Neural mechanism for generating and switching motor patterns of rhythmic movements of ovipositor valves in the cricket

In adult female crickets (Gryllus bimaculatus), rhythmic movements of ovipositor valves are produced by contractions of a set of ovipositor muscles that mediate egg-laying behavior. Recordings from implanted wire electrodes in the ovipositor muscles of freely moving crickets revealed sequential changes in the temporal pattern of motor activity that corresponded to shifts between behavioral steps: penetration of the ovipositor into a substrate, deposition of eggs, and withdrawal of the ovipositor from the substrate. We aimed in this study to illustrate the neuronal organization producing these motor patterns and the pattern-switching mechanism during the behavioral sequence. Firstly, we obtained intracellular recordings in tethered preparations, and identified 12 types of interneurons that were involved in the rhythmic activity of the ovipositor muscles. These interneurons fell into two classes: ‘initiator interneurons’ in which excitation preceded the rhythmic contractions of ovipositor muscles, and ‘oscillator interneurons’ in which the rhythmic oscillation and spike bursting occurred in sync with the oviposition motor rhythm. One of the oscillator interneurons exhibited different depolarization patterns in the penetration and deposition motor rhythms. It is likely that some of the oscillator interneurons are involved in producing different oviposition motor patterns. Secondly, we analyzed oviposition motor patterns when the mecahnosensory hairs located on the inside surface of the dorsal ovipositor valves were removed. In deafferented preparations, the sequential change from deposition to withdrawal did not occur. Therefore, the switching from deposition pattern to withdrawal pattern is signaled by the hair sensilla that detect the passage of an egg just before it is expelled.     

A database of computational models of a half-center oscillator for analyzing how neuronal parameters influence network activity

A half-center oscillator (HCO) is a common circuit building block of central pattern generator networks that produce rhythmic motor patterns in animals. Here we constructed an efficient relational database table with the resulting characteristics of the Hill et al.’s (J Comput Neurosci 10:281–302, 2001) HCO simple conductance-based model. The model consists of two reciprocally inhibitory neurons and replicates the electrical activity of the oscillator interneurons of the leech heartbeat central pattern generator under a variety of experimental conditions. Our long-range goal is to understand how this basic circuit building block produces functional activity under a variety of parameter regimes and how different parameter regimes influence stability and modulatability. By using the latest developments in computer technology, we simulated and stored large amounts of data (on the order of terabytes). We systematically explored the parameter space of the HCO and corresponding isolated neuron models using a brute-force approach. We varied a set of selected parameters (maximal conductance of intrinsic and synaptic currents) in all combinations, resulting in about 10 million simulations. We classified these HCO and isolated neuron model simulations by their activity characteristics into identifiable groups and quantified their prevalence. By querying the database, we compared the activity characteristics of the identified groups of our simulated HCO models with those of our simulated isolated neuron models and found that regularly bursting neurons compose only a small minority of functional HCO models; the vast majority was composed of spiking neurons.     

Organization of the larval pre-ecdysis motor pattern in the tobacco hornworm,Manduca sexta

The tobacco hornworm, Manduca sexta, undergoes several larval molts before transforming into a pupa and then an adult moth. Each molt culminates in ecdysis, when the old cuticle is shed. Prior to each larval ecdysis, the old cuticle is loosened by pre-ecdysis behavior, which consists of rhythmic compressions that are synchronous along the abdomen and on both body sides, and rhythmic retractions of the abdominal prolegs. Both pre-ecdysis and ecdysis behaviors are triggered by a peptide, eclosion hormone. The aim of the present study was to investigate the neural circuitry underlying larval preecdysis behavior. The pre-ecdysis motor pattern was recorded in isolated nerve cords from eclosion hormone-treated larvae, and the effects of connective transections and ionic manipulations were tested. Our results suggest that the larval pre-ecdysis compression motor pattern is coordinated and maintained by interneurons in the terminal abdominal ganglion that ascend the nerve cord without chemical synaptic relays; these interneurons make bilateral, probably monosynaptic, excitatory connections with identified pre-ecdysis motor neurons throughout the abdominal nerve cord. This model of the organization of the larval pre-ecdysis motor pattern should facilitate identification of the relevant interneurons, allowing future investigation of the neural basis of the developmental weakening of the pre-ecdysis motor pattern that accompanies the larval-pupal transformation.Abbreviations A3, A4... abdominal ganglia 3, 4... - AT terminal abdominal ganglion - ALE anterior lateral external muscle - DN dorsal nerve - DN_A anterior branch of the dorsal nerve - DN_L lateral branch of the dorsal nerve - DN_P posterior branch of the dorsal nerve - EH eclosion hormone - TP tergopleural muscle - VN ventral nerve - VN_A anterior branch of the ventral nerve - VN_L lateral branch of the ventral nerve - VN_P posterior branch of the ventral nerve     

