Analgesia induced by combined action of Tramadol and microwave irradiation in somatic pain in mice

In experiments on albino male mice weighing 24 to 32 g, we studied the suppression of the pain reaction induced by injection of formalin into the dorsal surface of the foot, using a combination of injection of tramadol hydrochloride (Tramal) in a dose of 0.42 mg/kg and irradiation of the acupuncture point (AP) E-36 with low-intensity microwaves (frequency 30 to 300 GHz and power rate density 3·10⁻⁹ W/cm²). The combined use of tramadol injection and the action of microwaves on the AP led to a decrease in the duration of the pain reaction (licking of the pain nidus), on average, by 58.2%, as compared with that in the control animal group. The analgesic effect was more strong in the case of such a combination than after isolated injection of tramadol in doses of 0.83 and 0.42 mg/kg (by 14.4 and by 10.0%, respectively) and isolated microwave irradiation of the AP TA E-36 (by 48.7%). The data obtained demonstrate the possibility of effective analgesia using a combination of microwave irradiation of the AP and the pharmacological influence with a significant decrease in the dose of the analgesic. Neirofiziologiya/Neurophysiology, Vol. 38, No. 4, pp. 314–319, July–August, 2006.     

Analgesia Induced by Microwave Irradiation of an Acupuncture Point under Conditions of Visceral Pain in Mice: Role of the Serotonergic Cerebral System

We studied behavioral manifestations of analgesic effects induced in mice by irradiation of the E36 acupuncture point (AcP) by low-intensity microwaves under conditions of visceral pain evoked by i.p. injections of 0.08 ml of a 2% solution of acetic acid. We also examined changes in these analgesic effects resulting from a drop in the level of serotonin after i.p. injection of 300 mg/kg of a blocker of synthesis of serotonin, DL-parachlorophenylalanine (PChPhA). Two modes of irradiation were tested, with a wide frequency range (30 to 300 GHz) and amplitude modulation (mode 1) and with a stable frequency (61 ± ± 4 GHz, mode 2). Irradiation in mode 1 provided a higher level of analgesia than that in mode 2 (decreases in the duration of manifestations of the pain reaction were, on average, 35.7 and 20.4%, respectively). The level of analgesia dropped after injections of PChPhA; the durations of behavioral pain manifestations 24 h after such injections were greater than those in the group with no injections of the blocker by 41.3 and 12.1% in irradiation modes 1 and 2, respectively. The respective figures 48 h after PChPhA injections were 52.0 and 16.1%. Thus, under conditions of visceral pain, irradiation of the AcP by low-intensity microwaves provides noticeable analgesia, and the serotonergic brain system mediates the development of analgesia under the above-mentioned conditions. Neirofiziologiya/Neurophysiology, Vol. 37, No. 3, pp. 250–256, May–June, 2005.     

Combination of pharmacological analgesics and microwave irradiation of an acupuncture point for suppression of visceral pain in mice: Role of the opioid and serotonergic cerebral systems

We studied suppression of pain-related reactions induced in mice by i.p. injection of 0.08 ml of a 2% solution of acetic acid using pharmacological analgesics (analgin and tramadol) combined with low-intensity microwave irradiation of an acupuncture point (AP) E-36 (frequency 30 to 300 GHz and power rate density 3·10⁻⁹ W/cm²). The respective effects were also observed under conditions of suppression of the functions of opioid and serotonergic cerebral systems using injections of, respectively, naloxone and DL-p-chlorophenylalanine (p-CPA). We found that antinociceptive effects provided by analgesics used in a 50% mean single dose in the combination with microwave irradiation of the AP were significantly more intense than those induced by isolated injection of analgesics used in both 50% and full mean single doses and isolated microwave irradiation of the AP E-36. After injections of naloxone, analgesic effects caused by the combined action of analgin and microwave irradiation of the AP were considerably smaller. At the same time, after injection of p-CPA, analgesic effects, provided by the combination of injection of pharmacological agents and microwave irradiation of the AP, weakened in the case of use of both analgesics. This was manifested in a significant increase in the total duration of pain-related behavioral reactions. Therefore, the studied analgesic effects observed in the examined animal groups are realized due to the involvement of the opioid and serotonergic cerebral systems. Neirofiziologiya/Neurophysiology, Vol. 39, No. 6, pp. 468–477, November–December, 2007.     

