bluuebunny/crossref_metadata_2025 huggingface dataset:
Generation of specific behaviors in a locust by local release into neuropil of the natural neuromodulator octopamine
Authors: Sombati Sompong , Hoyle Graham
Published: January 2005

The natural insect neuromodulator octopamine (OCT) was released iontophoretically into regions of neuropil in locust metathoracic ganglia. A narrowly‐defined site was found on one side of the ganglion at which release caused a prolonged bout of repetitive flex‐extend‐flex movements of the tibia on the injected side, at a frequency of from 2–3.5 Hz. When a bout had terminated, repetition of the OCT release caused an extremely similar bout to occur, and again with further treatments, indefinitely. OCT iontophoresis at the equivalent site on the contralateral side caused the contralateral flexor to make stepping movements. Two sites were found, in each half of the ganglion, at which similar OCT release evoked a bout of flight motor activity at 10 Hz. The flight bout involved both sides synchronously and nearly equally, except for a slightly greater motor output on the injected side. Evoked bouts lasted from 20 sec to 25 min depending on the preparation and amount of OCT released. At a site in the 6th abdominal ganglion of mature female locusts OCT release suppressed ongoing rhythmic oviposition digging evoked by severing the ventral nerve cord. A number of previously undescribed DUM neurons was encountered and their dendritic patterns, which are distinctive, determined following dye injection. A hypothesis, termed the Orchestration Hypothesis is presented, which considers how modulator neurons such as locust octopaminergic neurons, might be involved in the generation of specific behaviors.
Glutamatergic central nervous transmission in locusts
Authors: Sombati Sompong , Hoyle Graham
Published: January 2005

It is generally believed that neural transmission in the central nervous systems of insects is cholinergic, on the basis of secondary evidence: the presence of cholinesterase, and sensitivity of a nonsynaptic region of the neuron, its cell body, to iontophoresed acetylcholine. In the present work a preparation has been developed which takes advantage of the availability of identified motor neurons in the locust metathoracic ganglion with known 3‐dimensional geometry of dendritic fields. These neurons transmit at their peripheral neuromuscular junctions with glutamate. The fast extensor tibiae motor neuron also makes excitatory central connections onto its functional antagonists the flexor tibiae motor neurons. Unless Dale's principle is contravened, transmission at these central synapses should also be glutamatergic. This transmission onto flexor motor neurons was found to be attenuated 70% by a glutamatergic blocker. Glutamate iontophoresed into selected areas of neuropil into which the motor neurons have dendritic branches caused the neurons to be depolarized, in a dose‐dependent manner. Individual motor neurons were directly excited to spike with suprathreshold iontophoretic current. With long durations of release they were desensitized, but recovered quickly with rest. The data provide evidence that central transmission onto motor neurons in the locust metathoracic ganglion is glutamatergic.
Dorsal unpaired median neurons of the cockroach metathoracic ganglion
Authors: Arikawa Kentaro , Washio Hiroshi , Tanaka Yoshitaka
Published: January 2005

On the dorsal surface in the metathoracic ganglion of the cockroach Periplaneta americana, eight large and a number of small somata described by Crossman et al., (1971) were reexamined. These eight large cells (40–60 μm in diameter) could be divided into three different types by Lucifer yellow or nickel injection, depending on the branching of their axons. No neuron was found which sent axons into either the anterior or posterior connectives. In the mesothoracic ganglion an interganglionic H‐shaped DUM neuron was found which had four axons, one into each anterior and posterior connective.
Control of swimming in the hydrozoan jellyfish Aequorea aequorea: Direct activation of the subumbrella
Authors: Satterlie Richard A.
Published: January 2005

The epithelial cells that overlie the inner nerve ring of the hydrozoan jellyfish Aequorea aequorea were investigated ultrastructurally and electrophysiologically. The structurally unspecialized epithelial cells are interconnected by gap junctions and are electrically active during swimming as a single, long‐duration action potential was recorded during each swim contraction. Intercellular electrical‐ and dye‐coupling was demonstrated within the epithelial region extending into the velum and subumbrellar regions.

Excitatory post‐synaptic potentials were recorded from epithelial cells following swim motorneuron spikes with a short latency. Psps were up to 60 mV in amplitude and, when triggered in bursts, showed summation provided the interpulse interval was less than 25–35 ms. The initial psp in each of a series of bursts showed facilitation with the first few swim contractions following a period of inactivity. In actively swimming medusae, psp amplitude was relatively constant. The reversal potential for epithelial psps was estimated at between 0 and +20 mV.

Spontaneous psps spread throughout the epithelial region electronically, but the amplitude decrease with conducting distance was less than that for current pulses injected into individual epithelial cells. This presumably represents the effect of widespread synaptic activation of epithelial cells via multiple input sites throughout the inner nerve ring as opposed to point‐source input in current injection experiments.

