Characterization of cardiac innervation in the nudibranch,Archidoris montereyensis

Summary The heart of the nudibranch mollusc Archidoris montereyensis is regulated by a small number of powerful effector neurons located in the right pleural and visceral ganglia. Two identifiable neurons in the pleural ganglion, a heart excitor (pl_HE) and a heart inhibitor (Pl_HI), are especially important regulators of cardiac function in that low levels of spontaneous activity in either cell significantly alters the amplitude and rate of heart contractions. These neurons have extensive dendritic arbors within the right pleural ganglion and branching axonal processes within the visceral ganglion. The visceral ganglion also contains a heart excitor neuron (V_HE) and at least two heart inhibitor neurons (V_HI cells), but their influence on cardiac activity is weaker than that of the pleural ganglion cells. All of these heart effector cells appear to be motor neurons with axons that terminate predominately in the atrio-ventricular valve region of the heart via the pericardial nerve. The simplicity and strength of these neuronal connections to the heart of Archidoris make this a favorable preparation for studies of cardiac regulation.Abbreviations Pl _HE pleural ganglion heart excitor neuron - Pl _HI pleural heart inhibitor neuron - V _HE visceral ganglion heart excitor neuron - V _HI cells, visceral heart inhibitor neurons - V _K visceral kidney excitor neuron - V _G visceral gill excitor neuron     

A neuroanatomical study on the organization of the central antennal pathways in insects

Summary Receptor cell axons from the antennal flagellum terminate in the glomeruli of the ipsilateral deutocerebrum in Periplaneta americana and Locusta migratoria. Processes from several groups of deutocerebral neurons also enter the glomeruli and terminate in characteristic branching patterns. There, they contact the antennal axons. Connections are both convergent and divergent. Not only do single central neurons collect the inputs from many receptor cells, but receptor axons were often observed to branch and terminate at more than one deutocerebral neuron. The axons from a portion of the neurons go to form the deutocerebral bundle of the tractus olfactorioglobularis. These axons of the bundle terminate in the ipsilateral calyx of the corpus pedunculatum and in the lateral lobus protocerebri. The processes of the majority of the deutocerebral neurons stay within the deutocerebrum itself and may serve as local interneurons. Part of some antennal fibers terminate in the lobus dorsalis. The lobus glomeratus receives inputs from the maxillary palps and also from processes of deutocerebral neurons.Electron microscopy of synaptic connections and anatomical experiments reveal a complicated pattern of connections between receptor axons and higher order neurons as well as between higher order neurons themselves within the glomeruli.The ratio of the number of antennal fibers to that of relay fibers could easily lead to the interpretation, that the deutocerebrum merely serves as a device for reducing the number of transmission channels. However, coupled with physiological data, anatomical details such as conand divergence of input and interconnections between input channels suggest rather a filtering system and a highly complicated integrative network.     

Oxidation of glycerolipids by maize 9-lipoxygenase and its A562G mutant

Lipoxygenases (LOXs) are key enzymes in the biosynthesis of oxylipins, the diverse class of bioregulators involved into developmental processes, signalling and defence. This work was undertaken to better understand how LOXs control production of hydroperoxides with different positional and stereochemistry. A number of glycerolipids were tested as substrates for maize 9-LOX (ZmLOX) and its A562G mutant form. Both the wild type (WT) ZmLOX and A562G mutant were shown to dioxygenate monolinolenoylglycerol (MLG) and 2-linoleoyl-sn-glycero-3-phosphorylcholine (lysoPC). Both the WT ZmLOX and A562G mutant form oxidized the MLG predominantly into (9S)-hydroperoxide. The A562G mutation did not affect the relative yield of 13-hydroperoxide, but increased the proportion of (13R)-enantiomer. LysoPC was a poor substrate for both wild type and A562G mutant form of ZmLOX. The oxidation of lysoPC exhibited the limited regio- and stereospecificity. Nevertheless, the WT ZmLOX produced some predominance of (13S)-hydroperoxide. In contrast, the A562G mutant produced some excess of (9S)-hydroperoxide of lysoPC. The bulky polar heads of glycerolipids like MLG and lysoPC cannot penetrate into the LOX active site. Thus, the obtained data indicate that both (9S)- and (13S)-hydroperoxides can be produced when substrate is arranged within LOX active site in the “methyl end first” orientation.     

