Burst-generating neurones in the dorsal horn in an in vitro preparation of the turtle spinal cord (original) (raw)
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Eur J Neurosci, 1992
The response properties of interneurons in the ventral horn were studied in transverse slices of segments D8 to S2 from the turtle spinal cord, using the current clamp technique. In about half of the neurons the response properties were dominated by their ability to generate plateau potentials. In these cells the plateau potential could account for delayed onset of spiking and a phase of increasing spike frequency during depolarizing current pulses and for a depolarizing afterpotential following the stimulus. The cells usually received monosynaptic and polysynaptic input from the ipsilateral dorsal root and occasionally from the contralateral root. The plateau potential was insensitive to tetrodotoxin but blocked by nifedipine and by replacing Ca2+ with Co2+ in the medium. It is concluded that the response properties of neurons in the ventral horn outside the motor nucleus have differentiated response properties that may well contribute to spinal motor function.
Plateau-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 laterally in the deep dorsal horn and dendrites radiating towards the pial surface, was distinguished by the ability to generate plateau potentials. Activation of the plateau potential by a suprathreshold depolarizing current pulse produced an increasing firing frequency during the first few seconds and a sustained after-discharge. 3. The plateau potential was assumed to be mediated by L-type Ca2+ channels since it was blocked by Co2+ (3 mM) and nifedipine (10 microM) and enhanced by Bay K 8644 (0.5-2 microM). 4. The threshold for activating the plateau potential declined during the first few seconds of depolarization. The decline in threshold gradually subsided over 3-10 s after repolarization. 5. Frequency potent...
The Journal of physiology, 1997
1. Modulation of plateau properties in dorsal horn neurones was studied in a transverse slice preparation of the spinal cord of the turtle. In plateau-generating neurones high frequency stimulation of the ipsilateral dorsal root (10-20 Hz, 0.5-2 min) produced a slow depolarization (2.9 +/- 0.6 mV, mean +/- S.E.M.; n = 6) and enhanced the properties mediated by dihydropyridine-sensitive Ca2+ channels. The tetanic stimulus facilitated wind-up and after-discharges even when fast synaptic transmission was blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 10-20 microM), (+/-)-2-amino-5-phosphonopentanoic acid (AP5, 100 microM), bicuculline (10-20 microM) and strychnine (5-20 microM). 2. Application of cis-(+/-)-1-aminocyclopentane-1,3-dicarboxylic acid (ACPD, 10-50 microM) produced a slow depolarization (5.9 +/- 0.5 mV, n = 21) accompanied by an increase in input resistance (28.8 +/- 5.1%, n = 12). 3. ACPD increased the excitability by facilitating the plateau properties. In the pre...
Journal of neurophysiology, 1997
Plasticity at the neuronal level commonly involves use-dependent changes in strength of particular synaptic pathways or regulation of postsynaptic properties by modulatory transmitters. Here we analyze a novel form of short-term plasticity mediated by use-dependent facilitation of postsynaptic responsiveness. Using current- and voltage-clamp recordings, we found that all spinal ventral horn neurons able to generate plateau potentials showed depolarization-induced facilitation of the underlying inward current. Facilitation was noticeable when the neurons were depolarized to more than -50 mV at intervals <4 s. When stimulation with fast triangular voltage ramps was used, the inward current activated at a less depolarized potential during the second ramp. The inward current and facilitation was eliminated by nifedipine, a selective antagonist of L-type calcium channels. Depolarization-induced facilitation of low-voltage-activated L-type calcium channels is suggested to be the underl...
Calcium conductance and firing properties of spinal motoneurones in the turtle
The Journal of physiology, 1988
1. The contribution of Ca2+ conductance to the firing properties of motoneurones was investigated in transverse slices of the turtle spinal cord. 2. In the presence of tetrodotoxin (TTX), tetraethylamonium (TEA) in low extracellular concentration (less than 5 mM) promoted Ca2+ spikes. In higher concentrations of TEA, a suprathreshold depolarizing current pulse was followed by an after-discharge of Ca2+ spikes riding on a Ca2+ plateau potential. 3. The Ca2+-dependent plateau was also promoted by Cs+, 4-aminopyridine (4-AP) and apamin. However, Ca2+ spikes during plateaux were an order of magnitude faster when promoted by Cs+ or 4-AP rather than TEA, and apamin did not promote Ca2+ spikes at all. 4. Ca2+ plateaux but not Ca2+ spikes were blocked by nifedipine. 5. In normal medium all effects of the transient Ca2+ influx during action potentials were attributable to its influence on the slow after-hyperpolarization. The nifedipine-sensitive, sustained Ca2+ influx was expressed exclusiv...
