Akiyoshi Namiki

Formalin-induced release of excitatory amino acids in the skin of the rat hindpaw

Application of glutamate to skin evokes pain-related behaviors [S.M. Carlton, G.L. Hargett, R.E. Coggeshall, Localization and activation of glutamate receptors in unmyelinated axons of rat glabrous skin, Neurosci. Lett., 197 (1995) 25-28; D.L. Jackson, C.B. Graff, J.D. Richardson, K.M. Hargreaves, Glutamate participates in the peripheral modulation of thermal hyperalgesia in rats, Eur. J. Pharmacol., 284 (1995) 321-325.] and peripherally-administered glutamate antagonists can prevent the nociception produced by inflammation [E.M. Davidson, R.E. Coggeshall, S.M. Carlton, Peripheral NMDA and non-NMDA glutamate receptors contribute to nociceptive behaviors in the rat formalin test, NeuroReport, 8 (1997) 941-946; Jackson et al., 1995.] In this study, the concentrations of glutamate and aspartate in the plantar of the rat hindpaws were measured before and after the subcutaneous administration of formalin. Increases in glutamate and aspartate concentrations were observed on the ipsilateral side, but not on the contralateral side, to the injection. This shows that nociception and inflammation caused by formalin injection induces the release of peripheral glutamate and aspartate, which would contribute to nociception and inflammatory pain.

Propofol Improves Functional and Metabolic Recovery in Ischemic Reperfused Isolated Rat Hearts

Propofol attenuates mechanical dysfunction, metabolic derangement, and lipid peroxidation by exogenous administration of H2 O2 in the Langendorff rat heart.In this study, we examined the effects of propofol on mechanical and metabolic changes, as well as on lipid peroxidation induced by ischemia-reperfusion, in isolated, working rat hearts. Rat hearts (in control-modified Krebs-Henseleit bicarbonate buffer) were treated with two doses (25 micro M and 50 micro M) of propofol in an intralipid vehicle. In the first protocol, propofol was administered during the preischemic and reperfusion period, whereas in the second, it was only administered during the reperfusion period. Ischemia (15 min) decreased peak aortic pressure (PAOP), heart rate (HR), rate-pressure product (RPP), coronary flow (CF), and tissue concentrations of adenosine triphosphate (ATP) and creatine phosphate. After postischemic reperfusion (20 min), the CF and tissue concentration of ATP recovered incompletely; however, PAOP, HR, and RPP did not. Ischemia-reperfusion also increased the tissue concentration of malondialdehyde (MDA). In both protocols, both doses of propofol enhanced recovery of PAOP, HR, RPP, CF, and tissue concentration of ATP during reperfusion, and inhibited the tissue accumulation of MDA. These results indicate that propofol improves recovery of mechanical function and the energy state in ischemic reperfused isolated rat hearts, and the mechanism may involve the reduction of lipid peroxidation during postischemic reperfusion. Implications: We evaluated the possible cardioprotective effects of propofol in isolated, working rat hearts subjected to 15-min ischemia, followed by 20-min reperfusion. We observed that propofol attenuated mechanical dysfunction, metabolic derangement, and lipid peroxidation during reperfusion. This latter finding seems to be one mechanism for cardioprotective effects of propofol. (Anesth Analg 1998;86:252-8)

