bluuebunny/crossref_metadata_2025 huggingface dataset:
Multiple innervation of purkinje cells by climbing fibers in the cerebellum of the adult staggerer mutant mouse
Authors: Mariani Jean , Changeux Jean‐Pierre
Published: January 2005

Intracellular recordings from Purkinje cells (PC) in the cerebellum of adult staggerer mutant mice revealed that the orthodromic response of PCs to juxtafastigial (JF) stimulation closely resembled a climbing fiber response (CFR). However, for most of the PCs studied, these responses were graded in a stepwise manner when the stimulus strength was increased. The underlying excitatory synaptic potentials (EPSPs) had the typical shape of EPSPs mediated through climbing fibers (CFs), but their size fluctuated in discrete steps, the highest one reaching the firing level. In the same PCs, the size of the spontaneous EPSPs fluctuated in a similar fashion and the frequency of each step was in the range of CF‐mediated EPSPs. These results strongly suggest that in staggerer mice several CFs synapse with each PC instead of a single CF as in normal adults. Furthermore, the activation through some of these CFs does not reach the firing level of the corresponding PC.
Calmodulin in mammalian nerve
Authors: Iqbal Zafar , Ochs Sidney
Published: January 2005

Calmodulin, a calcium‐dependent regulatory protein has been isolated from mammalian nerve. The protein has similarities to the calcium‐binding protein earlier shown to be transported at a fast rate in the nerve fibers. The implication is that calmodulin, which has been shown to be involved in various key cellular processes, may have a relation to axoplasmic transport.
Heterogeneity of excitatory synapses at the ends of single muscle fibers in lobster, Homarus americanus
Authors: Meiss D. E. , Govind C. K.
Published: January 2005

Crustacean neuromuscular synapses arising from a single excitor axon are known to be well differentiated among different muscle fibers but little is known about their condition along single fibers. Focal recording techniques were used to examine the quantal transmitter release and facilitation properties of synapses in the single excitatory innervated distal accessory flexor muscle of the lobster, Homarus americanus. Synapses were reliably differentiated with respect to quantal output so that those located near the tendon end were 1.15–4.12 times greater than those at the opposite, exoskeletal end (p < 0.01, paired t‐test). Regional differences were also seen in the amount of facilitation determined from twin pulse experiments. The fine structural basis for these differences was determined by serial section electron microscopy of 10‐μm segments at each end to ensure that the area of focal recording was sampled. No quantitative differences were found in the terminals or synapses in the two regions. Instead, the physiological diversity was correlated with number and size of presynaptic dense bars. Thus, the tendon end had a greater number and larger mean surface area of dense bars compared to the exoskeletal end. This heterogeneity of excitatory multiterminal innervation is correlated with the axonal branching pattern. Thus, the main axon and the larger primary axon branches lie in close proximity to the tendon end of the muscle fibers, whereas the exoskeletal end is innervated by smaller secondary and tertiary axonal branches. This proximity to the large axonal branches of the higher quantal output synapses at the tendon end may be regulated by some neural influence including a timing of innervation and/or access to greater amounts of metabolites in the larger branches which may be conducive to forming high‐output synapses.
L‐Proline as a glutamate antagonist at a crustacean neuromuscular junction
Authors: van Harreveld A.
Published: January 2005

The fast as well as the slow contractions of the adductor muscle in the claw of Procambarus clarkii are inhibited by L‐proline. This inhibition is dose dependent and decreases with increasing frequency of stimulation of the “slow” fiber. Contractions caused by perfusing the adductor muscle with L‐glutamate solutions are also inhibited by L‐proline. The inhibiting potency of L‐proline is small; the effective concentration of this amino acid is 50–100 times that of the L‐glutamate applied. It was postulated that the inhibitory effect of L‐proline is based on competition for excitatory receptor sites of L‐glutamate, which causes depolarization and contraction, and L‐proline, which lacks these actions. Theoretical considerations suggested a linear relationship between the stimulating L‐glutamate and the just‐inhibiting L‐proline concentrations. Experimental evidence supported this model.
Axonal transport: A quantitative study of retained and transported protein fraction in the cat
Authors: Muñoz‐Martínez E. J. , Núñez R. , Sanderson A.
Published: January 2005

The fast axoral transport of proteins was studied in the cat sciatic nerve after injection of [3H] leucine into the spinal ganglion or the ventral horn of the seventh lumbar segment. The amount of transported proteins after ganglion injection was linearly related to the amount of label present at the ganglion. At variable intervals after ganglion or spinal cord injection, the sciatic nerves were sectioned in some experiments. The transport of proteins continued in the peripheral nerve stump in a wavelike manner, but the advancing wave leaves a labeled trail behind. A fraction of this trail corresponds to proteins moving at slower velocities than thevelocity of proteins in the wave front. Another fraction of the trail corresponds to molecules retained by the axons. Each nerve segment of 5 mm in lenth retains 1.5% of the transported proteins, and the profile of retained proteins along the sciatic nerves follows a single exponential function. From the proportion of retained proteins, the concentration of transported proteins at the terminals of branching axons as a function of the branching ratio was estimated. In the case of motor axons innervating the soleus muscle of the cat, the concentration of recently transported proteins at the nerve terminals would be approximately 0.83% of the proteins leaving the spinal cord. This low concentration of transported proteins at the nerve terminals may explain the lability of neuromuscular synapses when axonal transport is decreased or interrupted.
The shadow response of the cockroach periplaneta americana
Authors: Meyer David J. , Margiotta Joseph F. , Walcott Benjamin
Published: January 2005

