CSF-contacting (CSF-c) cells are present in the walls of the brain ventricles and the central canal of the spinal cord and found throughout the vertebrate phylum. We recently identified ciliated somatostatin-/GABA-expressing CSF-c neurons in the lamprey spinal cord that act as pH sensors as well as mechanoreceptors. In the same neuron, acidic and alkaline responses are mediated through ASIC3-like and PKD2L1 channels, respectively. Here, we investigate the functional properties of the ciliated somatostatin-/GABA-positive CSF-c neurons in the hypothalamus by performing whole-cell recordings in hypothalamic slices. Depolarizing current pulses readily evoked action potentials, but hypothalamic CSF-c neurons had no or a very low level of spontaneous activity at pH 7.4. They responded, however, with membrane potential depolarization and trains of action potentials to small deviations in pH in both the acidic and alkaline direction. Like in spinal CSF-c neurons, the acidic response in hypothalamic cells is mediated via ASIC3-like channels. In contrast, the alkaline response appears to depend on connexin hemichannels, not on PKD2L1 channels. We also show that hypothalamic CSF-c neurons respond to mechanical stimulation induced by fluid movements along the wall of the third ventricle, a response mediated via ASIC3-like channels. The hypothalamic CSF-c neurons extend their processes dorsally, ventrally, and laterally, but as yet, the effects exerted on hypothalamic circuits are unknown. With similar neurons being present in rodents, the pH- and mechanosensing ability of hypothalamic CSF-c neurons is most likely conserved throughout vertebrate phylogeny. SIGNIFICANCE STATEMENT CSF-contacting neurons are present in all vertebrates and are located mainly in the hypothalamic area and the spinal cord. Here, we report that the somatostatin-/GABA-expressing CSF-c neurons in the lamprey hypothalamus sense bidirectional deviations in the extracellular pH and do so via different molecular mechanisms. They also serve as mechanoreceptors. The hypothalamic CSF-c neurons have extensive axonal ramifications and may decrease the level of motor activity via release of somatostatin. In conclusion, hypothalamic somatostatin-/GABA-expressing CSF-c neurons, as well as their spinal counterpart, represent a novel homeostatic mechanism designed to sense any deviation from physiological pH and thus constitute a feedback regulatory system intrinsic to the CNS, possibly serving a protective role from damage caused by changes in pH.

The lamprey network coordinating locomotion has been studied extensively. As in all other vertebrates investigated, the pattern generation is provided at the spinal-cord level, whereas the decision to activate the network is controlled primarily by the locomotor command centers in the brainstem (i.e., the mesencephalic locomotor region and diencephalic locomotor region), which in turn are controlled from the basal ganglia in the forebrain. The core of the segmental locomotor network is formed by pools of excitatory interneurons that can excite each other and generate burst activity . Inhibitory glycinergic or GABAergic neurons are not required in this process. Therefore, there is a core unit CPG on each side of the spinal cord that can operate without inhibitory mechanisms. The latter do, however, play a critical role for left–right coordination between the two sides. This chapter will discuss the segmental rhythm-generating circuits and the mechanism underlying intersegmental coordination.

For survival of the organism, acid-base homeostasis is vital [1, 2]. The respiratory and renal systems are central to this control. Here we describe a novel mechanism, intrinsic to the spinal cord, with sensors that detect pH changes and act to restore pH to physiological levels by reducing motor activity. This pH sensor consists of somatostatin-expressing cerebrospinal fluid-contacting (CSF-c) neurons, which target the locomotor network. They have a low level of activity at pH 7.4. However, at both alkaline and acidic pH, the activity of the individual CSF-c neuron is markedly enhanced through the action of two separate channel subtypes. The alkaline response depends on PKD2L1 channels that have a large conductance and an equilibrium potential around 0 mV, both characteristics of mouse PKD2L1 channels [3-5]. The acidic response is due to an activation of ASIC3 [6]. The discharge pattern of the CSF-c neurons is U-shaped with a minimum frequency around pH 7.4 and a marked increase already at slightly lower and higher pH. During ongoing locomotor activity in the isolated spinal cord, both an increase and as a decrease of pH will reduce the locomotor burst rate. A somatostatin antagonist blocks these effects, suggesting that CSF-c neurons are responsible for the suppression of locomotor activity. CSF-c neurons thus represent a novel innate homeostatic mechanism, designed to sense any deviation from physiological pH and to respond by causing a depression of the motor activity. Because CSF-c neurons are found in all vertebrates, their pH-sensing function is most likely conserved.