During a radial response, action potential amplitude was decreased and rise time increased due to decremental conduction through the inhibited region. It is postulated that conduction of a full action potential requires that electrotonic current spread from adjacent, active epithelial cells occur in synchrony with synaptic input from swim motoneurons.
Chronic exposure to lead causes persistent alterations in the electric membrane properties of neurons in cell culture
Authors: Scott Brian , Lew James
Published: January 2005

The effects of chronic lead (Pb) exposure on neuronal electric membrane properties (EMP) were determined using neural cell cultures of adult mouse dorsal root ganglia (DRG). Cultures were exposed to Pb concentrations ranging from 0 to 100 μM for 12 days (8 DIV to 20 DIV). EMP were determined in Pb‐free medium either immediately after withdrawal (IWD), or 6 days after withdrawal (6WD) from Pb.

For IWD, regression analysis indicated that a number of EMP varied significantly with increasing Pb concentration. The largest such change occurred for electrical excitability which decreased significantly with increasing Pb (P = 0.000), being reduced by approximately two‐thirds for neurons exposed to 100 μM Pb; resting membrane potential increased with Pb (P = 0.000); membrane time constant decreased with Pb (P = 0.007); action potential afterhyperpolarization decreased with Pb (P = 0.023). There was also evidence that the time course of action potentials was accelerated with increasing Pb concentrations, the rate of fall of neurons with biphasic falling phases being particularly increased (P = 0.047). This general pattern of altered EMP was observed for the 6WD condition also, indicating that chronic exposure to Pb caused persistent abnormalities in neuronal membranes even after 6 days of cultivation in Pb‐free medium.

The patterns of alterations in EMP suggested that chronic Pb exposure caused a prolonged increase in potassium permeability. It was proposed that the latter was mediated through a Pb‐induced increase in intracellular ionic calcium and the associated disruption of calcium homeostasis.
Effects of octopamine, dopamine, and serotonin on production of flight motor output by thoracic ganglia of Manduca sexta
Authors: Claassen Dale E. , Kammer Ann E.
Published: January 2005

Effects of biogenic amines on a centrally generated motor pattern in Manduca sexta were examined by pressure injecting nanomole to micromole amounts of octopamine, dopamine or serotonin into thoracic ganglia. Motor output was recorded extracellularly from a pair of antagonistic flight muscles and their motor neurons. The monoamines were found to alter production of a motor pattern that produces rhythmic wing flapping (10 Hz) and exhibits phase relationships similar to those in the flight pattern of intact moths.

In mesothoracic ganglia with sensory nerves intact, octopamine (4 × 10−9 mol) injected into lateral regions evoked regular firing of a single motor neuron, whereas a higher dose (4 × 10−8 mol) often elicited the flight motor pattern. In the absence of sensory input, these doses of octopamine had little effect. Low doses (10−10 mol) greatly enhanced motor responses to electrical stimulation of a wing sensory nerve.

Dopamine (2 × 10−10 mol) injected into the medial region of the mesothoracic ganglion elicited the flight motor pattern in the presence or absence of sensory input. Rhythmic output induced by dopamine (5 × 10−10 mol) was suppressed by injecting serotonin (5 × 10−10 mol) into the same region.

These findings demonstrate that dopamine, octopamine, and serotonin have different effects on motor output in Manduca and suggest that these amines are involved in initiating, maintaining and terminating flight behavior, respectively. Octopamine may elicit flight production by enhancing the efficacy of sensory transmission thereby increasing excitability or arousal. Dopamine may act on interneurons involved in generating the flight motor pattern.
Fast axonal transport by neurons from the jellyfish Cyanea capillata
Authors: Anderson Peter A. V. , Schwab Walter E. , Gilbert Susan , Allen Robert D.
Published: January 2005

Neurons of the motor nerve net of Cyanea capillata were examined using video‐enhanced DIC optics. A variety of organelles were visible within the axons and many were mobile. To quantify the movement organelles were divided into three classes (large, medium, and small) and the rates, direction, and types of movement displayed by the different particle types examined. The overall behavior and rates of movement of transported particles were camparable with those in axons from other species. The largest particles, mainly mitochondria were the slowest moving but were the only particles to reverse their direction of movement or to undergo interactions with other particles. The fastest movement was by the small particles, but both they and medium sized particles were transported continuously. In addition, the linear elements in these axons underwent considerable lateral movement.
A hormone‐sensitive communication system in an electric fish
Authors: Bass Andrew H.
Published: January 2005

The electric communication system includes both special muscle‐derived cells or electrocytes that produce species‐typical electric signals, or electric organ discharges (EODs), and specialized sensory receptors, or electroreceptors, that encode the electric fields set up by EODs. Steroid hormones can influence the characteristic properties of both EODs and electroreceptors. Steroids appear to directly effect the anatomy and physiology of the electrocytes that generate an EOD. In contrast, the steroid effect on electroreceptors may be predominantly via an indirect mechanism whereby changes in the spectral characteristics of the EOD appear to induce changes in the spectral sensitivity of electroreceptors. Continued studies of electrosensory and electromotor systems will offer insights into the cellular bases for the development and evolution of steroid‐sensitive pathways in the vertebrate nervous system.
Extension and retraction of axonal projections by some developing neurons in the leech depends upon the existence of neighboring homologues. I. The HA cells
Authors: Gao Wei‐Qiang , Macagno Eduardo R.
Published: January 2005

