Primitive nervous systems: electrical activity in ventral nerve cords of the flatworm, Notoplana acticola.

Electrical activity evoked in the major cords of the ventral submuscular nerve plexus were measured. Recording and stimulation utilized suction electrodes attached directly to exposed nerve cords. Four categories of potentials have been recorded: (a) short latency spikes which have relatively high thresholds and appear to be single units; (b) short duration fast compound spikes that are made up of a small number of large units; (c) long duration compound potentials that are made up from a large number of smaller units, and (d) small amplitude potentials with long latencies and a characteristic shape. These can be conducted diffusely through the nerve plexus. The first two categories of spikes are called "fast" potentials because of their characteristic rise and fall times and the last categories are known as "diffuse" potentials. The spikelike fast potentials were only recorded from the main trunks (nerves VI), while diffuse potentials could also be recorded from side branches of these nerves. The diffuse potential appears to be conducted throughout the plexus but preferential conducting pathways occur around lesions. Both diffuse and fast potentials show facilitation of response to repeated stimulation. Facilitation can be demonstrated in the presence of high Mg2+ concentrations. Conductance of the diffuse potential also occurs in the presence of high ambient Mg2+. In Ca2+-free medium containing 1-mM EGTA one can also observe facilitatory events. The possibility of Mg2+-insensitive synapses is discussed.     

Primitive nervous systems: Action of aminergic drugs and blocking agents on activity in the ventral nerve cord of the flatworm Notoplana acticola

Electrically evoked activity in the submuscular ventral longitudinal nerve cords of Notoplana acticola is depressed by GABA and glycine in the presence of high magnesium concentrations. This inhibition occurs with 0.001–0.01 millimolar concentrations of these putative aminergic neurotransmitters and is reversible when washed out. The action of GABA and glycine was reversed nonspecifically by picrotoxin, bucuculline, and strychnine. PTZ (Pentylenetetrazole) was shown to mimic the effects that these blocking agents had on evoked activity when they were tested alone. The release of inhibition by these blocking agents is similar to that of decerebration. Three possible mechanisms responsible for synaptic activity in high Mg²⁺ concentrations are discussed and the possibility that the effector site of interaction may be the chloride ionophore is explored.     

Primitive nervous systems: action of aminergic drugs and blocking agents on activity in the ventral nerve cord of the flatworm Notoplana acticola.

Electrically evoked activity in the submuscular ventral longitudinal nerve cords of Notoplana acticola is depressed by GABA and glycine in the presence of high magnesium concentrations. This inhibition occurs with 0.001--0.01 millimolar concentrations of these putative aminergic neurotransmitters and is reversible when washed out. The action of GABA and glycine was reversed nonspecifically by picrotoxin, bicuculline, and strychnine. PTZ (Pentylenetetrazole) was shown to mimic the effects that these blocking agents had on evoked activity when they were tested alone. The release of inhibition by these blocking agents is similar to that of decerebration. Three possible mechanisms responsible for synaptic activity in high Mg2+ concentrations are discussed and the possibility that the effector site of interaction may be the chloride ionophore is explored.     

Primitive nervous systems: electrophysiology of inhibitory events in flatworm nerve cords.

Evoked potentials from the major longitudinal nerve cords of Notoplana acticola are potentiated if the preparation is decerebrated or if certain nerves in the ventral submuscular plexus are severed. Concomitant with an increase in amplitude of the response (in some preparations over fourfold) is a decrease in latency of the response and a decrease in the threshold stimulus intensity needed to evoke activity. Evoked activity can also be depressed with moderate increases in stimulus intensity and is induced some distance from the recording site. The depressant effects can be lifted if the brain is bisected, if the contralateral nerve VI is severed close to the brain, and if the commissures between the two nerves VI are cut. The depressant effects of nerves V and VI are additive. Depression and the subsequent lifting of the inhibition occur in Ringer baths containing either normal sea water or equal mixtures of sea water and isotonic MgCl2. The possibility of inhibitory synapses immune to high concentrations of magnesium ions is discussed.     

