Activity-dependent accumulation of Ca2+ in axon and dendrites of the leech Leydig neuron

We have investigated Ca2+ changes evoked by single action potentials (APs) in axon and dendrites of leech Leydig neurons. Dendritic Ca2+ transients induced by an AP were twice as large as in the axon, and Ca2+ recovery was significantly faster in the dendrites as compared to the axon. The AP-induced Ca2+ transients were blocked by Co2+ and suppressed in Ca2+-free saline, indicating Ca2+ influx through voltage-activated channels. During a train of APs, Ca2+ accumulated significantly more in the axon than in the dendrites. Suppression of the Ca2+ influx changed the shape of the action potential and increased the firing frequency. The results suggest a functional role of Ca2+ influx and Ca2+ accumulation during electrical activity in different neuronal subcompartments.

Olfactory receptor axons influence the development of glial potassium currents in the antennal lobe of the moth Manduca sexta

In the olfactory (antennal) lobe of the moth Manduca sexta, olfactory receptor axons strongly influence the distribution and morphology of glial cells. In the present study, we asked whether the development of the electrophysiological properties of the glial cells is influenced by the receptor axons. Whole-cell currents were measured in antennal lobe glial cells in acute brain slices prepared from animals at different stages of metamorphic development (stages 3, 6, and 12). Outward currents were induced by depolarizing voltage steps from a holding potential of -70 mV. At all developmental stages investigated, the outward currents were partly blocked by bath application of the potassium channel blocker 4-aminopyridine (4AP, 10 mM) or by including tetraethylammonium (TEA, 30 mM) in the pipette solution. The relative contribution of the 4AP-sensitive current to the outward current increased from 18% at stages 3 and 6 to 42% at stage 12, while the TEA-sensitive current increased from 18% at stage 3 to 81% at stage 6, and then declined again to 40% at stage 12. In contrast, in the absence of receptor axons, these changes in the contribution of the TEA- and 4AP-sensitive currents to the total outward current did not occur; rather, the current profile remained in the most immature state (stage 3). The results suggest that olfactory receptor axons are essential for development of the mature pattern of glial potassium currents.

Decrease of effectivity of "competing" synaptic input requires protein synthesis

We describe that tetanus-induced long-term increase of the response amplitude in one input to an identified neuron is accompanied by a decrease of synaptic responses in another, non-tetanized input. Induction of the decrease of responses in non-tetanized inputs was prevented by bath application of protein synthesis blockers (anisomycin or cycloheximide). The decrease of responses also did not occur in experiments when tetanization was substituted by short-term serotonin applications or extracellular stimulation of serotonergic cells known to potentiate investigated synaptic inputs. The results suggest that the heterosynaptically evoked decrease of synaptic response amplitude may be due to involvement of postsynaptic protein synthesis-dependent mechanisms.

Innervation of the heart and aorta of Manduca sexta

Innervation of the heart and aorta of Manduca sexta was studied by using anatomic, neuronal tracing and immunocytochemical techniques. The study was undertaken to provide a foundation for investigating the neural mechanisms controlling cardiac reversal in adults. Lateral cardiac nerves were not found in the larval or adult heart. The larval heart and aorta seem to lack innervation, but a neurohemal system for the release of a cardioactive peptide is associated with the larval alary muscles. At adult metamorphosis, this neurohemal system regresses, and, at the same time, processes grow onto the anterior aorta. These processes seem to be neurohemal and originate from two pairs of neurosecretory cells located in the subesophageal ganglion. This system is immunoreactive to cardioactive peptides and may function, therefore, in hormonal modulation of the activity of the adult heart. Also during metamorphosis, synaptic innervation develops on the terminal heart chamber, and this innervation is from axons extending through the seventh and eighth dorsal nerves of the terminal abdominal ganglion. These axons originate from cells that have been identified as serial homologs of motor neuron-1 of other abdominal ganglia. These neurons are immunoreactive to a cardioactive peptide, and this peptide probably modulates the synaptic innervation of the terminal heart chamber. During metamorphosis, the target of the motor neurons-1 of the seventh and eighth segments becomes respecified from larval skeletal muscles to the terminal chamber of the adult heart.

