Laszlo Gyermek

Pharmacology of serotonin as related to anesthesia

Serotonin (5-hydroxytryptamine) is an important biogenic amine that fulfills the role of neurotransmitter and neuromodulator. It has been a focus of interest during the last decade. Its diversity of pharmacologic actions is related to a wide variety of receptors and effector mechanisms. Seven serotonin receptor families have been identified thus far. They are genetically different transmembrane proteins composed of several hundred amino acids. The majority of these are G-protein-coupled, except the 5-HT3 receptors, which are directly ligand gated to fast ion channels. Serotonin is widely distributed in the body within the central and peripheral nervous systems, smooth muscles, and platelets, in particular. Consequently, its effects manifest mainly in these organs and influence a wide variety of neural, vascular, smooth muscle, and platelet functions. (Melatonin, a physiologically active metabolite of serotonin, is also instrumental in affecting many neural and hormonal functions.) Several selective agonists and particularly many selective antagonists have been developed for serotonin, which helped the serotonin receptor subtype classification. Some of these drugs are also used therapeutically in the treatment of migraine (eg, sumatriptan, which is a 5-HT1 receptor agonist), vascular disorders (5-HT2 antagonists), and nausea and vomiting (5-HT3 antagonists, eg, dolasetron, granisetron, ondansetron, and tropisetron), and have been investigated in gastrointestinal motility disorders (5-HT4 antagonists) and behavioral psychopathologies (5-HT1 agonists and 5-HT2-4 antagonists). Serotonin reuptake inhibitors are of particular clinical importance in the treatment of psychological illness. Future use of these drugs is also envisioned in the treatment of certain types of pain syndromes. Awareness of the serotonergic drugs and the recognition of possible drug interactions among drugs that influence serotonergic mechanisms in humans are becoming increasingly important in the practice of anesthesiology.

Analgesic Interaction between Intrathecal Midazolam and Glutamate Receptor Antagonists on Thermal-induced Pain in Rats

Background Two major neurotransmitters, [Greek small letter gamma]-aminobutyric acid (GABA) and the excitatory amino acid, glutamate, may be involved in nociception in the spinal cord. GABA and glutamate receptors may operate in concert to modify signals in the central nervous system. The purpose of this study was to investigate the spinal analgesic interaction between midazolam, a benzodiazepine-GABAA receptor agonist, and two glutamate receptor antagonists on acute thermal nociception. Methods Sprague-Dawley rats were implanted with chronic lumbar intrathecal catheters and were tested for their tail withdrawal response by the tail flick test after intrathecal administration of saline, midazolam (1–100 [micro sign]g), AP-5 (1–30 [micro sign]g), or YM872 (0.3–30 [micro sign]g). AP-5 is an N-methyl-D-aspartate (NMDA) receptor antagonist and YM872 is an [Greek small letter alpha]-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor antagonist. The combination of midazolam and the other two agents were also tested by isobolographic analyses. Motor disturbance and behavioral changes were observed. Results Dose-dependent increases in the tail flick latency were observed with midazolam, AP-5, and YM872 with 50% effective dose values of 1.57 +/- 0.34 (SEM) [micro sign]g, 5.54 +/- 0.19 [micro sign]g, and 1.0 +/- 0.22 [micro sign]g, respectively. A potent synergy in analgesia with decreased behavioral changes and motor disturbance was obtained when combining midazolam with AP-5 or YM872. Conclusions Spinally administered midazolam and an NMDA- or an AMPA-receptor antagonist exhibited potent synergistic analgesia on acute thermal nociception in rats. Side effects, shown by behavioral changes and motor disturbance, decreased with the combination of the agents. These results point out an important direction for the study of acute nociception.

The Spinal Antinociceptive Effects of a Novel Competitive Ampa Receptor Antagonist, Ym872, on Thermal or Formalin-induced Pain in Rats

