Exercise and the Endocannabinoid System

1. Exercise and the Endocannabinoid System The Neurobiology of the Runner’s High

2. What are Cannabinoids? • A diverse group of chemical compounds • Act upon cannabinoid receptors • Common across plants and animals • Synthetic Cannabinoids • Dronabinol (Marinol) – THC • Sativex (CBD. THC) – Therapeutic • Rimonabant(SR141716) – CB1 agonist • Anti-obesity, anti-smoking drug

3. AEA THC 2-AG CBD

4. Cannabinoids • Name derived from Cannabis sativa L. • In use by H. sapiens since 5,000 BCE • Used as a drug since 1st-millenium BCE • “"The Scythians, as I said, take some of this hemp-seed [presumably, flowers], and, creeping under the felt coverings, throw it upon the red-hot stones; immediately it smokes, and gives out such a vapour as no Grecian vapour-bath can exceed; the Scyths, delighted, shout for joy.” Herodotus, The Histories 440 BCE

5. Cannabinoids • Produced on leaves and flowers of C. sativa • Resins on the glandular trichomes • 85 cannabinoid compounds have been isolated in C. sativa • Cannabinoids are well-known lipophilic molecules (hence pot-brownies) • Previously thought to act by altering membrane lipids • 1964 – Chemical Structure of THC discovered • 1974 – Structural selectivity of THC indicates drug-receptor interaction • 1990 – Orphan G-protein coupled receptor (GPCR) identified, named CB1 • 1992 – Anandamideidentified as endogenous ligand of CB1 receptor

6. Endocannabinoid System • Neuromodulatory chemicals, receptors and enzymes • Appetite • Pain • Mood • Memory • Modulates actions of Cannabis use • CB1 Receptor • Pre-synaptic inhibitor • Activated by AEA, 2-AG, THC (psychoactive) • CB2 Receptor • Primarily activated by 2-AG

7. Anandamide • From Sanskrit word ‘ananda’: joy, bliss, delight • Modulates CB1 receptors in CNS • Feeding behavior • Pleasure • Motivation • CB2 Receptor – Periphery • Immune suppression • Cell migration • Implantation of blastocyst into uterine wall

8. Endocannabinoid Synthesis • Created in post-synaptic neurons in response to signaling • Breakdown of phospholipids of intra-cellular membranes • Increases intracellular Ca+ • Exclusive synthesis (AEA/2-AG)

9. Endocannabinoid Synthesis

10. Endocannabinoidsand exercise • Are they related? • So… probably Endocannabinoids: -Stress response physiology -Analgetic effects -Increase appetite -Induce sleep -Lighten mood Exercise: -Stress response physiology -Suppress pain -Increase appetite Induce sedation -Improves mood

11. Sparling et al., 2003 • Exercise makes you feel good • Analgesia and Anxiolysis • Previously thought to be due to endorphins • Cannabinoid system reduces pain • Central and peripheral levels • Could exercise induced-analgesia be related?

12. Sparling et al., 2003 • Experiment: • 24 male college students • Consistent runners/cyclers • Running (8) Cycling (8) Sedentary (8) • 45 minutes of exercise – moderate intensity • Blood collected pre and post-exercise • Measured for AEA levels

13. Sparling et al., 2003

14. Sparling et al., 2003 • Elevated AEA in blood supports hypothesis • ECBs are the mechanism of exercise-induced analgesia • AEA is synthesized in peripheral sensory neurons • AEA  Nociception via peripheral pain-related CB1 receptors • What about the brain? Anxiolysis? • AEA crosses blood-brain barrier rapidly • THC acts on CNS CB1 receptors • Induces similar feelings to those experienced by endurance athletes • Perhaps increased AEA levels are accomplishing the same feat (perhaps) • But How???

15. Endocannabinoidsand anxiety • Post-synaptic release of ECBs modulates presynaptic action • Short and long term scale • Memory modulation • Extinction of aversive memories • Endocannabinoids: • Stress response physiology • Analgeticeffects • Increase appetite • Induce sleep • Lighten mood

16. Höfelmann et al., 2013 • Serotonergic system • Affects wide range of behaviors and emotional states • 5-HT3 receptors modulate the release of several neurotransmitters • Antagonistic tests show inconsistent effects on anxiety • Suggests role of additional actors • Modulation of/by ECBs could explain contradictory results • Amygdala • Analgesia and emotional behavior • CB1 and 5-HT3 are co-localized in BLA • Synergy?

