Burrowing in the Antarctic anemone, Halcampoides sp., from Signy Island, Antarctica

Antarctic anemones of the genus Halcampoides inhabit low intertidal and shallow subtidal zones. They readily burrow into soft sediments following disturbance. The process of re-burying was recorded using time-lapse video in the aquarium of the British Antarctic Survey with specimens of a species collected from the shallow sublittoral (<1 m depth) at Signy Island. Penetration of the sediment takes place by a similar mechanism to that employed by burrowing anemones such as Peachia hastata from lower latitudes. Penetration initially is brought about by peristaltic contractions that involve only the modified base, or physa. Later, as the column becomes buried, the peristaltic contractions start in the upper part of the scapus and pass down the column before extending the physa. At this stage penetration is aided by contractions of the longitudinal muscles that draw the column down into the sediment. At 0 degrees C the frequency of initiation of peristaltic contractions down the column, and of contractions of the longitudinal muscles are on average >1.6 and >4.0 times slower, respectively, compared with those of Peachia hastata from Scotland, recorded at approximately 11-14 degrees C. Q(10) values calculated from these data are in the range 1.4-3.0, and thus provide little evidence supporting any evolutionary acclimation of the processes involved in burrowing has occurred in Halcampoides from the Antarctic, although the data are limited.     

Functional coordination of motor activity in colonic smooth muscles in rat experimental model

Spontaneous and electrically-elicited motor activity was recorded by triple organ bath in rat segment-model preparation as display of excitation of local nerve networks and ascending or descending reflex pathways underlying contractile potency and functional coordination of colonic longitudinal and circular muscles. Spontaneous high-amplitude contractions, but not relaxations, appeared synchronously in both muscles. Electrical field stimulation applied to proximal or distal part of segments elicited both tetrodotoxin (0.1 microM)-sensitive local motor responses of the stimulated part and ascending or descending motor responses of the contralateral, nonstimulated part of the preparations. Contractions characterized the local response of longitudinal muscle. The circular muscle responded with relaxation followed by contraction. Synchronous ascending contractions and descending contraction of the longitudinal muscle and relaxation followed by contraction of the circular muscle were observed when the middle part of segments was stimulated, thus indicating that locally-induced nerve excitation propagated via intrinsic ascending or descending nerve pathways that could be synchronously coactivated by one and the same stimulus. The ascending motor responses were more pronounced and the motor responses of longitudinal muscle were expressed more than those of circular muscle suggesting an essential role of ascending reflex pathways and longitudinal muscle in the coordinated motor activity of colon.     

Reflex activation of locust flight motoneurones by proprioceptors responsive to muscle contractions

 This report investigates the reflex activation of locust flight motoneurones following their spiking activity. As shown elsewhere, an electrical stimulus applied to a flight muscle produces multiple waves of delayed excitation in wing elevator and depressor motoneurones. Nerve ablation experiments show that this response is initiated by the mechanical movement of the stimulated muscle, and not the antidromic spike evoked in the motoneurone. The delayed excitation still occurs in the absence of inputs from the wing receptor systems, and also when all other sources of afferent feedback are abolished, excepting thoracic nerve 2. Following complete deafferentation, spikes in flight motoneurones had no influence on other flight motoneurones. Numerous afferents in the purely sensory nerve 2 are excited by flight muscle contractions. The responses are consistent for repeated contractions of the same muscle, but differ when other muscles are stimulated. During tethered flight, changes in the activation of single flight muscles are reflected in changes of the nerve 2 discharge pattern. Electrical stimulation of this nerve causes delayed excitation of flight motoneurones, and can initiate flight activity. It is suggested that internal proprioceptors, such as those associated with nerve 2, will contribute to shaping the final motor output for flight behaviour. Accepted: 24 April 1996     

Effect of low-molecular nonelectrolytes and hypotonia on the contractile responses of frog sartorius muscles

The potentiation of contractile responses during prolonged incubation of frog sartorius muscles in a conventional Ringer solution and in a calcium-free Ringer solution which contained 400 mM of urea, acetamide or ethylene glycol was observed when stimulation with single electric impulses and with caffeine was carried out. When the muscles were exposed to a hypotonic solution the reduction in the amplitude of caffeine contractures or their complete disappearance were registered, whereas the electrical stimulation of muscles in the same medium exerted an increase in the amplitude of contractile responses. The addition of 400 mM glycerol to the hypotonic solution caused an increase in the amplitude of contractions under both types of stimulation.     

