Meperidine Suppresses the Excitability of Spinal Dorsal Horn Neurons

Background: In addition to local anesthetics, meperidine has been successfully used for local anesthesia. When applied intrathecally, the dorsal horn neurons of the superficial laminae are exposed to high concentrations of meperidine. These cells represent an important point for the transmission of pain information. This study investigated the blocking effects of meperidine on different ionic currents of spinal dorsal horn neurons and, in particular, its impact on the generation of action potentials.

Methods: Using a combination of the patch clamp technique and the entire soma isolation method, the action of meperidine on voltage-gated Na+ and K+ currents in spinal dorsal horn neurons of rats was described. Current clamp recordings from intact neurons showed the functional relevance of the ion current blockade for the generation of action potentials.

Results: Externally applied meperidine reversibly blocked voltage-gated Na+ currents with a half-maximum inhibiting concentration (IC50) of 112 [mu]m. During repetitive stimulation, a slight phasic block occurred. In addition, A-type K+ currents and delayed-rectifier K+ currents were affected in a dose-dependent manner, with IC50 values of 102 and 52 [mu]m, respectively. In the current clamp mode, single action potentials were suppressed by meperidine. The firing frequency was lowered to 54% at concentrations (100 [mu]m) insufficient for the suppression of a single action potential.     

Actions of Midazolam on Excitatory Transmission in Dorsal Horn Neurons of Adult Rat Spinal Cord

Background: Although intrathecal administration of midazolam, a water-soluble imidazobenzodiazepine derivative, has been found to produce analgesia, how it exerts this effect at the neuronal level in the spinal cord is not fully understood.

Methods: The effects of midazolam on electrically evoked and spontaneous excitatory transmission were examined in lamina II neurons of adult rat spinal cord slices using the whole cell patch clamp technique.

Results: Bath-applied midazolam (1 [mu]m) diminished A[delta]- and C-fiber evoked polysynaptic excitatory postsynaptic currents in both amplitude and integrated area. However, it affected neither A[delta]- and C-fiber evoked monosynaptic excitatory postsynaptic currents in amplitude nor miniature excitatory postsynaptic currents in amplitude, frequency, and decay time constant. In the presence of a benzodiazepine receptor antagonist, flumazenil (5 [mu]m), midazolam (1 [mu]m) did not diminish A[delta]-fiber evoked polysynaptic excitatory postsynaptic currents, suggesting that midazolam modulate the [gamma]-aminobutyric acid interneurons in the dorsal horn.     

Changes in Properties of Spinal Dorsal Horn Neurons and Their Sensitivity to Morphine after Spinal Cord Injury in the Rat

Background: To gain a better understanding of spinal cord injury (SCI)-induced central neuropathic pain, the authors investigated changes in properties of spinal dorsal horn neurons located rostrally and caudally to the lesion and their sensitivity to morphine in rats after SCI.

Methods: The right spinal cord of Sprague-Dawley rats was hemisected at the level of L2. At 10 to 14 days after the SCI, when mechanical hyperalgesia/allodynia had fully developed, spontaneous activity and evoked responses to mechanical stimuli of wide-dynamic-range (WDR) and high-threshold neurons rostral and caudal to the lesion were recorded. Effects of cumulative doses of systemic (0.1-3 mg/kg) and spinal (0.1-5 [mu]g) administration of morphine on spontaneous activity and evoked responses to the stimuli of the neurons were evaluated.

Results: Spontaneous activity significantly increased in WDR neurons both rostral and caudal to the SCI site, but high-frequency background discharges with burst patterns were only observed in neurons rostral to the SCI site. Significant increases in responses to the mechanical stimuli were seen both in WDR and high-threshold neurons located both rostrally and caudally to the lesion. The responses to nonnoxious and noxious stimuli were significantly greater in caudal WDR neurons than in rostral WDR neurons. In contrast, the responses to pinch stimuli were significantly higher in rostral high-threshold neurons than those in caudal high-threshold neurons. Systemically administered morphine had a greater effect on responses to nonnoxious and noxious stimuli of rostral WDR neurons than those of caudal WDR neurons. Spinally administered morphine significantly suppressed responses of WDR neurons in SCI animals to nonnoxious stimuli compared with those in sham-operated control animals.     

