Cross references: Lamprey Lamprey Nervous System
Lamprey Motor Nerves Lamprey Striatum Lamprey Nucleus Accumbens
Lamprey Muscles Lamprey Fast-Slow Twitch Lamprey GABA
Lamprey Neurotransmitters Initiation of Locomotion in Lampreys
Activity of Reticulospinal Neurons During Locomotion
Amphioxus Locomotion Salamander Locomotion Subcortical Brain
Thalamus Motor Relay Brainstem Lamprey Thalamus
The list of links in "Cross references", above, to pages in Children of the Amphioxus is intended to provide general background to lamprey locomotion.
lamprey locomotion - Mozilla Yahoo Search Results - 143,000 references
lamprey locomotion - Google Search - 87,400 references
lamprey locomotion - PubMed - 416 references
Activities of identified interneurons, motoneurons, and muscle fibers during fictive swimming in the lamprey and effects of reticulospinal and dorsal cell stimulation.
"1. Application of D-glutamate to the isolated spinal cord of the lamprey produces phasic activity in ventral roots, which is similar to that of the muscles of the intact swimming animal. Therefore, the isolated spinal cord may be used as a convenient model for the investigation of the generation of locomotor rhythms in a vertebrate.
2. Almost all slow muscle fibers exhibited excitatory junctional potentials (EJPs) during swimming activity. The number of EJPs per cycle increased with the intensity of ventral root (VR) bursting. Few twitch fibers were active, and these fired action potentials only during high intensities of VR bursts. (See: Lamprey Fast-Slow Twitch .)
3. ... myotomal motoneurons had oscillating membrane potentials during fictive swimming which, on the average, reached a peak depolarization in the middle of the VR burst ... Membrane potential oscillations in fin motoneurons were antiphasic to those of nearby myotomal motoneurons ...
4. Lateral interneurons had oscillating membrane potentials in synchrony with those of myotomal motoneurons ... Interneurons with axons projecting contralaterally and caudally (CC interneurons) had oscillating membrane potentials that peaked significantly earlier in the cycle ...
5. Edge cells were only weakly modulated during fictive swimming. Their peak depolarizations occurred near the end of the VR burst ... Most giant interneurons were not phasically modulated during fictive swimming.
6. Repetitive intracellular stimulation of Müller cells during fictive swimming generally evoked an increased burst intensity in ipsilateral VRs and a decreased burst intensity in contralateral VRs. The cells M3, B1, and B2 also produced increases or decreases in the frequency of VR bursts. Repetitive intracellular stimulation of sensory dorsal cells could also change the intensities and timing of VR bursts.
7. This study is an initial survey of lamprey spinal interneurons that participate in swimming activity. Lateral interneurons and CC interneurons are active during fictive swimming and probably help coordinate the undulations of the body, but their roles in pattern generation are not known. The central pattern generator is subject to modification by descending and sensory inputs."
509 Related citations:
17 Cited by's:
Mechanisms underlying the serotonergic modulation of the spinal circuitry for locomotion in lamprey (PubMed)
Only abstract available online.
"The central nervous system of the lamprey contains serotonergic (5-hydroxytryptamine, 5-HT) neurones both in the spinal cord and in the brainstem. Endogenously released 5-HT from these systems modulates the pattern of fictive locomotion induced in the in vitro preparation; the burst rate is lowered and burst discharges become longer and of higher intensity. Local application of 5-HT, mimicking activation of the 5-HT systems, has a specific effect on the late phase of the afterhyperpolarization (AHP) in motoneurones and interneurones. 5-HT markedly reduces the amplitude of the late AHP without affecting passive membrane properties or the shape or threshold of the action potential. This 5-HT effect appears to result from a direct action on the calcium-dependent potassium channels underlying the late phase of the AHP. A reduction of the amplitude of the AHP will result in altered spike discharge characteristics, with potentiation of the response (discharge rate) to a given excitatory input in all neurones influenced by 5-HT.
