bluuebunny/crossref_metadata_2025 huggingface dataset:
Carbon–13 NMR studies of tautomerism in some 2‐substituted imidazoles and benzimidazoles
Authors: Papadopoulos E. Paul , Hollstein Ulrich
Published: May 2005

The 13C NMR spectra of several 2‐substituted imidazoles and benzimidazoles have been measured. The substituent was CH3, COOH and CONHR, where R = H, n‐Bu, p‐tolyl or m‐chlorophenyl. Carbons 4 and 5 in the imidazoles and the carbon pairs 8/9, 4/7 and 5/6 become equivalent by proton transfer from N‐1 to N‐3, possibly through intermolecular association. The rate of this proton exchange increases with concentration and temperature. It decreases with extension of the 2‐substituent (rate CH3≫CONH‐phenyl > CONH‐p‐tolyl ≃ CONH‐m‐chlorophenyl ≫ CONH‐n‐butyl) due to steric hindrance at the site of the (benz)imidazole nitrogen.
The NMR spectra of porphyrins 20—proton and 13C characterization of porphyrin atropisomers
Authors: Abraham Raymond J. , Plant James , Bedford Geoffrey R.
Published: May 2005

The preparation, isolation and characterization by proton and 13C NMR of the four possible atropisomers of meso‐tetra(2‐methoxy‐1‐naphthyl)porphyrin is described. Chemical shift differences due to atropisomerization effects are observed in the porphyrin and naphthyl rings. Comparison of the naphthyl chemical shifts with those of the model compound 1‐isopropenyl‐2‐methoxynaphthalene allows the shifts due to the porphyrin ring current to be isolated. The observed Δδ values of the naphthyl protons agree well with those calculated from the previously described porphyrin ring current model, and allow both the angle of tilt of the naphthyl ring and the dihedral angle of the 2‐methoxy substituent to be estimated. In contrast, the Δδ values for the naphthyl carbons bear no relationship to the calculated ring current shifts. Calculations of the total ring current contribution (porphyrin plus naphthyl rings) at the different naphthyl rings of the unsymmetric type III isomer show that at least part of the observed atropisomerism effects are due to the long‐range current shifts of the naphthyl rings. The results also provide a clear demonstration of the identity of the porphyrin ring current in the free base and porphyrin dication.
Conformations of side chains of somatostatin very high field proton NMR studies
Authors: Live David H. , Davis Donald G. , Agosta William C. , Cowburn David
Published: May 2005

The high field proton NMR spectra (500 and 600 MHz) of the peptide hormone somatostatin in D2O are reported. The results obtained are used to derive values of the couplings and chemical shifts related to the solution conformation of several of the side chains. This work resolves a discrepancy in the literature concerning the assignments of resonances in the spectrum. It also provides a means of testing the accuracy of obtaining values for these couplings and shifts in previous 2D NMR studies at lower field from strongly coupled multiplets in spectra of this complexity.
Isomerization and conjugation characteristics of the CN double bond. III—15N NMR studies of tautomerism in 2‐phenylamino‐2‐thiazoline and its thiazine analogue
Authors: Tóth Gábor , Almásy Attila
Published: May 2005

15N NMR Spectroscopy shows, contrary to earlier suggestions, that 2‐phenylamino‐2‐thiazoline and its thiazine analogue are present in chloroform as an equilibrium of imino and amino tautomers in the ratio of 62:38 and 74:26, respectively.
Carbon‐13 NMR study of some isomeric n‐nitroindazole derivatives
Authors: Cohen‐Fernandes Pauline , Erkelens Cornelis , Habraken Clarisse L.
Published: May 2005

The 13C NMR spectra of 1,5‐ and 2,x‐dinitroindazoles “x=4‐7” and 3‐bromo‐1,x‐dinitroindazoles are recorded and discussed. The data on he 2,x‐dinitroindazoles confirm our previous structurea assignment based on 1H NMR spectroscopy. The 13C NMR spectra established that in the novel 3‐bromo‐1,x‐dinitroindazoles the N‐nitro group is attached at N‐1.
Structural assignment of monothiocarbonohydrazones by 1H NMR spectroscopy
Authors: Rajendran G. , Jain Sampat R.
Published: May 2005

Analysis of the 1H NMR spectra of several monothiocarbonohydrazones, some of them synthesized for the first time, shows that they exist as two structural isomers. Whereas, in general, the derivatives of aromatic aldehydes conform to a linear structure, the aliphatic carbonyl derivatives conform to heterocyclic or linear structures, depending on the size of the substituent groups. This dual behaviour is explained in terms of extended conjugation and steric hindrance.
Principal component analysis of the 13C NMR spectra of enamino ketones
Authors: Azzaro Marcel , Geribaldi Serge , Videau Bruno , Chastrette Maurice
Published: May 2005

The 13C NMR spectra of eleven 3‐N,N‐dialkylamino‐5,5‐dimethylcyclohex‐2‐en‐1‐ones have been determined. The chemical shifts of the three sp2 carbons and of the two methylene carbons on the cyclohexenone moiety have been subjected to factor analysis. Two factors are necessary and sufficient to account for more than 93% of the total variance. The more important axis (79%) corresponds to a factor closely related to the inductive and steric effects of the alkyl nitrogen substituents. The second parameter is more difficult to interpret and could correspond to the ‘ipso effects’ of amino groups.
A 1H and 13C NMR study of intramolecular rotations in syn‐ and anti‐o‐tolyl‐di‐tert‐butyl‐carbinols
Authors: Tiffon Bernard , Lomas John S.
Published: May 2005

