Isolated Nerve Cord Research Articles

Serotonergic modulation of social status-dependent behavioural plasticity of the crayfish avoidance reaction.

Small crayfish usually showed escape-like dart responses to mechanical stimulation of the tailfan. Following agonistic bouts with conspecifics, dominant crayfish showed a defensive-like turn response to the same sensory stimulus. During the dart response, both uropods closed and animals walked forwards with the abdomen extended, while during the turn response the uropod on the stimulated side opened and animals turned towards the stimulus source with the abdomen frequently flexed. Using an isolated nerve cord preparation, we found that the spike activities of both the abdominal postural and uropod motor neurones in response to sensory stimulation of the exopodite reversed in dominant animals. In naive and subordinate animals, extensor motor neurones were excited and antagonistic flexor motor neurones inhibited in response to sensory stimulation. Furthermore, the spike frequency of uropod closer motor neurones increased while that of the antagonistic opener motor neurones decreased. By contrast, in more than half of the dominant animals, flexor and opener motor neurones showed excitatory responses while extensor and closer motor neurones showed inhibitory responses to the same sensory stimulation. This reverse of activity of the abdominal postural and uropod motor neurones was also observed when serotonin of more than 12.5 μM in concentration was applied.

Quantification and analysis of ecdysis in the hornworm, Manduca sexta, using machine vision–based tracking

We have developed a machine vision-based method for automatically tracking deformations in the body wall to monitor ecdysis behaviors in the hornworm, Manduca sexta. The method utilizes naturally occurring features on the animal's body (spiracles) and is highly accurate (>95% success in tracking). Moreover, it is robust to unanticipated changes in the animal's position and in lighting, and in the event tracking of specific features is lost, tracking can be reestablished within a few cycles without input from the user. We have paired our tracking technique with electromyography and have also compared our in vivo results to fictive motor patterns recorded from isolated nerve cords. We found no major difference in the cycle periods of contractions during naturally occurring ecdysis compared to ecdysis initiated prematurely through injection of the peptide ecdysis-triggering hormone, and we confirmed that the ecdysis period in vivo is statistically similar to that of the fictive motor pattern.

Signal analysis of whole-body shortening behavior in Hirudo verbana

The European medicinal leech, Hirudo verbana, is a complex predator with a substantial repertoire of behaviors, most of which can be observed in the isolated nerve cord as “fictive” motor patterns. Each of the 21 midbody segmental ganglia of ~400 neurons is highly iterated and controls an individual body segment. Propagating behaviors (such as swimming, crawling, and shortening) rely on inter-ganglionic communications routed through connective nerves. However, for some observed behaviors, it is not known if the entire behavioral circuit is contained within each individual ganglion or if input from distal ganglia (> 2 segments away) plays a role in the resulting motor action and timing. Specifically in whole-body shortening (WBS), motor output is generated with left-right symmetry and propagates extremely rapidly towards the posterior of the animal, resulting in intense and rapid contraction of the body wall. Using en passant recordings (in which an extracellular electrode records all signals passing a specific location in the connective nerves) with extracellular motor neuron recordings, we have characterized the onset and latencies of WBS as a function of stimulation site. Our results indicate that WBS is primarily initiated locally and radiates outward with a fixed rapid propagation velocity. A possible explanation for the speed of WBS is the recruitment of the fast-conducting S cell network, which is known to conduct signals quickly enough to match the speed of WBS. However, our experiments reveal that lesioning Favre’s nerve to disrupt the S cell network results in a fixed delay past the lesion and no change to the propagation velocity. This suggests that pathways traveling through the lateral connectives may be re-recruiting the S cell network past the lesion. In order to identify the source of these neural signals, we use a novel application of the smoothed nonlinear energy operator to detect spikes and then class them by energy amplitude. The hierarchically classed spikes can then be removed from the data in an iterative process. This preprocessing improves our ability to separate sources in our highly overconstrained system. After separating our sources, superparamagnetic clustering is used to objectively sort spike sources. By measuring the variation in the timing of the sorted spike trains as a function of stimulus location and lesion presence, we hope to localize sources to specific ganglia. We will also use the observed patterns and timings to statistically characterize WBS for future experiments.

