THE NEURAL ARCHITECTURE OF THE SEA ANEMONE MIMETR1DIUM CRYPTUM

Mimetridium cryptum is a slender, elongated, New Zealand seaanemone. It shows fast contractions in the retractor musclesof its mesenteries, oral disc radial muscles, and tentacle longitudinalmuscles. The nervous system shows considerable regional differentiationin orientation of neurons, range of diameters of nerve fibers,and density of nerve net. Fast-contracting muscles are overlainby relatively dense nerve net, with many nerve fibers of morethan 2 ,µ diameter; slow-contracting muscles are overlainby a sparse nerve net whose nerve fibers are about 1µin diameter. A tendency for nerve fibers to run parallel ismarked in some regions. Individual neurons may run from onestructure to another, and even pass from the endoderm of themesenteries to the ectoderm of the oral disc.     

The fine structure of granular amoebocytes from the gonads of the sea anemoneActinia fragacea (Cnidaria: Anthozoa)

Summary The structure of granular amoebocytes of the intertidal sea anemoneActinia fragacea (Cnidaria: Anthozoa) has been investigated using the electron microscope. Cells from the gonads of large, intact individuals were studied in most detail, but other regions of the anemone were also examined. The amoebocytes are cells of variable appearance which are widely distributed both in the mesogloea and in the epithelial cell layers. They contain numbers of characteristic dense granules, which may enclose spherical cores of greater or lesser electron density. They also contain rough endoplasmic reticulum, Golgi apparatus and a range of inclusions, some of which may have lysosomal origins. They may contain extensive deposits of glycogen, and usually smaller quantities of lipid droplets. They may take on a variety of forms, depending partly on their location within the various types of mesogloea and epithelia. The amoebocytes appear to be motile and phagocytic, and may also be involved in the storage and transport of glycogen. They are involved with gametogenesis, both during the development of the oocytes and spermatogenic cysts and during the resorption of degenerating gametes. Their possible role in the secretion or maintenance of the mesogloea remains uncertain. No evidence of amoebocytes differentiating into other cell types was obtained.     

Nervous control of light responses in the sea anemone, Calamactis praelongus.

1. The burrowing sea anemone, Calamactis praelongus, responds to light with local, non-nervous contractions of the column. There are also more extensive responses of the column and retractor muscles co-ordinated by nerve net pulses (NNP's) under pacemaker control. 2. NNP's occur in at least two types of bursts and in sequences which sometimes indicate a rotating site of pulse initiation. 3. Light-evoked NNP sequences can be tape recorded and used later to drive a stimulator to reproduce the original sequences in the same or different anemones, evoking muscular responses which approximate the originals. This technique separates the pacemaker-directed component of the light response from the local effects of light stimulation. 4. Isolated circular and parietal muscles contract slowly when stimulated by light or excited indirectly by NNP's. Retractor muscles are insensitive to light but produce rapid contractions when excited by closely spaced light-evoked NNP's. 5. A model for light responses is proposed which incorporates the characteristics of isolated muscles and intact anemones.     

Neurobiology of Polyorchis. II. Structure of effector systems

The gross and fine morphology of the major effector systems in the anthomedusan, Polyorchis penicillatus, is described and discussed in relation to the known physiological and behavioral properties of these systems. Swimming is controlled by an anastomosing network of giant neurons within the inner nerve ring and radial nerves. Although these neurons may be coupled by gap junctions it is likely that they form a syncytium. The photosensitivity of the “giants” is attributed to reflexive membranes within the cytoplasm. Giant neurons act as both the pre- and postsynaptic cell when forming synapses with other neurons of the inner nerve ring. Neuromuscular synapses between “giants” and the striated swimming muscle are found around the margin and along the radii. Swimming muscle cells are connected laterally by gap junctions and end-to-end by desmosomes which are sometimes elaborated with extra-thick filaments. Unstriated sphincter and radial muscles, the major muscles associated with crumpling, are both greatly folded over mesogloeal ridges and have processes that cross the mesogloea to contact the ring and radial canals, respectively. Synapses or other sites that might be responsible for exciting these muscles during crumpling have not been found. The ability of the endodermal lamella and canals to propagate action potentials can be accounted for by the numerous gap junctions that are seen in these tissues. The precise location where excitation is transferred to the nervous system to initiate crumpling is not known but epithelial bridges crossing the mesogloea are likely routes. Synapses between neurons originating in the outer nerve ring and tentacle longitudinal muscle can account for the control of tentacle length. Neurons of the outer nerve ring also synapse onto velar, radial fibers and the sphincter muscle. The inner and outer nerve rings have nervous connections. The organisation of the outer nerve ring and the arrangement of nerves within the endodermal plexus is described. A diagram showing the major connections and interactions of components of the effector systems is presented.     

