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Biomedical subjects

S Grillner

Publications and source records attributed to S Grillner.

At least 163 records · Page 9Linked to original sources
PubMed1989

Monosynaptic excitatory amino acid transmission from the posterior rhombencephalic reticular nucleus to spinal neurons involved in the control of locomotion in lamprey.

1. The reticulospinal neurons in the lamprey posterior rhombencephalic reticular nucleus (PRRN) and their projections to different types of spinal neurons have been investigated by the use of simultaneous paired intracellular recordings from one pre- and one postsynaptic cell. PRRN is of particular importance for the initiation of locomotion. 2. Intracellular stimulation of single PRRN neurons produced monosynaptic excitatory postsynaptic potentials (EPSPs) in simultaneously recorded motoneurons and spinal premotor interneurons of both the excitatory and inhibitory type. Individual PRRN neurons produced EPSPs in several different types of target cells, as revealed by signal averaging. Each single PRRN neuron had extensive monosynaptic connections to approximately 73% of the motoneuronal population. Conversely, several PRRN neurons converge on individual spinal neurons. The average amplitude of the EPSPs was 0.43 +/- 0.40 (SD) mV. The EPSPs varied in time course (time to peak = 7.5 +/- 2.8 ms; duration at one-half peak amplitude = 21.9 +/- 18.1 ms). 3. The EPSPs produced by reticulospinal cells were composed of either exclusively chemical, exclusively electrical, or mixed chemical and electrical components. The electrical EPSPs remained when the ordinary physiological solution was substituted for one without Ca2+ but with Mn2+. The chemical component of the EPSPs was always depressed when a broad-spectrum excitatory amino acid (EAA) antagonist, such as kynurenic acid, was applied, suggesting that the chemical component was because of EAA transmission. The chemical EPSP could have two components, one late, suppressed by N-methyl-D-aspartate (NMDA) antagonists, and one early because of activation of kainate/quisqualate receptors. 4. Three-dimensional reconstructions of Lucifer yellow-filled PRRN neurons were performed with a confocal laser scanning microscope. PRRN neurons producing monosynaptic excitatory amino acid EPSPs were found to have a fusiform cell body located near the surface of the fourth ventricle and an extensive fanlike dendritic tree extending to the ventral and lateral margin of the brain stem within the basal plate. The axons descend in the lateral funiculi of the spinal cord. 5. PRRN neurons utilizing EAA transmission are active during fictive locomotion. They presumably initiate and reinforce ongoing spinal locomotor activity by monosynaptically increasing the general excitability of the spinal premotor interneurons of the spinal locomotor networks by means of their extensive divergent and convergent monosynaptic connections.

Amino Acids↗
PubMed1989

Multiple forms of pancreatic polypeptide-related compounds in the lamprey CNS: partial characterization and immunohistochemical localization in the brain stem and spinal cord.

Although neuropeptide Y (NPY) is established as a transmitter in many regions of the nervous system, the role of other peptides of the pancreatic polypeptide (PP) family in the CNS is obscure. This study provides evidence that PP-like peptides in the "primitive" CNS of a cyclostome are composed of different molecular forms, which are stored in separate neuronal populations with apparently different functions. PP-like material was detected in extracts of brain and spinal cord from Lampetra fluviatilis by radioimmunoassay (RIA) using an antiserum to the C-terminal hexapeptide of mammalian PP. The PP-immunoreactive material consisted of several molecular forms, as shown by its complex elution profile on high-performance liquid chromatography (HPLC). The cellular distribution of PP-like immunoreactivity was studied with indirect immunofluorescence histochemistry using antisera toward porcine peptide YY (PYY), porcine neuropeptide Y (NPY), and bovine (BPP), rat (RPP), and avian (APP) pancreatic polypeptide. Adjacent sections from the brain stem and spinal cord of L. fluviatilis and Ichthyomyzon unicuspis, incubated with the different antisera, displayed 2 main patterns of PP immunoreactivity. The PYY and RPP antisera labeled groups of neurons and fibers in the rhombencephalic and mesencephalic reticular formation. One of the PYY/RPP-ir cell groups, located in the anterior rhombencephalic reticular nucleus, had a projection to the dorsolateral spinal cord. Fibers of this reticulospinal system were in close apposition to dendrites of intracellularly stained spinal motoneurons and sensory relay interneurons, indicating that they may receive PPergic input. In contrast, antisera to NPY and APP labeled local neurons systems in the spinal dorsal horn, in the lateral parts of the brain stem, including the rhombencephalic alar plate, and in the retina. The BPP antiserum recognized the NPY/APP as well as the PYY/RPP immunoreactive neuron systems, further supporting that they both contain PP-like peptides.