Altering cAMP levels within a central pattern generator modifies or disrupts rhythmic motor output

Cyclic AMP is a second messenger that has been implicated in the neuromodulation of rhythmically active motor patterns. Here, we tested whether manipulating cAMP affects swim motor pattern generation in the mollusc, Tritonia diomedea. Inhibiting adenylyl cyclase (AC) with 9-cyclopentyladenine (9-CPA) slowed or stopped the swim motor pattern. Inhibiting phosphodiesterase with 3-isobutyl-1-methylxanthine (IBMX) or applying dibutyryl-cAMP (dB-cAMP) disrupted the swim motor pattern, as did iontophoresing cAMP into the central pattern generator neuron C2. Additionally, during wash-in, IBMX sometimes temporarily produced extended or spontaneous swim motor patterns. Photolysis of caged cAMP in C2 after initiation of the swim motor pattern inhibited subsequent bursting. These results suggest that cAMP levels can dynamically modulate swim motor pattern generation, possibly shaping the output of the central pattern generator on a cycle-by-cycle basis.     

The brain can eat: Establishing the existence of a central pattern generator for feeding in third instar larvae of Drosophila virilis and Drosophila melanogaster

To establish the existence of a central pattern generator for feeding in the larval central nervous system of two Drosophila species, the gross anatomy of feeding related muscles and their innervation is described, the motor units of the muscles identified and rhythmic motor output recorded from the isolated CNS. The cibarial dilator muscles that mediate food ingestion are innervated by the frontal nerve. Their motor pathway projects from the brain through the antennal nerves, the frontal connectives and the frontal nerve junction. The mouth hook elevator and depressor system is innervated by side branches of the maxillary nerve. The motor units of the two muscle groups differ in amplitude: the elevator is always activated by a small unit, the depressor by a large one. The dorsal protractors span the cephalopharyngeal skeleton and the body wall hence mediating an extension of the CPS. These muscles are innervated by the prothoracic accessory nerve. Rhythmic motor output produced by the isolated central nervous system can simultaneously be recorded from all three nerves. The temporal pattern of the identified motor units resembles the sequence of muscle contractions deduced from natural feeding behavior and is therefore considered as fictive feeding. Phase diagrams show an almost identical fictive feeding pattern is in both species.     

A modeling comparison of projection neuron- and neuromodulator-elicited oscillations in a central pattern generating network

Many central pattern generating networks are influenced by synaptic input from modulatory projection neurons. The network response to a projection neuron is sometimes mimicked by bath applying the neuronally-released modulator, despite the absence of network interactions with the projection neuron. One interesting example occurs in the crab stomatogastric ganglion (STG), where bath applying the neuropeptide pyrokinin (PK) elicits a gastric mill rhythm which is similar to that elicited by the projection neuron modulatory commissural neuron 1 (MCN1), despite the absence of PK in MCN1 and the fact that MCN1 is not active during the PK-elicited rhythm. MCN1 terminals have fast and slow synaptic actions on the gastric mill network and are presynaptically inhibited by this network in the STG. These local connections are inactive in the PK-elicited rhythm, and the mechanism underlying this rhythm is unknown. We use mathematical and biophysically-realistic modeling to propose potential mechanisms by which PK can elicit a gastric mill rhythm that is similar to the MCN1-elicited rhythm. We analyze slow-wave network oscillations using simplified mathematical models and, in parallel, develop biophysically-realistic models that account for fast, action potential-driven oscillations and some spatial structure of the network neurons. Our results illustrate how the actions of bath-applied neuromodulators can mimic those of descending projection neurons through mathematically similar but physiologically distinct mechanisms.     

