Identification of excitatory interneurons contributing to generation of locomotion in lamprey: structure, pharmacology, and function

1989 ◽  
Vol 62 (1) ◽  
pp. 59-69 ◽  
Author(s):  
J. T. Buchanan ◽  
S. Grillner ◽  
S. Cullheim ◽  
M. Risling
Keyword(s):  
Spinal Cord ◽  
Membrane Potential ◽  
Excitatory Amino Acid ◽  
Postsynaptic Membrane ◽  
Fictive Locomotion ◽  
Potential Oscillations ◽  
And Function ◽  
Spherical Vesicles ◽  
Membrane Potential Oscillations

1. In the in vitro preparation of the lamprey spinal cord, paired intracellular recordings of membrane potential were used to identify interneurons producing excitatory postsynaptic potentials (EPSPs) on myotomal motoneurons. 2. Seventy-nine interneurons (8.4% of all neuron-motoneuron pairs tested) elicited unitary EPSPs that followed one-for-one at short, constant latencies and were therefore considered monosynaptic according to conventional criteria. Evidence was obtained for selectivity and divergence of excitatory interneuron (EIN) outputs and for convergence of EIN input to motoneurons. 3. The neurotransmitter released by EINs may be an excitatory amino acid such as glutamate, because the EPSPs were depressed by antagonists of excitatory amino acids. 4. Intracellular dye injection revealed that EINs have small cell bodies (average 11 x 27 microns), transversely oriented dendrites, and thin (less than 3 microns) slowly conducting axons (0.7 m/s) that project caudally and ipsilaterally. One EIN exhibited a system of thin multi-branching axon collaterals with periodic swellings. Ultrastructurally, these swellings contained clear spherical vesicles, and they apposed postsynaptic membrane specializations. 5. During fictive locomotion, the membrane-potential oscillations of EINs were greater in amplitude than, but similar in shape and timing to, those of their postsynaptic motoneurons. EINs fired action potentials during fictive locomotion and contributed to the depolarization of motoneurons. 6. These interneurons are proposed to be a source of excitation to motoneurons and interneurons in the lamprey spinal cord, participating in motor activity including locomotion.

Central modulation of stretch receptor neurons during fictive locomotion in lamprey

1996 ◽  
Vol 76 (2) ◽  
pp. 1224-1235 ◽  
Author(s):  
L. Vinay ◽  
J. Y. Barthe ◽  
S. Grillner
Keyword(s):  
Spinal Cord ◽  
Membrane Potential ◽  
Receptor Antagonist ◽  
Chloride Ions ◽  
Stretch Receptor ◽  
Fictive Locomotion ◽  
Gamma Aminobutyric Acid ◽  
Potential Oscillations ◽  
Receptor Neurons ◽  
Membrane Potential Oscillations