We show that the “escape response” (running) of the cockroach Periplaneta americana is interrupted when the insect runs through a shadow. Shadows were cast by holding an opaque plastic sheet so that the cockroach ran beneath it. In control experiments, a similarly positioned clear plastic sheet was ineffective. Removal of the shadow stimulus allowed running to continue. The likelihood that cockroaches would resume running after removal of the shadow stimulus decreased with the time they were allowed to remain in shadow.
Is octopamine a transmitter mediating hormone release in insects?
Authors: Orchard I. , Loughton B. G.
Published: January 2005

The release of hyperlipemic hormone from the glandular cells of the corpus cardiacum (CC) of Locusta migratoria is under the synaptic control of axons in nervus corpus cardiacum II (NCC II). The effects of aminergic agonists and antagonists on the release of the hyperlipemic hormone induced by electrical stimulation of NCC II have been examined. CC isolated from reserpine‐injected locusts did not release hormone when subjected to electrical stimulation of NCC II but continued to release hormone in response to high‐potassium saline. The electrically stimulated release of hormone from isolated CC was abolished by the α‐adrenergic blocking agent, phenoxybenzamine, but potentiated by the ß‐adrenergic blocking agent, propranolol. Phenoxybenzamine did not interfere with release induced by high‐potassium saline. It is suggested that the postsynaptic receptors on the glandular cells are similar to the β‐adrenergic receptors of vertebrates. Octopamine was found to be present in the glandular lobe of the CC at concentrations of 0.62 pmole per gland pair. Reserpine depleted the content to 0.3 pmole per pair. Bathing the CC in 10−7 M octopamine resulted in the release of hyperlipemic hormone, and this release was blocked by phenoxybenzamine. It is concluded that the neurotransmitter involved in the synapse between axons of NCC II and the cells releasing hyperlipemic hormone is aminergic, possibly octopaminergic. Octopamine may well be a transmitter mediating hormone release in insects.
The effect of antiserum to S 100 protein on behavior and amount of S 100 in brain cells
Authors: Hydén H. , Lange P. W.
Published: January 2005

Since antiserum raised against the S 100 protein has an impairing effect on acquisition in behavioral tests, when interacting with S 100 on hippocampal cells, the effect of S 100 antiserum was studied in rats on the S 100 content of the hippocampus and thalamus, as well as on behavior. The operant reversal of handedness test and a light discrimination test were used. S 100 antiserum, 2 × 30 μl, was injected intraventricularly before and during the sessions of two different learning tests. The S 100 protein was determined by quantitative immunoelectrophoresis. In the antiserum‐injected animals, the levels of S 100 protein was increased by up to 30%, the incorporation values of 3H‐valine increased in proteins of high molecular weight. Further acquisition was inhibited compared to controls, in which antiserum absorbed with pure S 100 protein was injected intraventricularly. The stimulation of S 100 synthesis, probably by the glia, may have occurred by a negative feedback effect, as has been observed in thymocytes.
Organization of motor neurons to a multiply innervated insect muscle
Authors: Phillips Christine E.
Published: January 2005

Nine excitatory motor neurons have been identified as innervating the locust metathoracic flexor tibiae. The anatomical organization of the flexor motor neurons within the ganglion was examined with both light and electron microscopy. Flexor motor neurons were physiologically identified prior to intracellular staining with Procion or cobalt. Some of the cobalt‐stained neurons were then silver intensified. The reliability of soma location and variability of neurite branching were examined. While the position of a soma could vary within its cluster by up to one radius, the anterior, posterior, and lateral soma clusters bore a consistent relationship to each other. The density of neurite branching varied greatly for any particular flexor. The ultrastructure of the tract containing the flexor neurites revealed the individual neurites to be glial wrapped, while the tract itself was isolated from the neuropil by additional glia. The hypothesis that subsets of the flexor motor neuron pool are recruited for different behaviors is discussed in light of the last two findings.
Effects of furosemide on neural mechanisms in aplysia
Authors: Scappaticci Karen A. , Dretchen Kenneth L. , Carpenter David O. , Pellmar Terry C.
Published: January 2005

The effects of furosemide on action potentials and responses to several neurotransmitters have been studied in the neurons of Aplysia. Furosemide (10−7 and 10−3M) does not visibly affect the normal action potential in R15 neurons. However, when TTX (30μM) is used to block the sodium component in R15, the remaining spike (presumably the calcium component) is increased in amplitude in the presence of furosemide. Furosemide also alters transmitter‐induced conductances. Furosemide greatly reduces the amplitude and shifts, in a depolarizing direction, the reversal potential of chloride‐dependent responses to γ‐aminobutyric acid (GABA) and acetylcholine (ACh). This suggests that furosemide both blocks the chloride channel and inhibits a chloride pump. ACh‐induced sodium responses were also reduced by furosemide but to a lesser extent than chloride responses. The potassium response to ACh and a voltage‐dependent calcium response to serotonin were not altered. These results indicate that furosemide could alter synaptic responses both presynaptically by enhancement of calcium flux during the action potential and postsynaptically by blockade of chloride and sodium conductances.
Mechanical properties of a slow muscle in the cockroach
Authors: Chesler Mitchell , Fourtner Charles R.
Published: January 2005