Primitive nervous system: Electrophysiology of inhibitory events in flatworm nerve cords

Evoked potentials from the major longitudinal nerve cords of Notoplana acticola are potentiated if the preparation is decerebrated or if certain nerves in the ventral submuscular plexus are severed. Concomitant with an increase in amplitude of the response (in some preparations over fourfold) is a decrease in latency of the response and a decrease in the threshold stimulus intensity needed to evoke activity. Evoked activity can also be depressed with moderate increases in stimulus intensity and is induced some distance from the recording site. The depressant effects can be lifted if the brain is bisected, if the contralateral nerve VI is severed close to the brain, and if the commissures between the two nerves VI are cut. The depressant effects of nerves V and VI are additive. Depression and the subsequent lifting of the inhibition occur in Ringer baths containing either normal sea water or equal mixtures of sea water and isotonic MgCl₂. The possibility of inhibitory synapses immune to high concentrations of magnesium ions is discussed.     

The ultrastructure of neuromuscular systems in Notoplana acticola,a free-living polyclad flatworm

Summary Neuromuscular junctions in the marine polyclad flatworm, Notoplana acticola were studied with the electron microscope. Synapses were found between nerve endings and specialized extensions of the muscle cells. Characteristically these processes contained clear cytoplasm with a basal mitochondrion and numerous microtubules aligned parallel to the long axis of the extension. Sarcoplasmic diverticuli which contained the nucleus had granular cytoplasm with an assortment of membranes and organelles. We have proposed the term sarconeural junction to describe synapses between long sarcoplasmic extensions and nerve cells in flatworms as well as other animals.Tight junctions between adjacent contractile portions of muscle cells were common. As groups of cells appeared to be connected by tight junctions or shared common nerve terminals we conjectured that these formed discrete functional motor-units.     

Neuronal repair and avoidance behavior in the flatworm,Notoplana acticola

In Notoplana avoidance behavior is lost after bisection of the brain or removal of one of its lobes. Behavioral recovery usually occurs within 3–10 days. Recovery of individuals may be gradual or abrupt. Grouped data shows gradual linear repair of turning behavior. Most animals with all connectives between the two lobes of the brain severed recovered preoperative responses, while those with one lobe of the brain removed averaged about 60% of the preoperative level of response. Some individuals in both groups recovered completely. Histological evidence of neuronal repair was found in all animals. Where the lobes of the brain were separated, connectives between them appeared to re-form. In worms with one lobe of the brain removed, the nerves disconnected by the excision joined the remaining lobe. Action potentials are conducted across repaired tissue in both split-brain and half-brain worms in both seawater and Mg²⁺-rich solutions. CNS repair appears to involve functional synaptic contacts. Notoplana does not replace ganglionic tissue but does compensate adequately for CNS damage.     

Nerve repair and behavioral recovery following brain transplantation in Notoplana acticola, a polyclad flatworm

Although Notoplana acticola, a marine polyclad, cannot regenerate brain tissue, neuronal repair is rapid. Brains were transplanted into decerebrate flatworms to determine the anatomical patterns and functionality of neural connections established between a new brain and the peripheral nerve network of the recipient animal. Sixty-nine transplants were performed. Four brain transplant orientations were used: normal, reversed, inverted, and reversed inverted. The functionality of the transplanted brains was tested and measured using both behavioral and electrophysiological criteria. Within 23 days, 56% of the transplants that survived and retained the transplants recovered the four behaviors tested: righting behavior, avoidance turning, ditaxic locomotion, and feeding. Nerves exiting the brain tended to join with the peripheral nerves closest to them. Anatomical connections were made within 24 hr of surgery. Some normal behavior was seen within the first 36 hrs after surgery. Control decerebrate worms did not recover behavior. Preliminary intracellular recordings from three types of identified brain sensory interneurons, in transplants, revealed normal electrophysiological properties and this implied that appropriate connections with peripheral sensory cells had been reestablished. Intracellular dye-marking of these neurons in reverse-oriented brains revealed that, although individual nerve processes apparently leave the brain and associate with inappropriate nerve cords, some of the processes turn 180 degrees to reinervate nerve cords, which they normally occupy in unoperated animals. Thus, although anatomical and functional neural connections apparently were made rapidly following brain transplantation, the specificity of the reconnections remains to be shown.     