1. In lamprey, stretch receptor neurons (SRNs), also referred to as edge cells, are located along the lateral margin of the spinal cord. They sense the lateral movements occurring in each swim cycle during locomotion. The isolated lamprey spinal cord in vitro was used to investigate the activity of SRNs during fictive locomotion induced by bath-applied N-methyl-D-aspartate (NMDA). Intracellular recordings with potassium acetate filled electrodes showed that 63% of SRNs had a clear locomotor-related modulation of their membrane potential. 2. Of the modulated SRNs, two-thirds had periods of alternating excitation and inhibition occurring during the ipsilateral and the contralateral ventral root bursts, respectively. The phasic hyperpolarization could be reversed into a depolarizing phase after the injection of chloride ions into the cells; this revealed a chloride-dependent synaptic drive. The remaining modulated SRNs were inhibited phasically during ipsilateral motor activity. 3. Experiments with barriers partitioning the recording chamber with the spinal cord into three pools, allowed an inactivation of the locomotor networks within one pool by washing out NMDA from the pool in which the SRN was recorded. This resulted in a marked reduction, but not an abolishment, of the amplitude of the membrane potential oscillations. Both the excitatory and the inhibitory phases were reduced, resulting from removal of input from inhibitory and excitatory interneurons projecting from the adjacent pools. If the glycine receptor antagonist strychnine (1 microM) was applied in one pool, the phasic hyperpolarizing phase disappeared without affecting the excitatory phase. 4. Bath application of the gamma-aminobutyric acid (GABA)A receptor antagonist, bicuculline (50-100 microM) blocked the spontaneous large unitary inhibitory postsynaptic potentials, which occurred without a clear phasic pattern. Bicuculline had no significant effect on the peak to peak amplitude of the locomotor-related membrane potential oscillations. The inhibition in SRNs therefore has a dual origin: glycinergic interneurons provide phasic inhibition, while the GABA system can exert a tonic inhibition via GABAA receptors. 5. These data show that, in addition to the stretch-evoked excitation, which SRNs receive during each locomotor cycle, most of them also receive excitation from the central pattern generator network during the ipsilateral contraction, which may ensure a maintained high level of sensitivity to stretch during the shortening phase of the locomotor cycle. This arrangement is analogous to the efferent control of muscle spindles exerted by gamma-motoneurons in mammals, which as a rule are coactivated with alpha-motoneurons to the same muscle (alpha-gamma linkage).

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.

In vitro microelectrode study of the electrical properties of smooth muscle in equine ileum

2001 ◽  
Vol 149 (23) ◽  
pp. 707-711 ◽  
Author(s):  
N. P. H. Hudson ◽  
I. G. Mayhew ◽  
G. T. Pearson
Keyword(s):  
Smooth Muscle ◽  
Membrane Potential ◽  
Smooth Muscle Cells ◽  
Longitudinal Muscle ◽  
Muscle Cells ◽  
Muscle Layer ◽  
Potential Oscillations ◽  
Longitudinal Muscle Layer ◽  
Membrane Potential Oscillations

Intracellular microelectrode recordings were made from smooth muscle cells in cross-sectional preparations of equine ileum, superfused in vitro. Membrane potential oscillations and spike potentials were recorded in all preparations, but recordings were made more readily from cells in the longitudinal muscle layer than from cells in the circular layer. The mean (se) resting membrane potential (RMP) of smooth muscle cells in the longitudinal muscle layer was -51.9 (1.2) mV, and the membrane potential oscillations in this layer had a mean amplitude of 4.8 (0.4) mV, a frequency of 9.0 (0.1) cycles per minute and a duration of 5.8 (0.2) seconds. The membrane potential oscillations were preserved in the presence of tetrodotoxin. A waxing and waning pattern of membrane potential oscillation activity was observed. Nifedipine abolished the spiking contractile activity of the smooth muscle, did not abolish the membrane potential oscillations but did alter their temporal characteristics.

Synaptically Evoked Membrane Potential Oscillations Induced by Substance P in Lamprey Motor Neurons

2002 ◽  
Vol 87 (1) ◽  
pp. 113-121 ◽  
Author(s):  
Erik Svensson ◽  
Sten Grillner ◽  
David Parker
Keyword(s):  
Spinal Cord ◽  
Membrane Potential ◽  
Protein Kinase ◽  
Substance P ◽  
Receptor Antagonist ◽  
Motor Neurons ◽  
Network Activity ◽  
Membrane Properties ◽  
Potential Oscillations ◽  
Membrane Potential Oscillations

