bluuebunny/crossref_metadata_2025 huggingface dataset:
Conduction velocity and spike duration during afterdischarge in neuroendocrine bag cells of Aplysia
Authors: Dudek F. Edward , Kossatz Anne
Published: January 2005

Changes in conduction velocity and spike duration during electrically triggered afterdischarges were determined with extracellular recordings from bag‐cell neurites of Aplysia. Spikes with high conduction velocity and short duration occurred at the onset of the afterdischarge during the period of high‐frequency firing and regular interspike intervals. Later in the afterdischarge, spike frequency and conduction velocity decreased, while spike duration increased. During the short bursts within the later part of the afterdischarge, conduction velocity was highest for the first spike and decreased for successive spikes in the burst. That conduction velocity and spike frequency were both maximal during the first minute of the afterdischarge and lower during the later periods of the spike train supports the hypothesis that changes in the excitability of the bag‐cell neurites occur during this firing pattern. Furthermore, the slower conduction velocity and longer duration of spikes from the bag‐cell neurites late in the afterdischarge, and late in the individual bursts within the afterdischarge, suggest the hypothesis of enhanced hormone release per action potential during these periods.
Seasonal modulation of synthesis of the neurosecretory egg‐laying hormone of Aplysia
Authors: Berry Robert W.
Published: January 2005

Biosynthesis of the peptide egg‐laying hormone by the bag cells of Aplysia was monitored throughout the year to determine whether the synthesis of neurosecretory proteins is modulated in accordance with secretory demand. The rate of synthesis of precursors to the hormone was found to vary seasonally, being approximately twofold higher during the late summer egg‐laying season than during midwinter. Since there was no change in the distribution of radioactivity among members of the proteolytic processing sequence leading to the hormone, these data imply a seasonal modulation of the production of the secretory product. The synthetic rate showed no correlation with animal maturity or recent egg‐laying history. However, there was a significant interaction between the seasonal effect and elevation of hormone synthesis induced by exposure to elevated external potassium, suggesting that these two modulatory factors exert their effects at a common point in the mechanism of hormone biosynthesis.
Variability and frequent failure of lucifer yellow to pass between two electrically coupled neurons in Lymnaea stagnalis
Authors: Audesirk Gerald , Audesirk Teresa , Bowsher Peggy
Published: January 2005

The electrically coupled giant neurosecretory neurons VD1 and RPD2 of Lymnaea stagnalis were found to have coupling coefficients ranging from ca. 0.1–0.6. When the fluorescent dye Lucifer Yellow was injected intracellularly into one of the neurons, in most preparations no dye was observed to pass through into the coupled cell body or the process leading to it. There was no apparent correlation between the amount of dye coupling and the length of time allowed for diffusion of the dye in the cells. In eight preparations, the electrical coupling coefficient was measured before dye was injected. There was no correlation between dye coupling and the electrical coupling coefficient.
Prolonged alteration in composition of fast transported protein in axons prevented from regenerating after injury
Authors: Bisby M. A.
Published: January 2005

A previous study revealed a characteristic alteration in the ratio of labeling of two fast axonally transported polypeptides identified as S1 (22,000 daltons) and S2 (18,000 daltons) and their ratio (S2/S1) in rat motoneuron axons following axonal injury and subsequent regeneration. In this study the S2/S1 ratio was determined for axons which were resected and ligated proximally and which did not regenerate to reinnervate muscle. While the initial increase in the S2/S1 ratio following section was the same as that following a crush, the S2/S1 ratio did not return towards normal values after 42 days, but remained elevated for at least 98 days after injury. It is concluded that the return of S2/S1 ratio to normal values, like some other manifestations of the cell body reaction, is delayed if the injured axons do not regenerate.
Position‐sensitive detector studies of the axonal transport of a pulse of radioisotope
Authors: O'Brien D. W. , Snyder R. E.
Published: January 2005

Axonal transport of a pulse of 35S‐methionine‐labelled material was studied in vitro in amphibian sciatic nerve using position sensitive detectors. Following formation of a pulse of activity using the cold block technique, the nerve was ligated proximal and distal to the pulse and its movement monitored at room temperature (22.5–23.5°C) for up to 16 h. Material transported in the anterograde direction did so with an average maximum velocity of 147 mm/d. The pulse was found to disperse at an average rate of 0.23 mm/mm travel; however, dispersion was found to vary from preparation to preparation more than would be predicted from experimental error alone. Label was observed to reverse direction at the distal ligature in only 2 of 13 preparations. Reversal of label began within approximately 0.4 h of first arrival, and the most rapidly retrogradely transported material moved at a velocity of 80% that of the most repidly anterogradely transported material.
Unchanged rate of axonal regeneration by cyclophosphamide in rat sciatic nerve
Authors: Komiya Yoshiaki
Published: January 2005