The nicotinic alpha subunit MARA1 is necessary for cholinergic evoked calcium transients in Manduca neurons

The functional contribution of cloned subunits to insect nicotinic acetylcholine (ACh) receptors has been difficult to determine using heterologous expression. Instead, in this study we explore the subunit composition of naturally expressed functional receptors in an insect using RNA interference. The nicotinic alpha subunit, Manduca ACh Receptor Alpha 1 (MARA1) can be detected in neuronal cultures isolated from the ventral nerve cord of fifth instar larvae of Manduca sexta by in situ hybridization. It's presence correlates with large ACh induced, nicotinic Ca2+ responses. The expression of MARA1 is downregulated by treatment with dsRNA which significantly reduced both the number of responding cells and the amplitude of remaining Ca2+ responses. These results suggest that MARA1 is part of a nicotinic receptor functionally coupled to Ca2+ entry.

Pattern of expression of engrailed in relation to gamma-aminobutyric acid immunoreactivity in the central nervous system of the adult grasshopper

Engrailed (En) protein expression in neurons of the mesothoracic and metathoracic ganglia of the adult grasshopper, Schistocerca americana, was examined by immunohistochemistry. Each neuromere had a dorsally located cluster of En-positive neurons within the dorsal unpaired median (DUM) group, comprising one cluster in the mesothoracic ganglion (T2) and four clusters in the metathoracic ganglion, one for each component neuromere (T3, A1, A2, A3). Ventrally, En-positive neurons occurred in the posterior one-third of each neuromere. In T2 and T3, three ventral groups of neurons were labeled bilaterally. In the abdominal neuromeres, many fewer ventral neurons were En-positive. These also were bilaterally symmetrical, but did not occur in patterns that allowed assignment of homology with the T2 and T3 groups. Altogether, En-positive neurons comprised roughly 10% of the ganglionic populations. In the bilateral groups, as in the DUM groups, En expression was restricted to interneurons, consistent with the suggestion that En expression contributes to some aspect of interneuronal phenotype. En-positive neurons in the DUM groups also expressed gamma-aminobutyric acid (GABA) immunoreactivity. Further study showed that all neurons in one En-positive bilateral group and some neurons in another bilateral group were GABA immunoreactive, but that neurons in a third bilateral group were En-positive only. Additionally, several discrete clusters of neurons were GABA-immunoreactive but En-negative. A provisional morphological scheme is presented, which relates the several neuronal clusters to their likely neuroblasts of origin, as a basis for further research into the composition of neuronal lineages.

Three-dimensional computer-aided reconstruction of FMRFamide immunopositive neuron distribution in the ventral ganglion of the barnacle Balanus amphitrite (Cirripedia, Crustacea)

We have implemented a simple program to solve three of the problems related to 3D reconstruction (3D-Rec) of soft tissues: alignment of sections, distortions, and estimation of the spatial position of elements of interest inside the tissues. As a model, we chose the distribution of FMRFamide-like immunopositive neurons in the ventral ganglion of the barnacle Balanus amphitrite collected during different seasonal periods. Images of immunostained sections were acquired by means of a CCD-camera-equipped microscope and a PC and the reference points were taken inside the sections. The FMRFamide-like immunopositive neurons detected in the barnacle ventral ganglion were grouped into four different classes according to size, shape and staining intensity. More numerous FMRFamide-like immunopositive neurons were detected in the autumn-collected barnacle than in the summer counterpart. The two 3D reconstructions obtained from transverse and longitudinal ventral ganglion sections were efficaciously compared after 90 degrees rotation of one of them. Comparison of these two 3D-Rec suggests the presence of at least two groups of FMRFamide-like immunopositive neurons that are seasonally-related and probably involved in reproduction.

[Non-synaptic integration of neuronal cell bodies in the snail central nervous system]

Approach to regions occupied by perikarya of the snail 5-HT-ergic neurons produced excitation. The strongest action was recorded on the PedA cluster surface, and it was further enhanced by adding the 5-HT precursor. The findings suggest that the mechanisms underlying 5-HT-dependent behaviour include a mutual excitatory co-operation between somata of neighbouring 5-HT-ergic neurons.