The syn and anti rotamers of o‐tolyl‐di‐tert‐butylcarbinol, 2a and 2b, respectively, have been studied by 1H NMR at 200 MHz and by natural abundance 13C NMR at 50 MHz. 1H‐{1H} NOE enhancement factors are consistent with the known structures and the calculated geometries of these compounds. The relaxation time, T1, of the 2‐Me protons in 2b is unexpectedly higher than that for 2a. The 13C relaxation times of the 2‐Me and the quaternary carbon of the tert‐butyl group are also both higher in 2b than in 2a, suggesting that the rotation of these groups is faster in the less stable isomer. The activation energies for t‐Bu rotation, measured by 1H DNMR, agree with this conclusion. Further confirmation is provided by theoretical calculation of the 2‐Me and t‐Bu rotation barriers based on Allinger's MM2 force field. Comparison of measured ΔG‡ values from this work and from the literature with MM2‐calculated ΔH‡ values indicates that this force field systematically underestimates rotation barriers in open‐chain systems by a factor of approximately 0.64.
NMR spectra of carotenoporphyrins. Computer‐assisted conformational analysis
Authors: Chachaty Claude , Gust Devens , Moore Thomas A. , Nemeth Gregory A. , Liddell Paul A. , Moore Ana L.
Published: May 2005

A computer‐assisted method of conformational analysis for porphyrin molecules bearing flexible side‐chains has been developed. The method utilizes the ring current‐induced chemical shift changes of the side‐chain protons which arise from the porphyrin macrocycle and any attached aryl rings. The treatment has been applied to a series of carotenoporphyrin molecules, which are important as models for a variety of photophysical processes in biological systems. Chemical shift data of sufficient accuracy for the conformational analysis were obtained from 500 MHz NMR experiments. The conformations of the carotenoporphyrins varied from extended ones with the carotenoid well away from the porphyrin ring to tightly folded species, depending on molecular constitution. The analytical method can be extended to other porphyrin‐based systems.
1H NMR investigation of ring mobility of 1,5‐benzodiazepine‐2,4‐diones
Authors: Chidichimo Giuseppe , Longeri Marcello , Menniti Giuseppina , Romeo Giovanni , Ferlazzo Alida
Published: May 2005

The ring mobility of some 1,5‐benzodiazepine‐2,4‐diones and 1,4‐benzodiazepin‐2‐one has been investigated by the temperature dependence of their 1H NMR spectra. The activation parameters have been obtained, and the influence of N‐1 substitution on the ring mobility is discussed, taking into account previously reported data for similar compounds.
Structure assignment by 1H and 13C NMR of two epimers derived from glycyrrhetic acid
Authors: Bongini Alessandro , Contento Michele , Orena Mario , Pifferi Giorgio , Erba Roberto
Published: May 2005

A full assignment of the 13C signals of four pentacyclic triterpenes confirms the results obtained by 1H NMR analysis of steroidal methyls, resolving the stereochemistry of the oxidation product of 3‐β‐acetoxyolean‐12‐en‐30‐oic acid methyl ester.
The transport of proteins in Mauthner axon in fish as studied by autoradiography and interference microscopy
Authors: Jakoubek B. , Semiginovský B. , Bass A. , Scott D.
Published: May 2005

Using 1 C‐Leucine the rate of transport of proteins in single nerve fiber was investigated by quantitative autoradiography using the desheathed, hand‐free isolated Mauthner axons of fish.

After different times of incubation of living fish in the radioactive medium a non‐uniform labelling of the isolated axons along their length was observed, which showed a characteristic pattern. The distribution of the label indicates: (a) a continuous supply of labelled proteins from the cell body to the axon, (b) accumulation of labelled proteins near the terminal end of the axon, (c) two different rates of the somato‐axonal transport of proteins (30–40 mm 24hr; 3.5 mm/24 hr).

After the transection of the spinal cord no incorporation into the segments of the axon below the lesion was detectable.

No changes of the dry mass between the proximal and distal parts of the Mauthner axon were detectable in interference microscope.

The alternative explanations for the observed pattern of axonal labelling, i.e. local protein synthesis in axons and somato‐axonal flow of proteins, are discussed.
A statistical analysis of timing behavior
Authors: Suzuki Hisao , Saito Mizuo
Published: May 2005

(1) When rabbits were trained on a differential reinforcement of low rate (DRL) 10 sec schedule, they successively made bar‐press response so that a sequence of inter‐response time (IRT) intervals were obtained for each training session. This sequence was subjected to the following statistical analysis. (2) The serial correlation coefficients of order 1 to 50 were calculated on each sequence. They were between –0.2 and +0.2, and seemed to be essentially zero. (3) The distribution of IRT intervals was found to be represented by a composite Weibull distribution function. (4) The relation between one of the Weibull parameters, shape parameter, and the hazard function of the bar‐pressing was discussed.
The effect of monocular deprivation on the synaptic contacts of the visual cortex
Authors: Fifková E.
Published: May 2005