The rates of axonal regeneration and initial delay in motor and sensory axons of cyclophosphamide‐treated and control rat sciatic nerves after cold injury were determined by using fast axoplasmic transport. The rates in motor and sensory nerves were not significantly different between the two groups. The difference of initial delay in motor nerve was not significant, but in sensory nerve the drug‐treated group showed a longer initial delay than the control. These results suggest that the enhancement of motor function recovery by cyclophosphamide is not due directly to an increased rate of axonal regeneration, nor to a decreased initial delay.
Calcium‐dependent proteolysis in neural tissue is activated at physiologic intracellular Ca2+ levels and inhibited by some anticonvulsants
Authors: Nosek Thomas M. , Crosland Marcia B.
Published: January 2005

The level of calcium‐activated neutral protease (CANP) activity in the brain and nerve cord of the crayfish Procambarus clarkii was assayed by measuring the degradation of casein yellow by tissue homogenates. When care was taken to maintain the ionic strength of all incubation media at 0.15M and to buffer the Ca2+activity of the media with 5mM EGTA, CANP was found to be very sensitive to Ca2+; maximal activity was achieved at 1 × 10−3M Ca2+, with 50% of this maximum present at the physiologic intracellular Ca2+activity of 1 × 10−7M. We found that the anticonvulsant agent phenytoin was without effect on CANP activity while pentobarbital and a relatively new anticonvulsant agent, valproic acid (an eight‐carbon branched fatty acid), significantly inhibited CANP activity in a dose‐dependent manner. The inhibitory effect of valproic acid was shared by a straight‐chain eight‐carbon fatty acid, caprylic acid. These findings demonstrate that inhibition of CANP activity is not limited to agents with a specific molecular structure. They also suggest that CANP plays a role in the normal turnover of proteins that control various cellular functions.
Neurotrophic regulation of GABA receptors at a crayfish inhibitory synapse
Authors: Craelius William , Tiberio Angela , Pomerantz Jeffrey
Published: January 2005

Experiments were done on the inhibitory synapse of crayfish tonic muscle receptor organs (MROs) to determine whether gamma‐aminobutyric acid (GABA) receptors would be affected by denervation or axotomy. It was found that severing the dorsal nerve containing the MRO sensory and inhibitory neurons usually induced, in 30 days or less, a dramatic transformation in the responses of MROs to ionophoretically applied GABA. In contrast to normal MROs which show only inhibitory responses to GABA, transformed MROs were substantially depolarized and excited by GABA application to numerous points found on the axon, soma, and dendrites. Interspersed among the points of excitation, normal inhibitory points could still be found on the transformed cells. The results suggested that chronic lesions can induce structural changes in GABA receptors, whereby the Cl− ionophore is replaced by a cationic channel. It was possible to compare the effects of postsynaptic axotomy alone with those of postsynaptic plus presynaptic axotomy by testing MROs from animals whose ventral nerve cord was sectioned. These experiments suggested that interruption of the presynaptic neuron is an important factor in the transformation. It was not determined whether complete degeneration of the inhibitory synapse is necessary for the transformation, but the rapidity of the effect, coupled with the probability of long‐term survival of synaptic contacts, suggested that complete degeneration was not necessary. Similarities were found in the GABA responses of transformed MROs and those MROs which normally receive no innervation, which are located in the sixth abdominal segment. These results support the idea that trophic regulation from inhibitory neurons is a factor in stabilizing the association of the Cl− ionophore with GABA receptors.
Modifications of dynamic and static behavior by small‐length perturbations in crayfish stretch receptor organs
Authors: Buño W. , Bustamante J. , Fuentes J.
Published: January 2005

To investigate whether static and dynamic sensitivities of slowly and rapidly adapting stretch receptor organs (SAO and RAO, respectively) of crayfish are different when perturbed compared with those in conventional laboratory experiments, receptors were submitted to ramplike length changes of different velocities separated by long‐duration, constant lengths of different values. They were perturbed at random by fast, small‐amplitude length variations called “jitter.” First‐order afferent discharges were recorded extracellularly. Quantifications involved the separate estimation of static and dynamic response components. In the SAO, jitter (1) augmented the static sensitivity, (2) decreased the dynamic sensitivity, (3) simplified response profiles by decreasing nonlinearities and increasing transduction fidelity in terms of coding length. In the RAO, jitter (1) changed the behavior from phasic to tonic with length sensitivity, (2) decreased the dynamic sensitivity to values close to those of the unperturbed SAO, (3) increased transduction fidelity for stimulus length and decreased nonlinearities. Perturbation effects suggest that differences between SAO and RAO are more quantitative than qualitative. Moreover, they have general implications and are relevant to other mechanoreceptors at other levels in the CNS.
Possible temperature‐dependent blockage of synaptic vesicle recycling induced by a single gene mutation in drosophila
Authors: Kosaka Toshio , Ikeda Kazuo
Published: January 2005

