Dopamine produces muscle contractions and modulates motoneuron-induced contractions inAplysia gill

1. Dopamine has been reported to exist in unusually large quantities in Aplysia gill. The physiological role of this neurotransmitter in this organ was examined. 2. The addition of dopamine to a gill perfusate results in the contractions of the lateral and medial external pinnule muscles, the circular and longitudinal muscles of the afferent vessel, and the circular muscles of the efferent vessel. 3. Dopamine-induced contractions persist after chemical synaptic transmission is eliminated in the gill. This suggests that excitatory dopamine receptors are present on gill smooth muscle fibers themselves. 4. Dopamine also potentiates the gill response to action potentials in single identified gill motoneurons. Evidence presented suggests that muscle contractions and modulation of motoneuron contractions are independent phenomena. 5. While modulation may in part be mediated by increases in excitatory junction potential (EJP) amplitude, in many cases large increases in muscle contractions occur while the enhancement of EJPs is disproportionately small. 6. Dopamine's ability to produce muscle contractions suggests that there may be dopaminergic motoneuron innervation of the gill. We suggest that dopamine's modulatory actions may be mediated via modification of excitation-contraction coupling in smooth muscle fibers.     

Modulation of the Aplysia gill withdrawal reflex by dopamine

The ability of dopamine to modulate gill contractions was tested in Aplysia. When dopamine was perfused through the gill vasculature, gill contractions caused by siphon stimulation (gill withdrawal reflex) and by depolarization of the gill motor neuron L7 were increased in amplitude, as compared with those evoked during seawater perfusion. Habituation of gill movements, brought about by repetitive stimulation of the siphon or of L7, was prevented by dopamine. Despite the absence of reflex habituation, the number of action potentials in central gill motor neurons, evoked by siphon stimulation, showed normal decrement. Dopamine's effects were blocked when the ctenidial nerve was cut or when L7 hyperpolarized. These data suggest that dopamine acts peripherally to increase the efficacy of L7's synaptic transmission onto gill muscle or elements of the gill neural plexus.     

The organization of serotonin-, dopamine-, and FMRFamide- containing neuronal elements and their possible role in the regulation of spontaneous contraction of the gastrointestinal tract in the snail Helix pomatia

Summary The distribution of serotonin-, tyrosine hydroxylase-, and FMRFamide-immunoreactive neuronal elements, as well as the concentrations of serotonin and dopamine in the different parts of the gastrointestinal tract, were studied in the snail Helix pomatia. The sensitivity of the spontaneous contractions of the alimentary tract to serotonin, dopamine, and FMRFamide was also tested. Serotonin-, tyrosine hydroxylase-, and FMRFamide-immunoreactive elements could be demonstrated in each part of the gastrointestinal tract, but they showed different innervation patterns. Serotonin- and tyrosine hydroxylase-immunoreactive elements were dominant in the submucosal layer, whereas FMRFamide-immunoreactive elements were dominant in both the mucosal and submucosal layers. Tyrosine hydroxylase-immunoreactive elements were confined to the longitudinal muscle trabeculae of submucosa, whereas serotonin-immunoreactive elements were distributed throughout the submucosal layer. No serotonin-immunoreactive cell bodies, but only fibers, could be detected in the gastrointestinal tract, and therefore they represent extrinsic elements. Tyrosine hydroxylase- and FMRFamide-immunoreactive cell bodies represent intrinsic elements of the tract. The occurrence and density of the serotonin- and tyrosine hydroxylase-immunoreactive elements showed significant differences in the different parts of the alimentary tract, in accordance with HPLC assays, which revealed a significant frontocaudal decrease in both the serotonin (from 2.11 to 1.21 pM/mg) and dopamine (from 3.28 to 0.52 pM/mg) contents of the different parts of the alimentary tract. Dopamine at 10-5 M concentration proved to be effective only on the longitudinal muscles by increasing the tone and frequency of contractions, but was ineffective on the circular muscles. Serotonin affected both the longitudinal and circular muscles. Serotonin at 10-5 M concentration decreased the tone and increased the frequency of low-amplitude contractions of the longitudinal muscles of the esophagus and the gizzard but increased both the tone and frequency of the crop. Serotonin at 10-9 M concentration slightly decreased the tone and blocked the contractions of the circular muscles in the crop but at 10-5 M concentration induced contractions of the circular muscles in the gizzard. FMRFamide at 10-6 M concentration decreased the tone and was shown to block the contractions of both the longitudinal and circular muscles.     

