The Stomatogastric ganglion ofPanulirus interruptus contains about 30 neurons, and controls the movements of the lobster's stomach When experimentally isolated, the ganglion continues to generate complex rhythmic patterns of activity in its motor neurons which are similar to those seen in intact animals

Organization of the stomatogastric ganglion of the spiny lobster

Investigations of the electrophysiology of crustacean cardiac ganglia over the last half-century are reviewed for their contributions to elucidating the cellular mechanisms and interactions by which a small (as few as nine cells) neuronal network accomplishes extremely reliable, rhythmical, patterned activation of muscular activity-in this case, beating of the neurogenic heart. This ganglion is thus a model for pacemaking and central pattern generation. Favorable anatomy has permitted voltage- and space-clamp analyses of voltage-dependent ionic currents that endow each neuron with the intrinsic ability to respond with rhythmical, patterned impulse activity to nonpatterned stimulation. The crustacean soma and initial axon segment do not support impulse generation but integrate input from stretch-sensitive dendrites and electrotonic and chemically mediated synapses on axonal processes in neuropils. The soma and initial axon produce a depolarization-activated, calcium-mediated, sustained potential, the "driver potential," so-called because it drives a train of impulses at the "trigger zone" of the axon. Extreme reliability results from redundancy and the electrotonic coupling and synaptic interaction among all the neurons. Complex modulation by central nervous system inputs and by neurohormones to adjust heart pumping to physiological demands has long been demonstrated, but much remains to be learned about the cellular and molecular mechanisms of action. The continuing relevance of the crustacean cardiac ganglion as a relatively simple model for pacemaking and central pattern generation is confirmed by the rapidly widening documentation of intrinsic potentials such as plateau potentials in neurons of all major animal groups. The suite of ionic currents (a slowly inactivating calcium current and various potassium currents, with variations) observed for the crustacean cardiac ganglion have been implicated in or proven to underlie a majority of the intrinsic potentials of neurons involved in pattern generation.

Reliable, responsive pacemaking and pattern generation with minimal cell numbers: the crustacean cardiac ganglion.

Arterially cannulated rabbit interventricular septal tissue was exposed to 5–40 µM La in 2.5 mM Ca perfusate. Immediately following perfusion with La two concurrent events were consistently observed: (a) a rapid decline of active tension to a lesser steady-state value, and (b) an abrupt, release of short duration of tissue-bound Ca. The magnitude of both events was directly related to the [La]o. If the duration of exposure to La was brief, contractility returned toward normal upon return to the La-free perfusate. Elevation of [Ca]o during exposure to La counteracted its effect and induced a concurrent displacement of tissue-bound La. Cellular action potentials recorded during brief perfusion with La demonstrated that essentially normal regenerative depolarization was maintained. Analysis of the quantities of 45Ca released following exposure to 10 µM La indicated that this La-susceptible Ca was being displaced from a homogeneous pool—the one previously shown by Langer to represent contractile dependent Ca. These data led to the following conclusions: During perfusion with 2.5 mM Ca contractile dependent Ca was derived primarily from "superficially" located sites. La effected the release of contractile dependent Ca by modifying the normal permselectivity of this "superficial" membrane for activator Ca. These and other data infer that contractile dependent Ca is derived primarily from superficially located sites.

https://rupress.org/jgp/article-pdf/56/2/191/1244895/191.pdf

Specific Uncoupling of Excitation and Contraction in Mammalian Cardiac Tissue by Lanthanum Kinetic studies

The sections in this article are:


