scholarly journals Radial Symmetry and the Organization of Central Neurones in a Hydrozoan Jellyfish

1984 ◽  
Vol 110 (1) ◽  
pp. 69-90 ◽  
Author(s):  
A. N. SPENCER ◽  
S. A. ARKETT
Keyword(s):  
Action Potentials ◽  
Functional Organization ◽  
Lucifer Yellow ◽  
Morphological Characteristics ◽  
Radial Symmetry ◽  
Nerve Ring ◽  
Rapid Reduction ◽  
Potential Oscillations ◽  
Polyorchis Penicillatus ◽  
Motor Neurones

1. Two discrete networks of neurones in the outer nerve-ring of Polyorchis penicillatus can be identified by their physiological and morphological characteristics. 2. The ‘B’ system is characterized by the regular, spontaneous firing pattern that can be recorded intracellularly. Bursts of up to six spikes are produced in response to a rapid reduction in the light intensity. 3. Neurones of the ‘B’ system are electrically coupled to one another. 4. Action potentials in the ‘B’ system produce unitary EPSPs in swimming motor neurones and in epithelial cells overlying the outer nerve-ring. 5. Lucifer Yellow injected into a ‘B’ neurone diffuses rapidly through neighbouring neurones to reveal a condensed network of neurones in the centre of the nerve-ring and a more diffuse network passing up and around each tentacle. 6. The ‘O’ system is characterized by very regular (approx. 1 Hz), spontaneous membrane potential oscillations. Action potentials are never recorded. 7. Neurones of the ‘O’ system are electrically coupled to one another. 8. There is evidence of interaction between the ‘O’ system and swimming motor neurones. 9. Lucifer Yellow injected into an ‘O’ neurone diffuses through member neurones to show an anastomosing network of neurones extending across the width of the outer nerve-ring and tracts of neurones extending up the sides of each tentacle towards the ocelli. 10. The restriction of injected Lucifer Yellow to each of the networks and the blockade of interaction between systems by Mg2+ anaesthesia are evidence that signalling between different central networks is by chemical means. 11. The adaptive advantages of this type of functional organization of central neurones in radially symmetrical animals are discussed. Such an organization is compared with that found in bilateral animals.

scholarly journals Primary Culture of Identified Neurones from a Cnidarian

1989 ◽  
Vol 142 (1) ◽  
pp. 97-113 ◽  
Author(s):  
JAN PRZYSIEZNIAK ◽  
ANDREW N. SPENCER
Keyword(s):  
Sea Water ◽  
Lucifer Yellow ◽  
Divalent Cations ◽  
Polyorchis Penicillatus ◽  
Potential Shape ◽  
Motor Neurones ◽  
Clear Cytoplasm ◽  
Carboxy Terminal

Several types of neurones were dissociated from the nerve-rings of the hydrozoan jellyfish Polyorchis penicillatus, using collagenase digestion preceded, and if necessary followed, by removal of external divalent cations. The neurones were cultured for up to 2 weeks in artificial sea water, on a mesogloeal substratum. One subset of large neurones, the swimming motor neurones (SMNs; soma approx. 20×50 μm), exhibited distinct morphological features in vitro, such as large size, wide processes, clear cytoplasm and membranous inclusions around the nucleus. These neurones retained their characteristic action potential shape in culture, with spikes measuring 50±11 mV (N=18) in peak amplitude and 37 ± 11 ms in duration. SMNs could be labelled in vivo with carboxyfluorescein or Lucifer Yellow, subsequently dissociated, and identified in vitro. Two subsets of small neurones were also identifiable. One exhibited electrophysiological similarities with B system neurones, known to be presynaptic to the SMNs in vivo, showing a burstlike pattern of spikes of short duration (5.4 ± 1.4 ms; N=6) and small amplitude (25 ± 7mV). Another subset of small neurones could be labelled with antiserum against the carboxy-terminal peptide moiety, Arg-Phe-amide. Biophysical and neurotransmitter studies at the level of the single identified hydrozoan neurone will be easier in isolated cell culture. This approach will avoid problems encountered in studying the semidissected nerve-ring preparation.