The mechanical properties of the metacoxal muscle, 177d, in the cockroach, Periplaneta americana, was investigated. The muscle exhibited a mean resting tension of 2.6 ± 1.3g SD. Neurally evoked tension summed with the resting tension and the relaxation phase of the evoked tension varied from less than 1 s to several minutes. This residual tension varied not only in duration but also in amplitude. Stimulation of inhibitory axons increased the rate of relaxation and thereby abolished the residual tension. However, inhibitory stimulation never reduced the resting tension. Stimulation of the main leg nerve at several times the threshold of the inhibitory axons could evoke residual tension. Recording of synaptic potentials from the two histochemically different fiber types (dorsal and ventral groups) revealed large hyperpolarizations in the ventral fibers and decreased duration and amplitude of excitatory potentials in the dorsal fibers. These results suggest that there are a variety of ways in which tension can be evoked, maintained, and controlled in these muscles.
Increased effectiveness of a motorneuron after partial denervation of its target muscle in the cricket Teleogryllus oceanicus
Authors: Donaldson P. Lynn , Josephson Robert K.
Published: January 2005

Fibers of the metathoracic extensor tibia muscle of the cricket Teleogryllus oceanicus are innervated by a slow excitatory axon (slow fibers), a fast excitatory axon (fast fibers), or by both slow and fast axons (dual fibers). Sectioning metathoracic nerve 5 removes the fast axon input to the muscle but not that of the slow axon. Following such partial denervation, the mechanical responses initiated by the slow axon increase progressively for at least 30 days; twitch tensions reach 5–10 times those of control muscles and tetanic tensions 10–30 times control values. After sectioning nerve 5, resting membrane potentials decrease in those fibers which originally received fast axon input and the input resistance of all fiber types increases, including that of slow fibers which are not innervated through nerve 5. Excitatory junctional potentials (EJPs) initiated by the slow axon become larger following partial denervation, accounting in part for the larger contraction amplitudes. The increased input resistance is adequate to account for the larger EJPs in slow fibers but not for the proportionally greater increase in EJP amplitude in fibers which were formerly dually innervated. The change in EJP amplitude is abrupt in slow fibers and gradual in formerly dual fibers.
Dynamic analysis of cockroach giant interneuron activity evoked by forced displacement of cercal thread‐hair sensilla
Authors: Buño W. , Crispino L. , Monti‐Bloch L. , Mateos A.
Published: January 2005

This investigation involved extracellular recordings of cockroach abdominal giant interneuron (GI) action potentials evoked by cercal “threadlike” hair sensilla (THS) stimulation with a galvanometric device, by controlled displacements of about seven THS. Small and large GIs, distinguished by their amplitudes, were studied simultaneously. Only the small GIs were spontaneously active. Responses to sine, pulse, and ramp stimulation of sensilla produced phasic responses in both GI types. Some GIs were directionally sensitive and had shorter response latencies in the direction of best sensitivity while others were omnidirectional. Contralateral stimulation decreased responses to homolateral stimuli. In experiments using paired pulses (less than 50‐ms intervals) there is a period of hyperexcitability, in large GIs, in which the response to the second stimulus is greater. Repeated stimulation caused an exponential decline in the response which was steeper in all GIs at higher stimulating frequencies and had a faster time course in large GIs. Because of this last property GIs function as low‐pass filters limiting the flow of information, with large GIs having a lower frequency “cutoff” than smaller GIs.
Physiology and in situ identification of putative aminergic neurotransmitters in the nervous system of Gyrocotyle fimbriata, a parasitic flatworm
Authors: Keenan Larry , Koopowitz Harold
Published: January 2005

The longitudinal nerve cords (LNC) in Gyrocotyle fimbriata do not change their activity in response to catecholamines but are excited by the amino acids glutamate and aspartate at concentrations less than 10−5M. This activity can be blocked by application of 2‐amino‐4‐phosphonobutyrate (APB), an aminergic blocking agent. In situ measurements of fluorescent spectra from LNC neurites have a λmax at 513.6 nm. Treatment with HCl shifts the peak to 510 nm. Both glutamate and aspartate fluoresce and behave similarly with peak emissions of 512.5 nm before HCl treatment and 511 nm and 509 nm, respectively, after treatment. Dopamine and norepinephrine both fluoresce at 512.2 nm but the peaks shifts to 516.5 and 528, respectively, following acid treatment. These experiments indicate that the fluorescing substance in the neurons is not a known catecholamine and could be an amino acid.
Chemoreception in gastropod molluscs: Electron microscopy of putative receptor cells
Authors: Davis W. J. , Matera Eugene M.
Published: January 2005