Peripheral and central photoreception in Aplysia fasciata.

Extraocular photosensitivity in Aplysia fasciata was studied in the skin and in the central nervous system (CNS). Local illumination causes contractions of the muscles of the body wall, which are obviously mediated by the peripheral nervous system (PNS). Afferent sensory activity is supposedly mainly dependent on stretch reception. Light-induced peripheral reflexes habituate after repetitive stimulation in preparations in which the CNS is present. In preparations without CNS light-induced contractions are remarkably stronger and do not habituate after repititive stimulation. Central responses to peripheral stimulation could be evoked by both "light on" and "light off" stimulation, indicating that 2 types of photosensitive elements are present in the periphery. Observations on isolated CNS-preparations revealed that in the central ganglia photoreceptive elements are also present. Here, too, elements responding to the onset as well as elements responding to the offset of light have been detected.     

A comparative study of motor patterns during pre-flight warm-up in hawkmoths

Summary Temporal patterns of activation of flight muscles were recorded by means of wires placed extracellularly in thoracic muscles. In the five species of hawkmoths studied, wingstrokes of small amplitude were produced during a preflight warm-up by synchronous contractions of certain groups of muscles which are antagonists in flight. The main depressor muscle, the dorsal longitudinal, was excited in synchrony with some or all of the indirect elevator muscles. Three direct muscles, the subalar, basalar and third axillary muscles, were usually excited out of phase with the dorsal longitudinal muscle. However, details of the motor pattern varied from species to species. During fixed flight phase changes comparable in magnitude to those which occur during the transition from warm-up to flight were observed in Manduca sexta and Smerinthus cerisyi. The results (summarized in Table 2) suggest that a variety of warm-up patterns evolved within the Sphingidae as modifications of a common mechanism generating flight motor patterns.I thank Dr. Harry Lange for assistance in the initial collecting of Manduca sexta and for identifying specimens of this species.     

Modulation of Hydra attenuata rhythmic activity: phase response curve.

We investigated the effect of photic stimulation on the frequency of Hydra attenuata column contractions. We used positive or negative abrupt light transitions, single or repetitive light or darkness pulses, and alternation of light and darkness periods. The main results are: (a) The frequency of the contraction pulse trains (CPTs) varies transiently in response to an abrupt variation of the light intensity. (b) CPTs in progress can be inhibited by different types of photic stimuli. (c) The response time to a single photic stimulus varies during the inter-CPT interval and depends also on the polarity of the stimulus. (d) The CPTs are entrainable with repetitive light stimulation of various frequencies. (e) Long-lasting variations of the frequency of CPTs occur after the end of a repetitive light stimulation. We suggest that the mechanism responsible for the rhythym of column contractions is quite similar to that on which other biological rhythmic phenomena are based.     

Neurobiology of Stomotoca. II. Pacemakers and conduction pathways.