Branchial musculature of a venerid clam: pharmacology,distribution, and innervation

This study was meant to analyze the neural control of the branchial muscles of the clam Mercenaria mercenaria. Gills isolated from the animal contract in response to 5-hydroxytryptamine (5HT), dopamine (DA), and acetylcholine (ACh); but the ACh contraction occurred only if the gills had been pretreated with the cholinesterase inhibitor eserine. The 5HT antagonists cyproheptadine and mianserin blocked the contractile effects of all of the agonists. However, gills exposed to the 5HT antagonists and eserine relaxed in response to ACh. The DA antagonist SCH-83566 inhibited the effects of DA, but had no effect on contractions induced by 5HT and ACh. The ACh antagonist hexamethonium inhibited both the excitatory and inhibitory effects of ACh, but had no effect on contractions induced by 5HT and DA. 5HT and DA in gill tissue were visualized by using immunohistochemistry. Within each gill filament are dorsoventral neurons running adjacent to the epithelium and containing immunoreactive 5HT and DA. A complex network of 5HT-positive fibers is associated with the septa, blood vessels, and muscles, whereas DA-positive fibers are restricted to the septa. We propose that 5HT is the excitatory transmitter to the gill muscles, and that DA and ACh exert their excitatory effects by stimulating 5HT motor nerves. ACh may also be an inhibitory transmitter of the muscles.     

Aminergic cellular organization in the gills of Aplysia species

The constituent elements of the gills of Aplysia kurodai and A. juliana were examined for the presence of biogenic amines using histochemical, immunocytochemical, and HPLC techniques. Aminergic elements were revealed by glyoxylic acid-induced fluorescence in the branchial nerve, branchial ganglion, branchial vessels, and pinnules in both species. Three types of fluorescent cells were found in the neural plexus of the gill in each species. Two of them might be sensory neurons. Although HPLC analysis showed the presence of serotonin and dopamine in all gill structures including fluorescent neural elements, there were regional differences in concentrations of the monoamines. It was noted in the pinnules that there was a much higher concentration of dopamine than serotonin. Serotonin immunocytochemistry revealed neural processes which were immunoreactive to antiserotonin antibody, but serotonin immunoreactivity could not be found in a population of branchioganglionic neuron (BGN) somata. Serotonergic elements in the ganglion may be processes of the central ganglion, while dopaminergic elements may be processes of neurons in the neural plexus, located beyond the branchial ganglion. BGNs were activated by bath-applied dopamine and serotonin. These results suggest that dopaminergic sensory inputs from the neural plexus and serotonergic descending inputs from the abdominal ganglion may be among the inputs received by BGNs. It was found that serotonin depressed excitatory junctional potentials in muscle cells of the efferent branchial vessel, which were induced by an identified neuron of the abdominal ganglion. The aminergic cellular organization of the gill may involve serotonergic presynaptic-inhibitory fibers arising from the abdominal ganglion.     

The possible roles of the monoaminergic system in the feeding of the snail Helix pomatia

The possible role of serotonin and dopamine in the feeding of Helix pomatia was studied applying immunocytochemical, biochemical, and behavioral techniques as well as bioassay experiments. Immunocytochemistry showed that dopamine-containing (thyrosin-hydroxylase-immunoreactive) neuronal elements of the crop and the gizzard belong to the intrinsic part, whereas serotonin-containing (serotonin-immunoreactive) neuronal elements belong to the extrinsic part of the gastrointestinal nervous system. Bioassay studies on the spontaneous contractions of the crop and the gizzard showed that dopamine affected only the longitudinal muscle contractions by increasing both the tonus and contractility, whereas serotonin was effective on both the longitudinal and circular muscle contractions. Serotonin increased the tonus and contractility of longitudinal muscles in the crop but decreased them in the gizzard. Serotonin decreased the tonus and contractility of the circular muscles in the crop but increased them in the gizzard. Serotonin effects on the circular muscle of the gizzard were concentration dependent between a range of 10(-5) M-3 x 10(-5) M. HPLC measurements of monoamines in starved and satiated animals showed that the concentration of both dopamine and serotonin significantly decreased in both the CNS and different parts of the gastrointestinal tract of satiated animals, suggesting a significant monoamine liberation during feeding. The injection of monoamines (10(-3) and 10(-2) M) into the body cavity of starved animals showed that only dopamine was able to induce feeding whereas serotonin increased the general activity of the animals suggesting that the initiation of feeding is rather dopamine than serotonin dependent.     