Differential Effects of Propofol and Sevoflurane on Heart Rate Variability

Background Propofol is reported to reduce both sympathetic and parasympathetic tone; however, it is not clear whether the changes in heart rate variability are associated with depth of anesthesia. The purposes of the present study were (1) to evaluate the changes in heart rate variability at different depths of hypnosis and (2) to compare the effects of propofol on heart rate variability with that of sevoflurane. Methods Thirty patients were randomly allocated into the propofol or sevoflurane for induction of anesthesia. The depth of hypnosis was monitored by the Bispectral Index (BIS). Spectral analysis of heart rate variability using a maximum-entropy method resulted in a characteristic power spectrum with two main regions, a high frequency (HF) and a low frequency (LF). Hemodynamics, entropy, LF, HF, and LF/HF were monitored when the patients were awake and after induction of anesthesia. Results Both propofol and sevoflurane decreased blood pressure in a BIS-dependent manner, whereas heart rate showed no significant changes during the study period. In the propofol group, entropy and HF decreased with a reduction in the BIS value. Although LF decreased after induction of anesthesia, propofol caused no further decrease in LF in spite of a reduction in the BIS value. In the sevoflurane group, LF decreased with a reduction in the BIS value. Entropy and HF decreased after induction of anesthesia (BIS at 80); however, no further decreases were observed in spite of a reduction in the BIS value. Conclusions Induction of anesthesia with propofol decreased blood pressure, entropy, and HF in a BIS-dependent manner, indicating that propofol reduces cardiac parasympathetic tone depending on the depth of hypnosis. Conversely, sevoflurane did not show the BIS-dependent decreases in heart rate, blood pressure, HF, and entropy, indicating that sevoflurane has little or no effect on cardiac parasympathetic tone.

Comparison between celiac plexus block and morphine treatment on quality of life in patients with pancreatic cancer pain

Twenty-one patients with pancreatic cancer pain were studied to evaluate the effectiveness of celiac plexus block (CPB) on pain relief and quality of life (QOL), compared to the traditional NSAID-morphine treatment. The criteria were morphine consumption, visual analogue pain scale (VAS), performance status (PS) determined by medical and nursing staffs, and answers to QOL questionnaires. Morphine consumption, VAS, PS, and self-assessed QOL scores were taken when the administration of morphine was necessary for pain relief and those scores were used as control. Morphine consumption and the VAS score were recorded at regular weekly intervals and the PS and QOL scores were measured every 2 weeks thereafter. CPB was performed within 2-3 days after the control measurement. The VAS scores of the patients receiving CPB (n = 10) were statistically lower for the first 4 weeks after the procedure than those of the patients receiving the standard NSAID-morphine treatment (n = 11) during the same time period after the control measurement. Morphine consumption was significantly lower in weeks 4-7 (inclusive) following the procedure in the CPB group and continued to be lower thereafter, though not significantly so. Although the PS score slightly improved at the 2nd week after CPB, it was not improved by the start of the NSAID-morphine treatment. Self-assessed QOL scores did not ameliorate statistically after CPB; however, they did deteriorate remarkably in the patients treated only with morphine-NSAID during their survival periods, while they deteriorated only slightly in the CPB group. There were fewer side effects after CPB. These results indicate CPB does not directly improve QOL in patients with pancreatic cancer pain, but it may prevent deterioration in QOL by the long-lasting analgesic effect, limitation of side effects and the reduction of morphine consumption, compared to treatment only with NSAID-morphine.

Experimental incision-induced pain in human skin: effects of systemic lidocaine on flare formation and hyperalgesia