消化管括约肌部VIP免疫活性神经细胞分布

应用免疫组织化学方法研究了食管下部,幽门和回盲部肌间神经丛内ＶＩＰ免疫活性神经细胞的分布。ＶＩＰ免疫活性神经细胞在括约肌部比相邻部位数量多。并用Ｏｐｅｎ－ｔｉＰ法测量了刺激迷走神经后食管下段括约肌部压力的变化。用高阈值参数电刺激迷走神经引起预先投给阿托品的狗食管下段括约肌部压力的降低;这样条件下延长迷走神经刺激引起肌间神经丛内ＶＩＰ免疫活性神经细胞数量明显增加。由此结果提示含有或产生ＶＩＰ的神经细胞可能接受迷走神经的控制。由于刺激节前迷走神经纤维可能作用到这些细胞。     

THE CERIANTHAR1AN NERVOUS SYSTEM

Evidence supporting the presence of nerve cells in the columnand tentacles of Pacliycerianthiis is described. G. F. Gwilliamhas shown that electrical stimuli can be transmitted to theectodermal muscle by the intact epithelium and subepithelialnetwork of the ectoderm of the column. In these preparationsthe ectodermal muscle, mesogloea, and endoderm were cut. Incontrast, preparations in which the ectodermal muscle has beenleft intact and the epithelium and subepithelial network cutdo not show such transmission. The author and Gwilliam have independently used different silverstain methods to demonstrate large cells, piobably nerve cells,with cell bodies in the base of the epithelium and with fibersrunning into the subepithelial network. The author has foundsimilar bipolar cells in the tentacles and column by using macerationtechniques. These cells are compared with other cell types foundin the tentacles.     

Identification of a new member of the GLWamide peptide family: physiological activity and cellular localization in cnidarian polyps

KPNAYKGKLPIGLWamide, a novel member of the GLWamide peptide family, was isolated from Hydra magnipapillata. The purification was monitored with a bioassay: contraction of the retractor muscle of a sea anemone, Anthopleura fuscoviridis. The new peptide, termed Hym-370, is longer than the other GLWamides previously isolated from H. magnipapillata and another sea anemone, A. elegantissima. The amino acid sequence of Hym-370 is six residues longer at its N-terminal than a putative sequence previously deduced from the cDNA encoding the precursor protein. The new longer isoform, like the shorter GLWamides, evoked concentration-dependent muscle contractions in both H. magnipapillata and A. fuscoviridis. In contrast, Hym-248, one of the shorter GLWamide peptides, specifically induced contraction of the endodermal muscles in H. magnipapillata. This is the first case in which a member of the hydra GLWamide family (Hym-GLWamides) has exhibited an activity not shared by the others. Polyclonal antibodies were raised to the common C-terminal tripeptide GLWamide and were used in immunohistochemistry to localize the GLWamides in the tissue of two species of hydra, H. magnipapillata and H. oligactis, and one species of sea anemone, A. fuscoviridis. In each case, nerve cells were specifically labeled. These results suggest that the GLWamides are ubiquitous among cnidarians and are involved in regulating the excitability of specific muscles.     

Species specificity in cell-substrate interactions in medusae

A new system is described for the study of ECM-tissue interactions, using the ECM (called mesogloea) of various cnidarians and isolated striated muscle and endodermal tissue of jellyfish. The mesogloea consists mainly of water and collagen. It is present in all cnidarians and can be isolated without enzyme treatment. It can be used as a substrate to which cells and tissues adhere and on which they spread and migrate. Tissues of striated muscle and endoderm adhere and spread not only on mesogloea from regions they normally cover, but also from other regions of the animal. However, adhesion and spreading are highly species-specific. Species-specific adhesion is found throughout the whole mass of mesogloea even at regions where cells do not occur naturally. The cell adhesion factor can be extracted from the mesogloea so that the mesogloea no longer shows any cell adhesion properties. The extract consists mainly of a cysteine-containing collagen.     