Primitive nervous systems: electrophysiology of the pharynx of the polyclad flatworm, Enchiridium punctatum.

1. Electrical activity accompanying motor activity can be recorded from the excised pharynx of Enchiridium punctatum. Multiple stimuli elicit behaviour which consists of an initial aperture closure followed by extension and then peristalsis. If the stimulus parameters are increased the preparation bends from side to side instead of proceeding through the behavioural sequence. Bending appears to inhibit other movements differentially. 2. The conduction involved with peristalsis is polarized and proceeds in a proximal direction. 3. With stimulus intensities greater than those needed to produce the behavioural response an initial muscle potential (IMP) is evoked. The IMP is frequency sensitive. Maximum facilitation occurs within 100 ms and drops to 50% of maximum within 250 ms. 4. Conduction velocities of the IMP range from 0-05 m s-1 to 1-9 m s-1. Conduction velocities appear to increase with facilitation.     

Comparison of the nervous system of the rhabdocoel Mesostoma ehrenbergii with that of the polyclad Notoplana acticola

The neuromuscular organization of the free-living marine polyclad Notoplana acticola (Boone) can be compared with that of the fresh water rhabdocoel Mesostoma ehrenbergii (Focke). These examples act as outgroups for each other, belonging to different clades of the Turbellaria and similarities between the two can be taken as synapomorphies to indicate features that might be primitive and general features of flatworm nervous systems. The fluorescent dye Lucifer Yellow was used to fill cells in the brains of the two species and the neuronal anatomies were photographed or drawn. Many different cell types have been found in both species. The predominant cell types in Mesostoma were heteropolar bipolar and heteropolar multipolar cells with isopolar bipolar and isopolar multipolar cells in much lower numbers; only a few unipolar cells were found. In Notoplana, many of the cells penetrated were also heteropolar bi- or multipolar cells. There were also neurons and architectural features that were morphologically very similar to each other, in the two animals, such as the BRA cells and commissural tracts. These shared features suggest that many of the peculiarities of polyclad nervous systems may be general flatworm features.     

Neuronal Repair and Recovery of Function in the Polyclad Flatworm, Notoplana acticola

SYNOPSIS. Polyclad flatworms are unable to regenerate or replaceparts of their central nervous systems but are able to repairlesions in the cerebral ganglion or peripheral nerve plexusesRepair of nerve lesions is very rapid and functional activityis reestablished within 48 hr Bilateral coordination can bereestablished in animals with either split brains or in animalswhere half of the brain, on one side has been excised Animalswith transplanted brains display normal behavior even if thebrain has been rotated and inverted Likewise, in animals whichhad the brain transplanted into the tail region, cerebral dominancewas reestablished even after the brain was rotated through 180°A time sequence of events during healing of cut nerves has beenestablished Sprouting starts approximately 4 hr after injuryContact between a filopodium from the proximal section and distalstump occurs approximately 14 hr after the injury Filopodiaare subsequently retracted and the area of contact between thetwo segments increased After 72 hr there are no filopodia andthe axon appears to be intact Healing between the two cut ends,therefore appears to involve fusion of the cut axons Indirectevidence suggests that neurones recognize their own specificsegments.     