&NA; In order to try to gain a better understanding of the mechanisms of post‐operative pain, this study was designed to psychophysically determine physiological and pharmacological characteristics of experimental pain induced by a 4‐mm‐long incision through the skin, fascia and muscle in the volar forearm of humans. In experiment 1, the subjects (n=8) were administered lidocaine systemically (a bolus injection of 2 mg/kg for a period of 5 min followed by an intravenous infusion of 2 mg/kg/h for another 40 min), and then the incision was made. In experiment 2, cumulative doses of lidocaine (0.5–2 mg/kg) were systemically injected in the subjects (n=8) 30 min after the incision had been made, when primary and secondary hyperalgesia had fully developed. Spontaneous pain was assessed using the visual analog scale (VAS). Primary hyperalgesia was defined as mechanical pain thresholds to von Frey hair stimuli (from 7 to 151 mN) in the injured area. The area of secondary hyperalgesia to punctate mechanical stimuli was assessed using a rigid von Frey hair (151 mN). Flare formation was assessed in the first experiment using a laser doppler imager (LDI). Pain perception was maximal when the incision was made and then rapidly disappeared within 30 min after the incision had been made. Primary hyperalgesia was apparent at 15 min after the incision had been made and remained for 2 days. The incision resulted in a relatively large area of flare formation immediately after the incision had been made. The area of flare began to shrink within 15 min and was limited to a small area around the injured area at 30 min after incision. Secondary hyperalgesia was apparent at 30 min after incision and persisted for 3 h after incision and then gradually disappeared over the next 3 h. In experiment 1, pre‐traumatic treatment with systemic lidocaine suppressed primary hyperalgesia only during the first 1 h after the incision had been made. The lidocaine suppressed the development of flare formation without affecting the pain rating when the incision was made. The development of secondary hyperalgesia continued to be suppressed after completion of the lidocaine infusion. In experiment 2, post‐traumatic treatment with lidocaine temporarily suppressed primary as well as secondary hyperalgesia that had fully developed; however, the primary and secondary hyperalgesia again became apparent after completion of the lidocaine administration. These findings suggest that pre‐traumatic treatment with lidocaine reduces the excessive inputs from the injured peripheral nerves, thus suppressing development of flare formation and secondary hyperalgesia through peripheral and central mechanisms, respectively. Pre‐traumatic treatment with lidocaine would temporarily stabilize the sensitized nerves in the injured area, but the nerves would be sensitized after completion of the administration. Post‐traumatic treatment with lidocaine reduced primary and secondary hyperalgesia that had fully developed. However, the finding that the suppressive effect of lidocaine on secondary hyperalgesia was temporary suggests that the development and maintenance of secondary hyperalgesia are caused by different mechanisms.

Calcium channels--basic aspects of their structure, function and gene encoding; anesthetic action on the channels--a review.

PurposeTo review recent findings concerning Ca2+ channel subtype/structureAunction from electrophysiological and molecular biological studies and to explain Ca2+ channel diseases and the actions of anesthetics on Ca2+ channels.SourceThe information was obtained from articles published recently and from our published work.Principal findingsL’oltage-dependent Ca2+ channels serve as one of the important mechanisms for Ca2+ influx into the cells, enabling the regulation of intracellular concentration of free Ca2+. Recent advances both in electrophysiology and in molecular biology have made it possible to observe channel activity directly and to investigate channel functions at molecular levels. The Ca2+ channel can be divided into subtypes according to electrophysiological characteristics, and each subtype has its own gene. The L-type Ca2+ channel is the target of a large number of clinically important drugs, especially dihydropyridines, and binding sites of Ca2+ antagonists have been clarified. The effects of various kinds of anesthetics in a variety of cell types have been demonstrated, and some clinical effects of anesthetics can be explained by the effects on Ca2+ channels. It has recently become apparent that some hereditary diseases such as hypokalemic periodic paralysis result from calcium channelopathies.ConclusionRecent advances both in electrophysiology and in molecular biology have made it possible to clarify the Ca2+ channel structures, functions, genes, and the anesthetic actions on the channels in detail. The effects of anesthetics on the Ca2+ channels either of patients with hereditary channelopathies or using gene mutation techniques are left to be discovered.RésuméObjectifPasser en revue les découvertes récentes concernant le sous-type, la structure et la fonction du canal Ca2+ à partir des études électrophysiologiques et biologiques moléculaires et expliquer les lésions des canaux Ca2+ et les actions des anesthésiques sur ces canaux.SourceL’information provient d’articles publiés récemment et de nos travaux publiés.Constatations principalesLes canaux Ca2+ voltage-dépendants sont l’un des importants mécanismes pour le flux entrant de Ca2+ dans les cellules, ce qui facilite la régulation de la concentration intracellulaire de Ca2+ libre. Les progrès récents en électrophysiologie et en biologie moléculaire ont permis d’observer directement l’activité des canaux et d’étudier leurs fonctions au niveau moléculaire. Les canaux Ca2+ peuvent être divisés en sous-types selon les caractéristiques électrophysiologiques et chaque sous-type a son propre gène. Le type L de canal Ca2+ est la cible d’un grand nombre de médicaments importants en clinique, spécialement les dihydropyridines, et les antagonistes des sites de liaison du Ca2+ ont été mis en évidence. Les effets de différentes classes d’anesthésiques dans une diversité de types de cellules ont été démontrés et certains effets cliniques des anesthésiques peuvent être expliqués par les effets sur les canaux Ca2+. Récemment, il est devenu clair que certaines affections héréditaires, comme la paralysie périodique hypokaliémique, résulte de pathologies des canaux calciques.ConclusionLes découvertes récentes en électrophysiologie et en biologie moléculaire ont permis de clarifier les structures, fonctions et gènes des canaux Ca2+ et de fournir des détails sur les actions des anesthésiques sur les canaux. Il reste à découvrir les effets des anesthésiques sur les canaux Ca2+ des patients atteints de pathologies héréditaires des canaux calciques ou à utiliser des techniques de mutation génétique.