Modulation of synaptic events by heavy metals in the central nervous system of mollusks

Summary 1. The effects of heavy metals (Pb²⁺, Hg²⁺, and Zn²⁺) on synaptic transmission in the identified neural network ofHelix pomatia L. andLymnaea stagnalis L. (Gastropoda, Mollusca) were studied, with investigation of effects on inputs and outputs as wells as on interneuronal connections.2. The sensory input running from the cardiorenal system to the central nervous system and the synaptic connections between central neurons were affected by heavy metals.3. Lead and mercury (10^–5–10^–3 M) eliminated first the inhibitory, then the excitatory inputs running from the heart to central neurons. At the onset of action lead increased the amplitude of the excitatory postsynaptic potentials, but blockade of sensory information transfer occurred after 10–20 min of treatment.4. The monosynaptic connections between identified interneurons were inhibited by lead and mercury but not by zinc. Motoneurons were found to be less sensitive to heavy metal treatment than interneurons or sensory pathways.5. The treatment with Pb²⁺ and Hg²⁺ often elicited pacemaker and bursting-type firing in central neurons, accompanied by disconnection of synaptic pathways, manifested by insensitivity to sensory synaptic influences.6. Zn²⁺ treatment also sometimes induced pacemaker activity and burst firing but did not cause disconnection of the synaptic transmission between interneurons.7. A network analysis of heavy metal effects can be a useful tool in understanding the connection between their cellular and their behavioral modulatory influences.     

The neurosecretory system of the adult Melanogryllus desertus pall. (Orthoptera,Gryllidae)

Summary The cerebral neurohemal area of Melanogryllus desertus is located posteriorly among the neurons of nervus corporis cardiaci I (NCCI) on the ventral median surface of the protocerebrum where axons penetrate the neural lamella and terminate on its outer surface. Numerous neurosecretory fibers containing three different types of granule occur within and on the outer surface of the neural lamella.The release of neurosecretory granules is accomplished by exocytosis and the formation of synaptoids. It can also take place as a mass release of granules into the stroma.     

Patterns of serotonin-immunoreactive neurons in the central nervous system of the earthworm Lumbricus terrestris L.

Summary The distribution patterns of serotonin-immunoreactive somata in the cerebral and subpharyngeal ganglion, and in the head and tail ganglia of the nerve cord of Lumbricus terrestris are described from whole-mount preparations. A small number of serotonin-immunoreactive neurons occurs in the cerebral ganglion, in contrast to the large population of serotonin-immunoreactive neurons that exists in all parts of the ventral nerve cord. From the arrangement of serotonin-immunoreactive somata in the subpharyngeal ganglion, we suggest that this ganglion arises from the fusion of two primordial ganglia. In head and tail ganglia, the distribution of serotonin-immunoreactive somata resembles that in midbody segments. Segmental variations in the pattern and number of serotonin-immunoreactive somata in the different body regions are discussed on the background of known developmental mechanisms that result in metameric neuronal populations in annelids and arthropods.Abbreviations CG1, CG2 cerebral soma group 1, 2 - CNS central nervous system - GINs giant interneurons - 5-HT 5-hydroxytryptamine, serotonin - 5-HTi 5-HT-immunoreactive - N side nerve - SG19 subpharyngeal soma group 1–9 - SN segmental nerve     

Commissural ring nerve: A female-specific neurosecretory tract supplied by bifurcating median neurons in the cockroach Periplaneta americana (L.) and the cricket Teleogryllus commodus (Walker)