Animals↗
PubMed1988

The effect of an uptake inhibitor (dihydrokainate) on endogenous excitatory amino acids in the lamprey spinal cord as revealed by microdialysis.

Microdialysis was utilized to test the effects of the uptake inhibitor dihydrokainate (DHK) on endogenous amino acid levels in the lamprey spinal cord in vitro. The level of L-glutamate increased markedly (165%) in the presence of DHK, whereas the level of the glutamate precursor L-glutamine decreased (53%). Since DHK can potentiate or evoke fictive locomotion in the lamprey spinal cord, it is suggested that L-glutamate is released by neurons which take part in the activation of the spinal locomotor network.

Animals↗
PubMed1988

Simulation of the segmental burst generating network for locomotion in lamprey.

Recently a segmental network of inhibitory and excitatory interneurones, which are active during locomotion, has been described in the lamprey, a lower vertebrate. The interactions between the different neurones were established by paired intracellular recordings. A computer simulation of the segmental network has been performed, which shows that with the established neuronal connectivity rhythmic alternating burst activity can be generated within the upper part of the normal physiological range of locomotion. Three neurones of each kind were used (altogether 18 neurones). As shown previously the lower frequency range used in locomotion most likely depends on an activation of voltage-dependent N-methyl-D-aspartate (NMDA) receptors, which could, however, not be simulated with the present neuronal models.

Animals↗
PubMed1988

Immunohistochemical studies of cholecystokininlike peptides and their relation to 5-HT, CGRP, and bombesin immunoreactivities in the brainstem and spinal cord of lampreys.

The distribution of cholecystokinin (CCK)-like immunoreactivity in the brainstem and spinal cord of lampreys was studied by using CCK antisera with different properties. In the spinal cord, three separate systems reacted with CCK antisera: (1) A ventral and lateral fiber system descending from a group of neurons in the posterior reticular nucleus of the rhombencephalon was labeled by both a C-terminal-directed CCK antiserum and a monoclonal CCK antibody. (2) A dorsal root-dorsal column system of fibers originating from cell bodies in the dorsal root ganglia was labeled only by the C-terminal CCK antiserum. This CCK immunoreactivity could be abolished by preabsorption with calcitonin-gene-related peptide (CGRP), suggesting that it was due to cross-reactivity with a CGRP-like peptide. This system also contained 5-hydroxytryptamine (5-HT)-, bombesin-, and CGRP-like immunoreactivities. (3) An intraspinal system of 5-HT neurons was labeled with an antiserum to the midportion of CCK-33 but not by the other CCK antisera. The CCK labeling of this system was difficult to reduce by preabsorption with CCK peptide and thus appeared to be nonspecific. Groups of cell bodies in the middle reticular nucleus of the rhombencephalon, the reticular nucleus of the mesencephalon, and the hypothalamus were labeled by both the C-terminal and the monoclonal CCK antisera. The gut contained two types of CCK-like immunoreactivity, one of which appeared to be due to cross-reactivity with CGRP. A biochemical analysis showed that the content of CCK was low in the spinal cord compared to the brain, and these results agreed with the immunohistochemical findings.

Animals↗
PubMed1988

Possible target neurons of the reticulospinal cholecystokinin (CCK) projection to the lamprey spinal cord: immunohistochemistry combined with intracellular staining with lucifer yellow.

