Sheldon H. Roth

Carbachol-induced EEG ‘theta’ activity in hippocampal brain slices

Application of the cholinergic agonist carbachol (50 microM) produced theta-like rhythmical waveforms, recorded in the stratum moleculare of the dentate gyrus. Atropine sulfate (50 microM) antagonized the carbachol-induced theta-like activity, consistent with this action of atropine in vivo. These results provide the first direct evidence that hippocampal neurons are capable of producing synchronized slow-wave activity when isolated from pulsed rhythmic inputs of the medial septum and other brain regions.

The effects of general anesthetics on excitatory and inhibitory synaptic transmission in area CA1 of the rat hippocampus in vitro

UNLABELLED It is unclear whether general anesthetics induce enhancement of neural inhibition and/or attenuation of neural excitation. We studied the effects of pentobarbital (5 x 10(-4) mol/L), propofol (5 x 10(-4) mol/L), ketamine (10(-3) mol/L), halothane (1.5 vol%), and isoflurane (2.0 vol%) on both excitatory and inhibitory synaptic transmission in rat hippocampal slices. Excitatory or inhibitory synaptic pathways were isolated using pharmacological antagonists. Extracellular microelectrodes were used to record electrically evoked CA1 neural population spikes (PSs). In the presence of the gamma-aminobutyric acid type A (GABA(A)) receptor antagonist (bicuculline), the inhibitory actions of pentobarbital and propofol were completely antagonized, whereas those of ketamine, halothane, and isoflurane were only partially blocked. To induce the N-methyl-D-aspartate (NMDA) receptor-mediated PS (NMDA PS), the non-NMDA and GABA(A) receptors were blocked in the absence of Mg2+. Ketamine, halothane, and isoflurane decreased the NMDA PS, and pentobarbital and propofol had no effect on the NMDA PS. The non-NMDA receptor-mediated PS (non-NMDA PS) was examined using the antagonists for the NMDA and GABA(A) receptors. Volatile, but not i.v., anesthetics reduced the non-NMDA PS. These findings indicate that pentobarbital and propofol produce inhibitory actions due to enhancement in the GABA(A) receptor; that ketamine reduces NMDA receptor-mediated responses and enhances GABA(A) receptor-mediated responses; and that halothane and isoflurane modulate GABA(A), NMDA, and non-NMDA receptor-mediated synaptic transmission. IMPLICATIONS Volatile anesthetics modulate both excitatory and inhibitory synaptic transmission of in vitro rat hippocampal pathways, whereas i.v. anesthetics produce more specific actions on inhibitory synaptic events. These results provide further support the idea that general anesthetics produce drug-specific and distinctive effects on different pathways in the central nervous system.

Molecular Mechanisms of Hydrogen Sulfide Toxicity

Rationale. The toxicity of H2S has been attributed to its ability to inhibit cytochrome c oxidase in a similar manner to HCN. However, the successful use of methemoglobin for the treatment of HCN poisoning was not successful for H2S poisonings even though the ferric heme group of methemoglobin scavenges H2S. Thus, we speculated that other mechanisms contribute to H2S induced cytotoxicity. Experimental procedure. Hepatocyte isolation and viability and enzyme activities were measured as described by , and . Results. Incubation of isolated hepatocytes with NaHS solutions (a H2S source) resulted in glutathione (GSH) depletion. Moreover, GSH depletion was also observed in TRIS-HCl buffer (pH 6.0) treated with NaHS. Several ferric chelators (desferoxamime and DETAPAC) and antioxidant enzymes (superoxide dismutase [SOD] and catalase) prevented cell-free and hepatocyte GSH depletion. GSH-depleted hepatocytes were very susceptible to NaHS cytotoxicity, indicating that GSH detoxified NaHS or H2S in cells. Cytotoxicity was also partly prevented by desferoxamine and DETAPC, but it was increased by ferric EDTA or EDTA. Cell-free oxygen consumption experiments in TRIS-HCl buffer showed that NaHS autoxidation formed hydrogen peroxide and was prevented by DETAPC but increased by EDTA. We hypothesize that H2S can reduce intracellular bound ferric iron to form unbound ferrous iron, which activates iron. Additionally, H2S can increase the hepatocyte formation of reactive oxygen species (ROS) (known to occur with electron transport chain). H2S cytotoxicity therefore also involves a reactive sulfur species, which depletes GSH and activates oxygen to form ROS.