Scanning and transmission electron microscopy of the external surface of the gastropod mollusc Pleurobranchaea californica has revealed a new exteroreceptor, characterized by dense cilia (ca. 200/cell) that project from an intraepithelial soma and exhibit dilated, discoid‐shaped tips. The exteroreceptor is found in high densities (up to 5000/mm2) in areas of the body determined by behavioral assay to be chemosensitive, but nowhere else, suggesting that it is a chemoreceptor.
The effect of single giant interneuron lesions on wind‐evoked motor responses in the cockroach, Periplaneta americana
Authors: Westin Joanne , Ritzmann Roy E.
Published: January 2005

In order to determine the contribution of individual giant interneurons (GIs) to wind‐evoked motor outputs, responses were recorded from depressor and levator motor neurons in the cockroach Periplaneta americana to wind puffs of different directions. The depressor response was generally stronger to wind from the ipsilateral rear than to wind from the contralateral rear. The levator response was more variable but was more often stronger to wind from the contralateral rear than to wind from the ipsilateral rear. These results are as expected based on behavioral responses to wind puffs. (Camhi and Tom, 1978). The depressor response was nearly or totally abolished by severing the ipsilateral connective of the nerve cord but was little affected by severing the contralateral connective. The levator reponse was greatly reduced for some angles by severing the ipsilateral connective and for other angles by severing the contralateral connective. Blocking conduction in the ipsilateral GI 5 nearly or completely abolished the depressor response to wind from the ipsilateral rear. This is the first time that a GI has been shown to be necessary, not just sufficient, for a given motor output.
The identification and localization of a catecholamine in the motor neurons of the lobster cardiac ganglion
Authors: Ocorr Karen A. , Berlind Allan
Published: January 2005

The cardiac ganglion from Homarus americanus was investigated for the purpose of providing biochemical and histochemical information as to the identity of the neurotransmitter(s) utilized by this system. Three techniques were employed in this study: (1) the glyoxylic acid histofluorescence staining technique (GA), which showed fluorescence characteristic of catecholamines localized in the five motor neurons; (2) high‐voltage electrophoresis (HVE) in one dimension followed by ascending chromatography in the second dimension, which indicated incorporation of label from tritiated tyrosine into norepinephrine (NE) and small amounts of dopamine (DA); (3) high‐pressure liquid chromatography with electrochemical detection (HPLC/EC), which indicated the presence of endogenous norepinephrine.
Pure population of viable neurons from rabbit dorsal root ganglia, using gradients of percoll
Authors: Goldenberg S. S. S. , De Boni U.
Published: January 2005

Nonneuronal cells complicate the study of neurons in vitro. A pure population of viable neurons can be obtained easily using gradients of Percoll. For each experiment, 20 dorsal root ganglia (DRG) are minced, then sequentially dissociated in collagenase and trypsin, which digest all the intercellular connections. The dissociated tissue is separated first on the basis of density, creating an interphase fraction enriched in neurons and satellite cells, which are then further separated on the basis of size. The neurons, obtained in the final pellet, number approximately 50,000 (2500 per DRG), routinely exhibit a viability of over 80% initially and are of a purity of over 90%. The viability of the neurons is confirmed by the occurrence of neurite outgrowth in culture. Thus, a pure and viable neuronal population is obtained by a simple and rapid method.
Serotonin immunoreactive neurons in the central nervous system of an insect (Periplaneta americana)
Authors: Bishop Cynthia A. , O'shea Michael
Published: January 2005

Serotonin‐like immunoreactivity was mapped in the central nervous system (CNS) of the cockroach, Periplaneta americana. Immunoreactive staining occured in every ganglion of the CNS. The largest numbers of immunoreactive somata were detected in the optic lobes and the brain, and lowest numbers in the first and second toracic ganglia. Dense stained fibers, ramifications, and varicosities were found in all ganglia, and numerous axon like processes occurred in all interganglionic connectives. Immunoreactive processes were not, however, detected in most of the peripherally projecting nerve roots. Processes were found only in roots of the suboesophageal ganglion and the tritocerebral lobes of the brain. A comparison of the map for serotonin immunoreactivity with one generated for the pentapeptide transmitter proctolin suggests that the two systems overlap only in the suboesophageal ganglion and the tritocerebrum. The amine and peptide may co‐occur in neurons in these regions. The serotonin immunoreactive system appeared significantly different from the octopaminergic system of the ventral nerve cord. Seventy‐two potentially identifiable immunoreactive cells were located in the cockroach CNS. Some of these may be suitable for physiological study of the functional role of serotonin.
Spiral waves of spreading depression in the isolated chicken retina
Authors: Gorelova N. A. , Bureš J.
Published: January 2005