The effect of visual deprivation on synaptic contacts in the visual cortex was studied with the electron microscope. The deprivation was achieved by unilateral lid suture in 14‐day old white rats before eye opening after which the animals were kept for 8 weeks. The density and the size of synaptic contacts in the upper part of the visual cortex (from the surface of layer II up to V) were estimated. The mean density of synapses of the visual cortex supplied by the deprived eye was 20% less than on the control side, the upper levels of the cortex being more affected. The mean size of synaptic contacts was larger (+7.5%) in the upper levels of the deprived cortex. No right left difference in density and size were found in control animals.
Calcium accumulation by isolated nerve ending particles from brain. I. The site of energy‐dependent accumulation
Authors: Lust W. David , Robinson Joseph D.
Published: May 2005

Synaptosomes (isolated nerve ending particles) prepared from rat brain accumulated 45Ca in the presence of ATPd̊ and MgCl2. In order to localize the site of this energy‐dependent process the ability of synaptosomes to accumulate 45Ca was compared to that of a purified preparation of brain mitochondria, since mitochondria are contained within nerve endings. The purity of synaptosomal and mitochondrial fractions was monitored in terms of enzymatic markers and electron microscopy. The rate of accumulation by mitochondria was sufficient to account for the observed rate with synaptosomes, suggesting that the intra‐synaptosomal mitochondria were the site of accumulation in the nerve endings. Furthermore, subfractionation of synaptosomes that had accumulated 45Ca indicated that the bulk of the radioactivity was associated with the mitochondria recovered from the nerve ending. 45Ca accumulation was also supported by oxidizable substrates. This accumulation could not be blocked, either in synaptosomes or in mitochondria, by oligomycin. Since oligomycin blocked ATP‐energized accumulation, free ATP could therefore not be the energy source derived from these substrates, further implicating the intra‐synaptosomal mitochondria as the site of accumulation. Accumulation energized by oxidizable substrates was stimulated by Pi. No stimulation was apparent in the presence of ATP, probably due to the rapid release of Pi by ATPase activity, which was far greater than the rate of 45Ca accumulation. These findings suggest that mitochondria at the nerve ending may actively participate in regulating cytoplasmic Ca2+ levels, a vital role at that site.
Calcium accumulation by isolated nerve ending particles from brain. II. Factors influencing calcium movements
Authors: Lust W. David , Robinson Joseph D.
Published: May 2005

A synaptosomal preparation from rat brain accumulated 45Ca by a temperature‐sensitive process requiring ATPd̊ and Mg++. The uptake of 45Ca was correlated with a net increase in total calcium, and after brief incubations the concentration of 45Ca in the particles was several hundred times that remaining in the medium. Calcium accumulation was associated with a corresponding stoichiometric accumulation of phosphate. Synaptosomes that had accumulated 45Ca during a prior incubation lost the radioactivity during a subsequent incubation in the absence of ATP. NaCl increased the efflux of accumulated 45Ca, a process distinguishable from the non‐specific inhibition of 45Ca accumulation by various solutes corresponding with their effects on intra‐synaptosomal volume. The Na+‐induced efflux of 45Ca was not affected by ouabain. Since the intrasynaptosomal mitochondria have been identified as the site of 45Ca accumulation in synaptosomes, the data suggest that these mitochondria may function as reservoirs of releasable Ca++ within the nerve ending, possibly participating in the Ca++‐dependent process of neurotransmitter release.
Activity patterns of catecholamine‐containing pontine neurons in the dorso‐lateral tegmentum of unrestrained cats
Authors: Chu Nai‐Shin , Bloom Floyd E.
Published: May 2005

Single catecholamine‐containing neurons in the dorso‐lateral pontine tegmentum were recorded in unanesthetized, freely behaving cats. Microscopic lesions were made on each recorded unit and subsequently identified for catecholamines by fluorescence histochemical analysis. The majority of the NE‐containing neurons exhibited low spontaneous discharge rates in quiet wakefulness and in slow wave sleep. In paradoxical sleep, the medially located NE‐containing neurons tend to exhibit ursting discharges which are closely related to individual PGO waves. The laterally or dorsally situated NE units fire more slowly and tend to derease their firing activity during paradoxical sleep. Tonically active, relatively fast NE‐containing units were also found. Often, those neurons showed greatly increased activity before the cat awoke from either slow wave sleep or paradoxical sleep, with activity persisting during the early moments of waking. The combination of histochemical and electrophysiologic methods proved essential for correlating neurochemistry and function within the heterogeneous NE‐containing nuclei of the cat pons.
Neurobiology of Stomotoca. II. Pacemakers and conduction pathways
Authors: Mackie G. O.
Published: May 2005

Evidence is presented for separate conduction pathways for swimming and for tentacle coordination in the marginal nerves of the jellyfish Stomotoca. The effector muscles are fired through junctions sensitive to excess Mg++, probably represented by the neuromuscular synapses observed by electron microscopy. The swimming effector (striated muscle) fires one‐to‐one with nerve input signals and myoid conduction occurs. Tentacle responses (smooth muscle contractions) involve facilitation, presumably at the neuro‐effector junction; responses are graded and nonpropagating.

Electrical correlates of two further conducting systems using the marginal nerves have been recorded. Their functions are unknown. One, the bridge system, extends up the four radii and encircles the peduncle; the other (ring system) is confined to the margin.