Uterine Cervical Distension Induces cFos Expression in Deep Dorsal Horn Neurons of the Rat Spinal Cord

Background: Uterine cervical distension underlies labor pain, yet its neurophysiology and pharmacology of inhibition remain unexplored. The authors examined uterine cervical distension-evoked cFos immunoreactivity in rat spinal cords, and the inhibitory effect of spinal cyclo-oxygenase inhibition on cFos expression.

Methods: Female rats were anesthetized with halothane, and pairs of metal rods were inserted in each cervical os through a mid-line laparotomy. A submaximal distension force (75 g) was applied for either 30 or 60 min, or, in control animals, no force was applied. Other animals received cervical lidocaine infiltration prior to uterine cervical distension. At the end of the experiments, the spinal cord at T12 to L2 levels was harvested and immunostained for cFos protein. Other animals received intrathecal ketorolac (0, 5, 25, and 50 [mu]g; n = 5-6 for each group) prior to uterine cervical distension.

Results: Uterine cervical distension significantly increased cFos immunoreactivity in the spinal cord from T12 to L2, with most cFos expression in the deep dorsal and central canal regions. Surgical preparation alone without uterine cervical distension resulted in minimal cFos expression, primarily in the superficial dorsal horn. Uterine cervical distension-evoked cFos expression was prevented by prior infiltration of lidocaine into the cervix. Intrathecal ketorolac produced a dose-dependent inhibition of uterine cervical distension-induced cFos expression.     

Effects of Halothane and Isoflurane on Hyperexcitability of Spinal Dorsal Horn Neurons after Incision in the Rat

Background: The aim of this study was to determine whether halothane and isoflurane used during and after surgical injury attenuate subsequent hyperexcitability of spinal dorsal horn (SDH) neurons by preventing development of central sensitization.

Methods: Activity of a wide-dynamic-range neuron of the SDH was isolated in decerebrate-spinal Sprague-Dawley rats, and neuronal activity (receptive field size and responses to nonnoxious and noxious stimuli) was recorded. A 1-cm-long incision was made through the skin, fascia, and muscle under anesthesia with halothane (1.1% or 2.2%) and isoflurane (1.4% or 2.8%). Anesthesia was discontinued just after the incision had been made or was continued until 30 min after the incision, and activity of the SDH neurons was measured for up to 2 h after the incision. In a control group, the incision was made without anesthesia.

Results: In the control group, the incision resulted in maximum excitation in the SDH neurons during surgery; spontaneous activity significantly increased for up to 30 min after the incision (P < 0.05) but did not significantly increase thereafter, returning to the preincision value. Halothane and isoflurane suppressed excitation of the neurons during the incision in a concentration-related manner. Administration of 2.2% halothane and 2.8% isoflurane during the incision and for up to 30 min after the incision almost abolished activity of the neurons for 30 min after the incision. The magnitude of neuronal activity 2 h after the incision was not significantly different among all groups, including the control group.     

Blockade of Na sup + and K sup + Currents by Local Anesthetics in the Dorsal Horn Neurons of the Spinal Cord

Background: The dorsal horn of the spinal cord is a pivotal point for transmission of neuronal pain. During spinal and epidural anesthesia, the neurons of the dorsal horn are exposed to local anesthetics. Unfortunately, little is known about the action of local anesthetics on the major ionic conductances in dorsal horn neurons. In this article, the authors describe the effects of bupivacaine, lidocaine, and mepivacaine on voltage-gated Na sup + and K sup + currents in the membranes of these neurons.

Methods: The patch-clamp technique was applied to intact dorsal horn neurons from laminae I-III identified in 200-micro meter slices of spinal cord from newborn rats. Under voltage-clamp conditions, the whole-cell Na sup + and K sup + currents activated by depolarization were recorded in the presence of different concentrations of local anesthetics.