Existence of the theoretically predicted spiral waves of excitation in intact two‐dimensional networks of excitable elements has been experimentally confirmed in the isolated chicken retina. The preparation supports the waves of Leão's spreading depression (SD) the concentric propagation of which from the point of origin can be directly observed as a change of the optical properties of the retinal tissue. The propagation rate of 3.7 mm/min (35°C) decreased to 1.5 mm/min for SD waves elicited during relative refractory period. When a several‐mm long segment of the SD wave had been blocked by anodal polarization, the laterally opened ends of the wavefront started to spread after termination of polarization into the previously blocked tissue, gradually turning around and penetrating into the region recovering from the original SD. One or two simultaneously generated spiral waves of SD continued to rotate for several cycles. Spiral SD could also be elicited by punctiform cathodal polarization (1 mA) applied to the SD wave‐rear. Since the new SD wave could only spread into the recovering tissue it formed a laterally open wavefront, the free ends of which eventually turned around and started spiral SD. With continued reverberation the nucleus of the spiral SD wave gradually migrated across the retina until it approached an obstacle (e.g., pecten) which stopped further spiral propagation. Spiral SD waves were elicited in 31 retinal preparations and lasted for 4.5 cycles on the average. Average cycle duration was 4.7 min. Spontaneous spiral SD waves were observed in preparations incubated in Mg2+‐free media. The spiral SD waves in retina are compared with mathematical models of analogous phenomena. It is argued that spiral SD waves probably exist in the cerebral cortex of rats and account for generation of repetitive SD waves sometimes elicited by overlapping stimulation of two cortical regions.
Postsynaptic mechanism of withdrawal reflex sensitization in the snail
Authors: Balaban P. M.
Published: January 2005

Repeated tactile stimulation of the skin evoked sensitization and subsequent habituation of a behavioral avoidance reaction of pneumstome closure in the land snail, Helix lucorum L. Spike responses in putative command neurons for avoidance behavior increased and subsequently decreased parallel to behavioral events. Decrease of spike responses in command neurons was due to decreased synaptic input evoked by repeated tactile stimulation. Intracellular investigation of the increase in the spike response in command neurons for pneumostome closure, which underlies behavioral sensitization, revealed a synpatically‐evoked, long‐lasting depolarization. No conductance changes during this depolarization were found, but neuronal excitability was altered.
Maintained depolarization of synaptic terminals facilitates nerve‐evoked transmitter release at a crayfish neuromuscular junction
Authors: Wojtowicz J. M. , Atwood H. L.
Published: January 2005

Presynaptic and postsynaptic potentials were examined by intracellular recording at a crayfish neuromuscular junction. During normal synaptic transmission, the action potentials were recorded in the terminal region of the excitatory axon and postsynaptic responses were obtained in the muscle fibers. We found that it was possible to modify the synaptic transmission by applying depolarizing or hyperpolarizing currents through the presynaptic intracellular electrode. Typically, a 7 15 mV depolarization lasting longer than 50 msec leads to a large (500%) enhancement of transmitter release, even though the preterminal action potential is reduced in amplitude. Hyperpolarization increases the amplitude of the action potential, but slightly reduces the transmitter release. These results are different from those reported for other neuromuscular synapses and the squid giant synapse, but are similar in many respects to the results reported for several invertebrate central synapses. We conclude, first, that different synapses may have markedly different responses to conditioning by membrane polarization and, secondly, that maintained low‐level depolarization may induce a potentiated state in the nerve terminal, perhaps brought about by slow entry of calcium.
Influence of walking on swimmeret beating in the lobster Homarus gammarus
Authors: Cattaert D. , Clarac F.
Published: January 2005

Influence of walking on swimmeret beating in intact lobsters, Homarus gammarus, has been analyzed using a treadmill experimental device. Belt movement activates both leg stepping and swimmeret beating. The simultaneity of the onset of the two motor systems in this situation is demonstrated to be the result of a startle response initiated when the belt begins to move. This reaction consists of a non‐specific motor activity involving several antagonist postural and dynamic muscles. Abdominal extension and vigorous swimmeret beating are the main featurs of this reaction. The main characteristics of the swimmeret beating as defined by Davis (1969) has been observed here in sequences without walking. However during long walking sequences a very different swimmeret beating pattern occurs. It is suggested that this slow swimmeret beating is completely subordinate to the walking rhythm during sequences of absolute coordination. In more rapid swimmeret beating a relative coordination with leg stepping is very common. The functional meaning of this linkage between legs and swimmerets is discussed.
Axonal transport of [3H] GABA and [3H] glutamate in excitatory and inhibitory neurons innervating lobster exoskeletal musculature
Authors: Woodward William R.
Published: January 2005

This paper describes the results of intracellular injections of radiolabelled neurotransmitters and transmitter precursor substances, including glutamate, GABA, aspartate, octopamine, tyramine, tryptophan, and choline, into cell bodies of identified excitatory and inhibitory neurons innervating lobster extensor musculature. The distributions and identities of radioactive substances appearing in axons were examined at various times following injection and in vitro incubation. Injected GABA and glutamate were found in appreciable quantities in both excitatory and inhibitory axons and migrated down axons at an estimated rate of between 16 and 22 mm/day at 12° C, whereas the other substances tested were present in substantially smaller quantities and migrated at an estimated rate of less than 7.5 mm/day at 12° C. Injected GABA, D‐glutamate and L‐glutamate accumulated proximal to ligatures tied around nerves, whereas neither octopamine nor aspartate accumulated proximal to ligatures. Since GABA is the transmitter substance released by inhibitory neurons and L‐glutamate is thought to be released from excitatory nerve terminals, these results are consistent with the suggestion that amino acids serving as neurotransmitters are axonally transported. The specificity of axonal transport does not appear to be restricted to the cognate neurotransmitter, as indicated by the movement of L‐glutamate in inhibitory axons and GABA in excitatory axons and of D‐glutamate in both excitatory and inhibitory axons, but rather may be relaxed to include substances closely related to the neurotransmitter. Some restrictions, however, are apparently placed on axonal transport of small chaged molecules in these neurons in that other substances tested migrated down nerves at a considerably slower rate.
The possible role of “sibling neurite bias” in the coordination of neurite extension, branching, and survival
Authors: Smalheiser Neil R. , Crain Stanley M.
Published: January 2005