Different Mechanisms of Development and Maintenance of Experimental Incision-induced Hyperalgesia in Human Skin

BACKGROUND To determine the mechanisms of postoperative pain, the effects of local anesthesia on development and maintenance of surgical incision-induced hyperalgesia were evaluated in a crossover, double-blinded, placebo-controlled human study using 17 subjects. METHODS An experimental 4-mm-long incision through skin, fascia, and muscle was made in the volar forearm of each subject. In experiment 1, 1% lidocaine or saline in a volume of 0.2 ml was subcutaneously injected into the incision site pretraumatically and posttraumatically. In experiment 2, a 5-cm-long strip of skin was subcutaneously injected with 0.2 ml of 1% lidocaine near the incision site pretraumatically and posttraumatically. Flare, spontaneous pain, and primary and secondary hyperalgesia to punctate mechanical stimuli were assessed after the incision had been made. RESULTS Pretraumatic lidocaine injection prevented the occurrence of spontaneous pain and development of flare formation that was found surrounding the incision site immediately (1 min) after the incision had been made. The lidocaine suppressed primary hyperalgesia more effectively than did posttraumatic block, but only for the first 4 h after the incision. The preincision block prevented development of secondary hyperalgesia, whereas posttraumatic block did not significantly affect the fully developed secondary hyperalgesia. The area of flare formation and the area of secondary hyperalgesia did not extend over the strip of the skin that had been pretraumatically anesthetized, whereas the posttraumatic block did not significantly reduce the area of fully developed secondary hyperalgesia. CONCLUSIONS Pretraumatic injection of lidocaine reduces primary hyperalgesia more effectively than does posttraumatic injection, but only for a short period after incision. The spread of secondary hyperalgesia is mediated peripheral nerve fibers, but when secondary hyperalgesia has fully developed, it becomes less dependent on or even independent of peripheral neural activity originating from the injured site.

Fetal and postnatal development of Ca2+ transients and Ca2+ sparks in rat cardiomyocytes

OBJECTIVE The aim of this study was to characterize the spatio-temporal dynamics of [Ca(2+)](i) in rat heart in the fetal and neonatal periods. METHODS Using confocal scanning laser microscopy and the Ca(2+) indicator fluo-3, we investigated Ca(2+) transients and Ca(2+) sparks in single ventricular myocytes freshly isolated from rat fetuses and neonates. T-tubules were labeled with a membrane-selective dye (di-8-ANEPPS). Spatial association of dihydropyridine receptors (DHPR) and ryanodine receptors (RyR) was also examined by double-labeling immunofluorescence. RESULTS Ca(2+) transients in the fetal myocytes were characterized by slower upstroke and decay of [Ca(2+)](i) compared to those in adult myocytes. The magnitude of fetal Ca(2+) transients was decreased after application of ryanodine (1 microM) or thapsigargin (1 microM). However, Ca(2+) sparks were rarely detected in the fetal myocytes. Frequent ignition of Ca(2+) sparks was established in the 6-9-day neonatal period, and was predominantly observed in the subsarcolemmal region. The developmental change in Ca(2+) sparks coincided with development of the t-tubule network. The immunofluorescence study revealed colocalization of DHPR and RyR in the postnatal period, which was, however, not observed in the fetal period. In the adult myocytes, Ca(2+) sparks disappeared after disruption of t-tubules by glycerol incubation (840 mM). CONCLUSIONS The sarcoplasmic reticulum (SR) of rat ventricular myocytes already functions early in the fetal period. However, ignition of Ca(2+) sparks depends on postnatal t-tubule formation and resultant colocalization of DHPR and RyR.