Results: Externally applied bupivacaine, lidocaine, and mepivacaine produced tonic block of Na sup + currents with different potencies. Half-maximum inhibiting concentrations (IC50) were 26, 112, and 324 micro Meter, respectively. All local anesthetics investigated also showed a phasic, that is, a use-dependent, block of Na sup + channels. Rapidly inactivating K sup + currents (KA currents) also were sensitive to the blockers with IC50 values for tonic blocks of 109, 163, and 236 micro Meter, respectively. The block of KA currents was not use dependent. In contrast to Na sup + and KA currents, delayed-rectifier K sup + currents were almost insensitive to the local anesthetics applied.     

Changes in Response Properties and Receptive Fields of Spinal Dorsal Horn Neurons in Rats after Surgical Incision in Hairy Skin

Background: Mechanical hyperalgesia and allodynia associated with chemical irritant application are mediated by spinal high-threshold (HT) as well as wide-dynamic-range neurons as a result of "central sensitization." Because the pathophysiology of pain is thought to differ depending on the type of injury and may vary between hairy and glabrous skin, the authors examined changes in properties of spinal dorsal horn neurons after surgical incisions in hairy skin of rats to obtain insights into the mechanisms of postoperative pain.

Methods: Withdrawal responses to punctate mechanical stimulation and gentle brushing were measured in awake rats in an area adjacent to the injured site (primary area) and in an area 2 cm from the injured site (secondary area) after 1-cm longitudinal incisions through the hairy skin, fascia, and muscle had been made in the hindquarters. In a separate study, responses of spinal wide-dynamic-range, HT, and low-threshold neurons to nonnoxious and noxious stimuli were recorded before and after similar incisions had been made in the centers of their receptive fields. Effects of spinal application of the [gamma]-aminobutyric acid A receptor antagonist bicuculline (15 [mu]g) on responses of HT neurons were then studied.

Results: Awake rats showed primary and secondary hyperalgesia to punctate mechanical stimulation 30 min after the incision and thereafter for 4 days and 1 day, respectively. Mechanical allodynia associated with brush stimulation was only seen in the primary area 30 min after the incision and thereafter for 1 day. The incision resulted in increases in activity of wide-dynamic-range neurons (receptive field sizes and responses to both innocuous and noxious stimuli). HT neurons did not respond to innocuous stimulation and showed very small increases or no changes in receptive field size and responses to noxious stimuli after the incision. However, the majority of HT neurons began to respond to innocuous stimuli after application of bicuculline (15 [mu]g/50 [mu]l) to the spinal cord.     

Incision-induced Changes in Receptive Field Properties of Rat Dorsal Horn Neurons

Background: To learn more about pain mechanisms produced by surgery, responses of wide dynamic range (WDR) and high threshold (HT) dorsal horn neurons were studied before and after an incision. For this study, an incision was made in a mechanically insensitive area of the receptive field (RF) of the dorsal horn neuron in the plantar aspect of the foot and changes in mechanical response properties were studied.

Methods: Action potentials from single dorsal horn neurons were recorded in halothane anesthetized rats and these neurons were characterized as WDR or HT. Changes in background activity and responses to a variety of mechanical stimuli adjacent to the incision, distant to the injury, and in areas throughout the hindquarters were recorded.

Results: Fifty neurons were recorded (29 WDR, 21 HT cells); only nine of these had a sustained increase in background activity after incision. Marked decreases in threshold to von Frey filaments applied adjacent to the wound occurred in 9 of 28 WDR neurons but in none of 21 HT cells. Von Frey filament thresholds distant to the incision were largely not changed. A blunt mechanical stimulus activated 18 of 22 WDR neurons when applied directly on the incision. HT cells were largely not excited by this mechanical stimulus after incision. The RF to pinch was enlarged in 31 neurons to include areas outside the injury. Pinch RFs of both WDR and HT cells expanded.     

