dynorphins and anandamide

The pain, an unpleasant feeling, induces several central nervous system mechanisms, like sensory-discriminative, motivational-affective activities, behavioral changes and it activates various responses, including antinociceptive actions. Accordingly, signals from the nociceptive neurons in the spinal cord and the sensory trigeminal nucleus ascend in various neuronal pathways and target several brain areas. Here, five ascending pain-conducting neuronal pathways and two spinal reflex routes are briefly summarized. The spinal and supraspinal antinociceptive mechanisms are described in more detail. During the past two decades, endogenous opioids, cannabinoids and their receptors have been discovered, localized and cloned. Five groups of endogenous opiates are known: beta-endorphin, enkephalins, dynorphins, endomorphins, and nociceptin. Two endogenous cannabinoids have already been described in the brain: the anandamide and the 2-arachidonyl-glycerol. The site of their antinociceptive (analgesic) actions in the brain are briefly summarized.

Topics: Afferent Pathways; Animals; Arachidonic Acids; Brain; Cannabinoids; Dynorphins; Efferent Pathways; Endocannabinoids; Endorphins; Glycerides; Humans; Neural Conduction; Neural Pathways; Neurotransmitter Agents; Nociceptin; Opioid Peptides; Pain; Polyunsaturated Alkamides; Receptors, Neurotransmitter; Receptors, Opioid

The endogenous opioid dynorphin B was evaluated for its role in cannabinoid-induced antinociception. Previous work in our laboratory has shown that the synthetic, bicyclic cannabinoid, CP55,940, induces the release of dynorphin B whilst the naturally occurring cannabinoid, Delta(9)-tetrahydrocannabinol (Delta(9)-THC), releases dynorphin A. The dynorphins contribute in part to the antinociceptive effects of both cannabinoids at the level of the spinal cord. The present study compares dynorphin B released from perfused rat spinal cord in response to acute administration of anandamide (AEA), Delta(9)-THC and CP55,940 at two time points, 10 min and 30 min post administration, and attempts to correlate such release with antinociceptive effects of the drugs. Dynorphin B was collected from spinal perfusates of rats pretreated with Delta(9)-THC, CP55,940 or AEA. The supernatant was lyophilized and the concentrations of dynorphin B were measured via radioimmunoassay. At a peak time of antinociception (10 min), CP55,940 and Delta(9)-THC induced significant two-fold increases in the release of dynorphin B. AEA did not significantly release dynorphin B. Upon a 30-min pretreatment with the drugs, no significant dynorphin B release was observed, although antinociceptive effects persisted for CP55,940 and Delta(9)-THC. Previous work indicates that Delta(9)-THC releases dynorphin A while AEA releases no dynorphin A. This study confirms that although all three test drugs produced significant antinociception at 10 min, the endocannabinoid, AEA, does not induce antinociception via dynorphin release. Thus, our data indicate a distinct mechanism which underlies AEA-induced antinociception.

Topics: Analgesia; Analgesics; Analgesics, Non-Narcotic; Animals; Arachidonic Acids; Calcium Channel Blockers; Cannabinoid Receptor Modulators; Cannabinoids; Cyclohexanols; Dronabinol; Dynorphins; Endocannabinoids; Endorphins; Male; Pain; Polyunsaturated Alkamides; Rats; Rats, Sprague-Dawley; Spinal Cord

We evaluated delta-9 tetrahydrocannabinol (Delta9-THC), delta-8 tetrahydrocannabinol (Delta8-THC), CP55,940 (CP55), 1-deoxy-11-hydroxy-Delta8-THC-dimethylheptyl (deoxy-HU210, a CB2-selective cannabinoid that also binds the CB1 receptor) and the endogenous cannabinoid anandamide (ANA) via i.c.v. and/or intrathecal (i.t.) routes of administration, alone and in combination with SR141716A (SR), a CB1 antagonist, using the tail-flick test. Our studies were performed in order better to characterize potential diversity in interactions of the cannabinoids with the cannabinoid (CB1) receptor. When SR was administered i.c.v. or i.p. before Delta9-THC, Delta8-THC or CP55 (i.c.v. or i.t.), SR was a potent antagonist and the blockade was complete (AD50

Topics: Analgesics; Animals; Arachidonic Acids; Body Temperature; Brain; Cannabinoids; Dynorphins; Endocannabinoids; Male; Mice; Mice, Inbred ICR; Piperidines; Polyunsaturated Alkamides; Pyrazoles; Receptors, Cannabinoid; Receptors, Drug; Rimonabant; Spinal Cord

The endogenous ligand for the cannabinoid receptor, arachidonylethanolamide (anandamide), has been shown to produce antinociception using the tail-flick test following intrathecal administration. Anandamide was administered i.p. (40 mg kg) to mice four times per day for 3 days. Tolerance developed to anandamide: the ED50 for anandamide (i.t.) was shifted from 40 (26-61) to 139 (79-248) micrograms/mouse. Anandamide-tolerant mice were cross-tolerant to delta 9-THC and CP55,940, but not cross-tolerant to mu-, delta- or kappa- opioids, including dynorphins. Conversely, delta 9-THC-tolerant mice are cross-tolerant to anandamide, CP55,940 and kappa agonists. Our data indicate that anandamide and delta 9-THC differ in the mechanisms by which they induce tolerance, in particular the interaction with endogenous dynorphinergic systems.

Topics: Analgesics; Animals; Arachidonic Acids; Cannabinoids; Cyclohexanols; Dose-Response Relationship, Drug; Dronabinol; Drug Tolerance; Dynorphins; Endocannabinoids; Injections, Intraperitoneal; Injections, Spinal; Mice; Naltrexone; Narcotic Antagonists; Pain Measurement; Polyunsaturated Alkamides; Receptors, Cannabinoid; Receptors, Drug