Generation of rhythmic patterns of activity by ventral interneurones in rat organotypic spinal slice culture (original) (raw)
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Mechanisms controlling bursting activity induced by disinhibition in spinal cord networks
European Journal of Neuroscience, 2002
Disinhibition reliably induces regular synchronous bursting in networks of spinal interneurons in culture as well as in the intact spinal cord. We have combined extracellular multisite recording using multielectrode arrays with whole cell recordings to investigate the mechanisms involved in bursting in organotypic and dissociated cultures from the spinal cords of embryonic rats. Network bursts induced depolarization and spikes in single neurons, which were mediated by recurrent excitation through glutamatergic synaptic transmission. When such transmission was blocked, bursting ceased. However, tonic spiking persisted in some of the neurons. In such neurons intrinsic spiking was suppressed following the bursts and reappeared in the intervals after several seconds. The suppression of intrinsic spiking could be reproduced when, in the absence of fast synaptic transmission, bursts were mimicked by the injection of current pulses. Intrinsic spiking was also suppressed by a slight hyperpolarization. An afterhyperpolarization following the bursts was found in roughly half of the neurons. These afterhyperpolarizations were combined with a decrease in excitability. No evidence for the involvement of synaptic depletion or receptor desensitization in bursting was found, because neither the rate nor the size of spontaneous excitatory postsynaptic currents were decreased following the bursts. Extracellular stimuli paced bursts at low frequencies, but failed to induce bursts when applied too soon after the last burst. Altogether these results suggest that bursting in spinal cultures is mainly based on intrinsic spiking in some neurons, recurrent excitation of the network and auto-regulation of neuronal excitability.
Origin and classification of spontaneous discharges in mouse superficial dorsal horn neurons
Scientific reports, 2018
Superficial laminae of the spinal cord possess a considerable number of neurons with spontaneous activity as reported in vivo and in vitro preparations of several species. Such neurons may play a role in the development of the nociceptive system and/or in the spinal coding of somatosensory signals. We have used electrophysiological techniques in a horizontal spinal cord slice preparation from adult mice to investigate how this activity is generated and what are the main patterns of activity that can be found. The results show the existence of neurons that fire regularly and irregularly. Within each of these main types, it was possible to distinguish patterns of spontaneous activity formed by single action potentials and different types of bursts according to intra-burst firing frequency. Activity in neurons with irregular patterns was blocked by a mixture of antagonists of the main neurotransmitter receptors present in the cord. Approximately 82% of neurons with a regular firing pat...
European Journal of Neuroscience, 2013
The neural mechanisms generating rhythmic bursting activity in the mammalian brainstem, particularly in the pre-Bö tzinger complex (pre-Bö tC), which is involved in respiratory rhythm generation, and in the spinal cord (e.g. locomotor rhythmic activity) that persist after blockade of synaptic inhibition remain poorly understood. Experimental studies in rodent medullary slices containing the pre-Bö tC identified two mechanisms that could potentially contribute to the generation of rhythmic bursting: one based on the persistent Na + current (I NaP ), and the other involving the voltage-gated Ca 2+ current (I Ca ) and the Ca 2+ -activated nonspecific cation current (I CAN ), activated by intracellular Ca 2+ accumulated from extracellular and intracellular sources. However, the involvement and relative roles of these mechanisms in rhythmic bursting are still under debate. In this theoretical/modelling study, we investigated Na +dependent and Ca 2+ -dependent bursting generated in single cells and heterogeneous populations of synaptically interconnected excitatory neurons with I NaP and I Ca randomly distributed within populations. We analysed the possible roles of network connections, ionotropic and metabotropic synaptic mechanisms, intracellular Ca 2+ release, and the Na + /K + pump in rhythmic bursting generated under different conditions. We show that a heterogeneous population of excitatory neurons can operate in different oscillatory regimes with bursting dependent on I NaP and/or I CAN , or independent of both. We demonstrate that the operating bursting mechanism may depend on neuronal excitation, synaptic interactions within the network, and the relative expression of particular ionic currents. The existence of multiple oscillatory regimes and their state dependence demonstrated in our models may explain different rhythmic activities observed in the pre-Bö tC and other brainstem/spinal cord circuits under different experimental conditions. R Pump = 200 pA, Na ieq = 15 mM, K P = 15 mM Leakage I L g L ∈ [2, 3] nS