Fictive Flirting: Reproductive Behavioral Modules Are Revealed by Pharmacological Blockers

Event Abstract Back to Event Fictive Flirting: Reproductive Behavioral Modules Are Revealed by Pharmacological Blockers Krista L. Todd1*, William B. Kristan1 and Kathleen A. French1 1 University of California, San DIego, Neurobiology, United States Reproduction is sufficiently important to species survival that organisms have evolved highly stereotyped courtship and mating behaviors that ensure mating is successfully carried out only with an appropriate mate. These behaviors are often progressive, proceeding through a series of relatively stereotyped modules that may not culminate until the deposition of eggs or the birth and subsequent care of the offspring. These behaviors can play out over timescales ranging from a few minutes in many amphibian species, to many decades in some mammals, and in a broad range of species, they are influenced by neurohormones belonging to the vasopressin and oxytocin family. Previously, we have shown that the medicinal leech, Hirudo verbena, responds to injected homologs of vasopressin and oxytocin by initiating pre-copulatory courtship behavior. In addition, when we inject a leech with the vasopressin homolog conopressin it will also sometimes evert or extend its penis, ejaculate, and mimic egg-deposition. (Leeches are simultaneous hermaphrodites in which fertilization is internal.) We conclude that conopressin has the ability to initiate a succession of modules in a leech’s reproductive behavioral repertoire. To characterize the neuronal basis of conopressin-induced behavior, we superfused conopressin onto an isolated portion of a leech nerve cord that included the sex ganglia. In response, identified motor neurons began to fire in stereotyped patterns that we have shown to be part of the neuronal output driving pre-copulatory courtship behavior. This motor neuron activity began within ten minutes and continued for almost an hour. Over the next four to five hours, the nerve cords proceeded through four distinct firing patterns. These firing patterns were sequential and each lasted for 40 to 60 minutes. We hypothesize that these later behaviors are also part of the leech’s reproductive progression. When the reduced nerve cord preparation was bathed in Atosiban (an oxytocin-receptor antagonist), all conopressin-induced activity was delayed by nearly an hour, and the first activity observed in this condition closely resembled the second sequential behavior observed in conopressin alone. That is, the motor pattern seemed to skip the typical first conopressin-induced component, but at the normal time, initiated the second component. Based upon the responses of the isolated nerve cord to conopressin and Atosiban, we hypothesize that components of the sequence are governed by specific receptor subtypes. If so, leech pre-copulatory courtship behavior may be mediated by a receptor that is similar to the mammalian oxytocin receptor. Acknowledgements Many thanks to all present and past members of the Kristan lab for helping to advance this body of knowledge. This work was supported by NSF grant IOS0825741 and NIH grant MH43396 to William B. Kristan and NIH post-doctoral training grant NS007220 to Nick Spitzer. Keywords: Behavioral Module, central pattern generator, Conopressin, leech, Neurohormones, Reproduction Conference: Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012. Presentation Type: Poster (but consider for student poster award) Topic: Social Behavior Citation: Todd KL, Kristan WB and French KA (2012). Fictive Flirting: Reproductive Behavioral Modules Are Revealed by Pharmacological Blockers. Conference Abstract: Tenth International Congress of Neuroethology. doi: 10.3389/conf.fnbeh.2012.27.00056 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 02 May 2012; Published Online: 07 Jul 2012. * Correspondence: Dr. Krista L Todd, University of California, San DIego, Neurobiology, La Jolla, United States, kltodd@ucsd.edu Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Krista L Todd William B Kristan Kathleen A French Google Krista L Todd William B Kristan Kathleen A French Google Scholar Krista L Todd William B Kristan Kathleen A French PubMed Krista L Todd William B Kristan Kathleen A French Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Specialized brain regions and sensory inputs that control locomotion in leeches