The temperature‐sensitive Drosophila mutant, shibirets1 (shi), has been shown to exhibit a reversible block in synaptic transmission at 30°C. Various synaptic terminals (neuromuscular, sensory, central) of this mutant were observed by electron microscopy. At 19°C, all terminals of shi showed essentially the same structural features as those of wild‐type (Oregon‐R) flies, while at 30°C (5 or 10 min of exposure) shi terminals exhibited various structural changes not seen in the wild type. The major structural change observed in all of the various types of terminals was the accumulation of many pitlike structures on the plasma membrane near presynaptic sites. These structures consisted of a spherical head portion, about 50–100 nm in diameter, and a cylindrical neck portion, about 20 nm long and 20–25 nm in diameter. The neck portion was surrounded by a kind of cytoplasmic dense material, about 10 nm thick, reminiscent of a “collar.” Thus, these pits are referred to as “collared pits.” Similar kinds of pits were observed, although very rarely, in wild‐type flies at 19 and 30°C and in shi flies at 19°C. In addition, various degrees of vesicle depletion, and an increase in membranous structures (infoldings and cisternalike or tubulelike structures) often accompanied pit formation. The possibility that these pits are the result of a blocked step in the endocytotic process, which in turn causes vesicle depletion as exocytosis proceeds, is discussed.
Elicitation and abrupt termination of behaviorally significant catchlike tension in a primitive insect
Authors: Hoyle Graham , Field Laurence H.
Published: January 2005

Sustained steady contractural or catchlike tension (CT) occurs in the metathoracic extensor tibiae muscle of the primitive insect the weta (Orthoptera: Stenopelmatidae) during its characteristic leg‐extension defense behavior or following leg‐position conditioning. Similar action occurs occasionally in semi‐intact preparations and is abruptly turned off by a single peripheral inhibitory impulse. These phenomena were reproduced routinely by first infusing saline containing 10−8M (or stronger) octopamine into the muscle for 12 min, and then stimulating the slow excitatory motor neuron SETi with a brief burst. Direct stimulation of the dorsal unpaired median neuron, innervating the extensor tibiae (DUMETi) prior to SETi stimulation, also led to CT. Both octopamine and DUMETi markedly enhanced the tension developed in response to a burst of impulses in SETi.
Innervation and motor patterns of the abdominal superficial flexor muscles in larval lobsters
Authors: Kirk Mark D. , Govind C. K.
Published: January 2005

The pattern of innervation and motor program of the abdominal superficial flexor muscle was investigated electrophysiologically in larval lobsters (Homarus americanus). The muscle receives both excitatory and inhibitory innervation in the larval as well as in the embryonic stages. Individual muscle fibers receive a single inhibitory neuron (f5) and a maximum of three excitors. Based on spike heights these axons belong to either the small (f1 or f2) or large (f3, f4) motoneurons. While the small axons preferentially innervate the medial muscle fibers the large axons innervate medial as well as lateral fibers. This larval pattern of innervation resembles the pattern in the adult lobster. The resemblance extends to the firing patterns as well with both large and small excitors firing spontaneously. Furthermore, evoked activity in the larvae produces reciprocal (and occasionally cyclical) bursts of excitor and inhibitor neurons denoting abdominal extension and flexion and resembling the firing patterns in adults. Consequently motor programs employed in steering the pelagic larvae are reminiscent of the programs for maintaining posture in the benthic adult lobsters.
Increased regeneration rate in peripheral nerve axons following double lesions: Enhancement of the conditioning lesion phenomenon
Authors: Bisby M. A. , Pollock B.
Published: January 2005

The rate of regeneration of rat sciatic nerve sensory axons was measured using the pinch‐reflex test method, and confirmed by studying the transport of labelled protein into the regenerating axons. For nerves receiving a single test crush lesion the rate was 4.02 ± 0.03 (SE) mm/day. For nerves with a conditioning lesion made at the knee seven days prior to the test lesion at the hip the rate was 5.73 ± 0.06 mm/day, and for nerves where both conditioning and test lesions were made at the same site (hip or knee) but separated by seven days, the rate was 6.76 ± 0.04 mm/day, a 68% increase over the normal rate, showing that pre‐degeneration of the nerve distal to the site of the test lesion increases the rate of regeneration. It is concluded that the rate of axon regeneration can be influenced by the environment through which the regenerating axons grow.
Activation by dopamine of patterned motor output from the buccal ganglia of Helisoma trivolvis
Authors: Trimble Dorothea L. , Barker David L.
Published: January 2005

The buccal ganglia of the snail, Helisoma trivolvis, contain an intrinsic system of dopamine‐containing neurons (Trimble, Barker, and Bullard, 1983). Dopamine, when bath applied to the isolated buccal ganglia, activates patterned motor output in a dose‐dependent fashion. Haloperidol blocks the activating effect of dopamine, but the similar activation evoked by serotonin is not blocked by haloperidol. We suggest that there are two separate mechanisms for activating patterned motor output from the buccal ganglia. One is serotonergic, emanating from identified cerebral ganglion cells (Granzow and Kater, 1977), while the other is dopaminergic, involving neurons intrinsic to the buccal ganglia.
Cholinergic receptors in the Aplysia gill
Authors: Weiss Sam , Goldberg Jeff I. , Edstrom Jon P. , Lukowiak Ken
Published: January 2005

