Nerve Action Potential Conduction Research Articles

Inhibitory Actions of Clinical Analgesics, Analgesic Adjuvants, and Plant-Derived Analgesics on Nerve Action Potential Conduction

The action potential (AP) conduction in nerve fibers plays a crucial role in transmitting nociceptive information from the periphery to the cerebral cortex. Nerve AP conduction inhibition possibly results in analgesia. It is well-known that many analgesics suppress nerve AP conduction and voltage-dependent sodium and potassium channels that are involved in producing APs. The compound action potential (CAP) recorded from a bundle of nerve fibers is a guide for knowing if analgesics affect nerve AP conduction. This entry mentions the inhibitory effects of clinically used analgesics, analgesic adjuvants, and plant-derived analgesics on fast-conducting CAPs and voltage-dependent sodium and potassium channels. The efficacies of their effects were compared among the compounds, and it was revealed that some of the compounds have similar efficacies in suppressing CAPs. It is suggested that analgesics-induced nerve AP conduction inhibition may contribute to at least a part of their analgesic effects.

Hyperacute relapse of Lewis-Sumner syndrome during influenza A (H1N1) virus infection

BackgroundLewis-Sumner Syndrome (LSS) is considered an asymmetric sensory-motor variant of Chronic Inflammatory Demyelinating Polyneuropathy (CIDP), mostly affecting the limbs distally, with electrophysiological evidence of multifocal motor conduction blocks. Cranial nerve involvement is present in a minority. Various well-known infectious agents, directly or via the host’s immune responses, may trigger or exacerbate acute and chronic peripheral neuropathies, which may manifest clinically through a multitude of signs and symptoms.Case presentationWe present the case of a 57-year-old male with Lewis-Sumner Syndrome, whose clinical course was quite stable over many years. He developed severe hyperacute relapse of his neuropathic disease in the context of active pneumonia due to influenza A (H1N1) virus infection. During this exacerbation, besides the obvious worsening of the previous asymmetric limb involvement, the patient also manifested left peripheral facial palsy and dysphagia that rapidly evolved over minutes, mimicking a stroke. The patient also showed rapid recovery, with marked improvement of the acute neuropathic dysfunction, immediately after initiation of treatment with oseltamivir. Our hypothesis is that the direct modulation of Na + ion channel activity in the host’s peripheral nerve cell by H1N1 viral proteins could cause acute and potentially reversible dysfunction in the conduction of nerve action potentials. Direct viral neuritis could also have been the cause. Immunomodulatory agents, namely IVIg, were not administered due to the swift clinical improvement noticed in the following days.ConclusionsWe aim to raise awareness of the possibility of atypical neurological presentations of viral infections, especially relevant in the context of the pandemic the world is now facing.

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, α2-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.

Effect of papaverine on synaptic transmission in the guinea-pig ileum.

1. The effect of papaverine, a well known smooth muscle relaxant, was investigated on neural transmission within the enteric nervous system. Segments of guinea-pig ileum were placed in a partitioned bath to enable drugs, including papaverine, to be applied to enteric nerve pathways without interfering with the recording of the smooth muscle contraction. Ascending excitatory enteric nerve pathways were activated by electrical field stimulation in the anal compartment (10 Hz for 2 s, 45 mA, 0.5 ms pulse duration) and the resulting contraction of the intestinal circular muscle in the oral compartment was recorded isotonically. 2. Tetrodotoxin (0.6 microM) and hexamethonium (100 microM) both abolished, or greatly reduced, the contractions when applied to either compartment indicating that nicotinic synapses are involved in this pathway. 3. Papaverine (0.3-30 microM) applied independently to each compartment depressed in a concentration-dependent manner, the nerve-mediated contractions. The IC50 of this inhibitory effect was 3.53 microM for the oral and 4.76 microM for the anal compartments, respectively. Two other phosphodiesterase (PDE) inhibitors, 3-isobutyl-1-methylxanthine (IBMX 10-300 microM) and theophylline (30-1000 microM) added to the anal compartment also inhibited the nerve mediated contractions. Papaverine applied to the anal bath, after IBMX 100 microM (or theophylline 300 microM) further inhibited the nerve-mediated contractions, but was less effective than when applied alone. 4. Phentolamine (1 microM), an alpha-adrenoceptor antagonist, reduced the inhibitory effect of papaverine, but not that of IBMX (100 microM) or theophylline (300 microM). A combination of phentolamine and IBMX (or theophylline) prevented the inhibitory effect of papaverine. 5. Tetrodotoxin, but not papaverine or hexamethonium, inhibited the contraction elicited by electrical stimulation just anal to the partition indicating that papaverine did not affect the generation or conduction of nerve action potentials. 6. Verapamil (1 microM) and nifedipine (1 microM), two smooth muscle relaxants which act by blocking L-type calcium channels, only inhibited the contractions when applied directly to the recording (oral) compartment. This indicates that L-type Ca2+ channels are probably not involved in synaptic transmission in these ascending pathways and thus that the PDE inhibitors do not inhibit synaptic transmission by acting on these channels. omega-Conotoxin GVIA (10 nM), a potent inhibitor of the N-type Ca2+ channels, blocked the nerve-mediated contractions applied to either compartment. Whether the PDE inhibitors exert their inhibitory actions via these channels remains to be established. 7. The results indicate that the PDE inhibitors, papaverine, IBMX and theophylline inhibit excitatory enteric neural pathways by depressing synaptic transmission. The inhibitory effect of papaverine (but not IMBX or theophylline) involves, at least in part, the release of noradrenaline from sympathetic nerves acting on alpha-adrenoceptors on enteric neurones.

Genetic studies of membrane excitability in Drosophila: lethal interaction between two temperature-sensitive paralytic mutations.

Two mutants of Drosophila melanogaster, parats1 (1-53.9) and napts (2-56.2) both display similar temperature-sensitive paralysis associated with blockage in the conduction of nerve action potentials, suggesting that the two gene products have a similar function. This idea is supported by the observation that the double mutant is unconditionally lethal. Genetic analysis of this synergistic interaction has revealed the following: it specifically involves the para and nap loci; all para alleles interact with napts, but the strength of the interaction varies in an allele-dependent fashion; lethality of the double mutant occurs during the first larval instar with parats1 but differs with other para alleles; hypodosage of para+ causes lethality in a napts background. These results together with previous electrophysiological, behavioral and pharmacological studies of these mutants suggest that both para and nap affect sodium channels and possibly encode different subunits.