It is suggested that the modulatory effect of 5-HT on fictive locomotion can be attributed to its action on the late AHP and thereby to the potentiation of excitability in excitatory and inhibitory interneurones in the generator circuitry. This has been further corroborated in computer simulation studies of a network model, where the action of 5-HT was simulated by decreasing AHP amplitude, resulting in a slowing of the rhythm analogous to the effect demonstrated experimentally."
108 Related citations:
4 Cited by's:
Cellular network underlying locomotion as revealed in a lower vertebrate model: transmitters, membrane properties, circuitry, and simulation
No PubMed Abstract, but a Google Extract:
"A great deal of our current understanding of the brain originated from discoveries made at the cellular and molecular levels. However, even with all of the pieces of information at hand, it is very difficult to sort out the relevant mechanisms responsible for the operation of a neural system. Thus, we must use experimental models that are simple enough to understand and yet sufficiently complex to capture essential features of whatever function we want to consider. On the other hand, we need to be able to test the relative contribution of these features and therefore must recur to computer simulations of system models. In this paper, we deal with the motor system used for ambulation. Locomotion is a universal pattern of behavior generated by a family of different neural control systems: (1) generation of the propulsion (rhythmic limb or trunk movements); (2) visuomotor coordination adapting the movements to the environment..."
115 Related citations:
and 1 Cited by.
Neural networks that co-ordinate locomotion and body orientation in lamprey.
Only abstract available online.
"The networks of the brainstem and spinal cord that co-ordinate locomotion and body orientation in lamprey are described. The cycle-to-cycle pattern generation of these networks is produced by interacting glutamatergic and glycinergic neurones, with NMDA receptor-channels playing an important role at lower rates of locomotion.
The fine tuning of the networks produced by 5-HT, dopamine and GABA systems involves a modulation of Ca2+-dependent K+ channels, high- and low-threshold voltage-activated Ca2+ channels and presynaptic inhibitory mechanisms."
"The vestibular control of the body orientation during swimming is exerted via reticulospinal neurones located in different reticular nuclei. These neurones become activated maximally at different angles of tilt."
105 Related citations:
Interaction between the caudal brainstem and the lamprey central pattern generator for locomotion.
"Because of its remarkable simplicity and the robustness of the isolated preparation, the lamprey has been used as a model system to study locomotion and its central pattern generator. The function of the spinal cord is relatively well understood in this context, but the role of the brain or even the caudal brainstem remains less so.
We here present a study of the interaction between the caudal brainstem and the spinal pattern generator for locomotion. We show that the interaction is highly complex, with both feedforward input from the brainstem to spinal cord and feedback input from the spinal cord to brainstem playing a significant role in the motor output during locomotion.
The brainstem, when diffusely stimulated pharmacologically, can initiate fictive locomotion, or it can disrupt or alter the ongoing D-glutamate initiated motor output. The nature of the disruptions vary greatly, and can induce generalized irregularity, while the alterations can include accelerating or decelerating of the bursting. All behaviors are displayed with spectrograms of the motor nerve discharge. We also show that the unstimulated brainstem can disrupt as well as slow the bursting, but in a complex fashion. Finally, a slow episodic behavior initiated from the caudal brainstem is also described. This can be elicited either by D-glutamate to the brainstem or by ascending activity from the spinal cord pattern generator.
Thus, we demonstrate that the interaction between the brainstem and the spinal cord during the production of locomotion is highly complex. The locomotion that is exhibited by the combined brainstem-spinal cord preparation is extremely variable. This is in striking contrast to the variability of the locomotor output pharmacologically induced in the spinal cord alone. The latter preparation exhibits remarkable regularity, or upon occasion, irregularity, but not the routine irregularity or the systemic up and down changes in frequency seen with the brainstem present. However, the pattern of frequency changes induced by the brainstem is not predictable, and remains to be understood."
"... the interaction is highly complex, with both feedforward input from the brainstem to spinal cord and feedback input from the spinal cord to brainstem playing a significant role in the motor output during locomotion."
251 Related citations:
See the paper.
A mesencephalic relay for visual inputs to reticulospinal neurones in lampreys.