Involvement of the serotonergic cerebral system in microwave-induced analgesia in mice of different genotypes

Under conditions of the formalin test, we studied changes in the level of analgesia induced by the action of low-intensity microwaves on the antinociceptive acupuncture point (AP) E36 in mice of strains CBA/CaLac (CBA) and C57BL/6j (C57) and in albino mongrel mice. Measurements were performed under control conditions and with experimentally induced decrease in the serotonin level in the brain (by injections of DL-parachlorophenylalanine, p-CPA). In the latter cases, the duration of the pain behavioral reaction increased despite irradiation of the AP E36. In mongrel, CBA, and C57 mice, the intensity of pain manifestations was 114.4, 29.0, and 21.1% greater, respectively, than in mice of these groups with no injections of p-CPA. These facts show that the serotonergic brain system is profoundly involved in the formation of analgesia after irradiation of the AP by low-intensity microwaves, and this involvement significantly depends on the genotype of the animals. Neirofiziologiya/Neurophysiology, Vol. 38, Nos. 5/6, pp. 495–497, September–December, 2006.     

Involvement of the Serotonergic System in Analgesia Induced by the Influence of Low-Intensity Microwaves on an Antipain Acupuncture Point

In experiments on mice, we studied changes in the level of analgesia induced by irradiation of the antipain acupuncture point (AP) E36 by low-intensity microwaves under conditions of modification of the serotonin level in the brain; this level was modified by injection of 300 mg/kg DL-p-chlorophenylalanine (pCPA). The duration of the nociceptive behavioral reaction (licking the limb) caused by injection of the formalin solution into the foot dorsal surface increased 24, 48, and 72 h after pCPA injection by 99.9, 84.4, and 114.4%, as compared with those in animals subjected to microwave irradiation of the AP E36 with no preliminary pCPA injection. It is concluded that the brain serotonergic system is actively involved in the analgesia effects induced by irradiation of the AP by low-intensity microwaves.     

Suppression of nociceptive reactions in mice under low-intensity microwave irradiation of acupuncture points

We studied nociceptive responses to subcutaneous injections of formalin and electrical stimulation of the limbs in control mice and in mice whose acupuncture points (AP) were subjected to low-intensity microwave irradiation. In the latter animals, nociceptive reactions were significantly weaker than those in the control mice. The analgesic effect depended on what AP was selected and irradiated and on the duration and timing of microwave irradiation. In different experimental series, the duration of a formalin injection-induced nociceptive behavioral reaction decreased by 23.3–59.6%. The threshold of vocalization responses to stimulation on an electrified floor increased by 25.8±28.0%. The results demonstrate that a technique of analgesia by influencing the AP with microwave irradiation of a nonthermal intensity is rather effective.     

Roles of different neurochemical systems in mechanisms underlying the antinociceptive effect of extrahigh-frequency electromagnetic radiation

We studied the effect of low-intensity extrahigh-frequency (EHF) electromagnetic radiation (EMR) on the duration of a pain behavioral reaction in rats under conditions of experimental induction of tonic pain (formalin test). The antinociceptive effect of EHF irradiation was modulated by suppression of the activity of a few neurochemical systems resulting from the blockade of receptors of opioid peptides, α-and β-adrenoreceptors, receptors of dopamine and melatonin, as well as from inhibition of serotonin synthesis. We demonstrated that all the respective neurochemical systems are to a certain extent involved in the mechanisms underlying the analgesic action of EHF EMR. Within an early phase of pain stress, functioning of the opioidergic and noradrenergic systems and the effects of melatonin play leading roles, while the activity of the serotonergic system plays such a role within the second (tonic) phase. Neirofiziologiya/Neurophysiology, Vol. 39, No. 2, pp. 165–173, March–April, 2007.     

Circadian-Rhythm-dependent Effects of L-NG-Nitroarginine Methyl Ester (L-Name) on Morphine-Induced Analgesia

Circadian changes in the interactions between L-N^G-nitroarginine methyl ester (L-NAME), a nitric oxide synthase (NOS) inhibitor, and morphine-induced antinociception were investigated by the mouse hot-plate test. Born the basal pain sensitivity and morphine-induced analgesia undergo significant 24h variations. L-NAME (40 mg/kg, ip) alone did not show any antinociceptive activity, but potentiated morphine-induced analgesia when combined with morphine at all injection times. In terms of percentage absolute potentiation (%AP), L-NAME dramatically augmented the analgesic effect of morphine in the late dark period at 19 hours after lights on (HALO). It is concluded that nitric oxide (NO) is involved in the modulation of the analgesic effect of morphine; thus, the L-NAME and morphine combination might be beneficial in alleviating pain.     