Evolution of flatworm central nervous systems: Insights from polyclads

The nervous systems of flatworms have diversified extensively as a consequence of the broad range of adaptations in the group. Here we examined the central nervous system (CNS) of 12 species of polyclad flatworms belonging to 11 different families by morphological and histological studies. These comparisons revealed that the overall organization and architecture of polyclad central nervous systems can be classified into three categories (I, II, and III) based on the presence of globuli cell masses -ganglion cells of granular appearance-, the cross-sectional shape of the main nerve cords, and the tissue type surrounding the nerve cords. In addition, four different cell types were identified in polyclad brains based on location and size. We also characterize the serotonergic and FMRFamidergic nervous systems in the cotylean Boninia divae by immunocytochemistry. Although both neurotransmitters were broadly expressed, expression of serotonin was particularly strong in the sucker, whereas FMRFamide was particularly strong in the pharynx. Finally, we test some of the major hypothesized trends during the evolution of the CNS in the phylum by a character state reconstruction based on current understanding of the nervous system across different species of Platyhelminthes and on up-to-date molecular phylogenies.     

The structure of Archiannelid Dinophilus gyrociliatus ventral nerve cords

Dinophilus gyrociliatus is a typical representative of the synthetic group Archiannelida. Here we describe the structure of Dinophilus young adults ventral nerve cords. Five nerve cords, irregular commissures and intersegmental nerves are revealed by tubulin and FMRFamide immunostaining. 5-HT-stainning marks the complex varicose nerve plexus with numerous irregularly distributed small perikarya. Four nerve cords and solitary cell bodies occur after clyoxylic-induced reaction for catecholamines visualization. Altogether, our results indicated that morphology of Dinophilus ventral nerve cords differs from the Polychaetes archetype in many respects.     

Donor-recipient interconnections between giant nerve fibers in transplanted ventral nerve cords of earthworms

Twelve segments of ventral nerve cord (VNC) from donor earthworms, Eisenia foetida, were transplanted into recipient worms from which a comparable length of VNC had been removed. Within the first few days after transplantation, bud-like formations, containing outgrowths of the giant nerve fibers, were evident at the ends of transplanted and recipient VNC. Morphological and electrophysiological evidence indicated that by 4-10 days after transplantation, medial (MGF) and lateral (LGF) giant fibers within the transplanted VNC formed cell-specific connections with their counterparts in the recipient VNC. Although the diameters of the giant fiber connections in the transplant-recipient junctions were often larger than normal, spike conduction across the junction was initially slow (approximately 1.0 m/s) but gradually increased over the next 2-3 weeks. Within the transplant, giant fibers were initially normal in appearance, but spike conduction was slow (1-2 m/s). During the next few weeks velocities increased by as much as fourfold and then stabilized for the next several months. However, by 4-5 weeks after transplantation, giant fiber morphology within the transplant was altered significantly, as indicated by the formation of numerous branch-like extensions along the length of each giant fiber. By 9-10 months there were further morphological changes in the transplant, as indicated by decreased branching of the giant fibers and altered neuropile. Despite these morphological changes, through-conduction of giant fiber spikes remained reliable.     

Demonstration of motoneuron-12 sparing in cultured Manduca sexta ventral nerve cords

The emergence of the adult Manduca sexta moth is accompained by the death of half of the neurons present in the pupal abdominal nervous system (Truman, 1983). This developmental neuronal death is highly selective, so that the same neurons die at the same time relative to emergence in every moth. In the case of the MN-12 motoneurons, this cell death is regulated both by hemolymph concentrations of a steroid hormone, 20-hydroxyecdysone, and by actions exerted by adjacent ganglia (Truman and Schwartz, 1984; Fahrbach and Truman, 1987). This latter effect, which has been previously described in isolated abdomens and in moths with transected ventral nerve cords, has now been reproduced under controlled culture conditions in which the selectivity and extent of postemergence neuronal death is comparable to that seen in vivo. With respect to the MN-12 neurons found in the most anterior unfused abdominal ganglion, A₃, the pterothoracic ganglion appears to be the source of a factor that permits these neurons to die according to their usual developmental schedule. © 1992 John Wiley & Sons, Inc.     

