Cannabinoid system physiological effects Motor impairement Memory impairement Catalepsy Temperature decrease Analgesia Pressure modification Immune suppression/stimulation

Definition of pain and nociception Pain is “An unpleasent sensory and emotional experience associated with actual or potential tissue damage, or described in term of such damage” IASP 1979 Nociception is referred to the reception in the central nervous system of signals triggered by the activation of specialized receptors called nociceptors

Pain pathway I Receptor type Fiber groupQuality Nociceptors MechanicalAδ Sharp, pricking pain Thermal and mechano-thermalAδ Sharp, pricking pain Thermal and mechano-thermalC Slow, burning pain PolymodalC Slow, burning pain Cutaneous and subcutaneous mechanoreceptors Meissner’s corpuscleAβFlutter Pacinian corpusclesAβVibration Ruffini corpuscleAβ Steady skin indentation Merkel receptorAβ Steady skin indentation DRG Spinal cord Skin

Pain pathway II

Pain groupingEtiology NeuropathicPainful diabetic neuropathy (PDN) HIV-related neuropathic pain Postherpetic neuralgia (PHN) AcutePostoperative pain VisceralIrritable bowel syndrome Chronic pelvic pain Cancer related painSevere pain Metastatic bone pain Neuropathic pain (caused by nerve injury and chemotherapic agents) Breakthrough pain Musculoskeletal painPainful osteoarthritis Painful rheumatoid arthritis Chronic lowback pain Fibromyalgia HeadacheMigraine Chronic daily headache Type of pain

Preclinical pain models Ethical issues Legislation: Procedures involving animals and their care must be conducted in conformity with the institutional guidelines, in compliance with national and international law Experiments involving the study of pain on conscious animals must be reviewed by a specific committee; Is forbidden the use of animals paralyzed with a neuromuscular blocking agent without a general anesthetic or an appropriate surgical procedure that eliminates sensory awareness; The duration of experiments must be as short as possible, and the number of animals involved must be kept to the minimum.

A. Acute pain: B. Chronic pain: Inflammatory pain models Neuropathic pain models Phasic pain models Tonic pain models Preclinical pain models

Acute pain models The hot plate test (according to Woolfe and McDonald, 1944) The tail flick test (according to D'Amour & Smith, 1941) Phasic: short-duration stimulus-evoked models

Disease models Pain-like behaviour First phase Second phase Formalin test Tonic: short-duration spontaneous models

Chronic pain models 1. Metabolic disfunction STZ-induced diabetic neuropathy 2. Cancer pain Vincristine-induced neuropathic pain 3. Infectious disease Varicella zoster virus-induced neuropathy 4. Neuropathic pain Surgical manipulation of sciatic nerve 5. Post-tissue injury Injection of an irritant into a joint or hind paw 6. Inflammatory pain model Injection of CFA

Neuropathic pain models

Read outs: –Mechanical allodynia –Mechanical hyperalgesia –Cold allodynia –Hot allodynia Preclinical pain models Mechanical allodynia von Frey hair test Thermal allodynia (hot) plantar test Thermal allodynia cold plate test Mechanical hyperalgesia Randall-Selitto

Cannabinoid and nociception

Potential targets for intervention CB1 and CB2 receptors: –Use of agonists to induce analgesia. Endocannabinoids internalization: –Blockade of the transporter to elevate the extracellular level of endocannabinoids. Endocannabinoids degradation –Blockade of the endocannabinoid degrading enzymes (FAAH and/or MAGL) to elevate endocannabinoid extracellular level.

CB1 and nociception

CB1 localization (Hegyi et al 2009) Spinal cord dorsal horn