Short-lasting application (10 min) of tachykinin neuropeptides evokes long-lasting (>24 h) modulation of N-methyl-d-aspartate (NMDA)-evoked locomotor network activity in the lamprey spinal cord. In this study, the net effects of the tachykinin substance P on the isolated spinal cord have been examined by recording from motor neurons in the absence of NMDA and ongoing network activity. Brief bath application of substance P (30 s to 2 min) induced irregular membrane potential oscillations in motor neurons. These oscillations consisted of depolarizing and hyperpolarizing phases and were associated with phasic ventral-root activity. The oscillations were blocked by the tachykinin antagonist spantide II. They were also blocked by tetrodotoxin (TTX), suggesting that they were not dependent on intrinsic membrane properties of the motor neurons but were synaptically mediated. Substance P could also have a direct effect, however, because a membrane potential depolarization persisted in the presence of TTX. Protein kinase agonists and antagonists were used to investigate the intracellular pathways through which substance P acted. The oscillations were blocked by the selective protein kinase C (PKC) antagonist chelerythrine. However, the TTX-resistant membrane potential depolarization was not significantly affected by blocking PKC. The protein kinase A and G antagonist H8 did not affect either the oscillations or the direct TTX-resistant membrane potential depolarization. The glutamate receptor antagonist kynurenic acid abolished the substance-P-evoked oscillations, suggesting that they were dependent on glutamate release. The oscillations were abolished or reduced by the AMPA/kainate receptor antagonist 6-cyano-7-nitroquinoxalene-2,3-dione but were only reduced by the NMDA receptor antagonist d-AP5. The oscillations were thus mediated by glutamatergic inputs with a greater dependence on non-NMDA receptors. Blocking glycinergic inputs with strychnine resulted in large depolarizing plateaus and bursts of spikes. The glutamatergic and glycinergic inputs underlying the oscillations are apparently evoked through direct and indirect excitatory effects on inhibitory and excitatory premotor interneurons. Substance P thus has a distributed excitatory effect in the spinal cord. While it can activate premotor networks, this activation alone is not able to evoke a coordinated behaviorally relevant motor output.

scholarly journals Membrane Potential Oscillations in Reticulospinal and Spinobulbar Neurons During Locomotor Activity

2005 ◽  
Vol 94 (1) ◽  
pp. 273-281 ◽  
Author(s):  
James F. Einum ◽  
James T. Buchanan
Keyword(s):  
Spinal Cord ◽  
Membrane Potential ◽  
Locomotor Activity ◽  
Brain Stem ◽  
Excitatory Amino Acid ◽  
Rhythmic Activity ◽  
Ventral Root ◽  
Potential Oscillations ◽  
Bath Application ◽  
The Brain

Feedback from the spinal locomotor networks provides rhythmic modulation of the membrane potential of reticulospinal (RS) neurons during locomotor activity. To further understand the origins of this rhythmic activity, the timings of the oscillations in spinobulbar (SB) neurons of the spinal cord and in RS neurons of the posterior and middle rhombencephalic reticular nuclei were measured using intracellular microelectrode recordings in the isolated brain stem-spinal cord preparation of the lamprey. A diffusion barrier constructed just caudal to the obex allowed induction of locomotor activity in the spinal cord by bath application of an excitatory amino acid to the spinal bath. All of the ipsilaterally projecting SB neurons recorded had oscillatory membrane potentials with peak depolarizations in phase with the ipsilateral ventral root bursts, whereas the contralaterally projecting SB neurons were about evenly divided between those in phase with the ipsilateral ventral root bursts and those in phase with the contralateral bursts. In the brain stem under these conditions, 75% of RS neurons had peak depolarizations in phase with the ipsilateral ventral root bursts while the remainder had peak depolarizations during the contralateral bursts. Addition of a high-Ca2+, Mg2+ solution to the brain stem bath to reduce polysynaptic activity had little or no effect on oscillation timing in RS neurons, suggesting that direct inputs from SB neurons make a major contribution to RS neuron oscillations under these conditions. Under normal conditions when the brain is participating in the generation of locomotor activity, these spinal inputs will be integrated with other inputs to RS neurons.

