埼玉医科大学雑誌 第28巻第4号 (2001年10月) 179-183頁 (C) 2001 The Medical Society of Saitama Medical School
Halothane Attenuates Excitation and Inhibition of Dorsal Horn Wide Dynamic Range Neuronal Activity Induced by Intraarterial Injection of Bradykinin in Spinal Cord-Transected Cats
Yutaka MIZUMOTO, Hiroshi NAGASAKA ＊
Department of Anesthesiology, Saitama Medical School, Moroyama, Saitama
350-0495, Japan, ＊Department of Anesthesiology, Meikai University
School of Dentistry, Sakado, Saitama 350-0283, Japan
Spinal dorsal horn wide dynamic range (WDR) neurons can be excitated by low
intensity innocuous, as well as high-intensity noxious stimuli applied to specific
regions of the body (the excitatory receptive fields). These cells are known
to be involved in the central processing of pain-related information. It is
well known that anesthetic agents generally have depressant effects on the excitatory
response of these spinal WDR neurons evoked by noxious stimulation1-3).
WDR neurons are also known to possess widespread cutaneous inhibitory receptive fields4-7) depending on the innocuous or nociceptive nature of the applied stimulus. However, the role of the abovementioned inhibitory mechanism has not been completely investigated. The effect of anesthetic agents on the inhibitory WDR neuronal activity by noxious stimulation is also not clearly understood.
With regard to the effects of halothane on spinal dorsal horn WDR neurons, previous studies reported that halothane depresses the excitation of WDR neurons induced by noxious stimulation3,8-10). This depressant effect is thought to be mediated at a spinal level, as demonstrated in experiments using systemically-administered halothane in spinal animals, in which the descending inhibitory control of spinal dorsal horn neurons was eliminated. Although several studies have examined the effect of halothane on spinal WDR neurons, to our knowledge, none examined the effects of halothane on the propriospinal inhibitory response of WDR neurons to noxious or non-noxious stimuli.
In the present study, we investigated the effects of halothane on WDR propriospinal excitatory and inhibitory mechanisms induced by bradykinin (BK) injection as a noxious test stimulus, in decerebrate and spinal cord-transected cats.
|Materials and Methods|
Twenty mongrel cats of either sex weighing 2.5 to 4.5 kg were used in our
experiments. The experimental protocol was approved by the Institutional Animal
Care and Use Committee. A detailed description of procedure has been reported
previously11). Halothane, nitrous oxide and oxygen anesthesia were
used for tracheostomy, ligation of the right common carotid artery, and cannulation
of the left common carotid artery to monitor the arterial blood pressure and
of the left external jugular vein for intravenous administration of fluid and
drugs. The left and right femoral arteries were also cannulated for administration
of BK (10 μg･ml-1 in saline). A continuous drip infusion of pancronium
bromide was used for muscle relaxation and the animal was mechanically ventilated
throughout the experiment.
After fixation to a stereotaxic apparatus, a lumbar laminectomy was performed. The dura was removed to expose the spinal cord, and the cord was bathed with 36℃ liquid paraffin to control the temperature and prevent tissue dryness. Carotid artery pressure was recorded continuously on a polygraph paper and systolic blood pressure was maintained above 100 mmHg. Data were excluded from analysis when systolic blood pressure was below 100 mmHg. Ventilation was controlled to keep the expiratory CO2 concentration at about 4%. Rectal temperature was maintained at 36 to 37℃, and when necessary, the body was warmed with an infrared lamp. Lactated Ringer solution was administered at a rate of 10 ml･kg-1･hr-1 through the intravenous catheter. Decerebration was performed at the intracollicular level of the midbrain and the spinal cord was transected at level L1-2. Following completion of the surgical procedure, anesthesia was discontinued and the animals were ventilated using 100% oxygen.
Two hours later, the response of WDR neurons was determined by extracellular recording from the left side of the spinal cord. Cells with excitatory receptive field in the left hindlimb were identified and selected for experiment. The WDR neurons were identified by the evoked response to various peripheral stimuli including: air puff, light touch, light forceps pinch, and strong forceps squeeze. Neuronal activity was expressed as the number of impulses per 5 second and recorded on the polygraph. The protocol of halothane inhalation is shown in Fig. 1. Changes in the evoked response induced by halothane inhalation were expressed as percentage of the control values, and differences between control and post-inhalation values were analyzed statistically using the Student's paired t-test. All data were expressed as mean ± standard error of the mean (SEM). A P value less than 0.05 denoted the presence of a statistically significant difference.
|Fig. 1. The protocol used for halothane inhalation.|
Innocuous cutaneous stimuli (light touch) were routinely tested and found
to have no inhibitory effects on both hindlimbs. When 10 μg of BK (used as the
noxious stimulus) was injected into the femoral artery ipsilateral to the recording
sites, all (100%) WDR neurons exhibited excitatory responses. Halothane at 1.0%,
but not at 0.2% or 0.5% significantly depressed the excitatory neuronal activity
in WDR neurons (Fig. 2). When 10 μg of BK was injected into the femoral artery
ipsilateral to the recording sites, 13 of 13 (100%) WDR neurons showed excitatory
responses. Twenty minutes later, after contralateral BK injection, 7 of 13 (54%)
WDR neurons showed inhibitory responses, and 6 (46%) showed no response. Fig.