Summary In the American cockroach, Periplaneta americana, and the Australian field cricket, Teleogryllus commodus, the two nerves supplying the bases of the cerci are joined by a branch that crosses behind the last abdominal ganglion. This commissural ring nerve is restricted to females, and it contains many axons filled with granular and agranular vesicles. The axons stem from somata located within the ganglion. There are one (Periplaneta) or two (Teleogryllus) groups of median neurons with bilaterally symmetrical bifurcations, and a group of postero-ventral neurons on each side. In T. commodus, these neurons are distinct from others associated with the cerci. In the two species, the ring nerve neurons contribute to a neuropile near the root of each cereal nerve. The bifurcating median neurons arborize on both sides before entering the ring nerve, while the postero-ventral ones branch more extensively ipsilateral to their somata. The possibilities are discussed that the bifurcating neurons may be homologous to dorsal unpaired median neurons, and that the ring nerve may be a neurohemal area.     

Analysis of the efferent projections of the lateral geniculate nucleus with special reference to the innervation of the subcommissural organ and related areas

In order to define central neurons projecting to the subcommissural organ (SCO) and to related areas in the postero-medial diencephalon, Phaseolus vulgaris-leucoagglutinin (PHA-L) was injected into the lateral geniculate nucleus of the rat. PHA-L-labelled neurons send axonal processes medially through the posterior thalamic nuclei and the posterior commissure to the other hemisphere. Branches of fibres originating from this projection form a plexus of nerve terminals in the underlying precommissural nucleus and in the nucleus of the posterior commissure. A small number of PHA-L-immunoreactive nerve fibres penetrate from the precommissural nucleus into the lateral part of the SCO. A few labelled fibres penetrate directly from the posterior commissure into the medial part of the caudal SCO. Most of the PHA-L-immunoreactive fibres occur in the hypendymal layer, although a few terminate near the ependymal cells of the organ. Many labelled fibres are found in the ventricular ependyma adjacent to the SCO, some fibres lying close to the ventricular lumen. These results were obtained only if the tracer was delivered into the intergeniculate leaflet of the lateral geniculate nucleus (IGL). The IGL innervates both the suprachiasmatic nucleus and the pineal organ; the connections between the IGL and the midline structures, including the SCO, suggest that these areas are influenced by the circadian system.     

Characterization of NO/cGMP-Mediated Responses in Identified Motoneurons

1. Nitric oxide (NO) is thought to play a neuromodulatory role in the nervous system of vertebrate and invertebrate species. In the hornworm Manduca sexta, NO-mediated signaling has been implicated in behavioral and developmental processes, but its exact function in neurons is unknown. In this study, we identify specific neurons in the CNS of Manduca larvae that accumulate cGMP in response to treatment with NO donors in the presence of cGMP-phosphodiesterase inhibitors. Subsets of these neurons were identified as motoneuron-12 (MN12) and intersegmental motoneurons (ISMs), which innervate dorsal oblique muscles of the larvae. 2. To investigate the physiological role of NO-evoked increases in cGMP in these motoneurons we performed intracellular recordings; we found that application of NO donors caused an increase in neuronal excitability that was characterized by an increase in the spontaneous firing frequency. When action potentials and EPSPs were blocked, NO treatment evoked a depolarization of the resting membrane potential and a decrease in the measured input resistance in both MN12 and the ISMs. 3. Additional experiments with MN12 showed that treatment with the cGMP analogue, 8-Br-cGMP mimicked the NO effect on the resting potential and the input resistance. Furthermore, MN12 incubation with the NOS inhibitor, L-NNA, resulted in a small hyperpolarization of the resting potential and an increase in the input resistance, and incubation with the sGC inhibitor, ODQ blocked the NO-evoked depolarization of MN12. Finally, NO treatment during voltage clamping of MN12 evoked an inward positive current. 4. Taken together, these results suggest that NO can act as a “gain control” of neuronal excitability, which might have an important role in insect behavior.     

