Lobster Homarus Gammarus Research Articles

Conditional dendritic oscillators in a lobster mechanoreceptor neurone.

1. Intra- and extracellular recordings were made from in vitro preparations of the lobster (Homarus gammarus) stomatogastric nervous system to study the nature and origin of pacemaker-like activity in a primary mechanoreceptor neurone, the anterior gastric receptor (AGR), whose two bilateral stretch-sensitive dendrites ramify in the tendon of powerstroke muscle GM1 of the gastric mill system. 2. Although the AGR is known to be autoactive, we report here that in 20% of our preparations, rather than autogenic tonic discharge, the receptor fired spontaneously in discrete bursts comprising three to ten action potentials and repeating at cycle frequencies of 0.5-2.5 Hz in the absence of mechanical stimulation. Intrasomatic recordings revealed that such rhythmic bursting was driven by slow oscillations in membrane potential, the frequency of which was voltage sensitive and dependent upon the level of stretch applied to the receptor terminals of the AGR. 3. Autoactive bursting of the AGR originated from an endogenous oscillatory mechanism in the sensory dendrites themselves, since (i) during both steady, repetitive firing and bursting, somatic and axonal impulses were always preceded 1:1 by dendritic action potentials, (ii) hyperpolarizing the AGR cell body to block triggering of axonal impulses revealed attenuated somatic spikes that continued to originate from the two peripheral dendrites, (iii) the timing of burst firing could be phase reset by brief electrical stimulation of either dendrite, and (iv) spontaneous bursting continued to be expressed by an AGR dendrite after physical isolation from the GM1 muscle and the stomatogastric nervous system. 4. Although a given AGR in vitro could switch spontaneously from dendritic bursting to tonic firing and vice versa, exogenous application of micromolar (or less) concentrations of the neuropeptide F1 (TNRNFLRFamide) to the dendritic membrane could rapidly and reversibly switch the receptor firing pattern from repetitive firing to the bursting mode. Exposure of the somatic and axonal membrane of the AGR to F1 was without effect, as were applications of other neuroactive substances such as serotonin, octopamine and proctolin. 5. We conclude that, as for many oscillatory neurones of the central nervous system, the intrinsic activity pattern of this peripheral sensory neurone may be dynamically conferred by extrinsic modulatory influences, presumably according to computational demands. Moreover, the ability of the AGR to behave as an endogenous burster imparts considerable integrative complexity since, in this activity mode, sensory coding not only occurs through the frequency modulation of on-going dendritic bursts but also via changes in the duration of individual bursts and their inherent spike frequencies.

Ultrastructural Study of the Neurosecretory Granules and Crustacean Hyperglycemic Hormone (CHH) Immunolocalization in the Sinus Gland of Homarus gammarus

ABSTRACT Seven different types of neurosecretory granules have been observed in the axon terminals of the sinus gland of the adult female lobster Homarus gammarus. They were discriminated through morphometrical and morphological criteria such as size, shape, frequency of occurrence, electron density, and axon-matrix density. Each size distribution followed a single Gaussian-type distribution. Each axon terminal contained I type of granule. The mean granule diameter ranged from 50 nm (type 1) to 161 nm (type 7). Type 6 and type I axon terminals were, respectively, the most and least frequent. An immunopositive reaction against an anti-Homarus americanus CHH was detected in the 2 largest types of granules: type 6 (mean diameter, 128 nm) and type 7 (mean diameter, 161 nm).

Preliminary acoustic tracking of native and transplanted European lobsters (Homarus gammarus) in an open sea lagoon

In a larger release project, European lobsters (Homarus gammarus) under legal size have been captured, checked for magnetic microtags, externally tagged, and released to their home site for population and migration studies. To see if transplanted lobsters behave differently from native lobsters, four acoustically tagged males were released between three stationary hydrophones in an open sea lagoon and tracked continuously for 2–3 weeks. Lobster 1 was from the lagoon, Lobster 2 was transplanted less than 1000 m from its capture location, and Lobsters 3 and 4 were transplanted more than 5000 m. Within a few hours, Lobsters 1 and 2 took up residence in the area of their original home sites. Lobsters 3 and 4 took up residence in the lagoon after extended roaming. Six days after release, Lobsters 1 and 4 engaged in nocturnal activity, Lobster 2 changed locations occasionally without moving long distances, and Lobster 3 did not move. The odd movement patterns in the transplanted lobsters could be caused by their lack of local knowledge. Since rocks caused blocking of the acoustic signals, manual monitoring was needed to confirm the lobster positions. In cryptic animals such as lobsters, a continuous tracking system that can penetrate stones is required.