Muscular alteration of gill geometry in vitro: implications for bivalve pumping processes

In bivalves, water-pumping potential is determined both by ciliary activity and by the geometry of the system of passageways that acts as a conduit for water flow. Smooth muscles intrinsic to the gills of eulamellibranch bivalves possess the anatomical organization needed to regulate the dimensions of these water passageways. The tone of these muscles can be controlled experimentally using excitatory neurotransmitters to elicit muscle contraction and by removing Ca++ from the Ringer's solution to induce muscular relaxation. These experimental methods were used to investigate the effects of smooth muscle tone on the gill dimensions of two freshwater bivalves, Dreissena polymorpha and Corbicula fluminea, and one marine bivalve, Mercenaria mercenaria. In addition, endoscopic observations were made from the suprabranchial chamber of a freshwater unionid, Lampsilis anodontoides. Contraction of gill muscles led to a significant reduction in interfilament width, internal ostial area, and the cross-sectional area of the water tubes. Endoscopic observation from minimally disturbed L. anodontoides revealed rapid constriction of the water tubes upon contraction of the muscles of the gill and gill axis. Taken together, these data support the idea that alteration of smooth muscle tone in the gill provides a mechanism for controlling water-pumping activities.     

Dopamine modulation of gill reflex behavior in Aplysia.

We have studied the effects of dopamine on the gill withdrawal reflex evoked by tactile siphon stimulation in the margine mollusc Aplysia. Physiological concentrations of dopamine (diluted in seawater) were perfused through the gill during siphon stimulation series. The amplitude of the reflex was potentiated by dopamine and habituation of the reflex was prevented. This occurred with no change in the activity evoked in central motor neurons. These results lead us to conclude that the dopaminergic motor neuron L9 is modulating habituation in the periphery and that the central nervous system facilitatory control of the peripheral nervous system may act via a dopaminergic pathway.     

Functional morphology of feeding and gill irrigation in the anuran tadpole: electromyography and muscle function in larval Rana catesbeiana

This study provides the first data on muscle activity patterns during active feeding in a larval anuran. Data regarding muscle function during gill irrigation and hyperexpiration are also provided. Electromyographic and kinematic data were recorded from six mandibular and hyoid muscles in unanesthetized, unrestrained larvae of Rana catesbeiana. Only three (hyoangularis, orbitohyoideus, anterior interhyoideus) of the six muscles examined are active during gill irrigation. Feeding cycles are characterized by the recruitment of three additional muscles: intermandibularis, suspensorioangularis, and levator mandibulae longus superficialis. The latter two contribute, respectively, to wide opening and forceful closing of the mouth during feeding. Hyperexpiration is characterized by a reversal of water flow anteriorly out of the mouth. This hydrodynamic change occurs due to modulation of the timing of firing of the anterior interhyoideus, as well as recruitment of the posterior interhyoideus, which is only active during hyperexpiration. Both regions of the interhyoideus, which are responsible for evacuation of the buccal cavity, are active during the opening phase of hyperexpiration. Kinematically, transitioning from gill irrigation to feeding involves both an overall shortening of the gape cycle and a shift in the relative length of opening phase vs. closing phase. Our results corroborate many of the findings of Gradwell ([1972] Can J Zool 50:501-521) regarding muscle function during gill irrigation and hyperexpiration. Furthermore, we demonstrate that in larval anurans the transition from gill irrigation to feeding involves modulation of gape cycle kinematics, changes in the level of activity of muscles, and recruitment of muscles that are not active during irrigation. In light of new data presented here, a review of muscle function in tadpoles is also provided.     

Control of Ca2+ efflux and cyclic AMP by 5-hydroxytryptamine and dopamine in abalone gill.