Neural structures in the receptive field of pleural ganglion mechanosensory neurons of Aplysia californica

The peripheral processes of the mechanoafferents that, when stimulated, initiate the much-studied tail withdrawal reflex of Aplysia californica have not been characterized. We show that immunofluorescence staining for class III -tubulin highlights neurons and reveals nerve tracts and fine neuronal processes in Aplysia tissue. Coupled with transmission and scanning electron microscopy, class III -tubulin immunofluorescence is consistent with the possibility that mechanoafferents in the receptive field of pleural ganglion mechanosensory neurons penetrate the tail epidermis and terminate as ciliated endings. This view is reinforced by comparisons among neuronal processes in several mechanosensory epidermal regions and in a chemosensory epidermis.     

Optic tract cells projecting to the retina in the teleost,Pantodon buchholzi

Summary Horseradish peroxidase was employed to trace retino-fugal and retino-petal connections in the teleost fish, Pantodon buchholzi. Most of the reciprocal connections found were within the range also observed in previously studied species of teleosts. Of particular interest is the discovery of cells located within the optic tract and projecting to the retina. These neurons were investigated electron microscopically.     

Development of neural lineages derived from the sine oculis positive eye field of Drosophila

The Anlage of the Drosophila visual system, called eye field, comprises a domain in the dorso-medial neurectoderm of the embryonic head and is defined by the expression of the early eye gene sine oculis (so). Beside the eye and optic lobe, the eye field gives rise to several neuroblasts that contribute their lineages to the central brain. Since so expression is only very short lived, the later development of these neuroblasts has so far been elusive. Using the P-element replacement technique [Genetics, 151 (1999) 1093] we generated a so-Gal4 line driving the reporter gene LacZ that perdures in the eye field derived cells throughout embryogenesis and into the larval period. This allowed us to reconstruct the morphogenetic movements of the eye field derived lineages, as well as the projection pattern of their neurons. The eye field produces a dorsal (Pc1/2) and a ventral (Pp3) group of three to four neuroblasts each. In addition, the target neurons of the larval eye, the optic lobe pioneers (OLPs) are derived from the eye field. The embryonically born (primary) neurons of the Pp3 lineages spread out at the inner surface of the optic lobe. Together with the OLPs, their axons project to the dorsal neuropile of the protocerebrum. Pp3 neuroblasts reassume expression of so-Gal4 in the larval period and produce secondary neurons whose axonal projection coincides with the pattern formed by the primary Pp3 neurons. Several other small clusters of neurons that originate from outside the eye field, but have axonal connections to the dorsal protocerebrum, also express so and are labeled by so-Gal4 driven LacZ. We discuss the dynamic pattern of the so-positive lineages as a tool to reconstruct the morphogenesis of the larval brain.     

Evidence for intergeneric incompatibility in ferns

The archegonial mucilage ofAthyrium filix-femina andA. distentifolium paralyses spermatozoids ofDryopteris filix-mas (and in one caseD. inaequalis) before they penetrate the archegonial venter. The archegonial mucilage ofDryopteris filix-mas has a weak positive chemotactic influence on the spermatozoids of the twoAthyrium species. The spermatozoids ofDryopteris were never observed in the archegonia ofAthyrium. Incompatibility was not observed within and between the twoAthyrium species, withinDryopteris filix-mas or betweenAthyrium filix-femina and twoAsplenium species.Contribution No. 327.     

