Participation of D-serine and NR2 subunits in EphA4-mediated trigeminal neuropathic pain

The present study investigated the participation of D-serine and NR2 in antinociception produced by blockade of central erythropoietin-producing hepatocellular carcinoma (Eph) A4 (EphA4) signaling in rats with trigeminal neuropathic pain. Trigeminal neuropathic pain was modeled in male Sprague-Dawley rats using mal-positioned dental implants. The left mandibular second molar was extracted under anesthesia, and a miniature dental implant was placed to induce injury to the inferior alveolar nerve. Our current findings showed that nerve injury induced by malpositioned dental implants significantly produced mechanical allodynia; additionally, the inferior alveolar nerve injury increased the expression of D-serine and NR2 subunits in the ipsilateral medullary dorsal horn (trigeminal subnucleus caudalis). Intracisternal administration of EphA4-Fc, an EphA4 inhibitor, inhibited nerve injury-induced mechanical allodynia and upregulated the expression of D-serine and NR2 subunits. Moreover, intracisternal administration of D-amino acids oxidase, a D-serine inhibitor, inhibited trigeminal mechanical allodynia. These results show that D-serine and NR2 subunit pathways participate in central EphA4 signaling after an inferior alveolar nerve injury.Therefore, blockade of D-serine and NR2 subunit pathways in central EphA4 signaling provides a new therapeutic target for the treatment of trigeminal neuropathic pain.

Participation of Opioid Pathway in the Central Antinociceptive Effects of Eugenol

The aim of the present study was to evaluate the central antinociceptive effects of eugenol after intraperitoneal administration. Experiments were carried out using male Sprague-Dawley rats. Subcutaneous injection of 5% formalin-induced nociceptive behavioral responses was used as the pain model. Subcutaneous injection of 5% formalin significantly produced nociceptive responses by increasing the licking time during nociceptive behavior. Subsequent intraperitoneal injection of 100 mg/kg of eugenol led to a significant decrease in the licking time. However, low dose of eugenol (50 mg/kg) did not affect the nociceptive behavioral responses produced by subcutaneous injection of formalin. Intrathecal injection of 30 µg of naloxone, an opioid receptor antagonist, significantly blocked antinociceptive effects produced by intraperitoneal injection of eugenol. Neither intrathecal injection of methysergide (30 µg), a serotonin receptor antagonist nor phentolamine (30 µg), an α-adrenergic receptor antagonist influenced antinociceptive effects of eugenol, as compared to the vehicle treatment. These results suggest that central opioid pathway participates in mediating the antinociceptive effects of eugenol.

Preemptive application of QX-314 attenuates trigeminal neuropathic mechanical allodynia in rats

The aim of the present study was to examine the effects of preemptive analgesia on the development of trigeminal neuropathic pain. For this purpose, mechanical allodynia was evaluated in male Sprague-Dawley rats using chronic constriction injury of the infraorbital nerve (CCI-ION) and perineural application of 2% QX-314 to the infraorbital nerve. CCI-ION produced severe mechanical allodynia, which was maintained until postoperative day (POD) 30. An immediate single application of 2% QX-314 to the infraorbital nerve following CCI-ION significantly reduced neuropathic mechanical allodynia. Immediate double application of QX-314 produced a greater attenuation of mechanical allodynia than a single application of QX-314. Immediate double application of 2% QX-314 reduced the CCI-ION-induced upregulation of GFAP and p-p38 expression in the trigeminal ganglion. The upregulated p-p38 expression was co-localized with NeuN, a neuronal cell marker. We also investigated the role of voltage-gated sodium channels (Navs) in the antinociception produced by preemptive application of QX-314 through analysis of the changes in Nav expression in the trigeminal ganglion following CCI-ION. Preemptive application of QX-314 significantly reduced the upregulation of Nav1.3, 1.7, and 1.9 produced by CCI-ION. These results suggest that long-lasting blockade of the transmission of pain signaling inhibits the development of neuropathic pain through the regulation of Nav isoform expression in the trigeminal ganglion. Importantly, these results provide a potential preemptive therapeutic strategy for the treatment of neuropathic pain after nerve injury.

