bluuebunny/crossref_metadata_2025 huggingface dataset:
13C NMR spectroscopy of heteroaromatic compounds: A quantitative measure of electron deficiency and excessiveness
Authors: Paudler William W. , Jovanovic Misa V.
Published: May 2005

A quantitative measure, πΔ, for expressing the π‐deficiency and π‐excessiveness of heteroaromatic compounds has been developed through 13C NMR chemical shift studies. An example which correlates electrophilic reactivity in π‐excessive systems with πΔ of these compounds is given. The following decreasing order of π‐excessiveness and increasing π‐deficiency of a number of heteroaromatic systems has been established (numbers in parentheses correspond to πΔ): tellurophene (1.83), selenophene (1.43), thiophene (1.35), furan (1.31), benzene (1.00), pyrazine (1.00) pyridine (0.89), pyrimidine (0.77), pyridazine (0.71), 1,2,4‐triazine (0.64). These correlations also allow the prediction of 13C chemical shifts in substituted heteroaromatic compounds, where the ratio of the difference between a given substituted heterocyclic compound and its parent, and the identically substituted benzene derivative, has been determined.
INDO calculations of the solvent dependence of some spin–spin couplings of fluorocarbons
Authors: Shargi S. N. , Webb G. A.
Published: May 2005

The results of some SCPT and SOS calculations of 1J(CH), 1J(FC), 2J(FH), 3J(FH), 3J(FF) and 1J(CC) in a variety of solvents are reported. The calculations employ the solvaton model and INDO parameters. In almost all cases the coupling is predicted to increase as the dielectric constant of the solvent increases, the exception being 3J(FH)cis in trifluoroethylene which is supported by experimental results.
13C NMR studies of some hydroxycoumarins and related compounds
Authors: Sankar S. S. , Gilbert R. D. , Fornes R. E.
Published: May 2005

The 13C chemical shifts and one‐bond carbon‐hydrogen coupling constants have been obtained for some hydroxycoumarins and their corresponding acetoxy and methoxy derivatives. The changes in the one‐bond carbon‐hydrogen coupling constants resulting from the conversion of a hydroxy group to an acetoxy group represent a simple method of assignment of the 13C NMR signals in coumarins which contain one or more hydroxy groups in the benzenoid ring.
Low‐frequency vibrational modes and temperature dependence of NQR frequencies in 1,2,4,5‐tetrabromobenzene
Authors: Rao N. Bharateswara , Rangacharyulu M. , Venkatacharyulu P. , Premaswarup D.
Published: May 2005

A temperature variation study of the nuclear quadrupole resonance (NQR) frequencies for the two resonance lines in 1,2,4,5‐tetrabromobenzene was carried out in the range 77–300 K. The far‐infrared spectrum of 1,2,4,5‐tetrabromobenzene was recorded and the low‐frequency vibrational modes noted. From the nine observed frequencies, the torsional modes contributing to the change in NQR frequencies with temperature are identified by correlating the calculated values of the NQR frequencies at different temperatures with the observed values.
Determination of tautomeric phenotypes of β‐thioxo esters and characterization of the tautomeric enethiolic constituents by means of 13C NMR spectroscopy
Authors: Duus F. , Hansen P. E.
Published: May 2005

The 13C NMR spectra of 28 enethiolizable β‐thioxo esters and 6 enethiolizable β‐thioxo thioloesters have been recorded in order to establish the tautomeric phenotypes of these compounds. All compounds investigated are essentially enethiolic. The carbonyl‐conjugated (Z)‐enethiol form is the exclusive or predominant tautomer of open‐chain β‐thioxo esters and thioloesters, thioacylmalonates and medium‐sized 2‐alkoxycarbonylcycloalkanethiones. The carbonyl‐conjugated (E)‐enethiol form is identifiable for open‐chain α‐unsubstituted β‐thioxo esters and thioloesters, and abundant for open‐chain α‐substituted β‐thioxo esters. Non‐conjugated enethiol forms [i.e. (Z)‐ and (E)‐isomeric β,γ‐unsaturated β‐mercapto esters] are abundant tautomeric constituents of ω‐substituted and higher 2‐alkoxycarbonylcycloalkanethiones. The chemical shifts of the carbon atoms directly involved in the tautomeric change have been rationalized in terms of substituent screening contributions. Deuterium isotope effects on the central carbon atoms of selected deuterio‐enethiolic compounds have been measured in order to depict the ester group rotamerism in CO‐conjugated (Z)‐enethiols. The abundance of the CO‐conjugated (E)‐enethiols, as well as the preferred population of the non‐conjugated (Z)‐enethiol form relative to the non‐conjugated (E)‐enethiol form, is rationalized in terms of the occurrence of a no‐bond interaction between the lone‐pair electrons of the enethiolic sulphur atom and the ‘chelating’ methylene hydrogen atoms of cis‐alkyl groups.
Oxygen‐17 nuclear magnetic resonance study of some five‐membered heterocyclic derivatives
Authors: Chimichi Stefano , Nesi Rodolfo , De Sio Francesco
Published: May 2005