Acetylcholine has been suggested as a neurotransmitter released in the Aplysia gill by peripheral afferents of central neurons and by peripheral neurons within the gill. The perfused gill, isolated from the abdominal ganglion, was examined. At concentrations greater than 1 μM, acetylcholine elicited a slowly developing tonic contraction of the afferent vein that reversed upon washout. This effect was observed on both quiescent and active preparations. At concentrations less than 1 μM, acetylcholine perfusion resulted in a reduction of gill tone. The excitatory effect of acetylcholine was reduced 80 and 60% by the cholinergic antagonists atropine and hexamethonium, respectively. The acetylcholine‐evoked contraction was potentiated 2.5‐fold when curare was coinfused. Carbachol did not mimic the excitatory effects of acetylcholine. At all concentrations examined (1–100 μM), carbachol infusion reduced baseline tension, the amplitude of spontaneous contractions and contractions evoked by FMRFamide and dopamine. Contractions evoked by perfusion of p‐chlorophenylthiocyclic AMP were greatly reduced when carbachol was added to the perfusate. Further addition of curare reversibly blocked carbachol inhibition of the cyclic AMP%evoked contractions. These finding suggest that excitatory and inhibitory cholinergic receptors are involved in the regulation of gill contractile behavior by acetylcholine.
Sensitivity of Aplysia neurons in primary culture to putative neurotransmitters
Authors: Bodmer Rolf , Levitan Irwin B.
Published: January 2005

Aplysia neurons grown in primary cell culture (Dagan and Levitan, 1981) were exposed to the putative neurotransmitters acetylcholine and serotonin by local iontophoretic application, and changes in membrane potential or voltage clamp currents were examined. It was found that 47% of the neurons were sensitive to cholinergic agonists, 14% to serotonin, and 9% responded to both. Responses could be recorded upon application of the transmitters to the cell bodies as well as along the regenerated neurites. An identified group of neurons, the neurosecretory bag cells, exhibited similar responses to cholinergic agonists in culture and in situ. Pleural medial neurons exhibited cholinergic responses in culture similar to those previously reported in situ. Thus neurotransmitter receptor/ion channel complexes characteristic for a specific cell type in the intact ganglion are also present on this cell type in culture.
Central nervous sensitization and dishabituation of reflex action in an insect by the neuromodulator octopamine
Authors: Sombati Sompong , Hoyle Graham
Published: January 2005

Habituation of excitatory synaptic inputs onto identified motor neurons of the locust metathoracic ganglion, driven electrically and by natural stimuli, was examined using intracellular recording. Rapid progressive reduction in amplitude of EPSPs from a variety of inputs onto fast‐type motor neurons occurred. The habituated EPSPs were quickly dishabituated by iontophoretic release of octopamine from a microelectrode into the neuropilar region of presumed synaptic action. The zone within which release was effective for a given neuron was narrowly‐defined. With larger amounts of octopamine applied at a sensitive site the EPSP became larger than normal, and in many instances action potentials were initiated by the sensitized response. Very small EPSPs onto a motor neuron, which were associated with proprioceptive feedback, and which were originally too small to be detected above the noise, were potentiated to a level of several mV by the iontophoresed octopamine. A DUM neuron (presumed to be octopaminergic) was found, whose direct stimulation was followed by a strong dishabituating and sensitizing action leading to spikes, of inputs to an identified flexor tibiae motor neuron. The action and its time course were closely similar to those evoked by octopamine iontophoresed into the neuropil in the region of synaptic inputs to the motor neuron. It is concluded that DUM (octopaminergic) neurons exert large potentiating actions on central neuronal excitatory synaptic transmission in locusts.
Neural control of behavioral responses in the nudibranch mollusc Phestilla sibogae
Authors: Willows A. O. Dennis
Published: January 2005

The tropical aeoliacean nudibranch Phestilla sibogae, has a number of large and reidentifiable neurons in its centrally located cerebral‐pedal‐pleural ganglion complex. In studies involving nearly intact animal preparations, neurons were identified which control specific movements of the dorsal cerata, the oral veil tentacles, and the margins of the foot. Responses of neurons to mechanical vibrations in the environment, and responses to light not mediated by the eyes are described. Finally, a pair of large cerebral neurons are identified that are superficially similar in structure, location, and function to the metacerebral giants found in several other opisthobranchs. These neurons are electrically coupled and control stereotyped movements of the mouth. These anatomical and neurophysiological features, when coupled with the fact that the generation time of Phestilla (30 days) is comparable to that of Drosophila suggests that this nudibranch may prove useful in combined studies of neurophysiology, behavior and genetics.
The central morphology of the giant interneurons and their spatial relationship with the thoracic motorneurons in the cockroach, Periplaneta americana (insecta)
Authors: Collin Shaun P.
Published: January 2005

Three groups of giant fibers are found in the cockroach ventral nerve cord. A latero‐dorsal group (dorsal GIs), a latero‐ventral group (ventral GIs) and a medio‐ventral group. The morphology of all three groups of fibers within the thoracic ganglia is described. The morphology of the dorsal and ventral GI pathways in the abdominal and suboesophageal ganglia is also described. The projection patterns of the neurons in each ganglion are remarkably similar which suggests a common function. When motorneurons 5rl (depressor) and 6Br4 (levator) are stained simultaneously with the dorsal and ventral GI groups, some branches from both motor and giant neurons converge. The branching of the remaining medio‐ventral group of fibers and their proximity to areas receiving motorneuronal input suggests that these are the small diameter axons described by Dagan and Parnas (1970).
Morphological and physiological properties of the giant interneuron of the hermit crab (Pagurus pollicaris)
Authors: Stephens Philip J.
Published: January 2005