Botulinum toxin type A enhances the inhibitory spontaneous postsynaptic currents on the substantia gelatinosa neurons of the subnucleus caudalis in immature mice

Botulinum toxin type A (BoNT/A) has been used therapeutically for various conditions including dystonia, cerebral palsy, wrinkle, hyperhidrosis and pain control. The substantia gelatinosa (SG) neurons of the trigeminal subnucleus caudalis (Vc) receive orofacial nociceptive information from primary afferents and transmit the information to higher brain center. Although many studies have shown the analgesic effects of BoNT/A, the effects of BoNT/A at the central nervous system and the action mechanism are not well understood. Therefore, the effects of BoNT/A on the spontaneous postsynaptic currents (sPSCs) in the SG neurons were investigated. In whole cell voltage clamp mode, the frequency of sPSCs was increased in 18 (37.5%) neurons, decreased in 5 (10.4%) neurons and not affected in 25 (52.1%) of 48 neurons tested by BoNT/A (3 nM). Similar proportions of frequency variation of sPSCs were observed in 1 and 10 nM BoNT/A and no significant differences were observed in the relative mean frequencies of sPSCs among 1–10 nM BoNT/A. BoNT/A-induced frequency increase of sPSCs was not affected by pretreated tetrodotoxin (0.5 µM). In addition, the frequency of sIPSCs in the presence of CNQX (10 µM) and AP5 (20 µM) was increased in 10 (53%) neurons, decreased in 1 (5%) neuron and not affected in 8 (42%) of 19 neurons tested by BoNT/A (3 nM). These results demonstrate that BoNT/A increases the frequency of sIPSCs on SG neurons of the Vc at least partly and can provide an evidence for rapid action of BoNT/A at the central nervous system.

Participation of central GABAA receptors in the trigeminal processing of mechanical allodynia in rats

Here we investigated the central processing mechanisms of mechanical allodynia and found a direct excitatory link with low-threshold input to nociceptive neurons. Experiments were performed on male Sprague-Dawley rats weighing 230-280 g. Subcutaneous injection of interleukin 1 beta (IL-1β) (1 ng/10 µL) was used to produce mechanical allodynia and thermal hyperalgesia. Intracisternal administration of bicuculline, a gamma aminobutyric acid A (GABAA) receptor antagonist, produced mechanical allodynia in the orofacial area under normal conditions. However, intracisternal administration of bicuculline (50 ng) produced a paradoxical anti-allodynic effect under inflammatory pain conditions. Pretreatment with resiniferatoxin (RTX), which depletes capsaicin receptor protein in primary afferent fibers, did not alter the paradoxical anti-allodynic effects produced by the intracisternal injection of bicuculline. Intracisternal injection of bumetanide, an Na-K-Cl cotransporter (NKCC 1) inhibitor, reversed the IL-1β-induced mechanical allodynia. In the control group, application of GABA (100 µM) or muscimol (3 µM) led to membrane hyperpolarization in gramicidin perforated current clamp mode. However, in some neurons, application of GABA or muscimol led to membrane depolarization in the IL-1β-treated rats. These results suggest that some large myelinated Aβ fibers gain access to the nociceptive system and elicit pain sensation via GABA(A) receptors under inflammatory pain conditions.

Peripheral Cellular Mechanisms of Artemin-induced Thermal Hyperalgesia in Rats

In the present study, we investigated the role of peripheral ionotropic receptors in artemin-induced thermal hyperalgesia in the orofacial area. Male Sprague-Dawley rats weighting 230 to 280 g were used in the study. Under anesthesia, a polyethylene tube was implanted in the subcutaneous area of the vibrissa pad, which enabled drug-injection. After subcutaneous injection of artemin, changes in air-puff thresholds and head withdrawal latency time were evaluated. Subcutaneous injection of artemin (0.5 or 1 µg) produced significant thermal hyperalgesia in a dose-dependent manner. However, subcutaneous injection of artemin showed no effect on air-puff thresholds. IRTX (4 µg), a TRPV1 receptor antagonist, D-AP5 (40 or 80 µg), an NMDA receptor antagonist, or NBQX (20 or 40 µg), an AMPA receptor antagonist, was injected subcutaneously 10 min prior to the artemin injection. Pretreatment with IRTX and D-AP5 significantly inhibited the artemin-induced thermal hyperalgesia. In contrast, pretreatment with both doses of NBQX showed no effect on artemin-induced thermal hyperalgesia. Moreover, pretreatment with H-89, a PKA inhibitor, and chelerythrine, a PKC inhibitor, decreased the artemin-induced thermal hyperalgesia. These results suggested that artemin-induced thermal hyperalgesia is mediated by the sensitized peripheral TRPV1 and NMDA receptor via activation of protein kinases.