"Visual stimuli elicit motor responses in lampreys. These responses rely, in part, on the activation of reticulospinal (RS) neurones which constitute the main descending pathway in these early vertebrates. This study sought to identify and characterize possible mesencephalic relays for visual inputs to RS neurones of the rhombencephalon.
The anatomical substrate subserving this function was investigated by iontophoretically ejecting cobalt-lysine, a retrograde tracer, in the middle rhombencephalic reticular nucleus in the in vitro isolated brainstem preparation of young adult Petromyzon marinus. Several populations of cells were retrogradely labeled in the brainstem. Of particular interest were the cell populations found on each side of rostral mesencephalon, located in the tectum and pretectum. There were, on average, 113 cells labeled contralateral to the injection site and 80 cells labeled ipsilateral to the injection site. The cells were morphologically similar on both sides, except that the contralateral group had larger cell bodies as compared to the group on the ipsilateral side.
To determine whether the axons of the cells contacted reticulospinal neurones, electrophysiological experiments were carried out in which the region containing these cells was microstimulated. Large post-synaptic potentials were recorded intracellularly in RS neurones. Furthermore, microstimulation of the optic nerve on the same side as the recorded cell (i ON) evoked responses with a pattern similar to those resulting from stimulation of the optic tectum contralateral to the cell recorded (co OT), except for the longer response latencies. Local ejection of xylocaine (1% lidocaine hydrochloride) or CNQX (1 mM) onto the co OT reversibly abolished the responses evoked from stimulation of the i ON. There were no significant effects observed when the drug was ejected onto optic tectum ipsilateral to the cell.
Taken together, the results from this study indicate that the crossed tectoreticular pathway is involved in relaying optic nerve inputs to RS neurones of the middle rhombencephalic reticular nucleus. Moreover, cells of origin of this pathway appear, in all respect, homologous to cells giving rise to the crossed tectobulbar pathway in other vertebrates."
"Taken together, the results from this study indicate that the crossed tectoreticular pathway is involved in relaying optic nerve inputs to RS neurones of the middle rhombencephalic reticular nucleus. Moreover, cells of origin of this pathway appear, in all respect, homologous to cells giving rise to the crossed tectobulbar pathway in other vertebrates."
214 Related citations:
See the paper for the links.
Monosynaptic input from cutaneous sensory afferents to fin motoneurons in lamprey.
"The sensory control of lamprey dorsal fin motoneurons was studied by using paired intracellular recordings combined with a morphological analysis.
Dorsal cells innervating the skin of the dorsal fin and fin motoneurons were retrogradely labeled by injecting fluoresceincoupled dextran amines into the dorsal fin. Labeled motoneurons and dorsal cells showed close appositions, suggesting that the dorsal cells innervating the fin region make monosynaptic connections with fin motoneurons.
By using conventional electrophysiological criteria, monosynaptic excitatory connections were found between fin dorsal cells and fin motoneurons. In addition, Lucifer yellow injection followed by confocal three-dimensional (3-D) reconstructions of monosynaptically connected pairs, revealed close apposition between dorsal cell axons and the distal dendrites of fin motoneurons. Each fin motoneuron received monosynaptic excitatory input from at least four different afferents. The amplitude of the monosynaptic excitatory postsynaptic potential (EPSP)s was reduced by administration of the N-methyl-D-aspartate (NMDA) receptor antagonist DL,2 amino-5-phosphovaleric acid (APV).
Sensory stimulation could also elicit di- or oligosynaptic inhibitory postsynaptic potential (IPSP)s, which were blocked by the glycine antagonist strychnine, resulting in the appearance of large monosynaptic EPSPs, which could induce action potentials."
" By using conventional electrophysiological criteria, monosynaptic excitatory connections were found between fin dorsal cells and fin motoneurons."
229 Related citations:
See the paper for the links.
Organization of the lamprey striatum - transmitters and projections.
"The purpose of the present study is to characterize the striatum of the lamprey by immunohistochemical and tracing techniques.