1
Properties of Muscle
11
Anatomic Organization

12
Contraction Speed

13
Strength and Extent of Contraction

14
Thresholds for Excitation-Contraction Coupling

15
Correlations with Innervation

16
Dependence of Tension on Recent History




2
Motor Neurons and the Motor Unit
21
Motor Neuron Morphology

22
Correlations Between Motor Neuron Morphology and Function

23
Neuromuscular Transmission

24
Excitation-Contraction Coupling

25
Peripheral Motor Unit Organization

26
Matching of Central and Peripheral Properties

27
Ontogeny and Regeneration




3
Reflex Organization
31
Proprioceptive Reflexes

32
Exteroreceptive Reflexes

33
Righting Reflexes

34
Optomotor Reflexes

35
Control of Reflex Excitability




4
Central Organization of Motor Systems
41
Structure of Motor Programs

42
Storage of Motor Programs

43
Release of Motor Programs by Command Elements

44
Central Versus Peripheral Control of Motor Output

45
Development of Pattern-Generating Networks

46
Complex Behavioral Phenomena




5
Conclusion

Organization of Invertebrate Motor Systems

From somata of the pacemaker neurons in the Squilla heart ganglion, pacemaker potentials for the spontaneous periodic burst discharge are recorded with intracellular electrodes. The electrical activity is composed of slow potentials and superimposed spikes, and is divided into four types, which are: (a) "mammalian heart" type, (b) "slow generator" type, (c) "slow grower" type, and (d) "slow deficient" type. Since axons which are far from the somata do not produce slow potentials, the soma and dendrites must be where the slow potentials are generated. Hyperpolarization impedes generation of the slow potential, showing that it is an electrically excitable response. Membrane impedance increases on depolarization. Brief hyperpolarizing current can abolish the plateau but brief tetanic inhibitory fiber stimulation is more effective for the abolition. A single stimulus to the axon evokes the slow potential when the stimulus is applied some time after a previous burst. Repetitive stimuli to the axon are more effective in eliciting the slow potential, but the depolarization is not maintained on continuous stimulation. Synchronization of the slow potential among neurons is achieved by: (a) the electrotonic connections, with periodic change in resistance of the soma membrane, (b) active spread of the slow potential, and (c) synchronization through spikes.

/pdf/pacemaker-potentials-for-the-periodic-burst-discharge-in-the-3xgxrxb18q.pdf

Pacemaker potentials for the periodic burst discharge in the heart ganglion of a stomatopod, Squilla oratoria.

In the Squilla heart ganglion, the pacemaker is located in the rostral group of cells. After spontaneous firing ceased, the electrophysiological properties of these cells were examined with intracellular electrodes. Cells respond to electrical stimuli with all-or-none action potentials. Direct stimulation by strong currents decreases the size of action potentials. Comparison with action potentials caused by axonal stimulation and analysis of time relations indicate that with stronger currents the soma membrane is directly stimulated whereas with weaker currents the impulse first arises in the axon and then invades the soma. Spikes evoked in a neuron spread into all other neurons. Adjacent cells are interconnected by electrotonic connections. Histologically axons are tied with the side-junction. B spikes of adjacent cells are blocked simultaneously by hyperpolarization or by repetitive stimulation. Experiments show that under such circumstances the B spike is not directly elicited from the A spike but is evoked by invasion of an impulse or electrotonic potential from adjacent cells. On rostral stimulation a small prepotential precedes the main spike. It is interpreted as an action potential from dendrites.

/pdf/electrical-properties-of-the-pacemaker-neurons-in-the-heart-mhonhrsj34.pdf

Electrical properties of the pacemaker neurons in the heart ganglion of a stomatopod, Squilla oratoria.

Excitability of Crayfish Giant Axons in Media with Trivalent Cations in Place of Divalent Cations

Giant axons of crayfish were excitable in sodium-free external media containing hydrazinium, hydroxylamine, or guanidinium ions. Action potentials in these solutions were slightly smaller in size and a little longer in duration than those in standard Harreveld's solution. The resting potential was not affected in hydrazine or in hydroxylamine saline, but decreased in gaunidine saline. The membrane potential at the peak of the spike (V) was plotted against the univalent cation concentrations in the external medium. The relationship could be expressed by an equation: V = VO + (RT/F) ln ([Na] + alpha[C]), where VO and alpha are constants and [Na] and [C] are concentrations of sodium ions and the tested cations, respectively. The parameter alpha was considered as an indicator to express the ability of substitution of the cation for sodium ion. The order of the ability of the substitution was Hydroxylamine greater than Hydrazinium greater than Guanidinium greater than Choline.

Katsuto Yumoto

Papers

Electrical properties of the pacemaker neurons in the heart ganglion of a stomatopod, Squilla oratoria.

Excitability of Crayfish Giant Axons in Media with Trivalent Cations in Place of Divalent Cations

Excitability of crayfish giant axons in sodium-free external media containing hydrazinium, hydroxylamine, or guanidinium ions.

Time Course Analysis of Cation Influxes during the Prolonged Action Potential in Prefused Squid Giant Axon