The role of homologues in the establishment of the pattern of axonal projections of identified segmentally homologous neurons was investigated by means of selective cell ablation and dye injection. The cells studied were the bilateral pairs of heart accessory (HA) neurons found in the fifth and sixth segmental ganglia of the leech ventral nerve cord. Homologues start their morphological differentiation with identical axonal projections, and segmental differences are manifested later, when specific branches stop growing and disappear. The deletion of single HA cells at early stages, however, permits these branches to survive in their ipsilateral homologues and to grow and take over the projections of the deleted neurons. In addition, if both HA homologues on the same side of the nerve cord, or three of the four HA cells, are deleted in an animal, the remaining HA cells often extend novel projections. These observations suggest that either competition for targets, inputs or growth factors, or direct interactions among homologous cells may play a role in the differentiation of segment specific patterns of axonal projections.
Formation, maintenance, and functional uncoupling of connections between identified Helisoma neurons in situ
Authors: Cohan C. S. , Haydon P. G. , Mercier A. J. , Kater S. B.
Published: January 2005

Previous work with identified Helisoma neurons has characterized an array of neuroplastic responses to axotomy that include the generation of new neuritic outgrowth, the reinnervation of target organs, and the formation of new electrical synapses. These responses are not random, but rather occur in a precise, predictable manner under a variety of culture conditions. The present investigation demonstrates that specific identified neurons display similar neuroplastic “behavior” within the living animal. In response to in situ nerve crushes, neurons B4 and B5 generate new neuritic outgrowth, neuron B4 functionally reinnervates the salivary glands, and new electrical synapses form between the left and right neurons B5.

The in situ paradigm employed in the present experiments made it possible to examine responses to axotomy over longer periods than in earlier studies with organ cultures. New B5R‐B5L connections, previously found to be stable over the short term in culture, gradually decreased in strength in situ, and the cells effectively uncoupled by 8 weeks after axotomy. This uncoupling did not depend upon target reinnervation and occurred in the continued presence of neurites in the buccal commissure. It is suggested that the stability of new connections is related to whether the connection previously existed in the unperturbed nervous system. The similarities between the ability of identified neurons to grow and to form synaptic connections in situ and in culture suggests that neurons are endowed with a specific program of regenerative responses that can be expressed reliably in a wide variety of environmental conditions.
Effect of auditory deafferentation on the synaptic connectivity of a pair of identified interneurons in adult field crickets
Authors: Brodfuehrer Peter D. , Hoy Ronald R.
Published: January 2005

In adult crickets, Teleogryllus oceanicus, unilateral auditory deafferentation causes the medial dendrites of an afferent‐deprived, identified auditory interneuron (Int‐1) in the prothoracic ganglion to sprout and form new functional connections in the contralateral auditory neuropil. The establishment of these new functional connections by the deafferented Int‐1, however, does not appear to affect the physiological responses of Int‐1's homolog on the intact side of the prothoracic ganglion which also innervates this auditory neuropil. Thus it appears that the sprouting dendrites of the deafferented Int‐1 are not functionally competing with those of the intact Int‐1 for synaptic connections in the remaining auditory neuropil following unilateral deaferentation in adult crickets. Moreover, we demonstrate that auditory function is restored to the afferent‐deprived Int‐1 within 4–6 days following deafferentation, when few branches of Int‐1's medial dendrites can be seen to have spouted. The strength of the physiological responses and extent of dendritic sprouting in the deafferented Int‐1 progressively increase with time following deafferentation. By 28 days following deafferentation, most of the normal physiological responses of Int‐1 to auditory stimuli have been restored in the deafferented Int‐1, and the medial dendrites of the deafferented Int‐1 have clearly sprouted and grown across into the contralateral auditory afferent field. The strength of the physiological responses of the deafferented Int‐1 to auditory stimuli and extent of dendritic sprouting in the deafferented Int‐1 are greater in crickets deafferented as juveniles than as adults. Thus, neuronal plasticity persists in Int‐1 following sensory deprivation from the earliest juvenile stages through adulthood.
Generation of motor patterns for walking and flight in motoneurons supplying bifunctional muscles in the locust
Authors: Ramirez J. M. , Pearson K. G.
Published: January 2005

In the flight system of Locusta migratoria certain muscles move a wing and a leg (bifunctional muscles) and are active during the performance of walking and flight. A preparation that allowed intracellular recordings during these behaviors was developed to analyze the activity of motoneurons supplying these and other muscles.

Motoneurons innervating bifunctional muscles were active during walking and flight, whereas motoneurons innervating unifunctional flight muscles were active only during flight.

Both motor patterns, walking and flight, were sometimes generated simultaneously in our preparation. In bifunctional motoneurons the two patterns were superimposed, whereas in unifunctional motoneurons only the flight motor pattern was observed.

All flight interneurons we examined were either inactive or tonically inhibited during walking. All interneurons that were strongly modulated during walking were either inactive, inhibited, or only weakly modulated during flight.

Anatomical investigations showed that unifunctional flight motoneurons have their main processes in the extreme dorsal region of neuropil. With the exception of the second basalar motoneurons, all bifunctional motoneurons have their processes extending more ventrally in the neuropil. Flight interneurons have their processes restricted to the dorsal neuropil. Interneurons that were rhythmically active during walking had their processes distributed more ventrally.

