Toshizo Ishikawa

Mild and Moderate Hypothermia Provide Better Protection than a Burst-suppression Dose of Thiopental against Ischemic Spinal Cord Injury in Rabbits

Background: Controversy exists over the efficacy of different methods for protecting the spinal cord against experimental ischemic injury. Therefore, the authors compared the protective effects of thiopental with those of hypothermia (35 degrees Celsius and 32 degrees Celsius) on hindlimb motor functions and histopathology after transient spinal cord ischemia. Methods: Twenty‐seven New Zealand white rabbits were assigned to one of the four groups: a thiopental‐normothermia group (burst‐suppression dose of thiopental; esophageal temperature = 38 degrees Celsius; n = 7), a halothane‐mild hypothermia group (halothane, 1%; esophageal temperature = 35 degrees Celsius; n = 7), a halothane‐moderate hypothermia group (halothane, 1%; esophageal temperature = 32 degrees Celsius; n = 6), and a halothane‐normothermia group (halothane, 1%; esophageal temperature = 38 degrees Celsius; n = 7). The animals were then subjected to 20 min of spinal cord ischemia produced by occlusion of the aorta distal to the origin of left renal artery. Hindlimb motor function was observed for 48 h after reperfusion. Histopathology of the lumbar spinal cord also was examined. Results: All animals in the halothane‐mild hypothermia and halothane‐moderate hypothermia groups were neurologically normal 48 h after ischemia. There was no statistical difference in the final neurologic status and histopathology between the thiopental‐normothermia and halothane‐normothermia groups. However, the final neurologic status and histopathology in both groups were worse than in the halothane‐mild hypothermia or halothane‐moderate hypothermia groups. There was a strong correlation between the final neurologic status and the numbers of normal neurons in the anterior spinal cord. Conclusions: These results suggest that mild and moderate hypothermia protects against ischemic spinal cord injury in rabbits, and a burst‐suppression dose of thiopental does not offer any advantage over halothane.

Central noradrenergic mediation of nitrous oxide-induced analgesia in rats

PurposeAlthough several studies have demonstrated that both supra opiate receptors and spinal α2 adrenoceptors play a mediating role in nitrous oxide(N2O) analgesia, controversy still exists. The present study was undertaken to evaluate further the involvement of noradrenergic (NA) neuronal activity in N2O analgesia by investigating tail-flick latency and supra-and spinal NA levels in rats.MethodsIn an analgesia study, effect of N2O 75% and its modification were evaluated using the tail-flick test in male Wistar rats. Results were expressed as % maximum possible effect (MPE). Modification of N2O analgesia was examined in rats pretreated with either the α2 receptor agonist, clonidine(CLO: 150 μg·kg−1, ip), α2 receptor antagonist, idazoxone(IDZ: 100 μg·kg−1, iv) by lesioning the locus coeruleus (LC) seven days before exposure to N2O, or naloxone (5mg·kg−1, iv). Also, in a NAergic neuronal transmission study, the changes in NA content at LC and spinal cord were determined using HPLC-ECD.ResultsNitrous oxide produced analgesia, % MPE increased to a maximum of 78% at 30min, thereafter declining to 38% at 120min. Clonidine potentiated the analgesic effect of N2O at 120 min (80%). The analgesic effect of N2O was attenuated by IDZ or by LC lesioning, However, naloxone, in a dose sufficient to block morphineinduced analgesia, had no effect. With N2O exposure, NA content was decreased by 52% in the LC and by 20% at spinal cord. With morphine, NA content did not differ from the control group.ConclusionThe data suggest that N2O-induced analgesia is principally mediated by activation of the descending inhibitory NAergic system and/or increased NA release at spinal cord which may lead to presynaptic inhibition of primary afferent neurotransmitter release and hyperpolarize the dorsal horn neurons by α2 receptors.RésuméObjectifBien que plusieurs études aient démontré que les suprarécepteurs opiacés et les récepteurs α2-adrénergiques rachidiens jouent un rôle de médiation dans l’analgésie au protoxyde d’azote (N2O), la controverse persiste. La présente étude a été entreprise pour évaluer plus amplement la participation de l’activité neuronale noradrénergique (NA) dans l’analgésie avec N2O en examinant le temps de latence des coups de queue et les niveaux noradrénergiques des suprarécepteurs et des récepteurs rachidiens.MéthodeDans une étude sur l’analgésie, l’effet du N2O 75 % et des modifications qu’il produit ont été évalués en utilisant la technique du coup de queue chez des rats mâles Wistar. Les résultats ont été exprimés en termes de pourcentage de l’effet maximal possible (EMP). La modification de l’analgésie au N2O a été étudiée chez des rats prétraités avec l’agoniste du récepteur α2, la clonidine (CLO : 150 μg·kg−1, ip), l’antagoniste du récepteur α2, l’idazoxone (IDZ : 100 μg·kg−1, iv) en sectionnant le locus coeruleus (LC) sept jours avant l’exposition au N2O, ou avec du naloxone (5mg·kg−1, iv). Également, dans l’étude de la transmission neuronale noradrénergique, les changements de contenu de noradrénaline dans le LC et dans la moelle épinière ont été déterminés en utilisant la CLHP (Chromatographie liquide à haute performance) et le DCE (détecteur à capture d’électrons).RésultatsLors de l’analgésie produite par le protoxyde d’azote, le pourcentage de l’EMP a augmenté pour atteindre 78% à 30 min, pour décliner par la suite à 38 % à 120 min. La clonidine a potentialisé l’effet analgésique du N2O à 120 min (80%). Leffet analgésique du N2O a été diminué par l’IDZ ou par la section du LC. Cependant, le naloxone, en dose suffisante pour bloquer l’analgésie induite par la morphine, n’a pas eu d’effet. Avec l’exposition au N2O, le contenu de noradrénaline a diminué de 52 % dans le LC et de 20 % à la moelle épinière. Avec la morphine, le contenu de noradrénaline n’a pas été différent de celui du groupe témoin.ConclusionLes données suggèrent que l’analgésie induite par le N2O bénéficie principalement de la médiation de l’activation du système noradrénergique inhibiteur descendant et/ou de la libération accrue de noradrénaline au niveau de la moelle épinière qui peut mener à une inhibition présynaptique de la libération du neurotransmetteur afférent primaire et à l’hyperpolarisation des neurones de la corne supérieure par les récepteurs α2.

