A Mechanism for Fatigue of Epithelial Action Potentials in the Hydromedusa, Polyorchis Penicillatus: Acaseof Non-Neuronal Habituation

2021 ◽  
pp. 461-473
Author(s):  
Nikita Grigoriev ◽  
Andrew N. Spencer
Keyword(s):  
Action Potentials ◽  
Polyorchis Penicillatus

Voltage-activated potassium currents in isolated motor neurons from the jellyfish Polyorchis penicillatus

1994 ◽  
Vol 72 (2) ◽  
pp. 1010-1019 ◽  
Author(s):  
J. Przysiezniak ◽  
A. N. Spencer
Keyword(s):  
Motor Neurons ◽  
Action Potentials ◽  
Voltage Dependence ◽  
Primary Cultures ◽  
Potassium Currents ◽  
Whole Cell ◽  
Time To Peak ◽  
Polyorchis Penicillatus ◽  
Slow Onset

1. We describe two voltage-activated potassium currents in the swim motor neurons (SMNs) of the hydrozoan jellyfish, Polyorchis penicillatus. Recordings from neurons isolated in primary cultures were made using the tight-seal, whole-cell technique. 2. One current, IK-fast, turned on rapidly (time to peak = 6–15 ms), was half-activated at -10 to 0 mV, decayed with two exponential phases (tau were approximately 70 ms and approximately 1 s), and was half-inactivated by prepulses around -53 mV. It likely plays an important role in regulating the duration of SMN action potentials. IK-fast has features shared by delayed rectifiers and A-like currents in other invertebrates and vertebrates. 3. Another current, IK-slow, elicited from a holding potential of -30 mV, exhibited a slow onset (tau = 65–250 ms), was half-activated approximately +24 mV, exhibited a shallower voltage dependence than IK-fast, and did not inactivate. It was slower than most known delayed rectifiers.

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.

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.

Characteristics of action potentials in Helianthus annuus

1991 ◽  
Vol 83 (4) ◽  
pp. 601-604 ◽  
Author(s):  
Tadeusz Zawadzki ◽  
Eric Davies ◽  
Halina Dziubinska ◽  
Kazimierz Trebacz
Keyword(s):  
Helianthus Annuus ◽  
Action Potentials
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