Propofol and Sevoflurane Depress Spinal Neurons In Vitro via  Different Molecular Targets

2004 ◽  
Vol 101 (5) ◽  
pp. 1167-1176 ◽  
Author(s):  
Christian Grasshoff ◽  
Bernd Antkowiak
Keyword(s):  
Spinal Cord ◽  
Action Potential ◽  
Gabaa Receptors ◽  
Molecular Targets ◽  
Glycine Receptors ◽  
Spinal Neurons ◽  
Action Potential Firing ◽  
Spontaneous Action Potential ◽  
Potential Firing ◽  
Spontaneous Action

Background The capacity of general anesthetics to produce immobility is primarily spinally mediated. Recently, compelling evidence has been provided that the spinal actions of propofol involve gamma-aminobutyric acid type A (GABAA) receptors, whereas the contribution of glycine receptors remains uncertain. The relevant molecular targets of the commonly used volatile anesthetic sevoflurane in the spinal cord are largely unknown, but indirect evidence suggests a mechanism of action distinct from propofol. Methods The effects of sevoflurane and propofol on spontaneous action potential firing were investigated by extracellular voltage recordings from ventral horn interneurons in cultured spinal cord tissue slices obtained from embryonic rats (embryonic days 14-15). Results Propofol and sevoflurane reduced spontaneous action potential firing of neurons. Concentrations causing half-maximal effects (0.11 microm propofol, 0.11 mm sevoflurane) were lower than the median effective concentration immobility (1-1.5 microm propofol, 0.35 mm sevoflurane). At higher concentrations, complete inhibition of action potential activity was observed with sevoflurane but not with propofol. Effects of sevoflurane were mediated predominantly by glycine receptors (45%) and GABAA receptors (38%), whereas propofol acted almost exclusively via GABAA receptors (96%). Conclusions The authors' results suggest that glycine and GABAA receptors are the most important molecular targets mediating depressant effects of sevoflurane in the spinal cord. They provide evidence that sevoflurane causes immobility by a mechanism distinct from the actions of the intravenous anesthetic propofol. The finding that propofol acts exclusively via GABAA receptors can explain its limited capacity to depress spinal neurons in the authors' study.

scholarly journals Cholinergic Modulation of Sevoflurane Potency in Cortical and Spinal Networks In Vitro 

2007 ◽  
Vol 106 (6) ◽  
pp. 1147-1155 ◽  
Author(s):  
Christian Grasshoff ◽  
Berthold Drexler ◽  
Harald Hentschke ◽  
Horst Thiermann ◽  
Bernd Antkowiak
Keyword(s):  
Action Potential ◽  
Gabaa Receptor ◽  
Gabaa Receptors ◽  
Receptor Function ◽  
Action Potential Firing ◽  
Newborn Mice ◽  
Organophosphate Intoxication ◽  
Spontaneous Action Potential ◽  
Potential Firing ◽  
Spontaneous Action

Background Victims of organophosphate intoxication with cholinergic crisis may have need for sedation and anesthesia, but little is known about how anesthetics work in these patients. Recent studies suggest that cholinergic stimulation impairs gamma-aminobutyric acid type A (GABAA) receptor function. Because GABAA receptors are major targets of general anesthetics, the authors investigated interactions between acetylcholine and sevoflurane in spinal and cortical networks. Methods Cultured spinal and cortical tissue slices were obtained from embryonic and newborn mice. Drug effects were assessed by extracellular voltage recordings of spontaneous action potential activity. Results Sevoflurane caused a concentration-dependent decrease in spontaneous action potential firing in spinal (EC50=0.17+/-0.02 mM) and cortical (EC50=0.29+/-0.01 mM) slices. Acetylcholine elevated neuronal excitation in both preparations and diminished the potency of sevoflurane in reducing action potential firing in cortical but not in spinal slices. This brain region-specific decrease in sevoflurane potency was mimicked by the specific GABAA receptor antagonist bicuculline, suggesting that (1) GABAA receptors are major molecular targets for sevoflurane in the cortex but not in the spinal cord and (2) acetylcholine impairs the efficacy of GABAA receptor-mediated inhibition. The latter hypothesis was supported by the finding that acetylcholine reduced the potency of etomidate in depressing cortical and spinal neurons. Conclusions The authors raise the question whether cholinergic overstimulation decreases the efficacy of GABAA receptor function in patients with organophosphate intoxication, thereby compromising anesthetic effects that are mediated predominantly via these receptors such as sedation and hypnosis.