The hydroxyl radical scavenger Nicaraven inhibits glutamate release after spinal injury in rats

NEURONAL degeneration after trauma is mediated in part by release of excitatory amino acids (EAAs) and oxygen free radicals (OFR). We evaluated the effect of i.v. treatment with a hydroxyl radical scavenger ((±)-N, N′-propylenedinicotinamide; AVS) and spinal hypothermia (3 3°C) on spinal CSF glutamate release after spinal trauma. In a control group, spinal compression evoked at 1 0 min a significant increase (5-fold) in glutamate which declined over 4 h (2.1-fold). AVS treatment attenuated glutamate release but had no additive effect. These data suggest that this compound can be effective in modulating spinal excitotoxicity resulting from increased OFR synthesis and corresponding potentiation of EAA release.

Sequential changes in cerebral blood flow, early neuropathological consequences and blood-brain barrier disruption following radiofrequency-induced localized hyperthermia in the rat

We investigated the temperature distribution, early histological changes, blood brain barrier (BBB) disruption and sequential changes in cerebral blood flow (CBF) following hyperthermia ranging from 37 to 45 degrees C in a new rat model of radiofrequency-induced localized cerebral hyperthermia. Significant histological changes and BBB disruption were observed in brain regions heated to 43 degrees C and above. In the cortex heated to 41 degrees C, the CBF doubled 20 min after hyperthermia induction, and then returned gradually to the pre-hyperthermic level. In the cortex heated to 43 degrees C, the CBF increased to 134% of the baseline level 10 min after hyperthermia induction, and then fell gradually to reach its minimum level (31% of the baseline level). In the cortex heated to 45 degrees C, the CBF decreased immediately after hyperthermia induction to reach 10% of the baseline level. The results indicate that hyperthermia-induced cellular injury in the central nervous system is associated with cerebral ischaemia and the threshold temperature for such injury is 43 degrees C. This model is useful for investigating the effects of hyperthermia on various cerebral functions and the CBF changes demonstrated in the present study may provide key information for the analysis of other cerebral functions.