17. Höfelmann et al., 2013

18. Höfelmann et al., 2013 • Experiment One: Serotonergic System and Fear Conditioning • Mice underwent Auditory Fear Conditioning • Measure freezing time after a loud stimulus • BLA dependent • Followed by administration of 5-HT3 receptor agonist (SR57227A) • 5-HT3 activation impaired extinction of fear

19. Höfelmann et al., 2013 • Experiment Two: Serotonergic System and Fear Conditioning • Mice pre-treated with 5-HT3 antagonist (Trop) • Mice underwent Auditory Fear Conditioning • Measure freezing time after a loud stimulus • BLA dependent • 5-HT3 antagonist reduced expression of conditioned fear

20. Höfelmann et al., 2013 • Experiment Three: Interaction of 5-HT3 and CB1receptors in Fear • Mice pre-treated with 5-HT3 antagonist (Trop) • And CB1 inversive agonist (Rim) • Mice underwent Auditory Fear Conditioning • Measure freezing time after a loud stimulus • BLA dependent • 5-HT3 antagonist reduced expression of conditioned fear • CB1 agonist overruled these effects

21. Höfelmann et al., 2013 Fig 3

22. Höfelmannet al., 2013 Fig 2

23. Höfelmann et al., 2013

24. Höfelmann et al., 2013 • No interaction between ECBs and 5-HT3 in BLA • LTDi was unaffected by 5-HT3 agonism/antagonism • CB1 and 5-HT3 receptors are tightly co-localized • Any interaction doesn’t come in this form of synaptic plasticity though • ECBS and Serotonergic Systems do not interact via GABA neurotransmission in the BLA • Not the mechanism of ECB anxiolysis

25. Hill et al,. 2012 • Pyramidal neurons in the Amygdala • Primary output neurons • Suppression of BLA excitation reduces anxiety • Facilitation of excitation in BLA produces hypervigilance, anxiety • Chronic stress increases excitability, growth of pyramidal neurons in BLA • Likely mechanism in the development of anxiety • ECB in the BLA • Known to modulate stress • Contributes to synaptic plasticity

26. Hill et al,. 2012 • What if mechanism of ECB action in BLA comes at a different point? • Does ECB act on anxiety in BLA via Fatty Acid Amid Hydrolase (FAAH)? • Known to be modulated by stress • Contributes to synaptic plasticity

27. Hill et al,. 2012 • Experiment: • FAAH Deficient Mice / Wild Type • Stress/Non Stress • Stress: 6hrs restraint for 21 days • Anxiety Test 24hrs after final restraint stress • Elevated Plus Maze • Open Field Test

28. Hill et al,. 2012Figure 1

29. Hill et al,. 2012Figure 2

30. Hill et al,. 2012Figure 3

31. Hill et al,. 2012Figure 4

32. Hill et al,. 2012 • Chronic Stress increases action of FAAH • Decreases levels of AEA in tissue • No effect on CB1site density or affinity in Amygdala • Therefore, FAAH deficiency prevents dendritic arborization response • FAAH deficiency also prevents the promotion of anxiety behavior • EPM open-arm entries remain the same • FAAH represent likely mechanism of interaction between ECB and anxiety response

33. Ecbs, Exercise and anxietywhere do we stand? • Hill 2012 points to a likely area for ECB System to interact with anxiety response in BLA • FAAH may be a target for treatment of anxiety disorders • Open questions: • How does the ECBS act to reduce anxiety? • What is the mechanism by which exercise activates the ECBS? • How on earth do I tie all of these disparate notions together????

34. Synthesis – Raichlen et al,. 2012 • Goal-oriented behaviors with high energy costs • Motivated by neurological rewards • Conditions fitness enhancement • ECBS may or may not immediately impact anxiety system • But, rewarding the exercise effort could select for beneficial traits • Shown in other cursorial mammals

35. Synthesis – Raichlen et al,. 2012

36. Synthesis – Raichlen et al,. 2012

37. The Big Picture, Bro