The action of LSD on the isolated frog spinal cord: Electrophysiological and ultrastructural data

Extracellular potassium accumulation and transmission in frog spinal cord

The anesthetic urethane is commonly used in physiological experiments. We tested urethane's actions on GABA receptors on the primary afferents in the spinal cord, which are one of the few areas in the adult central nervous system (CNS) that are depolarized by GABA, and on ligand-gated excitatory amino acid (EAA) receptors located on motoneurons. Both receptor types are critically important during anesthetic immobilization. We used the isolated hemisected spinal cord of the frog in a sucrose gap chamber to record glutamate-, N-methyl-D-aspartate (NMDA)-, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-, kainate-, and gamma-aminobutyric acid (GABA)-induced depolarizations of the dorsal root (DR) and ventral root (VR). DR potentials (DRPs) and VR potentials (VRPs) evoked by single supramaximal afferent stimuli were also studied. Urethane (10-80 mM) was applied for 10-30 min. Urethane depressed EAA responses on the motoneurons in a dose-dependent manner. At a clinical anesthetic concentration (10 mM), EAA-induced depolarizations were reduced by 8.1 ± 2.2 % (n = 7, P = 0.025), but increasing the concentration to 40 mM revealed a larger, 24.7 ± 3 % (n = 53, P = 0.0001) depressing effect of urethane on all EAA responses in the motoneurons. However, GABA and K(+) responses recorded in the DR were not altered by the presence of 10 or 40 mM urethane. Evoked DRPs and VRPs were reduced by urethane and spontaneous DR and VR potentials were suppressed by 10 or blocked by 40 mM urethane. Urethane appears to be selective for EAA-, sparing GABA responses at a clinical anesthetic concentration. Only a 10 % reduction of EAA activity seems to be necessary to induce anesthesia.

Dorsal root potentials in the isolated frog spinal cord: Amino acid neurotransmitters and magnesium ions

The immaturity of interactions between GABA-and benzodiazepine binding sites in the frog spinal cord

Serum from patients with multiple sclerosis (MS) and other diseases was added to the medium perfusing isolated hemisected frog spinal cord, and the effect on ventral root responses (VRR) tested. As control, a standardized commercial human serum (Moni-trol I) was used. In 25 out of 40 spinal cord preparations Moni-trol gave inhibition of VRR ranging from 2.8 to 23.1%. 76% of the tests with confirmed MS sera showed inhibition of VRR, after deduction of the control serum effect, while 53% of the tests with sera from other diseases were inhibitory. Sera from cases of suspected but clinically unconfirmed MS gave strong inhibition (above 20%).

1. The isolated frog spinal cord was used to study the action of amino acids and their antagonists on primary afferent terminals and motoneurones. The direct effects of these substances were observed by bathing the cord in 20 mM magnesium sulphate (thus blocking synaptic transmission) and recording the polarization level of the dorsal and ventral roots.2. gamma-Aminobutyric acid (GABA) and glutamic acid depolarized the dorsal root and reduced dorsal-root potentials, while glycine produced only weak and variable effects. Glutamic acid also depolarized the ventral root; GABA usually produced either a hyperpolarization or had little effect, while glycine caused variable effects.3. Bicuculline and picrotoxin antagonized all the synaptic potentials recorded on the dorsal root, as well as the GABA responses on both dorsal and ventral roots.4. All the synaptic potentials examined remained and were markedly prolonged in the absence of external chloride except the ventral root-dorsal root potential. Replacement of the physiologic complement of chloride during chloride-free perfusion restored the potentials to their original time courses.5. Depolarizing amino acid responses remained in the absence of external chloride, while hyperpolarizing responses were reversed into depolarizations. Return to normal Ringer solution re-established the hyperpolarizations.6. Removal of external sodium reversibly abolished the amino acid depolarizations but had little effect on the depolarizations in response to applications of high external potassium concentrations.7. The results support the hypotheses (a) that GABA mediates presynaptic inhibition by depolarizing primary afferent terminals and (b) that the GABA-mediated depolarization is sodium dependent.8. The results also indicate that GABA utilizes different ionic mechanisms to mediate presynaptic inhibition (sodium) and post-synaptic inhibition (chloride) in the amphibian (and presumably in the mammal).