17O NMR spectra have been obtained in the FT mode for some furan and isoxazole derivatives. The chemical shifts, mainly governed by the electronegativities of the atoms bonded to the central oxygen, are also affected by alkylation on the different positions of the ring systems, which gives rise to β and γ effects similar to those observed for simple aliphatic ethers.
1H and 13C NMR spectral assignments of isoquinuclidine‐3,5‐dione derivatives
Authors: Quirante Josefina , Diaba Faïza , Vila Xavier , Bonjoch Josep
Published: May 2005

The 1H and 13C NMR spectra of six 5‐substituted 2‐azabicyclo[2.2.2]octane derivatives were fully assigned by COSY and HSQC experiments. Copyright © 2005 John Wiley & Sons, Ltd.
The turnover of phosphatidyl choline in rat cerebral cortex membranes in vivo
Authors: Lapetina E. G. , Lunt G. G. , De Robertis E.
Published: May 2005

The incorporation of [Me‐14] choline administered by intraventricular injection in vivo into the phosphatidyl choline of the membranes of rat cerebral cortex was studied, and it was demonstrated that the radioactive choline was incorporated almost exclusively into phosphatidyl choline in each of the fractions. The various membranous fractions had different half‐lives of phosphatidyl choline. The half‐life of the phosphatidyl choline of myelin was 167 days, the longest of any fraction, while the value of 27 days for mitochondria was the shortest. Phosphatidyl choline of microsomal membranes and synaptic vesicles had very similar half‐lives, whereas the purest fraction of nerve ending membranes gave a half‐life double that of synaptic vesicles.
Somal site of synthesis of fast transported materials in mammalian nerve fibers
Authors: Ochs S. , Sabri M. I. , Ranish N.
Published: May 2005

The crest of labelled materials carried down the fibers of cat sciatic nerve by the fast transport system was blocked by puromycin or cycloheximide injected into the lumbar 7th ganglion 20–30 min before the precursor 3H‐ leucine. The protein synthesis blocking agents were less effective when given 5 min after 3H‐leucine injection and ineffective when injected 20 min or more afterwards. Differential centrifugation of the labelled components of nerve showed a relatively high specific activity (counts/min/mg protein) present in the small particulate and supernatant fractions of nerves removed 5–6 hrs after ganglion injection. Sephadex G‐200 column gel filtration of the supernatant fraction showed the presence of labelled soluble proteins with molecular weights of 450,000 (peak Ia) and 68,000 (peak Ib), polypeptides with a molecular weight of 5,000, and a small amount of free leucine (peak II). In nerves taken 16–22 hrs after ganglion injection, a relatively greater specific activity was found in the peak Ia soluble protein. Labelled materials carried down by fast transport were allowed to enter the axons for a period of 5–6 hrs, and then further outflow from the somas prevented by ligations made just distal to the ganglia. After an additional 16 hrs in the animal it was found that the polypeptides and free leucine, which had entered these nerve fibers earlier, were not then later synthesized into the higher molecular weight proteins characteristic of the later downflows. These studies show a rapid synthesis of labelled materials carried down the fiber by the fast transport system and a translocation in the somas of another portion, mainly protein which is then carried out into the axon at later times.
Parametric studies of the response decrement produced by mechanical stimuli in the protozoan, Stentor coeruleus
Authors: Wood David C.
Published: May 2005