Technique of selective spinal cord cooling in rat : methodology and application

In a number of interventions, it is desirable to be able to produce a rapid but readily reversible change in spinal cord temperature (SCT) without altering general body temperature and to maintain this selective spinal cord hypothermia stable for an extended interval. To accomplish this, we developed a technique of subcutaneous perfusion cooling in rat. This was accomplished by constructing a copper heat exchanger which was readily implanted into subcutaneous space overlying the upper thoracic to upper sacral spinal segments. The heat exchanger was then perfused with fluid from an external temperature bath maintained at (8 degrees C) at a perfusion rate of 100 ml/min. The temperature of the heat exchanger was controlled by regulating the pump with a feed back controller driven by a thermocouple placed percutaneously into the paraspinal musculature. A series of studies were performed to demonstrate the characteristics and utility of this cooling technique. Lowering the pump set point to 24 degrees C resulted in a fall in the intrathecal temperature (ITT) to 27 +/- 0.3 degrees C within 15 min with no significant changes observed in rectal temperature (37.5- > 37.2 degrees C). Change in intrathecal temperature showed a highly significant correlation with changes in paravertebral muscle temperature (r = 0.977). The hypothermic state could be readily maintained for extended intervals up to 5 h and an underbody heating pad was used to maintain rectal temperature between 35-36.5 degrees C. Lowering the ITT from 37 degrees C-27 degrees C evoked a temperature-dependent increase in the latency of precooling spinal somatosensory evoked potentials (SSEPs) with the highest sensitivity observed in postsynaptic components. Returning the set point temperature back to 37 degrees C produced a rapid recovery of the SSEPs latencies. Consistent with previously published data, selective spinal cord hypothermia (27 degrees C) provided complete protection against otherwise injurious interval of normothermic ischemia produced by balloon occlusion of the descending aorta. This technique provides a simple, relatively non-invasive and reliable experimental tool for studying the effect of selective, acute and/or prolonged spinal cord hypothermia.

Modification of the relationship between cerebral metabolism, blood flow, and electroencephalogram by stimulation during anesthesia in the dog.

The effects of stimulation of the sciatic nerve for 5 min on the cerebral metabolic rate for oxygen (CMRO2), cerebral blood flow (CBF) and EEG were investigated in anesthetized dogs. With halothane, 0.5 and 0.9 per cent, CMRO2 maximally increased by 19 and 20 per cent at 1 min with EEG activation, and CBF by 17 and 43 per cent, respectively. With halothane, 1.4 per cent, CMRO2 and EEG remained unchanged, but mean CBF increased by 30 per cent for 5 min. With methoxyflurane, 0.12 and 0.25 per cent, CMRO2 increased by 16 and 15 per cent at 1 min with EEG activation, and CBF by 23 and 26 per cent, respectively. With methoxyflurane, 0.38 percent, CMRO2 and EEG remained unchanged, but mean CBF increased by 9 per cent for 5 min. With morphine, 0.5 and 1.5 mg/kg, CMRO2 increased by 15 and 17 per cent at 1 min with EEG activation, and CBF by 25 and 21 per cent, respectively. With morphine, 1.5 mg/kg, plus nitrous oxide, 60 per cent, CMRO2 and CBF increased by 19 and 39 per cent at 1 min with EEG activation, and mean CBF by 24 per cent for 5 min. In all instances where EEG was activated it was attenuated with time during stimulation and was associated with a less pronounced or insignificant increase in CMRO2. These results suggest that the coupling of CMRO2 and EEG was maintained in all anesthetic circumstances, but the coupling of CMRO2 and CBF varied with individual anesthetic doses.

Differential effects of lidocaine and mexiletine on relaxations to ATP-sensitive K+ channel openers in rat aortas.

