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S Grillner

Publications and source records attributed to S Grillner.

At least 91 records · Page 5Linked to original sources
PubMed1995

Activity-related calcium dynamics in lamprey motoneurons as revealed by video-rate confocal microscopy.

In lamprey spinal cord, intracellular calcium ([Ca2+]i) plays a key role in mechanisms regulating neuronal activity in the segmental network for locomotion. In this report, measurements of [Ca2+]i with fluo-3 in various regions of motoneurons in the intact spinal cord were obtained on a high speed confocal microscope following electrical stimulation. Likewise, rhythmic calcium fluctuations within dendrites and axons were seen during "fictive swimming" and were directly correlated with electrical activity. Antidromic stimulation of motoneuron axons induced large calcium transients and revealed spatially restricted "hot spots," both of which required external calcium and were blocked by nickel, but not by known calcium channel antagonists. These results suggest that lamprey spinal cord axons may possess a pharmacologically novel class of calcium channel.

Aniline Compounds↗
PubMed1995

Neurotensin-induced modulation of spinal neurons and fictive locomotion in the lamprey.

1. Neurotensin containing interneurons are present in the spinal cord of both mammalian and nonmammalian vertebrates, but as yet little is known about their functional role. In this study we examine the effect of neurotensin on spinal cells and on the central pattern generator for locomotion in the lamprey spinal cord. 2. Bath application of neurotensin (10(-8) to 10(-6) M) slowed down the fictive locomotor activity induced by the glutamate agonist N-methyl-D-aspartate in the isolated spinal cord. The duration of the bursts of activity in the ventral roots increased in proportion to the increase of the locomotor cycle duration. 3. Intracellular recordings from grey matter neurons and intraspinal stretch receptors neurons showed that neurotensin induced a depolarization [4.4 +/- 0.5 (SE) mV, n = 19]. This depolarization could still be obtained after a blockade of voltage-sensitive sodium channels with tetrodotoxin (1.5 +/- 0.5 mV; n = 6), and after removal of calcium (2.8 +/- 0.4 mV; n = 5). Moreover no consistent change occurred in the fast and slow phase of the afterhyperpolarization (AHP) both of which are carried by potassium currents.

Animals↗
PubMed1995

Initiation of locomotion by lateral line photoreceptors in lamprey: behavioural and neurophysiological studies

The lateral line system of lampreys includes photoreceptors distributed in the skin of the tail region. These are innervated by the trunk lateral line nerves, and the afferents terminate bilaterally in the medial octavolateral nucleus, crossing the midline through the cerebellar commissure. Stimulation of the dermal photoreceptors by tail illumination initiates locomotion. The present study was performed to characterize the response to illumination in larval and adult lampreys in detail and to elucidate the neuronal pathways responsible for the activation of locomotion. In both larval and adult quiescent lampreys, the response to unilateral illumination of the tail was found to consist of an initial turn followed by rectilinear swimming. The sign and magnitude of the turning angle were not correlated with the laterality of the optic stimulus. In mechanically restrained lampreys, spinalized at the level of segments 15&shy;20, tail illumination evoked a complex motor response in the rostral part of the body, with switches between different patterns of coordination (turns in different directions, locomotion, and turns combined with locomotion). Thus, the response to tail illumination is not a simple reflex, but includes a behavioural choice. Reticulospinal neurones play a crucial role in the initiation of locomotion in lampreys. The response to unilateral tail illumination in rhombencephalic reticular cells was studied with extracellular single-unit recordings. It was found that neurones in the middle and posterior rhombencephalic reticular nuclei were activated bilaterally. Tonic activity or slow bursts (<0.5 Hz) were evoked, in some cases lasting up to 60 s after the stimulation. The response remained bilateral after transection of one lateral line nerve and the cerebellar commissure. Afferents from one side can thus activate reticulospinal cells on both sides through a pathway outside the cerebellar commissure. This bilateral activation of reticulospinal neurones is presumably responsible for the activation of spinal locomotor networks, without any directional bias to the left or the right side, and for the rectilinear swimming observed in behavioural experiments. In the caudal part of the termination area of the lateral line nerve afferents, neurones with contralateral projections were retrogradely stained with horseradish peroxidase. These neurones appear to be likely candidates for mediating the contralateral effects of the lateral line fibres.