A decrement in the probability of eliciting a response is observed during the course of repetitive stimulation in many response systems of both metazoa and protozoa. Those forms of metazoan response decrement called habituation have recently been characterized behaviorally. In the studies reported here, the response decrement of the contractile protozoan, Stentor coeruleus, to repeated mechanical stimulation was systemically characterized to provide a comparison with metazoan habituation. This change in response probability was closely approximated by a negative exponential function after the first few stimuli. Animals responded to parametric variations of stimulus amplitude, interstimulus interval and retention period in a manner paralleling that observed in metazoa. However, neither interpolated large amplitude mechanical stimuli nor suprathreshold electrical stimuli produced dishabituation in Stentor though these stimuli are among the most effective dishabituating stimuli for metazoan tactile response systems. Behavioral analysis of the response decrement proceeded on the assumption that Stentor contains receptor and effector mechanisms only. Since the response decrement was not correlated with a change in responsiveness to electrical stimuli, the ability of the animal to contract appears to be unaltered by the process producing the response decrement. On the other hand, weak mechanical prestimuli were found to increase the rate of the response decrement which suggests that a process of receptor adaption is operative.
Motor and sensory mechanisms of feeding in Pleurobranchaea
Authors: Lee Richard M. , Liegeois Richard J.
Published: May 2005

Nerves of the cerebropleural ganglion play a major role in the sensory and motor aspects of feeding in the marine mollusk, Pleurobranchaea. Investigations of these nerves were carried out using whole‐body preparations capable of essentially normal feeding behavior. Chemosensory nerves which function in food arousal are the rhinophore, tentacle (large branch) and large oral veil nerves, and a nerve of the pedal ganglion (P3). Recordings from these nerves are consistent with previous behavioral findings concerned with the location of receptor regions.

The feeding cycle of proboscis extension, thrusting, and withdrawal, is controlled primarilly by cerebral nerves. The mouth nerve and small oral veil nerve supply muscles which control the oral tube. When these muscles contract, the oral tube and mouth are pulled open, and the buccal mass, which forms the core of the proboscis, advances part way. At his time, the body wall musculature, innervated by the body wall nerve and a pedal nerve (P4), contracts behind the buccal mass, forcing it out of the open mouth. Proboscis thrusting is accomplished by rhythmic bursts of the mouth and small oral veil nerves. Withdrawal of the buccal mass is accomplished essentially by the reverse process.

This conception of the feeding cycle was developed by considering the muscular anatomy and by behavior simulation. It was confirmed by recording motor nerve output and muscle activity during food stimulation.
Innervation pattern and electric organ discharge waveform in Gymnotus carapo (Teleostei; Gymnotiformes)
Authors: Trujillo‐Cenóz O. , Echagüe J. A. , Macadar O.
Published: May 2005

The electrogenic organ (EO) of Gymnotus carapo has two main portions: a posterior region consisting of four bilaterally arranged electrocyte rows; and an anterior portion composed of only two. The lateral row (LR) of the anterior portion contains doubly innervated electrocytes with axon terminals from different nerves on their rostral and caudal faces. The LR is continuous with the most dorsal row of the caudal region. This row also contains doubly innervated electrocytes. The medial row (MR) electrocytes of the anterior region and ventral rows of the caudal region are exclusively caudally innervated. All caudal faces of the anterior or abdominal region are supplied by two nerves which originate from spinal roots VIII to XXI. Roots I to VII give origin to pure rostral nerves whose electromotor axons terminate on the rostral surfaces of the first seven LR electrocytes.

A given doubly innervated electrocyte is supplied on its caudal face by a nerve originating several segments (usually seven) posterior to the spinal root supplying its rostral face.

Transections of the spinal cord at the level of root VIII isolate the activity of the rostral surfaces of the first electrocytes. The EO discharge (EOD) then appears as a head negative deflection which arises from abdominally located electrocytes. Its monophasic character reveals that the activity remains restricted to the rostral electrocyte surfaces. Damage of the abdominal portion of the EO abolishes the first negative deflection of the normal pulse.

Transections of the spinal cord at the level of root XXI isolate the activity of the whole abdominal portion of the EO. Since both doubly and singly innervated electrocytes remain active, the EOD appears biphasic.