Serotonin-like immunoreactivity in the central nervous system of two ixodid tick species

Immunocytochemistry was used to describe the distribution of serotonin-like immunoreactive (5HT-IR) neurons and neuronal processes in the central nervous system (CNS), the synganglion, of two ixodid tick species; the winter tick, Dermacentor albipictus and the lone star tick, Amblyomma americanum. 5HT-IR neurons were identified in the synganglion of both tick species. D. albipictus had a significantly higher number of 5HT-IR neurons than A. americanum. The labeling pattern and number of 5HT-IR neurons were significantly different between sexes in D. albipictus, but were not significantly different between sexes in A. americanum. 5HT-IR neurons that were located in the cortex of the synganglion projected processes into the neuropils, invading neuromeres in the supraesophageal ganglion including the protocerebrum, postero-dorsal, antero-dorsal and cheliceral neuromeres. In the subesophageal ganglion, dense 5HT-IR neuronal processes were found in the olfactory lobes, pedal, and opisthosomal neuromeres. Double-labeling with neurobiotin backfilled from the first leg damaged at the Haller’s organ revealed serotoninergic neuronal processes surrounding the glomeruli in the olfactory lobes. The high number of the 5HT-IR neurons and the extensive neuronal processes present in various regions of the synganglion suggest that serotonin plays a significant role in tick physiology. This article reports the results of research only. Mention of a proprietary product does not constitute an endorsement or a recommendation by the USDA for its use. The U.S. Government’s right to retain a non-exclusive, royalty free license in and to any copyright is acknowledged.     

Mapping of serotonin-immunoreactive neurons in the larval nervous system of the flies Calliphora erythrocephala and Sarcophaga bullata

Summary Serotonin-immunoreactive (5-HTi) neurons were mapped in the larval central nervous system (CNS) of the dipterous flies Calliphora erythrocephala and Sarcophaga bullata. Immunocytochemistry was performed on cryostat sections, paraffin sections, and on the entire CNS (whole mounts).The CNS of larvae displays 96–98 5-HTi cell bodies. The location of the cell bodies within the segmental cerebral and ventral ganglia is consistent among individuals. The pattern of immunoreactive fibers in tracts and within neuropil regions of the CNS was resolved in detail. Some 5-HTi neurons in the CNS possess axons that run through peripheral nerves (antenno-labro-frontal nerves).The suboesophagealand thoracico-abdominal ganglia of the adult blowflies were studied for a comparison with the larval ventral ganglia. In the thoracico-abdominal ganglia of adults the same number of 5-HTi cell bodies was found as in the larvae except in the metathoracic ganglion, which in the adult contains two cell bodies less than in the larva. The immunoreactive processes within the neuropil of the adult thoracico-abdominal ganglia form more elaborate patterns than those of the larvae, but the basic organization of major fiber tracts was similar in larval and adult ganglia. Some aspects of postembryonic development are discussed in relation to the transformation of the distribution of 5-HTi neurons and their processes into the adult pattern.     

<Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> as a Model System for Graft Union Development in Homografts and Heterografts

Homografting of Arabidopsis thaliana scions on stocks of A. thaliana and heterografting on other species were used to study the compatibility and the ontogeny of graft union formation. Highly compatible homografting with scions of young leafy inflorescence stems was obtained on stocks of inflorescence stems growing from large 3-month-old A. thaliana plants. Histologic analysis revealed four developmental stages of graft union formation in Arabidopsis homografting: (1) development of a necrotic layer, (2) callus proliferation in the grafted scion, (3) differentiation of new vascular tissues within the scion, and (4) a full vascular graft union formation between the scion and the stock. Vascular connections were formed within the callus bridge between rootstocks and scions 15 days after grafting. Heterografts of Arabidopsis on two members of Brassicaceae, cabbage (Brassica) and radish (Raphanus), showed partial incompatible interaction with a lower level of vascular differentiation. Arabidopsis grafting on tomato (Solanaceae) rootstock showed complete incompatibility and limited noncontinuous differentiation of new vascular tissues that did not cross the scion/stock boundary. Although lacking scion/stock vascular connections, Arabidopsis scions grafted onto tomato rootstock flowered and produced seeds. This may indicate some nonvascular functional connections between the two plants, probably of parenchyma cells, further emphasizing the usefulness of Arabidopsis as a model plant for studying various levels of the complicated scion/stock relationships expressed in grafting biology. Experiments with dye transport in the xylem showed that although in general there was an agreement between the histologic study and dye transport, in Arabidopsis homografts water transport frequency was lower than functional and histologic compatability. We conclude that homografting and heterografting of Arabidopsis inflorescence stems is a convenient and reproducible method for studying the fundamental cellular genetic and molecular aspects of grafting biology.     