We conclude that motoneurons innervating bifunctional muscles are active during both motor patterns, walking and flight, and that these patterns are produced by two distinct interneuronal networks. The pattern‐generating network for flight appears to be located in the extreme dorsal regions of the thoracic ganglia, and the network for walking is located more ventrally.
Joint hormonal and sensory stimulation modulate neuronal number in adult canary brains
Authors: Bottjer Sarah W. , Dignan Timothy P.
Published: January 2005

Treatment of adult female canaries with testosterone (T) causes them to produce male‐typical vocalizations and results in striking growth of brain nuclei that control song behavior (Nottebohm, 1980). The song‐control nucleus HVc (caudal nucleus of the ventral hyperstriatum) contains cells that concentrate testosterone or its metabolites, suggesting that steroid hormones may induce the growth of HVc directly by regulating the expression of specific genes in those HVc neurons that have steroid receptors. However, we have previously provided evidence that is inconsistent with the idea that steroids promote growth of HVc solely via a direct action on hormone receptors: testosterone treatment of deafened adult females results in very little growth of HVc, relative to T‐treated hearing birds (Bottjer et al., 1986b). Thus, birds in the former group undergo very little overall growth of HVc despite high circulating levels of hormone. We show here that the slightly increased size of HVc in T‐treated deaf birds is attributable to an increase in neuronal spacing; the greatly increased size of HVc in T‐treated hearing birds is due to an increase in neuronal number as well as spacing. There was virtually no increase in number of HVc neurons in T‐treated deafened birds relative to control groups, whereas T‐treated hearing birds showed a marked increase in neuron number. The song‐control nucleus RA (robust nucleus of the archistriatum), which receives direct afferent input from HVc, also increases in size in response to testosterone treatment. However, the volume of RA increases in both hearing and deafened birds; this increase is primarily due to an increase in neuronal spacing as well as a small increase in neuron number. These results demonstrate that the number of neurons in a specific vocal‐control nucleus (HVc) can change dramatically in adult canaries and suggest that some synergistic action of hormonal and sensory stimulation is necessary to induce such a change.
The differential regulation of formation of chemical and electrical connections in Helisoma
Authors: Haydon P. G. , Kater S. B.
Published: January 2005

Novel chemical and electrical connections form between neurons not normally connected in the buccal ganglia of the snail Helisoma. We examined the cellular and environmental conditions required for the formation of each type of connection. Previous work in situ showed that novel electrical connections could form in response to axotomy. We have now found that axotomy can evoke the formation of novel unidirectional chemical connections between neurons B5 and B4 in addition to a novel electrical connection. The novel chemical connections display all of the normal properties of chemical synapses in Helisoma ganglia. These connections, however, are transient in nature and break 4 days following axotomy.

Previous work has shown that conjoint outgrowth is required for the formation of electrical connections. In cell culture we have investigated whether conjoint outgrowth is also required for chemical synaptogenesis. Using neurons B5 and B19 we have found that when neuron pairs make contact in cell culture, under conditions of synchronous neurite extension, both electrical and chemical synapses form. However, if one neuron has ceased extension prior to contact by a growing neuron, electrical synapses never form (Hadley et al., 1983, 1985) but chemical synapses do form. Furthermore, the addition of serotonin (10−6 M) to culture medium to inhibit neurite extension of B19, but not that of B5, selectively prevents the formation of electrical connections while permitting the formation of chemical synapses. Thus, the timing of contact in relation to the state of neurite extension can specify the type of connection a given neuron can form.
Absence of competitive interactions among axon terminals of regenerating motor neurons
Authors: Denburg Jeffrey L. , Powell Susan L. , Murphy Bernard F.
Published: January 2005

Competition among axon terminals is usually considered to contribute to the formation of patterned synaptic connections. During axonal regeneration of motor neurons in the cockroach, leg muscles initially become innervated by appropriate and inappropriate motor neurons. All axon terminals from inappropriate neurons eventually are eliminated, resulting in the reformation of the original innervation pattern. Destruction of an identified motor neuron by the intracellular injection of pronase did not prevent the eilimenation of inappropriate axon terminals in the muscle normally innervated by that motor neuron. Therefore, competition does not play a role in the reinnervation of the leg muscles. This indicates a major role for specific cell‐cell recognition.
Involvement of the Golgi apparatus in sorting of materials to opposite ends of frog rod retinal photoreceptors
Authors: Schmied Robert , Holtzman Eric
Published: January 2005

We have studied the rod cells of retinas of Rana pipiens by phosphatase cytochemistry and immunocytochemistry. We find that the Golgi apparatus of these cells, although different in its intracellular distribution from that of other neurons, has a cis‐trans organizations like that of other neurons as regards morphological features and the distribution of phosphatase activities. Antibodies against opsin bind to several sacs of the rod Golgi apparatus, especially those at the trans side of the Golgi stack. This suggests that Golgi involvement in the packaging of opsin for eventual delivery to the photoreceptive outer segments of the cell involves passage through trans Golgi systems. Proteins destined for the opposite end of the cell—the presynaptic terminal—also seem to pass through trans Golgi systems, as in indicated both by immunocytochemical localization of the synaptic vesicle protein p38 (synaptophysin) and by the presence of thiamine pyrophosphatase activity in some of the synaptic vesicles. Our findings suggest that sorting of membrane proteins destined for opposite ends of the photoreceptor takes place in systems at or near the trans Golgi face.
The refinement of invertebrate synapses during development
Authors: Lnenicka G. A. , Murphey R. K.
Published: January 2005

