sb-366791 and arachidonyl-2-chloroethylamide

The midbrain dorsal periaqueductal gray (dPAG) has an important role in orchestrating anxiety- and panic-related responses. Given the cellular and behavioral evidence suggesting opposite functions for cannabinoid type 1 receptor (CB₁) and transient receptor potential vanilloid type-1 channel (TRPV1), we hypothesized that they could differentially influence panic-like reactions induced by electrical stimulation of the dPAG. Drugs were injected locally and the expression of CB₁ and TRPV1 in this structure was assessed by immunofluorescence and confocal microscopy. The CB₁-selective agonist, ACEA (0.01, 0.05 and 0.5 pmol) increased the threshold for the induction of panic-like responses solely at the intermediary dose, an effect prevented by the CB₁-selective antagonist, AM251 (75 pmol). Panicolytic-like effects of ACEA at the higher dose were unmasked by pre-treatment with the TRPV1 antagonist capsazepine (0.1 nmol). Similarly to ACEA, capsazepine (1 and 10 nmol) raised the threshold for triggering panic-like reactions, an effect mimicked by another TRPV1 antagonist, SB366791 (1 nmol). Remarkably, the effects of both capsazepine and SB366791 were prevented by AM251 (75 pmol). These pharmacological data suggest that a common endogenous agonist may have opposite functions at a given synapse. Supporting this view, we observed that several neurons in the dPAG co-expressed CB₁ and TRPV1. Thus, the present work provides evidence that an endogenous substance, possibly anandamide, may exert both panicolytic and panicogenic effects via its actions at CB₁ receptors and TRPV1 channels, respectively. This tripartite set-point system might be exploited for the pharmacotherapy of panic attacks and anxiety-related disorders.

Topics: Anilides; Animals; Arachidonic Acids; Capsaicin; Cinnamates; Drug Interactions; Electric Stimulation; Male; Microinjections; Panic; Periaqueductal Gray; Piperidines; Pyrazoles; Rats; Rats, Wistar; Receptor, Cannabinoid, CB1; TRPV Cation Channels

To determine whether local administration of the cannabinoid 1 (CB(1)) receptor agonist arachidonyl-2-chloroethylamide (ACEA) can modulate joint nociception in control rat knee joints and in experimental osteoarthritis (OA).. OA was induced in male Wistar rats by intraarticular injection of 3 mg of sodium mono-iodoacetate, with a recovery period of 14 days. Electrophysiologic recordings were made of knee joint primary afferent nerve fibers in response to normal rotation and noxious hyperrotation of the joint both before and after close intraarterial injection of different doses of ACEA.. Local application of the CB(1) agonist significantly reduced the firing rate of afferent nerve fibers by up to 50% in control knee joints (n=19) and up to 62% in OA knee joints (n=29; P<0.01). Coadministration of the CB(1) receptor antagonist AM251 or the transient receptor potential vanilloid 1 (TRPV-1) ion channel antagonist SB366791 significantly reduced the desensitizing effect of ACEA. The CB(1) receptor antagonist AM251 by itself had no effect in the control joint but significantly increased the firing rate of afferent nerve fibers in the OA joint.. These findings indicate that activation of peripheral CB(1) receptors reduces the mechanosensitivity of afferent nerve fibers in control and OA knee joints. Blockade of either the CB(1) receptor or the TRPV-1 channel significantly reduced the efficacy of ACEA, which suggests that both receptors are involved in cannabinoid-mediated antinociception. The increased nerve activity observed following CB(1) receptor antagonism suggests a tonic release of endocannabinoids during OA. As such, peripheral CB(1) receptors may be important targets in controlling OA pain.

Topics: Afferent Pathways; Anilides; Animals; Arachidonic Acids; Cinnamates; Knee Joint; Male; Nociceptors; Osteoarthritis, Knee; Pain; Piperidines; Pyrazoles; Rats; Rats, Wistar; Receptor, Cannabinoid, CB1; TRPV Cation Channels