Blockade of Trigeminal Glutamate Recycling Produces Anti-allodynic Effects in Rats with Inflammatory and Neuropathic Pain

The present study investigated the role of spinal glutamate recycling in the development of orofacial inflammatory pain or trigeminal neuropathic pain. Experiments were carried out on male Sprague-Dawley rats weighing between 230 and 280 g. Under anesthesia, a polyethylene tube was implanted in the atlanto-occipital membrane for intracisternal administration. IL-1β-induced inflammation was employed as an orofacial acute inflammatory pain model. IL-1β (10 ng) was injected subcutaneously into one vibrissal pad. We used the trigeminal neuropathic pain animal model produced by chronic constriction injury of the infraorbital nerve. DL-threo-β -benzyloxyaspartate (TBOA) or methionine sulfoximine (MSO) was administered intracisternally to block the spinal glutamate transporter and the glutamine synthetase activity in astroglia. Intracisternal administration of TBOA produced mechanical allodynia in naïve rats, but it significantly attenuated mechanical allodynia in rats with interleukin (IL)-1 β-induced inflammatory pain or trigeminal neuropathic pain. In contrast, intracisternal injection of MSO produced anti-allodynic effects in rats treated with IL-1β or with infraorbital nerve injury. Intracisternal administration of MSO did not produce mechanical allodynia in naive rats. These results suggest that blockade of glutamate recycling induced pro-nociception in naïve rats, but it paradoxically resulted in anti-nociception in rats experiencing inflammatory or neuropathic pain. Moreover, blockade of glutamate reuptake could represent a new therapeutic target for the treatment of chronic pain conditions.

Participation of IL-1β in temporomandibular nociception in rats with CFA-induced inflammation

The aim of the present study was to develop an animal model for evaluation of temporomandibular (TMJ) nociception under TMJ inflammation. We also investigated the participation of IL-1β in inflammation-induced TMJ nociception. Experiments were carried out using male Sprague-Dawley rats. Intra-articular injection of 3% formalin was administered to evaluate hyperalgesia 3 days after CFA injection. Intra-articular injection of 3% formalin did not produce nociceptive behavior in normal rats. Although intra-articular injection of 3 doses of CFA produced TMJ inflammation, only 1:3 diluted CFA produced hyperalgesia when formalin was injected intra-articularly 3 days after CFA injection. Co-administration of IL-1 receptor inhibitor with formalin into the TMJ cavity 3 days after CFA injection was performed. Co-administration of IL-1 receptor inhibitor significantly inhibited formalin-induced hyperalgesia in rats with CFA-induced TMJ inflammation. These results suggested that intra-articular injection of formalin produced hyperalgesia under chronic TMJ inflammation. Moreover, IL-1β plays an important role in TMJ hyperalgesia under chronic inflammation and blockade of IL-1β is a potential therapeutic target for inflammatory TMJ pain.

Vitamin E Potentiates the Anti-nociceptive Effects by Intraperitoneal Administration of Lidocaine in Rats