Journal Article↗
PubMed1995

Spatial orientation in the lamprey. I. Control of pitch and roll

Two major tasks must be fulfilled during locomotion: propulsion and spatial orientation. In the lamprey, the propulsive force is generated by laterally directed body undulations propagated from the rostral to the caudal end of the body. The neuronal networks underlying this basic locomotor pattern have been described in considerable detail. The present study was undertaken to provide the necessary behavioural background for parallel studies of the vestibular neuronal networks responsible for spatial orientation during locomotion. The following results were obtained. 1. The lamprey actively stabilized its pitch angle during swimming and usually kept a linear trajectory in the sagittal plane, despite large changes in the speed of swimming. During repeated tests, a certain preferred pitch angle could be maintained over a period of several minutes, even if the initial starting angle of the animal was changed considerably. 2. Two different strategies were observed for active turning in the downward direction: a smooth turn accomplished by weak ventral flexion of the whole body, and a sharp turn accomplished by localized ventral flexion of a region of the body just posterior to the gills. 3. The lampreys were oriented with the dorsal side up while swimming at any pitch angle. The control systems for pitch and roll can thus operate independently. When swimming, lampreys kept the tail region flexed somewhat ventrally. This body configuration will cause lateral movements of the tail to generate a torque that rotates the body around its longitudinal axis. This mechanism is presumably used to correct deviations from the dorsal-side-up orientation. After amputation of the dorsal and tail fins, lampreys maintained a proper spatial orientation during swimming. 4. After a unilateral labyrinthectomy, swimming lampreys continuously rolled towards the lesioned side. Unilaterally labyrinthectomized animals displayed a tonic twisting of the body into a helical shape. This presumably represents an additional strategy for performing roll turns. Bilaterally labyrinthectomized animals never maintained a linear trajectory in any plane, but turned continuously in all directions.

Journal Article↗
PubMed1995

Spatial orientation in the lamprey. II. Visual influence on orientation during locomotion and in the attached state

The responses of attached lampreys to homogeneous visual stimulation and the role of visual stimuli in orientation during locomotion were investigated. Experiments were performed by video recording the responses of intact and lesioned animals to illumination. The following results were obtained. 1. In lampreys attached with their sucker mouth to the bottom of the aquarium, illumination of one eye evoked several possible motor responses (ordered after mean latency): (a) movement of the illuminated eye downwards, and the contralateral eye upwards; (b) rotation of the body around the longitudinal axis, with the illuminated side tilting downwards; (c) deviation of the caudal part of the anterior dorsal fin in the contralateral direction (away from the light); and (d) flexion of the neck and body towards the side of illumination. 2. Illumination of one eye in attached lampreys often resulted in detachment and subsequent movement in a direction away from the light source (negative phototaxis). This response was not related to the degree of roll tilt before detachment, so the negative phototaxis does not appear to be a consequence of the vestibular stimulation. 3. Negative phototaxis was also seen during locomotion: lampreys turned through 180 &deg; when they approached a brightly illuminated area. Photostimulation also affected their orientation in the transverse plane during swimming. Illumination of one eye from the side induced a roll movement, so that the illuminated side tilted downwards and the dorsum of the lamprey became turned towards the light. This is similar to the 'dorsal light response' of fish and shows that vision also plays a role in postural control in lampreys. 4. The behaviour of blinded animals differed strikingly from that of intact ones. Whereas intact animals preferentially swam close to the bottom, along horizontal trajectories, blinded animals showed episodes of continuous swimming upwards, near the water surface. During horizontal swimming, their orientation in the transverse plane remained normal, with the dorsal side up.

Journal Article↗
PubMed1995

Neural networks that co-ordinate locomotion and body orientation in lamprey.

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. Mathematical modelling has been used to explore the capacity of these biological networks. 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.

Animals↗
PubMed1994

Extrasynaptic localization of taurine-like immunoreactivity in the lamprey spinal cord.