5-Hydroxytrptamine increased the rate of Ca²⁺ efflux and the concentration of endogenous cyclic AMP in abalone gill in both 10 mM and 50 mM CaCl₂ concentrations externally. Dopamine decreased the rate of Ca²⁺ efflux in 50 mM CaCl₂ but slightly increased the efflux rate in 10 mM CaCl₂. At both external Ca²⁺ concentrations, dopamine increased the endogenous cyclic AMP concentration in the gill. 5-Hydroxytryptamine but not dopamine was found to activate adenylate cyclase in broken cell preparations of abalone gill. Cyclic AMP-dependent protein kinase activity was also demonstrated in homogenate fractions of abalone gill. It is suggested that both Ca²⁺ and cyclic AMP act as second messengers in the response of abalone gill to 5-hydroxytryptamine and dopamine.     

Development of cranial muscles in the actinopterygian fish Senegal bichir,Polypterus senegalus Cuvier, 1829

Polypterus senegalus Cuvier, 1829 is one of the most basal living actinopterygian fish and a member of the Actinopterygii. We analyzed the spatial and temporal pattern of cranial muscle development of P. senegalus using whole‐mount immunostaining and serial sectioning. We described the detailed structure of the external gill muscles which divided into dorsal and ventral parts after yolk exhaustion. The pattern of the division is similar to that of urodeles. We suggest that, the external gill muscles of P. senegalus are involved in spreading and folding of the external gill stem and the branches. The fibers of the external gill muscles appear postero‐lateral to the auditory capsule. In addition, the facial nerve passes through the external gills. Therefore, the external gill muscles are probably derived from the m. constrictor hyoideus dorsalis. In contrast to previous studies, we described the mm. interhyoideus and hyohyoideus fibers as independent components in the yolk‐sac larvae. The m. hyohyoideus fibers appear lateral to the edge of the ventral portion of the external gill muscles, which are probably derived from the m. constrictor hyoideus dorsalis. These findings suggest that the m. hyohyoidues is derived from the m. constrictor hyoideus dorsalis in P. senegalus . In other actinopterygians, the m. hyohyoideus is derived from the m. constrictor hyoideus ventralis; therefore, the homology of the m. hyohyoidues of P. senegalus and other actinopterygians remains unclear. J. Morphol. 278:450–463, 2017. © 2017 Wiley Periodicals, Inc.     

The neurotoxic effects of manganese on the dopaminergic innervation of the gill of the bivalve mollusc, Crassostrea virginica

We examined effects of manganese on the nervous system and innervation of lateral cilia of Crassostrea virginica. While essential in trace amounts, tissue manganese accumulation is neurotoxic, inducing Manganism, a Parkinson's-like disease in humans. Lateral cilia of the gill of C. virginica are controlled by a reciprocal serotonergic-dopaminergic innervation from their ganglia. Oysters were incubated 3 days in the presence of up to 1 mM manganese, followed by superfusion of the cerebral ganglia, visceral ganglia or gill with dopamine or serotonin. Beating rates of cilia were measured by stroboscopic microscopy of isolated gill preparations or gill preparations with the ipsilateral cerebral and/or visceral ganglia attached. Acute manganese treatments impaired the dopaminergic, cilio-inhibitory system, while having no effect on the serotonergic, cilio-excitatory system, which is in agreement with the proposed mechanism of manganese toxicity in humans. Manganese treatments also decreased endogenous dopamine levels in the cerebral and visceral ganglia, and gills, but not serotonin levels. We demonstrated that manganese disrupts the animal's dopaminergic system, and also that this preparation can be used to investigate mechanisms that underlie manganese neurotoxicity. It also may serve as a model in pharmacological studies of drugs to treat or prevent Manganism and other dopaminergic cell disorders.     

Effects of dopamine on human retinal vessel diameter and its modulation during flicker stimulation

We performed a randomized, subject-blinded, placebo and time-controlled, two-way crossover study in 12 healthy male subjects. Placebo or dopamine was administered on two separate study days. After saline infusion, dopamine hydrochloride was infused in three consecutive doses (5, 10, and 15 microg x kg(-1) x min(-1)). Plasma levels of dopamine were determined at each perfusion step. Arterial and venous retinal vessel diameters were measured with the use of a Zeiss retinal vessel analyzer. Diffuse luminance flicker stimuli of 8 Hz were applied for 60 s. Blood pressure and pulse rate were monitored continuously. Flicker stimulation (8 Hz) increased retinal vessel diameters under basal conditions. The response to 8-Hz flicker light was significantly reduced by dopamine administration. In addition, dopamine slightly but significantly increased retinal vessel diameters. Dopamine hydrochloride significantly increased systolic but not diastolic or mean arterial pressure. The present study indicates that dopamine has a distinct effect on retinal vessel diameters also attenuating the flicker-induced response reactivity of retinal vessels. This implies a role of dopamine in retinal blood flow hemodynamics.     

