Ampulla Morphogenesis in Anural and Urodele Molgulid Ascidians

Vascular ampulla morphogenesis was studied in two anural-developing molgulids and one urodeledeveloping molgulid. In all three species, each juvenile developed one longer ampulla (termed the primary ampulla) and several shorter ampullae (termed secondary ampullae). Ampulla growth was accompanied by the formation of contraction rings that moved in a proximal to distal direction. Contraction ring formation was initiated by the epidermal cells situated in the proximal region of each ampulla. The formation of an expanding bubble-like region within each lumen preceded ring formation. These rings moved at approximately 120 μm/min. Rings were produced for several days until the ampullae retracted towards the body wall.
In all three species, hemoblast cells were evident at day 4 within the developing mantle sinus (hemocoel). Ampulla growth was studied by positioning chalk particles on the tunic surface near the tips of ampullae. During the growth phase, chalk particles moved towards the body of the zooid. This report is the first to describe contraction ring formation and the polarized transport of tunic components during ampulla morphogenesis in two anural ascidian species.     

THE MECHANISM OF THE NEPHRIDIAL APPARATUS OF PARAMECIUM MULTIMICRONUCLEATUM : II. The Filling of the Vesicle by Action of the Ampullae

Our recent analysis of the nephridial apparatus of Paramecium multimicronucleatum by high-speed cinematography (300 fps at X 250) indicates that before the water expulsion vesicle ("contractile vacuole") is completely voided of fluid during expulsion, the ampullae surrounding and confluent with the vesicle swell with fluid entering from their respective nephridial tubules. Once the membranes of the excretory pore at the base of the excretory canal (leading from the vesicle proper to the outside) have constricted and resealed the excretory pore, the up till then constricted injection tubules of the ampullae which conduct fluid to the vesicle open as waves of contraction along the coacervate gel around the ampulla and proceed along each ampulla from distal to proximal end. The coacervate gel around any one ampulla does not necessarily contract in phase with that of any other ampulla. Each ampulla acts independently. The fluid from the ampullae is thus pumped sequentially, but not in predetermined order, into the water expulsion vesicle, refilling and distending it. Our previous studies (Organ et al., 1968a) suggest that an actomyosinoid ATP-using mechanism may be functional in the ampullary contractions.     

Reception of millimeter-band electromagnetic radiation by the ampullae of Lorenzini of skates

During recording of impulse activity from single nerve fibers of electroreceptors of the ampullae of Lorenzini of skates, we studied the responses to electromagnetic radiation (EMR) at a frequency of 37–55 GHz and an intensity of 1–100 mW/cm².Exposure of the ampullar canal pore to EMR at an intensity of 1–5 mW/cm² and a distance of 1–10 mm evoked a transient increase in the frequency of low-threshold receptor activity (current threshold was 0.04–0.2 µA). An increase in EMR intensity by more than 8–10 mW/cm² produced, together with elevation of receptor activity, an inhibition due to a rise in temperature of 1–3°C in the region exposed. The phase of increase in frequency of activity was absent in high current-threshold receptors (0.3–2.0 µA) when exposed to EMR. The receptors responded to irradiation of the ampullar canal pore at a distance of 15–20 mm by an increase in discharge frequency for 20 min. Direct irradiation of the ampullae of Lorenzini induced only inhibitory responses in receptor cells regardless of their excitability.The results obtained indicate that the sensory receptors of vertebrates are sensitive to EMR. It is concluded that the excitatory effects are due to direct reception of EMR by electroreceptors, and the inhibitory effects are related to local heating of the Lorenzini ampullar pore.Neirofiziologiya/Neurophysiology, Vol. 25, No. 5, pp. 325–329, September–October, 1993.     