A fifth conducting system is inferred in the case of the pointing response and its distribution is plotted. Signals have not been obtained from it. Pointing is accompanied by a burst of muscle potentials in the radial smooth muscles and is exhibited after a lengthy latency, indicating a local pacemaker.

A sixth conducting pathway is the epithelial system, which mediates crumpling, a response involving the radial muscles without pacemaker intervention.

Characteristic conduction velocities and wave forms are noted for the first four systems and for epithelial pulses. All systems, except perhaps the pointing conduction system, through‐conduct under excess Mg++.

Spontaneous activity patterns are described for the swimming, tentacle pulse, and ring systems. Abrupt increases in light intensity inhibit spontaneous activity, sudden decreases augmenting it. In the absence of specialized photoreceptors, light is presumed to act directly on central neurons.

Epithelial pulses inhibit swimming, apparently by blocking the generation or conduction of the primary nervous events. This observation, taken in conjunction with evidence of feedback inhibition of the primary swimming system by the cells it fires, is discussed in relation to possible mechanisms whereby the output of nerve cells might be altered by activity in the excitable epithelial cells which envelop them.
A further study of the fine structure and membrane properties of neuroglia in the optic nerve of Necturus
Authors: Bracho H. , Orkand P. M. , Orkand R. K.
Published: May 2005

The optic nerve of Necturus maculosus consists of a homogeneous population of astroglia and bundles of unmyelinated axons. The glial cell processes ramify within the nerve roughly delineating fascicles of axons and come together at the periphery to form a complete external limiting membrane interrupted only by narrow clefts between adjacent processes. They are frequently “attached” to one another, forming specialized junctions. Blood vessels are entirely outside the nerve which is surrounded by a basal lamina. The temperature dependence of the glial membrane potential is accurately predicted by the Nernst relation. The membrane potential is unaffected by changes in Cl, Na, Li, and guanidinium which are apparently impermeant. The permeability of the glial membrane to other cations is in the sequence Tl> K> Rb> Cs> NH4. This suggests that the chemical nature of the site of potassium permeability in glial cells is similar to that in the neuron.
Voltage clamping with a single microelectrode
Authors: Wilson W. A. , Goldner Marcia Monahan
Published: May 2005

A technique is described which allows neurons to be voltage clamped with a single microelectrode, and the advantages of this circuit with respect to conventional bridge techniques are discussed. In this circuit, the single micro electrode is rapidly switched from a current passing to a recording mode. The circuitry consists of: (1) an electronic switch; (2) a high impedance, ultralow input capacity amplifier; (3) a sample‐and‐hold module; (4) conventional voltage clamping circuitry. The closed electronic switch allows current to flow through the electrode. The switch then opens, and the electrode is in a recording mode. The low input capacity of the preamplifier allows the artifact from the current pulse to rapidly abate, after which time the circuit samples the membrane potential. This cycle is repeated at rates up to 10 kHz. The voltage clamping amplifier senses the output of the sample‐and‐hold module and adjusts the current pulse amplitude to maintain the desired membrane potential. The system was evaluated in Aplysia neurons by inserting two microelectrodes into a cell. One electrode was used to clamp the cell and the other to independently monitor membrane potential at a remote location in the soma.
A comparison of the escape behaviors of the cockroaches Blaberus craniifer and Periplaneta americana
Authors: Simpson Barbara S. , Ritzmann Roy E. , Pollack Alan J.
Published: May 2005

A comparison of wind‐mediated escape behavior of two species of cockroaches revealed striking differences. In contrast to Periplaneta americana, Blaberus craniifer was unable to escape from a live predator or move away from a synthetically generated puff of wind. Other behavioral differences included degree of preference for areas of low light intensity and propensity to dig and thus bury oneself when disturbed. Anatomical differences, although present, did not seem sufficient to account for the behavioral differences. Also, B. craniifer was able to escape from generated wind puffs but not a live predator when its temperature was raised. These points suggest that the behavioral differences in escape behavior can be attributed to differences in the physiological state of the two nervous systems.
Transient depletion of serotonin in the nervous system of Helisoma
Authors: Gadotti Daniela , Bauce Lorenzo G. , Lukowiak Ken , Bulloch Andrew G. M.
Published: May 2005

The present study shows that the drug 5,7‐dihydroxytryptamine (5,7‐diHT) can be used reliably to deplete the neurotransmitter serotonin (5‐HT) from the nervous system of the snail Helisoma. The depletion is more effective in axonal and synaptic regions (85–90%) than in the somata (55%), is reasonably specific for serotonin (dopamine is affected to a much lesser extent), and is transient, with normal levels of neurotransmitter being restored by 2 months. A physiological correlate of 5‐HT depletion has been shown in that an EPSP elicited by a cerebral serotonergic neuron (C1) onto a buccal motoneuron (B19) is much smaller during depletion and also recovers with time as 5‐HT regains normal concentration. Despite the severe 5‐HT depletion and physiological impairment, the gross morphology of neuron C1 remains indistinguishable from controls. Serotonergic depletion is not accompanied by development of receptor supersensitivity nor by the production of serotonin in extraneuronal sources.
Epithelial axon guidance in Drosophila
Authors: Palka J.
Published: May 2005