Locomotor systems are often controlled by specialized cephalic neurons and undergo modulation by sensory inputs. In many species, dedicated brain regions initiate and maintain behavior and set the duration and frequency of the locomotor episode. In the leech, removing the entire head brain enhances swimming, but the individual roles of its components, the supra- and subesophageal ganglia, in the control of locomotion are unknown. Here we describe the influence of these two structures and that of the tail brain on rhythmic swimming in isolated nerve cord preparations and in nearly intact leeches suspended in an aqueous, "swim-enhancing" environment. We found that, in isolated preparations, swim episode duration and swim burst frequency are greatly increased when the supraesophageal ganglion is removed, but the subesophageal ganglion is intact. The prolonged swim durations observed with the anterior-most ganglion removed were abolished by removal of the tail ganglion. Experiments on the nearly intact leeches show that, in these preparations, the subesophageal ganglion acts to decrease cycle period but, unexpectedly, also decreases swim duration. These results suggest that the supraesophageal ganglion is the primary structure that constrains leech swimming; however, the control of swim duration in the leech is complex, especially in the intact animal.

Modeling Biological Membranes with Circuit Boards and Measuring Electrical Signals in Axons: Student Laboratory Exercises

This is a demonstration of how electrical models can be used to characterize biological membranes. This exercise also introduces biophysical terminology used in electrophysiology. The same equipment is used in the membrane model as on live preparations. Some properties of an isolated nerve cord are investigated: nerve action potentials, recruitment of neurons, and responsiveness of the nerve cord to environmental factors.

Modeling Biological Membranes with Circuit Boards and Measuring Electrical Signals in Axons: Student Laboratory Exercises

This is a demonstration of how electrical models can be used to characterize biological membranes. This exercise also introduces biophysical terminology used in electrophysiology. The same equipment is used in the membrane model as on live preparations. Some properties of an isolated nerve cord are investigated: nerve action potentials, recruitment of neurons, and responsiveness of the nerve cord to environmental factors.

Local-Distributed Integration by a Novel Neuron Ensures Rapid Initiation of Animal Locomotion

Animals are adapted to respond quickly to threats in their environment. In many invertebrate and some vertebrate species, the evolutionary pressures have resulted in rapidly conducting giant axons, which allow short response times. Although neural circuits mediating escape behavior are identified in several species, little attention has been paid to this behavior in the medicinal leech, a model organism whose neuronal circuits are well known. We present data that suggest an alternative to giant axons for the rapid initiation of locomotion. A novel individual neuron, cell E21, appears to be one mediator of this short-latency action in the leech. In isolated nerve cord and semi-intact preparations, cell E21 excitation initiates and extends swimming and reduces the cycle period. The soma of this cell is located caudally, but its axon extends nearly the entire length of the nerve cord. We found that cell E21 fires impulses following local sensory inputs anywhere along the body and makes excitatory synapses onto the gating cells that drive swimming behavior. These distributed input-output sites minimize the distance information travels to initiate swimming behavior, thus minimizing the latency between sensory input and motor output. We propose that this single cell E21 functions to rapidly initiate or modulate locomotion through its distributed synaptic connections.

Potassium fluxes across the blood brain barrier of the cockroach, Periplaneta americana

Potassium fluxes across the blood–brain barrier of the cockroach Periplaneta americana were measured using the scanning ion-selective microelectrode technique. In salines containing 15 mM or 25 mM K +, an efflux of K + from the ganglia of isolated nerve cords was counterbalanced by an influx across the connectives. Metabolic inhibition with CN − resulted in an increase in K + efflux across both the ganglia and the connectives. Depletion of K + by chilling the nerve cords in K +-free saline was associated with subsequent K + influx across the connectives in K +-replete saline at room temperature. There were dramatic increases in K + efflux across both ganglia and connectives when the nerve cords were exposed to the pore-forming antibiotic amphotericin B. K + fluxes across the ventral nerve cord were also altered when paracellular leakage was augmented by transient exposure to 3 M urea. K + efflux was reduced by the K + channel blockers Ba 2+ and tetraethylammonium or by exposure to Ca 2+-free saline and K + efflux from the ganglia was increased by addition of ouabain to the bathing saline. The results provide direct support for a model proposing that K + is cycled through a current loop between the ganglia and the connectives and that both the Na +/K +-ATPase and K + channels are implicated in extracellular K + homeostasis within the central nervous system.