Le système nerveux des cténaires

Summary Ultrastructural evidence is given of the occurrence of nervous elements in the mesoglea of Ctenophores based on the presence of the typical synapses of this phylum.In Beroids, nervous fibers from the ectodermal nerve-net cross the epithelial basal membrane and run through the mesoglea; they are devoid of any ensheathing cell. These neurites build highly differentiated synapses upon the muscles and upon peculiar cells, tentatively named mesenchymal cells.In Cydippids, nerve fibers and nerve cell-bodies have been observed in the mesoglea of the tentacles. The mesogleal core of each tentacle contains mesenchymal cells and a thick strand of neurons and neurites, forming a kind of elongated ganglion. Neurites of either the axial neurones or the epithelial nerve-net neurones form numerous radial nerve strands across the tentacular muscles. Interneural, neuro-muscular and neuro-mesenchymal junctions are very frequent in the tentacle.As far as the organization of the mesoglea is concerned, the Ctenophora thus appear closer to Turbellaria than to Cnidaria.

Ce travail a bénéficié de la collaboration technique de Madame J. Amsellem que nous remercions vivement.     

Jellyfish mesogloea collagen. Characterization of molecules as alpha 1 alpha 2 alpha 3 heterotrimers

The mesogloea collagen of a primitive animal, the jellyfish Stomolophus nomurai, belonging to the class Scyphozoa in the Coelenterata, was studied with respect to its chain structure. Most of the mesogloea collagen was solubilized by limited digestion with pepsin and isolated by selective precipitation at 0.9 m NaCl in 0.5 M acetic acid. Upon denaturation, the pepsin-solubilized collagen produced three distinct alpha chains, alpha 1, alpha 2, and alpha 3, in comparable amounts which were separable by CM-cellulose chromatography. The nonidentity of these alpha chains was confirmed by amino acid and carbohydrate analyses and peptide mapping. Furthermore, the introduction of intramolecular cross-links into native molecules by formaldehyde yielded a large proportion of gamma 123 chain with chain structure alpha 1 alpha 2 alpha 3, as judged by chromatographic behavior and peptide maps. We concluded that mesogloea collagen is comprised of alpha 1 alpha 2 alpha 3 heterotrimers and is chemically like vertebrate Type V collagen. On the other hand, sea anemone mesogloea collagen from the class Anthozoa was previously reported to comprise (alpha)3 homotrimers (Katzman, R. L., and Kang, A. H. (1972) J. Biol. Chem. 247, 5486-5489). On the basis of these findings, we assume that alpha 1 alpha 2 alpha 3 heterotrimers arose in evolution with the divergence of Scyphozoa and Anthozoa.     

THE FINE STRUCTURE OF NERVE CELL BODIES AND THEIR MYELIN SHEATHS IN THE EIGHTH NERVE GANGLION OF THE GOLDFISH

The eighth cranial nerve ganglion consists of bipolar nerve cell bodies each occupying part of an internodal segment. The perikaryal sheaths range from a single layer of Schwann cell cytoplasm on the smallest cells to typical thick compact myelin on the largest. On most perikarya, the sheath displays an intermediate form, consisting of multiple layers of Schwann cell cytoplasm (loose myelin), or of loose and compact myelin continuous with each other. Internodes beyond the one containing the cell body bear only compact myelin. In loose myelin the thickness of each layer of Schwann cell cytoplasm is about 100 A. It may be much greater (~ 3000 A) particularly in the outermost layers of the sheath, or the cytoplasm may thin and even disappear with formation of a major dense line. The cytoplasmic layers are separated from each other by a light zone, 40 to 200 A wide, which in its broader portions may contain an intermediate line. Desmosomes sometimes occur between lamellae. In addition to the usual organelles, the perikaryal cytoplasm contains granular and membranous inclusions. Large cells covered by compact myelin have a consistently higher concentration of neurofilaments, and some of the largest cells, in addition, show a reduced concentration of ribosomes. The functional significance and possible origins of perikaryal myelin sheaths are discussed.     

Innervation of the anterior byssal retractor muscle in Mytilus edulis L.

