Inhibition by general anesthetic propofol of compound action potentials in the frog sciatic nerve and its chemical structure

Anesthetic- and Analgesic-Related Drugs Modulating Both Voltage-Gated Na+ and TRP Channels

Nociceptive information is transmitted by action potentials (APs) through primary afferent neurons from the periphery to the central nervous system. Voltage-gated Na+ channels are involved in this AP production, while transient receptor potential (TRP) channels, which are non-selective cation channels, are involved in receiving and transmitting nociceptive stimuli in the peripheral and central terminals of the primary afferent neurons. Peripheral terminal TRP vanilloid-1 (TRPV1), ankylin-1 (TRPA1) and melastatin-8 (TRPM8) activation produces APs, while central terminal TRP activation enhances the spontaneous release of L-glutamate from the terminal to spinal cord and brain stem lamina II neurons that play a pivotal role in modulating nociceptive transmission. There is much evidence demonstrating that chemical compounds involved in Na+ channel (or nerve AP conduction) inhibition modify TRP channel functions. Among these compounds are local anesthetics, anti-epileptics, α2-adrenoceptor agonists, antidepressants (all of which are used as analgesic adjuvants), general anesthetics, opioids, non-steroidal anti-inflammatory drugs and plant-derived compounds, many of which are involved in antinociception. This review mentions the modulation of Na+ channels and TRP channels including TRPV1, TRPA1 and TRPM8, both of which modulations are produced by pain-related compounds.

Astragaloside depresses compound action potential in sciatic nerve of frogs involved in L-type Ca2+-channel dependent mechanism

The sciatic nerve is the largest sensorimotor nerve within the peripheral nervous system (PNS), possessing the ability to produce endogenous neurotrophins. Compound nerve action potentials (CNAPs) are regarded as a physiological/pathological indicator to identify nerve activity in signal transduction of the PNS. Astragaloside (AST), a small-molecule saponin purified from Astragalus membranaceus, is widely used to treat chronic disease. Nonetheless, the regulatory effects of AST on the sciatic nerve remain unknown. Therefore, the present investigation was undertaken to study the effect of AST on CNAPs of frog sciatic nerves. Here, AST depressed the conduction velocity and amplitude of CNAPs. Importantly, the AST-induced responses could be blocked by a Ca2+-free medium, or by applying all Ca2+ channel antagonists (CdCl2/LaCl3) or L-type Ca2+ channel blockers (nifedipine/diltiazem), but not the T-type and P-type Ca2+ channel antagonist (NiCl2). Altogether, these findings suggested that AST may attenuate the CNAPs of frog sciatic nerves in vitro via the L-type Ca2+-channel dependent mechanisms.

Effect of Systemic Lidocaine on Postoperative Early Recovery Quality in Patients Undergoing Supratentorial Tumor Resection

Purpose

Lidocaine has been gradually used in general anesthesia. This study was designed to investigate the effect of systemic lidocaine on postoperative quality of recovery (QoR) in patients undergoing supratentorial tumor resection, and to explore its brain-injury alleviation effect in neurosurgical anesthesia.

Patients and Methods

Sixty adult patients undergoing elective supratentorial tumor resection. Patients were randomly assigned either to receive lidocaine (Group L: 1.5 mg/kg bolus completed 10 min before anesthesia induction followed by an infusion at 2.0 mg/kg/h) or to receive normal saline (Group C: received volume-matched normal saline at the same infusion rate). Primary outcome measures were Quality of Recovery-40 (QoR-40) scores on postoperative day (POD) 1 and 2. Plasma concentrations of S100B protein (S100B), neuron specific enolase (NSE), interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) before anesthesia induction and at the end of surgery were assessed. Visual Analogue Scale (VAS) scores were assessed at 1, 2, 6, 12, 24 and 48 h after surgery. Perioperative parameters and adverse events were also recorded.

Results

Patients between two groups had comparable baseline characteristics. Global QoR-40 scores on POD 1 and POD 2 were significantly higher (P <0.001) in group L (165.5±3.8 vs 173.7±4.7) than those in group C (155.6±4.0 vs 163.2±4.5); and scores of physical comfort, emotional state, and pain in group L were superior to those in group C (P <0.05). In group L, patients possessed lower plasma concentration of pro-inflammatory factors (IL-6, TNF-α) and brain injury-related factors (S100B, NSE) (P <0.05), consumed less remifentanil and propofol, and experienced lower pain intensity. Multiple linear regression analysis demonstrated age and pain were correlated with postperative recovery quality.

Conclusion

Systemic lidocaine improved early recovery quality after supratentorial tumor resection with general anesthesia, and had certain brain-injury alleviation effects. These benefits may be attributed to the inflammation-alleviating and analgesic properties of lidocaine.

Inhibition of Fast Nerve Conduction Produced by Analgesics and Analgesic Adjuvants-Possible Involvement in Pain Alleviation

Nociceptive information is transmitted from the periphery to the cerebral cortex mainly by action potential (AP) conduction in nerve fibers and chemical transmission at synapses. Although this nociceptive transmission is largely inhibited at synapses by analgesics and their adjuvants, it is possible that the antinociceptive drugs inhibit nerve AP conduction, contributing to their antinociceptive effects. Many of the drugs are reported to inhibit the nerve conduction of AP and voltage-gated Na⁺ and K⁺ channels involved in its production. Compound action potential (CAP) is a useful measure to know whether drugs act on nerve AP conduction. Clinically-used analgesics and analgesic adjuvants (opioids, non-steroidal anti-inflammatory drugs, ₂-adrenoceptor agonists, antiepileptics, antidepressants and local anesthetics) were found to inhibit fast-conducting CAPs recorded from the frog sciatic nerve by using the air-gap method. Similar actions were produced by antinociceptive plant-derived chemicals. Their inhibitory actions depended on the concentrations and chemical structures of the drugs. This review article will mention the inhibitory actions of the antinociceptive compounds on CAPs in frog and mammalian peripheral (particularly, sciatic) nerves and on voltage-gated Na⁺ and K⁺ channels involved in AP production. Nerve AP conduction inhibition produced by analgesics and analgesic adjuvants is suggested to contribute to at least a part of their antinociceptive effects.