Taurine is an endogenous amino acid that can occur in nerve terminals in the central nervous system and that can produce inhibitory neuronal responses. It is unclear, however, whether this amino acid can function as a synaptic transmitter. To examine the distribution of taurine at high anatomical resolution in a vertebrate, light and electron microscopic immunocytochemical postembedding techniques were applied to the lamprey spinal cord (Ichtyomyzon unicuspis and Lampetra fluviatilis), which contains many large, unmyelinated axons. The most intense immunolabeling occurred in a population of liquor-contacting cells (tanycytes), located around the central canal, which extended processes to the dorsal, lateral, and ventral margins of the spinal cord. In addition, a proportion of the taurine-immunoreactive cells contained gamma-aminobutyric acid (GABA)-like immunoreactivity. A moderate level of taurine immunoreactivity was also present in ependymal cells, located around the central canal, as well as in astrocytes throughout all regions of the spinal cord. At the ultrastructural level, the taurine immunoreactivity showed an even distribution in the cytoplasm of the labeled cells. In contrast to the glial labeling, neuronal cell bodies and axons exhibited very low levels of taurine labeling, which were similar to the level of background labeling. The synaptic vesicle clusters within the axons did not show any clear accumulation of taurine immunoreactivity. These results suggest that taurine may have metabolic roles in the lamprey spinal cord, and, as in other systems, it may take part in osmoregulation. However, the lack of immunolabeling in presynaptic elements is not consistent with a role of taurine as a synaptic transmitter.

Animals↗
PubMed1994

Effects of metabotropic glutamate receptor activation on the cellular and network level in the lamprey spinal cord.

The effects of the metabotropic glutamate receptor (mGluR) agonist ACPD ((1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid) on single neurones and on the network underlying locomotion in the lamprey have been analysed. ACPD induces a depolarization in lamprey spinal cord neurones, which is insensitive to tetrodotoxin (TTX) and ionotropic glutamate receptor antagonists, but is reversibly blocked by the mGluR antagonist MCPG ((+)-alpha-methyl-4-carboxyphenylglycine). The ACPD-induced depolarization persists in a calcium-free solution or when the calcium channel blocker cadmium is added to the solution. At the network level ACPD causes an increased burst frequency during fictive locomotion by increasing the excitability level of network neurones.

Animals↗
PubMed1994

5-HT innervation of reticulospinal neurons and other brainstem structures in lamprey.

In order to determine if reticulospinal neurons involved in the control of locomotion and responsive to exogenously applied 5-hydroxytryptamine (5-HT) are innervated by fibers that contain serotonin, the serotoninergic innervation of reticulospinal neurons, identified by retrograde labeling with fluorescein-conjugated dextran-amine (FDA), was investigated by immunohistochemistry in the lamprey brainstem. A widespread distribution of 5-HT immunoreactive (5-HT-ir) fibers was seen within the basal plate of the brainstem, an area containing reticulospinal somata and dendritic aborizations. Numerous 5-HT varicose fibers were found in close relation to large reticulospinal cell bodies, particularly in the middle and anterior rhombencephalic reticular nuclei (MRRN and ARRN). Some of these reticulospinal somata were surrounded by a very dense pericellular 5-HT innervation. 5-HT-ir fibers were also seen in other brain structures that are known to influence reticulospinal neurons such as the rhombencephalic alar plate containing sensory relay interneurons, cranial nerves (III-X), cerebellum, and tectum. These findings suggest that, as in the spinal cord, motor behavior controlled by reticulospinal neurons may be subject to a serotoninergic modulation.

Animals↗
PubMed1994

A functional role for nitric oxide in locus coeruleus: immunohistochemical and electrophysiological studies.

Immunohistochemical analysis of the localization of nitric oxide synthase-(NOS)-like immunoreactivity revealed the presence of this enzyme in a few neuronal cell bodies and in dendritic and axonal processes within the rat locus coeruleus (LC). Also cells in the pericoeruleus area were NOS-positive. Intracellular recordings were made from LC neurons in brain slices. Bath application of the NOS inhibitors nitro-L-arginine methyl ester (L-NAME) or NG-monomethyl-L-arginine (L-NMMA) potently enhanced the excitatory postsynaptic potential (EPSP) evoked by focal electrical stimulation of the slice. Hemoglobin, which binds extracellular NO, also enhanced the EPSP. This enhancement was reversed by coadministration of L-arginine, a precursor of neuronal nitric oxide (NO). Neither NOS inhibitors, L-arginine, nor hemoglobin had effects on the resting membrane potential or impedance. These results suggest a role for NO in synaptic transmission in the LC.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1994

Calcium-dependent potassium channels play a critical role for burst termination in the locomotor network in lamprey.

