scholarly journals Neuronal control of swimming in the medicinal leech. V. Connexions between the oscillatory interneurones and the motor neurones

1978 ◽  
Vol 75 (1) ◽  
pp. 45-63
Author(s):  
M. Poon ◽  
W. O. Friesen ◽  
G. S. Stent
Keyword(s):  
Activity Pattern ◽  
Nerve Cord ◽  
Ventral Nerve Cord ◽  
Medicinal Leech ◽  
Exceptional Case ◽  
Motor Neurone ◽  
Phasic Activity ◽  
Neuronal Control ◽  
Motor Neurones ◽  
Pattern Characteristic

A network of intra- and intersegmental synaptic connexions has been identified in the ventral nerve cord of the leech that links the set of oscillatory interneurones of the central swim oscillator to the motor neurones commanding the swimming rhythm. Excitatory connexions lead from oscillatory interneurones to both excitatory and inhibitory motor neurones, whereas inhibitory connexions lead from oscillatory interneurones to only the inhibitory motor neurones. Connexions leading from a motor neurone back to the oscillatory interneurones were found in only one exceptional case, an inhibitory motor neurone previously known to have access to the central swim oscillator. This network of identified connexions can account reasonably well for the mechanism by which the oscillatory interneurones drive their follower motor neurones into the phasic activity pattern characteristic of the swimming movement.

Neuronal control of swimming in the medicinal leech. IV. Identification of a network of oscillatory interneurones

1978 ◽  
Vol 75 (1) ◽  
pp. 25-43
Author(s):  
W. O. Friesen ◽  
M. Poon ◽  
G. S. Stent
Keyword(s):  
Nerve Cord ◽  
Ventral Nerve Cord ◽  
Body Wave ◽  
Medicinal Leech ◽  
The Body ◽  
Cycle Period ◽  
Neuronal Control ◽  
Swimming Movement ◽  
Analogue Models ◽  
Motor Neurones

Four oscillatory interneurones that appear to be the principal components of the central swim oscillator of Hirudo medicinalis have been identified on each side of the segmental ganglia of the ventral nerve cord. During ‘swimming’ episodes of an isolated nerve cord preparation each interneurone undergoes a polarization rhythm that is phase-locked with the impulse burst rhythm of the motor neurones known to drive the swimming movement. Passage of current into any of the interneurones can shift the phase of the swim rhythm. One of the interneurones projects its axon rearward to posterior ganglia and the other three project their axons frontward to anterior ganglia. The oscillatory interneurones are connected both intra- and interganglionically to form a topologically complex intersegmental network of concatenated ring circuits that possess the feature of recurrent cyclic inhibition. Theoretical analysis and electronic analogue models show that the network is inherently oscillatory and can produce both a cycle period and intra- and intersegmental phase relations of its elements that are appropriate for generating the body wave of the swimming movement.

scholarly journals Habituation of swimming activity in the medicinal leech

1985 ◽  
Vol 116 (1) ◽  
pp. 169-188
Author(s):  
E. A. Debski ◽  
W. O. Friesen
Keyword(s):  
Nerve Cord ◽  
Ventral Nerve Cord ◽  
Body Wall ◽  
Spontaneous Recovery ◽  
Medicinal Leech ◽  
The Body ◽  
Swimming Activity ◽  
Stimulus Generalization ◽  
Anterior Segments ◽  
Stimulation Of

Tactile stimulation (light stroking) of a body wall flap attached to the ventral nerve cord of the medicinal leech evokes episodes of swimming activity. This swimming response undergoes habituation, involving changes in swim initiation and swim maintenance. Repeated stimulation of the body wall flap evoked swimming activity between three and 39 times before this response failed. During repetitive stimulation, the length of swim episodes decreased by about 50%. The number of swim episodes which could be elicited was not correlated with swim episode length. Following habituation, swim initiation showed significant spontaneous recovery, but swim episode length returned only to 60% of control values. In preparations where spontaneous recovery was followed by rehabituation, the number of swim episodes elicited declined with each habituation-recovery sequence. Additional stimulation immediately following habituation trials had a dual effect: recovery of the swimming response was delayed, but the lengths of swim episodes following spontaneous recovery were increased. Pinching the body wall flap immediately restored the swimming response in an habituated preparation. Swim initiation habituated more rapidly during stimulation of anterior body wall flaps than during stimulation of mid-body or posterior flaps. However, swim length was independent of this regional variation in swim responsiveness. The number of swim episodes elicited by stimulation of body wall flaps attached to posterior or anterior segments depended upon whether this segment was stimulated before or after other flaps. In contrast, in mid-body segments there was no evidence for such stimulus generalization. The lengths of swim episodes elicited during sequential stimulation of several body wall flaps were independent of the stimulation sequence. We propose that separate processes control swim initiation and swim maintenance. These processes must be repeated in most, if not all, of the segmental ganglia of the leech ventral nerve cord.

