• The Korean Journal of Physiology
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• 제24권2호
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• pp.305-317
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• 1990

The present study was performed to investigate modification in the electrophysiological characteristics of cat dorsal horn cells during neurogenic inflammation induced by mustard oil. The results obtained were summarized as follows: 1) Following subcutaneous injection of mustard oil the majority of wide dynamic range (WDR) cells (10/15 units) showed enhanced responses (80%) to brush, while the responses to all types of mechanical stiumli were enhanced in 3/15 units. One cell was further activated by pinch and the another was not affected at all after induction of inflammation. 2) The sensitization of WDR cell was resulted from subcutaneous injection of mustard oil either inside or outside of the receptive field (RF), whereas the spontaneous activity increased only after mustard oil was injected inside of the RF. 3) In the animal with inflammation the responses of high threshold (HT) cell to noxious stimulus were not altered, while HT cell responded to such mechanical stimulus as pressure which was usually ineffective in normal animals. 4) After induction of inflammation, low threshold (LT) cell appeared to be converted to WDR cell, showing responses not only to brush but also to pressure and pinch. 5) The mustard oil-induced inflammation enhanced responses of WDR and HT cells to the thermal stimuli and also resulted in a pronounced after-discharge in WDR cells. 6) After subcutaneous injection of lidocaine, the increased background activity of WDR cells due to inflammation was almost completely abolished. 7) A subcutaneous injection of mustard oil inside of the RF invariably desensitized the dorsal horn cells which receive sensory inputs from the inflamed RF. From the results of Present study it was revealed that a neurogenic inflammation induced by mustard oil resulted in an enhancement of responses of cat dorsal horn cells to mechanical and thermal stimuli.

• The Korean Journal of Physiology
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• 제23권1호
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• pp.151-167
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• 1989

The present study was undertaken to investigate modification in electrophysiological characteristics of cat dorsal horn cells resulting from carrageenin-induced inflammation. The followings were studied; 1) the time-course of changes in responses of the WDR (wide dynamic range) cell 1-3h after subcutaneous injection of carrageenin in its receptive field; 2) the responses of the same dorsal hern cells before and after induction of inflammation; 3) the effect of inflammation on the responsiveness of dorsal horn neurons to algogens (bradykinin & potassium); and 4) the effect of inflammation on the activity of WDR cell following administration of indomethacin and clonidine. Though responses of WDR neuron were increased dramatically during first 1h, the maximal enhancement was observed 3h after induction of inflammation especially by repetitive light tactile stimulus. Following carrageenin injection the majority of WDR neurons (10/15 units) showed enhanced responses to all the mechanical stimuli while in 3 cases responsiveness were intensified during activation by one tactile stimulus (brush or pressure). One cell was unaffected by inflammation and in another case the response was enhanced only to noxious stimulus. Five of 9 cells that could initially be driven by noxious stimulus were activated more strongly by same stimulus and even by tactile stimulus (pressure) following inflammation. In 2 cases neurons were sensitized only to noxious stimulus whereas in another 2 cells that did not show enhanced responses to noxious stimulus responses to light tactile stimulus (pressure) appeared after inflammation. Of 16 LT cells tested 6 responded to squeeze while 4 showed the characteristics of WDR cell following inflammation. No modification in responsiveness was recognized in 3 cells whereas response to only brush was enhanced in another 3 neurons. Following carrageenin injection responses of LT cell to bradykinin or $K^{+}$ were not altered whereas those of WOR neurons to bradykinin or $K^{+}$ were suppressed in 22.2% and 33.3% of cases, respectively. In two of 8 activity of HT cells were inhibited by bradykinin while in five of 8 responsiveness to $K^{+}$ were rather enhanced by inflammation. In the rest inflammation was ineffective. In inflammation-induced animal the receptive field of LT cell was not changed whereas those of WDR cell and HT cell were tremendously expanded. The enhanced responses of WDR neurons to mechanical stimuli resulted from inflammation were suppressed by intravenously injected indomethacin and clonidine suggesting that postaglandin is involved in inflammation-induced sensitization of these cells. The involvement of peripheral and central mechanisms in the modification in responsiveness of dorsal horn cells in the carrageenin-induced inflammation was discussed.

• The Korean Journal of Physiology
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• 제28권2호
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• pp.123-132
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• 1994

The present study was undertaken to elucidate the desensitization of cutaneous receptors and the conduction block of the afferent nerves induced by direct application of allyl isotheocyanate (mustard oil) to the receptive field (RF) or onto the afferent nerve, respectively. Dorsal horn cell responses to mechanical stimulations of RF were completely suppressed when mustard oil was applied to either the afferent nerve or the whole area of RF. C-fiber responses of dorsal horn cells were more susceptive to mustard oil than A-fiber activities. This was confirmed by the experiment in which the compound action potentials recorded from rat tibial nerve before and after topical application of mustard oil were compared. The higher the concentration of mustard oil and the longer the application time, the more powerful desensitization or conduction block was induced. From the results of the present study, it is suggested that the desensitization of the afferent fiber and sensory receptors induced by mustard oil results mainly from the conduction block of C-fiber in the primary afferent nerve.

