Cyclic Guanosine Monophosphate Modulates Locomotor Acceleration Induced by Nitric Oxide but not Serotonin in Central Pattern Generator Swim Interneurons.

Both nitric oxide (NO) and serotonin (5HT) mediate swim acceleration in the marine mollusk,  . In this study, we examine the role that the second messenger, cyclic guanosine monophosphate (cGMP), plays in mediating NO and 5HT-induced swim acceleration. We observed that the application of an analog of cGMP or an activator of soluble guanylyl cyclase (sGC) increased fictive locomotor speed recorded from Pd-7 interneurons of the animal's locomotor central pattern generator.

Pedal serotonergic neuron clusters of the pteropod mollusc, Clione limacina, contain two morphological subtypes with different innervation targets.

Each pedal ganglion of the pteropod mollusc Clione limacina contains a cluster of serotonin-immunoreactive neurons that have been shown to modulate contractions of the slow-twitch musculature of the wing-like parapodia, and contribute to swim accelerations. Each cluster has a variable number of neurons, between 5 and 9, but there is no significant difference between right and left ganglia. In experiments with electrophysiological recordings followed by dye-injection (carboxyfluorescein), the clusters were found to contain two subsets of neurons.

Organization of Buccal Cone Musculature in the Pteropod Mollusc .

The pteropod mollusc is a feeding specialist, preying on shelled pteropods of the genus . Specialized prey-capture structures, called buccal cones, are hydraulically everted from within the mouth to capture the prey. Once captured, the prey is manipulated so the shell opening is over the mouth of .

Tentacle Musculature in the Cubozoan Jellyfish Carybdea marsupialis.

The diploblastic cnidarian body plan comprising the epidermis and gastrodermis has remained largely unchanged since it evolved roughly 600 Ma. The origin of muscle from the mesoderm in triploblastic lineages is a central evolutionary question in higher animals. Triploblasts have three embryonic germ layers: the endoderm, mesoderm, and ectoderm, which develop into organs, muscle, and skin, respectively.

Control of vortex rings for manoeuvrability.

Manoeuvrability is critical to the success of many species. Selective forces acting over millions of years have resulted in a range of capabilities currently unmatched by machines. Thus, understanding animal control of fluids for manoeuvring has both biological and engineering applications.

Cnidarian Nerve Nets and Neuromuscular Efficiency.

Cnidarians are considered "nerve net animals" even though their nervous systems include various forms of condensation and centralization. Yet, their broad, two-dimensional muscle sheets are innervated by diffuse nerve nets. Do the motor nerve nets represent a primitive organization of multicellular nervous systems, do they represent a consequence of radial symmetry, or do they offer an efficient way to innervate a broad, two-dimensional muscle sheet, in which excitation of the muscle sheet can come from multiple sites of initiation? Regarding the primitive nature of cnidarian nervous systems, distinct neuronal systems exhibit some adaptations that are well known in higher animals, such as the use of oversized neurons with increased speed of conduction, and condensation of neurites into nerve-like tracts.

The search for ancestral nervous systems: an integrative and comparative approach.

Even the most basal multicellular nervous systems are capable of producing complex behavioral acts that involve the integration and combination of simple responses, and decision-making when presented with conflicting stimuli. This requires an understanding beyond that available from genomic investigations, and calls for a integrative and comparative approach, where the power of genomic/transcriptomic techniques is coupled with morphological, physiological and developmental experimentation to identify common and species-specific nervous system properties for the development and elaboration of phylogenomic reconstructions. With careful selection of genes and gene products, we can continue to make significant progress in our search for ancestral nervous system organizations.

Multiple conducting systems in the cubomedusa Carybdea marsupialis.

Acute responses to mechanical, electrical, and photic stimuli were used to describe neural conducting systems in the cubomedusan jellyfish Carybdea marsupialis underlying three behaviors: contractile responses of single tentacles, protective crumple responses, and alterations of swimming activity by the visual system. Responses of single tentacles consisted of tentacular shortening and inward pedalial bending, and were accompanied by bursts of extracellularly recorded spike activity that were restricted to the stimulated tentacle. With nociceptive stimuli delivered to the subumbrella or margin, all four tentacles produced similar responses in a crumple response.

Organization of the ectodermal nervous structures in medusae: cubomedusae.

At least two conducting systems are well documented in cubomedusae. A variably diffuse network of large neurons innervates the swim musculature and can be visualized immunohistochemically using antibodies against α- or β-tubulin. Despite the non-specificity of these antibodies, multiple lines of evidence suggest that staining highlights the primary motor networks.

Organization of the ectodermal nervous structures in jellyfish: scyphomedusae.

Antibodies to α- or β-tubulin and to the bioactive peptide FMRFamide were used to investigate the organization of the ectodermal nervous structures in five species of scyphomedusae. Within the swim system, morphological evidence, including a developmental sequence, suggests that the tubulin-immunoreactive nerve net in the subumbrella is the Giant Fiber Nerve Net (Motor Nerve Net) that directly activates the swim musculature, and the FMRFamide-immunoreactive nerve net is the Diffuse Nerve Net that serves a sensory function and also enhances swim muscle activity. Similar dual labeling was found in other structures, including those involved in feeding and protective reactions (pedalia and tentacles, radial strips of smooth muscle), and in the exumbrella, where the networks were associated with batteries of nematocysts.

Toward an organismal neurobiology: integrative neuroethology.