Intracellular records of carbachol-induced theta rhythm in hippocampal slices ☆

Intracellular recordings were made in the CA1, CA3 and dentate cell layers prior to, during and after the bath perfusion of 50 microM carbachol on hippocampal slices. Fifty-six percent of the cells in this sample were termed theta (theta)-related, i.e., they exhibited membrane potential oscillations of 5-28 mV and rhythmic spike discharges related to the carbachol-induced extracellular theta-rhythm. The remaining 44% of the cells did not show the above relationships to the extracellular theta-rhythm. Carbachol produced an overall depolarization in all cells, in the range of 10-20 mV. These results demonstrated the cellular basis of carbachol-induced theta in hippocampal slices. This preparation will be a valuable model for studying cellular mechanisms and network properties underlying electroencephalographic activity.

Hyperalgesia during sedation: effects of barbiturates and propofol in the rat.

Subhypnotic doses of thiopentone are considered to possess antianalgesic or hyperalgesic properties. In this study, we have tested the hypothesis that the coincidence of sedation and hyperalgesia is a property of both barbiturate and non- barbiturate anaesthetic agents. In a randomized, prospective, blinded study, the effects of slow (20 min) iv infusions of thiopentone, pentobarbitone, methohexitone or propofol on nociceptive threshold were measured in rats by tail pressure analgesimetry and compared with saline- infused control animals. Nociceptive thresholds were correlated with measurements of plasma drug concentrations and behavioural assessments. Comparison of pre- infusion nociceptive threshold with the lowest threshold obtained during drug infusion revealed decreases in all four treatment groups. As a percentage of the pre- infusion values, the decreases were: thiopentone: 42.5% (P < 0.001), pentobarbitone : 27.8% (P = 0.014), methohexitone: 24.9% (P = 0.013), propofol: 21.6% (P = 0.006). There were no changes in nociceptive threshold in the control groups. The relationship between nociceptive threshold and plasma drug concentration was usually characterized by an initial decline followed by a rise in nociceptive threshold as the plasma concentration and degree of sedation increased. The results support the hypothesis that hyperalgesia is a property of different anaesthetic agents when administered at sub- hynotic concentrations.RésuméOn considère que les doses sous- hypotiques de thiopentone possèdent des propriétés antianalgésiques ou hyperalgésiques. Cette étude vérifie l’hypothèse selon laquelle la coïncidence de la sédation avec l’hyperalgie constitue à la fois une propriété des agents anesthésiques barbituriques et des non barbituriques. Au cours d’une élude randomisée, prospective et à l’aveugle, les répercussions sur le seuil nociceptif d’une perfusion lente (20 min) de thiopentone, pentobarbitone, méthohexitone et de propofol sont mesurées par analgésiométrie de compression sur la queue du rat et comparées avec des animaux de contrôle sous perfusion au soluté physiologique. Les seuils nociceptifs sont correlés avec les mesures de concentration plasmatique des drogues et par l’évaluation du comportement. La comparaison du seuil nociceptif avant la perfusion avec le seuil le plus bas obtenu pendant la perfusion révèle des diminutions dans tous les groupes de traitement. En pourcentage des valeurs de préinfusion, les diminutions sont les suivantes: thiopentone: 42,5% (P < 0.001), pentobarbitone: 27,8% (P = 0,014), méthohexitone: 24.9% (P = 0,013), propofol: 21,6% (P = 0,006). Il n’y a pas de changement dans les groupes contrôle au regard du seuil nociceptif. La relation entre le seuil nociceptif et la concentration plasmatique des drogues est ordinairement caractérisée par une baisse initiale suivie par une augmentation du seuil nociceptif à mesure que la concentration plasmatique et le niveau de sédation augmentent. Ces résultats supportent l’hypothèse selon laquelle l’hyperalgie serait une propriété de plusieurs anesthésiques quand ils sont administrés à des concentrations sous- hypnotiques.

Alteration of the morphology and neurochemistry of the developing mammalian nervous system by hydrogen sulphide.

1. Hydrogen sulphide (H2S) is a broad spectrum toxicant that occurs widely in nature and is also released by a variety of industrial activities and processes.

Plasma, Brain, and Spinal Cord Concentrations of Thiopental Associated with Hyperalgesia in the Rat