In this review we consider a novel mechanism, “sibling neurite bias,” which may explain aspects of the coordination of elongation, branching, and resorption among different neurites growing from the same neuronal cell body. In this model, growing neurites which incorporate structural precursors at higher rates would deplete the cellular pool of precursors available to their “sibling” neurites; neurites would compete for survival, but in addition they would bias each other's behavior during active growth. Evidence is reviewed that “sibling neurite bias” may contribute to the establishment and stabilization of specific neural connections. Specific examples examined include the loss of polyinnervation at the developing neuromuscular junction, contextual mapping in the retino‐tectal system, and selective neurite growth patterns and synaptic connections in nerve tissue culture model systems.
Central generation of swimming activity in the hydrozoan jellyfish Aequorea aequorea
Authors: Satterlie Richard A.
Published: January 2005

Swimming in Aequorea is controlled by a network of electrically coupled neurons (swim motorneurons) located in the inner nerve ring. The network is made up of the largest neurons in the ring, up to 22 μm in diameter. Intracellular recordings from swim motorneurons reveal slow membrane potential oscillations and a superimposed barrage of synaptic “noise.” The synaptic noise, but not the slow oscillations, is eliminated in seawater containing an elevated Mg++ concentration. The swim motorneurons produce a rapid burst of two to eight action potentials preceding each contraction of the subumbrella. Spontaneous bursting persists in high‐Mg++ seawater. Injected ramp currents indicated a “bursty” character of the swim motorneurons as suprathreshold depolarizations produced repetitive bursting with an increasing burst frequency with increased depolarization. Hyperpolarizing currents locally blocked spiking in swim motorneurons.

Intercellular coupling was demonstrated with Lucifer Yellow injection and dual electrode recordings. In dye fills, only the large neurons of the inner nerve ring were dye‐coupled.

Two pieces of evidence suggest that swim motorneurons activate the overlying epithelial cells via chemical synapses. First, direct synaptic connections have been noted in ultrastructural examination of the inner nerve ring region. Second, dual recordings from a swim motorneuron and an epithelial cell reveal a 1:1 correspondence between neuron spikes and epithelial synaptic potentials. The synaptic potentials occur with a latency as short as 3 ms which is constant in any one recording session. The results suggest that the swim motorneuron network of Aequorea not only performs a motorneuron function, but also serves as the pattern generator for swimming activity.
Quantification of ultrastructural symmetry at molluscan chemical synapses
Authors: McCarrager Gary , Chase Ronald
Published: January 2005

Two criteria were developed to identify symmetrical synapses in the tentacle ganglion of the snail Achatina fulica. First, the concentration of electron lucent vesicles within 20 nm of one membrane had to be less than three times the concentration at the opposed membrane. Second, paramembranous densities had to be present in both cells, as unanimously judged by three independent observers. Nine synapses (27% of sample) satisfied both criteria. It is suggested that these synapses transmit chemically in two directions.
Neuromuscular relationships in the abdomen of the Californian shore crab Pachygrapsus crassipes
Authors: Stephens Philip J. , Leferovich John M. , Klainer Peter
Published: January 2005

There are two pairs of muscles in each abdominal segment of the crab; one pair of flexors and one pair of extensors. In the early larval stages the muscles have short sarcomeres—a property of fast fibers—and high thin to thick filament ratios—a property of slow fibers. In the adult the abdominal muscles are intermediate and slow, since they have fibers with intermediate and long sarcomeres, high thin to thick filament ratios, low myofibrillar ATPase activity, and high NADH diaphorase activity. The different fiber types are regionally distributed within the flexor muscle.

Microelectrode recordings from single flexor muscle fibers in the adult showed that most fibers are supplied by three excitatory motor axons, although some are supplied by as many as five efferents. One axon supplies all of the flexor muscle fibers in its own hemisegment, and the evoked junctional potentials exhibit depression. This feature together with the innervation patterns of the fibers are similar to those reported for the deep flexor muscles of crayfish and lobsters. Therefore, in the adult crab, the abdominal flexor muscles have some features in common with the slow superficial flexors of crayfish and other features in common with the fast deep flexor muscles.
Central connections of Limulus ventral photoreceptors revealed by intracellular staining
Authors: Batra Ranjan , Chamberlain Steven C.
Published: January 2005