Alpha-conotoxin ImI disrupts central control of swimming in the medicinal leech

Medicinal leeches ( Hirudo spp.) swim using a metachronal, front-to-back undulation. The behavior is generated by central pattern generators (CPGs) distributed along the animal's midbody ganglia and is coordinated by both central and peripheral mechanisms. Here we report that a component of the venom of Conus imperialis, α-conotoxin ImI, known to block nicotinic acetyl-choline receptors in other species, disrupts swimming. Leeches injected with the toxin swam in circles with exaggerated dorsoventral bends and reduced forward velocity. Fictive swimming in isolated nerve cords was even more strongly disrupted, indicating that the toxin targets the CPGs and central coordination, while peripheral coordination partially rescues the behavior in intact animals.

Dopamine Activates the Motor Pattern for Crawling in the Medicinal Leech

Locomotion in segmented animals is thought to be based on the coupling of "unit burst generators," but the biological nature of the unit burst generator has been revealed in only a few animal systems. We determined that dopamine (DA), a universal modulator of motor activity, is sufficient to activate fictive crawling in the medicinal leech, and can exert its actions within the smallest division of the animal's CNS, the segmental ganglion. In the entire isolated nerve cord or in the single ganglion, DA induced slow antiphasic bursting (approximately 15 s period) of motoneurons known to participate in the two-step elongation-contraction cycle underlying crawling behavior. During each cycle, the dorsal (DE-3) and ventral (VE-4) longitudinal excitor motoneurons fired approximately 180 degrees out of phase from the ventrolateral circular excitor motoneuron (CV), which marks the elongation phase. In many isolated whole nerve cords, DE-3 bursting progressed in an anterior to posterior direction with intersegmental phase delays appropriate for crawling. In the single ganglion, the dorsal (DI-1) and ventral (VI-2) inhibitory longitudinal motoneurons fired out of phase with each DE-3 burst, further confirming that the crawl unit burst generator exists in the single ganglion. All isolated ganglia of the CNS were competent to produce DA-induced robust fictive crawling, which typically lasted uninterrupted for 5-15 min. A quantitative analysis indicated that DA-induced crawling was not significantly different from electrically evoked or spontaneous crawling. We conclude that DA is sufficient to activate the full crawl motor program and that the kernel for crawling resides within each segmental ganglion.

Static magnetic field expose enhances neurotransmission in crayfish nervous system

Purpose: To investigate the effects of static magnetic field (SMF) exposure on the synaptic transmission in a tail-flip circuit of crayfish.Materials and methods: An O-shaped permanent magnet (35 mT intensity) was placed under the isolated nerve cord of crayfish to provide static magnetic field exposure. Using electrophysiological methods, the excitatory post synaptic potential (EPSP) before and after field exposure in the lateral giant interneuron were measured and compared.Results: The EPSP produced via electrical and chemical synapses in the lateral giant neuron were enhanced after 30 min of SMF exposure (8.08 mT). Perfusion of field-exposed crayfish bath solution or preloading of Ca2+ chelator and intracellular Ca2+ release blocker failed to observe the SMF-induced enhancement on EPSP.Conclusions: Exposure of SMF increases the efficacy of synaptic-transmission in crayfish tail-flip escape circuit and this SMF-induced potentiation is a Ca2+ dependent phenomenon.

Activation of two forms of locomotion by a previously identified trigger interneuron for swimming in the medicinal leech

Higher-order projection interneurons that function in more than one behavior have been identified in a number of preparations. In this study, we document that stimulation of cell Tr1, a previously identified trigger interneuron for swimming in the medicinal leech, can also elicit the motor program for crawling in isolated nerve cords. We also show that motor choice is independent of the firing frequency of Tr1 and amount of spiking activity recorded extracellularly at three locations along the ventral nerve cord prior to Tr1 stimulation. On the other hand, during Tr1 stimulation there is a significant difference in the amount of activity elicited in the ventral nerve cord that correlates with the motor program activated. On average, Tr1 stimulation trials that lead to crawling elicit greater amounts of activity than in trials that lead to swimming.