The physiological and morphological properties of the giant interneurons in the hermit crab Pagurus pollicaris are described. The cell bodies are located anteriorly in the supraesophageal ganglion, close to the mid‐line. Each cell sends a neurite posteriorly and then laterally, so that they cross over in the center of the ganglion. Each axon then branches: one branch runs laterally while the other travels posteriorly and leaves the ganglion in the circumesophageal connective on the side contralateral to the cell body. The giant axons travel in the circumesophageal connectives and through the thoracic and abdominal ganglia without branching. Each giant axon makes synaptic contact with its ipsilateral giant abdominal flexor motor neuron and with a second flexor motor neuron that has its axon in the contralateral third root.

In the supraesophageal ganglion there is a bidirectional synapse between the two giant interneurons. Intracellular recordings from the giant axons show that there is a delay of 0.5 to 0.75 ms that cannot be accounted for by spike propagation along the axons, and may be accounted for by a chemical synapse between the giant interneurons.
Effect of early malnutrition on dynamic properties of axodendritic synapses in the rat prefrontal cortex
Authors: Hernández A. , Ruiz S. , Pérez H. , Soto‐Moyano R.
Published: January 2005

The influence of early protein–calorie malnutrition on synaptic transmission in the rat prefrontal cortex was studied by evoking direct cortical responses with different trains of threshold electrical pulses. Malnutrition resulted in a requirement for increased pulse train stimulating current, reflecting a diminished release of neurotransmitter from the preterminal endings. In addition there was an increase in the time constant of pyramidal cells, indicating that axodendritic synapses have a disability for integrating high frequency inputs at the post synaptic level. It is concluded that early malnutrition alters dynamic properties of axodentritic synapses at both the pre‐ and the postsynaptic levels.
Modulatory effects of proctolin on a crab ventilatory muscle
Authors: Mercier A. Joffre , Wilkens Jerrel L.
Published: January 2005

Proctolin enhances nerve‐evoked, phasic contractions of a selected respiratory muscle of the shore crab, Carcinus maenas, but has no effect on muscle tonus. Proctolin also increases the work and power output of this muscle. These effects are functionally appropriate in view of previous reports that proctolin stimulates the ventilatory rhythm. They also suggest that proctolin exerts coordinated modulatory control at the central and peripheral levels of the gill ventilatory system. In contrast, serotonin, dopamine and octopamine have no effect on this muscle.
Steroid control of neuron and muscle development during the metamorphosis of an insect
Authors: Weeks Janis C. , Truman James W.
Published: January 2005

Insect metamorphosis is controlled by a small ensemble of developmental hormones including a class of steroids—the ecdysteroids. In the tobacco hornworm, Manduca sexta, the progession from the larval to pupal to adult stages is controlled by the relative blood titers of ecdysteroids and juvenile hormone (JH). The cellular events in the nervous and muscular systems which accompany metamorphosis resemble those of embryonic development, but they occur in an animal which is larger and experimentally more tractable than an embryo. In this paper we review the role of ecdysteroids in directing the metamorphosis of the nervous and muscular systems in Manduca, and how JH modifies the cellular responses to the steroids. In particular, we describe how these hormones control muscle degeneration, changes in the structure and function of identified neurons, and programmed neuron death. One general finding is that interactions between cells (e.g., neurons and their target muscles) are not involved in their hormonal responses, but rather the hormones act independently and in parallel at the different sites. Another key finding is that the critical periods and hormonal requirements for the commitment to a particular differentiative pathway, and the phenotypic expression of that pathway, can differ, and are therefore experimentally separable. Finally, we find that the significance of a hormonal signal (e.g., a rise in blood ecdysteroids) is interpreted differently depending upon the previous history of hormone exposure of a neuron or muscle. This progressive change in the interpretation of hormonal signals is a major mechanism by which a limited number of hormones can orchestrate a complicated phenomenon such as metamorphosis.
Effect of synthetic bag cell and atrial gland peptides on identified nerve cells in Aplysia
Authors: Rock M. K. , Shope S. B. , Blankenship J. E. , Schlesinger D. H.
Published: January 2005

We have examined the effects of peptides on the neuroendocrine bag cells, the R2 neuron and the left upper quadrant (LUQ) neurons of the abdominal ganglion of Aplysia californica. Peptides include those extracted from the atrial gland, a reproductive organ; those released by an afterdischarge of the bag cells; and 2 synthetic peptides: the amidated 9‐amino acid C‐terminal portion of atrial gland peptides A/B/ERH (B26–34), and the 8‐amino acid alpha‐bag cell peptide (α‐BCP1–8). Peptides were applied by superfusion, arterial perfusion, pressure ejection from micropipettes, or by inducing a bag cell afterdischarge.

Both α‐BCP1–8 and B26–34 are able to produce a bag cell afterdischarge when applied to the abdominal ganglion but are not as effectively able to trigger the bag cells when applied selectively to the ganglia of the head ring.