scholarly journals Motor Output of the Denervated Thoracic Ventral Nerve Cord in the Stick Insect Carausius Morosus

1983 ◽  
Vol 105 (1) ◽  
pp. 127-145 ◽  
Author(s):  
ULRICH BÄSSLER ◽  
U. T. A. WEGNER
Keyword(s):  
Nerve Cord ◽  
Ventral Nerve Cord ◽  
Intact Animal ◽  
Stick Insect ◽  
Motor Output ◽  
The Other ◽  
Chordotonal Organ ◽  
Motor Neurones ◽  
Leg Movements ◽  
Stimulation Of

The denervated thoracic ventral nerve cord produces a motor output which is similar to that observed in the intact animal during irregular leg movements (seeking movements) or rocking, but not walking. When the nerves to some legs are left intact, and the animal walks on a wheel, the motor output in the protractor and retractor motor neurones of the denervated legs is modulated by the stepping frequency of the walking legs. The modulation is similar to that observed in the motor output to a not actually stepping leg of an intact walking animal. When only the crural nerve of one leg is left intact, stimulation of the trochanteral campaniform sensilli induces protractor and retractor motor output to that leg and the leg behind it. In this case the motor output to the ipsilateral leg is in phase. Stimulation of the femoral chordotonal organ influences activity in motor neurones of the extensor tibiae (FETi and SETi) but not those of the protractor and retractor coxae muscles. In a restrained leg of an intact animal stretching of the femoral chordotonal organ excites FETi and SETi as long as the other legs walk (as in a walking leg) and inhibits FETi and SETi (as in a seeking leg) when the other legs are unable to walk.

Physiology of Water Motion Detection in the Medicinal Leech

1981 ◽  
Vol 92 (1) ◽  
pp. 255-275
Author(s):  
W. OTTO FRIESEN
Keyword(s):  
Neuronal Activity ◽  
Water Waves ◽  
Nerve Cord ◽  
Action Potentials ◽  
Ventral Nerve Cord ◽  
Body Wall ◽  
Medicinal Leech ◽  
Afferent Input ◽  
Excitatory Input ◽  
Simultaneous Action

1. Neuronal activity resulting from stimulation by water waves occurs in ventral nerve cord-body wall preparations of the medicinal leech, Hirudo medicinalis. In segmental nerves, this activity consists of afferent compound action potentials with graded amplitudes resulting from simultaneous action potentials in many small sensory axons. Afferent input impinging on one segmental ganglion activates neuronal activity along much of the ventral nerve cord. 2. Previously identified tactile mechanoreceptors are insensitive to low-amplitude wave stimulation. Touch-cell impulse activity can be evoked by moderate or strong wave stimulation, but these impulses appear to arise near the cell body, not from the peripheral receptor endings. 3. The transduction sites for wave stimulation are localized at or very near the segmental sensilla. Because of their location and modality the receptors were named ‘sensillar movement receptors’ (SMR). 4. S cells (Rohde's fibre) receive suprathreshold excitatory input during SMR activation without concomitant activity in the tactile mechanoreceptors. 5. The annulus erector motor neurones contralateral to the afferent SMR inflow are inhibited by SMR activation. This inhibition is also observed in ganglia adjacent to the ganglion receiving the afferent input and provides a neuronal basis for reflexive smoothing of the leech body wall. 6. Two neurones in the anterior median packet of segmental ganglia receive powerful synaptic input during SMR activation. One, cell 202, receives 10 mV excitatory potentials while the other, cell 201, receives 10 mV inhibitory potentials.