UNLABELLED Alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor antagonists have spinally mediated analgesic effects on acute nociception; however, their current formulations are not water-soluble and have toxic side effects. A new competitive AMPA antagonist, YM872 (2,3-dioxo-7-[1H-imidazol-1-yl]-6-nitro-1,2,3,4-tetrahydro-1-quinoxal inyl acetic acid) is water-soluble and may have fewer side effects. The purpose of this study was to investigate the analgesic effects of YM872 on both acute thermal and irritant-induced pain. Sprague-Dawley rats were implanted with chronic lumbar intrathecal catheters and were tested for their tail withdrawal response by the tail flick test and for their paw flinches by formalin injection after the intrathecal administration of YM872. The tail flick latency increased dose-dependently with a 50% effective dose (ED50) value of 1.0 microg. The number of flinches in both Phase 1 and Phase 2 of the formalin test decreased with increasing dose of YM872. ED50 values were 0.24 microg in Phase 1 and 0.21 microg in Phase 2. YM872 10 and 30 microg induced motor disturbance and flaccidity. In rats, the intrathecal administration of YM872 had analgesic effects on both acute thermal and formalin-induced nociceptions. Transient motor disturbance and flaccidity occurred only with large doses. YM872 may have potential in the clinical management of both acute and chronic pain. IMPLICATIONS A novel alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor antagonist, YM872, may have an analgesic effect on both acute and chronic pain when administered intrathecally.

Neuromuscular Pharmacology of Taac3, a New Nondepolarizing Muscle Relaxant with Rapid Onset and Ultrashort Duration of Action

We selected bis [N-(3,4-diacetoxybenzyl) tropanium-3&agr;-yl] glutarate dibromide (TAAC3) from many new tropinyl diester derivatives to evaluate its neuromuscular blocking (NMB) and autonomic side effects on anesthetized rats, rabbits, guinea pigs, cats, pigs, dogs, and monkeys. NMB potency, onset, recovery index, and duration of action were determined. Comparisons of these pharmacologic variables were made between TAAC3 and rocuronium. In the cat, the degrees of train-of-four and tetanic fade, posttetanic potentiation, and pharmacologic antagonism were evaluated. For determination of the NMB maintenance dose, TAAC3 was also given to rabbits and pigs in the initial dose/maintenance infusion mode. Cardiac vagal block was evaluated in the rat, pig, cat, and guinea pig on the basis of the inhibition of the bradycardia to stimulation of the vagus nerve. Sympathetic ganglion block was studied on the superior cervical ganglion-nictitating membrane preparation of the cat. TAAC3 produced nondepolarizing NMB. Its NMB 90% effective doses ranged from 90 to 425 &mgr;g/kg, depending on the species. TAAC3 had a faster onset (0.8–1.0 min), shorter recovery index (0.6–1.1 min), and shorter duration of action (1.8–3.5 min) than rocuronium. It produced a slight cumulative effect on infusion, but not on repeated single-dose administration. Cardiac vagal block was present at doses exceeding the NMB 90% effective dose. In the cat and pig at equipotent NMB doses, the degree of cardiac vagal block was similar to that of rocuronium. There was no demonstrable sympathetic ganglion block in the cat. In view of its favorable NMB characteristics, TAAC3 is now undergoing detailed preclinical studies.

The systemically administered competitive AMPA receptor antagonist, YM872, has analgesic effects on thermal or formalin-induced pain in rats.

UNLABELLED A new competitive alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor antagonist, (2,3-dioxo-7-[1H-imidazol-1-yl]-6-nitro-1,2,3,4-tetrahydro-1-quinoxal inyl) acetic acid (YM872) has analgesic effects on acute thermal- and formalin-induced nociception by intrathecal administration. The purpose of this study was to determine the analgesic effects of systemically administered YM872 in both acute thermal- and irritant-induced pain. Sprague-Dawley rats were tested for tail withdrawal response by the tail flick test and for paw flinches by formalin injection after intraperitoneal administration of YM872. The tail flick latency increased dose-dependently with a 50% effective dose value of 156.3 microg. The number of flinches in both first and second phases of the formalin test decreased with increasing the dose of YM872. The 50% effective dose values were 1.0 microg in the first phase and 38.7 microg in the second phase. Transiently, intraperitoneal administration of 1 and 10 mg of YM872 induced motor disturbance and 10 mg induced loss of pinna reflex. We conclude that intraperitoneal administration of YM872 had analgesic effects on both acute thermal- and formalin-induced nociceptions in rats. Transient motor disturbance and loss of pinna reflex occurred only with large doses. IMPLICATIONS Intraperitoneally administered YM872, a new alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor antagonist, had analgesic effects on thermal- and formalin-induced pain in rats. Larger doses induced transient motor disturbance and loss of pinna reflex mediated in the brain.

Synergistic analgesic effects of intrathecal midazolam and NMDA or AMPA receptor antagonists in rats.