Supraspinal injection of Substance P attenuates allodynia and hyperalgesia in a rat model of inflammatory pain

The neuropeptide Substance P (SP), that has a high affinity for the neurokinin 1 (NK1) receptor, is involved in modulation of pain transmission. Although SP is thought to have excitatory actions and promote nociception in the spinal cord, the peptide induces analgesia at the supraspinal level. The aim of this study was to evaluate the role of supraspinal SP and the NK1 receptor in inflammatory pain induced by injection of carrageenan in the hind paw of the rat. There are two nociceptive behavioral responses associated with this pain state: mechanical allodynia and heat hyperalgesia. Because the NK1 receptor colocalizes with the MOP receptor in supraspinal sites involved in pain modulation, we also decided to study the possible involvement of the opioid system on SP-induced analgesia. We found that treatment with SP, at doses of 3.5, 5 and 7 μg/5 μl/rat i.c.v., clearly showed inhibition of allodynia and hyperalgesia. Pretreatment with the selective NK1 antagonist L-733,060 (10mg/kg i.p.) blocked the SP-induced analgesia, suggesting the involvement of the NK1 receptor. This SP-induced analgesia was significantly reduced by administration of the opioid antagonist naloxone (3mg/kg s.c.). This reduction occurred when SP was administered either before or after the carrageenan injection. These results suggest a significant antinociceptive role for SP and the NK1 receptor in inflammatory pain at the supraspinal level, possibly through the release of endogenous opioids.     

Pharmacological analysis of inhomogeneous static magnetic field-induced antinociceptive action in the mouse

The effect of inhomogeneous, 2-754 mT static magnetic field (SMF) on visceral pain elicited by intraperitoneal injection of 0.6% acetic acid (writhing test) was studied in the mouse. Exposure of mice to static magnetic field (permanent NdFeB N50 grade 10 mm x 10 mm cylindrical magnets with alternating poles) during the nociceptive stimulus (0-30 min) resulted in inhibition of pain reaction: the number of writhings decreased from 9 +/- 2, 32 +/- 4 and 30 +/- 3 to 2 +/- 0.03, 15 +/- 1.6, and 14 +/- 1.6, respectively, measured in 0-5th, 6-20th, and 21-30th min following the acetic acid challenge. The pain reaction during the total observation period was reduced by 57% (P < 0.005). The analgesic action induced by SMF was inhibited by subcutaneous administration of naloxone (1 and 0.2 mg kg(-1)), irreversible micro-opioid receptor antagonist beta-funaltrexamine (20 mg kg(-1)) and delta-opioid receptor antagonist naltrindole (0.5 mg kg(-1)), but the kappa-opioid receptor antagonist norbinaltorphimine (20 mg kg(-1)) failed to affect the SMF-induced antinociception. In contrast to the subcutaneous administration, the intracerebroventricularly injected naloxone (10 microg mouse(-1)) did not antagonize the antinociceptive effect of SMF. The results suggest that acute exposure of mice to static magnetic field results in an opioid-mediated analgesic action in the writhing test in the mouse. The antinociceptive effect is likely to be mediated by micro and (to a lesser extent) delta-opioid receptors.     

Suppression of synthesis of serotonin: Effect on antinociception induced by microwave irradiation and analgesic remedies

We studied isolated and combined antinociceptive effects of analgesics (Analginum and Tramadol), as well as of microwave irradiation of an acupuncture point, in mice under conditions of suppression of synthesis of serotonin by an inhibitor of this synthesis, DL-p-chlorophenylalanine (p-CPA). Preliminary introduction of p-CPA weakened the antinociceptive effect of microwave irradiation and also moderated the combined effects of analgesics and microwave irradiation. Neirofiziologiya/Neurophysiology, Vol. 38, Nos. 5/6, pp. 498–499, September–December, 2006.     