The present study was to evaluate effects of vitamin E on intravenous administration of lidocaine-induced antinociception. Experiments were carried out using male Sprague-Dawley rats. Orofacial formalin-induced nociceptive behavioral responses were used as the orofacial animal pain model. Subcutaneous injection of formalin produced significant nociceptive scratching behavior. Intraperitoneal injection of 5 and 10 mg/kg of lidocaine attenuated formalin-induced nociceptive behavior in the 2nd phase, compared to the vehicle-treated group. Intraperitoneal injection of 1 g/kg of vitamin E also attenuated the formalin-induced nociceptive behavior in the 2nd phase, compared to the vehicle-treated group. However, low dose of vitamin E (0.5 g/kg) did not affect the nociceptive behavioral responses produced by subcutaneous injection of formalin. The present study also investigated effects of intraperitoneal injection of both vitamin E and lidocaine on orofacial formalin-induced behavioral responses. Vehicle treatment affected neither formalin-induced behavioral responses nor lidocaine-induced antinociceptive effects. However, intraperitoneal injection of 0.5 g/kg of vitamin E enhanced the lidocaine-induced antinociceptive effects in the 2nd phase compared to the vehicle-treated group. Intraperitoneal injection of naloxone, an opioid receptor antagonist, did not affect antinociception produced by intraperitoneal injections of both vitamin E and lidocaine. These results suggest that treatment with vitamin E enhances the systemic treatment with lidocaine-induced antinociception and reduces side effects when systemically treated with lidocaine. Therefore, the combined treatment with vitamin E and lidocaine is a potential therapeutic for chronic orofacial pain.

Botulinum Toxin Type A Attenuates Activation of Glial Cells in Rat Medullary Dorsal Horn with CFA-induced Inflammatory Pain

The activation of glial cells in the spinal cord has been contribute to the initiation and maintenance of pain facilitation induced by peripheral inflammation and nerve injury. The present study investigated effects of botulinum toxin type A (BoNT-A), injected subcutaneously or intracisternally, on the expression of microglia and astrocytes in rats. Complete Freund's Adjuvant (CFA)-induced inflammation was employed as an orofacial chronic inflammatory pain model. A subcutaneous injection of 40 microL CFA into the vibrissa pad was performed under 3% isoflurane anesthesia in SD rats. Immunohistochemical analysis for changes in Iba1 (a microglia marker) and GFAP (an astrocyte marker), were performed 5 days after CFA injection. Subcutaneous injection of CFA produced increases in Iba1 and GFAP expression, in the ipsilateral superficial lamia I and II in the medullary dorsal horn of rats. Subcutaneous treatment with BoNT-A attenuated the up-regulation of Iba1 and GFAP expressions induced by CFA injection. Moreover intracisternal injection of BoNT-A also attenuated the up-regulated Iba1 and GFAP expressions. These results suggest that the anti-nociceptive action of BoNT-A is mediated by modulation activation of glial cells, including microglia and astrocyte.

Antinociceptive Effects of Transcytosed Botulinum Neurotoxin Type A on Trigeminal Nociception in Rats

We examined the effects of peripherally or centrally administered botulinum neurotoxin type A (BoNT-A) on orofacial inflammatory pain to evaluate the antinociceptive effect of BoNT-A and its underlying mechanisms. The experiments were carried out on male Sprague-Dawley rats. Subcutaneous (3 U/kg) or intracisternal (0.3 or 1 U/kg) administration of BoNT-A significantly inhibited the formalin-induced nociceptive response in the second phase. Both subcutaneous (1 or 3 U/kg) and intracisternal (0.3 or 1 U/kg) injection of BoNT-A increased the latency of head withdrawal response in the complete Freund's adjuvant (CFA)-treated rats. Intracisternal administration of N-methyl-D-aspartate (NMDA) evoked nociceptive behavior via the activation of trigeminal neurons, which was attenuated by the subcutaneous or intracisternal injection of BoNT-A. Intracisternal injection of NMDA up-regulated c-Fos expression in the trigeminal neurons of the medullary dorsal horn. Subcutaneous (3 U/kg) or intracisternal (1 U/kg) administration of BoNT-A significantly reduced the number of c-Fos immunoreactive neurons in the NMDA-treated rats. These results suggest that the central antinociceptive effects the peripherally or centrally administered BoNT-A are mediated by transcytosed BoNT-A or direct inhibition of trigeminal neurons. Our data suggest that central targets of BoNT-A might provide a new therapeutic tool for the treatment of orofacial chronic pain conditions.