Functional anatomy of the valves in the ambulacral system of sea urchins (Echinodermata,Echinoida)

Summary The water vascular system of sea urchins is examined with special reference to the valves positioned between the radial vessel and the ampullae of the tube feet. The lips of the valve protrude into the ampulla. Thus the valve functions mainly like a check valve that allows the unidirectional flow of fluid towards the ampulla. Each ampulla-tube foot compartment acts as a semi-autonomous hydraulic system. The lumina of the ampulla and the tube foot are lined with myoepithelia except for the interconnecting channels that pierce the ambulacral plate. The contraction of the ampulla results in an increasing hydraulic pressure that protrudes the tube foot, provided that the valve is closed. The retraction of the tube foot results in a backflow of fluid independent of the condition of the valve. The lips of the valve are folds of the hydrocoel epithelium. The pore slit lies in the midline. The perradial faces of the lips are covered with the squamous epithelium of the lateral water vessel. The ampullar faces are specialized parts of the ampulla myoepithelium. Turgescent cells which form incompressible cushions take the place of the support cells. The valve myocytes run parallel to the pore slit and form processes that run along the base of the ampulla and the perradial channel up to the podial retractor muscle. The findings lead to the hypothesis of multiple control of the ampulla-tube foot system: (1) The mutual activity of the ampulla and the tube foot is indirectly controlled by the lateral and podial nerves which release transmitter substances that diffuse through the connective tissue up to the muscle layers. (2) A muscle-to-muscle conduction causes the simultaneous contraction of the ampulla or the podial retractor muscles. (3) The valve muscles are directly controlled by the processes of the valve myocytes which make contact with the podial retractor. In extreme conditions a backflow of hydrocoel fluid towards the radial water vessel occurs.     

Cutaneous mechanism of electroreceptor temperature sensitivity of the ampullae of Lorenzini

The potential difference on the receptor epithelium of the ampullae of Lorenzini and on the skin and also spike discharges of single electroreceptor nerve fibers in response to temperature stimulation of the region of the pores of the ampullae were studied in the Black Sea skateRaja clavata. Heating the skin in the region of the pore led to the appearance of a positive potential on the skin and on the epithelium of the ampulla, and to inhibition of spike activity. The time course of the change in potential reflected the course of change of temperature; the temperature coefficient was 100–150 µV/°C. Cooling the skin was accompanied by a negative deviation of potential on the skin and in the ampullary canal and by excitation of spike activity. During cooling the temperature coefficient was 30–50 µV/°C. It is concluded that spike activity of electroreceptors reflects changes in potential on the skin due to changes in temperature. The mechanism and biological significance of the phenomena discovered are discussed.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 13, No. 3, pp. 307–314, May–June, 1981.     

Investigation of the mechanism of temperature sensitivity of the electroreceptors of ampullae of lorenzini

In experiments on Black Sea skates (Raja clavata), the potential of the receptor epithelium of the ampullae of Lorenzini and spike activity of single nerve fibers connected to them were investigated during electrical and temperature stimulation. Usually the potential within the canal was between 0 and –2 mV, and the input resistance of the ampulla 250–400 k. Heating of the region of the receptor epithelium was accompanied by a negative wave of potential, an increase in input resistance, and inhibition of spike activity. With worsening of the animal's condition the transepithelial potential became positive (up to +10 mV) but the input resistance of the ampulla during stimulation with a positive current was nonlinear in some cases: a regenerative spike of positive polarity appeared in the channel. During heating, the spike response was sometimes reversed in sign. It is suggested that fluctuations of the transepithelial potential and spike responses to temperature stimulation reflect changes in the potential difference on the basal membrane of the receptor cells, which is described by a relationship of the Nernst's or Goldman's equation type.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. I. M. Sechenov, Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Pacific Institute of Oceanology, Far Eastern Scientific Center, Academy of Sciences of the USSR, Vladivostok. Translated from Neirofiziologiya, Vol. 12, No. 1, pp. 67–74, January–February, 1980.     