scholarly journals Circadian- and Light-Dependent Regulation of Resting Membrane Potential and Spontaneous Action Potential Firing of Drosophila Circadian Pacemaker Neurons

2008 ◽  
Vol 99 (2) ◽  
pp. 976-988 ◽  
Author(s):  
Vasu Sheeba ◽  
Huaiyu Gu ◽  
Vijay K. Sharma ◽  
Diane K. O'Dowd ◽  
Todd C. Holmes
Keyword(s):  
Membrane Potential ◽  
Action Potential ◽  
Activity Patterns ◽  
Burst Firing ◽  
Resting Membrane Potential ◽  
Action Potential Firing ◽  
Pacemaker Neurons ◽  
Spontaneous Action Potential ◽  
Potential Firing ◽  
Spontaneous Action

The ventral lateral neurons (LNvs) of adult Drosophila brain express oscillating clock proteins and regulate circadian behavior. Whole cell current-clamp recordings of large LNvs in freshly dissected Drosophila whole brain preparations reveal two spontaneous activity patterns that correlate with two underlying patterns of oscillating membrane potential: tonic and burst firing of sodium-dependent action potentials. Resting membrane potential and spontaneous action potential firing are rapidly and reversibly regulated by acute changes in light intensity. The LNv electrophysiological light response is attenuated, but not abolished, in cry b mutant flies hypomorphic for the cell-autonomous light-sensing protein CRYPTOCHROME. The electrical activity of the large LNv is circadian regulated, as shown by significantly higher resting membrane potential and frequency of spontaneous action potential firing rate and burst firing pattern during circadian subjective day relative to subjective night. The circadian regulation of membrane potential, spontaneous action potential firing frequency, and pattern of Drosophila large LNvs closely resemble mammalian circadian neuron electrical characteristics, suggesting a general evolutionary conservation of both physiological and molecular oscillator mechanisms in pacemaker neurons.

Effects of Small Concentrations of Volatile Anesthetics on Action Potential Firing of Neocortical Neurons In Vitro 

1998 ◽  
Vol 88 (6) ◽  
pp. 1592-1605 ◽  
Author(s):  
Bernd Antkowiak ◽  
Charlotte Helfrich-Forster
Keyword(s):  
Action Potential ◽  
General Anesthesia ◽  
Volatile Anesthetics ◽  
Synaptic Inhibition ◽  
Action Potential Firing ◽  
Gaba A ◽  
Neocortical Neurons ◽  
Spontaneous Action Potential ◽  
Potential Firing ◽  
Spontaneous Action

Background Volatile general anesthetics depress neuronal activity in the mammalian central nervous system and enhance inhibitory Cl- currents flowing across the gamma-aminobutyric acid A (GABA(A)) receptor-ion channel complex. The extent to which an increase in GABA(A)-mediated synaptic inhibition contributes to the decrease in neuronal firing must be determined, because many further effects of these agents have been reported on the molecular level. Methods The actions of halothane, isoflurane, and enflurane on the firing patterns of single neurons were investigated by extracellular recordings in organotypic slice cultures derived from the rat neocortex. Results Volatile anesthetics depressed spontaneous action potential firing of neocortical neurons in a concentration-dependent manner. The estimated median effective concentration (EC50) values were about one half the EC50 values for general anesthesia. In the presence of the GABA(A) antagonist bicuculline (20 microM), the effectiveness of halothane, isoflurane, and enflurane in reducing the discharge rates were diminished by 48-65%, indicating that these drugs act via the GABA(A) receptor. Conclusions Together with recent investigations, our results provide evidence that halothane, isoflurane, and enflurane reduced spontaneous action potential firing of neocortical neurons in cultured brain slices mainly by increasing GABA(A)-mediated synaptic inhibition. At concentrations, approximately one half the EC50 for general anesthesia, volatile anesthetics increased overall GABA(A)-mediated synaptic inhibition about twofold, thus decreasing spontaneous action potential firing by half.

scholarly journals Zinc Enhances the Inhibitory Effects of Strychnine-Sensitive Glycine Receptors in Mouse Hippocampal Neurons