Differential Role of Central GABA Receptors in Nociception of Orofacial Area in Rats

The present study investigated the role of central GABA(A) and GABA(B) receptors in orofacial pain in rats. Experiments were conducted on Sprague-Dawley rats weighing between 230 and 280 g. Intracisternal catheterization was performed for intracisternal injection, under ketamine anesthesia. Complete Freund's Adjuvant (CFA)-induced thermal hyperalgesia and inferior alveolar nerve injury-induced mechanical allodynia were employed as orofacial pain models. Intracisternal administration of bicuculline, a GABA(A) receptor antagonist, produced mechanical allodynia in naive rats, but not thermal hyperalgesia. However, CGP35348, a GABA(B) receptor antagonist, did not show any pain behavior in naive rats. Intracisternal administration of muscimol, a GABA(A) receptor agonist, attenuated the thermal hyperalgesia and mechanical allodynia in rats with CFA treatment and inferior alveolar nerve injury, respectively. On the contrary, intracisternal administration of bicuculline also attenuated the mechanical allodynia in rats with inferior alveolar nerve injury. Intracisternal administration of baclofen, a GABA(B) receptor agonist, attenuated the thermal hyperalgesia and mechanical allodynia in rats with CFA treatment and inferior alveolar nerve injury, respectively. In contrast to GABA(A) receptor antagonist, intracisternal administration of CGP35348 did not affect either the thermal hyperalgesia or mechanical allodynia. Our current findings suggest that the GABA(A) receptor, but not the GABA(B) receptor, participates in pain processing under normal conditions. Intracisternal administration of GABA(A) receptor antagonist, but not GABA(B) receptor antagonist, produces paradoxical antinociception under pain conditions. These results suggest that central GABA has differential roles in the processing of orofacial pain, and the blockade of GABA(A) receptor provides new therapeutic targets for the treatment of chronic pain.

Participation of Central P2X7 Receptors in CFA-induced Inflammatory Pain in the Orofacial Area of Rats

We investigated the role of central P2X receptors in inflammatory pain transmission in the orofacial area in rats. Experiments were carried out using male Sprague-Dawley rats weighing 230-280g. Complete Freund's adjuvant (CFA, 40 microL) was applied subcutaneously to the vibrissa pad to produce inflammatory pain. The intracisternal administration of iso-PPADS tetrasodium salt, a non-selective P2X receptor antagonist, A317491 sodium salt hydrate, a P2X2/3 receptor antagonist, 5-BDBD, a P2X4 receptor antagonist, or A438079 hydrochloride, a P2X7 receptor antagonist, was performed 5 days after CFA injection. Subcutaneous injections of CFA produced increases in thermal hypersensitivity. Intracisternal injections of iso-PPADS (25 microg) or A438079 (25 or 50 microg) produced significant anti-hyperalgesic effects against thermal stimuli compared to the vehicle group. A317491 or 5-BDBD did not affect the head withdrawal latency times in rats showing an inflammatory response. Subcutaneous injections of CFA resulted in the up-regulation of OX-42, a microglia marker, and GFAP, an astrocyte marker, in the medullary dorsal horn. The intracisternal administration of A438079 reduced the numbers of activated microglia and astrocytes in the medullary dorsal horn. These results suggest that a blockade of the central P2X7 receptor produces antinociceptive effects, mediated by inhibition of glial cell function in the medullary dorsal horn. These data also indicate that central P2X7 receptors are potential targets for future therapeutic approaches to inflammatory pain in the orofacial area.

High dose of QX-314 produces anti-nociceptive effect without capsaicin in rats with inflammatory TMJ pain

The present study investigated the effects of QX-314 on inflammatory pain of the temporomandibular joint (TMJ). Experiments were carried out on male Sprague-Dawley rats weighing 220-280 g. Under anesthesia, the TMJ of each animal was injected with 50 microL of formalin (5%). The number of noxious behavioral responses, including rubbing or scratching of the facial region including the TMJ area, was recorded over 9 sequential 5 min intervals for each animal. Although 2.5% QX-314 did not affect formalin-induced nociceptive behavior, administration of 5% QX-314 with formalin significantly decreased the number of scratches produced by the formalin injection. Co-administration of capsaicin, a TRPV1 agonist, with 2.5% QX-314 produced significant anti-nociceptive effects whereas 2.5% QX-314 alone did not. However, the co-administration of capsaicin did not enhance the anti-nociceptive effects in the 5% QX-314-treated rats. Moreover, the co-administration of capsazepine, a TRPV1 antagonist, did not attenuate anti-nociceptive effects in the 5% QX-314-treated rats. These findings suggest that TRPV1 is effective in the transport of low but not high doses of QX-314. Moreover, a high dose of QX-314, which is not mediated by peripheral TRPV1 activity, may be viable therapeutic strategy for inflammatory pain in the TMJ.