We stained the central terminations of Limulus ventral photoreceptors by intracellular injection of cobalt chloride into the cell bodies. Axons of these photreceptors enter the protocerebrum via the ventral optic nerve and pass to the medulla. As they reach the surface of the medullar neuropil they branch profusely in fine processes with intermittent varicosities. Each axonal arborization covers about 0.01–0.02 mm2 of this surface immediately adjacent to the medullar ganglion cell layer. Each point on the surface of the medullar neuropil receives, on the average, input from about 6 ventral photoreceptor axons.
Adenosine in cerebral homeostatic role: Appraisal through actions of homocysteine, colchicine, and dipyridamole
Authors: McIlwain Henry , Poll Janet D.
Published: January 2005

Mammalian neocortical tissues were incubated in [14C] adenine‐containing fluids and their newly‐synthesized adenine derivatives examined after periods of superfusion. Increased [K+] released adenine derivatives from the tissues, a release diminished by homocysteine. Homocysteine acted also to diminish the tissue content of adenosine plus its metabolites hypoxanthine and inosine, while increasing that of S‐adenosylhomocysteine. Hypoxia also increased the tissue content and the output of adenosine plus its metabolites, and again homocysteine augmented the S‐adenosylhomocysteine. Glutamic acid also increased tissue content and output of adenosine and derivatives, an action diminished by homocysteine and associated with augmented S‐adenosylhomocysteine. Colchicine or dipyridamole did not prevent augmentation of S‐adenosylhomocysteine by the reagents described; the sequence from adenosine phosphates to S‐adenosylhomocysteine is concluded to be intracellular and not to involve extracellular formation of precursor adenosine. Adenosine displayed properties consistent with its being involved in two distinct categories of homeostasis, and also with its exerting an inhibitory tone in normal cerebral systems.
Morphology and physiology of a hair plate sensory organ located on the antenna of the rock lobster Palinurus vulgaris
Authors: Vedel J. P.
Published: January 2005

At the level of the J1 joint of each antenna of the rock lobster Palinurus vulgaris a hair plate sensory organ (hp) similar to those described in insects has been observed. The hp is located on the internal side of the S2 segment of the antenna, close to the soft articulating membrane of the J1 joint. It is formed by a triangular surface of cuticle about 3mm2 in area, covered with numerous hairs of different lengths (Figs. 1 and 2). Details of the hp were studied by scanning electron microscopy (Fig. 2). Physiological stimulation of the hp hairs occurs during medial movement of the J1 joint. Under this condition the soft articulating membrane rolls over the hairs and bends them progressively back onto the cuticle. Flexion of all the hairs corresponds to a medial movement of the J1 through 40°. During this type of movement, the number of successively flexed hairs increases linearly (Fig. 3). Electrophysiological recordings of the hp sensory nerve correlated with selective mechanical stimulation of individual hairs demonstrated that each hair is innervated by a single sensory fiber. This sensory neurone responds phasically when the hair is flexed back onto the cuticle (as during an S2 medial movement) and when it returns to its resting position (as during an S2 lateral movement). Most of the sensory neurones are sensitive to the movement velocity of the hairs (Figs. 4 and 5). When the hair is maintained flexed its sensory neurone discharges tonically (Fig. 4). Electrical stimulation of the hp sensory nerve induced reflex actions in the external and internal rotator muscles of the segment S1. These effects were found to selectively activate the tonic motor command of these muscles (Fig. 6).
Tubulin synthesis in the regenerating rat superior cervical ganglion: A biphasic response
Authors: Quesada Marilee H. , Millar David B. , Smejkal Ruthann
Published: January 2005

Axotomy of a major cranial post ganglionic branch of the superior cervical ganglion of an adult rat resulted in increased radiolabeling of tubulin and microtubule‐associated proteins after an in vitro 5‐h incubation with [14C]‐methionine. The increased incorporation of the radiolabel began at day 1 postoperatively and exhibited a biphasic response, peaking at days 3 and 8.
Neuroeffectors for vocalization in Xenopus laevis: Hormonal regulation of sexual dimorphism
Authors: Kelley Darcy B.
Published: January 2005

South African clawed frogs use sex‐specific vocalizations during courtship. In the male, vocalizations are under the control of gonadal androgen. Though females have moderate levels of circulating androgen, they do not give male‐typical mate calls. Both muscles of the vocal organ and neurons of the central nervous system (CNS) vocal pathway are sexually dimorphic and androgen‐sensitive. Recent studies suggest that the failure of androgen to masculinize adult females results from a male‐specific, androgen‐regulated developmental program. At metamorphosis the larynx is sexually monomorphic and feminine in morphology, muscle fiber number and androgen receptor content. During the next six months, under the influence of increasing androgen titers and high receptor levels, myoblasts proliferate in the male and muscle fibers increase at an average rate of 100/day. Females have much lower hormone levels, receptor values decline and they display no net addition of fibers. At metamorphosis, both males and females have approximately 4000 muscle fibers. By adulthood, males have eight times the female fiber number. In the CNS, adult laryngeal motor neurons are more numerous with larger somata and dendritic trees in males than in females. Certain connections of neurons in the vocal pathway are also less robust in females. Unlike the periphery, motor neuron number does not appear to be established by androgen‐induced proliferation. Our current hypothesis is that androgen acts at the level of laryngeal muscle to produce more muscle fibers and thus provide more target for motor neurons in the male. This process could regulate cell number by ontogenetic cell death. In the CNS, androgen‐target neurons become capable of accumulating hormone shortly before metamorphosis. Androgen receptor in larygeal motor neurons may permit the dendritic growth characteristic of males by increasing sensitivity to afferent stimuli. Such a process could account for the observed differences in CNS vocal “circuitry” in X. laevis and thus behavioral differences between the sexes.
Central actions of R15, a putative peptidergic neuron in Aplysia
Authors: Brown Richard O. , Mayeri Earl
Published: January 2005