Alterations in Ascending Dorsal Horn Neurons by a Surgical Incision in the Rat Foot

Background: Little is known about the mechanisms of pain caused by a surgical incision. The authors have developed a rat model of postoperative pain characterized by decreased withdrawal thresholds to punctate mechanical stimuli after plantar incision. The present studies examined the response characteristics of dorsal horn neurons receiving input from the plantar aspect of the foot before and after a plantar incision placed adjacent to the low threshold area of the receptive field (RF).

Methods: Individual dorsal horn neurons from the lumbar enlargement were antidromically identified and characterized as low threshold, wide dynamic range (WDR), and high threshold (HT) based on their responses to brush and pinch. Thresholds (in millinewtons), the pinch RF, and stimulus-response functions (SRFs) to von Frey filaments characterized the neurons. SRFs were analyzed using area under the curve. Changes in background activity, punctate mechanical thresholds, SRFs, and RF were recorded after an incision was made adjacent to the most sensitive area of the RF.

Results: In all cells, an incision increased background activity; this remained elevated in 3 of 9 HT and 16 of 28 WDR neurons 1 h later. The SRFs were enhanced in 10 of 27 WDR neurons and in 2 of 8 HT cells after incision. Only the WDR neurons were responsive to filaments that produced withdrawal responses after incision in behavioral experiments. Increases in the RFs outside of the injured area occurred after incision in 15 of 29 WDR and 2 of 9 HT cells.     

Suppression of Potassium Conductance by Droperidol Has Influence on Excitability of Spinal Sensory Neurons

Background: During spinal and epidural anesthesia with opioids, droperidol is added to prevent nausea and vomiting. The mechanisms of its action on spinal sensory neurons are not well understood. It was previously shown that droperidol selectively blocks a fast component of the Na+ current. The authors studied the action of droperidol on voltage-gated K+ channels and its effect on membrane excitability in spinal dorsal horn neurons of the rat.

Methods: Using a combination of the patch-clamp technique and the "entire soma isolation" method, the action of droperidol on fast-inactivating A-type and delayed-rectifier K+ channels was investigated. Current-clamp recordings from intact sensory neurons in spinal cord slices were performed to study the functional meaning of K+ channel block for neuronal excitability.

Results: Droperidol blocked delayed-rectifier K+ currents in isolated somata of dorsal horn neurons with a half-maximum inhibiting concentration of 20.6 [mu]m. The A-type K+ current was insensitive to up to 100 [mu]m droperidol. At droperidol concentrations insufficient for suppression of an action potential, the block of delayed-rectifier K+ channels led to an increase in action potential duration and, as a consequence, to lowering of the discharge frequency in the neuron.     

Effects of Halothane and Isoflurane on Fast and Slow Inactivation of Human Heart hH1a Sodium Channels

Background: Cloning and heterologous expression of ion channels allow biophysical and molecular studies of the mechanisms of volatile anesthetic interactions with human heart sodium channels. Volatile anesthetics may influence the development of arrhythmias arising from cardiac sodium channel dysfunction. For that reason, understanding the mechanisms of interactions between these anesthetics and cardiac sodium channels is important. This study evaluated the mechanisms of volatile anesthetic actions on the cloned human cardiac sodium channel (hH1a) [Greek small letter alpha] subunit.

Methods: Inward sodium currents were recorded from human embryonic kidney (HEK293) cells stably expressing hH1a channels. There effects of halothane and isoflurane on current and channel properties were evaluated using the whole cell voltage-clamp technique.

Results: Halothane at 0.47 and 1.1 mM and isoflurane at 0.54 and 1.13 mM suppressed the sodium current in a dose- and voltage-dependent manner. Steady state activation was not affected, but current decay was accelerated. The voltage dependence of steady state fast and slow inactivations was shifted toward more hyperpolarized potentials. The slope factor of slow but not fast inactivation curves was reduced significantly. Halothane increased the time constant of recovery from fast inactivation. The recovery from slow inactivation was not affected significantly by either anesthetic.     

