Serotonin Modulates Dendritic Calcium Influx in Commissural Interneurons in the Mouse Spinal Locomotor Network

2007 ◽  
Vol 98 (4) ◽  
pp. 2157-2167 ◽  
Author(s):  
Manuel Díaz-Ríos ◽  
Daniel A. Dombeck ◽  
Watt W. Webb ◽  
Ronald M. Harris-Warrick
Keyword(s):  
Spinal Cord ◽  
Voltage Clamp ◽  
Neuronal Excitability ◽  
Calcium Influx ◽  
Active Role ◽  
Calcium Currents ◽  
Detectable Effect ◽  
Lumbar Region ◽  
Fictive Locomotion ◽  
Voltage Dependent

Commissural interneurons (CINs) help to coordinate left–right alternating bursting activity during fictive locomotion in the neonatal mouse spinal cord. Serotonin (5-HT) plays an active role in the induction of fictive locomotion in the isolated spinal cord, but the cellular targets and mechanisms of its actions are relatively unknown. We investigated the possible role of serotonin in modifying dendritic calcium currents, using a combination of two-photon microscopy and patch-clamp recordings, in identified CINs in the upper lumbar region. Dendritic calcium responses to applied somatic voltage-clamp steps were measured using fluorescent calcium indicator imaging. Serotonin evoked significant reductions in voltage-dependent dendritic calcium influx in about 40% of the dendritic sites studied, with no detectable effect in the remaining sites. We also detected differential effects of serotonin in different dendritic sites of the same neuron; serotonin could decrease voltage-sensitive calcium influx at one site, with no effect at a nearby site. Voltage-clamp studies confirmed that serotonin reduces the voltage-dependent calcium current in CINs. Current-clamp experiments showed that the serotonin-evoked decreases in dendritic calcium influx were coupled with increases in neuronal excitability; we discuss possible mechanisms by which these two seemingly opposing results can be reconciled. This research demonstrates that dendritic calcium currents are targets of serotonin modulation in a group of spinal interneurons that are components of the mouse locomotor network.

The development of voltege-dependent ionic conductances In murine spinal cord neurones in culture

1988 ◽  
Vol 66 (10) ◽  
pp. 1328-1336 ◽  
Author(s):  
C. Krieger ◽  
T. A. Sears
Keyword(s):  
Spinal Cord ◽  
Sodium Current ◽  
Potassium Conductance ◽  
Calcium Currents ◽  
Delayed Rectifier ◽  
Patch Clamp Technique ◽  
Calcium Dependent ◽  
Ionic Conductances ◽  
Voltage Dependent

The development of voltage-dependent ionic conductances of foetal mouse spinal cord neurones was examined using the whole-cell patch-clamp technique on neurones cultured from embryos aged 10–12 days (E10–E12) which were studied between the first day in vitro (V1) to V10. A delayed rectifier potassium conductance (IK) and a leak conductance were observed in neurones of E10.V1, E11, V1, and E12, V1 as well as in neurones cultured for longer periods. A rapidly activating and inactivating potassium conductance (IA) was seen in neurones from E11, V2 and E12, V1 and at longer times in vitro. A tetrodotoxin (TTX) sensitive sodium-dependent inward current was observed in neurones of E11 and E12 from V1 onwards. Calcium-dependent conductances were not detectable in these neurones unless the external calcium concentration was raised 10- to 20-foid and potassium conductances were blocked. Under these conditions calcium currents could be observed as early as E11, V3 and E12, V2 and at subsequent times in vitro. The pattern of development of voltage-dependent ionic conductances in murine spinal neurones is such that initially leak and potassium currents are present followed by sodium current and subsequently calcium current.

scholarly journals Intracellular QX-314 Causes Depression of Membrane Potential Oscillations in Lamprey Spinal Neurons During Fictive Locomotion

2002 ◽  
Vol 87 (6) ◽  
pp. 2676-2683 ◽  
Author(s):  
Guo-Yuan Hu ◽  
Zoltán Biró ◽  
Russell H. Hill ◽  
Sten Grillner
Keyword(s):  
Spinal Cord ◽  
Membrane Potential ◽  
Dendritic Tree ◽  
Cell Voltage ◽  
Fictive Locomotion ◽  
Spinal Neurons ◽  
Potential Oscillations ◽  
Short Pulses ◽  
Voltage Dependent ◽  
Membrane Potential Oscillations