CurrentMotoneurons by Facilitating an L-Type Calcium Receptors Promote Plateau Potentials in Turtle
2016
The effects of serotonin (5-HT) on intrinsic properties of spinal motoneurons were investigated with intracellular recordings in a slice preparation from adult turtles. In 55% of the cells that were recorded, addition of 5-HT to the extracellular medium promoted plateau potentials as revealed by the response to depolarizing current pulses applied through the intracellular electrode. In the remaining 45% of cells, 5-HT had an inhibitory effect. However, when tested with an applied electric field that preferentially polarizes distal dendrites, 5-HT facilitated plateau potentials in 100% of the cells. Plateau potentials were also promoted by 5-HT focally applied on a dendrite by iontophoresis. Applied near the soma, 5-HT either promoted plateau potentials or inhibited spike generation. The latter effect was accompanied by a decrease in input resistance. Voltage-clamp recordings showed that the facilitation of plateau potentials mediated by L-type Ca 2ϩ channels was due to activation of 5-HT 2 receptors. These findings show that 5-HT regulates intrinsic properties of motoneurons in opposite ways: activation of 5-HT receptors in the soma region inhibits spike generation and plateau potentials, while activation of 5-HT 2 receptors in the dendrites and the soma region promotes spiking by facilitation of plateau potentials mediated by L-type Ca 2ϩ channels.
Short-term plasticity in turtle dorsal horn neurons mediated by L-type Ca2+ channels
Neuroscience, 1994
Windup-the gradual increase of the response-of atory postsynaptic response to dorsal root (DR) dorsal horn neurons to repeated activation of primary stimulation was found in deep dorsal horn neurons afferents is an elementary form of short-term plasticity (Fig. ID) in slices of the turtle spinal cord. A short that may mediate central sensitization to pain. In deep sequence of single, high-intensity electric shocks dorsal horn neurons of the turtle spinal cord in vitro we applied to the ipsilateral DR produced a progressreport windup of the response to repeated depolarizing ively increasing response which lengthened after current pulses as well as to repeated stimulation of the each subsequent stimulus (Fig. lA), provided that ipsilateral dorsal root. We found both forms of windup the frequency of stimulation was 0.1 Hz or higher. to be mediated by a depolarizing potential produced by The increased excitability developed slowly and the increasing activation of postsynaptic L-type Ca*+ short latency synaptic response did not change channels. These results suggest a central role for substantially (Fig. lA, right). As in mammals, a intrinsic postsynaptic properties in nociceptive plas-prolonged afterdischarge was often observed.'4,24*2s'7 ticity and for L-type Ca2+ channels as a promising Windup was sometimes produced more effectively by target for therapeutic intervention. repetition of short trains of stimuli (Fig. 1B). Compared with other sensory modalities nociception exhibits a remarkable degree of peripheral and central plasticity. The mechanisms involved range from habituation33 and sensitization34,35 to poorly defined changes in the global performance of the nociceptive system. " In deep dorsal horn neurons, the response to activation of unmyelinated primary afferents gradually increases in magnitude and duration when repeated every three seconds or faster.24 This elementary type of plasticity, termed windup, is thought to be an intermediate step in the development of central sensitization to pain.23 Therefore, the cellular basis of windup is important for understanding early nociceptive processing. A role for N-methyl-D-aSpartate
European Journal of Neuroscience, 2003
L-type calcium channels mediate the persistent inward current underlying plateau potentials in spinal motoneurons. Electrophysiological analysis shows that plateau potentials are generated by a persistent inward current mediated by low threshold L-type calcium channels located in the dendrites. As motoneurons express L-type calcium channels of the Ca V 1.2 and Ca V 1.3 subtypes, we have investigated the subcellular distribution of these channels using antibody labelling. The plateau generating a persistent inward current is modulated by the activation of metabotropic receptors. For this reason, we also examined the relationship between Ca V 1.2 and Ca V 1.3 subunits in motoneurons and presynaptic terminals labelled with antibodies against synapsin 1a. Motoneurons in the spinal cord of the adult turtle were identified as large neurons, immunopositive for choline acetyltransferase, located in the ventral horn. In these neurons, Ca V 1.2 subunits were present in the cell bodies and axons. Patches of Ca V 1.3 subunits were seen in association with the cell membrane of the somata and both the proximal and distal dendrites. Double labelling with an antibody against synapsin 1a showed that Ca V 1.3 subunits, but not Ca V 1.2 subunits, were always located at synaptic sites. The distribution of Ca V 1.2 and Ca V 1.3 strongly suggests that the persistent inward current underlying plateau potentials in spinal motoneurons is mediated by Ca V 1.3 and not by Ca V 1.2. Our findings also show that Ca V 1.3 may be located in the somatic and dendritic membrane adjacent to particular presynaptic terminals.