Peptides released by the bag cells inhibit R2 and LUQ neurons; whereas atrial gland extract mildly excites LUQ neurons and powerfully excites R2. The inhibitory effect of the LUQ cells and R2 following an afterdischarge of the bag cells in mimicked by α‐BCP1–8. The excitatory effect of the atrial gland extract cannot be duplicated with B26–34. Rather, instead of having an excitatory effect on R2 and LUQ cells, B26–34 seems to mimick α‐BCP1–8 and inhibit these neurons. Both peptides produce a membrane conductance increase in R2 and LUQ cells.
Effects of octopamine and forskolin on excitatory junction potentials of developing and adult moth muscle
Authors: Fitch Greg K. , Kammer Ann E.
Published: January 2005

Intracellular recordings were made from the dorsal longitudinal muscle of Manduca sexta to determine the effects of development and octopamine on the excitatory junction potential (EJP) produced in response to electrical stimulation of the motor nerve. Observations were made on pharate moths during the last 3 days before eclosion and on adults.

In saline, the highest values for EJP amplitude and maximum rate of rise and for resting membrane potential are reached on the nineteenth day of the pupal period, the day the animal ecloses; adult values are slightly lower.

In animals of all ages tested, DL‐octopamine (5 × 10−6M) increases EJP amplitude and maximum rate of rise. Increases in amplitude are greater in animals at stage day 17 and 18 than in animals at stage day 19 and adult. Octopamine has no effect on EJP rise time (onset to peak) or recovery time (peak of EJP to 70% recovery). Octopamine causes a hyperpolarization of about 6 mV. The results show that developmental changes in synapse properties are paralleled only in part by changes induced by octopamine. Both development and octopamine increase EJP amplitude and maximum rate of rise, and neither alter rise time. EJP recovery time changes with development but not in response to octopamine.

Forskolin (10−4M) mimics the effects of octopamine on day 17 animals. EJP amplitude and maximum rate of rise are inceased by forskolin, and rise time and recovery time are unaffected. Forskolin, like octopamine, causes a 6 mV hyperpolarization of the muscle fiber. These results suggest that octopaminergic modulation at the Manduca sexta dorsal longitudinal neuromuscular junction may be mediated by changes in intracellular levels of cyclic AMP.
Embryonic and larval development of the sonic motor nucleus in the oyster toadfish
Authors: Galeo Anthony J. , Fine Michael L. , Stevenson James A.
Published: January 2005

The sonic motor nucleus (SMN), a likely homologue of the hypoglossal nucleus, provideds the final common pathway for sound production in the oyster toadfish (Opsanus tau). SMN neurons increase in size and number for 7–8 years postnatally, and the swimbladder‐sonic muscle complex grows throughout life. This study describes the normal embryonic and larval development of the SMN from its initial differentiation on about day 19 through day 40, when the yolk sac is resorbed and the fish is free swimming.

In contrast to the rapid development of CNS nuclei in mammals, the SMN gradually increased in maturity with more active growth at the beginning and end of the observation period and a relatively static period in the middle. Consistent with a hypoglossal homology, the SMN differentiated within the spinal cord, added cells rostrally, and eventually extended into the medulla. Immature neurons appeared to originate from precursor cells in the ventral portion of the ventricular zone of the central canal. Such cells were initially round with little cytoplasmic development and later added processes and Nissl substance. The number of neurons increased 10‐fold from a median of 35 to 322 cells, and no evidence of cell death was observed. Soma area approximately doubled from 20.6 to 41.2 m̈m2, and cell nucleus area followed a similar pattern. [3H]‐thymidine autoradiography demonstrated that neurons were added continuously throughout the nucleus during embryonic and larval development.
Differences in surface molecules of motor axon terminals correlated with cell–cell recognition
Authors: Denburg Jeffrey L. , Caldwell Robert T. , Marner Joyce M.
Published: January 2005

The cell–cell interactions leading to the formation of synaptic connections among cells in the nervous system may be mediated by cell surface macromolecules. In the cockroach the specific reformation of the original innervation pattern of a set of leg muscles during axonal regeneration indicates a significant contribution from cell–cell recognition. Macromolecules mediating such a process would be expected to be distributed differentially among the axon terminals of the various motor neurons. Monoclonal antibodies have been isolated that selectively bind to the surfaces of axon terminals of some motor neurons and not others. Preliminary biochemical characterization indicates that these antigens are glycoproteins and are good candidates for consideration as recognition macromolecules.
Mechanism for amine modulation of the neurogenic Limulus heart: Evidence for involvement of cAMP
Authors: Groome James R. , Watson Winsor H.
Published: January 2005

