Existence and stability criteria for phase-locked modes in ring neural networks based on the spike time resetting curve method

We developed a systematic and consistent mathematical approach to predicting 1:1 phase-locked modes in ring neural networks of spiking neurons based on the open loop spike time resetting curve (STRC) and its almost equivalent counterpart—the phase resetting curve (PRC). The open loop STRCs/PRCs were obtained by injecting into an isolated model neuron a triangular shaped time-dependent stimulus current closely resembling an actual synaptic input. Among other advantages, the STRC eliminates the confusion regarding the undefined phase for stimuli driving the neuron outside of the unperturbed limit cycle. We derived both open loop PRC and STRC-based existence and stability criteria for 1:1 phase-locked modes developed in ring networks of spiking neurons. Our predictions were in good agreement with the closed loop numerical simulations. Intuitive graphical methods for predicting phase-locked modes were also developed both for half-centers and for larger ring networks.     

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.     

The anatomy and physiology of the stomatogastric nervous system ofSquilla

Summary The stomatogastric nervous system of a mantis shrimp,Squilla oratoria, is described. The motor nerves of the stomatogastric ganglion (STG) and their innervation of muscles of the posterior cardiac plate (pcp) and pyloric systems are detailed.The STG contains more than 25 neurons. It sends out one pair of major output nerves. The pcp-pyloric cycle recorded from the motor axons in this nerve consists of rhythmic bursts of several units which fire with a characteristic phase relationship to each other. The rhythm is intrinsic to the STG itself, but it is modifiable.Recordings from the peripheral nerves reveal that identifiable cardiac plate, pyloric dilator and pyloric neurons control sequential contractions of the pcp and pyloric muscles to constrict or dilate a number of their attached ossicles.Several modulatory input fibres in the stomatogastric nerve, activated via stimulation of the superior or inferior oesophageal nerve (son, ion), prime or trigger the cyclic motor outputs. The son inputs induce distinct effects on the cardiac and pcp-pyloric pattern generators, while the ion inputs, via the oesophageal ganglion, excite only the pcp-pyloric generator.On the basis of anatomical and physiological observations, the possible functions of motor neurons involved in the pcp-pyloric cycle are described with reference to opening of the pcp and pyloric channels.This stomatogastric nervous system inSquilla is compared to that in decapods which has been well analyzed.Abbreviations CG commissural ganglion - ion inferior oesophageal nerve - lvn lateral ventricular nerve - OG oesophageal ganglion - pep posterior cardiac plate - son superior oesophageal nerve - STG stomatogastric ganglion - stn stomatogastric nerve - ivn inferior ventricular 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.     

Multiple motor patterns in the stomatogastric ganglion of the shrimp Penaeus japonicus

 Motor patterns of the cardiac sac, the gastric and the pyloric network in the stomatogastric nervous system of the shrimp Penaeus japonicus, the most primitive decapod species, were studied. Single neurons can switch from the gastric or the pyloric pattern to the cardiac sac pattern. Some of the pyloric neurons fire with the gastric pattern. All of the gastric neurons fire with the pyloric pattern, unlike those in reptantians. Proctolin activates and modulates the cardiac sac and the pyloric rhythm, and promotes reconfiguration of the networks. Neurons of the three networks have so many interconnections that they construct a multifunctional neural network like those in Cancer. This network may function in different configurations under the appropriate conditions. Several modes of interactions between the networks found in different reptantian species can apply to the penaeidean shrimp. Such interactions are general features of the stomatogastric nervous system in decapods. Phylogenetic differences among the decapod infraorders are seen in the number and orientation of muscles and the innervation pattern of muscles. The multifunctional networks have existed in the most primitive decapod species, and types of configurations of the networks would have evolved to produce a wide range of motor patterns as the foregut structure has become complex. Accepted: 26 October 1999     

Locomotory activity and exploration behaviour of juvenile European lobsters (Homarus gammarus) in the laboratory