The Parameters and Properties of a Group of Electrically Coupled Neurones in the Central Nervous System of a Hydrozoan Jellyfish

1981 ◽  
Vol 93 (1) ◽  
pp. 33-50
Author(s):  
A. N. Spencer
Keyword(s):  
Action Potentials ◽  
Electrical Coupling ◽  
Membrane Resistance ◽  
Initiation Site ◽  
Pass Filter ◽  
Low Pass Filter ◽  
Polyorchis Penicillatus ◽  
Low Pass ◽  
Motor Neurones ◽  
Spontaneous Action

1. Swimming of the jellyfish Polyorchis penicillatus is controlled by a network of large, electrically coupled, motor neurones in the inner nervering (Fig. 3). Recordings from pairs of neurones, even at widely separated positions, display essentially the same electrical activity (Fig. 1). 2. Electrical coupling between neurones is via gap-junctions and is very strong, giving the network a space constant of approximately 7.1 mm (Figs. 2, 4, 5). The network acts as a low-pass filter progressively attenuating signals with frequencies greater than 1 Hz (Figs. 4, 6). 3. I/V experiments demonstrate that the neurones show rectifying properties since membrane resistance decreases noticeably with depolarizations greater than about 25 mV (Figs. 7, 8). 4. A number of electrical constants of the network were measured or calculated: rm = 3.55 MΩ cm−1, Rm = 98 kΩ cm2, ri = 7 MΩ cm−1, Rinput = 2.5 MΩ, Cm = 1.52 μF cm−2. 5. Stimulated action potentials are conducted in the network at approximately 112 cm s−1 while spontaneous action potentials have velocities up to 200 cm s−1. As an action potential propagates from its initiation site its duration decreases from about 30 ms to 8 ms when it reaches the opposite side of the margin. 6. Epithelial impulses, which mediate crumpling, cause large i.p.s.p.s in the motor network that can inhibit swimming for several seconds.

Electrophysiology of mammalian tectal neurons in vitro. I. Transient ionic conductances

1988 ◽  
Vol 60 (3) ◽  
pp. 853-868 ◽  
Author(s):  
J. Lopez-Barneo ◽  
R. Llinas
Keyword(s):  
Superior Colliculus ◽  
Action Potentials ◽  
Lucifer Yellow ◽  
Morphological Characteristics ◽  
Resting Potential ◽  
Repetitive Firing ◽  
High Threshold ◽  
Base Line ◽  
Ionic Conductances

1. The electrophysiologic properties and ionic conductances of neurons located in the stratum griseum medium (SGM) of the guinea pig superior colliculus (SC) were studied by intracellular techniques in an in vitro mesencephalic slice preparation. 2. Cells were stained with Lucifer yellow and demonstrated a uniform appearance. They had an ovoid soma with dendrites directed toward the dorsal surface. These dendrites crossed the stratum opticum, and their fine ramifications reached the stratum zonale. 3. SGM cells had a mean resting potential of 59.4 +/- 5.1 (SE) mV (n = 30), a mean slope input resistance of 26.6 +/- 10 M omega (n = 30), and a mean time constant of 4.13 +/- 1.3 ms (n = 27). 4. Direct depolarization of SC neurons produced tonic repetitive firing. These Na+-dependent action potentials showed spike-frequency adaptation. After addition of tetrodotoxin (TTX) and replacement of Ca2+ by Ba2+, slow, high-threshold spikes were also generated. The trains of Ba2+ spikes did not show adaptation. 5. In about half of the cells direct hyperpolarization elicited a slow return of the membrane potential to base line at the termination of the pulse (probably due to activation of an A-type conductance) and no anomalous rectification. The remaining cells did not have an A-type conductance but demonstrated anomolous rectification which was reversibly abolished by Cs+ but unaffected by Ba2+. 6. Some cells could be anti- and/or orthodromically activated by a stimulating electrode placed at the intercollicular commissure. These, and action potentials elicited by direct activation, had a shoulder on their falling phase. The shoulder disappeared after removal of external Ca2+ or addition of Cd2+ to the bath. 7. During repetitive firing in those cells that demonstrated an A-type conductance, the shoulder became progressively more accentuated during the train of spikes, due to inactivation of this A-type conductance. This resulted in an increase in spike duration. 8. The electrophysiological properties of these cells and their morphological characteristics suggest that they may serve as the element integrating visual and nonvisual information at the superior colliculus.