ArticlesHabituation of a monosynaptic response in vertebrate central nervous system: lateral column-motoneuron pathway in isolated frog spinal cordP. B. Farel, D. L. Glanzman, and R. F. ThompsonP. B. Farel, D. L. Glanzman, and R. F. ThompsonPublished Online:01 Nov 1973https://doi.org/10.1152/jn.1973.36.6.1117MoreSectionsPDF (2 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmailWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformationCited ByThe development of serotonergic raphespinal projections in Xenopus laevisInternational Journal of Developmental Neuroscience, Vol. 4, No. 5Activation of brainstem serotoninergic pathways decreases homosynaptic depression of monosynaptic responses of frog spinal motoneuronsBrain Research, Vol. 280, No. 2The nictitating membrane response: An electrophysiological study of the abducens nerve and nucleus and the accessory abducens nucleus in rabbitBrain Research, Vol. 258, No. 2Habituation of the Hoffmann reflexBrain Research, Vol. 220, No. 2Disruption of vertebrate monosynaptic habituation by ethyl alcoholBrain Research, Vol. 212, No. 1The effects of hyposmolality on spinal cord activityLife Sciences, Vol. 28, No. 8Effects of changes in osmolality on spinal cord activityExperimental Neurology, Vol. 68, No. 3Alterations in spontaneous miniature potential activity during habituation of a vertebrate monosynaptic pathwayBrain Research, Vol. 189, No. 2Evidence against conduction failure as the mechanism underlying monosynaptic habituation in frog spinal cordBrain Research, Vol. 174, No. 2The bulbo-spinal indoleaminergic pathway in the frogBrain Research, Vol. 172, No. 2Inhibition of the monosynaptic responses in frog spinal motoneuronsNeuroscience, Vol. 4, No. 7Habituation of the nictitating membrane reflex response in the intact frogPhysiology & Behavior, Vol. 22, No. 6Effect of temperature on habituation of the LC-VR reflex of the frog spinal cordPhysiology & Behavior, Vol. 22, No. 4Reflex activity of regenerating frog spinal motoneuronsBrain Research, Vol. 158, No. 2Action of Mg2+ at low concentrations on the response to habituating stimuli and spontaneous activity of frog spinal cord motoneuronsBrain Research, Vol. 142, No. 1The efects of Ca2+ and Mg2+ on the habituating LCVR reflex of the frog spinal cordBrain Research, Vol. 139, No. 1The pharmacology of the amphibian spinal cordProgress in Neurobiology, Vol. 11, No. 1Brainstem reticular formation mechanisms subserving generalized seizures: Effects of convulsants and anticonvulsants on sensory-evoked responsesProgress in Neuro-Psychopharmacology, Vol. 2, No. 4Monosynaptic habituation in the vertebrate forebrain: The dentate gyrus examined in vitroBrain Research, Vol. 115, No. 3Long-term and short-term plasticity in the CA1, CA3, and dentate regions of the rat hippocampal sliceBrain Research, Vol. 110, No. 3Ultrastructural observations in the frog spinal cord in relation to the generation of primary afferent depolarizationNeuroscience Letters, Vol. 2, No. 3Criteria for distinguishing between monosynaptic and polysynaptic transmissionBrain Research, Vol. 105, No. 1The relation between monosynaptic spinal reflex amplitudes and some EEG alpha activity parametersElectroencephalography and Clinical Neurophysiology, Vol. 40, No. 3Sensitization and habituation of the plantar cushion reflex in catsBrain Research, Vol. 103, No. 2The effects of 5,6-dihydroxytryptamine in the amphibian spinal cord using silver staining techniquesBrain Research, Vol. 78, No. 2The effect of p-CPAand lesions of the dorsal raphe nucleus on habituation of the flexor withdrawal reflexBrain Research, Vol. 77, No. 3Dual processes control response habituation across a single synapseBrain Research, Vol. 72, No. 2Persistent increase in synaptic efficacy following a brief tetanus in isolated frog spinal cordBrain Research, Vol. 66, No. 1 More from this issue > Volume 36Issue 6November 1973Pages 1117-1130 Copyright & PermissionsCopyright © 1973 the American Physiological Societyhttps://doi.org/10.1152/jn.1973.36.6.1117PubMed4543415History Published online 1 November 1973 Published in print 1 November 1973 Metrics

Habituation and dishabituation to dorsal root stimulation in the isolated frog spinal cord

Presynaptic modulation of synaptic effectiveness of afferent and ventrolateral tract fibers in the frog spinal cord

Effects of changes in osmolality on spinal cord activity

Effects of naloxone on spinal reflexes in the isolated frog spinal cord.

The interaction of porphyrin precursors with GABA receptors in the isolated frog spinal cord

Pharmacological activation of locomotor patterns in larval and adult frog spinal cords

Substitution of synthetic buffers (Tris, TES, HEPES, or 3,3-dimethylglutarate) for CO2-bicarbonate buffer in Ringer solution perfusing the isolated in vitro frog spinal cord preparation altered membrane properties and reflex activity. Perfusion with Ringer solution gassed with O2 and containing synthetic bu,fers consistently produced a depolarization of motoneurons and dorsal root fibers, decreased the amplitude (and usually the duration) of ventral and dorsal root potentials, and had variable effects on motoneuron and dorsal root reflex discharges. With Tris-Ringer these discharges decreased in amplitude; with Ringer containing one of the other synthetic buffers, these discharges were augmented. All changes were reversible when the cord was returned to bicarbonate-buffered Ringer aerated with 95% O2/5% CO2. The use of a combined buffer system-one containing a synthetic buffer and bicarbonate-induced smaller or minimal changes in bioelectric activity. At present the data are insufficient to allow firm conclusions concerning the mechanisms underlying these results; but it is evident 1) that changes in PCO2 and bicarbonate concentration and 2) that the pharmacological properties of synthetic buffers are important variables.

The action of Co2+ on the isolated frog spinal cord was studied by extracellular application of the ion in the superfusing solution. A complete and reversible blockade of chemical synaptic transmission by Co2+ (3 mmol/l) could be achieved after a superfusion period of 20-30 min. During continued Co2+ application (greater than 60 min) the following effects upon the motoneuron membrane, dorsal root and ventral root fibres were observed. Motoneurons and ventral root fibers: 1. prolongation of initial segment action potential to a maximum of 30 ms, 2. blockade of the long afterhyperpolarization, 3. abolition of adaptation, 4. increased duration of fibre action potential in the ventral root, 5. backfiring after ventral root stimulation. Dorsal root fibres: 1. prolongation of the extraspinal fibre action potential, 2. marked prolongation of the action potential of the terminal region, 3. backfiring of multiple action potentials after dorsal root stimulation. Even in the presence of Co2+, when synaptic transmission was completely blocked, strong convulsive reactions of the isolated spinal cord were observed. Intracellular injection of Co2+ into motoneurons did not affect the action potential, but led to a shift of the EIPSP towards the membrane potential. The results indicate that the induction of convulsive reactions by Co2+ is mainly due to a prolongation of action potentials. The plateau-like deformation of the action potential of the initial segment membrane and presumably of the terminal region of nerve endings results in retrograde propagation of action potentials and in some cases induces oscillatory discharge of single neurons.