The nervous system control of lateral ciliary activity of the gill of the bivalve mollusc, Crassostrea virginica

Lateral cilia of the gill of Mytilus edulis are controlled by a reciprocal serotonergic-dopaminergic innervation from their ganglia. Other bivalves have been studied to lesser degrees and lateral cilia of most respond to serotonin and dopamine when applied directly to the gill indicating a possible neuro or endocrine mechanism. Lateral cilia in Crassostrea virginica are affected by serotonin and dopamine, but little work has been done regarding ganglionic control of their cilia. We examined the role of the cerebral and visceral ganglia in innervating the lateral ciliated cells of the gill epithelium of C. virginica. Ciliary beating rates were measured in preparations which had the ipsilateral cerebral or visceral ganglia attached. Superfusion of the cerebral or visceral ganglia with serotonin increased ciliary beating rates which was antagonized by pretreating with methysergide. Superfusion with dopamine decreased beating rates and was antagonized by ergonovine. This study demonstrates there is a reciprocal serotonergic-dopaminergic innervation of the lateral ciliated cells, similar to that of M. edulis, originating in the cerebral and visceral ganglia of the animal and this preparation is a useful model to study regulatory mechanisms of ciliary activity as well as the pharmacology of drugs affecting biogenic amines in nervous systems.     

Comparative anatomy of the heart–glomerulus complex of Cephalodiscus gracilis (Pterobranchia): structure,function, and phylogenetic implications

Cephalodiscus gracilis Harmer, 1905 is a semi-sessile deuterostome that shares with fish-like chordates pharyngeal gill slits and a dorsally situated brain. In order to reveal structures potentially homologous among deuterostomes and to infer their functional roles, we investigated the axial complex, associated blood vessels and structures of C. gracilis using transmission electron microscopy, light microscopy, and digital 3D reconstructions. We describe the smooth, bipartite cephalic shield retractor muscles that originate as solid compact muscles and fan out to traverse the protocoel as individual muscle cells. The axial complex consists of a cap-shaped coelomic sac, the pericardium that surrounds the central heart. The pericardium is constituted of myoepithelial cells, with the cells facing the heart being thicker and richer in myofilaments. A prominent dorsal median blood vessel opens into the heart, which gives rise to a short median ventral vessel that opens into the paired glomeruli connected to the ventral side of the stomochord. The tip of the curved stomochord rests precisely above the connection of the dorsal median vessel with the heart, a position that would allow the stomochord to function as a valve facilitating unidirectional blood flow. Glomeruli are lined by podocytes of the spacious protocoel and are considered to be the site of ultrafiltration. Two pairs of blood vessels enter the median dorsal blood vessel from the tentacles. The median dorsal blood vessel is separated from the brain by a thin basement membrane. This arrangement is consistent with the hypothesis that blood vessels in the tentacles increase oxygen supply for the brain. Based on detailed similarities, the heart–glomerulus complex of C. gracilis is considered homologous with the heart–glomerulus complex in Rhabdopleura spp., and Enteropneusta, and the axial complex in Echinodermata. In addition, we hypothesize homology to the excretory complex including Hatschek’s nephridium in Cephalochordata. Thus, the heart–glomerulus complex does not support a sister-group relationship between Echinodermata and Hemichordata, whereas the organization of the cephalic shield retractor muscles is consistent with the evolution of pterobranchs within enteropneusts.     