From competent larva to exotrophic juvenile: a morphofunctional study of the perimetamorphic period of Paracentrotus lividus (Echinodermata, Echinoida)

 The perimetamorphic period in Paracentrotus lividus lasts for 8–12 days. It starts from the acquisition of larval competence, includes the change in form (metamorphosis) and the endotrophic postlarval life, and stops with the appearance of the exotrophic juvenile. All major postlarval appendages already occur in competent larvae being either grouped into the echinoid rudiment (terminal plates, early spines and primary podia) or scattered within the larval integument (genital plates and sessile pedicellariae). Competent larvae show particular behaviour which brings them close to the substratum. The latter is tested by primary podia protruding through the vestibular aperture of the larva. Primary podia are sensory–secretory appendages that are deprived ampullae. They are able to adhere to the substratum in order to allow evagination of the echinoid rudiment (i.e. metamorphosis) and substatum adhesion of the postlarva. Particular spines are borne by the postlarva; these are multifid non-mobile appendages forming a kind of protective armour. Like those of the larva, all characteristic structures of the postlarva (primary podia, multified spines and sessile pedicellariae) are transitory and regress either at the end of postlarval life (primary podia) or during early juvenile life (multifid spines and sessile pedicellariae). Other appendages that develop during postlarval life (i.e. podia with ampulla, point-tipped spines and sphaeridiae) are similar to those borne by the adults and become functional when the individual enters its juvenile life. Thus, the perimetamorphic period appears to be a fully fledged period in the life-cycle of P. lividus, and presumably in the life-cycle of any other sea-urchin species. Accepted: 7 October 1997     

Unconventional signalling in tunicates

The zooids in colonial tunicates do not appear to be directly interconnected by nerves, but this has not prevented the evolution of coordinated behaviour in several groups. In Botryllus and other colonial styelid asci‐dians the endothelium lining the blood vessels is excitable and transmits action potentials from cell to cell via gap junctions. These signals mediate protective contractions of the zooids and synchronize contractions of the vascular ampullae. In didemnid ascidians such as Diplosoma a network of myocytes in the tunic serves to transmit excitation and to cause contractions of the cloacal apertures. Individual zooids of Pyrosoma protect themselves by closing their siphons and arresting their branchial cilia when stimulated. At the same time a flash of light is emitted. Neighbouring zooids sense the flash with their photoreceptors and respond in turn with protective responses and light emission. Protective responses thus spread by photic signalling and propagate from zooid to zooid through the colony in a saltatory manner. In chains of Salpafusifortnis, changes in the direction and/or speed of swimming are transmitted from zooid to zooid via adhesion plaques. When a zooid is stimulated, its body‐wall epithelium conducts action potentials to the plaque connecting it to the next zooid, exciting receptor neurons in that zooid. These receptors have sensory processes that bridge the gap between the two zooids. The sensory neurons so excited in the second zooid conduct impulses to the brain where they alter the motor output pattern, and at the same time generate epithelial action potentials that travel to the next zooid in line, where the same thing happens.

It is not clear why these unconventional signalling methods have evolved but the tunic may be an inhospitable environment for nerves, making conventional nervous links impossible.     

Electrical model of the electroreceptor of the ampulla of Lorenzini

On the basis of experimental data [2] a model of electrical processes taking place on the receptor epithelium of the ampulla of Lorenzini was developed. The basic assumption made in the model is that the apical membrane of the receptor cell has a stationary current-voltage characteristic curve with a region of negative resistance. The model explains logically the unusual sign of the spike response of the ampullae (excitation on application of a cathode to the apical surface of the epithelium) and experimental data obtained by various workers [2,7–10], including some concerned with the most complex forms of electrical and spike responses.     

On the ampullary organs of the South-American paddle-fish Sorubim lima (Siluroidea,Pimelodidae)

Summary Ampullary organs were found in the epidermis of the paddle-fish Sorubim lima; they are distributed all over the skin surface of the fish but are particularly densely grouped in the head region and on the dorsal surface of the paddle. Histological and electron microscopical observations show that their structure is similar to the type of cutaneous ampullary organs characteristic of other Siluroidea. Composed of a relatively large mucus-filled ampulla, the organ possesses a short and narrow canal which leads to the outer epidermal surface. The wall of the ampulla is formed of several layers of flat epidermal cells. In general four sensory cells, each one surrounded by supporting cells, compose the sensory epithelium at the bottom of the ampulla. The inner surface of the sensory cells in contact with the ampullary mucus bears only microvilli. The contact between the nerve endings and the sensory cells show the characteristic structure of an afferent neuro-sensory junction. Two ampullae are innervated in some cases by the same afferent nerve fibre.The author expresses her gratitude to Dr. Szabo for his scientific advice during her stay in Gif sur Yvette     