Evidence is presented for separate conduction pathways for swimming and for tentacle coordination in the marginal nerves of the jellyfish Stomotoca. The effector muscles are fired through junctions sensitive to excess Mg++, probably represented by the neuromuscular synapses observed by electron microscopy. The swimming effector (striated muscle) fires one-to-one with nerve input signals and myoid conduction occurs. Tentacle responses (smooth muscle contractions) involve facilitation, presumably at the neuro-effector junction; responses are graded and nonpropagating. Electrical correlates of two further conducting systems using the marginal nerves have been recorded. Their functions are unknown. One, the bridge system, extends up the four radii and encircles the peduncle; the other (ring system) is confined to the margin. A fifth conducting system is inferred in the case of the pointing response and its distribution is plotted. Signals have not been obtained from it. Pointing is accompanied by a burst of muscle potentials in the radial smooth muscles and is exhibited after a lengthy latency, indicating a local pacemaker. A sixth conducting pathway is the epithelial system, which mediates crumpling, a response involving the radial muscles without pacemaker intervention. Characteristic conduction velocities and wave forms are noted for the first four systems and for epithelial pulses. All systems, except perhaps the pointing conduction system, through-conduct under excess Mg++. Spontaneous activity patterns are described for the swimming, tentacle pulse, and ring systems. Abrupt increases in light intensity inhibit spontaneous activity, sudden decreases augmenting it. In the absence of specialized photoreceptors, light is presumed to act directly on central neurons. Epithelial pulses inhibit swimming, apparently by blocking the generation or conduction of the primary nervous events. This observation, taken in conjunction with evidence of feedback inhibition of the primary swimming system by the cells it fires, is discussed in relation to possible mechanisms whereby the output of nerve cells might be altered by activity in the excitable epithelial cells which envelop them.     

Isolation of Leu-Pro-Pro-Gly-Pro-Leu-Pro-Arg-Pro-NH2 (Antho-RPamide), an N-terminally protected, biologically active neuropeptide from sea anemones.

Using a radioimmunoassay against the C-terminal sequence Arg-Pro-NH2 (RPamide), we have isolated the peptide Leu-Pro-Pro-Gly-Pro-Leu-Pro-Arg-Pro-NH2 (Antho-RPamide) from an extract of the sea anemone Anthopleura elegantissima. Antho-RPamide is located in neurons of sea anemones. Application of low concentrations of Antho-RPamide to tentacle preparations of sea anemones strongly increased the frequency and duration of spontaneous contractions, suggesting that this peptide is involved in neurotransmission. Antho-RPamide has a free N-terminus, yet its X-Pro-Pro sequence makes it relatively resistant to degradation by nonspecific aminopeptidases. Thus, we have discovered another strategy by which sea anemones protect the N-termini of their bioactive neuropeptides.     

CHANGES IN THE ULTRASTRUCTURE OF SYMBIOTIC ZOOXANTHELLAE (SYMBIODINIUM SP., DINOPHYCEAE) IN FED AND STARVED SEA ANEMONES MAINTAINED UNDER HIGH AND LOW LIGHT1

The ultrastructure of symbiotic dinoflagellates (Symbiodinium sp., zooxanthellae) in the sea anemone Aiptasia pallida Verrill was examined in well-fed or starved (up to 120 days) anemones maintained under two light levels (5 and 50 μmol · m^?2· s^?1). Cell size of zooxanthellae was not affected by feeding history; however, both light and feeding history affected the relative cell volume of chloroplasts, lipids, and vacuoles. Stereological analysis of transmission electron micrographs showed that algae in low-light starved anemones had 10 times as much lipid (17.4% of cell volume) as those in well-fed anemones under the same light conditions (1.8%). The lipid content of algae from anemones in high light increased from 15.4% in well-fed anemones to 30.1% in starved anemones. The starch content of zooxanthellae in low-light anemones was law (4.1%) and not affected by feeding history, while the starch content of zooxanthellae in high-light anemones was greater (10.7%), with some differences among groups. Algal photoacclimation to low light included an increase in chloroplast relative volume from 17% (in well-fed high-light anemones) to 33% in well-fed low-light anemones. Starvation of the host resulted in a significant decrease in chloroplast volume in zooxanthellae in anemones at both light levels. Morphometry provides quantitative confirmation of biochemical and physiological data on zooxanthellae, because the changes in zooxanthellae with starvation of the host are consistent with other indicators of nutrient limitation of zooxanthellae of A. pallida held without food for long periods of time.     

Colonial conduction systems in the Anthozoa: Octocorallia.