Comparative studies have shown that the EOD of Hypopomus sp. lacks any early negative wave and correspondingly all its electrocytes are exclusively caudally innervated.
Modified cobalt staining and silver intensification techniques for use with whole‐mount gastropod ganglion preparations
Authors: Croll Roger P.
Published: May 2005

While silver intensification of cobalt‐filled cells is a common procedure for use with many arthropod preparations, it has not been routinely applied to gastropods. Several modifications in cobalt‐staining techniques currently used with gastropods along with adaptations of silver intensification techniques used in insects are described. Cobalt was introduced into cells through axonal filling of cut nerve trunks or by either pressure injection or iontophoresis from intracellular, micropipette electrodes that had previously had their tips etched in dilute hydrofluoric acid. Etching produced consistent, sharp tips with large lumina. Further procedural modifications allowed complete, even intensification of neurons in large gastropod ganglia. These techniques have proved to be reliable and apparently broadly applicable, having been successfully used on three diverse gastropod species.
Neurites show pathway specificity but lack directional specificity or predetermined lengths in Xenopus embryos
Authors: Huang Sen , Jacobson Marcus
Published: May 2005

The earliest outgrowth of nerve fibers from identified spinal neurons labeled with horseradish peroxidase (HRP) was traced along surgically rearranged pathways in the central nervous system (CNS) of Xenopus embryos. Parts of the CNS were misaligned or inverted rostrocaudally by grafting a segment of labeled spinal cord in place of the same or different spinal cord segment of an unlabeled embryo or by joining two rostral half embryos (head‐to‐head) or two caudal half embryos (tail‐to‐tail), one half of which was derived from a labeled embryo in each combination. Donor embryos were labeled by injection of HRP into a selected blastomere at the 16‐ or 32‐cell stage. Host embryos were unlabeled. Grafts from labeled donors to unlabeled host embryos were made at early neural tube stages before out‐growth of any nerve fibers had started (Jacobson and Huang, 1985). Routes taken by labeled nerve fibers growing into unlabeled CNS were observed at later stages, and the rates of nerve fiber elongation were calculated. Labeled nerve fibers were normal in appearance, and elongated without branching, at normal rates (22–71 μm/h). In head‐to‐head and tail‐to‐tail embryos and in embryos with inverted spinal cord grafts, nerve fibers continued elongating without branching in the direction opposite to normal in the CNS. Many fibers reached lengths that were far greater than normal. No reorientation of such maldirected nerve fibers was seen. These results indicate that nerve fiber elongation is not guided by axially polarized pathway cues or markers and that nerve fibers do not grow to predetermined lengths. However, neurites preferred to grow along streotyped nerve fiber pathways even when forced to grow in the wrong direction or when confronted with nonneural tissue.
Brain cells that command sexual behavior in the snail Helix aspersa
Authors: Chase Ronald
Published: May 2005

Evidence is presented indicating that the mesocerebrum of the terrestrial snail, Helix aspersa, has a major role in the control of sexual behavior. Morphological and physiological results demonstrate a right‐sided bias in the mesocerebrum that is consistent with the fact that sexual behavior is executed almost entirely on the animal's right side. Thus, the right lobe has 23% more neurons than the left lobe, and they are 24% larger. Excitatory synaptic inputs derive predominately from neurons on the right side. The axons of right‐side mesocerebral neurons go to the right pedal ganglion almost without exception, and even the axons of left‐side neurons travel mostly in right‐side connective nerves. Direct evidence for a role of the mesocerebrum in commanding sexual behavior comes from experiments with electrical stimulation.

Extracellular stimulation of the right mesocerebrum, but not the left mesocerebrum, resulted in movements of the “love dart” sac and the penis. Intracellular stimulation of neurons in the right mesocerebrum evoked measurable movements of either the dart sac or the penis, or both, in 17% of the cells tested. The latencies ranged between 5 and 50 s. In an intact animal, these movements would cause a release of the dart and an eversion of the penis. The motor effects were mediated through the right cerebropedal connective and the pedal nerve NCPD, with the motorneurons probably situated in the right pedal ganglion.
Control of leech swimming activity by the cephalic ganglia
Authors: Brodfuehrer Peter D. , Friesen W. Otto
Published: May 2005