Absence of Non-Thermal Microwave Effects on the Function of Giant Nerve Fibers

Functioning of the giant axon of the isolated earthworm ventral nerve cord was examined during exposure to 6.45 GHz microwaves. We used continuous wave and pulsed irradiation, either synchronized with stimuli or asynchronous, lasting for 10–50 min at specific absorption rate from 30 to 230 W/kg. Action potential (AP) conduction velocity and the capability of nerve fiber to answer long-lasting high-frequency stimulation served as indices of microwave effect. Under some experimental conditions the nerve appeared to have extreme sensitivity to subtle temperature changes, induced by irradiation, but no non-thermal microwave effects were detected.     

Effects of melatonin, morphine and diazepam on formalin-induced nociception in mice

The possible analgesic effect of melatonin was investigated in young male ICR mice. The formalin test which elicits typically 2 phases of pain response, the acute (first) phase and tonic (second) phase, was used. The test was performed in the late light period when the mice have been reported to be more sensitive to pain. Compared to control mice, no significant difference in nociceptive response was observed when melatonin was injected intraperitoneally at doses of 0.1, 5, and 20, mg/kg body weight. The combined effects of melatonin with diazepam and/or morphine, were also investigated. Melatonin, injected at 20 mg/kg 15 min before formalin test, significantly increased the antinociceptive response of diazepam (1 mg/kg) or morphine (5 mg/kg) in the second phase. In addition, when melatonin was given at 20 mg/kg together with diazepam and morphine, antinociceptive responses in both the first and second phase were increased. These data indicate the synergistic analgesia effect of melatonin with morphine and diazepam and suggest the possible involvement of melatonin as an adjunct medicine for pain patients.     

Analgesic effect of tianeptine in mice

The effects of tianeptine, a novel and unusual tricyclic antidepressant drug, on tail-flick and hot-plate tests, which are two thermal analgesia evaluating methods, have been investigated in mice. Tianeptine (5 and 10 mg/kg), para-chlorophenylalanine (pCPA) (100 mg/kg) and a combination of pCPA and tianeptine (10 mg/kg) or saline were injected to mice intraperitoneally. pCPA (100 mg/kg) was injected 24 h before tianeptine or saline treatment when it was combined with tinaeptine (10 mg/kg) or tested alone. The tail-flick latencies and hot-plate reaction times of the mice were measured between 15th and 180th minutes following injections. Tianeptine (10 mg/kg) exhibited a significant antinociceptive activity that could be measured by both tests as compared to groups which were treated with saline or pCPA alone between 15th and 180th min of the observation period. The lower dose of tianeptine (5 mg/kg) or pCPA (100 mg/kg) did not produce any significant changes on tail-flick latency or hot-plate reaction time of the mice. However, pretreatment with pCPA completely blocked the antinociceptive effect induced by tianeptine (10 mg/kg) in both tests used in the present study. Furthermore, tianeptine (10 mg/kg) did not cause any significant impairment effects on rotarod performance of the mice. Our results suggested that tianeptine has a prominent thermal antinociceptive activity in mice and that increased serotonergic activity may be responsible for the analgesic effect of tianeptine.     

Effects of fluoxetine and LY 367265 on tolerance to the analgesic effect of morphine in rats

Morphine is widely used to treat chronic pain, however its utility is hindered by the development of tolerance to its analgesic effects. The aim of this study was to investigate effects of fluoxetine, a specific serotonin (5-HT) reuptake inhibitor, and LY 367265, an inhibitor of the 5-HT transporter and 5-HT2A receptor antagonist, on tolerance induced to the analgesic effect of morphine in rats. The study was carried out on male Wistar Albino rats (weighing 170-190 g). To constitute morphine tolerance, animals received morphine (50 mg/kg; s.c.) once daily for 3 days. After last dose of morphine, injected on day 4, morphine tolerance was evaluated. The analgesic effects of fluoxetine (10 mg/ kg; i.p.), LY 367265 (3 mg/kg; i.p.) and morphine were considered at 30-min intervals by tail-flick and hot-plate tests. The results showed that fluoxetine and LY 367265 significantly attenuated the development and expression of morphine tolerance. The maximal antinociceptive effects were obtained 30 min after administration of fluoxetine and 60 min after administration of LY 367265. In conclusion, we observed that co-injection of morphine with fluoxetine and LY 367265 increased the analgesic effects of morphine and delayed development of tolerance to morphine analgesia.     