Synchronous bursting can arise from mutual excitation, even when individual cells are not endogenous bursters.

Mutual excitation between two neurons is generally thought to raise the excitation level of each neuron or, if they are both bursty, to act to synchronize their bursts. If only one is bursty, it can induce synchronized bursts in the other cell. Here we show that two nonbursty cells can be induced to burst in synchrony by mutual excitatory synaptic connections, provided the presynaptic threshold for graded synaptic transmission at each synapse is at a different level. This mechanism may operate in a recently discovered network in the lobster Homarus gammarus. By a duality between presynaptic threshold and injected current, we also show that two identical, nonbursty, mutual excitatory cells could be induced to burst in synchrony by injecting differing amounts of current in the two cells. Finally we show that differential oscillations between two mutual excitatory cells could be stopped by a slow-tailed hyperpolarizing current pulse into one cell or a slow-tailed depolarizing pulse into the other.

ULTRASTRUCTURAL STUDY OF THE NEUROSECRETORY GRANULES AND CRUSTACEAN HYPERGLYCEMIC HORMONE (CHH) IMMUNOLOCALIZATION IN THE SINUS GLAND OF HOMARUS GAMMARUS

ABSTRACT Seven different types of neurosecretory granules have been observed in the axon terminals of the sinus gland of the adult female lobster Homarus gammarus. They were discriminated through morphometrical and morphological criteria such as size, shape, frequency of occurrence, electron density, and axon-matrix density. Each size distribution followed a single Gaussian-type distribution. Each axon terminal contained I type of granule. The mean granule diameter ranged from 50 nm (type 1) to 161 nm (type 7). Type 6 and type I axon terminals were, respectively, the most and least frequent. An immunopositive reaction against an anti-Homarus americanus CHH was detected in the 2 largest types of granules: type 6 (mean diameter, 128 nm) and type 7 (mean diameter, 161 nm).

The mechanism of the colour shift of astaxanthin in α-crustacyanin as investigated by 13C MAS NMR and specific isotope enrichment

Abstract

Within‐burrow behaviour of juvenile European lobstershomarus gammarus(L.)

The behaviour of juvenile European lobsters (Homarus gammarus (L.)) in artificial burrows was observed in the laboratory to determine features of within‐burrow behaviour likely to be important in their survival and well‐being during the early benthic phase of life. Burrow construction methods and within‐burrow behaviour of individually held, hatchery reared, juvenile lobsters (12 to 20 mm CL) in mid‐intermoult were observed in clear plastic aquaria half filled with cohesive mud taken from Newcastle Bay. Eleven separate behaviour categories were identified although it was found that most activities did not occur on their own or, necessarily, in one particular location. Behaviour categories included pleopod fanning, cleaning, food burying and retrieval, feeding, substrate probing and picking, sieving and moving substrate and resting. Factors affecting burrow occupancy and the durations of selected activities inside the burrow were burrow chamber size, number of entrances, water flow, moulting and hunger. Hu...

Nature and metabolism of carotenoid pigments during the embryogenesis of the European lobster Homarus gammarus (Linné, 1758)

Abstract The carotenoid concentration of the whole developing egg of the lobster Homarus gammarus remains unchanged during the embryogenesis. The decrease of pigment amounts in the vitellin mass corresponds to the transfer of carotenoids to the forming embryo. Esterified astaxanthin (mono and diester forms) appear during the early metanauplius stage EI 90. Unesterified astaxanthin is the main pigment occurring in the vitellus. Esterified forms were found to increase whereas free astaxanthin decreases up to hatch. The esterification of astaxanthin permits the storage of pigment in the tissues as an adaptative feature related to the formation of the embryo.

Modulation of a Neural Network by Physiological Levels of Oxygen in Lobster Stomatogastric Ganglion