BACKGROUND In cardiac myocytes, lidocaine reduces but mexiletine increases adenosine triphosphate (ATP)-sensitive K+ currents, suggesting that these class Ib antiarrhythmic drugs may differentially modify the activity of ATP-sensitive K+ channels. The effects of lidocaine and mexiletine on arterial relaxations induced by K+ channel openers have not been studied. Therefore, the current study was designed to evaluate whether lidocaine and mexiletine may produce changes in relaxations to the ATP-sensitive K+ channel openers cromakalim and pinacidil in isolated rat thoracic aortas. METHODS Rings of rat thoracic aortas without endothelia were suspended for isometric force recording. Concentration-response curves were obtained in a cumulative fashion. During submaximal contractions to phenylephrine (3 x 10(-7) M), relaxations to cromakalim (10(-7) to 3 x 10(-5) M), pinacidil (10(-7) to 3 x 10(-5) M), or diltiazem (10(-7) to 3 x 10(-4) M) were obtained. Lidocaine (10(-5) to 3 x 10(-4) M), mexiletine (10(-5) to 10(-4) M) or glibenclamide (5 x 10(-6) M) was applied 15 min before addition of phenylephrine. RESULTS During contractions to phenylephrine, cromakalim and pinacidil induced concentration-dependent relaxations. A selective ATP-sensitive K+ channel antagonist, glibenclamide (5 x 10(-6) M), abolished these relaxations, whereas it did not alter relaxations to a voltage-dependent Ca2+ channel inhibitor, diltiazem (10(-7) to 3 x 10(-4) M). Lidocaine (more than 10(-5) M) significantly reduced relaxations to cromakalim or pinacidil in a concentration-dependent fashion, whereas lidocaine (3 x 10(-4) M) did not affect relaxations to diltiazem. In contrast, mexiletine (more than 10(-5) M) significantly augmented relaxations to cromakalim or pinacidil. Glibenclamide (5 x 10(-6) M) abolished relaxations to cromakalim or pinacidil in arteries treated with mexiletine (10(-4) M). CONCLUSIONS These results suggest that lidocaine impairs but mexiletine augments vasodilation mediated by ATP-sensitive K+ channels in smooth muscle cells.

Hypothermia prevents biphasic glutamate release and corresponding neuronal degeneration after transient spinal cord ischemia in the rat.

Abstract1. Spinal cord ischemia evoked a biphasic increase in CSF-Glu during 20 min of ischemia (40%) and at 2 hr after reperfusion (70%) in the nontreated group that was attenuated by all treated groups. But MK-801(15 μg i.t.) did not affect the increased Glu at 2 hr (80%).2. The argyrophilia observed in laminae II–V at 8 hr after reperfusion was attenuated by hypothermia (33°C) and combination with MK-801, but the attenuation was less with MK-801.3. Mild hypothermia attenuated the biphasic increase in CSF-Glu and corresponding development of neuronal damage after spinal cord ischemia.4. Mild hypothermia with NMDA antagonism did not yield any further effects, suggesting that hypothermia itself plays a pivotal role in the protection.

Mild hypothermia inhibits IL‐10 production in peripheral blood mononuclear cells

Background:  Hypothermia is often associated with compromised host defenses and infections. Deterioration of immune functions related to hypothermia have been investigated, but the involvement of cytokines in host defense mechanisms and in infection remains unclear. Therefore, we determined whether mild hypothermia affects the production of several types of cytokines in peripheral blood mononuclear cells (PBMCs), and the balance between pro‐inflammatory and anti‐inflammatory states.

Mild hypothermia promotes pro-inflammatory cytokine production in monocytes.

Hypothermia is often associated with compromised host defenses and infection. Deteriorations of immune functions related to hypothermia have been investigated, but the involvement of cytokines in host defense mechanisms and in infection remains unclear. We have previously shown that mild hypothermia modifies cytokine production by peripheral blood mononuclear cells. In this study, the effects of hypothermia on the monocytic production of several cytokines and nitric oxide (NO) were determined. Monocytes obtained from 10 healthy humans were cultured with lipopolysaccharide (LPS) under hypothermic (33°C) or normothermic (37°C) conditions for 48 hours. We performed flow cytometric analysis for simultaneous measurement of interleukin (IL)-8, IL-1β, IL-6, IL-10, IL-12p70, and tumor necrosis factor (TNF)-α in culture supernatants. NO production was quantified as accumulation of nitrite in the medium by a colorimetric assay. Compared with normothermia, mild hypothermia raised the levels of IL-1β, IL-6, IL-12p70, and TNF-α produced by monocytes stimulated with LPS. On calculating the ratios of these elevated cytokines to IL-10, however, only IL-12p70/IL-10 and TNF-α/IL-10 ratios were significantly elevated under hypothermic conditions. In contrast, hypothermia did not affect NO production. This study demonstrates that mild hypothermia affects the balance of cytokines produced by monocytes, leading to a pro-inflammatory state. Specifically, monocytic IL-12 and TNF-α appear to be involved in the immune alterations observed in mild hypothermia. However, the clinical significance of these phenomena remains to be clarified.