The behaviour of juvenile European lobsters (Homarus gammarus) in the wild is little understood. A laboratory system was designed with a maze-like environment as an alternative to the large technological expenditure of a field study. It provided an apparently endless runway with uniform thigmotactical cues. Juvenile lobsters having a total length of 68 to 115 mm were studied. The lobsters showed an extensive nocturnal locomotory activity. They established home shelters in which they spent the day and covered distances of 1200 to 1600 m during the night. On average, the lobsters performed 136 excursions from their shelters, of which 10% led only to the immediate surroundings of the shelters. Of all the excursions 90% were shorter than 16 m. In some exceptional cases distances of several hundred meters were covered in the maze between shelter visits. Excursions of less than 16 m lasted on average less than 5 min. The frequencies of shelter visits during the dark phase were highest in small lobsters (300 visits) and lowest in larger lobsters (50 visits). The time spent within shelters decreased from 10% to less than 2% with lobster size. A distinct change in behaviour was obvious at a body length of 75 to 80 mm. Smaller lobsters behaved defensively and relied on shelter protection. Larger lobsters were less dependent on shelter protection and thus were able to explore and utilize their environment more intensively.     

Neurons with histaminelike immunoreactivity in the segmental and stomatogastric nervous systems of the crayfishPacifastacus leniusculus and the lobsterHomarus americanus

Summary We used a polyclonal antiserum against histamine to map histaminelike immunoreactivity (HLI) in whole mounts of the segmental ganglia and stomatogastric ganglion of crayfish and lobster. Carbodiimide fixation permitted both HRP-conjugated and FITC-conjugated secondary antibodies to be used effectively to visualize HLI in these whole mounts. Two interneurons that send axons through the inferior ventricular nerve (ivn) and the stomatogastric nerve to the stomatogastric ganglion had strong HLI, both in crayfish and in lobster. These ivn interneurons were known from other evidence to be histaminergic. The neuropil of the stomatogastric ganglion in both crayfish and lobster contained brightly labeled terminals of axons that entered the ganglion from the stomatogastric nerve. No neuronal cell bodies in this ganglion had HLI. Each segmental ganglion contained at least one pair of neurons with HLI. Some neurons in the subesophageal ganglion and in each thoracic ganglion labeled very brightly. Axons of projection interneurons with strong HLI occurred in the dorsal lateral tracts of each segmental ganglion, and sent branches to the lateral neuropils and tract neuropils of each ganglion. All the labeled neurons were interneurons; no HLI was observed in peripheral nerves.     

Early appearance of catecholaminergic neurons in the central nervous system of precocial and altricial avian species

Summary The early appearance of catecholaminergic neurons, as revealed by fluorescence histochemistry, has been determined in the central nervous system of quail, pheasant, and pigeon embryos. The first neuronal assemblies displaying specific fluorescence are the locus coeruleus and the nucleus subcoeruleus ventralis. Taking into account the differences in the length of the prehatching period of these three avian species, the first catecholamine-containing neurons appear earlier in the precocial quail and pheasant than in the altricial pigeon.Investigation supported by grants from the Italian National Research Council (CNR) No 83.02058.04 (R.G.) and No 83.00492.04 (G.C.P.).     

Ontogeny of the rhythmic melatonin production in a precocial and an altricial bird,the Japanese quail and the European starling