A subpopulation of reticulospinal neurons in the posterior rhombencephalic reticular nucleus in lamprey contains a cholecystokinin (CCK)-like peptide. Varicosities of these neurons, visualized by immunohistofluorescence, were found to be in close apposition to Lucifer yellow-filled spinal motoneurons and giant relay interneurons. Certain other types of interneurons and primary sensory neurons had no, or very few, close contacts with CCK-immunoreactive boutons.

Animals↗
PubMed1988

The dorsal cell, one class of primary sensory neuron in the lamprey spinal cord. I. Touch, pressure but no nociception--a physiological study.

The dorsal cells in the lamprey spinal cord are primary sensory neurons. The cells were classified by Martin and Wickelgren in 1971 into 3 different groups, touch, pressure and nociceptive, according to their responses to mechanical stimulation of the skin. While confirming the presence of touch and pressure cells in the present study, we found no evidence for the existence of nociceptive spinal dorsal cells. Further we show that touch and pressure cells have different response latencies to a 40-ms hyperpolarizing current pulse. Measured from the end of the pulse to the initiation of the action potential, touch cells have a response latency shorter than 11 ms, whereas the pressure cells have a response latency longer than 11 ms.

Action Potentials↗
PubMed1988

The dorsal cell, one class of primary sensory neuron in the lamprey spinal cord. II. A light- and electron microscopical study.

Dorsal cells, are primary sensory neurons located in the lamprey spinal cord. They are of two types conveying touch (T) and pressure (P) and they have an ascending and/or a descending axon which joins the dorsal column. Dorsal cells have no initial axon segment. In the electron microscope synaptic boutons with spherical synaptic vesicles were found in contact with the cell membrane of T-cells while no boutons have been observed on P-cells. No other morphological differences between T- and P-cells could be detected ultrastructurally or in the light microscope. No output synapses have been observed from the dorsal cell bodies or the small processes extending from the cell body.

Animals↗
PubMed1988

A new class of small inhibitory interneurones in the lamprey spinal cord.

Paired intracellular recordings of interneurones and motoneurones have been performed in the lamprey spinal cord in vitro. One new type of small interneurone (10-15 microns in diameter) which produces monosynaptic inhibitory postsynaptic potentials (IPSPs) in motoneurones is described. The IPSP is strychnine-sensitive and thus presumably glycinergic. This type of interneurone undergoes rhythmical membrane potential oscillations during fictive locomotion and intracellular stimulation can have a profound effect on the burst generation occurring during fictive locomotion.

Animals↗
PubMed1988

Three-dimensional reconstruction of transmitter-identified central neurons by "en bloc" immunofluorescence histochemistry and confocal scanning microscopy.

A new method for three-dimensional reconstruction of transmitter-identified neurons is presented which involves "en bloc" immunofluorescence histochemistry and confocal scanning microscopy. The technique was applied to different types of neurons in the rat brain and lamprey spinal cord. Thick sections or tissue "blocs" (50-200 micron thick) were incubated with antisera against neuropeptides or monoaminergic markers, followed by fluorescent secondary antibodies. Three-dimensional reconstructions were obtained by scanning the preparations in sequential focal planes with a thin laser beam, while sampling the emitted light in each focal plane. The method is convenient and can be applied to a wide variety of neuron types. The reconstructions obtained are accurate since the "optical serial sections" of the specimen are perfectly aligned, and optic disturbances such as "halo" phenomena do not occur.

Animals↗
PubMed1988

Three-dimensional reconstruction of neurons in the lamprey spinal cord in whole-mount, using a confocal laser scanning microscope.

When investigating the detailed morphology of nerve cells, three-dimensional structural information is often of great value. We present here a technique by which 'optical sectioning' and three-dimensional reconstruction of fluorescence-labelled neurons in the lamprey spinal cord has been performed by means of a confocal microscope scanner with a laser beam as the light source. In confocal microscopy only a small spot of the specimen is being illuminated at any one time, and only light from the illuminated spot is detected. This gives several advantages compared with traditional microscopy: (1) Lateral resolution is improved, and any 'halo' effects occurring around structures with intense fluorescence are drastically reduced. In addition (2), a unique depth resolution is obtained due to the strong attenuation of structures that are out of focus. This allows the system presented here to (3) perform a detailed three-dimensional computer reconstruction of the neuron, without any need for physical sectioning of the tissue. The volume of data points sampled can subsequently be treated in various ways, including selection of different viewing angles, enhancement of contours, and background suppression.