Evidence is offered that the axons of developing sensory neurons in the wing of Drosophila are guided (given both location and polarity information) by the epithelium over which they grow. This guidance is effective in the absence of such potential additional cues as guidepost neurons and physical channels.
The myth of the inflexible invertebrate: Competition and synaptic remodelling in the development of invertebrate nervous systems
Authors: Murphey R. K.
Published: May 2005

As this quote and the article it was taken from reflect, it is a commonly held belief that the development of invertebrate nervous systems is so rigidly programmed that it is qualitatively different from that of vertebrates. The facts do not support this assertion, and I will show, using examples from among the arthropods, that appropriate experiments often reveal competition, feedback, and prolonged periods of malleability much as they do for the vertebrates. Indeed, given the well known advantages of studying the invertebrate nervous system, I think it likely that invertebrates can serve as important and useful preparations for studying, at the cellular level, the same biological phenomena that Easter et al. (1985) are trying to understand in vertebrates.
Presynaptic terminals persist following degeneration of “flight” muscle during development of a flightless grasshopper
Authors: Arbas Edmund A. , Tolbert Leslie P.
Published: May 2005

We have studied the development of a neuromuscular system for which mature function has been lost through evolution in the grasshopper, Barytettix psolus (Cohn and Cantrall, 1974). Barytettix is flightless throughout life and has only vestigial wings that are incapable of active movement. Adult Barytettix lack muscles homologous to the indirect flight muscles of locusts and grasshoppers that fly, while other thoracic muscles are similar. We have found, using light and electron microscopic examination of tissues from various developmental stages, that the metathoracic dorsal longitudinal muscle is present and is innervated during nymphal life but is absent in adults. Yet its nerve persists and, in the adult, contains axonal presynaptic specializations opposite inappropriate targets such as glial processes and basal lamina. Our findings indicate that selective muscle death during development is one mechanism underlying the reduction of the flight system of Barytettix through evolution. The finding that presynaptic terminals persist in the absence of the muscle indicates that the muscle and its innervation follow programs of development that are at least partially independent and reinforces the concept that in insects motorneurons, and perhaps neurons in general, are not dependent upon trophic influences from their targets for survival and maintenance of their differentiated phenotype.
Inhibition of fast axonal transport in bullfrog nerves by dibenzazepine and dibenzocycloheptadiene calmodulin inhibitors
Authors: Lavoie P.‐A. , Tiberi M.
Published: May 2005

The effects of the calmodulin inhibitors amitriptyline, desipramine, imipramine, and clomipramine on fast axonal transport, oxidative metabolism, and density of axonal microtubules were measured in bullfrog spinal nerves in vitro. The four drugs tested inhibited the fast orthograde transport of [3H]leucine‐labelled proteins and the fast retrograde transport of acetylcholinesterase at a concentration of 0.2 mM. Amitriptylin, desipramine, and imipramine were equipotent inhibitors of transport, and clomipramine was a more potent inhibitor than imipramine. The adenosine triphosphate content of the nerves was reduced by at most 19% by the compounds under study; such a reduction cannot account for the inhibition of fast axonal transport. Desipramine and imipramine had no significant effect on the density of microtubules in unmyelinated axons, whereas amitriptyline only reduced it by 18%; the inhibition of axonal transport by these three drugs can therefore not be explained by microtubule disruption. Clomipramine reduced microtubular density by 40%, and this effect may have contributed to the inhibition of fast axonal transport. The inhibition of fast axonal transport by desipramine, imipramine, and amitriptyline may be related to the inhibition of calmodulin function by these drugs. The similar potency of these three durgs as inhibitors of fast axonal transport goes in parallel with their known similar potency as calmodulin antagonists.
Cobalt blocks the decrease in MEPSP frequency on depolarization in calcium‐free hypertonic media
Authors: Landò Luca , Giovannini Joseph , Zucker Robert S.
Published: May 2005

Media made hyperosmotic with sucrose increase the frequency of spontaneously released quanta of transmitter, or miniature excitatory postsynaptic potentials (MEPSPs). In calcium‐free medium, depolarization with high potassium reduces the MEPSP frequency, presumably due to calcium efflux in the reversed gradient condition. This effect of depolarization in blocked by cobalt, supporting the above interpretation of the effects of hypertonicity and depolarization and suggesting that cobalt can block efflux as well as influx through calcium channels.
The effect of serotonin and octopamine on the optokinetic response of the crab Leptograpsus variegatus
Authors: Erber J. , Sandeman D. C.
Published: May 2005

A standard optokinetic response of the ipsilateral and contralateral (driven) eyes of the crab Leptograpsus variegatus to a sinusoidally oscillating striped drum was established. Optokinetic responses were then measured of animals that had been treated by introducing serotonin and octopamine into the blood stream via the heart and also into the neural tissue of the optic lobes via a micropipette. Both serotonin and octopamine enhance the optokinetic effect when applied in low doses. Experiments show that serotonin is most likely acting closer to the sensory input in the optokinetic system.
Regeneration of an identifiable motoneuron in the crayfish. I. Patterns of reconnection and synaptic strength established in normal and altered target areas
Authors: Hunt William P. , Vélez Samuel J.
Published: May 2005