The role of cyclic nucleotides as intracellular second messengers mediating the excitatory chronotropic and inotropic actions of octopamine (OCT) and dopamine (DA) on the neurogenic Limulus heart was investigated. Tissue levels of cAMP, but not cGMP, were significantly increased in isolated cardiac ganglia and cardiac muscle following 10 min exposure to 10−5 M OCT or 10−5M DA. In both tissues, OCT elicited larger increases in cAMP than did DA. Amine‐induced cAMP accumulation in the cardiac ganglion and in the cardiac muscle was prevented by the alpha‐adrenergic blocker phentolamine. The adenylate cyclase activator forskolin and the phosphodiesterase inhibitor IBMX produced amine‐like chronotropic and inotropic effects when applied to the isolated heart preparation. However, the kinetics of the responses differed for the two agents. Additional pharmacological agents (RO‐20‐1724, papaverine, SQ 20,009, and 8‐parachloro‐phenylthio cAMP) also had amine‐like effects but to a lesser extent. The chronotropic, but not inotropic, effects of OCT and DA were potentiated in the presence of IBMX. These data suggest that a cAMP‐dependent mechanism underlies the excitatory effects of the neuromodulators OCT and DA on the Limulus heart.
Multiple transmitter neurons in Tritonia. III. Modulation of central pattern generator controlling feeding
Authors: Willows A. O. Dennis , Lloyd Philip E. , Masinovsky Boris P.
Published: January 2005

Feeding behavior in the gastropod mollusc Tritonia diomedea is controlled by a central pattern generator (CPG) in the buccal ganglia. The medially located, large dorsal white cells (B11) have been shown to contain two small cardioactive peptides (SCPs). A smaller nearby neuron (B12) also appears to contain the SCPs. B11's have also been shown to contain acetycholine (ACh), whereas B12's do not.

We have shown earlier that intracellular stimulation of B11's drives contractions of the foregut. Here we show that intracellular electrical stimulation of B11's also elicits excitation of neurons B5 and stimulates the patterned motor output of the CPG. We showed earlier that B12's also stimulate contractions in the foregut, but they are in the opposite direction from those elicited by B11. We show here that electrical stimulation of B12's inhibits the output of the CPG.

We showed earlier that superfusion of the isolated gut with SCPB enhances peristalsis, and here we report that superfusion of the buccal ganglion with SCPB elicits enhanced coordinated motor output from the CPG. The peptide has two effects on the bursting output of motor neurons. It produces an increase in (1) the rate of bursting and (2) the spike frequency during each burst. On the other hand, we reported earlier that ACh applied directly to isolated foregut inhibits ongoing peristalsis. Here we demonstrate that ACh superfusion of the buccal ganglion also inhibits the CPG output.

Our evidence supports the view that in addition to stimulating foregut contractility, B11's modulate the output of the swallowing CPG by releasing a peptide from central terminals. We suggest roles for B11, B12, the SCPs, and ACh in controlling both central and peripheral aspects of feeding behavior.
Connections between the nucleus isthmi and the tectum in larval and post‐metamorphic axolotls
Authors: Fisher Mark D. , Udin Susan B.
Published: January 2005

The nucleus isthmi (NI) is the primary relay for the frog's ipsilateral visuotectal projection. Using electrophysiological methods, ipsilateral visuotectal activity has been recorded in thyroxine‐treated, postmetamorphic axolotls but not in larval axolotls. In order to determine whether changes in isthmotectal projections are responsible for this change in electrophysiological responsiveness, we have investigated the connections between the tectum and the NI using horseradish peroxidase. Our results indicate that the axolotl's isthmotectal pathways are strikingly similar to those of the frog NI, and that the NI sends bilateral projections to the tecta in both larval and thyroxine‐treated, postmetamorphic axolotls. Thus, the anatomical connections underlying the ipsilateral visuotectal projection are present during larval stages, despite the lack of electrophysiological evidence for the larval ipsilateral visuotectal projection. We hypothesize that thyroxine‐induced metamorphosis produces changes in the terminal arborizations of the crossed isthmotectal projection which allow them to be detected by presynaptic electrophysiological techniques.
Intersegmental modulation of abdominal postural responses initiated by mechanostimulation of the swimmeret in lobster
Authors: Kotak Vibhakar C. , Page Charles H. , Abenante Frank
Published: January 2005

In a multiganglionic preparation of the lobster abdominal nerve cord, composed of the first through fifth ganglia (A1–A5) and attached second swimmeret, tactile stimulation of the cuticular surface of the swimmeret initiates a postural motor program in A2 for abdominal extension, whereas deflection of feathered hair sensilla that fringe the swimmeret rami does not affect postural motor activity recorded from A2 (Kotak and Page, 1986a). This report demonstrates that partial isolation of A2 from adjacent abdominal ganglia by sectioning the A1–A2 or the A2–A3 connectives both increases the strength of the extension response evoked by cuticular stimulation and disinhibits a postural flexion inhibition response initiated by feathered hair stimulation. Complete isolation of A2, by cutting the A1–A2 and the A2–A3 connectives, further increases the strength of these postural responses. Intersegmental inhibition of these responses originates in the ganglia adjacent to A2, since mechanoresponsiveness of A2 is not affected by resection of a more distant connective (A3–A4). These results provide evidence for the presence in adjacent abdominal ganglia of intersegmental interneurons that regulate the access of swimmeret sensory activity to the postural motor neurons in A2.
Disruption of muscle reorganization by lesions of the peripheral nerve in transforming claws of snapping shrimps
Authors: Mellon DeForest , Quigley Michael M.
Published: January 2005