Ultrastructure of the ampullae of Lorenzini of <Emphasis Type="Italic">Aptychotrema rostrata</Emphasis> (Rhinobatidae)

Small epidermal pores of the electrosensory ampullae of Lorenzini located both ventrally and dorsally on the disk of Aptychotrema rostrata (Shaw and Nodder, 1794) open to jelly-filled canals, the distal end of which widens forming an ampulla that contains 6 ± 0.7 alveolar bulbs (n = 13). The sensory epithelium is restricted to the alveolar bulbs and consists of receptor cells and supportive cells. The receptor cells are ellipsoid and their apical surfaces are exposed to the alveolar lumen with each bearing a single central kinocilium. Presynaptic bodies occur in the basal region of the receptor cell immediately proximal to the synaptic terminals. The supportive cells that surround receptor cells vary in shape. Microvilli originate from their apical surface and extend into the alveolar lumen. Tight junctions and desmosomes connect the supportive cells with adjacent supportive and receptor cells in the apical region. The canal wall consists of two cell layers, of which the luminal cells are squamous and interconnect via desmosomes and tight junctions, whereas the cells of the deeper layer are heavily interdigitated, presumably mechanically strengthening the canal wall. Columnar epithelial cells form folds that separate adjacent alveoli. The same cells separate the ampulla and canal wall. An afferent sensory nerve composed of up to nine myelinated nerve axons is surrounded by several layers of collagen fibers and extends from the ampulla. Each single afferent neuron can make contacts with multiple receptor cells. The ultrastructural characteristics of the ampullae of Lorenzini in Aptychotrema rostrata are very similar to those of other elasmobranch species that use electroreception for foraging.     

Ultrastructural evidence for secretion from the epithelium of ampulla ductus deferentis of the fan-throated lizard Sitana ponticeriana Cuvier

Among reptiles, an ampulla ductus deferentis has been reported only in Squamata. Fairly detailed studies are available only for two species, the lizard Calotes versicolor (Fam: Agamidae) and the snake Seminatrix pygaea (Fam: Colubridae). The light microscopic study on C. versicolor revealed the ampulla to be a prominent organ, whereas the light and transmission electron microscopic study in S. pygaea revealed it to be discernable only in histological preparations. Further, the epithelium of the ductal portion of vas deferens as well as the ampulla of C. versicolor appears to contribute to the seminal plasma and can also phagocytose dead sperm, whereas in S. pygaea neither of these roles has been established. Thus, we hypothesize that there may be variations in the anatomy, histology, and the role of the vas deferens in general, and the ampulla in particular, of the squamate reptiles. In this study, the ductus deferens of the small fan-throated lizard Sitana ponticeriana (Fam: Agamidae) was subjected to light and transmission electron microscopic analysis. In this lizard the ampulla is more prominent than in C. versicolor. The epithelium of the ductal portion of vas deferens consists of principal cells (with features reflecting roles in endocytosis and phagocytosis of dead sperm), dark cells (which are absent in the epithelium of the ductal portion of vas deferens of snakes), and basal cells. The ampulla of S. ponticeriana is differentiated into storage and glandular portions. The epithelium of the storage portion is like that in the ductal portion of the vas deferens, whereas that of the glandular portion, consisting of dark and light principal cells and foamy cells, is tall and forms into smooth villous folds. All three cell types show evidence for a role in secretion, in all likelihood different from each other, for release into the lumen to contribute to seminal plasma. These cells do not provide evidence of a role in phagocytosis of dead sperm. It appears that within the Squamata, the ductal ampulla differs in structure as well as function. We suggest that the ductal ampulla of agamid lizards is a composite gland of the ampulla ductus deferentis and seminal vesicles of mammals.     

Responses of the ampullae of Lorenzini in a uniform electric field

A linear relationship was established by analysis of discharges from electroreceptors of the ampullae of Lorenzini in a uniform electric field between the potential difference on a single ampulla and the relative change in the spike response of a single fiber. This relationship can serve as the basis for a model of activity of ampullary groups considered as functional units of the electroreceptor system.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 11, No. 2, pp. 158–166, March–April, 1979.     