Electrical properties and innervation of fibers in the orbital layer of rat extraocular muscles

1989 ◽  
Vol 61 (1) ◽  
pp. 116-125 ◽  
Author(s):  
J. Jacoby ◽  
D. J. Chiarandini ◽  
E. Stefani
Keyword(s):  
Electrical Properties ◽  
Nerve Stimulation ◽  
Action Potentials ◽  
Time Course ◽  
Lucifer Yellow ◽  
Extraocular Muscles ◽  
Resting Potential ◽  
Inferior Rectus ◽  
End Plate ◽  
Orbital Layer

1. The inferior rectus muscle of rat, one of the extraocular muscles, contains two populations of multiply innervated fibers (MIFs): orbital MIFs, located in the orbital layer of the muscle and global MIFs, found in the global layer. The electrical properties and the responses to nerve stimulation of orbital MIFs were studied with single intracellular electrodes and compared with those of twitch fibers of the orbital layer, MIFs of the global layer, and tonic fibers of the frog. 2. About 90% of the orbital MIFs did not produce overshooting action potentials. In these fibers the characteristics and time course of the responses to nerve stimulation varied along the length of the fibers. Within 2 mm of the end-plate band of the muscle, the responses consisted of several small end-plate potentials (EPPs) and a nonovershooting spike. Distal to 2 mm, the responses in most fibers consisted of large and small EPPs with no spiking response. Some fibers produced very small spikes surmounted on large EPPs. 3. Overshooting action potentials were observed in approximately 10% of the orbital MIFs recorded between the end-plate band and 2 mm distal. The presence or absence of action potentials was not related to the magnitude of the resting potential of the fibers. 4. The threshold of nerve stimulated responses in orbital MIFs was the same as that in orbital twitch fibers. A large number of orbital MIFs had latencies equal to those for the orbital twitch fibers recorded at the same distance from the end-plate band, but the average latency was greater in the MIFs. The latency of orbital MIFs was about one-half of that for the MIFs of the global layer. The values for the effective resistance and membrane time constant of orbital MIFs fell between those for orbital twitch fibers on the one hand, and global MIFs and frog tonic fibers on the other. 5. In order to compare electrical properties with innervation patterns, fibers identified electrophysiologically as orbital MIFs were injected with the fluorescent dye Lucifer yellow and then traced in Epon-embedded, serial transverse sections. In addition to numerous superficial endings distributed along the fibers, a single "en plaque" ending was also found in the end-plate band that resembled the end plates of the adjacent orbital twitch fibers. 6. From these results we conclude that the electrical activity of orbital MIFs varies along the length of the fibers.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Multicellular rosettes organize neuropil formation

2020 ◽  
Author(s):  
Christopher A. Brittin ◽  
Anthony Santella ◽  
Kristopher Barnes ◽  
Mark W. Moyle ◽  
Li Fan ◽  
...  
Keyword(s):  
Functional Organization ◽  
Critical Role ◽  
Ring Structure ◽  
Nerve Ring ◽  
Cell Behaviors ◽  
Dense Networks ◽  
C Elegans ◽  
Single Axon ◽  
Organizational Features