The superficial flexor muscles of the crayfish are innervated in a position‐dependent connectivity pattern, which can be reestablished when the nerve to the muscle is cut. This article deals with the regeneration of the largest excitor motoneuron under three different target scenarios: (1) a normal target with all the muscle fibers present, (2) a reduced target lacking the medial or the lateral muscle fiber population, and (3) when the nerve enters the target in the middle of the muscle field. In scenario 1 the neuron is able to regenerate the normal connectivity pattern within 10 weeks after surgery: all the lateral fibers become innervated, with a linear decline in the probability of connections over the medial fibers. The medial fibers become transiently hyperinnervated before the normal pattern of connections is established. In scenario 2 the normal pattern of connections is established only when the lateral fibers were present; with only medial cells as a target, the transient hyperinnervation stage is stable and no decline in connections was observed. Analysis of regenerated junction potential sizes during the stable hyperinnervation stage show abnormal patterns, suggesting that some aspects of the regeneration program of this neuron can be affected when signals from its prime target cells are missing. In scenario 3 growth begins in both directions until the entire muscle becomes innervated. The normal pattern of connectivity finally emerges after continued lateral growth and diminished medial growth, suggesting that the position of the muscle fibers influences connectivity patterns during the final stages of regeneration.
Localization of the enhanced input to cockroach giant interneurons after partial deafferentation
Authors: Volman Susan F.
Published: May 2005

The ventral giant interneurons (GIs) in the cockroach have two distinct dendritic fields: a small one ipsilateral to the soma, and a larger, contralateral field from which the axon arises. The major input to these GIs is from the cercus on the axon side; when this cercus is ablated in the last instar before the adult stage, input from the other cercus becomes more effective within 30 days (Vardi and Camhi, 1982b). I wished to determine if the input from the intact, soma‐ipsilateral cercus contacted the GIs purely ipsilaterally and if EPSPs at this site were larger in deafferented animals. Consistent with earlier anatomical findings, intracellular recordings from the GI somata showed that the majority of cercal inputs synapse on their own side of the ganglion in normal animals. This was evidenced by differences in the size and shape of the synaptic potentials evoked from the two cerci and by the presence of large EPSPs after a ganglion had been split along the midline. Unitary EPSPs produced by stimulation of single, identified cercal afferents, ipsilateral to the soma, were compared between normal and deafferented animals. Column “h” afferents were chosen because they make a large contribution to the receptive fields of GIs 1 and 2 after ablation of the contralateral cercus. In addition, the arbors of these afferents, when stained with cobalt, did not cross the ganglionic midline in normal animals. Unitary EPSPs recorded in GI 2 were significantly larger in the deafferented animals. There was, however, no significant change in the size of EPSPs in GI 1. Nevertheless, the results from GI 2 suggest that partial deafferentation in the central nervous system can increase the efficacy of synapses distant from the locus of denervation.
Mechanisms of elimination, remodeling, and competition at frog neuromuscular junctions
Authors: Herrera Albert A. , Werle Michael J.
Published: May 2005

Mechanisms governing synapse elimination, synaptic remodeling, and polyneuronal innervation were examined in anatomical and electrophysiological studies of frog neuromuscular junctions. There was a substantial level of polyneuronal innervation in adult junctions and this varied seasonally. Nerve terminal retraction and synapse elimination occurred during normal growth and following reinnervation. Synapse elimination was not inevitable, however. Repeated in vivo observations of some identified junctions showed that polyneuronal innervation could persist for over a year, while at other junctions it arose de novo by terminal sprouting. We concluded that polyneuronal innervation in adult muscles was governed by an equilibrium between processes of retraction and elimination on one hand, and sprouting and synaptogenesis on the other. Other observations revealed that structural remodeling was a common feature of adult junctions. Most often, remodeling involved the simultaneous growth and retraction of different parts of the same junction. The net result was usually junctional growth that, in small frogs, appeared to provide a good match between synaptic size and the electrical demands of transmission. In larger animals, pre‐ and postsynaptic sizes were not as well matched, providing morphological evidence for a growth‐associated decline in synaptic efficacy. Finally, electrophysiology was used to describe some of the functional correlates and consequences of competitive interactions between the terminals of different axons. These results are explained by a hypothetical mechanism that involves trophic support provided by the muscle to the motoneuron, the overall level of nerve‐muscle activity, and the synchrony of pre‐ and postsynaptic activity.
Competition or inhibition? Developmental strategies in the establishment of peripheral projections by leech neurons
Authors: Macagno E. R. , Gao W.‐Q. , Baptista C. A. , Passani M. B.
Published: May 2005

Leech neurons, like those of other invertebrates and those of vertebrates, undergo specific interactions during development which serve to define their adult morphologies and synaptic connections. We review here several observations and experiments that illustrate these interactions. In particular, we consider how they shape and constrain peripheral arborizations and whether the evidence favors competition or inhibition as their mode of action.
Assembly of the cricket cercal sensory system: Genetic and epigenetic control
Authors: Murphey R. K. , Chiba A.
Published: May 2005