• The Korean Journal of Physiology
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• 제22권1호
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• pp.89-100
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• 1988

Effect of clonidine on the dorsal horn cell responses to mechanical stimulations were studies in 3 spinalized cats and 10 cats with intact spinal cord. The type of dorsal horn cells was determined according to their response patterns to four graded mechanical stimulations (brush, pressure, pinch and squeeze) applied to the respective receptive fields. In the present study the results obtained only from the wide dynamic range (WDR) cells were included. The responses of the WDR cells to noxious mechanical stimuli were selectively suppressed following intravenous administration of clonidine into the experimental animals. The clonidine-induced changes in responses of the WDR cells to mechanical stimulation were not affected by naloxone or propranolol whereas effect of clonidine on WDR cell responses was almost completely abolished after intravenous administration of yohimbine. Also in the spinalized cats results parallel to those observed in cats with intact spinal cord were obtained. The results of present study strongly implies that analgesic action of clonidine can be mediated through excitation of ${\alpha}_{2}-adrenoceptor$ even at the spinal cord level without supraspinal mechanism.

• The Korean Journal of Physiology and Pharmacology
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• 제4권6호
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• pp.455-461
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• 2000

Zinc contained in the neurons of central nervous system is activity-dependently released and then attenuates NMDA (N-methyl-D-aspartate)-induced neurotoxicity while augmenting non-NMDA-induced neurodegeneration. Zinc also has been reported to produce antinociceptive action on the inflammation- and nerve injury-induced hyperalgesia in the behavioral test. In this study, we investigated the effects of zinc on the responses of dorsal horn cells to NMDA, kainate and graded electrical stimulation of C-fibers. In the majority of WDR cells (70.6%), zinc current-dependently inhibited WDR cell responses to NMDA and in the remaining cells, produced biphasic responses; excitation followed by inhibition. Zinc augmented the responses of WDR cells to iontophoretical application of kainate. The dominant effect of $Zn^{2+}$ on the responses of WDR cells to C-fiber stimulation was excitatory, but inhibition, excitation-inhibition and no change of the responses to C-fiber stimulation were induced. $Ca^{2+}-EDTA$ antagonized the excitatory or inhibitory effects of $Zn^{2+}$ on the WDR cell responses. These experimental findings suggest that $Zn^{2+}$ modulates the transmission of sensory information in the rat spinal cord.

• The Korean Journal of Physiology and Pharmacology
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• 제3권3호
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• pp.237-244
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• 1999

Magnesium ion is known to selectively block the N-methyl-D-aspartate (NMDA)-induced responses and to have anticonvulsive action, neuroprotective effect and antinociceptive action in the behavioral test. In this study, we investigated the effect of $Mg^{2+}$ on the responses of dorsal horn neurons to cutaneous thermal stimulation and graded electrical stimulation of afferent nerves as well as to excitatory amino acids and also elucidated whether the actions of $Ca^{2+}$ and $Mg^{2+}$ are additive or antagonistic. $Mg^{2+}$ suppressed the thermal and C-fiber responses of wide dynamic range (WDR) cell without any effect on the A-fiber responses. When $Mg^{2+}$ was directly applied onto the spinal cord, its inhibitory effect was dependent on the concentration of $Mg^{2+}$ and duration of application. The NMDA- and kainate-induced responses of WDR cell were suppressed by $Mg^{2+}$, the NMDA-induced responses being inhibited more strongly. $Ca^{2+}$ also inhibited the NMDA-induced responses current-dependently. Both inhibitory actions of $Mg^{2+}$ and $Ca^{2+}$ were additive, while $Mg^{2+}$ suppressed the EGTA-induced augmentation of WDR cell responses to NMDA and C-fiber stimulation. Magnesium had dual effects on the spontaneous activities of WDR cell. These experimental findings suggest that $Mg^{2+}$ is implicated in the modulation of pain in the rat spinal cord by inhibiting the responses of WDR cell to noxious stimuli more strongly than innocuous stimuli.