1. The octocorals Alcyonium digitatum, Pennatula phosphorea and Virgularia mirabilis each have a through-conducting nerve net. The nerve net demonstrated electrophysiologically may well be the same as that previously shown by the use of histological techniques. 2. It exhibits both facilitation and defacilitation in the rate of conduction of pulses. 3. The distance of spread of nerve net activity is not limited by the number of stimuli applied. 4. The nerve net controls fast muscle contractions; the frequency of pulses is important in determining which muscles contract and in which sequence. 5. The nerve net is 'spontaneously' active. 6. A previously undescirbed slow system has been identified in Pennatula. It has many of the properties of slow systems in sea anemones and may well be ectodermal. It is suggested that multiple conduction systems are of common occurrence in the Anthozoa.     

Responses of group III and IV muscle afferents to distension of the peripheral vascular bed.

This study was undertaken to test the hypothesis that group III and IV afferents with endings in skeletal muscle signal the distension of the peripheral vascular network. The responses of these slowly conducting afferents to pharmacologically induced vasodilation and to acute obstruction of the venous drainage of the hindlimbs were studied in barbiturate-anesthetized cats. Afferent impulses arising from endings in the triceps surae muscles were recorded from the L(7) and S(1) dorsal roots. Fifteen of the 48 group IV and 3 of the 19 group III afferents tested were stimulated by intra-aortic injections of papaverine (2-2.5 mg/kg). Sixty-two percent of the afferents that responded to papaverine also responded to isoproterenol (50 microg/kg). Seven of the 36 group IV and 2 of the 12 group III afferents tested were excited by acute distension of the hindlimb venous system. Four of the seven group IV afferents responding to venous distension also responded to papaverine (57 vs. 13% for the nonresponding). Finally, we observed that most of the group IV afferents that were excited by dynamic contractions of the triceps surae muscles also responded either to venous distension or to vasodilatory agents. These results are consistent with the histological findings that a large number of group IV endings have their receptive fields close to the venules and suggest that they can be stimulated by the deformation of these vascular structures when peripheral conductance increases. Moreover, such a mechanism offers the possibility of encoding both the effects of muscle contraction through intramuscular pressure changes and the distension of the venular system, thereby monitoring the activity of the veno-muscular pump.     

THE RELATIONS OF THE INDIVIDUAL AMPULL? OF THE SEMICIRCULAR CANALS TO THE INDIVIDUAL EYE MUSCLES : I. THE HORIZONTAL CANALS.

1. The reflex effect of direct mechanical stimulation of the exposed ampulla of the horizontal canal has been graphically recorded for each of the six extrinsic muscles of the eyeball. 2. Stimulation of a horizontal ampulla evokes a strong contraction of the homolateral rectus internus and of the contralateral rectus externus; at the same time the homolateral rectus externus and the contralateral rectus internus relax. 3. A single mechanical stimulus applied to the horizontal ampulla is sometimes followed by a nystagmus resulting from a series of rhythmic contractions of the externus and internus muscles. 4. Excitation of a horizontal ampulla gives rise to weak contractions of the superior and inferior recti and of the two oblique muscles of both eyes, simultaneously with the stronger contractions of the externus and internus respectively. 5. It is pointed out that the small simultaneous contractions of the four muscles just mentioned provide a virtual axis upon which the eyeball rotates. In other words these four act as fixation muscles. 6. It is suggested that some of the abnormal responses to horizontal rotation, seen in clinical cases, are due to the inaction of one or more of the fixation muscles.     