Participation of Peripheral P2X Receptors in Orofacial Inflammatory Nociception in Rats

The present study investigated the role of peripheral P2X receptors in inflammatory pain transmission in the orofacial area in rats. Experiments were carried out on male Sprague-Dawley rats weighing 220 to 280 g. Formalin (5%, 50 microL) and complete Freund's adjuvant (CFA, 25 microL) was applied subcutaneously to the vibrissa pad to produce inflammatory pain. TNP-ATP, a P2X(2,2/3,4) receptor antagonist, or OX-ATP, a P2X(7) receptor antagonist, was then injected subcutaneously at 20 minutes prior to formalin injection. One of the antagonists was administered subcutaneously at three days after CFA injection. The subcutaneous injection of formalin produced a biphasic nociceptive behavioral response. Subcutaneous pretreatment with TNP-ATP (80, 160 or 240 microg) significantly suppressed the number of scratches in the second phase produced by formalin injection. The subcutaneous injection of 50 microg of OX-ATP also produced significant antinociceptive effects in the second phase. Subcutaneous injections of CFA produced increases in mechanical and thermal hypersensitivity. Both TNP-ATP (480 microg) and OX-ATP (100 microg) produced an attenuation of mechanical hypersensitivity. However, no change was observed in thermal hypersensitivity after the injection of either chemical. These results suggest that the blockade of peripheral P2X receptors is a potential therapeutic approach to the onset of inflammatory pain in the orofacial area.

Animal Models for Orofacial Neuropathic Pain / 한양의대학술지

Orofacial neuropathic pain is initiated by extraction of teeth or nerve injury from trauma in the trigeminal nerve that innervates the facial area. In the experiment, orofacial neuropathic pain usually occurred following injury of peripheral trigeminal nerve including infra-orbital nerve, inferior alveolar nerve, or mental nerve. In addition, pathology from trigeminal nerve root or ganglion is involved in orofacial neuropathic pain. This study introduced various animal models that help us study the underlying mechanisms of development or maintenance of orofacial neuropathic pain. One of the most typical symptoms of orofacial neuropathic pain is hypersensitivity to the innocuous mechanical stimuli. Our study presents a novel method to evaluate mechanical allodynia in rats with orofacial neuropathic pain. Recently, accumulate evidence support participation of central glial cells in the development or maintenance of orofacial neuropathic pain. Signaling molecules in glial cells also play an important role in neuropathic pain in the orofacial area.

Ultrastructural analysis of low-threshold mechanoreceptive vibrissa afferent boutons in the cat trigeminal caudal nucleus / 대한해부학회지

Ultrastructural parameters related to synaptic release and their correlation with synaptic connectivity were analyzed in the low-threshold mechanoreceptive vibrissa afferent boutons in laminae III and IV of the trigeminal caudal nucleus (Vc). Rapidly adapting vibrissa afferents were intra-axonally labeled, and quantitative ultrastructural analyses with serial sections were performed on the labeled boutons and their presynaptic endings (p-endings). The volume of the labeled boutons was widely distributed from small to large ones (0.8~12.3 microm3), whereas the p-endings were small and uniform in size. The volume of the labeled boutons was positively correlated with the ultrastructural parameters such as mitochondrial volume (correlation coefficient, r=0.96), active zone area (r=0.82) and apposed surface area (r=0.79). Vesicle density (r=-0.18) showed little correlation to the volume of labeled boutons, suggesting that the total vesicle number of a bouton is proportional to its volume. In addition, the bouton volume was positively correlated with the number of p-endings (r=0.52) and with the number of dendrites postsynaptic to the labeled bouton (r=0.83). These findings suggest that low-threshold mechanoreception conveyed through vibrissa afferents is processed in a bouton size-dependent manner in the Vc, which may contribute to the sensory-motor function of laminae III/IV in Vc.