Endogenous release of 5-HT modulates the plateau phase of NMDA-induced membrane potential oscillations in lamprey spinal neurons

2014 ◽  
Vol 112 (1) ◽  
pp. 30-38 ◽  
Author(s):  
Di Wang ◽  
Sten Grillner ◽  
Peter Wallén
Keyword(s):  
Spinal Cord ◽  
Membrane Potential ◽  
Calcium Channels ◽  
Nmda Receptors ◽  
Plateau Phase ◽  
Spinal Neurons ◽  
Potential Oscillations ◽  
Voltage Dependent ◽  
Endogenous Release ◽  
Membrane Potential Oscillations

The lamprey central nervous system has been used extensively as a model system for investigating the networks underlying vertebrate motor behavior. The locomotor networks can be activated by application of glutamate agonists, such as N-methyl-D-aspartic acid (NMDA), to the isolated spinal cord preparation. Many spinal neurons are capable of generating pacemaker-like membrane potential oscillations upon activation of NMDA receptors. These oscillations rely on the voltage-dependent properties of NMDA receptors in interaction with voltage-dependent potassium and calcium-dependent potassium (KCa) channels, as well as low voltage-activated calcium channels. Upon membrane depolarization, influx of calcium will activate KCa channels, which in turn, will contribute to repolarization and termination of the depolarized phase. The appearance of the NMDA-induced oscillations varies markedly between spinal cord preparations; they may either have a pronounced, depolarized plateau phase or be characterized by a short-lasting depolarization lasting approximately 200–300 ms without a plateau. Both types of oscillations increase in frequency with increased concentrations of NMDA. Here, we characterize these two types of membrane potential oscillations and show that they depend on the level of endogenous release of 5-HT in the spinal cord preparations. In the lamprey, 5-HT acts to block voltage-dependent calcium channels and will thereby modulate the activity of KCa channels. When 5-HT antagonists were administered, the plateau-like oscillations were converted to the second type of oscillations lacking a plateau phase. Conversely, plateau-like oscillations can be induced or prolonged by 5-HT agonists. These properties are most likely of significance for the modulatory action of 5-HT on the spinal networks for locomotion.

scholarly journals Reticulospinal Neurons Receive Direct Spinobulbar Inputs During Locomotor Activity in Lamprey

2004 ◽  
Vol 92 (3) ◽  
pp. 1384-1390 ◽  
Author(s):  
James F. Einum ◽  
James T. Buchanan
Keyword(s):  
Spinal Cord ◽  
Membrane Potential ◽  
Locomotor Activity ◽  
Brain Stem ◽  
Oscillation Amplitude ◽  
Ringer Solution ◽  
Experimental Chamber ◽  
Potential Oscillations ◽  
Reticulospinal Neurons

Reticulospinal neurons of the lamprey brain stem receive rhythmic input from the spinal cord during locomotor activity. The goal of the present study was to determine whether such spinal input has a direct component to reticulospinal neurons or depends on brain stem interneurons. To answer this question, an in vitro lamprey brain stem-spinal cord preparation was used with a diffusion barrier placed caudal to the obex, separating the experimental chamber into two baths. Locomotor activity was induced in the spinal cord by perfusion of d-glutamate or N-methyl-dl-aspartate into the spinal cord bath. The brain stem bath was first perfused with normal Ringer solution followed by a high-Ca2+, -Mg2+ solution, which reduced polysynaptic transmission. The amplitudes of membrane potential oscillations of reticulospinal neurons in the posterior and middle rhombencephalic reticular nuclei (PRRN and MRRN, respectively) recorded with sharp intracellular microelectrodes did not significantly change from normal to high-divalent solution. This finding suggests a large part of the spinal input creating the oscillations is direct to the reticulospinal neurons. Application of strychnine to the high-Ca2+, -Mg2+ solution decreased membrane potential oscillation amplitude, and injection of Cl− reversed presumed inhibitory postsynaptic potentials, indicating a role for direct spinal inhibitory inputs. Although reduced, the persistence of oscillations in strychnine suggests that spinal excitatory inputs also contribute to the oscillations. Thus it was concluded that both excitatory and inhibitory spinal neurons provide direct rhythmic inputs to reticulospinal cells of the PRRN and MRRN during locomotor activity. These inputs provide reticulospinal cells with information regarding the activity of the spinal locomotor networks.

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