A single pair of interneurons controls motor neuron activity during pre-ecdysis compression behavior in larval Manduca sexta

Manduca sexta molts several times as a larva (caterpillar) before becoming a pupa and then an adult moth. Each molt culminates in ecdysis behavior, during which the old cuticle is shed. Prior to each larval ecdysis, the old cuticle is loosened by pre-ecdysis behavior, which includes rhythmic, synchronous compressions of the abdomen. A previous study indicated that motor neuron activity during pre-ecdysis compression behavior is driven by an ascending neural pathway from the terminal abdominal ganglion. The present study describes a pair of interneurons, designated IN-402, that are located in the terminal ganglion and belong to the ascending pathway. Each IN-402 is synchronously active with pre-ecdysis compression motor bursts, and bilaterally excites compression motor neurons throughout the abdominal nerve cord via apparently monosynaptic connections. The pair of IN-402s appears to be the sole source of rhythmic synaptic drive to the motor neurons during the pre-ecdysis compression motor pattern. These interneurons play a key role in the production of larval pre-ecdysis behavior, and are candidates for contributing to the developmental weakening of pre-ecdysis behavior at pupation.Abbreviations A3, A4... abdominal ganglion 3, abdominal ganglion 4... - AT terminal abdominal ganglion - DN _A anterior branch of the dorsal nerve - EH eclosion hormone - EPSP excitatory postsynaptic potential     

Interactions of suboesophageal ganglion and frontal ganglion motor patterns in the locust

Although locust feeding has been well studied, our understanding of the neural basis of feeding-related motor patterns is still far from complete. This paper focuses on interactions between the pattern of rhythmic movements of the mouth appendages, governed by the suboesophageal ganglion (SOG), and the foregut movements, controlled by the frontal ganglion (FG), in the desert locust. In vitro simultaneous extracellular nerve recordings were made from totally isolated ganglia as well as from fully interconnected SOG-FG and brain-SOG-FG preparations. SOG-confined bath application of the nitric oxide donor, SNP, or the phosphodiesterase antagonist, IBMX, each followed by the muscarinic agonist pilocarpine, consistently induced robust fictive motor patterns in the SOG. This was observed in both isolated and interconnected preparations. In the brain-SOG-FG configuration the SOG-confined modulator application had an indirect excitatory effect on spontaneous FG rhythmic activity. Correlation between fictive motor patterns of the two ganglia was demonstrated by simultaneous changes in burst frequency. These interactions were found to be brain-mediated. Our results indicate the presence of intricate neuromodulation-mediated circuit interactions, even in the absence of sensory inputs. These interactions may be instrumental in generating the complex rhythmic motor patterns of the mandibles and gut muscles during locust feeding or ecdysis-related air swallowing.     

Qualitative validation of the reduction from two reciprocally coupled neurons to one self-coupled neuron in a respiratory network model

The pre-Bötzinger complex of the mammalian brainstem is a heterogeneous neuronal network, and individual neurons within the network have varying strengths of the persistent sodium and calcium-activated nonspecific cationic currents. Individually, these currents have been the focus of modeling efforts. Previously, Dunmyre et al. (J Comput Neurosci 1–24, 2011) proposed a model and studied the interactions of these currents within one self-coupled neuron. In this work, I consider two identical, reciprocally coupled model neurons and validate the reduction to the self-coupled case. I find that all of the dynamics of the two model neuron network and the regions of parameter space where these distinct dynamics are found are qualitatively preserved in the reduction to the self-coupled case.     