1. The possible involvement of calcium-dependent potassium channels (KCa) in the termination of locomotor bursts was investigated by administration of a specific blocker, apamin, in the lamprey spinal cord in vitro. The effects were examined by recording the efferent activity in ventral roots and by intracellular recording from interneurons and motoneurons. During fictive locomotion induced by N-methyl-D-aspartate (NMDA), apamin was found to affect both the frequency of bursting and the regularity of the locomotor pattern. 2. At the single cell level, NMDA can induce pacemaker-like membrane potential oscillations in individual neurons after administration of tetrodotoxin. Apamin (2.5 microM) produced a marked increase of the duration of the depolarizing plateau phase occurring during these NMDA-induced oscillations; this shows that the repolarization of the plateau is initiated by a progressive activation of apamin-sensitive KCa-channels. 3. The action potential is followed by an afterhyperpolarization (AHP) with a fast and a slow phase (sAHP). The latter is known to be caused by apamin-sensitive KCa-channels. During repetitive firing, the interspike interval is dependent on the amplitude and the duration of the sAHP. Apamin caused a reduction of the spike frequency adaptation with a concomitant increase in the firing frequency. In some cells, apamin in addition reduced the threshold for the action potential. Apamin-sensitive KCa-channels thus will be involved in controlling both the onset and the duration of neuronal firing in the lamprey spinal cord. 4. During fictive locomotion induced by NMDA (40-200 microM), a blockade of KCa-channels by apamin produced an increase of the coefficient of variation (mean = 167%, n = 26), which was statistically significant in 21 out of 26 experiments. At 40-150 microM NMDA, an average increase in cycle duration was 77% and statistically significant in 15 out of 20 preparations. At 200 microM NMDA (corresponding to higher burst rate), on the other hand, the average increase was only 6% and the increase was statistically significant in only 1 out 6 cases. For a given experiment, the strength of the apamin effect depended on the level of NMDA drive used, being more pronounced at slow rhythms, when it often caused a complete disruption of the locomotor pattern. At high burst rates, however, the cycle duration was less affected and a disruption of the regular burst pattern did not occur.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

Presence of low voltage activated calcium channels distinguishes touch from pressure sensory neurons in the lamprey spinal cord.

Touch (T) and pressure (P) primary sensory neurons (dorsal cells) in the lamprey spinal cord differ not only with regard to their mechanoreceptive properties but also in their membrane properties. Touch cells have a significantly shorter time delay to the spike onset on a rebound of a hyperpolarizing current pulse than the pressure cells. Different time constants and input resistances partially explain these findings but cannot fully account for the observed differences between T- and P-cells. A more detailed study of membrane properties was therefore required. 3-D reconstructions of dorsal cells reveal a round shape with few processes and thus that they are suitable for voltage clamp analysis. Voltage activated calcium channels with a low threshold were found in a subpopulation of dorsal cells after administration of tetrodotoxin and K+ channel antagonists. These channels were blocked by addition of Co2+. In the short latency T-cells Co2+ increased the latency under current clamp conditions, and inhibited the facilitatory effect on spike activation upon increased hyperpolarization. This effect of Co2+ was not observed in the long latency P-cells. It is likely that the presence of low voltage calcium channels in T-cells are responsible for the differences observed between T- and P-cells. Voltage activated calcium channels with a higher threshold were observed in dorsal cells of both types. These channels were blocked by Co2+ or cadmium. Late outward 'tail' currents were shown to include calcium dependent potassium channels.

Action Potentials↗
PubMed1993

Role of dermal photoreceptors and lateral eyes in initiation and orientation of locomotion in lamprey.

The response to illumination, and the functional roles of skin photoreceptors and lateral eyes, were examined in the adult river lamprey (Lampetra fluviatilis L.). Illumination of one side of the lamprey evoked a turning movement away from the light source followed by locomotion. The lateral eyes were responsible for directing the movements away from the source of light. A selective illumination of one lateral eye consistently evoked a negative phototactic reaction, whereas a selective illumination of tail skin photoreceptors evoked locomotion, without any preferential orientation relative to the source of light. Experiments were performed by video recording the locomotor responses to localized illumination, and analyzed frame by frame. The horizontal turning movement during negative phototaxis consisted of an asymmetric laterally directed mechanical wave, of higher amplitude and lower velocity than the normal locomotory waves, which was propagated from the rostral to the caudal end of the body.