A distinct daily rhythm of melatonin production was found in the pineal gland of both precocial Japanese quail (Coturnix coturnix japonica) and altricial European starling (Sturnus vulgaris) during the first day of postembryonic life. Rhythmic melatonin production was reflected in a rhythmic profile in the general circulation. Significant day-night differences in melatonin content were also observed in the eyes of Japanese quail.The amplitude of the rhythm in the quail pineal gland increased steadily during the first two weeks of postem-bryonic life. A transient increase in maximum melatonin concentration was observed at the end of the first week of life in the plasma but not in the pineal gland of quail suggesting that a metabolizing pathway or a changed ocular contribution may influence the melatonin profile in the circulation and its availability to other tissues. There was no delay in the postembryonic development of melatonin rhythmicity in the altricial starling in comparison with the precocial quail. The amplitude of the plasma melatonin rhythm did not increase over the first week of life in starlings as it did in quail and the only significant increase was found between 6- and 17-day old starlings.In general, the development of the rhythm resulted from an increase of dark-time values. The day-time concentrations were low in all age groups of both species. A one-hour light pulse suppressed the high dark-time melatonin concentrations in 1-, 7- and 14-day old Japanese quail as well as in 7- and 14-day old European starlings. The manner in which the rhythm develops suggests that the circadian pacemaker(s) as well as the mechanisms of photoreception and entrainment are developed in hatchlings of both species in spite of their otherwise different developmental strategies.     

Maintenance of dominance is mediated by urinary chemical signals in male European lobsters,Homarus gammarus

We studied the relevance of urine cues in Homarus gammarus dominance maintenance, hypothesising that urinary signals are necessary to mediate recognition of former opponents. Males in size-matched pairs interacted on two consecutive days with or without blocking urine release by adding catheters to both contestants on the second day. European lobsters established dominance in a first fight, and fight duration and aggression levels decreased strongly from first to second day in animals with free urine release, indicating the maintenance of this dominance relationship. If urine was blocked on the second day, fight durations were long in both first and second day interactions. Results demonstrate that urine signals contribute to the maintenance of dominance in H. gammarus males.     

Substance P-like immunoreactivity in the stomatogastric nervous systems of the crab Cancer borealis and the lobsters Panulirus interruptus and Homarus americanus

Summary The distribution of substance P-like immunoreactivity in the stomatogastric nervous systems of three decapod crustacean species, Cancer borealis, Homarus americanus, and Panulirus interruptus, was studied. The stomatogastric ganglion showed dense staining in the neuropil, but none in the somata. A single neuron stained in the esophageal ganglion. Lucifer yellow backfills and intracellular injections followed by incubation with the substance P antibody showed that the axons of this neuron project into the inferior esophageal nerves towards the paired commissural ganglia. The commissural ganglia showed a pronounced projection from a large bundle of fibers in the anterior medial portion of the circumesophageal connective. Additionally, less dense neuropil and stained somata were seen in the commissural ganglia. Staining was completely blocked by preabsorption with authentic substance P, physalaemin, eledoisin, and substance K. These data suggest that in the nervous system of crustacean species a molecule with C-terminal homology to substance P and other tachykinins is released as a neuroregulator in the stomatogastric ganglion.     

Localization of allatostatin-immunoreactive material in the central nervous system,stomatogastric nervous system,and gut of the cockroach Blattella germanica

Immunoreactivity against peptides of the allatostatin family having a typical YXFGL-NH₂ C-terminus has been localized in different areas of the central nervous system, stomatogastric nervous system and gut of the cockroach Blattella germanica. In the protocerebrum, the most characteristic immunoreactive perikarya are situated in the lateral and median neurosecretory cell groups. Immunoreactive median neurosecretory cells send their axons around the circumesophageal connectives to form arborizations in the anterior neuropil of the tritocerebrum. A group of cells in the lateral aspect of the tritocerebrum project to the antennal lobes in the deutocerebrum, where immunoreactive arborizations can be seen in the periphery of individual glomeruli. Nerve terminals were shown in the corpora allata. These terminals come from perikarya situated in the lateral neurosecretory cells in the pars lateralis and in the subesophageal ganglion. Immunoreactive axons from median neurosecretory cells and from cells positioned in the anteriormost part of the tritocerebrum enter together in the stomatogastric nervous system and innervate foregut and midgut, especially the crop and the valve between the crop and the midgut. The hindgut is innervated by neurons whose perikarya are located in the last abdominal ganglion. Besides immunoreactivity in neurons, allatostatin-immunoreactive material is present in endocrine cells distributed within the whole midgut epithelium. Possible functions for these peptides according to their localization are discussed. Arch. Insect Biochem. Physiol. 37:269–282, 1998. © 1998 Wiley-Liss, Inc.     