Conditional rescue of olfactory learning and memory defects in mutants of the 14-3-3zeta gene leonardo

Members of the ubiquitous 14-3-3 family of proteins are abundantly expressed in metazoan neurons. The Drosophila 14-3-3zeta gene leonardo is preferentially expressed in adult mushroom bodies, centers of insect learning and memory. Mutants exhibit defects in olfactory learning and memory and physiological neuroplasticity at the neuromuscular junction. Because strong mutations in this gene are lethal, we investigated the nature of the defects that precipitate the learning and memory deficit and the role of the two protein isoforms encoded by leonardo in these processes. We find that the behavioral deficit in the mutants is not caused by aberrant development, LEONARDO protein is acutely required for learning and memory, and both protein isoforms can function equivalently in embryonic development and behavioral neuroplasticity.

The enterins: a novel family of neuropeptides isolated from the enteric nervous system and CNS of Aplysia

To identify neuropeptides that have a broad spectrum of actions on the feeding system of Aplysia, we searched for bioactive peptides that are present in both the gut and the CNS. We identified a family of structurally related nonapeptides and decapeptides (enterins) that are present in the gut and CNS of Aplysia, and most of which share the HSFVamide sequence at the C terminus. The structure of the enterin precursor deduced from cDNA cloning predicts 35 copies of 20 different enterins. Northern analysis, in situ hybridization, and immunocytochemistry show that the enterins are abundantly present in the CNS and the gut of Aplysia. Using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry we characterized the enterin-precursor processing, demonstrated that all of the precursor-predicted enterins are present, and determined post-translational modifications of various enterins. Enterin-positive neuronal somata and processes were found in the gut, and enterins inhibited contractions of the gut. In the CNS, the cerebral and buccal ganglia, which control feeding, contained the enterins. Enterin was also present in the nerve that connects these two ganglia. Enterins reduced the firing of interneurons B4/5 during feeding motor programs. Such enterin-induced reduction of firing also occurred when excitability of B4/5 was tested directly. Because reduction of B4/5 activity corresponds to a switch from egestive to ingestive behaviors, enterin may contribute to such program switching. Furthermore, because enterins are present throughout the nervous system, they may also play a regulatory role in nonfeeding behaviors of Aplysia.

A fast and sensitive method for measuring picomole levels of total free amino acids in very small amounts of biological tissues

In the present study we describe a simple and fast method to measure the concentration of total free amino acids in very small amounts of biological tissues. The procedure described here is based on the reaction of free amino acids with o-phthaldialdehyde (OPA) in the presence of a reducing agent, beta-mercaptoethanol (MET), to give a complex which can be measured by fluorescence. It is a very rapid process and has the same reliability as the conventional ninhydrin method of Moore and Stein but is about 500 times more sensitive. The sensitivity of the new protocol is such to permit the determination with high reliability of very small amounts of free amino acids at picomole levels, either in a standard amino acid mixture or in biological tissues, without chromatographic separation of the amino acids. It is particularly useful when the amount of the sample is very low, e.g. on a single pituitary or pineal gland of small animals or on single cells, such as oocytes or eggs, as well as single ganglions or axons of marine invertebrates.

Serotonin-induced nitric oxide production in the ventral nerve cord of the earthworm, Eisenia fetida

Effect of serotonin on nitric oxide (NO) production in the ventral nerve cord (VNC) of the earthworm Eisenia fetida was investigated by a bio-imaging and an electrochemical technique. In the bio-imaging, the spatial pattern of NO production in VNC was visualized using an NO-specific fluorescent dye, diaminofluorescein-2 diacethyl (DAF-2 DA). Application of serotonin (100 microM) increased NO production in VNC by about 65% (P<0.05), compared with basal NO production. The increase was mainly from the nitergic neurons in the ventral side of VNC. In the electrochemical technique, real-time basal and serotonin-induced NO production was estimated with an NO-specific electrode. On the ventral surface of VNC, the estimated basal NO production was stable at 200+/-52 nM, and was transiently augmented to 840+/-193 nM by the addition of 10 microM serotonin. In conclusion, the estimated basal NO production in the earthworm VNC is relatively high compared with other nervous systems earlier reported, and transiently augmented by serotonin. Our results suggest that NO signaling in VNC is involved in neuromodulation by serotonin.