Neurobiology of Stomotoca. II. Pacemakers and conduction pathways

Evidence is presented for separate conduction pathways for swimming and for tentacle coordination in the marginal nerves of the jellyfish Stomotoca. The effector muscles are fired through junctions sensitive to excess Mg⁺⁺, probably represented by the neuromuscular synapses observed by electron microscopy. The swimming effector (striated muscle) fires one-to-one with nerve input signals and myoid conduction occurs. Tentacle responses (smooth muscle contractions) involve facilitation, presumably at the neuro-effector junction; responses are graded and nonpropagating. Electrical correlates of two further conducting systems using the marginal nerves have been recorded. Their functions are unknown. One, the bridge system, extends up the four radii and encircles the peduncle; the other (ring system) is confined to the margin. A fifth conducting system is inferred in the case of the pointing response and its distribution is plotted. Signals have not been obtained from it. Pointing is accompanied by a burst of muscle potentials in the radial smooth muscles and is exhibited after a lengthy latency, indicating a local pacemaker. A sixth conducting pathway is the epithelial system, which mediates crumpling, a response involving the radial muscles without pacemaker intervention. Characteristic conduction velocities and wave forms are noted for the first four systems and for epithelial pulses. All systems, except perhaps the pointing conduction system, through-conduct under excess Mg⁺⁺. Spontaneous activity patterns are described for the swimming, tentacle pulse, and ring systems. Abrupt increases in light intensity inhibit spontaneous activity, sudden decreases augmenting it. In the absence of specialized photoreceptors, light is presumed to act directly on central neurons. Epithelial pulses inhibit swimming, apparently by blocking the generation or conduction of the primary nervous events. This observation, taken in conjunction with evidence of feedback inhibition of the primary swimming system by the cells it fires, is discussed in relation to possible mechanisms whereby the output of nerve cells might be altered by activity in the excitable epithelial cells which envelop them.     

The senses of sea anemones: responses of the SS1 nerve net to chemical and mechanical stimuli

The ectodermal slow system (SS1) is one of 3 separate nerve nets in sea anemones. SS1 sensory responses coordinate swimming in Stomphia coccinea (escape response) and expansion to dissolved food substances in Urticina felina (pre-feeding response). Here we have studied Actinia equina, Anemonia viridis, and Anthopleura ballii. Although these anemones can escape from nudibranch predators, the SS1 response to attack by Aeolidia papillosa is probably evoked mechanically rather than chemically (cf. Stomphia). Multiple SS1 pulses to mechanical stimulation are described for the first time. Previous work has shown that in the pre-feeding response of Urticina the SS1 is excited by betaine; in Actinia however, the excitant is proline. The anemones studied can utilize the SS1 in 2 different behavioural responses (escape and pre-feeding/feeding) because the different receptors involved respond at different frequencies (at around 0.6 Hz in escape and 0.2 Hz in pre-feeding).     

The role of calcium in excitation--contraction coupling in crustacean muscle fibers

The evidence that calcium (Ca) plays an important role in electrical activity and an essential role in excitation--contraction (E--C) coupling in crustacean muscles is reviewed. These muscles produce graded electrical and mechanical responses to applied depolarizations. Removal of Ca from the bath solution eliminates both responses. Addition of Ba2+ or Sr2+ to Ca-free saline restores membrane electrogenesis, and all-or-none action potentials can be induced. With Sr2+ vigorous contractions are produced, whereas Ba action potentials evoke minimal or no tension, showing that rapid depolarization of the membrane potential is not sufficient per se for E--C coupling in crab and barnacle muscle. Several inorganic (e.g., multivalent cations) and organic (e.g., aminoglycoside antibiotics) which block membrane Ca channels block electrogenesis and contraction. However, the "Ca antagonists" verapamil and D600 also block Ca uptake at intracellular storage sites, resulting in spontaneous contractions and the delayed relaxation of small contractions associated with residual Ca currents. The evidence that the Ca which enters the fibres needs to release Ca from intracellular storage sites to produce contractions is detailed and discussed. Finally, a model for E--C coupling is discussed. This model includes the sites and mechanisms of action for several chemicals which modify E--C coupling in crustacean muscle fibres.     