Peripheral nitric oxide in carrageenan-induced inflammation

Recent studies have suggested that nitric oxide (NO) peripherally produced by different nitric oxide synthase (NOS) isoforms contributes to edema formation and development of hyperalgesia. The present study was designed to examine the effects of NOS isoforms on NO release in carrageenan-induced inflammation at various time points. A microdialysis probe was implanted subcutaneously into the glabrous skin of hindpaws of Sprague-Dawley rats under pentobarbital anesthesia. After sample collection to obtain the basal level of the total amount of nitrite and nitrate (NO2-/NO3-), modified Ringer solution, a non-selective NOS inhibitor, NG monomethyl-L-arginine acetate (L-NMMA), or an iNOS inhibitor, aminoguanidine hemisulfate (AG) was perfused through the microdialysis probe. 2 mg of carrageenan was injected into the plantar surface of the probe-implanted hindpaw. Carrageenan was also injected in rats that had undergone sciatic nerve sectioning. Carrageenan significantly increased the dialysate concentrations of NO2-/NO3- for more than 8 h. L-NMMA suppressed the carrageenan-induced increase in NO2-/NO3- concentration. Although AG did not suppress the increase in NO2-/NO3- for the first 2 h after carrageenan injection, significant suppression of the increase in NO2-/NO3- was observed from 2.5 h after carrageenan injection. In the rats in which the sciatic nerves had been denervated, the increases in concentrations of NO2-/NO3- were completely suppressed up to 3 h and partially suppressed 4.5-8 h after carrageenan injection. The results of the current study show that carrageenan induces peripheral release of NO, the production of which is mediated by nNOS in the early phase and by both nNOS and iNOS in the late phase of carrageenan-induced inflammation.

Bone cancer increases transient receptor potential vanilloid subfamily 1 expression within distinct subpopulations of dorsal root ganglion neurons.

Bone cancer pain has a strong impact on the quality of life of patients but is difficult to treat. Therefore, the mechanisms of bone cancer pain require elucidation for the purpose of development of new therapeutics. A recent study showed that activation of transient receptor potential vanilloid subfamily 1 (TRPV1) was involved in bone cancer pain. In this study, we re-evaluated the analgesic effects of pharmacological blockade of TRPV1 using the potent TRPV1 antagonist 5-iodoresiniferatoxin (I-RTX) and examined whether bone cancer can change TRPV1 expression and distribution in the primary sensory neurons in a mouse model of bone cancer pain. Implantation of osteosarcoma into the femur induced ongoing and movement-evoked bone cancer-related pain behaviors. These behaviors were significantly reduced by i.p. administration of I-RTX, compared with vehicle. Western blot and reverse transcription-polymerase chain reaction (RT-PCR) analyses revealed that TRPV1 level was significantly increased in dorsal root ganglions (DRGs) ipsilateral to sarcoma implantation. Immunohistochemical analysis showed that implantation of osteosarcoma induced not only an increase in the percentage of TRPV1-positive neurons among DRG neurons (24.3+/-1.3% in sham mice and 31.2+/-1.3% in mice with osteosarcoma implantation, P<0.05) but also an overall shift in the distribution of area of profiles to the right. Colocalization study showed that the percentages of colocalization of TRPV1 with neurofilament 200 kD (NF200) and calcitonin gene-related peptide (CGRP) but not isolectin B4 (IB4) among DRG neurons in mice with osteosarcoma implantation were increased compared with those in sham mice (from 0.8+/-0.1% to 2.1+/-0.3% for TRPV1 and NF200 and from 21.1+/-1.3% to 26.5+/-0.2% for TRPV1 and CGRP). In conclusion, TRPV1 activation plays a critical role in the generation of bone cancer pain, and bone cancer increases TRPV1 expression within distinct subpopulation of DRG neurons. These findings may lead to novel strategies for the treatment of bone cancer pain.