Depression of NMDA-receptor-mediated segmental transmission by ketamine and ketoprofen, but not L-NAME, on the in vitro neonatal rat spinal cord preparation

Spinal Actions of the NSAID Diclofenac on Nociceptive Transmission in Comparison to the Kv7 Channel Opener Flupirtine

NSAIDs are the drugs most commonly used to alleviate pain. Despite being a heterogeneous group of compounds, all of them share a mechanism of action based on blockade of COXs enzymes, which confers them anti-inflammatory and analgesic properties. Diclofenac is a NSAID with preferred activity on COX-2 isozymes, but additionally, other targets may be implicated in its analgesic activity. Among them, diclofenac may facilitate the activity of K_v7 channels, that have been previously recognized as potential therapeutic targets in analgesia. In this study, the antinociceptive actions of diclofenac acting at the spinal level and the role of K_v7 channels in its effects were evaluated. Electrophysiological recordings of spinal reflexes and responses of dorsal horn neurons were obtained using in vitro spinal cord preparations from neonatal mice. Diclofenac, applied at clinically relevant concentrations to the entire preparation, depressed wind-up of spinal reflexes with a pattern similar to that of flupirtine, an analgesic with activity as K_v7 channel opener. Depressant actions of both compounds were strongly reduced after K_v7 channel blockade with XE-991, indicating the implication of these channels in the observed effects. Flupirtine, but not diclofenac, also reduced action potential firing of dorsal horn neurons in response to electrical activation of nociceptive afferents, suggesting differences in the actions of both compounds on K_v7 channel configurations present in sensory areas of the cord. Results demonstrate previously unknown central actions of diclofenac on K_v7 channels located in spinal circuits, expanding the knowledge about its pharmacological actions.

Implication of Kv7 Channels in the Spinal Antinociceptive Actions of Celecoxib

Celecoxib is a nonsteroidal anti-inflammatory drug (NSAID) commonly used to treat pain conditions in humans. In addition to its blocking activity on cyclooxygenase (COX) enzymes, several other targets could contribute to its analgesic activity. Here we explore the spinal antinociceptive actions of celecoxib and the potential implication of Kv7 channels in mediating its effects. Spinal cord in vitro preparations from hind paw-inflamed animals were used to assess the segmental sensory-motor and the early sensory processing of nociceptive information. Electrophysiological recordings of ventral roots and dorsal horn neurones were obtained, and the effects of celecoxib and Kv7 modulators on responses to repetitive dorsal root stimulation at C-fiber intensity were assessed. Celecoxib applied at clinically relevant concentrations produced depressant effects on responses to dorsal root stimulation recorded from both ventral roots and individual dorsal horn neurones; by contrast, the non-nociceptive monosynaptic reflex was unaffected. The NSAID indomethacin had no effect on spinal reflexes, but further coapplication of celecoxib still produced depressant effects. The depressant actions of celecoxib were abolished after Kv7 channel blockade and mimicked by its structural analog dimethyl-celecoxib, which lacks COX-blocking activity. The present results identify Kv7 channels as novel central targets for celecoxib, which may be relevant to its analgesic effect. This finding contributes to better understand the pharmacology of celecoxib and reinforces both the role of Kv7 channels in modulating the excitability of central pain pathways and its validity as target for the design of analgesics.

Spinal Reflexes and Windup In Vitro: Effects of Analgesics and Anesthetics

The spinal cord is the first relay center for nociceptive information. Following peripheral injury, the spinal cord sensitizes. A sign of spinal sensitization is the hyper-reflexia which develops shortly after injury and can be detected in the isolated spinal cord as a "memory of pain." In this context, it is easy to understand that many analgesic compounds target spinally located sites of action to attain analgesia. In vitro isolated spinal cord preparations have been used for a number of years, and experience on the effects of compounds of diverse pharmacological families on spinal function has accumulated. Recently, we have proposed that the detailed study of spinal segmental reflexes in vitro may produce data relevant to the evaluation of the analgesic potential of novel compounds. In this review, we describe the main features of segmental reflexes obtained in vitro and discuss the effects of compounds of diverse chemical nature and pharmacological properties on such reflexes. Our aim was to compare the different profiles of action of the compounds on segmental reflexes in order to extract clues that may be helpful for pharmacological characterization of novel analgesics.

Intrathecal ketorolac enhances intrathecal morphine analgesia following total knee arthroplasty

Background:

Total knee arthroplasty represents one of the most painful surgeries. The aim of the study was to compare analgesia and adverse effects of intrathecal (IT) ketorolac versus IT morphine, versus the combination of IT ketorolac and morphine.