We report that the bursting pacemaker neuron R15 has central actions on other identified neurons in the abdominal ganglion of Aplysia californica. The follower cells are located on the dorsal surface of the left lower quadrant of the ganglion and include members of the LC cell cluster. A spontaneous burst of impulses in R15 produces a slow, graded, excitatory potential of up to 8 mV in follower cells. The response begins about 2–3 s after the first impulse in an R15 burst, and reaches its speak at about 4–6 s (corresponding approximately to the end of the R15 burst). In some preparations a biphasic response was seen composed of the early depolarization followed by a slower excitatory or inhibitory phase. All the responses were blocked when R15 was hyperpolarized to prevent spiking. The magnitude of the response was reduced in a graded fashion by prematurely terminating the R15 burst with hyperpolarizing current and was increased when depolarizing current was injected into R15 during a burst. Central actions of R15 were observed in only 28% of our preparations, and their presence may depend on unknown physiological factors. The effects are likely to be mediated by R15 neuropeptides. The accessibility of both R15 and its targets in this preparation should facilitate further analysis of this interaction.
Increased levels of testosterone have little effect on visual cortex plasticity in the kitten
Authors: Daw N. W. , Baysinger K. J. , Parkinson D.
Published: January 2005

We tested the hypothesis that increased levels of sex steroids preceeding puberty are an important factor in the termination of the critical period for monocular deprivation. Male kittens were injected with Depo‐testosterone in order to elevate plasma testosterone to a higher level than that in normal prepubertal male kittens. Control animals did not receive testosterone injections. All kittens were monocularly deprived for 7–18 days, then cells in the visual cortex were examined electrophysiologically, and an ocular dominance histogram was constructed.

Treated animals showed an increase in plasma testosterone (1.82–15.16 ng/mL) when compared with the control animals (0.80 ± 0.25 ng/mL). The fraction of cells driven exclusively by the experienced eye was slightly lower in the treated animals, and there was a slight increase in the dominance of cells by both eyes. However, in both groups of animals, the majority of cells were dominated by the experienced eye, with no significant difference in the weighted parameter used to describe this dominance. In summary, although there is a slight difference between treated and control animals, the results do not support the hypothesis that elevated levels of sex steroids play a crucial role in the termination of the critical period.
Seasonal variation in mammalian striated muscle mass and motoneuron morphology
Authors: Forger Nancy G. , Breedlove S. Marc
Published: January 2005

Feral white‐footed mice are seasonal breeders that undergo predictable cycles of reproductive function. Photoperiod‐induced fluctuations in gonadal function of white‐footed mice were associated with morphological changes in perineal muscles and their motoneurons. Exposure to short daylengths resulted in testicular regression, decreased perineal muscle mass, and shrinkage of somata and nuclei of motoneurons of the spinal nucleus of the bulbocavernosus (SNB). These effects were reversed by reinstatement of long daylengths. Similar reductions in muscle mass and SNB soma size were seen following gonadectomy of white‐footed mice. In addition, dendritic trees of SNB motoneurons were reduced in gonadectomized mice compared with dendritic arbors of intact mice or castrates provided with testosterone capsules. Androgen‐mediated annual changes in muscle mass and motoneuron morphology appear to be a natural part of this species' physiology.
The effect of temperature on flight initiation in the cockroach Periplaneta americana
Authors: Diekman Lynda J. , Ritzmann Roy E.
Published: January 2005

The effect of temperature during development of the flight system of the American cockroach was tested. Animals were raised at three different temperatures from egg cases to adulthood then various parameters of flight were tested. Animals raised at cooler temperatures were found to require significantly stronger wind puffs to initiate flight than did animals raised in warmer temperatures. Some animals were raised at one temperature during embryonic development (i.e. while the animals were still in egg cases) and then switched to a different temperature for nymphal development. In these cases only the temperature experienced during embryonic development had a significant permanent effect on flight. Parameters associated with pattern generation such as interburst interval were not affected by temperature during either developmental period.
Regenerated fibers of the lamprey spinal cord can coordinate fictive swimming in the presence of curare
Authors: Cohen Avis H.
Published: January 2005

Recently evidence was presented that, following transection, spinal cords of larval lampreys could regenerate functional connections. The demonstration in isolated spinal cord–notochord preparations consisted of fictive swimming coordinated across the lesion site. In the study reported here curare was added to the bath to eliminate the possible contribution from reflexes mediated by contractions from any remaining muscle fibers attached to the notochord. Coordination remained in the presence of curare, adding further evidence that indeed the regenerated fibers formed functionally appropriate connections.