节肢动物肠道及腹神经索的降解实验*

节肢动物的内部器官组织, 如消化系统和神经系统等精细结构在寒武纪化石中的保存特征对探索早期生命和地球环境的演化具有重要意义。近年来, 其原始形态与保存机理被广泛讨论, 说明此类型软躯体组织的保存行为还需多方面的实验和理论探索。实验埋藏学作为埋藏学的分支, 为解释生物化石化过程中解剖结构的变化及相应特异埋藏化石库的形成提供了重要理论支撑和实验技术手段。本文以节肢动物南美白对虾的肠道和腹神经索为材料, 在不同温度及组合条件下进行埋藏学实验, 以观察此类生物软组织的降解过程。实验结果显示, 肠道和腹神经索在不同温度下的降解趋势相似, 但降解速率不同: 肠道和腹神经索在25℃条件下的降解速率和降解程度明显大于其在10℃条件。同一温度条件下, 肠道与腹神经索的降解程度存在早期差异; 10℃条件下, 反应产生的微生物膜形态及规模有所不同, 肠道-腹神经索组合产生的微生物膜规模远大于肠道、腹神经索的单独处理组, 且难以辨认。由此可见, 温度是影响肠道和腹神经索降解速度和程度的重要因素。此外, 微生物在生物内部器官组织降解过程中起到了重要的生化作用。生物器官组织的降解过程, 以及不同条件下微生物膜的形成对化石的形态特征尤其是内部精细结构的保存解释具有重要影响。     

Primitive nervous systems: Peripheral habituation in decerebrate polyclad flatworms

The response to a vibration stimulus recorded from the cords of the ventral submuscular plexus of the polyclad flatworm, Notoplana acticola, consists of a burst of action potentials. The response can be abolished by the application of MgCl₂ to the sea water bathing the preparation. With repeated application of the stimulus, decreasing numbers of action potentials can be measured. This waning responsiveness can be dishabituated by applying a more intense vibration stimulus or with electrical shocks applied directly to the ventral nerve plexus. With electrical stimuli a number of shocks have to be applied before the response can be dishabituated. Changes in responsiveness can be measured simultaneously in a number of sites in the plexus even after the nerves between recording sites have been severed. With different interstimulus intervals the extent of habituation changes. As interstimulus intervals increase from 1 to 5 sec, there appears to be a decrease in responsiveness which recovers when interstimulus intervals become longer than 5 sec.     

Demonstration of motoneuron-12 sparing in cultured Manduca sexta ventral nerve cords.

The emergence of the adult Manduca sexta moth is accompanied by the death of half of the neurons present in the pupal abdominal nervous system (Truman, 1983). This developmental neuronal death is highly selective, so that the same neurons die at the same time relative to emergence in every moth. In the case of the MN-12 motoneurons, this cell death is regulated both by hemolymph concentrations of a steroid hormone, 20-hydroxyecdysone, and by actions exerted by adjacent ganglia (Truman and Schwartz, 1984; Fahrbach and Truman, 1987). This latter effect, which has been previously described in isolated abdomens and in moths with transected ventral nerve cords, has now been reproduced under controlled culture conditions in which the selectivity and extent of postemergence neuronal death is comparable to that seen in vivo. With respect to the MN-12 neurons found in the most anterior unfused abdominal ganglion, A3, the pterothoracic ganglion appears to be the source of a factor that permits these neurons to die according to their usual developmental schedule.     

The agonist action of substituted phenylethanolamines on octopamine receptors in cockroach ventral nerve cords

1. Effect of 72 ring or α-substituted phenylethanolamines (SPEAs) was examined on the adenylate cyclase prepared from ventral nerve cords of the American cockroach Periplaneta americana.2. Para-Cl-SPEA was the most effective octopaminergic agonist, followed by p-Br-, p-F-, p-Me-, p-NO₂- and p-CF₃-SPEA.3. Meta- and o-SPEAs were less active than p-SPEAs, in stimulating adenylate cyclase.4. SPEA analogs interact with the same binding site as octopamine in the nerve cords of American cockroach, since the level of evoked cAMP production by a combination of optimally effective concentrations of octopamine and SPEA was not greater than the stimulation by octopamine alone.5. Washing removed nearly all of the stimulatory activity of SPEA, suggesting that SPEA binds reversibly to the octopaminergic receptor.