Preventing Extracellular Diffusion of Trigeminal Nitric Oxide Enhances Formalin-induced Orofacial Pain

Nitric oxide (NO), a diffusible gas, is produced in the central nervous system, including the spinal cord dorsal horn and the trigeminal nucleus, the first central areas processing nociceptive information from periphery. In the spinal cord, it has been demonstrated that NO acts as pronociceptive or antinociceptive mediators, apparently in a concentration-dependent manner. However, the central role of NO in the trigeminal nucleus remains uncertain in support of processing the orofacial nociception. Thus, we here investigated the central role of NO in formalin (3%)-induced orofacial pain in rats by administering membrane-permeable or -impermeable inhibitors, relating to the NO signaling pathways, into intracisternal space. The intracisternal pretreatments with the NO synthase inhibitor L-NAME, the NO-sensitive guanylate cyclase inhibitor ODQ, and the protein kinase C inhibitor GF109203X, all of which are permeable to the cell membrane, significantly reduced the formalin-induced pain, whereas the membrane-impermeable NO scavenger PTIO significantly enhanced it, compared to vehicle controls. These data suggest that an overall effect of NO production in the trigeminal nucleus is pronociceptive, but NO extracellularly diffused out of its producing neurons would have an antinociceptive action.

Peripheral Analgesic Effect of Ketamine in Rat Formalin Test / 대한마취과학회지

BACKGROUND: This study was performed to compare the analgesic effects of the systemic versus local administration of ketamine and observe the effects of an NMDA receptor agonist on its peripheral analgesia using the rat formalin test. METHODS: Rats undergoing peripheral analgesia were divided into three groups; the administration of a subcutaneous (s.c.) injection of 0.1 ml of normal saline (Control), and intraperitoneal (i.p.) (Keta/IP) and s.c. (Keta/LO) injections of 2.5 mg/0.1 ml of ketamine administered 5 min before a s.c. injection of 50 ul of 5% formalin. All s.c. injections were performed at the same site: the right hind paw of the rat. To observe the effects of an NMDA receptor agonist, five groups were compared. In addition to the control and Keta/LO groups described above, following three groups with 1-Aminocyclopropanecarboxylic acid (ACPC), an NMDA receptor agonist, in addition to the Keta/LO group; local infiltration with 0.1 mM/0.1 ml ACPC 10 min before or after the administration of ketamine, and an i.p. injection 10 min before the administration of ketamine followed by a s.c. injection of formalin 5 min later. The pain behavior was compared according to the number of flinches during phase 2. RESULTS: All the ketamine groups showed fewer flinches compared to the control (P < 0.01). The Keta/Lo group showed fewer flinches than that of the Keta/IP group (P < 0.01). The analgesic effect of locally administered ketamine was reversed by pretreatment with either s.c. or i.p. ACPC, but not by post-treatment. CONCLUSIONS: These data suggest that locally administered ketamine has a potent peripheral analgesic effect, but the administration of ACPC prior to ketamine decreases the analgesic effect of ketamine.

Effect of local anesthesia on pulpal blood flow in mechanically stimulated teeth / 대한치과보존학회지

The aims of the study were to evaluate the effect of epinephrine-containing local anesthetics on pulpal blood flow (PBF) and to investigate its effect on cavity preparation-induced PBF change. PBF was recorded using a laser Doppler flowmeter (Perimed Co., Sweden) from canines of nine cats under general anesthesia before and after injection of local anesthetics and after cavity preparation. 2% lidocaine hydrochloride with 1 : 100,000 epinephrine was administered by local infiltration given apical to the mandibular canine at the vestibular area and the same volume of isotonic saline was injected on the contralateral tooth as a control. A round carbide bur was operated at slow speed with isotonic saline flushing to grind spherical cavities with increasing depth through the enamel and into the dentin on both teeth. The obtained data was analyzed with paired t-test. Cavity preparation caused significant increase of PBF (n = 9, p < 0.05). Local infiltration of lidocaine with epinephrine resulted in decreases of PBF (n = 9, p < 0.05), whereas there was no significant change of PBF with the physiologic saline as a control. Cavity preparation on tooth anesthetized with lidocaine with epinephrine caused significantly less increase of PBF than in control tooth (p < 0.05). Therefore, the result of the present study demonstrates that local infiltration of 2% lidocaine with 1 : 100,000 epinephrine effectively reduces PBF increase caused by cavity preparation.