Evidence is provided that during invertebrate development synapses undergo a period of refinement during which there are changes in synaptic connectivity and specific synaptic properties. It appears that extrinsic cues such as competition and neural activity are involved in guiding these synaptic changes in invertebrates. Comparisons are made with findings in the vertebrate literature.
Laser microbeam axotomy and conduction block show that electrical transmission at a central synapse is distributed at multiple contacts
Authors: Gu Xiaonan , Macagno Eduardo R. , Muller Kenneth J.
Published: January 2005

Touch (T) sensory neurons in the leech innervate defined regions of skin and synapse on other neurons, including other T cells, within the ganglionic neuropil. The cells' receptive fields in the periphery are comprised of a central region, innervated by thick axons, and adjoining regions (minor fields) innervated by thinner axons. Secondary branches, known to be sites of synapses, emerge from the thinner and thicker axons. Pairs of T cells appear to make up to 200 separate contacts distributed within the neuropil. When the T cell is hyperpolarized, as occurs during natural stimulation of the cell, action potentials generated in the minor field and travelling into the ganglion along the thin axons may fail to conduct at central branch points. Evidence is presented, using axon conduction block and laser axotomy of cells filled with 6‐carboxy‐fluorescein, that synapses between separate groups of branches can function independently. Thus, selective activation of branches of the thin anterior axon produced a synaptic potential 36 ± 6% of control amplitude, which was consistent with counts of 39 ± 6% of contacts made by these branches. Laser axotomy of postsynaptic neurons showed that the anterior contacts indeed made the principal or only contacts activated during anterior conduction block. The results show that conduction block can modulate transmission within the ganglion, and it operates by silencing particular contacts between cells.
Changes in protein phosphorylation in the eye of Aplysia associated with circadian rhythm regulation by serotonin
Authors: Zwartjes Raymond E. , Eskin Arnold
Published: January 2005

Serotinin (5‐HT) shifts the phase of the circadian oscillator of the eye of Aplysia californica in a phase dependent manner. This indicates that 5‐HT acts, either directly or through some intermediaries, on a component of the oscillator. Since our goal is to identify the components of the oscillator, we are following the pathway through which 5‐HT has its effect on the rhythm. The effect of 5‐HT on the rhythm has been shown to be mediated by an increase in intracellular cyclic adenosine‐3′,5′‐monophosphate (cAMP). The most likely action of cAMP is to activate cAMP‐dependent protein kinase. Therefore, we used two‐dimensional polyacrylamide gel electrophoresis to investigate changes in 32P labelled phosphoproteins which occur with 5‐HT and other treatements. Fourteen proteins showed increased incorporation of 32P when eyes were exposed to treatments of 5‐HT from CT 06 to 12. Two proteins showed decreased incorporation. 8‐bt‐cAMP mimicked all but one of the increases and both decreases in incorporation produced by 5‐HT. 8‐bt‐cAMP increased incorporation into three additional proteins and decreased incorporation into three additional proteins and decreased incorporation into three other that were not affected by 5‐HT. Incorporation into one protein was increased by 5‐HT but decreased by 8‐bt‐cAMP. By comparison, light, which has little or no effect on the rhythm at this phase, only affected one protein. The protein increased by light was also increased by 5‐HT. Tetradecanoic phorbol acetate (TPA), administered during CT 06‐12, also had little effect on the rhythm at this phase. TPA increased incorporation into twenty proteins and decreased incorporatoin into three. Seven of the increased proteins were also increased by 5‐HT. Some of the phosphoproteins altered by 5‐HT and cAMP analogue may mediate the effect of 5‐HT on the circadian rhythm.
Frequency‐dependent and cell‐specific effects of electrical activity on growth cone movements of cultured Helisoma neurons
Authors: Cohan Christopher S.
Published: January 2005

The present experiments address the question of how stimulation parameters, which evoke action potentials in neuronal cell bodies, influence growth cone movements of different identified neurons. The motility of growth cones of Helisoma buccal neurons B19 and B4 was monitored while somata were stimulated simultaneously via an intracellular microelectrode. The findings show that the responses of growth cones of B19 and B4 contain components that are common as well as unique to each neuron. Whereas rates of growth cone advance were suppressed in a graded fashion by stimulus frequencies beyond a threshold of 2 s−1 for both neurons, B4 was more sensitive to electrical stimulation and exhibited a new response, namely, growth rates were enhanced during the poststimulation recovery period after stimulation at specific frequencies. Thus, electrical activity can result in enhancement as well as in inhibition of growth cone movement. Changes in number of filopodia on B19 and B4 were graded also, with B4 again displaying greater sensitivity. The frequency dependence of filopodia compared to growth rate changes was different and suggests a possible dissociation between filopodial activity and growth cone motility. Patterned electrical acivity produced effects similar to constant stimulation for B19 growth cones, whereas it decreased the threshold frequency and eliminated the growth enhancement effect for B4. Taken together, these data demonstrate that the quantitative features of electrical activity as well as intrinsic properties of neurons both determine the growth cone response to changes in neuronal activity.
Mapping of the presumptive brain regions in the neural plate of Xenopus laevis
Authors: Eagleson Gerald W. , Harris William A.
Published: January 2005