Rhythmic swimming activity in neurones of the isolated nerve cord of the leech

1976 ◽  
Vol 65 (3) ◽  
pp. 643-668
Author(s):  
W. B. Kristan ◽  
R. L. Calabrese
Keyword(s):  
Nerve Cord ◽  
Body Shape ◽  
Sensory Input ◽  
Body Wall ◽  
Motor Neurone ◽  
The Body ◽  
Burst Duration ◽  
Cycle Period ◽  
Motor Neurones ◽  
Central Oscillator

1. Repeating bursts of motor neurone impulses have been recorded from the nerves of completely isolated nerve cords of the medicinal leech. The salient features of this burst rhythm are similar to those obtained in the semi-intact preparation during swimming. Hence the basic swimming rhythm is generated by a central oscillator. 2. Quantitative comparisons between the impulse patterns obtained from the isolated nerve cord and those obtained from a semi-intact preparation show that the variation in both dorsal to ventral motor neurone phasing and burst duration with swim cycle period differ in these two preparations. 3. The increase of intersegmental delay with period, which is a prominent feature of swimming behaviour of the intact animal, is not seen in either the semi-intact or isolated cord preparations. 4. In the semi-intact preparation, stretching the body wall or depolarizing an inhibitory motor neurone changes the burst duration of excitatory motor neurones in the same segment. In the isolated nerve cord, these manipulations also change the period of the swim cycle in the entire cord. 5. These comparisons suggest that sensory input stabilizes the centrally generated swimming rhythm, determines the phasing of the bursts of impulses from dorsal and ventral motor neurones, and matches the intersegmental delay to the cycle period so as to maintain a constant body shape at all rates of swimming.

Initiation, Maintenance and Modulation of Swimming in the Medicinal Leech by the Activity of a Single Neurone

1978 ◽  
Vol 77 (1) ◽  
pp. 71-88 ◽  
Author(s):  
JAMS C. WEEKS ◽  
WILLIAM B. KRISTAN JR.
Keyword(s):  
Horseradish Peroxidase ◽  
Nerve Cord ◽  
Tactile Stimulation ◽  
Medicinal Leech ◽  
Swimming Activity ◽  
Cycle Period ◽  
Impulse Frequency ◽  
Contraction Phase ◽  
Pattern Characteristic ◽  
Stimulation Of

A neurone (designated cell 204) has been identified in the segmental ganglia of the leech which, when stimulated intracellularly in isolated nerve cords, reliably initiates and maintains the neuronal activity pattern characteristic of swimming. In a minimally dissected leech, cell 204 activity results in normal swimming movements. Cell 204 is an unpaired, intersegmental interneurone which is present in most, if not all, of the segmental ganglia. Horseradish peroxidase injections indicate that cell 204 has extensive arborizations in its own ganglion and sends an axon both anteriorly and posteriorly via Faivre's Nerve. Cell 204 is normally quiescent, but during swimming activity becomes depolarized and produces impulse bursts in the ventral contraction phase of its own segment. Such activity is observed in every cell 204 in the nerve cord and is independent of the stimulus used to evoke the swimming episode. Activity in any cell 204 is sufficient for initiation and maintenance of swimming activity, whereas activity in any two of them is not necessary for swimming. During swimming activity, imposed increases in the impulse frequency of any cell 204 cause a decrease in the swim cycle period of the entire nerve cord. Tactile stimulation of the skin, which is an effective method of eliciting swimming episodes, excites cell 204. Our findings indicate that cell 204 may activate swimming in the intact leech.

Extracellular filaments in the perineurium of the florida lobster, Panulirus argus

1987 ◽  
Vol 45 ◽  
pp. 784-785
Author(s):  
Roy J. Baerwald ◽  
Lura C. Williamson
Keyword(s):  
Blood Brain Barrier ◽  
Glial Cells ◽  
Tannic Acid ◽  
Nerve Cord ◽  
Ventral Nerve Cord ◽  
Florida Keys ◽  
Panulirus Argus ◽  
Brain Barrier ◽  
Cacodylate Buffer ◽  
Nerve Cords

In arthropods the perineurium surrounds the neuropile, consists of modified glial cells, and is the morphological basis for the blood-brain barrier. The perineurium is surrounded by an acellular neural lamella, sometimes containing scattered collagen-like fibrils. This perineurial-neural lamellar complex is thought to occur ubiquitously throughout the arthropods. This report describes a SEM and TEM study of the sheath surrounding the ventral nerve cord of Panulirus argus.Juvenile P. argus were collected from the Florida Keys and maintained in marine aquaria. Nerve cords were fixed for TEM in Karnovsky's fixative and saturated tannic acid in 0.1 M Na-cacodylate buffer, pH = 7.4; post-fixed in 1.0% OsO4 in the same buffer; dehydrated through a graded series of ethanols; embedded in Epon-Araldite; and examined in a Philips 200 TEM. Nerve cords were fixed for SEM in a similar manner except that tannic acid was not used.

Sign in / Sign up

Export Citation Format

Share Document