Spontaneous motility of the oviduct in the anaesthetized pig

Intraluminal pressure microtransducers were placed at the uterotubal junction, the proximal isthmus, the ampullary-isthmic junction and the mid-ampulla. Spontaneous motility occurred throughout the oestrous cycle in all segments. During oestrus there were regular, high amplitude peristaltic waves in all segments, superimposed on basal activity. On Day 1 of the cycle the pattern was mostly antiperistaltic, presumably related to sperm transport. During the periovulatory period the number of peristaltic and antiperistaltic waves became equal, perhaps in relation to the transport of gametes to the fertilization site. During Day 3 there was no peristaltic activity; the motility patterns of the isthmus and ampullary-isthmic junction were similar (regular phasic contractions of high frequency and amplitude) while the ampullary motility was low. On Day 4, when the eggs enter the uterine lumen, the ampullary-isthmic junction and particularly the isthmus showed strong contraction waves (mostly peristaltic) superimposed on the basal phasic activity. This suggests an active role of the smooth muscle of the lower oviducal segments in ovum descent. During the mid- and late-luteal phases, the isthmus remained motile, with an irregular base line, but lost the pattern of basal contractions that dominated the activity during the first 4 days of the cycle. The ampulla showed low levels of spontaneous motility throughout the rest of the cycle.     

Comparative morphology of the stolonic vessel in a didemnid ascidian and some related tissues in colonial ascidians

The stolonic vessel is a tubular projection of the epidermis from the anterior part of the abdomen in the didemnid ascidians, and the vessel has been supposed to be closely related to the stolons, vascular appendages, and the posterior ends of the abdomen in other aplousobranch ascidians. We compared the morphology of the stolonic vessels of Diplosoma virens with similar or related tissue in other colonial ascidians, e.g. stolons of Clavelina, vascular appendages of Distaplia and Eudistoma, tunic vesicle of Aplidium, and vascular ampullae of Botrylloides. The epidermis of the stolonic vessel is composed of cuboidal cells in lateral wall and columnar cells at the distal tip of the vessel. The cuboidal cells have microvilli that probably anchor the stolonic vessel to the tunic. The columnar cells contain round granules that may concern with the secretion of some tunic components. The secretion of the granules, however, could not observed in this study. The stolonic vessel of D. virens is similar in morphology to the vascular ampullae of Botrylloides and the tunic vesicle of Aplidium rather than the other tissue examined here. Since the cell morphology is supposed to reflect its function but not the phylogenetic relationship, the present study could not provide conclusive evidences to prove the homology and the phylogenetic relationship among the tubular, epidermal projections in the colonial ascidians.     

Changes in transepithelial potential and spike responses of ampullae of Lorenzini of the skate to temperature stimulation

Response of the sensory epithelium of single ampullae of Lorenzini and spike responses of nerve fibers connected to them to temperature stimulation of the region of the sensory epithelium were studied in experiments on Black Sea skatesRaja clavata. Electrically isolated ampullae with input resistance R=500–800 k, to which an external load (a controllable resistance R_ext) could be connected through a feedback circuit, were investigated. Heating the ampulla was accompanied by the appearance of a negative potential in the canal, and other conditions being the same, its magnitude was an almost linear function of the resultant inward resistance of the preparation [R_in=(R_a·R_ext)/(R_a+R_ext)]. The character and intensity of the spike response of the nerve fiber also was determined by the magnitude of R_in. With a resistance of more than 400–500 k, quickening of spike activity occurred in response to heating, and the degree of quickening increased with an increase in R_in. With a smaller value of R_in, the discharge was inhibited, and the inhibition strengthened as the resistance decreased. The presence of two sources of potential, evoked by a change of temperature and giving rise to opposite spike responses, is discussed.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR. Leningrad I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 14, No. 1, pp. 11–18, January–February, 1982.     