Although a large body of literature has been devoted to the role of O2 in the CNS, how neural networks function during long-term exposures to low but physiological O2 partial pressure (PO2) has never been studied. We addressed this issue in crustaceans, where arterial blood PO2 is set in the 1-3 kPa range, a level that is similar to the most frequently measured tissue PO2 in the vertebrate CNS. We demonstrate that over its physiological range, O2 can reversibly modify the activity of the pyloric network in the lobster Homarus gammarus. This network is composed of 12 identified neurons that spontaneously generate a triphasic rhythmic motor output in vitro as well as in vivo. When PO2 decreased from 20 to 1 kPa, the pyloric cycle period increased by 30-40%, and the neuronal pattern was modified. These effects were all dose- and state-dependent. Specifically, we found that the single lateral pyloric (LP) neuron was responsible for the O2-mediated changes. At low PO2, the LP burst duration increased without change in its intraburst firing frequency. Because LP inhibits the pyloric pacemaker neurons, the increased LP burst duration delayed the onset of each rhythmic pacemaker burst, thereby reducing significantly the cycling frequency. When we deleted LP, the network was no longer O2-sensitive. In conclusion, we propose that (1) O2 has specific neuromodulator-like actions in the CNS and that (2) the physiological role of this reduction of activity and energy expenditure could be a key adaptation for tolerating low but physiological PO2 in sensitive neural networks.

Ageing the European lobster Homarus gammarus by the lipofuscin in its eyestalk ganglia

Ageing the European lobster Homarus gammarus by the lipofuscin in its eyestalk ganglia

Dopamine in the lobster Homarus gammarus: II. Dopamine-immunoreactive neurons and development of the nervous system.

Dopamine-immunoreactive neurons were revealed in lobster embryos, larvae, and postlarvae, and staining patterns were compared to neuronal labeling in the juvenile lobster nervous system (Cournil et al. [1994] J. Comp. Neurol. 344:455-469). Dopamine immunoreactivity is first detected by midembryonic life in 35-40 neuronal somata located anteriorly in brain and subesophageal ganglion. When the lobsters assume a benthic life during the first postlarval stage, an average of 58 cell bodies are labeled. The acquisition of dopamine in lobster neurons is a protracted event spanning embryonic, larval, and postlarval life and finally reaching the full complement of roughly 100 neurons in juvenile stages. Some of the dopaminergic neurons previously identified in the mature nervous system, such as the paired Br cells, L cells, and mandibular cells, are labeled in embryos and persist throughout development. In contrast, other neurons stain transiently for dopamine during the developmental period, but, by the adult stage, these neurons are no longer immunoreactive. Such transiently labeled neurons project to the foregut, the thoracic dorsal muscles, the neurohormonal pericardial plexus, and the pericardial pouches. It is proposed that these neurons are alive and functioning in adult lobster but that dopamine levels have been abolished, providing that neurotransmitter status is a dynamic, changing process.

Evolution of carotenoid metabolic capabilities during the early development of the European lobster Homarus gammarus (Linné, 1758)

The quantification of carotenoids during the early developmental stages of the European lobster Homarus gammarus, indicates a rapid decrease of pigment concentration, occurring immediately after hatching. Conversely, the carotenoid amount of the individual increases progressively at the end of larval stage I, as a result of an enhanced feeding activity. Free astaxanthin represents the bulk of carotenoids of the unhatched embryo ( metanauplius), whereas larval, post-larval and juvenile stages exhibit the typical adult carotenoid pattern, in which astaxanthin esterified forms (diester and monoester) appear preponderant. The Artemia strain used as food material is not found to contain astaxanthin, while important amounts of canthaxanthin are observed; nevertheless, this carotenoid is not detected in the larvae, indicating that metabolic transformation capabilities are already occurring in freshly hatched individuals.

Functional differentiation of adult neural circuits from a single embryonic network

The stomatogastric nervous system (STNS) of adult lobsters and crabs generates a number of different rhythmic motor patterns which control different regional movements of the foregut. Since these output patterns are generated by discrete neural networks that, in the adult, are well characterized in terms of synaptic and cellular properties, this system constitutes an ideal model for exploring the mechanisms underlying the ontogeny of neural network organization. The foregut and its rhythmic motor patterns were studied in in vitro STNS nerve-muscle preparations of the embryo and different larval stages of the lobster Homarus gammarus. The development of Homarus comprises a long embryonic stage in ovo followed by three pelagic larval stages prior to the onset of benthic life. During these stages the foregut itself develops slowly from a simple ectodermal invagination that occurs in the embryo. During successive larval stages it progressively acquires all the specialized structures and shape of the adult foregut. In contrast, the STNS is morphologically recognizable at early embryonic stages. In all recorded stages the STNS spontaneously expresses rhythmic motor activity. During development, this activity is progressively restructured, beginning with a single rhythmic motor pattern in the embryo where all the stomodeal muscles are strongly coordinated. In subsequent stages, however, this single pattern is progressively subdivided to give rise eventually to the three discrete rhythmic motor patterns characteristic of the adult STNS. Our data suggest that rather than a dismantling of redundant embryonic and larval neural networks, the different adult networks emerge as a progressive partitioning of discrete circuits from a single embryonic network.