Summary Studies on the intrinsic innervation of the anterior byssal retractor muscle (ABRM) in Mytilus edulis L. were continued at the ultrastructural level. Electron micrographs show nerve processes ensheathed by glio-interstitial cells running between muscle fibers. The glio-interstitial cells may represent all the types of osmiophilic cells previously described by the light microscopic ZIO technique in the anterior byssal retractor muscle.     

PURIFICATION AND EFFECT OF THE NEUROTOXIN FROM THE SEA ANEMONE PARASICYONIS ACTINOSTOLOIDES

— Three toxic components were isolated from the sea anemone, Parasicyonis actinostoloides. Among these components a main component had an effect on the neuromuscular transmission of the crayfish. The component was purified and found to be a basic polypeptide having a molecular weight of about 2000. Amplitudes of excitatory and inhibitory poslsynaptic potentials were increased by the toxin. It was found that the quantum content increased markedly in the excitatory synapse. The action of the toxin remained for a long time after the nerve–muscle preparation was thoroughly washed. These results suggest that the toxin has an effect on the presynaptic nerve.     

CAPABILITIES OF THE GOELENTERATE BEHAVIOR MACHINE

Animals are essentially predatory behavior machines. So alsoare insectivorous plants which have developed raptorial feedingdevices. Diploblastic and triploblastic animals meet the specificationof such machines in different ways. In the Cnidaria both muscleand nerve-net seem organised on the basis of two-dimensionalcontinuous sheets with local specialization. The condition issimplest in Anthozoa: in Scyphozoa, and still more in Hydrozoa,there are further complications. This simple picture of the Anthozoan nerve-net meets difficulties.Quick and slow contractions of the same muscle sheet are infact operated by the same nerve-net. The slow contraction involvesmuscle-conduction and recruitment. A method of directly observingthis is described. No complete explanation is yet forthcomingfor reciprocal inhibition. The preservation of functionallysignificant shape seems to require proprioceptive machinerynot yet discovered. It now seems well-established that both through-conduction andthe original notion of interneural facilitation are valid elementsin simple reflex responses. Knowledge of the importance of rhythmicphasic activity has, however, greatly increased in coelenteratesgenerally. Many of these sequences of rhythmic activity seemto be based on modifications of the similar pattern sequencesto meet different functional needs. Particularly in connection with these phasic activities, multipleaction potentials both in response to stimuli and by spontaneousoccurrence have been demonstrated. In Calliactis, 30% of recordsto threshold stimuli show evidence of multiple impulses. Thereis reason to associate such repetitive discharges with multipolarganglion cells. The relation of these multiple discharges tothe functional behavior is not always apparent. Complication of behavior in coelenterates is charactically onthe motor side. Contrasted with triploblastic animals with probablythe same order of number of nervecells (roughly 10⁵), thereis a striking difference in the sensory equipment: exteroceptiveinformation about the objects of the real world is lacking.A hunting-wasp with about that number of cells acts as thoughit had abstracted a world-model of objects, analogous to ourown model, from the information received. But an anthozoan showsno evidence of that power. The importance of key-stimuli inanthozoan behavior is significant in connection with this. Thesedeficiencies in complex behavior may be related to the topographicaldifficulty of complex correlation of sensory input in a two-dimensionalnet. The difficulty is easily overcome in the three-dimensionalnets of triploblasts. Nevertheless, recent studies of conductionin the two-dimensional coelenterate net show striking ‘pre-adaptive’features analogous to those of triploblast central nervous networksupon which sensory abstraction of information in these depends.     

THE INNERVATION AND PHYSIOLOGY OF THE EXTRINSIC BUCCAL RETRACTOR MUSCLES OF PHILINE APERTA (LINNAEUS)

Two buccal mass retractor muscles of Philine are innervatedby at least 4 excitatory motoneurons, whose cell bodies liein the buccal and the cerebral ganglia. The muscle fibres respondto action potentials generated in the motoneurons or their axonswith excitatory junction potentials (ejps), each of which isfollowed by a small twitch-like contraction. Both the electricaland mechanical responses facilitate and summate with repetitivestimulation. A large ventrally located cerebral neuron (VGC) inhibits tensiondevelopment in the muscle by reducing the amplitude of the excitatoryjunction potentials from and identified buccal motoneuron. Acetylcholinereversibly depolarises and causes tonic contraction of the muscles.This action is partially antagonised by hexamethonium, whichalso blocks the ejps from two axons in the buccal and one inthe pedal nerve 9. 5-Hydroxytryptamine potentiates the ejp fromthe identified buccal motoneuron and enhances the rate of relaxation.Histamine reduces the amplitude of the presumed cholinergicbuccal nerve ejps, but does not affect the hexamethonium sensitiveejp in the pedal nerve 9. In this respect its action resemblesthat of the ventral giant cell.     