Sensory Processing in the Deep Spinal Dorsal Horn of Neurokinin-1 Receptor Knockout Mice

Background: The neurokinin-1 receptor and its primary ligand, substance P, are widely recognized as contributing to the spinal processing of nociceptive stimuli, yet the specific function of the neurokinin-1 receptor remains unclear.

Methods: To better clarify these functions, the authors examined the neurophysiologic responses of L4-L5 neurons in the deep dorsal horn to acute mechanical, thermal, and electrical stimuli in knockout and wild-type mice. In addition, the capacity of knockout and wild-type mice to show wind-up to repeated C-fiber stimuli and to show sensitization after cutaneous mustard oil was assessed.

Results: A total of 68 nociceptive neurons (35 in knockout, 33 in wild type) in laminae III-V were studied. No differences in the acute responses of neurons in knockout and wild-type mice to graded mechanical, thermal, or electrical stimuli or in the acute responses to mustard oil were observed. However, wind-up to repeated electrical stimulation at C-fiber intensity was significantly attenuated in the knockout mice compared with wild type controls. In addition, mustard oil-induced mechanical hypersensitivity was significantly reduced in the knockout mice.     

Differential Presynaptic Effects of Opioid Agonists on Aδ- and C-afferent Glutamatergic Transmission to the Spinal Dorsal Horn

Background: Although intrathecal administration of opioids produces antinociceptive effects in the spinal cord, it has not been established whether intrathecal opioid application more effectively terminates C fiber-mediated pain than A fiber-mediated pain. Here, the authors focus on the differences in opioid actions on A[delta]- and C-afferent responses.

Methods: Using the whole cell patch clamp technique, the authors investigated the presynaptic inhibitory actions of [mu]-, [delta]-, and [kappa]-opioid receptor agonists on primary afferent-evoked excitatory postsynaptic currents (EPSCs) in substantia gelatinosa neurons of adult rat spinal cord slices.

Results: The [mu] agonist DAMGO (0.1, 1 [mu]m) reduced the amplitude of glutamatergic monosynaptic A[delta]- or C fiber-evoked EPSCs. C fiber-evoked EPSCs were inhibited to a greater extent than A[delta] fiber-evoked EPSCs. The [delta] agonist DPDPE (1, 10 [mu]m) produced modest inhibition of A[delta]- or C fiber-evoked EPSCs. In contrast, the [kappa] agonist U69593 (1 [mu]m) did not affect the amplitude of either A[delta] or C fiber-evoked EPSCs.     

Effects of Bupivacaine and Ropivacaine on High-voltage-activated Calcium Currents of the Dorsal Horn Neurons in Newborn Rats

Background: Local anesthetics, such as bupivacaine, have been reported to block calcium currents in primary sensory neurons and to interfere with the release of neurotransmitters in central nervous system neurons. However, it is unknown whether local anesthetics affect the calcium current activity of central nervous system neurons.

Methods: Using a traditional whole cell voltage clamp technique, effects of bupivacaine and ropivacaine on high-voltage-activated calcium currents (HVA-Ica) were investigated in enzymatically dissociated dorsal horn neurons of neonatal rats. Calcium currents were evoked by testing pulses from a holding potential of -90 to 0 mV.

Results: Bupivacaine significantly reduced HVA-Ica in a dose-dependent manner. The peak HVA-Ica decreased by 24.5 +/- 2.5, 32.0 +/- 6.8, 59.4 +/- 6.2, 88.3 +/- 1.5, and 91.6 +/- 1.1% in response to 10, 30, 50, 100 and 200 [mu]m bupivacaine, respectively. Unlike bupivacaine, ropivacaine markedly increased HVA-Ica at lower concentrations (< 50 [mu]m) but decreased HVA-Ica at higher concentrations (>= 50 [mu]m). The percent increases in peak HVA-Ica induced by 10 and 30 [mu]m ropivacaine were 95 +/- 19.1 and 41.6 +/- 8.3%, respectively. The percent decreases in response to 50, 100, and 200 [mu]m ropivacaine were 21.1 +/- 2.1, 63.2 +/- 6.0 and 79.1 +/- 7.6%, respectively. Results indicate that the inhibitory potency of ropivacaine on HVA-Ica was significantly lower than that of bupivacaine at the same concentrations.     