Long-term maintenance of channel distribution in a central pattern generator neuron by neuromodulatory inputs revealed by decentralization in organ culture

Organotypic cultures of the lobster (Homarus gammarus) stomatogastric nervous system (STNS) were used to assess changes in membrane properties of neurons of the pyloric motor pattern-generating network in the long-term absence of neuromodulatory inputs to the stomatogastric ganglion (STG). Specifically, we investigated decentralization-induced changes in the distribution and density of the transient outward current, I(A), which is encoded within the STG by the shal gene and plays an important role in shaping rhythmic bursting of pyloric neurons. Using an antibody against lobster shal K(+) channels, we found shal immunoreactivity in the membranes of neuritic processes, but not somata, of STG neurons in 5 d cultured STNS with intact modulatory inputs. However, in 5 d decentralized STG, shal immunoreactivity was still seen in primary neurites but was likewise present in a subset of STG somata. Among the neurons displaying this altered shal localization was the pyloric dilator (PD) neuron, which remained rhythmically active in 5 d decentralized STG. Two-electrode voltage clamp was used to compare I(A) in synaptically isolated PD neurons in long-term decentralized STG and nondecentralized controls. Although the voltage dependence and kinetics of I(A) changed little with decentralization, the maximal conductance of I(A) in PD neurons increased by 43.4%. This increase was consistent with the decentralization-induced increase in shal protein expression, indicating an alteration in the density and distribution of functional A-channels. Our results suggest that, in addition to the short-term regulation of network function, modulatory inputs may also play a role, either directly or indirectly, in controlling channel number and distribution, thereby maintaining the biophysical character of neuronal targets on a long-term basis.

Structure and response patterns of olfactory interneurons in the honeybee, Apis mellifera

To analyze morphologic and physiological properties of olfactory interneurons in the honeybee, Apis mellifera, antennal lobe (AL) neurons were intracellularly recorded and subsequently labeled with Neurobiotin. Additional focal injections were carried out with cobalt hexamine chloride and dextran fluorescent markers. Olfactory interneurons (projection neurons, PNs) project by means of five tracts, the lateral, the median, and three mediolateral antennocerebral tracts (l-, m-, and ml-ACT, respectively) to the mushroom bodies (MBs) and the protocerebral lobe (PL) of the ipsilateral protocerebrum. Uniglomerular PNs of the m- and l-ACT receiving input from a single glomerulus of the AL also arborize in different regions of the AL. The vast majority of l-ACT innervate the T1 region, whereas m-ACT neurons arborize exclusively in the T2, T3, and T4 regions (T1-4 : AL projection area of sensory cells from the antennae). In the calyces of the MB, uniglomerular PNs form varicosities in the basal ring and the lip region. Individual neurons of both types exhibit unequal innervation within and between the two calyces. In addition, m-ACT fibers ramify more densely within the lip neuropil and show a higher incidence of spine-like processes than l-ACTs. In the PL, l-ACTs arborize exclusively within the lateral horn, whereas some m-ACT neurons innervate a broader region. Multiglomerular neurons of the ml-ACT leave the AL by means of three subtracts (ml-ACT 1-3). Two different types can be distinguished according to their protocerebral target areas: ml-ACTs projecting to the lateral PL (LPL) and to the neuropil around the alpha-lobe (tracts 2 and 3) and neurons projecting only to the LPL (tract 1). Intracellular recordings indicate that both l- and m-ACT neurons respond to general odors but with different response properties, indicating that odor information is processed in parallel pathways with different functional characteristics. Just like m-ACT neurons, ml-ACT neurons respond to odors with complex activity patterns. Bilateral interneurons, originating in the suboesophageal ganglion, connect glomeruli of both AL, and send an axon through the m-ACT in each hemisphere of the brain, terminating in the lip region of the calyces. These neurons respond to contact chemical stimuli.