2007 ◽  
Vol 98 (6) ◽  
pp. 3666-3676 ◽  
Author(s):  
Hai Xia Zhang ◽  
Liu Lin Thio
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Hippocampal Neurons ◽  
Neuronal Excitability ◽  
Hippocampal Slices ◽  
Glycine Receptors ◽  
Inhibitory Effects ◽  
Action Potential Firing ◽  
Embryonic Mouse ◽  
Potential Firing

Although extracellular Zn2+ is an endogenous biphasic modulator of strychnine-sensitive glycine receptors (GlyRs), the physiological significance of this modulation remains poorly understood. Zn2+ modulation of GlyR may be especially important in the hippocampus where presynaptic Zn2+ is abundant. Using cultured embryonic mouse hippocampal neurons, we examined whether 1 μM Zn2+, a potentiating concentration, enhances the inhibitory effects of GlyRs activated by sustained glycine applications. Sustained 20 μM glycine (EC25) applications alone did not decrease the number of action potentials evoked by depolarizing steps, but they did in 1 μM Zn2+. At least part of this effect resulted from Zn2+ enhancing the GlyR-induced decrease in input resistance. Sustained 20 μM glycine applications alone did not alter neuronal bursting, a form of hyperexcitability induced by omitting extracellular Mg2+. However, sustained 20 μM glycine applications depressed neuronal bursting in 1 μM Zn2+. Zn2+ did not enhance the inhibitory effects of sustained 60 μM glycine (EC70) applications in these paradigms. These results suggest that tonic GlyR activation could decrease neuronal excitability. To test this possibility, we examined the effect of the GlyR antagonist strychnine and the Zn2+ chelator tricine on action potential firing by CA1 pyramidal neurons in mouse hippocampal slices. Co-applying strychnine and tricine slightly but significantly increased the number of action potentials fired during a depolarizing current step and decreased the rheobase for action potential firing. Thus Zn2+ may modulate neuronal excitability normally and in pathological conditions such as seizures by potentiating GlyRs tonically activated by low agonist concentrations.

scholarly journals Identification of Sodium Channel Isoforms That Mediate Action Potential Firing in Lamina I/II Spinal Cord Neurons

2011 ◽  
Vol 7 ◽  
pp. 1744-8069-7-67 ◽  
Author(s):  
Michael E Hildebrand ◽  
Janette Mezeyova ◽  
Paula L Smith ◽  
Michael W Salter ◽  
Elizabeth Tringham ◽  
...  
Keyword(s):  
Spinal Cord ◽  
Action Potential ◽  
Sodium Channel ◽  
Action Potential Firing ◽  
Spinal Cord Neurons ◽  
Lamina I ◽  
Potential Firing

Eclosion hormone provides a link between ecdysis-triggering hormone and crustacean cardioactive peptide in the neuroendocrine cascade that controls ecdysis behavior

1999 ◽  
Vol 202 (4) ◽  
pp. 343-352 ◽  
Author(s):  
S.C. Gammie ◽  
J.W. Truman
Keyword(s):  
Action Potential ◽  
Motor Program ◽  
Action Potential Firing ◽  
Nervous Systems ◽  
Eclosion Hormone ◽  
Bath Application ◽  
Crustacean Cardioactive Peptide ◽  
Potential Firing ◽  
Spontaneous Action ◽  
Ecdysis Triggering Hormone

Three insect peptide hormones, eclosion hormone (EH), ecdysis-triggering hormone (ETH) and crustacean cardioactive peptide (CCAP), have been implicated in controlling ecdysis behavior in insects. This study examines the interactions between these three peptides in the regulation of the ecdysis sequence. Using intracellular recordings, we found that ETH is a potent activator of the EH neurons, causing spontaneous action potential firing, broadening of the action potential and an increase in spike peak amplitude. In turn, electrical stimulation of the EH neurons or bath application of EH to desheathed ganglia resulted in the elevation of cyclic GMP (cGMP) levels within the Cell 27/704 group (which contain CCAP). This cGMP production increases the excitability of these neurons, thereby facilitating CCAP release and the generation of the ecdysis motor program. Extracellular recordings from isolated nervous systems show that EH has no effect on nervous systems with an intact sheath. In desheathed preparations, in contrast, EH causes only the ecdysis motor output. The latency from EH application to ecdysis was longer than that after CCAP application, but shorter than that when ETH is applied to a whole central nervous system. These data, along with previously published results, support a model in which ETH causes pre-ecdysis behavior and at higher concentrations stimulates the EH neurones. EH release then facilitates the onset of ecdysis by enhancing the excitability of the CCAP neurons.

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