Materials and Methods:

After ethical approval and patient consent, 80 patients undergoing knee arthroplasty were randomized to one of 4 groups. All groups received 15 mg IT bupivacaine plus IT test drug (2 ml). The control group (CG) received saline as IT test drug. The morphine group (MG) received IT 200 g morphine, the ketorolac group (KG) IT 2 mg ketorolac and the morphine-ketorolac group (MKG) 200 g morphine + 2 mg ketorolac as test drugs. Pain and adverse effects were evaluated. P > 0.05 was considered significant.

Results:

The MG and KG were similar in their times to time to first rescue analgesic (440 ± 38 min and 381 ± 44 min, respectively). Both groups were longer when compared to the CG (170 ± 13 min) (P > 0.01). The MG and KG had lesser ketoprofen consumption compared to the CG (P > 0.05). The time to first rescue analgesic was longer to the MKG (926 ± 222 min) (15 h) compared to CG (P > 0.001) and to the MG and the KG (P > 0.01). MKG displayed lesser ketoprofen consumption compared to MG and KG (P > 0.05) and to the CG (P > 0.02).

Conclusions:

The data suggest a role for spinal ketorolac and morphine in orthopaedic surgery because this combination of agents provided 15 h of analgesia compared to 7 h after each drug alone, with no significant side-effects.

Secondary hyperalgesia in the rat first degree burn model is independent of spinal cyclooxygenase and nitric oxide synthase

Various animal models of pain are dependent on activation of different glutamate receptor subtypes. First degree burn of the paw elicits a secondary hyperalgesia that is dependent on Ca2+ permeable alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), but not N-methyl-D-aspartate (NMDA) receptors. The present study takes advantage of that specificity by examining the effects of spinal pretreatments of agents on this secondary hyperalgesia. Rats with indwelling intrathecal catheters were pretreated with agents prior to paw injury. Mechanical withdrawal thresholds were measured before, and for three h after the injury. Spinal pretreatment with cyclooxygenase (10 and 30 microg (S)-(+)-ibuprofen; and 3 and 30 microg ketorolac) and nitric oxide synthase (33 and 100 microg N(G) Nitro-L-arginine methyl ester hydrochloride (L-NAME) and 10 microg thiocitrulline) inhibitors resulted in no specific anti-allodynia. In contrast, ziconotide (0.3, 1.0 and 3 microg), the N-type voltage gated calcium channel antagonist was very effective in blocking burn-induced sensitivity at all doses used. l-type (Diltiazam 230 microg) and P-type (Agatoxin IVA 0.3 microg) calcium channel blockers produced intermediate effects. Thus, cyclooxygenase and nitric oxide synthase are assumed not to be downstream of Ca2+ permeable AMPA receptors. Voltage gated calcium channels blockers could exert their effects either pre- or post-synaptically.

Synergistic depression of NMDA receptor-mediated transmission by ketamine, ketoprofen and L-NAME combinations in neonatal rat spinal cords in vitro

BACKGROUND AND PURPOSE

Spinal N-methyl-D-aspartate (NMDA) receptor/cyclooxygenase (COX) and nitric oxide synthase (NOS) pathways play a major role in nociceptive processing, and influencing them simultaneously may induce synergistic analgesia. This study determined the spinal antinociceptive interactions between ketamine (NMDA receptor channel blocker), ketoprofen (COX inhibitor) and L-NAME (NOS inhibitor) combinations.

EXPERIMENTAL APPROACH

Using an in vitro neonatal rat spinal cord preparation, two A-fibre-mediated reflexes, the monosynaptic reflex (MSR) and the low-intensity excitatory postsynaptic potential (epsp), and one C-fibre-mediated reflex, the high-intensity epsp, were evoked electrically. The effect of drugs and drug combinations on these reflexes was assessed and the type of interaction determined by isobolographic analysis.

KEY RESULTS

Infusion of ketamine alone decreased all three reflexes. That of ketoprofen decreased both the low and the high-intensity epsp only. Infusion of L-NAME alone produced no significant effects. Co-infusion of fixed ratios of IC(40) fractions of both (ketamine+ketoprofen) and (ketamine+L-NAME) were synergistic for depressing the low and the high-intensity epsps. The interaction was sub-additive for both combinations on the MSR. The only significant effect for the (ketoprofen+L-NAME) combination was synergism on the high-intensity epsp.

CONCLUSIONS AND IMPLICATIONS

All three combinations synergistically depressed nociceptive spinal transmission, and both ketamine and ketoprofen and ketamine and L-NAME combinations did so with potentially decreased motor side effects. If such combination profiles also occur in vivo, the present findings raise the possibility of ultimate therapeutic exploitation of increased analgesia with fewer side effects.