Aplysia ror forms clusters on the surface of identified neuroendocrine cells

The ror receptors are a highly conserved family of receptor tyrosine kinases genetically implicated in the establishment of cellular polarity. We have cloned a ror receptor from the marine mollusk Aplysia californica. Aplysia ror (Apror) is expressed in most developing neurons and some adult neuronal populations, including the neuroendocrine bag-cell neurons. The Apror protein is present in peripheral neuronal processes and ganglionic neuropil, implicating the kinase in the regulation of growth and/or synaptic events. In cultured bag-cell neurons, the majority of the protein is stored in intracellular organelles, whereas only a small fraction is expressed on the surface. When expressed on the cell surface, the protein is clustered on neurites, suggesting that Apror is involved in the organization of functional domains within neurons. Apror immunoreactivity partially colocalizes with the P-type calcium channel BC-alpha1A at bag-cell neuron varicosities, suggesting a role for Apror in organizing neuropeptide release sites.

The angiotensin system elements in invertebrates

In this review, the different components of the renin-angiotensin system (RAS) in invertebrates are discussed. This system is implicated in osmoregulation, reproduction, memory processes and immune system regulation. As the elements of this hormone-enzymatic system also exist in invertebrates, it appears that the RAS originated very early in evolution.

The Eps15 C. elegans homologue EHS-1 is implicated in synaptic vesicle recycling

Eps15 represents the prototype of a family of evolutionarily conserved proteins that are characterized by the presence of the EH domain, a protein-protein interaction module, and that are involved in many aspects of intracellular vesicular sorting. Although biochemical and functional studies have implicated Eps15 in endocytosis, its function in the endocytic machinery remains unclear. Here we show that the Caenorhabditis elegans gene, zk1248.3 (ehs-1), is the orthologue of Eps15 in nematodes, and that its product, EHS-1, localizes to synaptic-rich regions. ehs-1-impaired worms showed temperature-dependent depletion of synaptic vesicles and uncoordinated movement. These phenotypes could be correlated with a presynaptic defect in neurotransmission. Impairment of EHS-1 function in dyn-1(ky51) worms, which express a mutant form of dynamin and display a temperature-sensitive locomotion defect, resulted in a worsening of the dyn-1 phenotype and uncoordination at the permissive temperature. Thus, ehs-1 and dyn-1 interact genetically. Moreover, mammalian Eps15 and dynamin protein were shown to interact in vivo. Taken together, our results indicate that EHS-1 acts in synaptic vesicle recycling and that its function might be linked to that of dynamin.

Target-dependent modulation of neurotransmitter release in cultured Helix neurons involves adhesion molecules

The secretory capabilities of the serotonergic neuron C1 of cerebral ganglion of Helix pomatia were markedly reduced when it was cultured in contact with the wrong target neuron, C3. When the neuron B2, one of its physiological targets, was micromanipulated within the network made of intermingled neurites originating from the axonal stumps of both C1 and C3 neurons, C1 increased the amount of the evoked transmitter release, which, after 30 min, reached the level observed when cocultured with the appropriate target. The removal of the appropriate target brought C1 back to the low release condition. By imaging C1 neurites with a fluorescent dye, morphological changes involving a local increase in the number of varicosities could be observed as early as 30 min after contact with the appropriate target. Monoclonal antibody 4E8 against apCAM, a family of Aplysia adhesion molecules, recognizes apCAM-like molecules of the Helix central nervous system on immunocytochemistry and Western blot analysis. The contact with the appropriate target previously incubated in a 4E8 solution, which did not interfere with its capacity to respond to serotonin, failed to increase the transmitter release of C1 cocultured in the presence of the wrong target, C3. These results suggest that the apCAM-like antigens bound to the target membrane participate in the molecular processes responsible for the assembly of the "release machinery" present in the functional presynaptic structure.