BackgroundAlthough low doses of barbiturates are widely believed to increase sensitivity to pain, studies of the electrophysiologic effects of these drugs on the neurons involved in nociception in the spinal cord have detected only depressant effects. The goal of the studies reported here was to quantify the hyperalgesia resulting from low-dose thiopental infusions and to measure the associated concentrations of thiopental in the plasma, brain, and spinal cord. MethodsNociception was measured using the threshold for motor response to pressure stimulation of the tail (nociceptive threshold) and tail flick latency in the rat. Thiopental was administered by intravenous infusions designed to produce plasma concentrations that either slowly increased or remained at a steady state. Plasma and tissue thiopental concentrations were measured by high-performance liquid chromatography. ResultsWe observed a reduction in nociceptive threshold that was correlated with the plasma thiopental concentration over the range 2–20 μg.ml−1 (7.6–76 μM). The relationship was nonlinear. Nociceptive threshold reached a nadir (36% less than control values) at a mean plasma thiopental concentration of 13.7 μg.ml−1 (51.9 μM). The steady-state study showed a similar reduction in nociceptive threshold, with an equilibrium plasma thiopental concentration of 7.6 ± 1.3 μg.ml−1 (28.8 ± 4.9 μM). Concentrations of thiopental in brain and spinal cord samples were 1.7 ± 0.03 and 3.5 ± 1.7 μg.g−1, respectively. ConclusionsThese studies confirm previous reports of hyperalgesia in association with small doses of thiopental. Reductions in nociceptive threshold and tail flick latency were observed in association with spinal cord concentrations of thiopental in a range reported by others to depress the electrophysiologic activity of neurons involved in nociception.

Carbachol-induced EEG ‘theta’ in hippocampal formation slices: evidence for a third generator of theta in CA3c area

The topography of carbachol-induced EEG theta activity was studied using the hippocampal formation slice preparation. Systematic tracking with electrodes exhibited two amplitude maxima of cholinergic-induced theta, one located in the stratum oriens of the CA1 pyramidal cells and the other in a region of CA3c pyramidal neurons. In addition, mapping experiments demonstrated EEG theta in the CA3a and CA3b cell body layers, but not in the subicular and parasubicular regions, or the ventral blade of the dentate gyrus. Furthermore, transected slice (trans-slice) preparations used in the present study revealed that the CA3c region could generate carbachol-induced theta independently of CA1 and dentate gyrus generator zones and conversely, CA1 and dentate gyrus areas were capable of generating cholinergic-induced theta rhythm independently of the CA3c region. These results provide strong evidence for 3 independent, anatomically separated generators of theta: one located in the stratum oriens of CA1 neurons, a second in the stratum moleculare of the dentate gyrus and a third one in the region of Ca3c cells. In addition, the results support previous in vivo suggestions that theta rhythm can be either elicited or blocked by cholinergic agents acting on sites within the hippocampal formation.

Evidence that activation of in vitro hippocampal θ rhythm only involves muscarinic receptors

Abstract The present study was conducted for two purposes: the first was to evaluate whether activation of nicotinic receptors in the hippocampal formation in vitro (slice) preparation was capable of producing type 2 (atropine-sensitive) θ rhythm. The cholinergic nature and involvement of muscarinic receptors in this type of θ has been previously well documented. The second purpose was to determine whether perfusion of a number of (other) putative neurotransmitters shown to be present in the hippocampal formation could elicit type 1 (atropine-resistant) θ in the slice preparation. Further experiments were conducted to determine if these agents interacted in any manner with cholinergically-induced type 2 θ. Electroencephalic (EEG) θ activity was not induced by nicotine, providing evidence for an exclusive muscarinic receptor involvement in this cholinergically-induced type 2 θ. In addition, θ activity was not elicited by the application of γ-aminobutyric acid (GABA), glutamate, norepinephrine, dopamine or serotonin. The application of any of these agents did not significantly alter the production of cholinergically-induced θ. These results suggest that type 1 θ originates in regions extrinsic to the hippocampus, or is the result of the interaction of several neurotransmitters on different receptors.

The non‐specific membrane binding properties of ΔA9‐tetrahydrocannabinol and the effects of various solubilizers1

The binding of [3H]δ9‐tetrahydrocannabinol to crude and purified synaptosomal membrane suspended in either Krebs solution or 10mM sodium phosphate buffer was examined. The membrane/buffer partition coefficient was found to be 12 500, and was constant over a free concentration range of 10−8 to 10−6m. Binding was similar in both suspending media, and to both crude and purified synaptosomal membrane. The solubilizing agent Cremophor E.L. (8 μg ml−1) decreased the partition coefficient by one‐half, and by greater than 99 % at 0.4 mg ml−1. Similar effects were observed with Tween 80, while ethanol caused a maximum decrease of 60%. Membrane concentrations of THC were calculated at various effective concentrations reported in the literature, and were within the range predicted by the Meyer‐Overton rule of anaesthesia. An apparent non‐specific interaction with neuronal membranes and effective membrane concentrations of the order 2 times 10−1 to 1 times 10−2 mol kg−1 suggests THC may exert some of its effects by a mechanism analogous to the general anaesthetics, and thus may be classified as a partial anaesthetic.