A Central Pattern Generator Producing Alternative Outputs: Pattern, Strength, and Dynamics of Premotor Synaptic Input to Leech Heart Motor Neurons

The central pattern generator (CPG) for heartbeat in medicinal leeches consists of seven identified pairs of segmental heart interneurons and one unidentified pair. Four of the identified pairs and the unidentified pair of interneurons make inhibitory synaptic connections with segmental heart motor neurons. The CPG produces a side-to-side asymmetric pattern of intersegmental coordination among ipsilateral premotor interneurons corresponding to a similarly asymmetric fictive motor pattern in heart motor neurons, and asymmetric constriction pattern of the two tubular hearts, synchronous and peristaltic. Using extracellular recordings from premotor interneurons and voltage-clamp recordings of ipsilateral segmental motor neurons in 69 isolated nerve cords, we assessed the strength and dynamics of premotor inhibitory synaptic output onto the entire ensemble of heart motor neurons and the associated conduction delays in both coordination modes. We conclude that premotor interneurons establish a stereotypical pattern of intersegmental synaptic connectivity, strengths, and dynamics that is invariant across coordination modes, despite wide variations among preparations. These data coupled with a previous description of the temporal pattern of premotor interneuron activity and relative phasing of motor neuron activity in the two coordination modes enable a direct assessment of how premotor interneurons through their temporal pattern of activity and their spatial pattern of synaptic connectivity, strengths, and dynamics coordinate segmental motor neurons into a functional pattern of activity.

A Central Pattern Generator Producing Alternative Outputs: Phase Relations of Leech Heart Motor Neurons With Respect to Premotor Synaptic Input

The central pattern generator (CPG) for heartbeat in leeches consists of seven identified pairs of segmental heart interneurons and one unidentified pair. Four of the identified pairs and the unidentified pair of interneurons make inhibitory synaptic connections with segmental heart motor neurons. The CPG produces a side-to-side asymmetric pattern of intersegmental coordination among ipsilateral premotor interneurons corresponding to a similarly asymmetric fictive motor pattern in heart motor neurons, and asymmetric constriction pattern of the two tubular hearts: synchronous and peristaltic. Using extracellular techniques, we recorded, in 61 isolated nerve cords, the activity of motor neurons in conjunction with the phase reference premotor heart interneuron, HN(4), and another premotor interneuron that allowed us to assess the coordination mode. These data were then coupled with a previous description of the temporal pattern of premotor interneuron activity in the two coordination modes to synthesize a global phase diagram for the known elements of the CPG and the entire motor neuron ensemble. These average data reveal the stereotypical side-to-side asymmetric patterns of intersegmental coordination among the motor neurons and show how this pattern meshes with the activity pattern of premotor interneurons. Analysis of animal-to-animal variability in this coordination indicates that the intersegmental phase progression of motor neuron activity in the midbody in the peristaltic coordination mode is the most stereotypical feature of the fictive motor pattern. Bilateral recordings from motor neurons corroborate the main features of the asymmetric motor pattern.

A combined micro-resonance Raman and absorption set-up enabling in vivo studies under varying physiological conditions: The nerve globin in the nerve cord of Aphrodite aculeata

We hereby report on the design of a set-up combining micro-resonance Raman and absorption spectroscopy with a microfluidic system. The set-up enabled us to study the nerve globin of Aphrodite aculeata in the functional isolated nerve cord under varying physiological conditions for extended periods of time. The oxygenation cycle of the organism was triggered by utilizing the microfluidic system that allowed for a fast switch between aerobic and anaerobic conditions. The nerve globin was found to very easily shift from a penta-coordinated high spin ferrous form to the oxy state upon a change from anaerobic to aerobic conditions. The observed fast reaction to varying O 2 concentrations supports an oxygen-carrying and/or -storing function of the nerve globin. In addition, by combining resonance Raman and absorption spectroscopy, the physiological response could be distinguished from light-induced effects.