Cells immunoreactive for GABA and substance P (SP), and positive for acetylcholinesterase, are present in the lamprey striatum.
Immunoreactive (ir) fibers were detected by antisera raised against SP, dopamine, enkephalin and serotonin. These immunoreactive fibers were mainly located in the periventricular neuropil that borders the striatum and in which GABAergic striatal neurons distributed their dendritic arbors.
Putative connections between the striatum, the ventral part of the lateral pallium, and the diencephalic motor centers involved in the control of locomotion were studied by using fluorescein-coupled dextran amines (FDA) as a tracer. The striatum projects to the ventral part of the lateral pallium (lpv), where GABA-ir cells and SP-ir fibers were also present. The lpv in turn projects to the ventral thalamus, which has descending connections to the reticulospinal cells involved in the control of locomotion.
These results, together with previous findings of histaminergic and neurotensin projections, suggest that the lamprey striatum and its inputs with regard to neurotransmitters/modulators are very similar to those of modem amniotes, including primates, and are thus conserved to a high degree."
"The striatum projects to the ventral part of the lateral pallium (lpv), where GABA-ir cells and SP-ir fibers were also present. The lpv in turn projects to the ventral thalamus, which has descending connections to the reticulospinal cells involved in the control of locomotion."
Note mention of the "ventral thalamus".
116 Related citations:
Differential effects of the reticulospinal system on locomotion in lamprey.
"The main conclusion of the present study is that the proportion of RS neurons with different influences on the spinal locomotor network differs significantly among different parts of the reticular formation of the lamprey. The specificity of RS influences may represent a basis for modifications of the segmental locomotor output necessary for the control of equilibrium and steering during locomotion."
"... the proportion of RS neurons with different influences on the spinal locomotor network differs significantly among different parts of the reticular formation of the lamprey." Free full text
Unfortunately, there's no mention of neurotransmitters, so it doesn't provide any insight into the roles of glutamate vs GABA in locomotion.
1297 Related citations:
Vertebrate locomotion--a lamprey perspective.
"The forebrain, brain stem, and spinal cord contribution to the control of locomotion is reviewed in this chapter. The lamprey is used as an experimental model because it allows a detailed cellular analysis of the neuronal network underlying locomotion. The focus is on cellular mechanisms that are important for the pattern generation, as well as different types of pre- and postsynaptic modulation. Neuropeptides target different cellular and synaptic mechanisms and cause long-lasting changes ( > 24 h) in network function."
"The forebrain, brain stem, and spinal cord contribution to the control of locomotion ..."
121 Related citations
4 Cited by's.
Diencephalic and mesencephalic projections to rhombencephalic reticular nuclei in lampreys.
"Behavioral studies in lampreys of the northern genera, Ichthyomyzon, reveal that sensory inputs initiate and modulate locomotion by activation of reticulospinal (RS) neurones.
"The interneurones relaying afferent vestibular, trigeminal, lateral line, cutaneous and proprioceptive inputs are localized in the rhombencephalic region"
This is another example of behavior which was initiated, not by the Substantia Nigra pars Compacta (SNc) and not by the rhombocephalon, but by sensory input relayed by interneurones in the rhombencephalon. This may turn out to be what is actually happening in most cases.
The roles of spinal interneurons and motoneurons in the lamprey locomotor network.
"The isolated lamprey spinal cord offers a relatively simple and convenient adult preparation in which to investigate how nerve cells generate behavior and in particular the rhythmic motor patterns of locomotion. Nerve cell classes can be identified and their cellular and synaptic properties characterized, and a simple model based on demonstrated synaptic connectivity can account for major aspects of fictive swimming. Clearly, however, much remains to be learned. In particular, the properties of the spinal neurons have been shown to change during swimming activity but relatively little is known about how these changes occur or the effects that these changes have upon the activities of the network. In addition, much remains to be learned about the cell types and their synaptic interactions as demonstrated here with the newly discovered feedback connections from motoneurons, which have not been previously taken into account in modeling of the lamprey locomotor network."
