A . Radzievsky, O . Gordiienko , S. Alekseev and M.Ziskin .

1. INTRODUCTION DISCUSSION MILLIMETER WAVE TREATMENT IS INCOMPATIBLE WITH ORAL KETAMINE IN EXPERIMENTAL MODEL OF NEUROPATHIC PAIN IN MICE A. Radzievsky, O. Gordiienko, S. Alekseev and M.Ziskin. Center for Biomedical Physics, Temple University School of Medicine, Philadelphia Millimeter Wave Treatment (MWT) is based on the systemic effects following local skin exposure to low power electromagnetic waves of millimeter range. In our previous experiments we have determined that MWT-induced hypoalgesia is a specific and reproducible phenomenon that involves the peripheral and central nervous systems, as well as endogenous opioids. MWT was effective in suppressing acute, chronic non-neuropathic, and chronic neuropathic types of pain. The effect was power- and frequency-dependent. In the present set of experiments, to potentiate antinociception effect of the treatment for the most resistant to conventional treatment neuropathic pain, MWT was combined with different doses of oral ketamine (a non-competitive NMDA receptor antagonist, which was also shown to suppress neuropathic pain). NMDA receptor antagonists are rather effective therapeutic agents for the treatment of experimentally induced and clinical neuropathic pain conditions. However, NMDA receptors, nicotinic and muscarinic receptors (that also have been shown to interact with the most commonly used NMDA blocker Ketamine) are widely distributed in the CNS, and usage of this group of drugs in the treatment of neuropathic pain is limited because of their side effects (disturbances of cognition and mood). By administration of Ketamine per os we reduced possible side effects of the treatment. Only at the largest dose of Ketamine (100 mg/kg) did we observe some aggravation of neuropathic pain symptoms in the first 5 days following the treatment. Considering that MWT mostly acts through opioid receptor mechanisms, and Ketamine – by blocking NMDA receptors, we anticipated synergetic effect of the combined treatment. However, the results of the experiments were opposite. Both treatments significantly decreased the level of neuropathic pain in mice if applied separately: Ketamine (most effectively in the dosage of 50 mg/kg) during the treatment, and MWT – in the post-treatment period. But, when used together, the treatments canceled each other. Furthermore, when MWT was combined with 50 or 100 mg/kg of Ketamine, the level of neuropathic pain in experimental animals significantly increased. We concluded that Ketamine treatment should be considered as a contraindication for MWT. RESULTS Wire Surface Test Mirrors Dynamic of IIPD during and after the treatment with MW and Ketamine 1 mg/kg PAIN Chronic Pain Cage Camera B C Acute Pain Non-neuropathic Pain Neuropathic Pain • A cage (14x12x14 cm) with a wire mesh floor was used to conduct the test • The mice were placed into the cage for a period of 9 min (first 4 min – adjustment period; 5 min – observation period) • Endpoints of the test: Activation of nociceptive transducers in the presence of tissue damage (Typically < 1 month) Pain initiated or caused by a primary lesion or dysfunction in the nervous system Pain persisting > 1 month or recurring for > 3 months (2.66) (2.47) (1.85) D F Disease by itself Symptom of traumas or various diseases • Number of Paw Protective Movements (PPM) in horizontal position • Number of PPM in vertical position • Total Time (TT) the injured paw was held over the surface • Vertical Activity (VA) Number of times the animal is taking a vertical position. MATERIALS AND METHODS Integral Index of Pain and Discomfort (IIPD) 10 mg/kg Animals:Swiss-Webster mice; 18-20 gr at the beginning of the experiment (1.85) (1.33) (1.23) Experimental model of neuropathic pain: Unilateral Chronic Constriction Injury of the common sciatic nerve IIPD= hPPM x 0.141 + vPPM x 0.095 + TT x 0.083 – VA x 0.011 CONCLUSIONS • MWT significantly decreases the level of neuropathic pain in the post-treatment period in mice following CCI to the sciatic nerve • Ketamine (50 mg/kg) decreases the level of neuropathic pain during the treatment and in the early post-treatment period • Combination of MWT and oral Ketamine treatment results in exacerbation of symptoms of neuropathic pain in mice following CCI to the sciatic nerve • Ongoing treatment with Ketamine should be considered as a contraindication for MWT • Mechanisms of MWT-Ketamine interaction need to be studied further Ketamine - a non-competitive NMDA receptor antagonist “When first and second-line drugs such as opioids, anticonvulsants, or antidepressants fail to provide satisfactory analgesia for the patient with chronic pain, third-line drugs such as ketamine may provide a suitable option” Pain signal transmission in the spinal cord From G.Hocking et al, Anesth.& Analg., 2003 3 min 6 min 10 min 30 min NK1-R - Neurokinin1 receptor CCK - Cholecystokinin Op.-R - Opiate receptor Glu - Glutamate SP - Substance P 50 mg/kg Morphological changes in 30 days after surgery 2 ligatures (10-0; Alcon) tied loosely around the nerve Ketamine (non-competitive NMDA receptor antagonist) was administered for 10 consecutive days, starting from day 13 after the surgery The following doses of Ketamine were used: 1, 10, 50, and 100 mg/kg in 0.2 of H20 via gavage. Millimeter Wave Treatment Time-schedule of experiments 10 MWT+ Ketamine Training 0 Test Training 5 15 20 25 30 40 10 45 35 0 Days Arrival Surgery Experimental WST Baseline WST • Electromagnetic MW characteristics: • Frequency - 61.22 GHz Average Incident • Output Power - - 30 mW Power Density - 13.3 mW/cm2 • Peak Power Density - 56 mW/cm2 Duration - 15 min • Area of exposure -Nose Number of exposures - 10 Experimental groups: 1. CCI + Sham MWT Starting from the day 13 after the CCI, once a day, for 10 days animals were restrained for 15 min, but not exposed to MW 2. CCI + MWT 10 times, once a day, mice were exposed to MW only 3. CCI + Ket1 For 10 days, once a day, mice were treated with 1 mg/kg of oral Ketamine only 4. CCI + Ket10 10 mg/kg of oral Ketamine 5. CCI + Ket50 50 mg/kg of Ketamine 6. CCI + Ket100 100 mg/kg of Ketamine 7. CCI + Ket1 + MWT In addition to MWT, mice were treated with 1 mg/kg of oral Ketamine 8. CCI + Ket10 + MWT 9. CCI + Ket50 + MWT 10.CCI + Ket100 + MWT 100 mg/kg ACKNOWLEDGEMENTS ΔT 1oC Obligatory “blind” experimental settings: Grant PO1 - AT002025. 0oC Two researchers perform the test: One exposes the mice and records the tests, and the other analyzes the WST recordings Max ΔT during 15 min of exposure = 1.2 OC