Spinal neurons undergo large cyclic membrane potential oscillations during fictive locomotion in lamprey. It was investigated whether these oscillations were due only to synaptically driven excitatory and inhibitory potentials or if voltage-dependent inward conductances also contribute to the depolarizing phase by using N-(2,6-dimethylphenyl carbamoylmethyl)triethylammonium bromide (QX-314) administered intracellularly during fictive locomotion. QX-314 intracellularly blocks inactivating and persistent Na+ channels, and in some neurons, effects on certain other types of channels have been reported. To detail the effects of QX-314 on Na+ and Ca2+ channels, we used dissociated lamprey neurons recorded under whole cell voltage clamp. At low intracellular concentrations of QX-314 (0.2 mM), inactivating Na+ channels were blocked and no effects were exerted on Ca2+ channels (also at 0.5 mM). At 10 mM QX-314, there was, however a marked reduction of I Ca. In the isolated spinal cord of the lamprey, fictive locomotion was induced by superfusing the spinal cord with Ringer's solution containing N-methyl-d-aspartate (NMDA), while recording the locomotor activity from the ventral roots. Simultaneously, identified spinal neurons were recorded intracellularly, while infusing QX-314 from the microelectrode. Patch electrodes cannot be used in the intact spinal cord, and therefore “sharp” electrodes were used. The amplitude of the oscillations was consistently reduced by 20–25% in motoneurons ( P < 0.05) and unidentified spinal neurons ( P < 0.005). The onset of the effect started a few minutes after impalement and reached a stable level within 30 min. These effects thus show that QX-314 causes a reduction in the amplitude of membrane potential oscillations during fictive locomotion. We also investigated whether QX-314 could affect glutamate currents by applying short pulses of glutamate from an extracellular pipette. No changes were observed. We also found no evidence for a persistent Na+ current in dissociated neurons, but these cells have a much-reduced dendritic tree. The results indicate that there is an inward conductance, which is sensitive to QX-314, during membrane potential oscillations that “boosts” the synaptic drive during fictive locomotion. Taken together, the results suggest that inactivating Na+ channels contribute to this inward conductance although persistent Na+channels, if present on dendrites, could possibly also contribute to shaping the membrane potential oscillations.

GABAB receptor activation causes a depression of low- and high-voltage-activated Ca2+ currents, postinhibitory rebound, and postspike afterhyperpolarization in lamprey neurons

1993 ◽  
Vol 70 (6) ◽  
pp. 2606-2619 ◽  
Author(s):  
T. Matsushima ◽  
J. Tegner ◽  
R. H. Hill ◽  
S. Grillner
Keyword(s):  
Spinal Cord ◽  
Action Potential ◽  
Voltage Clamp ◽  
Calcium Current ◽  
Gabab Receptor ◽  
Receptor Activation ◽  
Calcium Currents ◽  
Gabab Receptors ◽  
Peak Amplitude ◽  
Duration Of Action

1. Activation of gamma-aminobutyric acid-B (GABAB) receptors during N-methyl-D-aspartate (NMDA)-induced fictive locomotor activity in the lamprey spinal cord reduces the burst frequency and changes the intersegmental coordination. Presynaptic inhibition of both the excitatory and inhibitory synaptic transmission from spinal premotor interneurons occurs through GABAB receptor activation. To further analyze the cellular mechanisms underlying the GABABergic modulation of the locomotor network, the present study investigates somatodendritic effects of GABAB receptor activation on interneurons and motoneurons in the lamprey spinal cord in vitro using single-electrode current- and voltage-clamp techniques. 2. High- (HVA) and low- (LVA) voltage-activated calcium currents were studied with single-electrode voltage clamp when Na+ and K+ currents were blocked--using tetrodotoxin, tetraethylammonium (TEA), and CsCl electrodes--after substituting Ca2+ with Ba2+. Cobalt-sensitive inward barium currents, activated at -50 mV, became larger when the holding potential was set to a more hyperpolarized level, thus suggesting the existence of an LVA calcium current. The presence of cobalt-sensitive inward barium currents activated at -30 and -10 mV suggests the existence of an HVA calcium current. GABAB receptor activation (baclofen) reduced the peak amplitude of both the LVA and HVA Ca2+ component. 3. The late phase of the afterhyperpolarization (AHP), which follows the action potential, was reduced in amplitude by cobalt, thus lending further support to the notion that the Ca2+ influx, and the subsequent activation of Ca(2+)-dependent K+ channels (KCa2+), constitutes the major part of the AHP generation. Application of the GABAB agonist baclofen also reduced the peak amplitude of the AHP in interneurons and motoneurons, and this reduction was counteracted by the GABAB antagonist 2(OH)saclofen. Baclofen reduced the duration of action potentials broadened by TEA, thus suggesting that the Ca2+ inflow was reduced. Intracellular injection of the GTP analogue GTP gamma S also reduced the duration of the action potential and the peak amplitude of the AHP in TEA, thus supporting the notion that a GTP-binding protein (G-protein)-mediated GABAB receptor activation reduced the calcium inflow, leading to less activation of KCa channels and, consequently, to a smaller peak amplitude of the AHP. 4. Baclofen suppressed the subthreshold depolarization induced by a depolarizing current pulse injection without affecting either the spike threshold or the resting membrane conductance.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Serotonin modulates multiple calcium current subtypes in commissural interneurons of the neonatal mouse