The sounds of silence: cessation of singing and song pausing are ultrasound-induced acoustic startle behaviors in the katydid Neoconocephalus ensiger (Orthoptera; Tettigoniidae)

Previous studies of acoustic startle in insects have dealt with behavioral and/or neural mechanisms employed in evading aerially hawking, echolocating bats; however, insects also face terrestrial predators. Here we describe an acoustic startle response of the nocturnal katydid, Neoconocephalus ensiger. Stridulating males disturbed in the field perform obvious anti-predatory behaviors – cessation of singing, freezing, jumping, and evasive flight. Under controlled laboratory conditions we found that cessation of singing and song pausing are ultrasound-specific behaviors: when stimulated with pulsed ultrasound (20–100 kHz), but not audio-sound (<20 kHz), males cease mate calling or insert pauses in their song. A second factor influencing acoustic startle is the phase of stimulation: an acoustic startle response occurs only when the pulse of ultrasound arrives during the window of silence between stridulatory syllables. The average startle threshold and response latency was 70 ± 5 dB SPL and 34.2 ± 6.0 ms, respectively. N. ensiger is particularly useful for examining acoustic startle responses of non-flying insects because (1) its calling song is broadband and contains ultrasound, thus the possibility exists of confusion over the biological meaning of ultrasound, and (2) this species shows the classic bat-avoidance response while flying, so a direct comparison between two types of acoustic startle is possible within the same species. Accepted: 6 November 1999     

Control of oscillation periods and phase durations in half-center central pattern generators: a comparative mechanistic analysis

Central pattern generators (CPGs) consisting of interacting groups of neurons drive a variety of repetitive, rhythmic behaviors in invertebrates and vertebrates, such as arise in locomotion, respiration, mastication, scratching, and so on. These CPGs are able to generate rhythmic activity in the absence of afferent feedback or rhythmic inputs. However, functionally relevant CPGs must adaptively respond to changing demands, manifested as changes in oscillation period or in relative phase durations in response to variations in non-patterned inputs or drives. Although many half-center CPG models, composed of symmetric units linked by reciprocal inhibition yet varying in their intrinsic cellular properties, have been proposed, the precise oscillatory mechanisms operating in most biological CPGs remain unknown. Using numerical simulations and phase-plane analysis, we comparatively investigated how the intrinsic cellular features incorporated in different CPG models, such as subthreshold activation based on a slowly inactivating persistent sodium current, adaptation based on slowly activating calcium-dependent potassium current, or post-inhibitory rebound excitation, can contribute to the control of oscillation period and phase durations in response to changes in excitatory external drive to one or both half-centers. Our analysis shows that both the sensitivity of oscillation period to alterations of excitatory drive and the degree to which the duration of each phase can be separately controlled depend strongly on the intrinsic cellular mechanisms involved in rhythm generation and phase transitions. In particular, the CPG formed from units incorporating a slowly inactivating persistent sodium current shows the greatest range of oscillation periods and the greatest degree of independence in phase duration control by asymmetric inputs. These results are explained based on geometric analysis of the phase plane structures corresponding to the dynamics for each CPG type, which in particular helps pinpoint the roles of escape and release from synaptic inhibition in the effects we find.     

Inferring and quantifying the role of an intrinsic current in a mechanism for a half-center bursting oscillation

This paper illustrates an informatic technique for inferring and quantifying the dynamic role of a single intrinsic current in a mechanism of neural bursting activity. We analyze the patterns of the most dominant currents in a model of half-center oscillation in the leech heartbeat central pattern generator. We find that the patterns of dominance change substantially over a cycle, allowing different local reductions to be applied to the model. The result is a hybrid dynamical systems model, which is a piecewise representation of the mechanism combining multiple vector fields and discrete state changes. The simulation of such a model tests explicit hypotheses about the mechanism and is a novel way to retain both mathematical clarity and scientific detail in answering mechanistic questions about a complex model. Several insights into the central mechanism of “escape-release” in the model are elucidated by this analysis and compared with previous studies. The broader application and extension of this technique is also discussed.     