Cerebrospinal fluid-contacting (CSF-c) cells are found in all vertebrates but their function has remained elusive. We recently identified one type of laterally projecting CSF-c cell in lamprey spinal cord with neuronal properties that expresses GABA and somatostatin. We show here that these CSF-c neurons respond to both mechanical stimulation and to lowered pH. These effects are most likely mediated by ASIC3-channels, since APETx2, a specific antagonist of ASIC3, blocks them both. Furthermore, lowering of pH as well as application of somatostatin will reduce the locomotor burst rate. The somatostatin receptor antagonist counteracts the effects of both a decrease in pH and of somatostatin. Lateral bending movement imposed on the spinal cord, as would occur during natural swimming, activates CSF-c neurons. Taken together, we show that CSF-c neurons act both as mechanoreceptors and as chemoreceptors through ASIC3 channels, and their action may protect against pH-changes resulting from excessive neuronal activity.

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 (K(Ca)) channels, as well as low voltage-activated calcium channels. Upon membrane depolarization, influx of calcium will activate K(Ca) 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 K(Ca) 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.

Cerebrospinal fluid-contacting (CSF-c) cells are found in all vertebrates, but their function remains elusive. In the lamprey spinal cord, they surround the central canal and some have processes passing the gray matter to the lateral edge of the flattened spinal cord. Stimulation of CSF-c cells at the central canal elicits GABAergic inhibitory postsynaptic potentials (IPSPs) in intraspinal stretch receptor neurons (edge cells). Here, we characterize laterally projecting CSF-c cells according to their morphology, phenotype, and neuronal properties by using immunohistochemistry, retrograde tracing, calcium imaging, and whole-cell recordings. We identify two types of CSF-c cells. Type 1 cells have a bulb-like ending that protrudes into the central canal and a lateral process that ramifies ventrolaterally and laterally with a dense plexus surrounding the mechanosensitive dendrites of the edge cells. Most type 1 cells fire spontaneous action potentials that are abolished by tetrodotoxin, and all display spontaneous excitatory postsynaptic potentials and IPSPs that remain in the presence of tetrodotoxin. GABA and somatostatin are colocalized in type 1 cells, and they express both GABA and glutamate receptors. Type 2 cells, on the other hand, have a flat ending protruding into the central canal and a laterally projecting process that ramifies only at the lateral edge. These cells show immunoreactivity to taurine, but they do not express GABA or somatostatin, nor do they have any active neuronal properties. Type 2 cells might be a form of glia. Type 1 CSF-c cells are neurons and may play a modulatory role by influencing edge cells and thus the locomotor-related sensory feedback.

The basic features of the vertebrate nervous system are conserved throughout vertebrate phylogeny to a much higher degree than previously thought. In this mini-review, we show that not only the organization of the different motor programs underlying eye, orienting, locomotor, and respiratory movements are similarly organized, but also that the basic structure of the fore-brain engaged in the control of movement is conserved. In the lamprey, which diverged already 560 million years ago from the vertebrate line of evolution leading up to primates, the basic components of the basal ganglia are similar to those of mammals in considerable detail. Moreover, the properties of the synaptic input are similar as well as transmitters/peptides in the direct and indirect pathway throughout the basal ganglia. The membrane properties of the striatal projection neurons with D1 and D2 receptors, respectively, are also similar, as are those of the pallidal output neurons. Our evidence suggests that the basal ganglia can be subdivided into functional modules controlling different motor programs, like locomotion and eye movements. What has happened during evolution is that the number of modules has increased in parallel with a progressively more complex behavioral repertoire. For value-based decisions, the circuitry through the lateral habenulae to the dopaminergic modulator neurons is also conserved, as well as the relay inhibitory interneurons involved. The habenular input is from a pallidal glutamatergic nucleus in lamprey as well as mammals, and this nucleus in turn receives input from the striosomal compartment within striatum and also from pallium (cortex in mammals).

The bioinspired approach has been key in combining the disciplines of robotics with neuroscience in an effective and promising fashion. Indeed, certain aspects in the field of neuroscience, such as goal-directed locomotion and behaviour selection, can be validated through robotic artefacts. In particular, swimming is a functionally important behaviour where neuromuscular structures, neural control architecture and operation can be replicated artificially following models from biology and neuroscience. In this article, we present a biomimetic system inspired by the lamprey, an early vertebrate that locomotes using anguilliform swimming. The artefact possesses extra- and proprioceptive sensory receptors, muscle-like actuation, distributed embedded control and a vision system. Experiments on optimised swimming and on goal-directed locomotion are reported, as well as the assessment of the performance of the system, which shows high energy efficiency and adaptive behaviour. While the focus is on providing a robotic platform for testing biological models, the reported system can also be of major relevance for the development of engineering system applications.