369 Related citations:
2 Cited by's.2000 196<416
Activity-dependent metaplasticity of inhibitory and excitatory synaptic transmission in the lamprey spinal cord locomotor network.
A cellular mechanism for the transformation of a sensory input into a motor command.
http://www.ncbi.nlm.nih.gov/pubmed/11050140 - Free full text -2009 99<417
"The initiation and control of locomotion largely depend on processing of sensory inputs. The cellular bases of locomotion have been extensively studied in lampreys where reticulospinal (RS) neurons constitute the main descending system activating and controlling the spinal locomotor networks. Ca(2+) imaging and intracellular recordings were used to study the pattern of activation of RS neurons in response to cutaneous stimulation.
Pressure applied to the skin evoked a linear input/output relationship in RS neurons until a threshold level, at which a depolarizing plateau was induced, the occurrence of which was associated with the onset of swimming activity in a semi-intact preparation.
The occurrence of a depolarizing plateau was abolished by blocking the NMDA receptors that are located on RS cells. Moreover, the depolarizing plateaus were accompanied by a rise in [Ca(2+)](i), and an intracellular injection of the Ca(2+) chelator BAPTA into single RS cells abolished the plateaus, suggesting that the latter are Ca(2+) dependent and rely on intrinsic properties of RS cells. The plateaus were shown to result from the activation of a Ca(2+)-activated nonselective cation current that maintains the cell in a depolarized state.
It is concluded that this intrinsic property of the RS neuron is then responsible for the transformation of an incoming sensory signal into a motor command that is then forwarded to the spinal locomotor networks."
"... reticulospinal (RS) neurons constitute the main descending system activating and controlling the spinal locomotor networks. " Free full text
138 Related citations:
18 Cited by's:
- Free full text -
The intrinsic function of a motor system--from ion channels to networks and behavior.
"The forebrain, brainstem and spinal cord contribution to the control of locomotion is reviewed in this article. The lamprey is used as an experimental model since it allows a detailed cellular analysis of the neuronal network underlying locomotion. The focus is on cellular mechanisms that are important for the pattern generation, as well as different types of pre- and postsynaptic modulation. This experimental model is bridging the gap between the molecular and cellular level to the network and behavioral level."
"... forebrain, brainstem and spinal cord contribution to the control of locomotion ..." Full length PDF
Full length PDF:
173 PubMed Related citations:
Stimulation of the mesencephalic locomotor region elicits controlled swimming in semi-intact lampreys.
Electrical microstimulation (2-10 Hz; 0. 1-5.0 microA) within a small periventricular region in the caudal mesencephalon elicited well-coordinated and controlled swimming that began within a few seconds after the onset of stimulation and lasted throughout the stimulation period. Swimming stopped several seconds after the end of stimulation. The power of swimming, expressed by the strength of the muscle contractions and the frequency and the amplitude of the lateral displacement of the body or tail, increased as the intensity or frequency of the stimulating current were increased. Micro-injection of AMPA, an excitatory amino acid agonist, into the MLR also elicited active swimming.
Electrical stimulation of the MLR elicited large EPSPs in reticulospinal neurons (RS) of the middle rhombencephalic reticular nucleus (MRRN), which also displayed rhythmic activity during swimming. The retrograde tracer cobalt-lysine was injected into the MRRN and neurons (dia. 10-20 microm) were labelled in the MLR, indicating that this region projects to the rhombencephalic reticular formation.
Taken together, the present results indicate that, as higher vertebrates, lampreys possess a specific mesencephalic region that controls locomotion, and the effects onto the spinal cord are relayed by brainstem RS neurons."
"Taken together, the present results indicate that, as higher vertebrates, lampreys possess a specific mesencephalic region that controls locomotion, and the effects onto the spinal cord are relayed by brainstem RS neurons."
190 Related citations:
18 Cited by's:
Ion channels of importance for the locomotor pattern generation in the lamprey brainstem-spinal cord. Free PMC Article
2001 108<349 Free Article
Heterogeneity of the population of command neurons in the lamprey.