Block of Human Heart hH1 Sodium Channels by the Enantiomers of Bupivacaine

Background: S(-)-bupivacaine reportedly exhibits lower cardiotoxicity but similar local anesthetic potency compared with R (+)-bupivacaine. The bupivacaine binding site in human heart (hH1) Na+ channels has not been studied to date. The authors investigated the interaction of bupivacaine enantiomers with hH1 Na+ channels, assessed the contribution of putatively relevant residues to binding, and compared the intrinsic affinities to another isoform, the rat skeletal muscle ([mu]1) Na+ channel.

Methods: Human heart and [mu]1 Na+ channel [alpha] subunits were transiently expressed in HEK293t cells and investigated during whole cell voltage-clamp conditions. Using site-directed mutagenesis, the authors created point mutations at positions hH1-F1760, hH1-N1765, hH1-Y1767, and hH1-N406 by introducing the positively charged lysine (K) or the negatively charged aspartic acid (D) and studied their influence on state-dependent block by bupivacaine enantiomers.

Results: Inactivated hH1 Na+ channels displayed a weak stereoselectivity with a stereopotency ratio (+/-) of 1.5. In mutations hH1-F1760K and hH1-N1765K, bupivacaine affinity of inactivated channels was reduced by ~ 20- to 40-fold, in mutation hH1-N406K by ~ sevenfold, and in mutations hH1-Y1767K and hH1-Y1767D by ~ twofold to threefold. Changes in recovery of inactivated mutant channels from block paralleled those of inactivated channel affinity. Inactivated hH1 Na+ channels exhibited a slightly higher intrinsic affinity than [mu]1 Na+ channels.     

Effect of Differential Delivery of Isoflurane to Head and Torso on Lumbar Dorsal Horn Activity

Background: The spinal cord appears to be the site where anesthetic agents prevent movement in response to noxious stimuli. When isoflurane is differentially delivered to the head and torso (with low torso concentrations), cranial anesthetic requirements increase compared with systemic administration. The aim of the current study was to test the hypothesis that isoflurane action in the brain has descending influences on spinal cord dorsal horn neurons. A secondary aim was to determine the association, if any, of high cranial concentrations of isoflurane (> 6%) with dorsal horn activity.

Methods: Ten goats were anesthetized with isoflurane and the carotid arteries and jugular veins isolated and cannulated for cerebral bypass. A laminectomy was performed for recording from single lumbar dorsal horn neurons with hind limb mechanical receptive fields (one cell per goat). A standard noxious mechanical stimulus was applied to the dew claw or hoof bulb during a control period with end-tidal isoflurane at 1.3% and during bypass with the following head/torso isoflurane concentrations: 1.3%/1.3%, 3.2%/1.3%, 9.4%/1.3%, 1.3%/0.2%, 3.0%/0.2% and 8.8%/0.3%.

Results: When torso isoflurane concentration was 1.3%, increasing cranial isoflurane concentration to 3% or 9% had no significant effect on the activity of dorsal horn units. When torso isoflurane was 0.2-0.3%, spontaneous activity increased; however, at these torso concentrations, evoked responses were significantly decreased (-60%) only when cranial isoflurane concentration was increased to 9%.     

Distinct Membrane Effects of Spinal Nerve Ligation on Injured and Adjacent Dorsal Root Ganglion Neurons in Rats

Background: Painful peripheral nerve injury results in disordered sensory neuron function that contributes to the pathogenesis of neuropathic pain. However, the relative roles of neurons with transected axons versus intact adjacent neurons have not been resolved. An essential first step is identification of electrophysiologic changes in these two neuronal populations after partial nerve damage.