Animals↗
PubMed1993

Possible morphological substrates for GABA-mediated presynaptic inhibition in the lamprey spinal cord.

Gamma-aminobutyric acid (GABA) neurons intrinsic to the lamprey spinal cord are known to modulate synaptic transmission from interneurons active during locomotion and from mechanosensory dorsal cells. Many of these physiological effects are presynaptic. To establish the morphological substrates for these axo-axonic interactions, an ultrastructural analysis was performed with an antiserum to fixed GABA. The GABA immunoreactivity (ir) was detected by postembedding peroxidase-antiperoxidase and immunogold techniques. GABA-ir terminals were found to make appositions with unlabelled axons located in the dorsal columns and in the ventrolateral aspect of the spinal cord. In the ventrolateral part of the cord, similar appositions between different GABA-ir terminals were also observed. The immunolabelled terminals contained spherical to pleomorphic synaptic vesicles, and also glycogen granules and dense core vesicles. In some cases, the fine structure of the contacts between immunogold-labelled terminals and unlabelled axons suggested a synaptic relationship. Such a relation was found in a relatively small proportion (2-3%) of the appositions studied. These specializations were always observed in close relation to an output synapse of the postsynaptic axon. It is suggested that the axo-axonal contacts described may provide an effective modulation of the synaptic transmission from axons in the lamprey spinal cord.

Animals↗
PubMed1993

Dorsal root and dorsal column mediated synaptic inputs to reticulospinal neurons in lampreys: involvement of glutamatergic, glycinergic, and GABAergic transmission.

This study was aimed at characterizing the inputs from dorsal roots and dorsal columns to reticulospinal neurons within the posterior rhombencephalic reticular nucleus in the lamprey. The in vitro isolated brainstem and spinal cord preparation was used. Microstimulation of dorsal roots and columns on both sides induced, in identified reticulospinal neurons, synaptic responses which consisted of large IPSPs mixed with excitation, particularly from stimulation on the ipsilateral side. When the spinal cord was selectively exposed to kynurenic acid or to Ca2+ free Ringer's containing 2mM Mn2+, synaptic responses to stimulation of dorsal roots and columns were not modified, whereas the same responses were abolished when the brainstem was exposed selectively to kynurenic acid, thus suggesting that the responses were carried by long fibres ascending directly to the brainstem. The excitatory and inhibitory synaptic responses are relayed by interneurons located in the brainstem. The ascending excitatory inputs to inhibitory interneurons and, most likely, also to excitatory interneurons, use excitatory amino acid transmission. Inhibitory responses were abolished by adding the glycinergic antagonist strychnine (5 microM) to the physiological solution, thus suggesting that inhibitory interneurons use glycine transmission. The synaptic transmission was depressed by (-)-baclofen, a GABAB agonist, probably acting at a presynaptic site. Taken together, the present results suggest that dorsal root and dorsal column stimulations give rise to disynaptic inhibition and excitation of reticulospinal neurons mediated by excitatory and inhibitory amino acid transmission via brainstem interneurons.

Animals↗
PubMed1993

Anatomical and physiological study of brainstem nuclei relaying dorsal column inputs in lampreys.

The course and sites of termination of dorsal column fibres in the lamprey brainstem are described along with their brainstem relays projecting to reticulospinal neurons. Dorsal column fibres ascend to the brainstem level where they intermingle with cells located in the alar plate close to the obex, a location that is analogous to that of the dorsal column nucleus in other vertebrates. Some dorsal column fibres continue further rostrally where they reach the octavolateralis and octavomotorii nuclei. Finally, a small contingent of fibres reach the cerebellum. Injections of cobalt-lysine into the posterior rhombencephalic reticular nucleus retrogradely label neurons within the dorsal column nucleus and within the octavolateralis and octavomotorii nuclei. Microstimulation of the dorsal column nucleus on either side elicits monosynaptic inhibitory responses in reticulospinal neurons while stimulation of octavolateralis and octavomotorius nuclei elicits excitation. By using intracellular recordings, it was shown that neurons within these alar plate nuclei receive monosynaptic inputs from the dorsal columns. It is thus proposed that disynaptic inputs from dorsal columns to reticulospinal neurons are relayed by these alar plate neurons: inhibition is relayed mainly by neurons in dorsal column nuclei and excitation by neurons in the octavolateralis and octavomotorii nuclei.

Afferent Pathways↗