2012 ◽  
Vol 107 (8) ◽  
pp. 2212-2219 ◽  
Author(s):  
Matthew D. Abbinanti ◽  
Ronald M. Harris-Warrick
Keyword(s):  
Spinal Cord ◽  
Voltage Clamp ◽  
Calcium Current ◽  
Potassium Current ◽  
Cell Voltage ◽  
Pattern Generator ◽  
Calcium Currents ◽  
Intrinsic Properties ◽  
Mouse Spinal Cord ◽  
Serotonergic Modulation

Calcium currents are critical to the intrinsic properties of neurons and the networks that contain them. These currents make attractive targets for neuromodulation. Here, we examine the serotonergic modulation of specific calcium current subtypes in neonatal (P0-5) intersegmental commissural interneurons (CINs), members of the hindlimb locomotor central pattern generator in the mouse spinal cord. Previous work in our lab showed that serotonin (5-HT) excited CINs in part by reducing a calcium current and thus indirectly reducing the calcium-activated potassium current ( Diaz-Rios et al. 2007 ). We have determined which calcium currents are targets of serotonin modulation. Utilizing whole cell voltage clamp and toxins to specific calcium current subtypes, we found that N- and P/Q-type currents comprise over 60% of the overall calcium current. Blockade of each of these subtypes alone with either ω-conotoxin GVIA or ω-agatoxin TK was unable to occlude 5-HT's reduction of the calcium current. However, coapplication of both blockers together fully occluded 5-HT's reduction of the calcium current. Thus, 5-HT decreases both N- and P/Q-type calcium current to excite neonatal CINs.

scholarly journals Two components of voltage-dependent calcium influx in mouse neuroblastoma cells. Measurement with arsenazo III.

1986 ◽  
Vol 88 (2) ◽  
pp. 149-165 ◽  
Author(s):  
S R Bolsover
Keyword(s):  
Intracellular Calcium ◽  
Calcium Current ◽  
Calcium Influx ◽  
Neuroblastoma Cells ◽  
Calcium Currents ◽  
Arsenazo Iii ◽  
Optical Absorbance ◽  
Mouse Neuroblastoma ◽  
Calcium Indicator ◽  
Voltage Dependent

N1E-115 mouse neuroblastoma cells were injected with the calcium indicator dye arsenazo III. Optical absorbance changes during voltage-clamp depolarization were used to examine the properties of the two calcium currents present in these cells. The rapidly inactivating calcium current (Moolenar and Spector, 1979b, Journal of Physiology, 292:307-323) inactivates by a voltage-dependent mechanism. The slowly inactivating calcium current is dominant in raising intracellular calcium during depolarizations to greater than -20 mV. Lowering the extracellular calcium concentration affects the two calcium currents unequally, with the slowly inactivating current being reduced more. Intracellular calcium falls very slowly (tau greater than 1 min) after a depolarization. The rapidly inactivating calcium current is responsible for a calcium action potential under physiological conditions. In contrast, it is unlikely that the slowly inactivating calcium current has an important electrical role. Rather, its function may be to add a further increment of calcium influx over and above the calcium influx through the rapidly inactivating calcium channels.