CARBOHYDRATE DIGESTION IN THE EUROPEAN LOBSTER HOMARUS GAMMARUS (L.)

ABSTRACT The ability of lobsters to utilize dietary carbohydrates is dependant upon the nature and amount of carbohydrases present in these crustaceans. Since this is a potential species for culture, a knowledge of its ability to digest carbohydrates could usefully be applied in the formulation of inert diets. The aim of this study was to identify the activities present in the gut and to assess the digestibility of physically modified starches using midgut-gland extracts. A range of carbohydrase activities including a-amylase (EC 3.2.1.1), maltase (EC 3.2.1.20), α-glucosidase (EC 3.2.1.20), β-glucanase (EC 3.2.1.39), β-glucosidase (EC 3.2.1.21), α- and β-galactosidases (EC 3.2.1.22 and EC 3.2.1.23) were detected in the midgut gland and in the gastric juice of the European lobster Homarus gammarus. Optimal activity for the above enzyme activities was in the pH range of 4.5-5.5 and highest levels were generally located in the gastric contents. α-Glucans were more readily digested than β-glucans; hydrolysis of pentosans was minimal and chitin was poorly hydrolyzed. Polysaccharides and disaccharides were well digested by gastric extracts, whereas the predominant digestive capacity of the midgut gland was toward disaccharides. Molecular weights of the midgut gland a-amylase and maltase activities were estimated by gel-filtration to be approximately 21 kDaltons and 63 kDaltons, respectively. Physical modification of starch granules enhanced their susceptibility to digestion by midgut-gland extracts and therefore pretreatment of dietary starches may be considered in order to increase their nutritional value in inert aquaculture diets.

A rhythmic modulatory gating system in the stomatogastric nervous system of Homarus gammarus. III. Rhythmic control of the pyloric CPG.

1. Two modulatory neurons, P and commissural pyloric (CP), known to be involved in the long-term maintenance of pyloric central pattern generator operation in the rock lobster Homarus gammarus, are members of the commissural pyloric oscillator (CPO), a higher-order oscillator influencing the pyloric network. 2. The CP neuron was endogenously oscillating in approximately 30% of the preparations in which its cell body was impaled. Rhythmic inhibitory feedback from the pyloric pacemaker anterior burster (AB) neuron stabilized the CP neuron's endogenous rhythm. 3. The organization of the CPO is described. Follower commissural neurons, the F cells, and the CP neuron receive a common excitatory postsynaptic potential from another commissural neuron, the large exciter (LE). When in oscillatory state, CP in turn excites the LE neuron. This positive feedback may maintain long episodes of CP oscillations. 4. The pyloric pacemaker neurons follow the CPO rhythm with variable coordination modes (i.e., 1:1, 1:2) and switch among these modes when their membrane potential is modified. The CPO inputs strongly constrain the pyloric period, which as a result may adopt only a few discrete values. This effect is based on mechanisms of entrainment between the CPO and the pyloric oscillator. 5. Pyloric constrictor neurons show differential sensitivity from the pyloric pacemaker neurons with respect to the CPO inputs. Consequently, their bursting period can be a shorter harmonic of the bursting period of the pyloric pacemakers neurons. 6. The CPO neurons seem to be the first example of modulatory gating neurons that also give timing cues to a rhythmic pattern generating network.

A rhythmic modulatory gating system in the stomatogastric nervous system of Homarus gammarus. I. Pyloric-related neurons in the commissural ganglia.