Fast and slow locomotor burst generation in the hemispinal cord of the lamprey.
"A fundamental question in vertebrate locomotion is whether distinct spinal networks exist that are capable of generating rhythmic output for each group of muscle synergists. In many vertebrates including the lamprey, it has been claimed that burst activity depends on reciprocal inhibition between antagonists.
This question was addressed in the isolated lamprey spinal cord in which the left and right sides of each myotome display rhythmic alternating activity. We sectioned the spinal cord along the midline and tested whether rhythmic motor activity could be induced in the hemicord with bath-applied D-glutamate or N-methyl-D-aspartate (NMDA) as in the intact spinal cord or by brief trains of electrical stimuli.
Fast rhythmic bursting (2-12 Hz), coordinated across ventral roots, was observed with all three methods. Furthermore, to diminish gradually the crossed glycinergic inhibition, a progressive surgical lesioning of axons crossing the midline was implemented. This resulted in a gradual increase in burst frequency, linking firmly the fast hemicord rhythm [6.6 +/- 1.7 (SD) Hz] to fictive swimming in the intact cord (2.4 +/- 0.7 Hz). Ipsilateral glycinergic inhibition was not required for the hemicord burst pattern generation, suggesting that an interaction between excitatory glutamatergic neurons suffices to produce the unilateral burst pattern. In NMDA, burst activity at a much lower rate (0.1-0.4 Hz) was also encountered, which required the voltage-dependent properties of NMDA receptors in contrast to the fast rhythm.
Swimming is thus produced by pairs of unilateral burst generating networks with reciprocal inhibitory connections that not only ensure left/right alternation but also downregulate frequency."
"Swimming is thus produced by pairs of unilateral burst generating networks with reciprocal inhibitory connections that not only ensure left/right alternation but also downregulate frequency."
475 Related citations:
20 Cited by's:
- Free full text -
Tectal control of locomotion, steering, and eye movements in lamprey.
"The intrinsic function of the brain stem-spinal cord networks eliciting the locomotor synergy is well described in the lamprey-a vertebrate model system. This study addresses the role of tectum in integrating eye, body orientation, and locomotor movements as in steering and goal-directed behavior.
Electrical stimuli were applied to different areas within the optic tectum in head-restrained semi-intact lampreys (n = 40). Motions of the eyes and body were recorded simultaneously (videotaped).
Brief pulse trains (<0.5 s) elicited only eye movements, but with longer stimuli (>0.5 s) lateral bending movements of the body (orientation movements) were added, and with even longer stimuli locomotor movements were initiated. Depending on the tectal area stimulated, four characteristic response patterns were observed.
In a lateral area conjugate horizontal eye movements combined with lateral bending movements of the body and locomotor movements were elicited, depending on stimulus duration. The amplitude of the eye movement and bending movements was site specific within this region.
In a rostromedial area, bilateral downward vertical eye movements occurred. In a caudomedial tectal area, large-amplitude undulatory body movements akin to struggling behavior were elicited, combined with large-amplitude eye movements that were antiphasic to the body movements. The alternating eye movements were not dependent on vestibuloocular reflexes.
Finally, in a caudolateral area locomotor movements without eye or bending movements could be elicited. These results show that tectum can provide integrated motor responses of eye, body orientation, and locomotion of the type that would be required in goal-directed locomotion."
"These results show that tectum can provide integrated motor responses of eye, body orientation, and locomotion of the type that would be required in goal-directed locomotion."
451 Related citations:
12 Cited by's:
Note: At this point PubMed seems to have changed the results for this search. I need to review the references starting here to see if there is anything that I didn't find the first time through which may be useful.
2008 (Apparently from a different search using different search terms.)
Descending brain-spinal cord projections in a primitive vertebrate, the lamprey: cerebrospinal fluid-contacting and dopaminergic neurons.
"We used Neurobiotin as a retrograde tract tracer in both larval and adult sea lampreys and observed a number of neuronal brainstem populations (mainly reticular and octaval populations and some diencephalic nuclei) that project to the spinal cord, in agreement with the results of previous tracer studies.