Interaction Between Disinhibited Bursting and Fictive Locomotor Patterns in the Rat Isolated Spinal Cord

1999 ◽  
Vol 82 (5) ◽  
pp. 2029-2038 ◽  
Author(s):  
M. Beato ◽  
A. Nistri
Keyword(s):  
Spinal Cord ◽  
Lumbar Region ◽  
Fictive Locomotion ◽  
Caudal Part ◽  
High K ◽  
Burst Amplitude ◽  
Continuous Application ◽  
Locomotor Patterns ◽  
Rostral Region ◽  
Caudal Area

Using a transverse barrier that allowed discrete application of neurochemicals to certain lumbar regions of the rat isolated spinal cord, we studied the intersegmental organization of rhythmic patterns recorded extracellularly from ventral roots and intracellularly from single motoneurons. Fictive locomotor patterns were elicited by serotonin (5-HT) and/or N-methyl-d-aspartate (NMDA) or high K+ solution applied to the rostral or caudal lumbar region of the cord. Neither 4-aminopyridine nor Mg2+-free solution shared this property. Coapplication of strychnine and bicuculline (blockers of fast synaptic inhibition) to the caudal part elicited slow bursting in the whole cord. These bursts could trigger episodes of fictive locomotion patterns in the rostral roots. When the rostral region was exposed to 5-HT and/or NMDA (during continuous application of strychnine and bicuculline caudally) a standard locomotor-like pattern was generated during each interburst interval and was surprisingly expressed with its typical pattern alternation even in the caudal area despite the local presence of strychnine and bicuculline. Midsagittal splitting of the caudal region did not change this alternating pattern, indicating that it was driven by rostral regions above the surgical cut. Discrete changes in the concentrations of NMDA rostrally modulated the burst amplitude recorded in the same region after caudal application of strychnine and bicuculline. The period of fictive locomotor patterns changed bimodally depending on the temporal relation with disinhibited bursts, indicating a tight interaction between these two rhythmic activities. These results are interpreted on the basis of a model that assumes a modular arrangement for the locomotor central pattern generator, made up by a series of unit burst generators with serial and crossed connections.

scholarly journals Facilitation of Somatic Calcium Channels Can Evoke Prolonged Tail Currents in Rat Hypoglossal Motoneurons

2007 ◽  
Vol 98 (2) ◽  
pp. 1042-1047 ◽  
Author(s):  
Anna T. Moritz ◽  
Gregory Newkirk ◽  
Randall K. Powers ◽  
Marc D. Binder
Keyword(s):  
Voltage Clamp ◽  
Calcium Currents ◽  
Whole Cell ◽  
Persistent Inward Currents ◽  
Hypoglossal Motoneurons ◽  
Pharmacological Tests ◽  
Voltage Ramp ◽  
Voltage Dependent ◽  
Inward Currents ◽  
Whole Cell Recordings

Voltage-dependent persistent inward currents (PICs) make an important contribution to the input-output properties of alpha motoneurons. PICs are thought to be mediated by membrane channels located primarily on the dendrites as evidenced by prolonged tail currents following the termination of a voltage step and by a clockwise hysteresis in the whole cell inward currents recorded in response to depolarizing then repolarizing voltage ramp commands. We report here, however, that voltage-clamp currents with these same features can be generated in isolated somatic membrane patches from rat hypoglossal motoneurons. Long-lasting (200–800 ms) tail currents after 1-s voltage-clamp pulses were observed in nucleated patches from 16 of 23 cells. Further, these somatic PICs display “facilitation” in response to conditioning depolarization as previously observed in whole cell recordings from intact neurons. Pharmacological tests suggest that the PICs were primarily mediated by Cav1 channels. Our results show that many of the features of persistent calcium currents recorded from intact motoneurons do not necessarily reflect a remote dendritic origin but can also be ascribed to the intrinsic properties of their Cav1 channels.