We investigated the role played by the cephalic nervous system in the control of swimming activity in the leech, Hirudo medicinalis, by comparing swimming activity in isolated leech nerve cords that included the head ganglia (supra‐ and subesophageal ganglia) with swimming activity in nerve cords from which these ganglia were removed. We found that the presence of these cephalic ganglia had an inhibitory influence on the reliability with which stimulation of peripheral (DP) nerves and intracellular stimulation of swim‐initiating neurons initiated and maintained swimming activity. In addition, swimming activity recorded from both oscillator and motor neurons in preparations that included head ganglia frequently exhibited irregular bursting patterns consisting of missed, weak, or sustained bursts. Removal of the two head ganglia as well as the first segmental ganglion eliminated this irregular activity pattern. We also identified a pair of rhythmically active interneurons, SRN1, in the subesophageal ganglion that, when depolarized, could reset the swimming rhythm. Thus the cephalic ganglia and first segmental ganglion of the leech nerve cord are capable of exerting a tonic inhibitory influence as well as a modulatory effect on swimming activity in the segmental nerve cord.
Aminergic cellular organization in the gills of Aplysia species
Authors: Kurokawa Makoto , Kuwasawa Kiyoaki , Otokawa Minoru , Yamada Chifumi , Kobayashi Hideshi
Published: May 2005

The constituent elements of the gills of Aplysia kurodai and A. juliana were examined for the presence of biogenic amines using histochemical, immunocytochemical, and HPLC techniques. Aminergic elements were revealed by glyoxylic acid‐induced fluorescence in the branchial nerve, branchial ganglion, branchial vessels, and pinnules in both species. Three types of fluorescent cells were found in the neural plexus of the gill in each species. Two of them might be sensory neurons. Although HPLC analysis showed the presence of serotonin and dopamine in all gill structures including fluorescent neural elements, there were regional differences in concentrations of the monoamines. It was noted in the pinnules that there was a much higher concentration of dopamine than serotonin. Serotonin immunocytochemistry revealed neural processes which were immunoreactive to antiserotonin antibody, but serotonin immunoreactivity could not be found in a population of branchioganglionic neuron (BGN) somata. Serotonergic elements in the ganglion may be processes of the central ganglion, while dopaminergic elements may be processes of neurons in the neural plexus, located beyond the branchial ganglion. BGNs were activated by bath‐applied dopamine and serotonin. These results suggest that dopaminergic sensory inputs from the neural plexus and serotonergic descending inputs from the abdominal ganglion may be among the inputs received by BGNs.

It was found that serotonin depressed excitatory junctional potentials in muscle cells of the efferent branchial vessel, which were induced by an identified neuron of the abdominal ganglion. The aminergic cellular organization of the gill may involve serotonergic presynaptic‐inhibitory fibers arising from the abdominal ganglion.
Multiple cAMP‐binding proteins in Aplysia tissues
Authors: Palazzolo Michael , Katz Flora , Kennedy Timothy E. , Schwartz James H.
Published: May 2005

While it is recognized that cAMP is able to regulate distinct cellular processes differentially, the molecular basis for the diversity of its effects remains unclear. Using photoaffinity labeling with 32P‐8 azido‐cAMP and two‐dimensional gel analysis, we have identified 26 electrophoretic variants of cAMP‐binding proteins in the six different tissues of the marine mollusc Aplysia californica sampled. Some of these proteins are found in most tissues, others only in a few; still others appear to be restricted to a single tissue. All of these proteins bind cAMP specifically. The two‐dimensional polyacrylamide gel electrophoretic patterns of binding proteins seen in the different tissues fall into three classes. One pattern is shared by the nervous system and embryos. The second is found in muscular tissues (heart, buccal muscle, siphon, and gill). The third pattern is specific to sperm. The presence of distinct subsets of cAMP‐binding proteins in different tissues suggests that at least some of the diversity in cAMP's regulatory function may result from diversity in the proteins that bind it.
Activity‐dependent tuning and the NMDA receptor
Authors: Debski Elizabeth A. , Cline Hollis T. , Constantine‐Paton Martha
Published: May 2005

The refinement of the topographic map of visual space within the optic tectum of the frog is activity‐dependent. The use of the three‐eyed frog preparation to assay the operation of this fine‐tuning mechanism indicates that this process is mediated by the NMDA receptor: Chronic in vivo treatment with APV, an NMDA antagonist, disrupts the segregation of retinal afferents into eye‐specific zones while NMDA treatment sharpens this pattern. This latter effect is accompanied by a decreased sensitivity of the system to applied NMDA. Activation of the NMDA receptor may mediate the fine‐tuning mechanism by initiating the stabilization of appropriate synapse. The requirements for NMDA receptor activation necessitate the convergence of terminals carrying correlated activity patterns. Such patterns of activity are provided by ganglion cells whose cell bodies lie near one another in the retina, and who should therefore, in an accurate visual map, terminate near one another in the tectum. Synapses from ganglion cells who do not neighbor one another in the retina have uncorrelated firing patterns and therefore do not activate the NMDA receptor. These synapses then would not be stabilized relative to one another.