Methods: Twenty days after spinal nerve ligation (SNL), intracellular recordings were obtained from axotomized fifth lumbar (L5) dorsal root ganglion neurons and adjacent, intact L4 neurons, as well as from control neurons and others subjected to sham-SNL surgery.

Results: Pronounced electrophysiologic changes were seen only in L5 neurons after SNL. Both A[alpha]/[beta] and A[delta] neuron types showed increased action potential duration, decreased afterhyperpolarization amplitude and duration, and decreased current threshold for action potential initiation. A[alpha]/[beta] neurons showed resting membrane potential depolarization, and increased repetitive firing during sustained depolarization developed in A[delta] neurons. The afterhyperpolarization duration in neurons with C fibers shortened after axotomy. In contrast to the axotomized L5 neurons, neighboring L4 neurons showed no changes in action potential duration, afterhyperpolarization dimensions, or excitability after SNL. Depolarization rate (dV/dt) increased after SNL in L4 A[alpha]/[beta] and A[delta] neurons but decreased in L5 neurons. Time-dependent rectification during hyperpolarizing current injection (sag) was greater after SNL in A[alpha]/[beta] L4 neurons compared with L5. Sham-SNL surgery produced only a decreased input resistance in A[alpha]/[beta] neurons and a decreased conduction velocity in medium-sized cells. In the L5 ganglion after axotomy, a novel set of neurons, consisting of 24% of the myelinated population, exhibited long action potential durations despite myelinated neuron conduction velocities, particularly depolarized resting membrane potential, low depolarization rate, and absence of sag.     

Functional μ Opioid Receptors Are Reduced in the Spinal Cord Dorsal Horn of Diabetic Rats

Background: The mechanisms of decreased spinal analgesic potency of morphine in neuropathic pain are not fully known. Agonist-stimulated [35S]GTP[gamma]S receptor autoradiography has been used to measure receptor activation of G proteins in vitro. Using this technique, we determined changes in the functional [mu] opioid receptors in the spinal dorsal horn in diabetic rats.

Methods: Rats were rendered diabetic with an intraperitoneal injection of streptozotocin. The lumbar spinal cord was obtained from age-matched normal and diabetic rats 4 weeks after streptozotocin treatment. [D-Ala2,N-MePhe4,Gly5-ol]-enkephalin (DAMGO, 10 [mu]m)-stimulated [35S]GTP[gamma]S binding was performed in both tissue sections and isolated membranes.

Results: The DAMGO-stimulated [35S]GTP[gamma]S binding in the spinal dorsal horn was significantly reduced (approximately 37%) in diabetic rats compared with normal rats. However, [35S]GTP[gamma]S bindings in the spinal dorsal horn stimulated by other G protein-coupled receptor agonists, including [D-Pen2,D-Pen5]-enkephalin, R (-)N6-(2-phenylisopropyl)-adenosine, and WIN-55212, were not significantly altered in diabetic rats. The basal [35S]GTP[gamma]S binding in the spinal dorsal horn was slightly (approximately 13%) but significantly increased in diabetic rats. Western blot analysis revealed no significant difference in the expression of the [alpha] subunits of Gi and Go proteins in the dorsal spinal cord between normal and diabetic rats.     

H-89对坐骨神经结扎大鼠触诱发痛和脊髓背角磷酸化CREB表达的影响

Neuropathicpain(NP)resultingfromvariousetiolo giessharessimilarcharacteristicfeatures :persistentspon taneouspain (burningpain) ,hyperralgesia(exaggeratedpaintonoxiousstimuli)andallodynia(paintoinnocuousstimuli) .NPisanareaoflargelyunmettherapeuticneed .Thecurrentpharmacologicalmainstaysofclinicalmanagementaretricyclicanti depressantsandcertainan ti convulsants ,1buttheseonlyachieveclinicallysignifi cant (greaterthan 5 0 %)painreliefinlessthan 5 0 %ofpatientsandareassociatedwithsub optimalsid…