Spatiotemporal characterization of rhythmic activity in rat spinal cord slice cultures
European Journal of Neuroscience, 2001
Rat spinal networks generate a spontaneous rhythmic output directed to motoneurons under conditions of increased excitation or of disinhibition. It is not known whether these differently induced rhythms are produced by a common rhythm generator. To investigate the generation and the propagation of rhythmic activity in spinal networks, recordings need to be made from many neurons simultaneously. Therefore extracellular multisite recording was performed in slice cultures of embryonic rat spinal cords grown on multielectrode arrays. In these organotypic cultures most of the spontaneous neural activity was nearly synchronized. Waves of activity spread from a source to most of the network within 35±85 ms and died out after a further 30±400 ms. Such activity waves induced the contraction of cocultured muscle ®bres. Several activity waves could be grouped into aperiodic bursts. Disinhibition with bicuculline and strychnine or increased excitability with high K + or low Mg 2+ solutions could induce periodic bursting with bursts consisting of one or several activity waves. Whilst the duration and period of activity waves were similar for all protocols, the duration and period of bursts were longer during disinhibition than during increased excitation. The sources of bursting activity were mainly situated ventrally on both sides of the central ®ssure. The pathways of network recruitment from one source were variable between bursts, but they showed on average no systematic differences between the protocols. These spatiotemporal similarities under conditions of increased excitation and of disinhibition suggest a common spinal network for both types of rhythmic activity.
Plateau properties in mammalian spinal interneurons during transmitter-induced locomotor activity
Neuroscience, 1996
We examined the organization of spinal networks controlling locomotion in the isolated spinal cord of the neonatal rat, and in this study we provide the first demonstration of plateau and bursting mechanisms in mammalian interneurons that show locomotor-related activity. Using tight-seal whole-cell recordings, we characterized the activity of interneurons from spinal regions previously suggested to be involved in locomotor rhythm generation. Most (63%) interneurons showed rhythmic, oscillating membrane potentials in phase with rhythmic ventral root activity induced by the glutamate receptor agonist, N-methyl-d-aspartate and 5-hydroxytryptamine or activation of muscarinic acetylcholine receptors. We focused our attention on these cells because they appeared most likely to be participating in locomotor networks. The rhythmic oscillations of most of these interneurons (88%) appeared to be driven mainly by excitatory and inhibitory synaptic inputs. A smaller number of interneurons, however, also displayed intrinsic plateau properties or bursting capabilities which amplified their response to excitatory input, and which were correlated with the presence of negative slope regions in the steady-state I–V curve, and with the ability to burst in the absence of synaptic drive.Although the bursting properties of these neurons may contribute to the generation of the locomotor rhythm, as suggested previously in studies of lower vertebrates, we suggest that a prime role of intrinsic plateau properties in mammalian locomotor networks is to facilitate or shape and time the propagation of information in the network.
Burst-generating neurones in the dorsal horn in an in vitro preparation of the turtle spinal cord
The Journal of physiology, 1996
1. In transverse slices of the spinal cord of the turtle, intracellular recordings were used to characterize and analyse the responses to injected current and activation of primary afferents in dorsal horn neurones. 2. A subpopulation of neurones, with cell bodies located centrally in the dorsal horn, was distinguished by the ability to generate a burst response following a hyperpolarization from rest or during a depolarization from a hyperpolarized holding potential. The burst response was inactivated at the resting membrane potential. 3. The burst response was mediated by a low threshold Ca2+ spike assumed to be mediated by T-type Ca2+ channels since it resisted tetrodotoxin and was blocked by 3 mM Co2+ or 100-300 microM Ni2+ and resembled the low threshold spike (LTS) described elsewhere. 4. Some burst-generating cells also displayed plateau potentials mediated by L-type Ca2+ channels. In these cells the burst following a hyperpolarizing current pulse, applied from the resting me...