Body size and symbiotic status influence gonad development in <Emphasis Type="Italic">Aiptasia pallida</Emphasis> anemones

Pale anemones (Aiptasia pallida) coexist with dinoflagellates (primarily Symbiodinium minutum) in a mutualistic relationship. The purpose of this study was to investigate the role of these symbionts in gonad development of anemone hosts. Symbiotic and aposymbiotic anemones were subjected to light cycles that induced gametogenesis. These anemones were then sampled weekly for nine weeks, and gonad development was analyzed histologically. Anemone size was measured as mean body column diameter, and oocytes or sperm follicles were counted for each anemone. Generalized linear models were used to evaluate the influence of body size and symbiotic status on whether gonads were present and on the number of oocytes or sperm follicles produced. Body size predicted whether gonads were present, with larger anemones being more likely than smaller anemones to develop gonads. Both body size and symbiotic status predicted gonad size, such that larger and symbiotic anemones produced more oocytes and sperm follicles than smaller and aposymbiotic anemones. Overall, only 22 % of aposymbiotic females produced oocytes, whereas 63 % of symbiotic females produced oocytes. Similarly, 6 % of aposymbiotic males produced sperm follicles, whereas 60 % of symbiotic males produced sperm follicles. Thus, while gonads were present in 62 % of symbiotic anemones, they were present in only 11 % of aposymbiotic anemones. These results indicate that dinoflagellate symbionts influence gonad development and thus sexual maturation in both female and male Aiptasia pallida anemones. This finding substantiates and expands our current understanding of the importance of symbionts in the development and physiology of cnidarian hosts.     

植物光毒素作用机理

光激发植物光毒素产生单线态氧或自由基,破坏核酸、脂质和蛋白质等,对病毒、细菌、真菌、线虫、昆虫和其他植物产生毒性,在植物的防护反应中具有重要作用．     

Influence of tenotomy on posttetanic responses of the rat fast and slow muscle

The effect of two weeks of tenotomy on posttetanic isometric contractile responses of the rat fast: Extensor digitorum longus and slow: soleus muscles was studied in experiments on isolated muscle preparations. Direct tetanic stimulation (100 impulses, 50 Hz) increased the force of contractions by 20-25% (p < 0.05) of both, control and tenotomized fast muscles. Identical to above tetanic stimulation of control, slow muscle resulted in posttetanic depression, a decrease in the amplitude of contractile responses. Tenotomized slow muscles did not develop posttetanic depression. Caffeine (4 mM) increased and dandrolene (10 microM) decreased the force of unitary and tetanic contractions of control and tenotomized muscles. Neither drug, however, affected development of posttetanic phenomena in ether fast or slow muscles. The fact that in extensor digitorum longus, posttetanic potentiation is preserved for at least forty days of tenotomy but disappears after only 2 weeks of denervation suggests important role of neurotrophic influences in regulation of posttetanic responses of fast muscles.     

The pressor response to voluntary and electrically evoked isometric contractions in man

Blood pressure and heart rate changes during sustained isometric exercise were studied in 11 healthy male volunteers. The responses were measured during voluntary and involuntary contractions of the biceps brachii at 30% of maximal voluntary contraction (MVC), and the triceps surae at 30% and 50% MVC. Involuntary contractions were evoked by percutaneous electrical stimulation of the muscle. Measurements of the time to peak tension of maximal twitch showed the biceps brachii (67.0 +/- 7.9 ms) muscle to be rapidly contracting, and the triceps surae (118.0 +/- 10.5 ms) to be slow contracting. The systolic and diastolic blood pressures increased linearly throughout the contractions, and systolic blood pressure increased more rapidly than diastolic. There was no significant difference in response to stimulated or voluntary contractions, nor was there any significant difference between the responses to contractions of the calf or arm muscles at the same relative tension. In contrast the heart rate rose to a higher level (P less than 0.01) in the biceps brachii than the triceps surae at given % MVC, and during voluntary compared with the electrically evoked contractions in the two muscle groups. It was concluded that the arterial blood pressure response to isometric contractions, unlike heart rate, is primarily due to a reflex arising within the active muscles (cf. Hultman and Sj?holm 1982) which is associated with relative tension but independent of contraction time and muscle mass.