We also observed small labeled neurons in the ventral hypothalamus, the mammillary region, and the paratubercular nucleus, nuclei that were not reported as spinal projecting. Notably, most of the labeled cells of the mammillary region and some of the ventral hypothalamus were cerebrospinal fluid-contacting (CSF-c) neurons.
Combined tract tracing and immunocytochemistry showed that some of the labeled neurons of the mammillary and paratubercular nuclei were dopamine immunoreactive. In addition, some CSF-c cells were labeled in the caudal rhombencephalon and rostral spinal cord, and many were also dopamine immunoreactive.
Results with other tracers (biotinylated dextran amines, horseradish peroxidase, and the carbocyanine dye DiI) also demonstrated that the molecular weight or the molecular nature of the tracer was determinant in revealing diencephalic cells with very thin axons.
The results show that descending systems afferent to the spinal cord in lampreys are more varied than previously reported, and reveal a descending projection from CSF-c cells, which is unknown in vertebrates. The present results also reveal the existence of large differences between agnathans and gnathostomes in the organization of the dopaminergic cells that project to the spinal cord."
"We ... observed a number of neuronal brainstem populations (mainly reticular and octaval populations and some diencephalic nuclei) that project to the spinal cord, in agreement with the results of previous tracer studies.
676 Related citations:
5 Cited by's:
I'm interested in projections to the spinal cord. The above mentions the DLR but not the MLR. What is the interaction between them?
Neural bases of goal-directed locomotion in vertebrates--an overview.
2008 57<349 Free Article
The activity of spinal commissural interneurons during fictive locomotion in the lamprey.
The Spinobulbar System in Lamprey
from the Abstract:
"Locomotor networks in the spinal cord are controlled by descending systems which in turn receive feedback signals from ascending systems about the state of the locomotor networks. In lamprey, the ascending system consists of spinobulbar neurons which convey spinal network signals to the two descending systems, the reticulospinal and vestibulospinal neurons.
Previous studies showed that spinobulbar neurons consist of both ipsilaterally and contralaterally projecting cells distributed at all rostrocaudal levels of the spinal cord, though most numerous near the obex. The axons of spinobulbar neurons ascend in the ventrolateral spinal cord and brainstem to the caudal mesencephalon and within the dendritic arbors of reticulospinal and vestibulospinal neurons. Compared to mammals, the ascending system in lampreys is more direct, consisting of excitatory and inhibitory monosynaptic inputs from spinobulbar neurons to reticulospinal neurons.
The spinobulbar neurons are rhythmically active during fictive locomotion, representing a wide range of timing relationships with nearby ventral root bursts including those in phase, out of phase, and active during burst transitions between opposite ventral roots. The spinobulbar neurons are not simply relay cells because they can have mutual synaptic interactions with their reticulospinal neuron targets and they can have synaptic outputs to other spinal neurons. Spinobulbar neurons not only receive locomotor inputs but also receive direct inputs from primary mechanosensory neurons. Due to the relative simplicity of the lamprey nervous system and motor control system, the spinobulbar neurons and their interactions with reticulospinal neurons may be advantageous for investigating the general organization of ascending systems in the vertebrate."
" In lamprey, the ascending system consists of spinobulbar neurons which convey spinal network signals to the two descending systems, the reticulospinal and vestibulospinal neurons."
122 Related citations:
5 Cited by's:
2009 46<349 Free PMC Article
Simple cellular and network control principles govern complex patterns of motor behavior.
2010 (Apparently from a different search using different search terms.)
Measured Motion: Searching for Simplicity in Spinal Locomotor Networks
http://www.ncbi.nlm.nih.gov/pubmed/?term=19896834Full length HTML and PDF available online for free.
"Spinal interneurons are organized into networks that control the activity and output of the motor system. This review outlines recent progress in defining the rules that govern the assembly and function of spinal motor networks, focusing on three main areas.
We first examine how subtle variations in the wiring diagrams and organization of locomotor networks in different vertebrates permits animals to adapt their motor programs to the demands of their physical environment.