Purpose: To investigate the interaction of midazolam and N-methyl-D-aspartate (NMDA) receptor or -amino-3-hydroxy-5-methyl isoxazole-4-propionic acid (AMPA) receptor antagonist on the effects of persistent inflammatory nociceptive activation.Methods: Male Sprague-Dawley rats were implanted with lumbar intrathecal catheters and were tested for their responses to subcutaneous formalin injection into the hindpaw. Saline, midazolam (1 to 100 µg), AP-5 (1 to 30 µg), a NMDA receptor antagonist, or YM872 (0.3 to 30 µg), an AMPA receptor antagonist was injected intrathecally 10 min before formalin injection. The combinations of midazolam and AP-5 or YM872 in a constant dose ratio based on the 50% effective dose (ED50) were also tested and were analysed with an isobologram.Results: Dose-dependent effects were observed with midazolam (ED50 was 1.34 µg and 1.21 µg in phase 1 and 2 of the formalin test, respectively), AP-5 (7.64 µg and 1.4 µg) and YM872 (0.24 µg and 0.21 µg). Synergistic effects in both phases were obtained with combining midazolam with AP-5 or YM872. The ED50 of midazolam decreased to 0.012 µg (phase 1) and 0.27 µg (phase 2) with AP-5 and to 0.09 µg (phase 1) and 0.35 µg (phase 2) with YM872 (P<0.01).Conclusions: These results suggest a functional coupling of benzodiazepine—aminobutyric acid (GABA)A receptor with NMDA and AMPA receptors in acute and persistent inflammatory nociceptive mechanisms in the spinal cord.RésuméObjectif: Examiner l’interaction du midazolam et d’un antagoniste du N-méthyl-D-aspartate (NMDA) ou d’un antagoniste du récepteur de l’acide-amino-3-hydroxy-5-méthylisoxazole-4-propionique (AAMP) sur les effects de l’activation nociceptive de l’inflammation persistante.Méthode: On a implanté à des rats males Sprague-Dawley des cathéters intrathécaux lombaires et on a testé leurs réactions à l’injection sous-cutanée de formaline dans la patte arrière. Une solution salée, du midazolam (1 à 100 µg), de l’AP-5 (1 à 30 µg), un antagoniste du récepteur NMDA ou le YM872 (0,3 à 30 µg), un antagoniste du récepteur AMPA a été administré en injection intrathécale 10 min avant l’injection de formaline. Les combinaisons de midazolam et d’AP-5 ou de YM872 en dose au rapport constant, fondée sur la dose efficace 50 % (ED50) ont été aussi testées et analysées à l’aide d’un isobologramme.Résultats: Des effects dépendants de la dose ont été observés avec le midazolam (ED50 a été de 1,34 µg et 1,21 µg en phases 1 et 2 du test de formaline, respectivement), avec AP-5 (7,64 µg et 1,4 µg) et avec YM872 (0,24 µg et 0,21 µg). Les effects synergiques des deux phases ont été obtenus en combinant le midazolam et AP-5 ou YM872. La ED50 du midazolam a baissé à 0,012 µg (phase 1) et à 0,27 µg (phase 2) avec AP-5 et à 0,09 µg (phase 1) et à 0,35 µg (phase 2) avec YM872 (P<0,01).Conclusion: Ces résultats suggèrent un couplage fonctionnel des récepteurs NMDA ou AMPA avec les récepteurs benzodiazépine-acide -aminobutyrique (GABA)A comme partie des mécanismes nociceptifs de l’inflammation aiguë et persistante dans la moelle épinière.

The analgesic interaction between intrathecal clonidine and glutamate receptor antagonists on thermal and formalin-induced pain in rats.

Clonidine, an &agr;2 adrenergic receptor agonist, inhibits glutamate release from the spinal cord. We studied the interaction of intrathecally administered clonidine and glutamate receptor antagonists on acute thermal or formalin induced nociception. Sprague-Dawley rats with lumbar intrathecal catheters were tested for their tail withdrawal response by the tail flick test and paw flinches produced by formalin injection after intrathecal administration of saline, clonidine, AP-5 (a N-methyl-D-aspartate receptor antagonist), or YM872 (an &agr;-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor antagonist). The combinations of clonidine and the other two agents were also tested by isobolographic analyses. Motor disturbance and behavioral changes were observed as side effects. The ED50 values of clonidine decreased from 0.26 &mgr;g (tail flick), 0.12 &mgr;g (Phase 1) and 0.13 &mgr;g (Phase 2) to 0.036 &mgr;g, 0.006 &mgr;g, and 0.013 &mgr;g with AP-5, and 0.039 &mgr;g, 0.057 &mgr;g, and 0.133 &mgr;g with YM872, respectively. Side effects were attenuated in both combinations. In conclusion, spinally administered clonidine and AP-5 or YM872 exhibited potent synergistic analgesia on acute thermal and formalin-induced nociception with decreased side effects in rats.