Key points Intrinsic NMDA‐induced oscillations of membrane potential are important for the operation of the spinal locomotor network in the lamprey, and involve a cyclic influx of calcium. The spatial and temporal calcium dynamics during oscillations were investigated, using calcium imaging combined with intracellular recordings. Calcium fluctuations were observed in both soma and dendrites, timed to the membrane potential oscillations, with the peak in distal dendritic locations typically occurring earlier than in the soma. The L‐type calcium channel antagonist nimodipine prolonged the plateau phase of membrane potential oscillations, whereas the agonist Bay K 8644 shortened the plateau. Bay K 8644 also increased the amplitude of calcium fluctuations, particularly in distal dendrites. On the contrary, nimodipine decreased calcium fluctuation amplitudes. Low‐voltage‐activated L‐type (CaV1.3‐like) calcium channels at distal dendrites are activated during membrane potential oscillations. The resulting calcium influx contributes to the activation of calcium‐activated potassium channels and thereby the control of the plateau duration during oscillations. Abstract NMDA receptor‐dependent, intrinsic membrane potential oscillations are an important element in the operation of the lamprey locomotor network. They involve a cyclic influx of calcium, leading to an activation of calcium‐activated potassium (KCa) channels that in turn contributes to the termination of the depolarized plateau and membrane repolarization. In this study, we have investigated the calcium dynamics in different regions of lamprey spinal neurons during membrane potential oscillations, using confocal calcium imaging in combination with intracellular recordings. Calcium fluctuations were observed in both soma and dendrites, timed to the oscillations. The calcium level increased sharply at the onset of membrane depolarization, to reach its maximum by the end of the plateau. The calcium peak in distal dendrites typically occurred earlier than in the soma during the oscillatory cycle. The L‐type calcium channel blocker nimodipine increased the duration of the depolarized plateau phase in most cells tested, whereas the agonist Bay K 8644 decreased plateau duration. Bay K 8644 increased the amplitude of calcium fluctuations, particularly in distal dendrites, whereas nimodipine caused a decrease, suggesting that L‐type low‐voltage‐activated calcium channels are mainly localized in these regions. Our results thus indicate that dendritic CaV1.3‐like calcium channels are activated during NMDA‐mediated membrane potential oscillations. This calcium influx activates KCa channels involved in plateau termination.

This paper describes the development of a new biorobotic platform inspired by the lamprey. Design, fabrication and implemented control are all based on biomechanical and neuroscientific findings on this eel-like fish. The lamprey model has been extensively studied and characterized in recent years because it possesses all basic functions and control mechanisms of higher vertebrates, while at the same time having fewer neurons and simplified neural structures. The untethered robot has a flexible body driven by compliant actuators with proprioceptive feedback. It also has binocular vision for vision-based navigation. The platform has been successfully and extensively experimentally tested in aquatic environments, has high energy efficiency and is ready to be used as investigation tool for high level motor tasks.

In this paper the development of a bio-robotic platform is described. The robot design exploits biomechanical and neuroscientific knowledge on the lamprey, an eel-like swimmer well studied and characterized thanks to the reduced complexity of its anatomy. The robot is untethered, has a compliant body, muscle-like high efficiency actuators, proprioceptive sensors to detect stretch and stereoscopic vision. Experiments on the platform are reported, including robust and autonomous goal-directed swimming. Extensive experiments have been possible thanks to very high energy efficiency (around five hour continuous operating) the platform is ready to be used as investigation tool for high level motor tasks.

Postinhibitory rebound (PIR) can play a significant role for producing stable rhythmic motor patterns, like locomotion, by contributing to burst initiation following the phase of inhibition, and PIR may also be a target for modulatory systems acting on the network. The current aim was to explore the PIR in one type of interneuron in the lamprey locomotor network and its dependence on low voltage-activated (LVA) calcium channels, as well as its modulation by 5-HT and dopamine. PIR responses in commissural interneurons, mediating reciprocal inhibition and left-right alternation in the network, were significantly larger than in motoneurons. The L-type calcium channel antagonist nimodipine reduced PIR amplitude by ∼ 50%, whereas the L-channel agonist BAY K 8644 enhanced PIR amplitude, suggesting that LVA calcium channels of the L-subtype (Ca(V)1.3) participate in the PIR response. The remainder of the response was blocked by nickel, indicating that T-type (Ca(V)3) LVA calcium channels also contribute. No evidence was obtained for the involvement of a hyperpolarization-activated current. Furthermore, 5-HT, acting via 5-HT(1A) receptors, reduced PIR, as did dopamine, acting via D(2) receptors. Coapplication of nimodipine caused no further PIR reduction, indicating that these modulators target Ca(V)1.3 channels specifically. These results suggest that PIR may play a prominent role in the generation of alternating network activity and that the Ca(V)1.3 and Ca(V)3 subtypes of LVA calcium channels together underlie the PIR response. 5-HT and dopamine both target PIR via Ca(V)1.3 channels, which may contribute significantly to their modulatory influence on locomotor network activity.