Two cell autonomous fluorescent labels (DiI and Hoechst) were used as vital markers in a fate map study of the Xenopus neural plate and ridge. Most areas of the brain derive from the neural plate in a fate map that is consistent with the topology of a sheet rolling into a tube, i.e., neighboring areas are maintained as neighbors. This has enabled us not only to plot the fates of larval brain structures, but also to suggest their primordial orientation in the neural plate. Since overlapping areas of the plate gave rise to overlapping regions of the central nervous system (CNS), we have been able to construct a space‐filling model of the neural plate, whereby the number of founder cells for each brain region fate‐mapped may be estimated roughly. Much of the telencephalon, ventral forebrain, and dorsal brain stem derives from the neural ridge and not the neural plate in the stage 15 Xenopus embryo. The strctures of the forebrain were examined in detail because there were indications of substantial cell movements in this region. The anterior pituitary arises from the mid‐anterior ridge, while hypothalamic structures arise from the midline regions of the anterior neural plate. Consistent groups of ventral hypothalamic structures were labeled when fluorescent markers were applied to these parts of the neural plate, indicating stereotyped cell movements. Detailed comparisons were made between the fate map of the Ambystoma neural plate (Jacobson, 1959) and that of Xenopus.
Development of synaptic transmission at autonomic synapses in vitro revealed by cytochrome oxidase histochemistry
Authors: Mawe G. M. , Gardette R. , D'Agostaro L. , Role L. W.
Published: January 2005

We have studied the development of synaptic transmission by innervating sympathetic neurons in vitro and monitoring synaptic activity with both physiological recording and cytochrome oxidase histochemistry. The onset of synaptic transmission was reflected in increased cytochrome oxidase reaction product within individual neurons. Within 24 hours of co‐culture, relatively low frequency suprathreshold potentials wer recorded in approximately 20% of the innervated neurons. At this stage the cytochrome oxidase activity of innervated neurons, as assessed by optical density of the histochemical reaction product, was increased twofold compared with uninnervated neurons. Over the next 2–4 days of innervation, changes in the pattern and extent of synaptic activity and superthreshold events were accompanied by a net fourfold increase in cytochrome oxidase activity levels compared with noninnervated neurons. The increase in density of cytochrome oxidase reaction product observed after innervation was reversed completely by blockade of synaptic transmission. Differences in the efficacy of synaptic input provided to the sympathetic neurons by appropriate versus inappropriate presynaptic sources was determined by co‐culturing sympathetic neurons with explants that contained either preganglionic neurons or somatic motor neurons. Although sympathetic neurons innervated by motor neuron explants had increased levels of cytochrome oxidase activity compared with noninnervated controls, the density of cytochrome oxidase reaction product was even greater in sympathetic neurons innervated by preganglionic explants. We conclude that both the onset of innervation of sympathetic neurons as well as the subsequent maturation of synaptic function is directly reflected in graded increases in cytochrome oxidase reaction product.
Elevated potassium shortens action potential duration by altering outward currents in chick dorsal root ganglia neurons
Authors: Yang Jay , Zorumski Charles F.
Published: January 2005

Dissociated embryonic chick dorsal root ganglion (DRG) neurons maintained in culture exhibit a mixed Na+/ Ca2+ action potential. The characteristic “shoulder” on the repolarizing phase is due to the relatively prolonged inward Ca2+ current. DRG neurons grown in an elevated K+ medium (25 versus. 5 mM) lack the plateau phase of the action potential. Voltage‐clamp analysis showed that this plastic change in action potential duration is not due to the loss of the inward Ca2+ current but is partly due to the appearance of a Ca2+ dependent, 4‐aminopyridine‐(4‐AP)‐sensitive transient outward current. Faster activation of the purely voltage‐dependent delayed rectifier outward current also contributes to the rapid repolarization observed in neurons cultured in elevated K+ medium.
Distribution and characterization of pedal peptide immunoreactivity in Aplysia
Authors: Pearson Wade L. , Lloyd Philip E.
Published: January 2005

Pedal peptide (Pep) is a very abundant neuropeptide in Aplysia. A radioimmunoassay (RIA) was developed to quantify Pep‐like immunoreactivity (IR‐Pep) in tissue extracts. IR‐Pep was present in very high concentrations in the central nervous system (CNS) and two peripheral tissues: the large hermaphroditic duct (LHD) and the foot. RIA of fractions from high‐pressure liquid chromatography (HPLC) indicated that Pep itself was the predominant immunoreactive species in each of these tissues. Lower concentrations of Pep were found in a number of other peripheral tissues. Incorporation of labelled amino acid indicated that Pep was synthesized in the LHD, whereas Pep in the foot was synthesized primarily in central neurons and transported to the foot. IR‐Pep was further localized by immunocytology. All peripheral IR‐Pep appeared to be associated with neuronal fibers, most commonly varicose axons. Immunoreactive innervation of the LHD and foot was particularly dense but positive staining was also observed in other tissues including tegument, gill, gut, and heart. IR‐Pep innervation in all tissues including the LHD appeared to be localized predominantly in muscular portions of the tissue. Spontaneous contractions of isolated LHD were accelerated by the application of Pep. Pep appears to act as a transmitter or neuromodulator at a number of different sites in Aplysia.
Hormonally mediated changes in simple reflex circuits during metamorphosis in Manduca
Authors: Levine Richard B. , Weeks Janis C.
Published: January 2005