Spinally mediated analgesia and receptor binding affinity of epibatidine analogs

Two epibatidine derivatives, (1R, 2R, 5S)-A-(2-chloropyridinyl) azabicyclo [3.2.1] octane; A=2 beta: analog 1, 2 alpha: analog 2, were investigated for their spinally mediated analgesic effects and binding affinity to nicotinic acetylcholine receptors. The tail flick response and behavioral side effects were studied after intrathecal agents in rats. The membrane preparations of the Torpedo Californica and rat cerebral cortices were used for radioligand binding utilizing [3H] epibatidine displacement. Their affinity to muscular and neuronal nicotinic acetylcholine receptors and spinally mediated analgesic potencies were 15, 20, and 3.8 times (analog 1) and 2000, 30,000, and 3.3 times (analog 2) less than epibatidine, respectively. Two times the analgesic 50% effective doses (ED(50)s) of the analogs did not induce side effects, while one-third of that of epibatidine induced motor disturbance. In summary, the two epibatidine analogs have higher potency ratio of spinally mediated analgesia/side effects than epibatidine.

Structure-activity relationships among derivatives of dicarboxylic acid esters of tropine

Several categories of neuromuscular blocking bisquaternary tropine and tropane derivatives were synthesized and studied in the past five decades, mainly with the purpose of arriving at meaningful information about structure-activity relationships. Such a structure-activity relationship database is important in the development of new muscle relaxants with improved pharmacological characteristics. Although quaternary tropine diesters were explored since 1952, most of them were developed in the last decade. Over 250 such agents are being reviewed here. The skeleton of the majority of them consists of two tropines, connected through their 3-OH group with various dicarboxylic acid ester linkages and quaternized by several mostly di- and trisubstituted benzyl groups. The significance of changing the quaternizing group; the diester linker; and, to a smaller extent, the substituents and their steric orientation on the tropane ring and some alterations of the tropane ring itself have been explored in in vivo experiments on anesthetized rats. Di- or trisubstituted alkoxy and/or acyloxybenzyl quaternaries of certain tropinyl diesters, e.g., glutaryl, fumaryl, and cyclobutane-1,2-dicarboxylyl, showed an optimal profile with respect to desirable neuromuscular blocking actions and side effects, which was confirmed on other experimental animal species. The details of the structural changes toward obtaining new ultrashort-acting nondepolarizing muscle relaxants are discussed.

ANALGESIC INTERACTION BETWEEN INTRATHECAL MIDAZOLAM AND GLUTAMATE RECEPTOR ANTAGONISTS ON THERMAL INDUCED PAIN IN RATS

BACKGROUND Two major neurotransmitters, gamma-aminobutyric acid (GABA) and the excitatory amino acid, glutamate, may be involved in nociception in the spinal cord. GABA and glutamate receptors may operate in concert to modify signals in the central nervous system. The purpose of this study was to investigate the spinal analgesic interaction between midazolam, a benzodiazepine-GABA(A) receptor agonist, and two glutamate receptor antagonists on acute thermal nociception. METHODS Sprague-Dawley rats were implanted with chronic lumbar intrathecal catheters and were tested for their tail withdrawal response by the tail flick test after intrathecal administration of saline, midazolam (1-100 microg), AP-5 (1-30 microg), or YM872 (0.3-30 microg). AP-5 is an N-methyl-D-aspartate (NMDA) receptor antagonist and YM872 is an alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor antagonist. The combination of midazolam and the other two agents were also tested by isobolographic analyses. Motor disturbance and behavioral changes were observed. RESULTS Dose-dependent increases in the tail flick latency were observed with midazolam, AP-5, and YM872 with 50% effective dose values of 1.57+/-0.34 (SEM) microg, 5.54+/-0.19 microg, and 1.0+/-0.22 microg, respectively. A potent synergy in analgesia with decreased behavioral changes and motor disturbance was obtained when combining midazolam with AP-5 or YM872. CONCLUSIONS Spinally administered midazolam and an NMDA- or an AMPA-receptor antagonist exhibited potent synergistic analgesia on acute thermal nociception in rats. Side effects, shown by behavioral changes and motor disturbance, decreased with the combination of the agents. These results point out an important direction for the study of acute nociception.