A model for switching between particulate-feeding and filter-feeding in the common bream,Abramis brama

Synopsis A model has been developed to describe the process of switching between particulate- and filter-feeding in common bream, Abramis brama, in relation to fish size and zooplankton density. The model assumes that the encounter rate of fish and zooplankton is determined by the density of zooplankton and the swimming speed of fish. However, if zooplankton density is so high as to allow at least one prey to be engulfed per random snap, the encounter rate is determined by the volume of the buccal cavity and by zooplankton density, but is independent of swimming speed. The snapping frequency will be maximal at the time of switching, decreasing with increasing zooplankton density because of the extra time needed for intra-oral prey handling. The model predicted switching from particulate- to filter-feeding only for bream> 15 cm standard length at zooplankton densities < 500 l^-1. The snap frequency of six size classes of bream (7.5, 10.4, 12.5, 15, 24 and 29.5 cm) was measured at varying densities of Daphnia. The model predictions for snap frequencies of all size classes corresponded to the highest values observed. The average of the observed snap frequencies was only 50% of the predicted values, probably because the calculated average distance between prey animals assumed an ideal swimming route of the fish and error-free vision for particulate-feeding, and the handling time was ignored.     

The nature of the coupling between segmental oscillators of the lamprey spinal generator for locomotion: A mathematical model

We present a theoretical model which is used to explain the intersegmental coordination of the neural networks responsible for generating locomotion in the isolated spinal cord of lamprey.A simplified mathematical model of a limit cycle oscillator is presented which consists of only a single dependent variable, the phase (t). By coupling N such oscillators together we are able to generate stable phase locked motions which correspond to traveling waves in the spinal cord, thus simulating fictive swimming. We are also able to generate irregular drifting motions which are compared to the experimental data obtained from cords with selective surgical lesions.     

A study on the relationship between vegetation pattern and environment in the upstream of Minjiang River, China

The vegetation pattern in the upstream of Minjiang River, and its relationship with environment factors, such as landscape position (elevation, slope, aspect), precipitation and temperature and soil are analyzed in this paper. The data used in this paper were based on the landscape map derived from 1994 TM imagery. The results were as follows: 1) dominant landscape types were forest, shrub land and grassland, which were very similar in terms of area ratio (32.87%, 31.85% and 28.44%, respectively); 2) the patch shape of conifer forest and mixed forest was complicated while that of broad-leaved forest and cultivated land was simple; 3) the fragmentation of conifer forest and mixed forest was serious in contrast with low fragmentation of broad-leaved forest and cultivated land; and 4) closed scrub and grassland had a high contagion and good connectivity while mixed forest had a lower contagion and bad connectivity. In addition, the vegetation distribution pattern of upstream of Minjiang River was closely related with elevation and temperature, but the relationship between vegetation and precipitation was not statistically significant. __________ Translated from Journal of Beijing Normal University (Natural Science), 2005,41(4) [译自: 北京师范大学学报(自然科学版), 2005,41(4)]     

A computational model of oxygen transport in skeletal muscle for sprouting and splitting modes of angiogenesis

Oxygen transport from capillary networks in muscle at a high oxygen consumption rate was simulated using a computational model to assess the relative efficacies of sprouting and splitting modes of angiogenesis. Efficacy was characterized by the volumetric fraction of hypoxic tissue and overall heterogeneity of oxygen distribution at steady state. Oxygen transport was simulated for a three-dimensional vascular network using parameters for rat extensor digitorum longus (EDL) muscle when oxygen consumption by tissue reached 6, 12, and 18 times basal consumption. First, a control network was generated by using straight non-anastomosed capillaries to establish baseline capillarity. Two networks were then constructed simulating either abluminal lateral sprouting or intraluminal splitting angiogenesis such that capillary surface area was equal in both networks. The sprouting network was constructed by placing anastomosed capillaries between straight capillaries of the control network with a higher probability of placement near hypoxic tissue. The splitting network was constructed by splitting capillaries from the control network into two branches at randomly chosen branching points. Under conditions of moderate oxygen consumption (6 times basal), only minor differences in oxygen delivery resulted between the sprouting and splitting networks. At higher consumption levels (12 and 18 times basal), the splitting network had the lowest volume of hypoxic tissue of the three networks. However, when total blood flow in all three networks was made equal, the sprouting network had the lowest volume of hypoxic tissue. This study also shows that under the steady-state conditions the effect of myoglobin (Mb) on oxygen transport was small.