Overt behavior is generated in response to a palette of external and internal stimuli and internal drives. Rarely are these variables introduced in isolation. This creates challenges for the organism to sort inputs that frequently favor conflicting behaviors.

Changes in wingstroke kinematics associated with a change in swimming speed in a pteropod mollusk, Clione limacina.

In pteropod mollusks, the gastropod foot has evolved into two broad, wing-like structures that are rhythmically waved through the water for propulsion. The flexibility of the wings lends a tremendous range of motion, an advantage that could be exploited when changing locomotory speed. Here, we investigated the kinematic changes that take place during an increase in swimming speed in the pteropod mollusk Clione limacina.

Do jellyfish have central nervous systems?

The traditional view of the cnidarian nervous system is of a diffuse nerve net that functions as both a conducting and an integrating system; this is considered an indicator of a primitive condition. Yet, in medusoid members, varying degrees of nerve net compression and neuronal condensation into ganglion-like structures represent more centralized integrating centers. In some jellyfish, this relegates nerve nets to motor distribution systems.

A hyperpolarization-activated inward current alters swim frequency of the pteropod mollusk Clione limacina.

The pteropod mollusk, Clione limacina, exhibits behaviorally relevant swim speed changes that occur within the context of the animal's ecology. Modulation of C. limacina swimming speed involves changes that occur at the network and cellular levels.

Ultrastructure of the retinal synapses in cubozoans.

Cubomedusae (box jellyfish) are well known for strong directional swimming, rapid responses to visual stimuli, and complex lensed eyes comparable to those of more advanced multicellular animals. They possess a total of 24 eyes that are of four morphologically different types, yet little is known about the neural organization of their eyes. The eyes are located on ganglion-like structures called rhopalia.

Control of swimming in the hydrozoan jellyfish Aequorea victoria: subumbrellar organization and local inhibition.

The subumbrella of the hydrozoan jellyfish Aequorea victoria (previously classified as Aequorea aequorea) is divided by numerous radial canals and attached gonads, so the subumbrellar musculature is partitioned into subumbrellar segments. The ectoderm of each segment includes two types of muscle: smooth muscle with a radial orientation, used for local (feeding and righting) and widespread (protective) radial responses, and striated muscle with a circular orientation which produces swim contractions. Two subumbrellar nerve nets were found, one of which stained with a commercial antibody produced against the bioactive peptide FMRFamide.

Hexamethonium sensitivity of the swim musculature of the pteropod mollusc, Clione limacina.

Swimming in reduced electrophysiological preparations of the pteropod mollusc, Clione limacina, was blocked by bath application of hexamethonium even though pattern generator activity continued with this treatment. Neuromuscular recordings indicated that hexamethonium blocked synaptic input from Pd-3 and Pd-4 motoneurons to slow-twitch muscle cells, while connections from Pd-1A and Pd-2A motoneurons to fast-twitch muscle cells were variable in their response to hexamethonium-synaptic inputs were suppressed in most cases and occasionally blocked, but the latter only with high concentrations and long incubations. Acutely dissociated wing muscle cells showed a concentration-dependency in the percentage of contracted cells with bath application of acetylcholine, and this contractile activity was blocked in preparations that were first bathed in hexamethonium.

The role of postinhibitory rebound in the locomotor central-pattern generator of Clione limacina.

In animals, networks of central neurons, called central-pattern generators (CPGs), produce a variety of locomotory behaviors including walking, swimming, and flying. CPGs from diverse animals share many common characteristics that function at the system level, circuit level, and cellular level. However, the relative roles of common CPG characteristics are variable among different animal species, in ways that suit different forms of locomotion in different environmental contexts.

Neuromechanics: an integrative approach for understanding motor control.

Neuromechanics seeks to understand how muscles, sense organs, motor pattern generators, and brain interact to produce coordinated movement, not only in complex terrain but also when confronted with unexpected perturbations. Applications of neuromechanics include ameliorating human health problems (including prosthesis design and restoration of movement following brain or spinal cord injury), as well as the design, actuation and control of mobile robots. In animals, coordinated movement emerges from the interplay among descending output from the central nervous system, sensory input from body and environment, muscle dynamics, and the emergent dynamics of the whole animal.

The contribution of the pleural type 12 interneuron to swim acceleration in Clione limacina.

The pteropod mollusc, Clione limacina, swims by alternate dorsal-ventral flapping movements of its wing-like parapodia. The basic swim rhythm is produced by a network of pedal swim interneurons that comprise a swim central pattern generator (CPG). Serotonergic modulation of both intrinsic cellular properties of the swim interneurons and network properties contribute to swim acceleration, the latter including recruitment of type 12 interneurons into the CPG.

Muscle organization of the cubozoan jellyfish Tripedalia cystophora Conant 1897.

The musculature of the cubomedusa Tripedalia cystophora was investigated using immunohistochemical staining with an anti-actin antibody and histochemical staining with fluorescent phalloidin. The subumbrella is lined with a sheet of circular, striated muscle that is interrupted at the perradii, and by the nerve ring. The sheet is continuous with circular, striated muscle of the velarium, which turns radially on each face of the four velarial frenula.

Cellular Mechanisms Underlying Swim Acceleration in the Pteropod Mollusk Clione limacina.

The pteropod mollusk Clione limacina swims by dorsal-ventral flapping movements of its wing-like parapodia. Two basic swim speeds are observed-slow and fast. Serotonin enhances swimming speed by increasing the frequency of wing movements.