The cercal sensory system of the cricket is being examined using anatomical, physiological, and computer simulation techniques in order to better understand the assembly of sensory systems. This particular sensory system is of interest because it functions like numerically more complex vertebrate sensory systems but offers, to the neuroscientist, the technical advantages of a small number of large identified neurons. Two aspects of sensory processing are being examined in this system; the spatial aspects of a stimulus that tell an animal where a target is in its environment, and the qualities of a stimulus that help the animal to identify the stimulus. The spatial aspects of a stimulus are analyzed by a topographic mapping of the animal's sensory environment. The feature extraction machinery for other aspects of the stimulus lacks any obvious anatomical order and is embedded within the topographic map. We are attempting to tease apart the genetic and the epigenetic components of the assembly process for this sensory system. Here we review our progress with emphasis on the epigenetic aspects of its assembly. We describe previously published work on plasticity as well as new experiments focussed on the role of neuronal activity in the assembly of this neural circuit. Finally, we briefly describe simulation experiments that are helping us understand the role of various forms of synaptic plasticity in the determination of receptive fields.
Mechanisms involved in activity‐dependent synapse formation in mammalian central nervous system cell cultures
Authors: Nelson Phillip G. , Fields R. Douglas , Yu Chang , Neale Elaine A.
Published: May 2005

Differences in neuronal activity produced by electrical stimulation lead to competition between synapses from sensory afferents converging on a common spinal cord neuron. Studies were performed on neurons dissociated form the mouse spinal cord and grown in culture dishes with three compartments. Synaptic efficacy from stimulated afferents was increased compared with unstimulated convergents, and the number of functional connections was increased by stimulation compared with control cultures. Blocking NMDA channel activation with 100 μM APV in medium containing 1.8 mM calcium inhibited this synaptic plasticity, but plasticity was not blocked by APV in medium in which the calcium concentration was elevated to 3 mM.

These experiments support the view that electrical activity differentially influences processes that cause a persistent decrease in synaptic efficacy or lead to synapse elimination and those that increase synaptic strength or lead to synapse augmentation. We interpret our results in terms of a model in which these antagonistic mechanisms are both regulated via changes in calcium levels and second messengers that are modulated by electrical activity. A significant portion of the activity‐related calcium influx relevant to synaptic plasticity passes through the NMDA channel, but other sources of calcium are involved. In particular, competitive elimination of synapses appears to occur during blockade of NMDA channels if the extracellular concentration of calcium is elevated moderately. The outcome of competition between the two calcium‐dependent but antagonistic processes may depend either on their differential sensitivity to intracellular calcium concentration or separate specificities to NMDA and non‐NMDA receptor‐linked mechanisms.
The origin and selective innervation of early muscle fiber types in the rat
Authors: Thompson Wesley J. , Condon Keith , Astrow Stephanie H.
Published: May 2005

The diversity of muscle fiber types present in adult animals is present also in the fetus. Fibers generated early and late in fetal development undergo a stereotyped sequence of myosin expressions in giving rise to these fiber types. The differentiation of these fetal fiber types does not require innervation. However, evidence obtained from experiments identifying the types of fibers innervated by single motors suggests that the nervous system comes to recognize this diversity, at least during early postnatal life. Reinnervation experiments suggest that this recognition can occur in the absence of the timing cues normally present in the genesis of fiber types. Thus, a selective innervation of muscle fiber types occurs during development. The role of rearrangement of initial synaptic connections in generating this selectivity is discussed.
Is androgen‐dependent aromatase activity sexually differentiated in the rat and dove preoptic area?
Authors: Steimer Th. , Hutchison J. B.
Published: May 2005

Aromatase activity is higher in the male than in the female anterior hypothalamic‐preoptic area (POA) in both the avian and the rodent adult brain. This sex difference is abolished after castration of the male and restored by androgen treatment. Gonadectomy has no effect on POA aromatase in the female. The aim of this study was to find out whether sex dimorphism in adult POA aromatase is only due to a sex difference in circulating gonadal hormones or dependent upon sexual differentiation of the brain. Aromatase activity was measured in vitro in microdissected POA samples using a sensitive radiometric assay. We examined the effects of gonadectomy and testosterone treatment on enzyme activity in adult rats and doves of both sexes. We also studied the effects of neonatal gonadectomy and hormone substitution in male and female rats. The results suggest that levels of POA aromatase in the adult depend primarily on gonadal activity, but that mechanisms involved in the regulation of aromatase and enzyme induction may be sex‐specific and could result from sexual differentiation of the brain in early life. Further work will be required to determine the developmental stage when this occurs and the exact mechanism(s) responsible for increased sensitivity of the adult male POA to the inductive effect of testosterone.
Lack of correspondence between mRNA expression for a putative cell death molecule (SGP‐2) and neuronal cell death in the central nervous system
Authors: Garden Gwenn A. , Bothwell Mark , Rubel Edwin W.
Published: May 2005