Patterns of Motor Activity in the Isolated Nerve Cord of the Octopus Arm

The extremely flexible octopus arm provides a unique opportunity for studying movement control in a highly redundant motor system. We describe a novel preparation that allows analysis of the peripheral nervous system of the octopus arm and its interaction with the muscular and mechanosensory elements of the arm's intrinsic muscular system. First we examined the synaptic responses in muscle fibers to identify the motor pathways from the axial nerve cord of the arm to the surrounding musculature. We show that the motor axons project to the muscles via nerve roots originating laterally from the arm nerve cord. The motor field of each nerve is limited to the region where the nerve enters the arm musculature. The same roots also carry afferent mechanosensory information from the intrinsic muscle to the axial nerve cord. Next, we characterized the pattern of activity generated in the dorsal roots by electrically stimulating the axial nerve cord. The evoked activity, although far reaching and long lasting, cannot alone account for the arm extension movements generated by similar electrical stimulation. The mismatch between patterns of activity in the isolated cord and in an intact arm may stem from the involvement of mechanosensory feedback in natural arm extension.

A Central Pattern Generator Producing Alternative Outputs: Temporal Pattern of Premotor Activity

The central pattern generator for heartbeat in medicinal leeches constitutes seven identified pairs of segmental heart interneurons. Four identified pairs of heart interneurons make a staggered pattern of inhibitory synaptic connections with segmental heart motor neurons. Using extracellular recording from multiple interneurons in the network in 56 isolated nerve cords, we show that this pattern generator produces a side-to-side asymmetric pattern of intersegmental coordination among ipsilateral premotor interneurons. This pattern corresponds to a similarly asymmetric fictive motor pattern in heart motor neurons and asymmetric constriction pattern of the two tubular hearts, synchronous and peristaltic. We provide a quantitative description of the firing pattern of all the premotor interneurons, including phase, duty cycle, and intraburst frequency of this premotor activity pattern. This analysis identifies two stereotypical coordination modes corresponding to synchronous and peristaltic, which show phase constancy over a broad range of periods as do the fictive motor pattern and the heart constriction pattern. Coordination mode is controlled through one segmental pair of heart interneurons (switch interneurons). Side-to-side switches in coordination mode are a regular feature of this pattern generator and occur with changes in activity state of these switch interneurons. Associated with synchronous coordination of premotor interneurons, the ipsilateral switch interneuron is in an active state, during which it produces rhythmic bursts, whereas associated with peristaltic coordination, the ipsilateral switch interneuron is largely silent. We argue that timing and pattern elaboration are separate functions produced by overlapping subnetworks in the heartbeat central pattern generator.

The Beat Goes On, and Up and Down.Focus on “Bursts of Information: Coordinating Interneurons Encode Multiple Parameters of a Periodic Motor Pattern”

The effective production of many motor behaviors requires the strict coordination of discrete motor pattern generating circuits ([Hill et al. 2003][1]). Locomotor behaviors usually require this coordination at several levels of the nervous system, within single limbs (interjoint coordination),

LINEAR AND NONLINEAR PROPERTIES OF PRESTIMULUS VENTRAL CORD SIGNALS DISTINGUISH SWIMMING RESPONSE OF THE LEECH TO INTRACELLULAR STIMULATION

Stimulation of a trigger interneuron of an isolated nerve cord preparation of the medicinal leech, Hirudo medicinalis, sometimes leads to swimming; sometimes it does not. The known synaptic interactions in the swim-initiating pathway do not adequately explain the observed behavioral variability. We investigate signals propagating in the ventral cord and show that, (i) prior to stimulation, the standard deviation of the signals that precede swimming (TS) is greater than that of the signals that do not (NS), (ii) linear correlations of NS signals are indistinguishable from those of TS signals, (iii) nonlinear correlations measured by mutual information of time-delayed epochs of TS signals are greater than those of NS signals, and (iv) for small time differences, the mutual information of time-delayed epochs of NS and TS signals are different from surrogates that have the same cross-correlations but are otherwise random.