Changes in the distribution of filament-containing septate junctions as coelenterate myoepithelial cells change shape

This paper describes the redistribution of septate junctions during an increase in diameter of myoepithelial cells from mesenteries of the sea anemone Metridium senile (L). Each septum was composed of a filament core, 9.5-10.2 nm in diameter, which had a double row of lateral projections from each side to the adjacent cell membrane. Septa were arranged in patches in which neighbouring septa lay parallel, 28-33 nm apart. When anaesthetized mesenteries were stretched, myoepithelial cell layers decreased from a mean of 32 to 8 micron thick; each cell shortened and its apical diameter increased. The integrity of the septate junctions was, however, maintained. The mean perimeter of septate junctions, corresponding to that of the cells, increased from 20 to 31 micron; mean depth decreased from 3.7 to 2.1 micron. There was no significant change in spacing between septa. Patches of septa, free to move in a fluid matrix of junction cell membranes, may form mobile attachment sites between cells, thus allowing those cells to change shape. Number and distribution density of microvilli decreased when cell diameter increased. This implies that the microvilli contribute membrane to the cell surface as its surface area increases. Gastrodermal cells are compared with epidermal cells that do not undergo dramatic changes in diameter.     

<Emphasis Type="Italic">In vivo</Emphasis> studies of development of the main functional systems in the heteronemertean pilidium larva

There is performed in vivo morphological study of the White Sea heteronemertines belonging to the type of Pilidium pyramidale (conussoidale). Based on the layer-by-layer microshooting with subsequent computer processing, development of the pilidium digestive, nervous, and muscle systems is described from the stage following at once the gastrula till the premetamorphosis larva. Peculiarities of structural organization of the main functional systems are revealed depending on the larva size and the stage of formation of imaginal discs. It is first shown that even in the not completely formed pilidium, neurons are located not only in envelopes and walls of the digestive tract, but also in the depth of cupola along the central muscle retractor. Their processes are distributed between the main body parts and organs by seeming to perform connections of the apical organ and central muscle retractor with the digestive tract, blades, and the nerve plexus of the cupola wall. In the digestive tract between pharynx and stomach in the formed pilidium, the sphincter is first revealed. It has been shown that in the course of larva development, the non-orderly arranged and poorly developed muscle fibers gradually form in the blade the fan-like, whereas in the cupola wall, the net-like structure.     

NERVOUS ORGANIZATION AND THE PROBLEM OF THE SYNAPSE IN ACTINIA EQUINA

The nervous system of Actinia equina was studied by routinehistological methods and by metallic impregnation techniques.Some preliminary results from electron microscopy are included. The organization of the nervous system of this species is morecomplex than that of other anthozoans; it consists of two interconnectednerve plexuses which are developed to differing degrees in variousparts of the body. These are: (1) a superficial (outer) plexuslying in the ectoderm, and (2) a deeper (inner) plexus constitutingthe main nerve net, lying in the mesoderm. The former is composedof bipolar and multipolar nerve cells, and the latter of multipolarcells. Receptor cells in the ectoderm make contact with fibersof the ectodermal plexus. Processes from the mesodermal plexusrun out to the muscle fibers. Connections between the receptor cells and the nerve processesof the superficial plexus and between the processes of the cteeperplexus and the muscle fibers appear to be of the discontinuous(synaptic) type. In the nerve nets themselves, although someconnections resembling synapses have been seen, most of thenerve elements stand in direct connection with one another,so that the system must be regarded as at least partly syncytial.Evidence is given for the growth of the nerve net, in step withthe general growth of the animal, by division of nuclei followedby their movement apart within the syncytium. The distribution of the nerve elements in various parts of thebody, the interconnections between these regions, and the cytologicalcharacteristics of the cells are described. Ways in which excitationcould pass from one part to another are discussed.