• The Korean Journal of Physiology
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• 제22권2호
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• pp.245-257
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• 1988

The present study was undertaken to investigate the effect of clonidine on the response of the dorsal horn cells to intra-arterially administered bradykinin $(BK:40{\mu}g)$ and $K^+(4mg)$ in spinal cats and cats with intact spinal cord. The change in the activities of low threshold (LT), high threshold (HT) and wide dynamic range (WDR) cells induced by BK and $K^+$ were determined before and after treatment of animals with clonidine. Also studied was mechanism of inhibitory action of clonidine on the responses of dorsal horn cells to the chemical algogenics. Number of WDR cell responded to intra-arterially administered BK and $K^+$ was greater in spinal animals than in cats with intact spinal cord. Following administration of BK or $K^+$ no change was observed in the activity of LT cell whereas activity of HT cell increased invariably. The increased response of HT cell to BK and $K^+$ was markedly suppressed by clonidine. On the other hand, such inhibitory actions of clonidine were almost completely blocked by yohimbine. The majority of WDR cells were activated by $K^+$ while response of WDR cells to BK was diverse (excitatory, inhibitory or mixed). These results indicate that clonidine inhibits responses of the dorsal horn cells not only to thermal or mechanical stimulations but also to chemical algogenics, and that the inhibitory action of clonidine is generally mediated through excitation of ${\alpha}_2-adrenoreceptors$.

• The Korean Journal of Physiology and Pharmacology
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• 제3권1호
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• pp.35-45
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• 1999

Excitatory amino acid (EAA) and substance P (SP) have been known to be primary candidates for nociceptive neurotransmitter in the spinal cord, and calcium ions are implicated in processing of the sensory informations mediated by EAA and SP in the spinal cord. In this study, we examined how $Ca^{2+}$ modified the responses of dorsal horn neurons to single or combined iontophoretical application of EAA and SP in the rat. All the LT cells tested responded to kainate, whereas about 55% of low threshold (LT) cells responded to iontophoretically applied NMDA. NMDA and kainate excited almost all wide dynamic range (WDR) cells. These NMDA- and kainate-induced WDR cell responses were augmented by iontophoretically applied EGTA, but suppressed by $Ca^{2+},\;Mn^{2+},$ verapamil and ${\omega}-conotoxin$ EVTA, effect of verapamil being more prominent and well sustained. $Ca^{2+}$ and $Mn^{2+}$ antagonized the augmenting effect of EGTA. On the other hand, prolonged spinal application of EGTA suppressed the response of WDR cell to NMDA. SP had triple effects on the spontaneous activity as well as NMDA-induced responses of WDR cells: excitation, inhibition and no change. EGTA augmented, but $Ca^{2+},\;Mn^{2+}$ and verapamil suppressed the increase in the NMDA-induced responses and spontaneous activities of WDR cells following iontophoretical application of SP. These results suggest that in the spinal cord, sensory informations mediated by single or combined action of EAA and SP can be modified by the change in calcium ion concentration.

• The Korean Journal of Physiology
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• 제24권1호
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• pp.171-180
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• 1990

In 19 cats anesthetized with ${\alpha}-chloralose$ effects of taurine and ${\beta}-alanine$ on the responses of wide dynamic range (WDR) cells to mechanical, chemical and thermal stimuli were investigated in the lumbar spinal cord of the cat. Also studied was an interaction of strychnine with taurine in affecting the activities of WDR cells. Following intravenous administration of taurine, the responses of WDR cells to all types of mechanical stimuli were markedly enhanced, demonstrating that the response to pressure was most sensitive to taurine action. When the receptive field was exposed to thermal stimuli ($50^{\circ}C$) for 20 sec. taurine increased activity of WDR cell to 169.5% of the control value. The $K^{+}$-induced activation of WDR cells was invariably suppressed after taurine administration. Intravenously administered strychnine remarkably reduced the enhanced response of WDR cell to natural stimuli resulting from intravenous administration of taurine. Also ${\beta}-alanine$ markedly activated the response of spinal dorsal horn cell to natural mechanical stimuli. These findings suggest that neutral amino acid and its derivative such as ${\beta}-alanine$ and taurine can enhance the response of WDR cells to different stimuli in cats.

• The Korean Journal of Physiology and Pharmacology
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• 제7권5호
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• pp.251-254
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• 2003

The present study was designed to examine whether the co-application of morphine with $Ca^{2+}$ channel antagonist $(Mn^{2+},\;verapamil)$, N-methyl-D-aspartate (NMDA) receptor antagonist (2-amino-5-phosphonopentanoic acid$[AP_5]$, $Mg^{2+}$) or protein kinase C inhibitor (H-7) causes the potentiation of morphine-induced antinociceptive action by using an in vivo electrophysiological technique. A single iontophoretic application of morphine or an antagonist alone induced weak inhibition of wide dynamic range (WDR) cell responses to iontophoretically applied NMDA and C-fiber stimulation. Although there was a little difference in the potentiating effects, the antinociceptive action of morphine was potentiated when morphine was iontophoretically applied together with $Mn^{2+}$, verapamil, $AP_5$, $Mg^{2+}$ or H-7. However, the potentiating action between morphine and each antagonist was not apparent, when the antinociceptive action evoked by morphine or the antagonist alone was too strong. These results suggest that the potentiating effect can be caused by the interaction between morphine and each antagonist in the spinal dorsal horn.