3 shows that BK injection into the contralateral (right) femoral artery resulted
in a significant reduction of discharge at one-minute period. These inhibitory
neuronal activities in WDR neurons were significantly depressed by 0.2%, 0.5%
and 1.0% halothane (Fig. 4).
|Fig. 2. Effects of halothane on excitation of dorsal horn WDR neurons induced by ipsilateral injection of BK into the recording site. Data from 7 neurons in each group. *P＜0.05 compared with the control.|
|Fig. 3. Comparison of effects of ipsilateral and contralateral BK injection. Time-course of the effects of BK injection on seven WDR neurons that were inhibited by contralateral BK injection (right) and ipsilateral BK injection (left). **P＜ 0.01, *P＜0.05 compared with the respective neuronal activity before BK injection.|
|Fig. 4. Effects of halothane on inhibition of dorsal horn WDR neuron activity induced by contralateral injection of BK into the recording site. (n＝ 7 ) **P＜0.01 compared with the control.|
1) Kitahata LM, Taub A, Sato I. Lamina-specific sup-pression of dorsal horn
unit activity by nitrous oxide and by hyperventilation. J Pharmacol Exp Ther
2) Kitahata LM, Taub A, Kosaka Y. Lamina-specific sup-pression of dorsal horn unit activity by ketamine hydrochloride. Anesthesiology 1973;38:4-11.
3) Kitahata LM, Ghazi-Saidi K, Yamashita M, Kosaka Y, Bonikos C, Taub A. The depressant effect of halothane and evoked activity of dorsal horn cells: Lamina specificity, time course, and dose dependent. J Pharmacol Exp Ther 1975;195:515-21.
4) Le Bars D, Dickenson AH, Besson JB. Diffuse noxious inhibitory controls (DNIC). I. Effects on dorsal horn convergent neurons in the rat. Pain 1979;6:283-304.
5) Gerhart KD, Yezierski RP, Giesler GJ Jr, Willis W. Inhibitory receptive fields of primates spinothalamic tract cells. J Neurophysiol 1981;46:1309-25.
6) Fitzgerald M. The contralateral input to the dorsal horn of the spinal cord in the decerebrate spinal rat. Brain Res 1982;236:275-87.
7) Kanui TI. Thermal inhibition of nociceptor-driven spinal cord neurons in the rat. Pain 1985;21:231-40.
8) de Jong RH, Robles R, Morikawa KI. Action of halothane and nitrous oxide on dorsal horn neurons ("the spinal gate"). Anesthesiology 1969;31:205-12.
9) Namiki A, Collins JG, Kitahata LM, Kikuchi H, Honma E, Thalhammer JG. Effects of halothane on spinal neuronal responses to graded noxious heat stimulation in the cat. Anesthesiology 1980;53:475-80.
10) Nagasaka H, Nakamura S, Genda T, Miyazaki T, Aikawa K, Matsumoto N, Matsumoto I, Hori T, Sato I. Effects of halothane on spinal dorsal horn WDR neuronal ativity in cats. Masui 1991;40:1096-101 (in Japanese with English abstract).
11) Nagasaka H , Nagasaka I, Sato I, Matsumoto N, Matsumoto I, Hori T. The effects of ketamine on the excitation and inhibition of dorsal horn WDR neuronal activity induced by bradykinin injection into the femoral artery in cats after spinal cord transection. Anesthesiology 1993;78:722-32.
12) Nagasaka H, Yaksh TL. Pharmacology of intrathecal adrenergic agonists: Cardiovascular and nociceptive reflexes in halothane-anesthetized rats. Anesthe-siology 1990;73:1198-207.
13) Nagasaka H , Sato I, Nagasaka I, Miyazaki T, Ichiki A, Aikawa K, et al. Thiamylal reduces the inhibition of dorsal horn lamina V type neuronal activity induced by bradykinin injection into the femoral artery contralateral to the recording site. Masui 1988;37:524-9 (in Japanese with English abstract).
14) Nagasaka H , Ishizuka K, Aikawa K, Matsumoto N, Hori T, Nagasaka I, et al. Effects of thiamylal on the unit activity of lamina V type cells of the lumbar dorsal horn. Masui 1987;36:1208-13 (in Japanese with English abstract).
15) Nagasaka H, Nakajima T, Takano Y, Sato I, Aikawa K, Matsumoto N, et al. Enflurane reduces the excitation and inhibition of dorsal horn WDR neuronal activity induced by BK injection in spinal cats. J Anesth 1990;4:102-9.
16) Tomlinson RWW, Gray BG, Dostrovsky JO. Inhib-ition of rat spinal cord dorsal horn neurons by non-segmental, noxious cutaneous stimuli. Brain Res 1987;279:291-4.
17) Shingu K, Osawa M, Omatsu Y, Komatsu T, Urabe N, Mori K. Naloxone does not antagonize the anesthetic-induced depression of nociceptor-driven spinal cord response in spinal cats. Acta Anaesth Scand 1981;25:526-32.
18) Nakahiro M, Yeh JZ , Brunner E, Narahashi T. General anesthetics modulates GABA receptor channel complex in rat dorsal root ganglion neurons. FASEB J 1989;3:1850-4.
19) Martin DC, Introna RP, Aronstam RS. Inhibition of neuronal 5-HT uptake by ketamine, but not halothane, involves disruption of substrate recognition by the transporter. Neurosci Lett 1990;112:99-103
水元 裕，長坂 浩＊
埼玉医科大学麻酔学教室 ， ＊明海大学歯学部総合臨床医学第二講座麻酔学