Intracellular injection of synapsin I induces neurotransmitter release in C1 neurons of Helix pomatia contacting a wrong target

The contact with the postsynaptic target induces structural and functional modifications in the serotonergic cell C1 of Helix pomatia. In previous studies we have found that the presence of a non-physiological target down-regulates the number of presynaptic varicosities formed by cultured C1 neurons and has a strong inhibitory effect on the action potential-evoked Ca(2+) influx and neurotransmitter release at C1 terminals. Since a large body of experimental evidence implicates the synapsins in the development and functional maturation of synaptic connections, we have investigated whether the injection of exogenous synapsin I into the presynaptic neuron C1 could affect the inhibitory effect of the wrong target on neurotransmitter release. C1 neurons were cultured with the wrong target neuron C3 for three to five days and then injected with either dephosphorylated or Ca(2+)/calmodulin-dependent protein kinase II-phosphorylated Cy3-labeled synapsin I. The subcellular distribution of exogenous synapsin I, followed by fluorescence videomicroscopy, revealed that only synapsin I phosphorylated by Ca(2+)/calmodulin-dependent protein kinase II diffused in the cytoplasm and reached the terminal arborizations of the axon, while the dephosphorylated form did not diffuse beyond the cell body. Evoked neurotransmitter release was measured during C1 stimulation using a freshly dissociated neuron B2 (sniffer) micromanipulated in close contact with the terminals of C1. A three-fold increase in the amplitude of the sniffer depolarization with respect to the pre-injection amplitude (190+/-29% increase, n=10, P<0.006) was found 5 min after injection of Ca(2+)/calmodulin-dependent protein kinase II-phosphorylated synapsin I that lasted for about 30 min. No significant change was observed after injection of buffer or dephosphorylated synapsin I. These data indicate that the presence of synapsin I induces a fast increase in neurotransmitter release that overcomes the inhibitory effect of the non-physiological target and suggest that the expression of synapsins may play a role in the modulation of synaptic strength and neural connectivity.

Synapsin controls both reserve and releasable synaptic vesicle pools during neuronal activity and short-term plasticity in Aplysia

Neurotransmitter release is a highly efficient secretory process exhibiting resistance to fatigue and plasticity attributable to the existence of distinct pools of synaptic vesicles (SVs), namely a readily releasable pool and a reserve pool from which vesicles can be recruited after activity. Synaptic vesicles in the reserve pool are thought to be reversibly tethered to the actin-based cytoskeleton by the synapsins, a family of synaptic vesicle-associated phosphoproteins that have been shown to play a role in the formation, maintenance, and regulation of the reserve pool of synaptic vesicles and to operate during the post-docking step of the release process. In this paper, we have investigated the physiological effects of manipulating synapsin levels in identified cholinergic synapses of Aplysia californica. When endogenous synapsin was neutralized by the injection of specific anti-synapsin antibodies, the amount of neurotransmitter released per impulse was unaffected, but marked changes in the secretory response to high-frequency stimulation were observed, including the disappearance of post-tetanic potentiation (PTP) that was substituted by post-tetanic depression (PTD), and increased rate and extent of synaptic depression. Opposite changes on post-tetanic potentiation were observed when synapsin levels were increased by injecting exogenous synapsin I. Our data demonstrate that the presence of synapsin-dependent reserve vesicles allows the nerve terminal to release neurotransmitter at rates exceeding the synaptic vesicle recycling capacity and to dynamically change the efficiency of release in response to conditioning stimuli (e.g., post-tetanic potentiation). Moreover, synapsin-dependent regulation of the fusion competence of synaptic vesicles appears to be crucial for sustaining neurotransmitter release during short periods at rates faster than the replenishment kinetics and maintaining synchronization of quanta in evoked release.

