therapy / Q000378:metabolism / Q000503:physiopathology; D010487:Periaqueductal Gray / Q000187:drug effects / Q000502:physiology*; D010880:Piperidines / Q000494:pharmacology; D053284:Polyunsaturated Alkamides; D017207:Rats, Sprague-Dawley; D043884:Receptor, Cannabinoid, CB1 / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects; D000099252:Fatty Acid Amide Hydrolases
chemical_list: D000581:Amidohydrolases; D001095:Arachidonic Acids; D001549:Benzamides; D052117:Benzodioxoles; D002219:Carbamates; D063388:Endocannabinoids; D005989:Glycerides; D008994:Monoacylglycerol Lipases; D010880:Piperidines; D053284:Polyunsaturated Alkamides; D043884:Receptor, Cannabinoid, CB1; D000099252:Fatty Acid Amide Hydrolases; C534333:JZL 184; C500528:cyclohexyl carbamic acid 3'-carbamoylbiphenyl-3-yl ester; C094503:glyceryl 2-arachidonate; C078814:anandamide