During insect metamorphosis, the nervous system must be reorganized to allow the production of unique behaviors during each life stage. In the hawkmoth, Manduca sexta, it has been possible to follow this postembryonic phase of neuronal development at the level of identified neurons. Of particular interest in the present context are sensory neurons, motoneurons, and interneurons which persist through metamorphosis, but participate in different types of behavior at different stages of life. Many of these neurons undergo striking changes in their dendritic arborizations and axonal projection patterns, which can be correlated with changes in their synaptic interactions with other neurons. Manipulations of the ecdysteroid and juvenile hormone titers, both in vivo and in vitro, implicate these hormones in the regulation of metamorphic changes within the nervous system. Taking advantage of this endocrine control, it has been possible to create heterochronic mosaic animals that allow the relationship between specific cellular changes and behavioral alterations to be tested directly.
Retrofitting larval neuromuscular circuits in the metamorphosing frog
Authors: Alley Keith E.
Published: January 2005

Maturation of vertebrate neuromuscular systems typically occurs in a continuous, orderly progression. After an initial period of developmental adjustment by means of cell death and axonal pruning, relatively stable relationships, with only subtle modifications, are maintained between motoneurons and their appropriate targets throughout life. However, among a restricted group of vertebrates (amphibians and especially the anuran amphibians) the sequential maturation of neuromuscular systems is altered by an abrupt reordering of the basic body plan that encompasses cellular changes in all tissues from skeleton to nervous system. Many anuran amphibians possess neuromuscular circuits that are remarkable by virtue of their complete reorganization during the brief span of metamorphosis. During this period motor systems initially designed for the behavioral patterns of aquatic tadpoles are adjusted to meet the drastically different motor activities of postmetamorphic terrestrial life. This adjustment involves the deletion of neural elements mediating larval specific activities, the accelerated maturation of neural circuits eliciting adult‐specific activities and the retrofitting of larval neuromuscular components to serve postmetamorphic behaviors. This review focuses on the cellular events associated with the neuromuscular adaptation in the jaw complex during metamorphosis of the leopard frog, Rana pipiens. As part of the metamorphic reorganization of the jaw apparatus there is a complete turnover of the myofiber complement of the adductor mandibulae musculature. Trigeminal motoneurons initially deployed to the larval myofibers are redirected to new muscle fibers. Simultaneously the cellular geometry and synaptic input to these motoneurons is revamped. These changes suggest that trigeminal neuromuscular circuitry established during embryogenesis is updated during metamorphosis and reused to provide the basis for adult jaw motor activity that is far different than its larval counterpart.
Postmetamorphic development of neuromuscular junctions and muscle fibers in the frog cutaneous pectoris
Authors: Herrera Albert A. , Banner Lisa R. , Werle Michael J. , Regnier Michael , Stevens Naomi Nagaya
Published: January 2005

Synaptic size, synaptic remodelling, polyneuronal innervation, and synaptic efficacy of neuromuscular junctions were studied as a function of growth in cutaneous pectoris muscles of postmetamorphic Rana pipiens. Recently metamorphosed frogs grew rapidly, and this growth was accompanied by hypertrophy of muscle fibers, myogenesis, and increases in the size and complexity of neuromuscular junctions. There were pronounced gradients in pre‐ and postsynaptic size across the width of the muscle, with neuromuscular junctions and muscle fibers near the medial edge being smaller than in more lateral regions. The incidence of polyneuronal innervation, measured physiologically and histologically, was also higher near the medial edge. Growth‐associated declines in all measures of polyneuronal innervation indicated that synapse elimination occurs throughout life. Electrophysiology also demonstrated regional differences in synaptic efficacy and showed that doubly innervated junctions have lower synaptic efficacy than singly innervated junctions. Repeated, in vivo observations revealed extensive growth and remodelling of motor nerve terminals and confirmed that synapse elimination is a slow process. It was concluded that some processes normally associated with embryonic development persist long into adulthood in frog muscles.
Induction of K‐channel expression in a neuroblastoma cell line
Authors: Smith‐Maxwell Catherine J. , Eatock Ruth Anne , Begenisich Ted
Published: January 2005