Neuronal death during nervous system development, a widely observed phenomenon, occurs through unknown mechanisms. Recent evidence suggests an active, destructive process requiring new gene expression. Sulfated glycoprotein‐2 (SGP‐2), a secretory product of testicular Sertoli cells has been shown to up‐regulate in several nonneural tissues undergoing programmed cell death and in several types of neuronal degeneration. In order to determine if this message up‐regulates in neurons undergoing developmentally determined cell death, we have studied the expression of SGP‐2 mRNA in the developing and adult rat central nervous system (CNS) with in situ hybridization. We also report on the expression of this message in nonneural tissues from several regions of the developing embryo. The developing and adult rat central nervous system as well as widely varied tissues in the rat embryo express SGP‐2 mRNA in a pattern that does not correlate with regions undergoing developmental cell death. In the nervous system, SGP‐2 mRNA is expressed in neuronal populations including motor neurons, cortical neurons, and hypothalamic neurons at ages when the period of developmental cell death has passed. In a nonneural tissue (palatal shelve epithelium) for which a developmental cell death period has been described, SGP‐2 mRNA was not present in the region where cell death occurs. We conclude that SGP‐2 mRNA expression cannot be correlated with programmed cell death in neural or nonneural tissues. The results of this study as well as recently reported SGP‐2 homologies indicate a possible role for this protein in secretion and lipid transport.
Co‐cultures of inferior olive and cerebellum: Electrophysiological evidence for multiple innervation of Purkinje cells by olivary axons
Authors: Mariani Jean , Knöpfel Thomas , Gähwiler Beat H.
Published: May 2005

Slices of inferior olive (IO) and cerebellum were co‐cultured for several weeks by means of the roller tube technique. Recordings were carried out intracellularly from Purkinje cells (PCs) which were identified morphologically by intracellular injection of the fluorescent dye Lucifer yellow, or by immunohistochemical stainings with antibodies raised against the 28 kD Ca2+‐binding protein calbindin. Following stimulation of olivary tissue, an all‐or‐none full complex spike response was recorded in some PCs consisting of a fast rising spike followed by a depolarizing potential. In other PCs, graded stimulation of the olivary explant induced synaptic potentials which were characterized by step‐wise variation in their amplitude and resembled the ones occurring spontaneously. In contrast, only smoothly graded synaptic potentials were observed in cerebellar mono‐cultures. These results indicate that some of the PCs in olivo‐cerebellar co‐cultures are innervated by several olivary neurons.
Sexually dimorphic, androgen sensitive, enkephalinergic afferents to a lumbar motor nucleus of rats
Authors: Coquelin Arthur , Micevych Paul E. , Arnold Arthur P.
Published: May 2005

In male rats, methionine‐enkephalin immunoreactivity (enkephalin‐ir) has been observed in the dorsal lateral nucleus (DLN), a longitudinal pool of motoneurons in the lumbar spinal cord. Within the DLN a mediodorsal crescent of intense enkephalin‐ir staining surrounds the motoneurons innervating the ischiocavernosus muscle of the penis, which suggests a function of the enkephalinergic afferents in male copulatory activities. The present study attempted to determine the roles of gender and adult exposure to androgen in shaping the striking subnuclear distribution of enkephalin‐ir. Transverse sections through L5–6 were obtained from mature male and female rats that were gonadally intact, gonadectomized, or gonadectomized and treated with testosterone, as well as from male rats genetically deficient in androgen receptors (Tfm). The sections were incubated with primary antiserum raised against methionine enkephalin and bound antibodies were visualized using the avidin‐biotin peroxidase technique. A microphotometer was used to compare the staining density in laminae I‐II of the dorsal horn, ventral grey matter, and the DLN. In all groups the DLN stained more darkly than the ventral grey, demonstrating the presence of enkephalin‐ir in the DLN regardless of gender or exposure to androgen. However, the mediodorsal crescent of dense staining in the DLN was obvious only in gonadally intact males, while the entire DLN stained darkly in both sexes of gonadectomized rats treated with androgen. Therefore, the preferential distribution of enkephalin‐ir in the mediodorsal crescent of the DLN is sexually dimorphic though the overall content of enkephalin‐ir within the DLN responds to androgen.
Mapping the early development of projections from the entorhinal cortex in the embryonic mouse using prenatal surgery techniques
Authors: Snyder Dianne C. , Coltman Bert W. , Muneoka Ken , Ide Charles F.
Published: May 2005

The purpose of this work was to study the development of specific projections from the postero‐lateral cortex during the third trimester of gestation in the mouse. To do this, we labeled undifferentiated lateral cortex with the fluorescent carbocyanine dye, Dil, in the embryonic day (E) 16 mouse embryo usingexo uterosurgical techniques (Muneoka, Wanek, and Bryant, 1986). Embryos were allowed to develop to term (postnatal day 0, P0) at which time the fiber patterns emanating from the marked regions were studied. Dye placement in the undifferentiated postero‐ventral cortex produced labeled fibers in the hippocampal formation. A robust projection of the angular bundle into the CA1 region of the hippocampus was heavily labeled. In addition, in some animals, cortical tracts, such as the anterior commissure, corpus callosum, and a corticotectal tract, were labeled. These tracts have been described previously as scaffolding pathways in the fetal cat (McConnell, Ghosh, and Shatz, 1989), and other vertebrates (Wilson, Ross, Parrett, and Easter, 1990). Dye placement in adjacent, more anterior or dorsal areas showed strong labeling in cortical structures but no labeling in the hippocampal formation. These data indicate that, by birth, the temporal cortex is subdivided along the rostro‐caudal axis as entorhinal cortex and perirhinal cortex, and along the dorso‐ventral axis, as entorhinal cortex and neocortex. Also, these earliest connections are similar to adult connections in their specificity of target area selection. Therefore, these early, yet specific, connections may play a role in the formation of future connections during postnatal development.