We have performed surgical transections on nerves in the transforming claws of snapping shrimps. In normal transformation muscle restructuring occurs, involving degeneration of some fibers and biochemical changes in others. Surgical section of the entire second limb nerve root or of its distal, dorsal branch—both of which contain the motor axons to the closer muscle—prevents muscle restructuring, even though transformation of external claw morphology proceeds. Furthermore, nerve lesions must be performed within a specific time period after transformation has been triggered in order for the effects to be observed. We suggest that transformation involves an early sensitization of the targeted muscle and that this process depends upon an intact nervous pathway within the second nerve root.
Anatomical specificity of regenerated muscle sensory afferents in the spinal cord of the bullfrog
Authors: Peng Yan‐Yi , Frank Eric
Published: January 2005

The specificity of central projections made by regenerated muscle sensory fibers in the brachial spinal cord was studied with anatomical tracing methods. Sensory fibers were interrupted by freezing dorsal roots in postmetamorphic bullfrogs. After several months, regenerated sensory fibers were labeled with horseradish peroxidase applied to the triceps brachii muscle nerve, and their arborizations within the spinal cord were reconstructed from serial cross sections.

Most of the regenerated projections from triceps muscle sensory afferents ended in or near their normal terminal field. A few branched and appeared to terminate more dorsally than normal, however, sometimes within the region where cutaneous afferents normally terminate. In contrast to the normal pathway followed by muscle afferents within the spinal cord, many regenerated afferents grew along the circumference of the spinal cord, just under the pial surface, and then turned abruptly toward the midline and into their appropriate terminal region. This suggests that regenerating afferents may actively seek out their appropriate targets and are not simply passively guided to them.
Mosaic Drosophila wings reveal regional heterogeneity in the guidance of ectopic axons
Authors: Blair Seth S. , Palka John
Published: January 2005

In most studies of axon guidance in the peripheral tissues of insects, the ability of experimentally pertubed axons to pathfind was examined only along their normal pathways. This means that regions normally devoid of axons have not been sampled for their ability to influence axonal trajectories. To examine this question, we have induced the formation of single sensory neurons in a variety of abnormal locations in the developing wing of Drosophila and have examined the course taken by their axons. The axons of such ectopic neurons have a regionally varying tendency to grow in the normal, proximal direction. This proximal bias approaches 100% for neurons located in the distal part of vein L2 and 70% in distal vein L4 but falls to chance (50%) along vein L5. Thus, neurons forming in ectopic regions of the wing, especially those found near the normal axon pathways (veins L1 and L3), have a high probability of growing axons in the correct direction. We conclude that information relevant to axon outgrowth is not restricted to the normal pathways. Whether this information is intrinsic or extrinsic to the neurons, and why its strength shows such conspicuous regional variation, awaits further study.
Central projections of a homoeotic regenerate, antennapedia, in a stick insect, Carausius morosus (Phasmida)
Authors: Edwards John S. , Reddy G. R. , Rani M. U.
Published: January 2005

Homoeotic appendages provide a system for the analysis of neuronal pathfinding in which the appendage is mismatched with its segmented ganglion. Central projections of sensory neurons from homoeotic antennapedia regenerates induced by antennal amputation in the stick insect, Carausius morosus, are described. The majority of afferent axons project to the olfactory lobe as in the normal antennal nerve, but they do not give rise to compact glomeruli. Nor does the form of the projection resemble that of leg sensory nerves in thoracic ganglia. The projection of antennapedia regenerate neurons in Carausius resembles the antennapedia mutant of Drosophila except that some primary afferents bypass the olfactory lobe and take several courses through the brain, sometimes reaching distant contralateral areas. It appears that these wandering fibers, having bypassed the olfactory lobe, tend to follow established tracts and to arborize or to deviate at circumscribed synaptic areas. The behavioral evidence for sensory input from antennapedia regenerates is equivocal.
Sensitivity of ocellar interneurons of the honeybee to constant and temporally modulated light
Authors: Baader A.
Published: January 2005

Sinusoidally modulated and discrete light pulses, the parameters of which approximated natural light conditions, were used to determine the response characteristics of ocellar first‐order interneurons of the worker honeybee (Apis mellifera carnica). Large ocellar interneurons which terminate within the brain (LB neurons) were recorded from intracellularly and were identified visually after dye injection.

Absolute sensitivity of LB neurons to light flashes ranges from 4 × 109 quanta/cm2s (Q) for MOC1,7 neurons to 1 × 1012 Q for MOC3,4. The slope of the response‐intensity (R/I) functions, which were calculated for intensities between 2 × 109 and 4 × 1013 Q, varies in different types of LB neurons. The strongest response is given by one group of median ocellar neurons. With constant light around 1013 Q, most LB neurons exhibit oscillatory hyperpolarizations which, upon increasing the stimulus to even higher intensities (1014–1015 Q), gradually evolve to a hyperpolarized plateau. The frequency of these oscillatory voltage fluctuations increases with the rate of modulation of the stimulating light and reaches maximum values at 5–15 Hz modulation frequency. Two groups of MOC neurons follow sinusoidally modulated light up to 32 ± 8 Hz (n = 5) and 29 ± 6 Hz (n = 3), respectively, whereas lateral ocellar neurons cut off at 17 ± 5 Hz (n = 4).

The possible role of LB neurons is discussed. They may be inactivated when the bee is flying in bright sunlight.