Whole‐cell currents were examined in mouse neuroblastoma cells of the N2AB‐1 line. In standard culture medium, N2AB‐1 cells exhibited large voltage‐dependent Na currents but no discernible K currents. Treatment of N2AB‐1 cells with either dimethylsulfoxide (DMSO) in low‐serum medium or with retinoic acid (RA) caused the expression of delayed rectifier K currents. Currents from two types of K channel with single channel slope conductances of 15.0 pS and 6.4 pS were observed in outside‐out patches from cells of both treatment groups. Thus, while N2AB‐1 cells did not exhibit K currents under standard culture conditions, they did possess the gene (s) encoding K channels. The treatments caused other changes that were not directly linked to K‐channel expression. RA treatment caused neurite extension in most, but not all, N2AB‐1 cells; however, all RA‐treated cells, including those without neurites, expressed K currents. RA treatment did not suppress cell division or cause hypertrophy. In contrast, treatment with DMSO/low serum suppressed cell division and caused cellular hypertrophy, but did not cause long neurites to form. Thus, the regulation of K channels was not coupled in a simple fashion to properties that have been associated with a differentiated neuronal phenotype: neurite elaboration, changes in cell size, and inhibition of cell division. These results suggest that N2AB‐1 cells may be a good model system for investigating the processes regulating K‐channel expression.
Dual muscarinic and nicotinic action on a motor program in Drosophila
Authors: Gorczyca Michael G. , Budnik Vivian , White Kalpana , Wu C. F.
Published: January 2005

The effect of cholinergic agonists and antagonists on the central pattern generator of the pharyngeal muscles has been studied in third instar larvae of Drosophila. The pharyngeal muscles are a group of rhythmically active fibers involved in feeding. Bath application of the cholinergic agonists carbachol, musarine, pilocarpine, and acetylcholine (ACh) to a semiintact preparation including the pharyngeal muscles and the central nervous system (CNS), initiated long‐lasting endogenous‐like bursting activity in the muscles. The muscarinic antagonists, atropine and scopolamine, blocked these responses as well as endogenous activity. Perfusion with nicotine elicited a short, tonic response that was marginally blocked by mecamylamine but not by curare, α‐bungarotoxin, hexamethonium, or the muscarinic antagonists. This is the first time that a response to cholinergic drugs has been examined in Drosophila. The pharyngeal muscle preparation may prove to be a valuable system for studying mutations of cholinergic metabolism, receptors, and second messengers.
Laminin‐like immunoreactivity in the snail Helisoma: Involvement of a ∼300 kD extracellular matrix protein in promoting outgrowth from identified neurons
Authors: Miller John D. , Hadley Robert D.
Published: January 2005

Polyclonal antibodies directed against laminin (LM), and against the A and B chains of reduced LM were used to identify antigenically related proteins in the extracellular matrix (ECM) of the snail Helisoma trivolvis Immunofluorescence of snail central ganglionic rings using either the anti‐LM or anti‐B chain antibodies labeled the ECM within ganglionic sheaths as well as basal laminae surrounding the ganglia. Both the anti‐LM and anti‐B chain antibodies recognized a prominent, ∼300‐kD protein on immunoblots of a snail central ganglion preparation enriched in ECM components. The anti‐A chain antibody failed to label any structures in sections of snail ganglia or to recognize any proteins on immunoblots of ganglionic ECM. A polyclonal antibody was raised against the ∼300‐kD snail protein. Immunofluorescence of snail ganglia with the anti‐∼300‐kD antibody gave a distribution of labeled structures comparable to that obtained with the anti‐LM antibody. Immunofluorescent labeling of sections of snail muscle and salivary gland with the anti‐∼300‐kD antibody revealed a distribution of reactive protein characteristic of an ECM component. Probing immunoblots of ganglionic ECM with the anti‐ ∼300‐kD antibody revealed the recognition of the same ∼ 300‐kD protein as identified by the anti‐LM antibodies. Media conditioned by Helisoma central ganglionic rings (CM) contains an unidentified neurite outgrowth promoting factor (NOPF). Immunoblots of CM probed with the anti‐B chain and anti‐ ∼300‐kD antibodies reveal the recognition of a soluble ∼300‐kD protein similar to the ∼300‐kD protein identified in snail ECM. The ganglionic ECM preparation containing the ∼300‐kD protein supported outgrowth from cultured snail buccal neurons B5, and addition of anti‐ ∼300‐kD Fab fragments to CM abolished its outgrowth promoting activity. These results suggest that the ∼300‐kD ECM protein may be the NOPF in CM and /or functions in promoting neurite outgrowth.
Development of palecortical projections through the anterior commissure of hamsters adopts progressive, not regressive, strategies
Authors: Lent Roberto , Guimarães Ricardo Z. P.
Published: January 2005

The perinatal development of anterior commissure projections was studied in hamsters by use of carbocyanine crystals implanted either into the commissure or into the ventrolateral prosencephalon. The earliest fascicles of growing commissural fibers had reached the midline on day 14 of gestation (E14). On E15, these fibers had entered the opposite hemisphere and reached the borders of their target regions. No waiting period was observed, since on E16 axons were already collateralizing into most targets. On P1, labelled cells were seen in all regions projecting through the anterior commissure in adults, namely, the anterior olfactory nucleus, olfactory tubercle, piriform cortex, nucleus of the lateral olfactory tract, bed nucleus of the stria terminalis, insular, perirhinal, entorhinal, and temporal cortices, as well as the amygdaloid complex. No evidence of topographical exuberance was detected. Counts of labelled neurons showed that the number of commissural cells increased gradually after birth. It is concluded that the development of paleocortical connections through the anterior commissure employs progressive strategies, lacking the regressive phenomena that are characteristic of the neocortical projections through the corpus callosum.