Burst firing in identified rat geniculate interneurons
Neuroscience, 1999
We used whole-cell patch recording to study 102 local interneurons in the rat dorsal lateral geniculate nucleus in vitro. Input impedance with this technique (607.0^222.4 MV) was far larger than that measured with sharp electrode techniques, suggesting that interneurons may be more electrotonically compact than previously believed. Consistent and robust burst firing was observed in all interneurons when a slight depolarizing boost was given from a potential at, or slightly hyperpolarized from, resting membrane potential. These bursts had some similarities to the low-threshold spike described previously in other thalamic neuron types. The bursting responses were blocked by Ni ϩ , suggesting that the lowthreshold calcium current I T , responsible for the low-threshold spike, was also involved in interneuron burst firing. Compared to the low-threshold spike of thalamocortical cells, however, the interneuron bursts were of relatively long duration and low intraburst frequency. The requirement for a depolarizing boost to elicit the burst is consistent with previous reports of a depolarizing shift of the I T activation curve of interneurons relative to thalamocortical cells, a finding we confirmed using voltage-clamp. Voltage-clamp study also revealed an additional long-lasting current that could be tentatively identified as the calcium activated non-selective cation current, I CAN , based on reversal potential and on pharmacological characteristics. Computer simulation of the interneuron burst demonstrated that its particular morphology is likely due to the interaction of I T and I CAN. In the slice, bursts could also be elicited by stimulation of the optic tract, suggesting that they may occur in response to natural stimulation. Synaptically triggered bursts were only partially blocked by Ni ϩ , but could then be completely blocked by further addition of (^)-2amino-5-phosphonopentanoic acid. The existence of robust bursts in this cell type suggests an additional role for interneurons in sculpting sensory responses by feedforward inhibition of thalamocortical cells. The low-threshold spike is a mechanism whereby activity in a neuron is dependent on a prior lack of activity in that same neuron. Understanding of the low-threshold spike in the other major neuron types of the thalamus has brought many new insights into how thalamic oscillations might be involved in sleep and epilepsy. Our description of this phenomenon in the interneurons of the thalamus suggests that these network oscillations might be even more complicated than previously believed.
Journal of Neurophysiology, 2002
Disinhibition of rat spinal networks induces a spontaneous rhythmic bursting activity. The major mechanisms involved in the generation of such a bursting are intrinsic neuronal firing of a subpopulation of interneurons, recruitment of the network by recurrent excitation, and autoregulation of neuronal excitability. We have combined whole cell recording with calcium imaging and flash photolysis of caged-calcium to investigate the contribution of [Ca2+]i to rhythmogenesis. We found that calcium mainly enters the neurons through voltage-activated calcium channels and N-methyl-d-aspartate (NMDA) channels as a consequence of the depolarization during the bursts. However, [Ca2+]i could neither predict the start nor the termination of bursts and is therefore not critically involved in rhythmogenesis. Also calcium-induced calcium release is not involved as a primary mechanism in bursting activity. From these findings, we conclude that in the rhythmic activity induced by disinhibition of spi...
Evidence for bursting pacemaker neurones in cultured spinal cord cells
Neuroscience, 1985
Intracellular recordings were made from dissociated mouse spinal cord cells in primary culture. One type of spinal cord neurone, with a large cell body (4CL50 pm), 3-5 short neurites, and a mean resting potential of-65 mV, was found to fire rhythmic bursts of action potentials with a phase duration of approximately Is when the membrane potential was depolarized to-55 mV. These bursts did not arise from spontaneous synaptic input, but appeared to result from endogenous ionic conductance properties of the membrane resembling those observed in molluscan bursting pacemaker neurones. Ionic conductances underlying this bursting activity were studied pharmacologically by local application of ionic conductance blockers. Pacemaker potentials depended on Na+ conductance, since tetrodotoxin and Na-free medium were the most potent agents for blocking spontaneous rhythmic activity. However, a Ca'+ conductance was involved in the depolarizing phase of membrane potential oscillations, since Ba2+ application increased oscillation amplitude. Action potentials observed during the bursts were Na+-and Cal+-dependent. They did not differ significantly from those observed in other spinal cord neurones in culture. Application of tetraethylammonium, CoCI,, BaCl, and 4-aminopyridine revealed at least three different potassium conductances which controlled this bursting pacemaker activity. A delayed potassium conductance controlled spike duration, a Ca-dependent potassium conductance controlled the duration of the burst and underlay the hyperpolarizing phase terminating the burst, and finally, a transient potassium conductance appeared to be involved in the control of phase duration. The demonstration that spinal cord neurones growing in monolayer culture display typical bursting pacemaker activity raises the possibility that bursting pacemaker neurones in the mammalian spinal cord may be involved in a phasic pattern generator that could control such activities as walking and the respiratory rhythm.