SummaryNeuropils are compartments in the nervous system containing dense networks of neurites and synapses which function as information processing centers. Neuropil formation requires structural and functional organization at and across different scales, achieving single-axon precision for circuits that carry out the core functions while simultaneously accommodating variability among individuals [1; 2; 3; 4]. How these organizational features emerge over development is poorly understood. The nerve ring is the primary neuropil in C. elegans, and its structure is thoroughly mapped [5; 6]. We show that prior to axon outgrowth, nerve ring neurons form a ring of multicellular rosettes with surrounding cells to organize the stratified nerve ring structure [7; 8]. Axon bundles which correspond to future nerve ring strata grow from rosette centers, travel along the ring on “bridge” cells that are simultaneously engaged in adjacent rosettes, and assemble into a topographic scaffold of the nerve ring. SAX-3/Robo is required for proper rosette formation and outgrowth from the center. Furthermore, axon contact sites that form early in development are more conserved than the later ones, indicating a temporal component in neuropil structural variability. Our results reveal an unexpected and critical role of collective cell behaviors prior to innervation to pattern a complex neuropil and orchestrate its formation across scales.

An Arthropod Muscle Innervated by Nine Excitatory Motor Neurones

1980 ◽  
Vol 88 (1) ◽  
pp. 249-258
Author(s):  
CHRISTINE E. PHILLIPS
Keyword(s):  
Action Potentials ◽  
Motor Neurone ◽  
Muscle Fibres ◽  
Relaxation Rates ◽  
Motor Neurones ◽  
The Individual ◽  
Contraction And Relaxation ◽  
High Degree ◽  
Individual Motor ◽  
Indirect Stimulation

The anatomical and physiological organization of the locust metathoracic flexor tibiae was examined by a combination of intracellular recording and electron microscopy. Nine excitatory motor neurones, three fast, three intermediate and three slow innervate the muscle; each is uniquely identifiable using a combination of physiological response and soma location. A simple spatial distribution of inputs to the muscle from the individual motor neurones was not found. Individual muscle fibres responded to as many as seven of the motor neurones in various combinations. The muscle fibres are heterogeneous, ranging from slow (tonic) to fast (phasic) in a continuum from predominantly phasic proximally to tonicdistally. This is demonstrated by contraction and relaxation rates to directand indirect stimulation, as well as contraction elicited by action potentials in a single flexor motor neurone. The fast and slow contractile properties of the muscle fibres are matched by appropriate ultrastructures. Such a high degree of complexity of neuromuscular innervation as that found in the metathoracic flexor tibiae has not previously been described for an arthropod muscle.

Processing of proprioceptive signals by ascending interneurones in the terminal abdominal ganglion of the crayfish

1999 ◽  
Vol 202 (21) ◽  
pp. 2975-2984
Author(s):  
H. Aonuma ◽  
P.L. Newland ◽  
T. Nagayama
Keyword(s):  
Action Potentials ◽  
Chordotonal Organ ◽  
Simultaneous Application ◽  
Proprioceptive Input ◽  
Proprioceptive Stimulation ◽  
Motor Neurones ◽  
Tail Flip ◽  
Local Circuits ◽  
Proprioceptive Inputs ◽  
Subthreshold Level

