Cannabinoids 101 Matthew Hill, Ph.D. Hotchkiss Brain Institute University of Calgary
Disclosures Have received honoraria for Scientific Consultation: Pfizer International GW Pharmaceuticals Receive operating funds from: GW Pharmaceuticals
Defining the cannabinoid system Exogenous compounds Phytocannabinoids THC, CBD, combinations Synthetic cannabinoids Nabilone, dronabinol K2, spice Endogenous cannabinoids Anandamide 2 arachidonyl glycerol Receptor targets CB1, CB2
Cannabinoids 101 Discovery of THC as the psychoactive component of cannabis April 20, 1964 Raphael Mechoulam (Hebrew University) HOW DOES THC WORK?
Cannabinoids 101 Cannabinoids are False Steroids (70s 80s) Cannabinoids exhibit a multi carbon ring structure similar to steroid hormones
Cannabinoids 101 Cannabinoids are False Steroids (70s 80s) A lot of similarities between the physiological effects of cannabinoids and corticosteroids (antiinflammatory, orexigenic, euphora, etc) Cannabinoids appear to exhibit some binding potential to steroid receptors
Cannabinoids 101 Cannabinoids modulate membrane fluidity (early 80s) Based on hypothesis that levels of cholesterol in membrane influenced neuronal excitability and actions of ion channels Non specific in nature, would affect neurons across the brain and could account for diverse effects on the CNS
Cannabinoids 101 Cannabinoids activate a receptor 1988: Allyn Howlett demonstrates that THC exerts effects in cells that seem to be consistent with the activation of a receptor Activation of intracellular signaling cascades Temperature sensitive Saturable
Cannabinoids 101 Radiolabelled CB1 agonist and mapping of cannabinoid receptors 1990: Miles Herkenham lab uses autoradiography to map distribution of CB1 binding sites in the brain Clear patterns of areas where there is a lot of CB1 and areas where there is very little. Consistent with binding to a receptor, yet no receptor identified
Cannabinoids 101 Cloning of CB1 Receptor 1990: Tom Bonner lab clones a gene for an orphan receptor In situ mapping of gene mrna looks strikingly reminiscent to autoradiograms of THC binding The cloned receptor binds THC, termed cannabinoid receptor type 1 (with expectation that additional receptors will be discovered)
Cannabinoids 101 Internal Bliss: The First Endo cannabinoid 1992: Raphael Mechoulam lab examining porcine brains to find a lipid that would be an endogenous cannabinoid and could bind to the newly discovered CB1 Conjugate of arachidonic acid and ethanolamine Termed anandamide Anand Sanskrit word for bliss
Cannabinoids 101 CB2 Receptors: The Peripheral Receptor 1993: Munro lab discovers a receptor in immune cells and spleen that also responds to cannabinoids No detectable mrna for CB2 found in the CNS, deemed to be the peripheral receptor of the cannabinoid system
Cannabinoids 101 The Second Endocannabinoid: 2 AG 1995: Sugiura and Mechoulam labs both find novel endogenous cannabinoid, 2 arachidonoylglycerol Similar to Anandamide, it s a conjugate of arachidonic acid with glycerol Binds to both CB1 and CB2 receptors Found at much higher levels in the CNS than anandamide
Cannabinoids 101 Neurons make endocannabinoids Piomelli and Di Marzo (1994): Cultured neurons are found to release endocannabinoids when stimulated This appears to be different from most neurotransmitters as here it seems that endocannabinoids are released from cell bodies and not axons
Cannabinoids 101 CB1 regulates neurotransmitter release Electrophysiology studies demonstrate that cannabinoids can effectively suppress the release of neurotransmitters into the synapse. Activation of CB1 suppresses calcium influx into axon to inhibit transmitter release Antibodies generated to visualize CB1 receptors show that CB1 is almost entirely expressed on axon terminals
Cannabinoids 101 Retrograde Signals 2001: Nicoll, Kano and Regher labs all publish high profile papers demonstrating that endocannabinoids are retrograde signals Produced by neurons to feedback to axon terminal and regulate neurotransmitter release Revolutionizes our understanding of the brain things can move in both directions!!
The Endocannabinoid System Ca 2+ channel K + channel AA + Glycerol MAGL CB1 2 AG CB1 AEA 2 AG NAPE PLD AEA NAPE AEA PE Ca 2+ PI DAG 2 AG AA + EA Morena, Patel, Bains and Hill, Neuropsychopharm 2016
CB1 Receptors Its Complicated Cannabinoid type 1 receptor (CB 1 ) Neuron type matters!!! CB1 regulates release of both excitatory (glutamate) and inhibitory (GABA) neurotransmitters
CB1 Receptors Its Complicated CB1 Receptors as a Circuit Breaker
CB1 Receptors Its Complicated CB1 Receptors as Hetero synaptic Regulators of Plasticity
CB1 Receptors Its Complicated Neuronal Subtype Differences Most CB1 expression is on GABA terminals, yet CB1 on glutamate terminals mediates basically all of the neurobehavioral effects of THC. Monory et al., 2006
CB1 Receptors Its Complicated Neuronal Subtype Differences CB1 in glutamate neurons is much more efficient at recruiting G proteins than in GABA neurons Glutamate GABA
CB1 Receptors Its Complicated CB1 changes over development, prior to puberty CB1 is very high on glutamate terminals and declines through adolescence, plateauing in adulthood Heng et al., 2011
CB1 Receptors Its Complicated
Cannabis and the Endocannabinoid System
Cannabinoid mechanisms Canadian Consortium for the Investigation of Cannabinoids
Lets Not Forget About CB2! Cannabinoid type 2 receptor (CB 2 ) Primarily found in immune cells, of many types Acts to suppress release of pro inflammatory cytokines, reduce adhesion molecules and prevent cell tissue entry Doesn t seem to do much to normal immune system but reduces hyperactivity Seems to be due to inducible nature of receptor, little to no expression at rest
Endocannabinoids Protect the brain CB1 activation reduces excess release of glutamate, prevents excitotoxic damage CB2 reduces the release of pro inflammatory cytokines, suppresses neuroinflammation Benefit in the context of aging, brain trauma/insult or neurodegenerative disease
Targets of Phytocannabinoids The two main cannabinoids in cannabis that are studies are: THC CBD (cannabidiol)
Targets of Phytocannabinoids THC exerts its effects primarily through the activation of CB1, particularly on glutamate terminals CBD has an unclear mechanism, but does NOT bind to CB1 or CB2 receptors. CBD has been shown to: Inhibit adenosine uptake Antagonist at GPR55 Activate 5 HT1A receptors Inhibit FAAH
Targets of Phytocannabinoids