Antinociceptive effects of low-intensity extrahigh-frequency electromagnetic radiation

We studied the effect of low-intensity extrahigh-frequency (EHF) electromagnetic radiation (EMR) on changes of behavior phenomena in rats observed under conditions of experimentally induced tonic somatic, visceral, and acute thermal pain. Preliminary irradiation of the animals with EHF EMR was found to exert clear antinociceptive effects. Decreases in the intensity of pain reactions were observed under conditions of both single and repeated irradiation sessions. Neirofiziologiya/Neurophysiology, Vol. 38, No. 4, pp. 331–341, July–August, 2006.     

Action of naloxone on emotionally positive and antinociceptive effects of hypothalamic stimulation in rats

Naloxone (5 mg/kg subcutaneously) failed to effect significantly the reaction of electric self-stimulation in rats with electrodes implanted into lateral hypothalamic area. In 3 rats the analgesic effect manifested in an increase of the threshold of painful vocalization under electrostimulation of the tail was revealed. The antinociceptive effect was abolished with naloxone. Morphine (3 mg/kg) potentiated self-stimulation while naloxone antagonized this action. The role of opiate receptors in effects of self-stimulation and centrally produced analgesia is discussed.     

Radioprotective effect of pyrazolone derivatives]

The intraperitoneal injection of analgin (1000 mg/kg), antipurine (400 mg/kg), amidopyrine (100 mg/kg) 3 hours before the irradiation of mice in a dose of 800 R led to survival of 30 to 45% of the animals (against 12.5% in control) and to increase in the average duration of life of the animals that perished. 80-95% of mice survived the period of "intestinal deaths" (the 7th day after the irradiation) after combined prophylactic use of purasolone derivatives and cystamine before the irradiation of these animals in a dose of 1050 R. The radioprotective effect of pyrasolone derivatives given in therapeutic doses was less pronounced.     

Analgesic properties of a systemically-administered synthetic dipeptide of 5-hydroxytryptophan

Synthetic peptides of 5-hydroxytryptophan (5-HTP), including N-acetyl-5-HTP-5-HTP amide (5-HTP-ACETYL-DP), specifically inhibit the binding of serotonin to serotonin binding protein. 5-HTP-ACETYL-DP also produces a long-lasting, opiate-sensitive analgesia following central, but not systemic administration. The present study evaluated an apolar derivative of 5-HTP dipeptide, N-hexanoyl-5-HTP-5-HTP amide (5-HTP-HEX-DP), for its analgesic properties in rats following systemic administration. 5-HTP-HEX-DP (5–50 mg/kg) significantly increased jump thresholds in a dose-dependent manner with peak analgesia occurring at 2.5 hr after injection, and lasting up to 5 hr. In the tail-flick assay, 5-HTP-HEX-DP (20 mg/kg) produced a significant antinociceptive effect at 1 hr post-injection using both high and low intensity levels of radiant heat. While 5-HTP-HEX-DP and morphine each elicited analgesia following acute administration, chronic (14 days) incremental dosing with 5-HTP-HEX-DP or morphine resulted in persistent analgesia in 5-HTP-HEX-DP-treated animals, and a loss of analgesia in morphine-treated rats. Thus, significant tolerance to morphine, but not 5-HTP-HEX-DP analgesia developed using this protocol. Hence, 5-HTP-HEX-DP is a systemically-active analgesic which fails to develop tolerance when administered daily over 14 days.     

Effects of systemically-administered beta-casomorphin-7 on nociception in rats]

The influence of food-derived heptapeptide beta-casomorphin-7 (beta-CM-7) on pain sensibility of white rats was studied by tail flick test. As shown for doses 10 and 20 mg/kg intraperitoneally, injected beta-CM-7 induced significant analgesia; lower peptide concentration (5 mg/kg) was ineffective. As a whole, there is a significant positive correlation between the intensity of analgesia and the quantity of administered exorphine. These changes of pain sensibility were observed for one hour after injection of heptapeptide; further measurements showed no significant difference of time reaction between control and experimental groups of rats. It was found out that animals with high native level of pain sensibility (4-8 sec) made the main contribution to manifestation of analgesia.