泥螺生殖系统的组织学

泥螺为雌雄同体。生殖系统包括交媾器和生殖器本部。交媾器包括刺激器、阴茎和摄护腺;生殖器本部主要包括两性腺、缠卵腺和蛋白腺。刺激器和阴茎都具有非常发达的肌肉组织,腔壁游离面具纤毛。阴茎腔壁为单层柱状细胞;摄护腺被膜为一层薄的肌纤维,里面具有许多分泌细胞;缠卵腺被膜为单层扁平上皮,下层为环肌,腺体组织由分泌小管构成。蛋白腺主要由皮质层和导管层组成,皮质层内充满了分泌细胞,导管层由许多分泌小管构成,管壁为柱状腺细胞。     

Blood Vessels and Related Structures in the Gill Bars of Glossobalanus minutus (Enteropneusta)

The branchial circulatory system of Glossobalanus minutus (Enteropneusta) is investigated by means of transmission electron microscopy. Primary gill bars, or septa, have a single blood vessel longitudinally located along the outer edge of the bar. Secondary gill bars, or tongue bars, show a vessel in their inner, pharyngeal edge. The walls of both vessels are made up of the basement membranes of surrounding epithelia, lacking an endothelium. No definite limits between the vessel lumen and the skeletal rods inside the bars can be seen. Furthermore, the blood seems to penetrate into the rods of both primary and secondary gill bars. In the secondary bars such a phenomenon gives rise to the so-called 'lateral vessels' reported in the light microscopical literature. The significance of these observations is discussed, with special reference to the gill circulatory system of amphioxus, which seems to be strongly similar from a morphological and ultrastructural point of view.     

A morphological study on posterior gills of the mangrove crab Ucides cordatus

Morphological and histological studies on posterior gills of the mangrove crab Ucides cordatus showed that the 5th gill (of 7) has a larger surface area and a greater number of lamellae compared to the 6th gill. Regular separation of gill lamellae, important when the gill is in air, is maintained by enlargements of the marginal canals. Conical, spine-like structures along the efferent vessel of both 5th and 6th gills were also observed. In addition, pillar cells, a discontinuous lamellar septum and a hypobranchial artery were observed. The presence of valve-like structures near the efferent vessel was also indicated. These structures, together with the pillar cells, may have a role in directing the hemolymph flow towards certain gills during particular physiological states. Localization of osmoregulatory epithelia in the lamellae of both gills was inferred from dimethylaminostyrylethylpyridiniumiodine staining. Apparently gills 5 and 6 have osmoregulatory epithelial cell patches of similar area, corresponding to 43% and 38% of the total lamellae area, respectively. However, their localization is quite different. Gill number 5 osmoregulatory patches seem to be restricted to the afferent region of the lamella whereas in gill number 6, they are more dispersed over the entire lamella. These differences may be related to the particular functional characteristics of these gills.     

黄斑篮子鱼和金钱鱼鳃的扫描电镜观察

对两种鲈形目鱼类黄斑篮子鱼(Siganus oramin)和金钱鱼(Scatophagus argus)的鳃结构进行扫描电镜观察。结果表明,黄斑篮子鱼和金钱鱼鳃的表面结构及微细结构与其他硬骨鱼类基本相似,鳃丝表面都具有规则或不规则分布的环形微嵴、沟、坑、孔等结构。黄斑篮子鱼的鳃片中部鳃丝表皮有大量凸起,而端部鳃丝表皮的凹凸程度明显较低,黄斑篮子鱼的鳃小片高度较金钱鱼鳃小片高。黄斑篮子鱼和金钱鱼鳃上皮的扁平上皮细胞、氯细胞和黏液细胞的形态结构及数量分布存在细微的差异。黄斑篮子鱼鳃片鳃丝的端部和中部表面有黏液细胞,金钱鱼鳃丝表面的黏液细胞很难观察到,与大多数淡水鱼类相似。黄斑篮子鱼鳃丝表面分布的氯细胞数量多于金钱鱼,这可能与两种鱼生活环境、生活习性的长期演变相关。     

Changes in monoamine transmitter concentration in freshwater mussel tissues.

Freshwater mussels were analyzed for biogenic amine transmitter substances in gill tissue, suprabranchial nerve and blood. Gill tissue from normal pondwater-acclimated mussels contained significant amounts of monoamine neurotransmitter substances. In comparison with the suprabranchial nerve the gill tissue contained 42% of the dopamine, 7% of the serotonin and 490% of norepinephrine. Exposing the animals to deionized water (salt-depleted) resulted in a loss of transmitter substances from gill tissue, but serotonin reduction was modest. The mussel gill tissue content of serotonin and the precursor tryptophan was regulated at nearly constant levels. Serotonin is an important transmitter substance in mussels and the many functions it controls, including sodium transport regulation, would depend on its continued presence.