Calcium currents and transmitter output in cultured spinal cord and dorsal root ganglion neurons

1986 ◽  
Vol 56 (5) ◽  
pp. 1257-1267 ◽  
Author(s):  
M. Jia ◽  
P. G. Nelson
Keyword(s):  
Spinal Cord ◽  
Dorsal Root Ganglion ◽  
Dorsal Root ◽  
Calcium Currents ◽  
Dorsal Root Ganglion Neurons ◽  
Ion Concentration ◽  
Drg Neurons ◽  
Voltage Dependent ◽  
Ganglion Neurons

The effects of repetitive activation upon voltage-dependent calcium currents (ICa) and transmitter release were studied in dissociated cell cultures of fetal mouse spinal cord and dorsal root ganglion. Sodium and potassium currents were suppressed with tetrodotoxin (TTX) and tetraethylammonium (TEA) ions, 4-aminopyridine (4-AP), and cesium sulfate. Calcium currents were compared under voltage clamp before and after a series of depolarizing clamp pulses in spinal cord (SC) and dorsal root ganglion (DRG) neurons. Repetitive activation resulted in an exponential decline in ICa, with the decrease in ICa being much more marked in DRG compared with SC neurons. Both voltage-dependent inactivation and inactivation related to the intracellular movement of Ca2+ appeared to be involved in the decrement in ICa with repetitive activation. A decrease in transmitter output occurred with repetitive activation in DRG neurons but not in SC neurons (either excitatory or inhibitory). DRG neuron synaptic boutons had fewer mitochondria than did the boutons of either excitatory or inhibitory of SC neurons. The decrement in both ICa and synaptic transmitter output in DRG neurons could last for prolonged periods (at least minutes) following repetitive activation. We hypothesize that this vulnerability of DRG neurons to repetitive activation may be related, at least in part, to a relative incapacity to maintain a low intracellular calcium ion concentration [Ca]i during periods of increased calcium ingress associated with excitation. Such an incapacity to buffer [Ca]i may be one mechanism leading to the inactive synapses seen in some studies in vitro and in vivo of synaptic transmission.

scholarly journals The effects of neurotransmitters on the integrative properties of spinal neurons in the lamprey

1993 ◽  
Vol 175 (1) ◽  
pp. 89-114
Author(s):  
L. E. Moore ◽  
J. T. Buchanan
Keyword(s):  
Amino Acids ◽  
Spinal Cord ◽  
Voltage Clamp ◽  
Excitatory Amino Acids ◽  
Neuronal Model ◽  
Spinal Neurons ◽  
Current Clamp ◽  
Impedance Function ◽  
Central Neurons ◽  
Voltage Dependent

1. The integrative behavior of lamprey central neurons was analyzed by white noise frequency domain methods and simulated with a minimal, non-linear neuronal model consisting of two voltage-dependent processes: (i) a depolarizing inwardly directed conductance carrying calcium and monovalent ions and (ii) a repolarizing outwardly directly conductance representing a generalized potassium conductance. In addition to normal properties, the effects of neurotransmitters were interpreted with the model. Specifically, N-methyl-D-aspartate (NMDA)-induced properties were simulated under conditions where the intrinsic voltage dependence of the potassium channels was constrained by properties of lamprey neurons. However, the NMDA channel kinetics were fixed by the single-channel properties of other neurons. The effects of focally applied neurotransmitters on the membrane properties of intact spinal cord neurons were quantitatively described with a reduced neuronal model that was also used to simulate transmitter-induced responses. In addition, transmitters were also released synaptically by KCl depolarization of projecting neurons. 2. Both synaptically released transmitters and focally applied putative excitatory or inhibitory transmitters directly applied to the spinal cord generally resulted in a decrease in the magnitude of the impedance function that was modeled by a decrease in membrane resistance (shunting effect). 3. Local application of the inhibitory neurotransmitters glycine or gamma-aminobutyric acid (GABA) led to small voltage responses when recorded near the resting potential. However, large decreases in the magnitude of the impedance function were observed in both current-clamp or voltage-clamp recording modes. 4. The excitatory amino acids quisqualate, kainate and glutamate evoked depolarizations in current clamp that activated intrinsic voltage-dependent conductances and obscured the direct effects of the transmitters. Under voltage-clamp conditions these transmitters caused a small decrease in the impedance magnitude that could be modeled by a shunt. 5. In contrast to the other excitatory amino acids, NMDA elicited large increases, rather than decreases, in both the magnitude and the phase lag of the impedance function. These changes were modeled by a negative conductance (a voltage-dependent conductance that produces an inward current). 6. The reduced neuron model provides an experimentally based description of the highly oscillatory and non-linear responses observed during NMDA activation of the spinal neurons involved in the pattern generation of locomotion. Simulations of sustained oscillatory behaviors consistent with experimental observations were carried out to illustrate the NMDA-induced integrative properties of central neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

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