We discuss how the membrane properties of spinal interneurons, and their synaptic interactions, underlie the modulation of motor circuits and encoded motor behaviors.
We also describe recent molecular genetic approaches to map and manipulate the connectivity and interactions of spinal interneurons and to assess the impact of such perturbations on network function and motor behavior."
from the HTML
"The first vertebrates to emerge, some 500 millions year ago, are today represented by lampreys ...
The lamprey locomotor network, arguably the ancestral doyen of vertebrate locomotor systems, generates a pronounced left-right alternation of motor output in each segment, while imposing a segmental phase lag that results in the propagation of an undulatory wave of motor activity along the body axis, from head to tail ( 5 ). This basic motor strategy is evident in most fish, in the larval stages of amphibia, and in a more limited form, in some mammals ( 8 , 10 , 6 , 11 ).
Some 100 million years after the emergence of agnathans, the acquisition of pectoral fins – paired appendages that represent the precursors of the tetrapod limb – permitted aquatic vertebrates to use them for steering and move them in either alternating or synchronous modes during locomotion.
Mammals, comparative newcomers that appeared on the scene only ?130 million years ago, have retained and embellished this versatile appendicular addition to the motor repertoire."
"The first vertebrates to emerge, some 500 millions year ago" ... "Mammals, comparative newcomers that appeared on the scene only ?130 million years ago"
101 Related citations:
A parallel cholinergic brainstem pathway for enhancing locomotor drive.
"The brainstem locomotor system is believed to be organized serially from the mesencephalic locomotor region (MLR) to reticulospinal neurons, which in turn project to locomotor neurons in the spinal cord. We identified brainstem muscarinoceptive neurons in lampreys (Petromyzon marinus) that received parallel inputs from the MLR and projected back to reticulospinal cells to amplify and extend the duration of locomotor output. These cells responded to muscarine with extended periods of excitation, received direct muscarinic excitation from the MLR and projected glutamatergic excitation to reticulospinal neurons. Targeted blockade of muscarine receptors over these neurons profoundly reduced MLR-induced excitation of reticulospinal neurons and markedly slowed MLR-evoked locomotion. The presence of these neurons forces us to rethink the organization of supraspinal locomotor control, to include a sustained feedforward loop that boosts locomotor output."
"The brainstem locomotor system is believed to be organized serially from the mesencephalic locomotor region (MLR) to reticulospinal neurons, which in turn project to locomotor neurons in the spinal cord. We identified brainstem muscarinoceptive neurons in lampreys (Petromyzon marinus) that received parallel inputs from the MLR and projected back to reticulospinal cells to amplify and extend the duration of locomotor output."
103 Related citations:
http://www.ncbi.nlm.nih.gov/pubmed?linkname=pubmed_pubmed&from_uid=20473293- Free PMC Article -
11 Cited by's:
Click on the active link, above.
Beyond connectivity of locomotor circuitry-ionic and modulatory mechanisms
"Discrete neural networks in the central nervous system generate the repertoire of motor behavior necessary for animal survival. The final motor output of these networks is the result of the anatomical connectivity between the individual neurons and also their biophysical properties as well as the dynamics of their synaptic transmission. To illustrate how this processing takes place to produce coordinated motor activity, we have summarized some of the results available from the lamprey spinal locomotor network. The detailed knowledge available in this model system on the organization of the network together with the properties of the constituent neurons and the modulatory systems allows us to determine how the impact of specific ion channels and receptors is translated to the global activity of the locomotor circuitry. Understanding the logic of the neuronal and synaptic processing within the locomotor network will provide information about not only their normal operation but also how they react to disruption such as injuries or trauma."
111 Related citations:
2 Cited by's.
Chapter 4--supraspinal control of locomotion: the mesencephalic locomotor region.
See: Mesencephalic Locomotor Region for full Abstract, Related citations and Cited by's.
Forebrain dopamine neurons project down to a brainstem region controlling locomotion.
140805 - 1750 modified