Cerebrin prohormone processing, distribution and action in Aplysia californica

The isolation, characterization, and bioactivity in the feeding circuitry of a novel neuropeptide in the Aplysia californica central nervous system are reported. The 17-residue amidated peptide, NGGTADALYNLPDLEKIamide, has been termed cerebrin due to its primary location in the cerebral ganglion. Liquid chromatographic purification guided by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry allowed the isolation of the peptide with purity adequate for Edman sequencing. The cerebrin cDNA has been characterized and encodes an 86 amino acid prohormone that predicts cerebrin and one additional peptide. Mapping using in situ hybridization and immunocytochemistry showed that cerebrin containing neuronal somata are localized almost exclusively in the cerebral ganglion, mostly in the F- and C-clusters. Both immunostaining and mass spectrometry demonstrated the presence of cerebrin in the neurohemal region of the upper labial nerve. In addition, immunoreactive processes were detected in the neuropil of all of the ganglia, including the buccal ganglia, and in some interganglionic connectives, including the cerebral-buccal connective. This suggests that cerebrin may also function as a local signaling molecule. Cerebrin has a profound effect on the feeding motor pattern elicited by the command-like neuron CBI-2, dramatically shortening the duration of the radula protraction in a concentration-dependent manner, mimicking the motor-pattern alterations observed in food induced arousal states. These findings suggest that cerebrin may contribute to food-induced arousal in the animal. Cerebrin-like immunoreactivity is also present in Lymnaea stagnalis suggesting that cerebrin-like peptides may be widespread throughout gastropoda.

Visualization of nitric oxide production in the earthworm ventral nerve cord

Distribution of nitric oxide (NO)-producible neurons in the ventral nerve cord (VNC) of the earthworm was investigated by nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) histochemistry. Some neurons (20-30 microm in diameter) were intensely stained and were localized in areas between the 1st and 2nd lateral nerves in the ventral side of VNC. In contrast, no neurons including giant fibers were stained in the dorsal side. Endogenous NO production from VNC was visualized using a fluorescent dye, diaminofluorescein-2 diacethyl (DAF-2 DA). When VNC was incubated in a saline, a relative high level of NO was produced from the ventral side, especially from NADPH-d-positive neurons. Under high-K+ stimulation, NO was also detected in the giant fibers in the dorsal side of VNC. Our results suggest that the earthworm VNC constantly and relative highly produces NO as a neuromodulator, and that NO produced from the ventral side sometimes reaches and affects the giant fibers. In conclusion, we successfully visualized NO in the earthworm VNC by clarifying both the distribution of NO-producible neurons and the endogenous NO production.

[Rf 0.58 protein in Helix command neurons during learning]

At early stages of aversive conditioning in Helix, a most considerable increase in the acid brain-specific protein Rf 0.58 occurred in LPa3 and PPa3 neurones. Later the content of this protein decreased in the PPa3 but went on increasing in LPa3. In sham learning, the protein content did not increase so obviously. Hence the protein Rf 0.58 metabolism in individual neurones of the snail CNS correlates with the draw step of receptor and effector fields in avoidance conditioning.

[Formation of transcription factors AP-1 during learning in Helix]

An increase in the DNA-binding activity for the AP-1-family factors was shown to occur after food aversion conditioning. Learning experiments in vitro enhanced the DNA-binding activity. Effects of simultaneous action of serotonine and calcium on activation of transcriptional AP-1 factors was suppressed by inhibitor of calcium/calmodulin-dependent protein-kinases KN62 as well as by inhibitor of MAP-kinases PD98059. The co-operative induction of transcriptional AP-1 family factors activation by serotonine-induced and calcium-dependent regulatory systems may be one of the mechanisms of aversive conditioning in the CNS of the land snail.

Growth cone collapse through coincident loss of actin bundles and leading edge actin without actin depolymerization

Repulsive guidance cues can either collapse the whole growth cone to arrest neurite outgrowth or cause asymmetric collapse leading to growth cone turning. How signals from repulsive cues are translated by growth cones into this morphological change through rearranging the cytoskeleton is unclear. We examined three factors that are able to induce the collapse of extending Helisoma growth cones in conditioned medium, including serotonin, myosin light chain kinase inhibitor, and phorbol ester. To study the cytoskeletal events contributing to collapse, we cultured Helisoma growth cones on polylysine in which lamellipodial collapse was prevented by substrate adhesion. We found that all three factors that induced collapse of extending growth cones also caused actin bundle loss in polylysine-attached growth cones without loss of actin meshwork. In addition, actin bundle loss correlated with specific filamentous actin redistribution away from the leading edge that is characteristic of repulsive factors. Finally, we provide direct evidence using time-lapse studies of extending growth cones that actin bundle loss paralleled collapse. Taken together, these results suggest that actin bundles could be a common cytoskeletal target of various collapsing factors, which may use different signaling pathways that converge to induce growth cone collapse.