Animals↗
PubMed1987

Voltage clamp analysis of lamprey neurons--role of N-methyl-D-aspartate receptors in fictive locomotion.

Spinal neurons in the lamprey have been subjected to a voltage clamp analysis of the excitatory currents generated during fictive locomotion with particular reference to the phasic activation of voltage dependent N-methyl-D-aspartate (NMDA) receptors. Voltage-clamped neurons observed during NMDA-induced fictive swimming show excitatory and inhibitory synaptic currents in phase with the ipsilateral and contralateral ventral root discharges, respectively. The excitatory synaptic currents showed a marked voltage dependence suggesting that potential sensitive conductances such as the NMDA ionophore are involved in the synaptic events underlying rhythmic locomotor activity. The effect of NMDA receptor activation during application of tetrodotoxin has also been analyzed during NMDA-induced pacemaker-like oscillations. Such NMDA-induced oscillations are essentially abolished during the voltage clamp. In the presence of NMDA current voltage plots reveal a negative slope conductance in the potential range of the inherent oscillations. The addition of tetraethyl ammonium (TEA) to NMDA solution enhanced a net steady state inward current by more than 10-fold due to a partial block of the outward currents. A kinetic analysis was done with a frequency domain technique using a white noise stimulus to linearly perturb the membrane potential over a wide range of frequencies. The analysis revealed that the induced negative conductance leads to a response which is nearly 180 degrees out of phase with the stimulus at low frequencies. This is an unstable condition which leads to the depolarizing phase of the induced oscillations.

Action Potentials↗
PubMed1987

Newly identified 'glutamate interneurons' and their role in locomotion in the lamprey spinal cord.

A new class of excitatory premotor interneurons that are important in the generation of locomotion in the lamprey has now been described. In the isolated spinal cord, these neurons act simultaneously with their postsynaptic motoneurons during fictive swimming. They are small and numerous, and they monosynaptically excite both motoneurons and inhibitory premotor interneurons. The excitatory postsynaptic potentials are depressed by an antagonist of excitatory amino acids. These interneurons receive reticulospinal input from the brain stem and polysynaptic input form skin afferents. A model of the network underlying locomotion based on the synaptic interactions of these neurons can now be proposed for the lamprey.

Animals↗
PubMed1987

Survey of neuropeptide-like immunoreactivity in the lamprey spinal cord.

The distribution of neural elements immunoreactive to several peptides with a possible messenger role was studied in the lamprey spinal cord by using an indirect immunofluorescence method. Different patterns of immunoreactive (IR) fibers were detected by antisera raised against cholecystokinin, metorphamide, bombesin, galanin, corticotropin-releasing factor, somatostatin, peptide YY, neurotensin, calcitonin and FMRFamide. Somatostatin-IR cell bodies were located around the central canal. All immunoreactivity could be abolished by preabsorption with the corresponding peptide. The results suggest that the lamprey spinal cord has several fiber systems containing peptides sharing immunogenic properties with mammalian neuropeptides.

Animals↗
PubMed1987

Reticulospinal neurones activate excitatory amino acid receptors.

Paired intracellular recordings were used to study the monosynaptic excitatory postsynaptic potentials (EPSP) in lamprey motoneurones evoked by stimulation of single reticulospinal Müller and Mauthner cells. The chemical component of the synaptic potentials was depressed by both application of the non-selective excitatory amino acid antagonists kynurenic acid and cis-2,3-piperidine dicarboxylate. The N-methyl-D-aspartate (NMDA) antagonists Mg2+ and 2-amino-5-phosphonovalerate caused a selective depression of a late component of the EPSP. Thus, fast-conducting reticulospinal neurones appear to release an excitatory amino acid acting at both NMDA and non-NMDA receptors.

2-Amino-5-phosphonovalerate↗