Reduction of Fe(II)EDTA-NO by a newly isolated <Emphasis Type="Italic">Pseudomonas</Emphasis> sp. strain DN-2 in NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> scrubber solution

Biological reduction of nitric oxide (NO) chelated by ferrous ethylenediaminetetraacetate (Fe(II)EDTA) to N₂ is one of the core processes in a chemical absorption–biological reduction integrated technique for nitrogen oxide (NO _x ) removal from flue gases. A new isolate, identified as Pseudomonas sp. DN-2 by 16S rRNA sequence analysis, was able to reduce Fe(II)EDTA-NO. The specific reduction capacity as measured by NO was up to 4.17 mmol g DCW⁻¹ h⁻¹. Strain DN-2 can simultaneously use glucose and Fe(II)EDTA as electron donors for Fe(II)EDTA-NO reduction. Fe(III)EDTA, the oxidation of Fe(II)EDTA by oxygen, can also serve as electron acceptor by strain DN-2. The interdependency between various chemical species, e.g., Fe(II)EDTA-NO, Fe(II)EDTA, or Fe (III)EDTA, was investigated. Though each complex, e.g., Fe(II)EDTA-NO or Fe(III)EDTA, can be reduced by its own dedicated bacterial strain, strain DN-2 capable of reducing Fe(III)EDTA can enhance the regeneration of Fe(II)EDTA, hence can enlarge NO elimination capacity. Additionally, the inhibition of Fe(II)EDTA-NO on the Fe(III)EDTA reduction has been explored previously. Strain DN-2 is probably one of the major contributors for the continual removal of NO _x due to the high Fe(II)EDTA-NO reduction rate and the ability of Fe(III)EDTA reduction.     

Control of systemically induced herbivore resistance by plant vascular architecture

Patterns of systemically induced resistance (SIR) in Eastern Cottonwood, Populus deltoides, measured by reduced feeding of the leaf-chewing beetle, Plagiodera versicolora, were shown to be directly related to the distribution of the plant vasculature. Mechanical damage to single leaves resulted in SIR in non-adjacent, orthostichous leaves (vertically aligned on the stem) with direct vascular connections, both up and down the shoot; but no SIR in adjacent, non-orthostichous leaves with less direct vascular connections. The control that the plant vasculature exerts over signal distribution following wounding can therefore be used to predict SIR patterns, explain variation in the distribution of SIR, and relate this ecologically important phenomenon to biochemical processes of systemic gene expression and biochemical resistance mechanisms.     

Isolation of a homothallic mutant in <Emphasis Type="Italic">Lentinula edodes</Emphasis>

To obtain a homothallic mutant in Lentinula edodes, basidiospores derived from the common Bmut dikaryon (A1B1mut × A2B1mut) were treated with UV irradiation. Of a total of approximately 5000 monosporous cultures recovered, a single basidiospore isolate was found to produce the hyphae bearing clamp connections without mating. This mutant strain could form fruit bodies, and all its single basidiospore isolates developed into colonies with clamp connections. Such homothallic behaviors were transmitted from the mutant strain to the next generation. During the germination and following hyphal elongation in a single basidiospore of mutant strain, clamp connections were clearly detected in multicellular hyphae, which contained two nuclei in each cell. Their clamp connections were morphologically variable, viz., pseudo, abnormal, and true clamps. Amplified fragment length polymorphism (AFLP) profiles among the basidiospore isolates of mutant strain were identical, indicating that the mutant strain produced isogenic basidiospore progeny. Contribution no. 385 from the Tottori Mycological Institute