1. Operation of the pyloric neural network in the crustacean stomatogastric ganglion (STG) depends on constant firing of modulatory inputs from anterior ganglia. We have identified two bilaterally symmetrical pairs of these inputs in the commissural ganglia (COGs) of the European rock lobster Homarus gammarus. During operation of the pyloric CPG, they fired in pyloric time, out of phase with the pyloric pacemakers. 2. One of the pair was the commissural pyloric (CP) neuron and the other was homologous to the P neuron described in the spiny lobster Panulirus interruptus. We describe their morphology and location in the COG. The CP neuron projected to the STG via the superior esophageal nerve (son) and the stomatogastric nerve (stn), whereas the P neuron projected via the inferior esophageal nerve (ion) and stn. 3. To determine the total number of commissural neurons projecting to the STG, we used cobalt and Lucifer yellow backfilling from their cut axons in the stn. With the ion cut, there were between 8 to 12 labeled somata in each COG including CP cell body, whereas only 2 somata (including P) were labeled with the son cut. Among these neurons, CP and P appeared to be the only commissural neurons that fired in pyloric time and projected in the STG on the pyloric network. 4. The CP neuron produced monosynaptic excitatory postsynaptic potentials (EPSPs) on the pyloric dilator (PD), lateral pyloric (LP), and inferior cardiac (IC) neurons, whereas the P neuron produced monosynaptic EPSPs on all pyloric motoneurons but IC. The P neuron was gamma-aminobutyric acid immunoreactive, and the P-derived EPSPs in pyloric neurons were reversibly blocked by bicuculline, picrotoxin, and D-tubocurarine. 5. The CP and P neurons were electrically coupled, and modification of membrane potential in either one of them appreciably changed the firing frequency of the coupled neuron. 6. A negative-feedback loop from the pyloric anterior burster (AB) interneuron provoked simultaneous rhythmic inhibitions in the P and CP neurons. Together with the electrical coupling, the rhythmic inhibition contributed to synchronize firing of the two commissural neurons. 7. The following papers in the series of describe the modulatory and rhythmic control exerted by the P and CP neurons over the pyloric pattern generator.

Dynamic construction of a neural network from multiple pattern generators in the lobster stomatogastric nervous system

In the stomatogastric nervous system (STNS) of the lobster Homarus gammarus, the rhythmic discharge of a pair of identified modulatory neurons (PS cells) is able to construct de novo a functional network from neurons otherwise belonging to other functional networks. The PS interneurons are electrically coupled and possess endogenous oscillatory properties that can be activated synaptically by stimulation of an identified sensory pathway. PS neurons themselves project synaptically onto the three major neural networks (esophageal, gastric mill, and pyloric) of the STNS. When a PS is rhythmically active in vitro, either spontaneously (rarely) or in response to direct stimulation, it dramatically restructures the otherwise independent activity patterns of all three target networks. This functional reconfiguration elicited by a single cell does not rely on changes in neuronal allegiance to pre-existing circuits, or on a simple merger of these different circuits. Rather, PS is responsible for the creation of an entirely new motor rhythm in that, via its widespread synaptic connections, the interneuron is able to subjugate the ongoing activity of the three STNS circuits and selectively appropriate individual elements to its own intrinsic rhythm. In addition, PS excites motor neurons that innervate dilator muscles of a valve situated between the esophagus and the stomach. The reorganization of the regional foregut motor rhythms by the interneuron is therefore coordinated to the opening of this valve, which itself carries sensory receptors that have been found to activate bursting in PS. Our data suggest that the role of PS in massively restructuring stomatogastric output is to generate a unique motor pattern appropriate for swallowing-like behavior. In a wider context, moreover, the results demonstrate that a neural network may not exist as a predefined entity within the CNS, but may be dynamically assembled according to changing behavioral circumstances.

Suspension feeding in adult Nephrops norvegicus (L.) and Homarus gammarus (L.) (decapoda)

Suspension feeding in adults of the Norway lobster Nephrops norvegicus (40–74 g) and the European lobster Homarus gammarus (280–350 g) was tested in experiments offering planktonic food items of different sizes from 200 to 600 μm and measuring the clearing capacity. Both lobster species were found to effectively clear water of food particles comprising nauplii of the brine shrimp Artemia salina of about 600 μm in size. These were reduced to 50% of the initial concentration within 5 h and to 90% within 12 h. When N. norvegicus was offered food particles averaging 200 μm, a significant reduction in average size occurred, indicating that the minimum retention size is around 200 μm. Fluorescently dyed Artemia salina were recovered in the stomach and intestine of lobsters proving that the filtered particles are passed to the digestive tract. Results from other experiments, using the blood pigment (haemocyanin) concentration as an index of nutritional state, indicated that the lobsters can get some nutritional advantage from suspension feeding. Suspension feeding in larger decapods has not been described previously, so the significance of this finding is discussed with respect to changes in behavioural and ecological role.

Accumulation of 241Am in subcellular structures of the hepatopancreas of the lobster Homarus gammarus

Accumulation of 241Am in subcellular structures of the hepatopancreas of the lobster Homarus gammarus

Temperature-specific rates of embryonic development of the European lobster Homarus gammarus (L.)

Berried Homarus gammarus (L.) females were reared at three constant temperatures (10, 15 and 20°C), and the rates of development of their embryos monitored by measuring embryonic eye index according to Perkins. An equation relating the increase in eye index to temperature was established, yielding the estimated time to hatch at different temperatures. It may be used to approximate the rate of hatch according to rearing temperature in H. gammarus.