Histology and Ultrastructure of the Body Wall in the Phoronid Phoronopsis harmeri

The histology and ultrastructure of the body wall in Phoronopsis harmeriwere studied using light microscopy and TEM. The ectoderm epithelium of tentacles, anterior body region, and ampulla consists of monociliary cells. Gram-negative bacteria were found between microvilli, in the protocuticle of the anterior region, and in the ampulla. The epithelium of the posterior body region lacks both monociliary cells and bacteria. The bundles of nerve fibers run between the layer of epithelial cells and basal membrane. The musculature of the body wall comprises circular and longitudinal muscles. The circular muscle fibers are applied to the basal membrane and constitute a solid layer extending almost throughout the length of the body. This pattern is broken in the posterior body region, where there is no solid layer of circular musculature, and the latter is arranged in isolated muscle bands. In the ampullar (terminal) body region, the inversion of circular and longitudinal muscle layers takes place, so that the latter appears to be pressed against the basal membrane. The apical surfaces of longitudinal muscle cells bear cytoplasmic processes; some of the cells have a flagellum. The basal portion of the longitudinal muscle cells forms a cytoplasmic process containing bundles of tonofilaments. The processes of all cells making up the muscle bands are interwoven and anchored to the basal membrane.     

Gross and fine structure of the antennal circulatory organ in cockroaches (Blattodea,Insecta)

The antennal circulatory organ of Periplaneta americana and Blaberus craniifer was investigated by light and electron microscopy. This organ consists of two pulsatile ampullae located near the antennal base which are interconnected by a large transverse muscle and associated blood vessels which run into the antennae. Diastole is caused simultaneously in both ampullae by the transverse muscle. Systole is produced passively by the elasticity of the wall of the ampullae and minute accessory tendons. Both elastic structures contain fine unbanded extracellular filaments. The antennal vessels possess two distinct regions: a proximal convoluted region lying within the hemocoel of the head and a narrower distal region running through the antenna and opening near the antennal apex. The length of the proximal portion increases markedly during ontogeny in correlation with the growing antenna. Its wall consists of a high-prismatic epithelium ensheathed by a thick layer of collagen fibrils. The structure of the wall cells is comparable to that found in some salt transporting epithelia: it shows a polar organization with basal infoldings, a large number of mitochondria, and typical arrangement of the junctions or mitochondrial-scalariform junctional complexes. The possible physiological function of this epithelium in ionic or osmoregulation of the hemolymph entering the antenna is discussed. The wall of the distal vessel region consists of a flat single-layered epithelium and seems to be specialized only for delivery of hemolymph to antennae. The structure and function of the antennal heart in cockroaches is compared to that found in other insects.     

Test cell migration and tunic formation during posthatching development of the larva of the ascidian, Ciona intestinalis

Morphological changes in the tunic layers and migration of the test cells during swimming period in the larva of the ascidian, Ciona intestinalis , were observed by light and electron microscopy. The swimming period was divided into three stages. In stage 1, further formation of juvenile tunic layer started only in the larval trunk and neck region. In stage 2, the layer became swollen in the ventral and dorsal sides of the neck region and in stage 3, the swelling expanded backward. Concomitantly with these changes, the outermost larval tunic layer (outer cuticular layer), which had been formed before hatching, also swelled in the neck region in stage 2 and formed two humps in stage 3, although the layer did not change in the tail region during the swimming period. Test cells that were present over the entire larval tunic layer in stage 1 began to move from the surface of the fin toward that of the side of the body in stage 2, and finally gathered to form six bands running radially from the anterior end to the posterior end of the trunk region and aligned along the lateral sides of body in the tail region in stage 3. In electron microscopic observations, pseudopodia protruding from the test cells invaded the larval tunic, following which they extended proximate to the juvenile tunic in the trunk region. In the tail region, which had no juvenile tunic layer as that described, the pseudopodia invaded and remained adjacent to the surface of the epidermis or the sensory cilia protruded from the epidermis. Metamorphosis of the larvae, further tunic formation, degradation of adhesive papilla, attachment of larva to the substratum and tail resorption commenced after these morphological changes occurred. The possible role of the test cells in metamorphosis is discussed.