Tip cell-derived RTK signaling initiates cell movements in the Drosophila stomatogastric nervous system anlage

The stomatogastric nervous system (SNS) of Drosophila is a simply organized neural circuitry that innervates the anterior enteric system. Unlike the central and the peripheral nervous systems, the SNS derives from a compact epithelial anlage in which three invagination centers, each giving rise to an invagination fold headed by a tip cell, are generated. Tip cell selection involves lateral inhibition, a process in which Wingless (Wg) activity adjusts the range of Notch signaling. Here we show that RTK signaling mediated by the Drosophila homolog of the epidermal growth factor receptor, DER, plays a key role in two consecutive steps during early SNS development. Like Wg, DER signaling participates in adjusting the range of Notch-dependent lateral inhibition during tip cell selection. Subsequently, tip cells secrete the DER ligand Spitz and trigger local RTK signaling, which initiates morphogenetic movements resulting in the tip cell-directed invaginations within the SNS anlage.     

Anatomy and in vivo activity of neurons connecting the crustacean stomatogastric nervous system to the brain

In decapod crustaceans, the inferior ventricular nerve connects the cerebral ganglia (brain) with the stomatogastric nervous system (STNS). In the ivn of the crayfish, eight axons with diameters between 3.5 microm and 10 microm were found in close proximity to the oesophageal ganglion. Two of these axons terminate with their cell body within the ivn. The projections of the other six axons spread inside many neuropiles of the brain, mainly within the protocerebrum and the neuropils of the first and second antennae. Several fibers also send neurites via the circumoesophageal connectives toward the paired commissural ganglia and further down to the ventral nerve cord. The activity of motoneurons within the STNS and of axons in the ivn was recorded with implanted electrodes before, during and after times of feeding. At the beginning of feeding all tonically active ivn neurons accelerated their discharge rate and initially silent neurons also started to fire. Spike frequency was correlated with the quantity of food consumed. The ivn response was accompanied by a corresponding increase in pyloric frequency and an initiation of a gastric rhythm. The two motor rhythms showed a strong phasic interaction, but there was no phase coupling to the ivn activity.     

FMRFamide-like immunoreactivity in the stomatogastric nervous system innervating the gut of the fly,Sarcophaga bullata

1. Distribution of FMRFamide-like peptide activity was examined in the stomatogastric nervous system of the adult fly, Sarcophaga bullata by the indirect immunofluorescent method.2. The neurons of the hypocerebral ganglion exhibit intense immunoreactivity and extend a thick axon bundle ventrally towards the proventriculus and crop.3. Near the mouth of the stomodeal valve a dense network of radial and circular immunoreactive processes branch off and innervate the proventriculus.4. Beyond the proventriculus, the crop duct and anterior midgut wall are also innervated by the FMRFamide-like immunoreactive processes of the nerve from the hypocerebral ganglion.5. From the pattern of innervation of the gut by FMRFamide-like immunoreactive processes it is suggested that this neuropeptide may regulate feeding activities in the adult fly.     

Symmetry-breaking bifurcation: A possible mechanism for 2:1 frequency-locking in animal locomotion

The generation and control of animal locomotion is believed to involve central pattern generators — networks of neurons which are capable of producing oscillatory behavior. In the present work, the quadrupedal locomotor central pattern generator is modelled as four distinct but symmetrically coupled nonlinear oscillators. We show that the typical patterns for two such networks of oscillators include 2:1 frequency-locked oscillations. These patterns, which arise through symmetry-breaking Hopf bifurcation, correspond in part to observed patterns of 2:1 frequency-locking of limb movements during electrically elicited locomotion of decerebrate and spinal quadrupeds. We briefly describe how our theoretical predictions could be tested experimentally.