Intersegmental interneurones are crucial for the appropriate coordination of the activity of local circuits located in different body segments. We have analysed the synaptic inputs to ascending intersegmental interneurones from a proprioceptor in the tailfan of the crayfish. Twenty identified interneurones responded during stimulation of the exopodite-endopodite chordotonal organ. Of these 20 interneurones, three were excited phaso-tonically, nine were excited phasically and eight were inhibited. All received convergent exteroceptive inputs from water-motion- or touch-sensitive hairs on the uropods. The effects of simultaneous exteroceptive and proprioceptive stimulation depended upon the identity of an interneurone. For interneurones that were inhibited by proprioceptive stimulation, suprathreshold exteroceptive responses were reduced to a subthreshold level by simultaneous proprioceptive stimulation. In contrast, for interneurones that were excited by proprioceptive stimulation, the simultaneous application of subthreshold proprioceptive and exteroceptive stimulation elicited action potentials. Two of the interneurones that receive proprioceptive input (NE-1 and RC-8) are known to be presynaptic to giant interneurones that mediate and coordinate the tail-flip. Many of the other interneurones that receive proprioceptive inputs in the tailfan are known to excite abdominal extensor motor neurones. Thus, proprioceptive input to these intersegmental interneurones could serve two roles: first, to extend the abdomen during postural movements or prior to escape and, second, to drive the tail-flip escape response.

Identification of a putative mechanosensory neuron in Lymnaea: characterization of its synaptic and functional connections with the whole-body withdrawal interneuron

1996 ◽  
Vol 76 (5) ◽  
pp. 3230-3238 ◽  
Author(s):  
T. Inoue ◽  
M. Takasaki ◽  
K. Lukowiak ◽  
N. I. Syed
Keyword(s):  
Sensory Neuron ◽  
Action Potentials ◽  
Synaptic Connection ◽  
Lucifer Yellow ◽  
Whole Body ◽  
Pond Snail ◽  
Mechanosensory Neuron ◽  
Functional Connections ◽  
Freshwater Pond ◽  
Withdrawal Behavior

1. In this study, we identified a putative mechanosensory neuron in the freshwater pond snail Lymnaea stagnalis. This sensory neuron, termed right parietal dorsal 3 (RPD3), mediates part of the whole-body withdrawal behavior via the activation of a withdrawal interneuron. 2. RPD3 is located in the central ring ganglia, where its soma is situated on the dorsal surface of the right parietal ganglion. Intracellular injection of the dye Lucifer yellow revealed that RPD3 has both central and peripheral axonal projections. 3. In isolated-CNS preparations, RPD3 was quiescent. In semi-intact preparations, however, a gentle/moderate mechanical touch (by a pair of blunt forceps) to the mantle cavity or columellar musculature elicited action potentials in RPD3 in the absence of prepotential activity. Furthermore, mechanical stimulus-induced action potentials in RPD3 persisted in the presence of zero Ca2+/ high Mg2+ and high Ca2+/high Mg2+ salines. Together, these data suggest that RPD3 is most likely to be a primary sensory neuron. 4. In both isolated-CNS and semi-intact preparations, intracellular depolarization of RPD3 excited the whole-body withdrawal interneuron right pedal dorsal 11 (RPeD11). This synaptic connection persisted in the presence of high Ca2+ and high Mg2+ saline, suggesting that it is likely to be monosynaptic. Moreover, when stimulated electrically, the interneuron RPeD11 induced an hyperpolarizing response in RPD3. The possibility of this connection being monosynaptic was not tested, however, in the present study. Together, these data demonstrate that RPD3 excites RPeD11, which in turn may inhibit RPD3 activity. 5. In the semi-intact preparation, a mechanical touch to the mantle edge excited RPD3, which in turn generated action potentials in RPeD11. Zero Ca2+ saline blocked this synaptic connection between RPD3 and RPeD11, suggesting that it is chemical. 6. To demonstrate that RPD3 was sufficient to induce the withdrawal response and that the withdrawal behavior was mediated indirectly via RPeD11, we made simultaneous intracellular recordings from these two neurons while monitoring muscle contractions via a tension transducer. Intracellular depolarization of RPD3 elicited action potentials in RPeD11, followed by the contraction of the columellar muscle. Similar stimulation of RPD3 failed to excite a simultaneously hyperpolarized RPeD11 and as a result, no contraction of the columellar muscle occurred. Direct intracellular depolarization of RPeD11, however, induced the contraction of the columellar muscle. These data suggest that RPD3-induced withdrawal behavior is mediated in part via RPeD11.

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