In this chapter, we review the extensive knowledge gained on the lamprey nervous system through an interactive process between experiments and modeling [1–3]. The organization of the locomotor system is to a large extent conserved through vertebrate phylogeny, and it is therefore also pertinent to explore to what extent this knowledge can be applied to the more complex mammalian nervous system. The overall aim is to account for this complex set of behaviors, based on an understanding of the intrinsic cellular mechanisms determining the operation of the different neuronal networks.

Event Abstract Back to Event Real-time imaging of calcium dynamics in rhythmically active neurons of thespinal network for locomotion Di Wang1*, Sten Grillner1 and Peter Wallén1 1 Karolinska Institutet, Sweden The neuronal network underlying locomotion in vertebrates has been investigated in considerable detail in the lamprey spinal cord in vitro model. The isolated spinal cord preparation can be made to produce well-coordinated rhythmic activity, with left-right alternation and intersegmental phase-coupling, corresponding to locomotion (swimming). The rhythm-generating capacity of the network is the result of an interplay between network connectivity properties and the dynamic membrane properties of the individual network neurons. These different kinds of membrane properties typically rely on localized influx of calcium, leading to, for instance, the activation of calcium-dependent potassium channels (KCa-channels). Among the key calcium-dependent membrane properties are the NMDA-receptor-dependent membrane potential pacemaker oscillations, the slow afterhyperpolarization (sAHP) following the action potential, and the postinhibitory rebound depolarization following a period of hyperpolarization. Although much is known about the detailed operation of the network, specific information on the calcium dynamics – both in the temporal and the spatial domain – is still to a large degree lacking. We are therefore investigating different membrane properties of lamprey spinal neurons by utilizing confocal calcium imaging in combination with intracellular membrane potential recordings. During rhythmic network operation (fictive locomotion), calcium fluctuations can be detected in dendrites of individual neurons, even during subthreshold membrane potential oscillations (cf. Bacskai et al., Neuron 14:19-28, 1995). Furthermore, during NMDA-dependent pacemaker oscillations in the presence of TTX, dendritic calcium fluctuations are also seen, timed to the membrane potential oscillations (Fig. 1). During burst firing, the sAHP´s following each spike will add and produce a pronounced summed sAHP, which contributes to the termination of the burst. Calcium imaging during spike trains has revealed a distinct influx of calcium in conjunction with the sAHP. This calcium enters via N (CaV 2.2)- and P/Q (CaV 2.1) types of HVA calcium channels, while L-type channels (CaV 1) are not involved. Correspondingly, blockade of N- and P/Q-type channels reduced the calcium influx in the soma and proximal dendrites, while blockade of L-type channels did not. This indicates that the calcium channels responsible for activating the KCa channels involved in the sAHP are primarily located in the soma and proximal dendrites of the cell. In contrast, L-type calcium channels appear to be mainly localized to distal dendrites in lamprey spinal neurons. Confocal fluorescence imaging of calcium influx, and other dynamic events, with high spatial and temporal resolution, in combination with electrophysiological recordings from the same neuron in the functional network, holds promise to reveal important insights into the cellular and subcellular mechanisms governing network operation. tn_image2 conference image2 conference Conference: Neuroinformatics 2008, Stockholm, Sweden, 7 Sep - 9 Sep, 2008. Presentation Type: Poster and Short Oral Presentation Topic: Neuroimaging Citation: Wang D, Grillner S and Wallén P (2008). Real-time imaging of calcium dynamics in rhythmically active neurons of thespinal network for locomotion. Front. Neuroinform. Conference Abstract: Neuroinformatics 2008. doi: 10.3389/conf.neuro.11.2008.01.060 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 25 Jul 2008; Published Online: 25 Jul 2008. * Correspondence: Di Wang, Karolinska Institutet, Stockholm, Sweden, di.wang@ki.se Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract Supplemental Data The Authors in Frontiers Di Wang Sten Grillner Peter Wallén Google Di Wang Sten Grillner Peter Wallén Google Scholar Di Wang Sten Grillner Peter Wallén PubMed Di Wang Sten Grillner Peter Wallén Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.