In addition to organizing the retinal projection, NMDA receptor activation may also modulate retinal ganglion cell arbor morphology, since chronic in vivo APV or NMDA treatments decrease arbor density. These results are discussed in terms of the effect of NMDA receptor activation on branch initiation and the rate of branch retraction.
Specification of synaptic connections between sensory and motor neurons in the developing spinal cord
Authors: Frank Eric , Mendelson Bruce
Published: May 2005

Experimental studies of mechanisms underlying the specification of synaptic connections in the monosynaptic stretch reflex of frogs and chicks are described. Sensory neurons innervating the triceps brachii muscles of bullfrogs are born throughout the period of sensory neurogenesis and do not appear to be related clonally. Instead, the peripheral targets of these sensory neurons play a major role in determining their central connections with motoneurons. Developing thoracic sensory neurons made to project to novel targets in the forelimb project into the brachial spinal cord, which they normally never do. Moreover, these foreign sensory neurons make monosynaptic excitatory connections with the now functionally appropriate brachial motoneurons. Normal patterns of neuronal activity are not necessary for the formation of specific central connections. Neuromuscular blockade of developing chick embroys with curare during the period of synaptogenesis still results in the formation of correct sensory‐motor connections. Competitive interactions among the afferent fibers also do not seem to be important in this process. When the number of sensory neurons projecting to the forelimb is drastically reduced during development, each afferent still makes central connections of the same strength and specificity as normal. These results are discussed with reference to the development of retinal ganglion cells and their projections to the brain. Although many aspects of the two systems are similar, patterned neural activity appears to play a much more important role in the development of the visual pathway than in the spinal reflex pathway described here.
Competitive and positional cues in the patterning of nerve connections
Authors: Fraser Scott E. , Perkel Donald H.
Published: May 2005

The visual system of lower vertebrates has served as an important testing ground for the mechanisms that generate topographic neuronal connections. During both the outgrowth and the regeneration of the optic nerve, a smoothly ordered map of the retina is formed on its major target, the optic tectum (the retinotectal projection). Experiments performed on this projection have offered support for a variety of mechanisms, including the matching of positional cues in the retina and tectum, the guidance of nerve fibers by interactions between fibers, competition for synaptic space, and the refinement of connections based on neuronal activity. Unfortunately, individual experiments that support any one of these mechanisms have been taken at times as evidence against the involvement of any other mechanism; for example, experiments demonstrating the importance of positional cues have been thought mistakenly to indicate that activity‐based interactions are unimportant. Computer simulations, in which multiple, somewhat opposed, mechanisms are allowed to operate in concert demonstrate that such a hybrid model is able to generate a full range of experimental results. More importantly, the elimination of any one of the mechanisms renders the model unable to fit entire classes of findings. Thus, the patterning of the retinotectal projection is best viewed as a process in which the optic nerve terminals attempt to satisfy multiple constraints in selecting their target sites.
Synaptic dynamics at the neuromuscular junction: Mechanisms and models
Authors: Van Essen David C. , Gordon H. , Soha J. M. , Fraser S. E.
Published: May 2005

During development, the neuromuscular junction passes through a stage of extensive polyinnervation followed by a period of wholesale synapse elimination. In this report we discuss mechanisms and interactions that could mediate many of the key aspects of these important developmental events. Our emphasis is on (1) establishing an overall conceptual framework within which the role of many distinct cellular interactions and molecular factors can be evaluated, and (2) generating computer simulations that systematically test the adequacy of different models in accounting for a wide range of biological data. Our analysis indicates that several relatively simple mechanisms are each capable of explaining a variety of experimental observations. On the other hand, no one mechanism can account for the full spectrum of experimental results. Thus, it is important to consider models that are based on interactions among multiple mechanisms. A potentially powerful combination is one based on (1) a scaffold within the basal lamina or in the postsynaptic membrane which is induced by nerve terminals and which serves to stabilize terminals by a positive feedback mechanism; (2) a sprouting factor whose release by muscle fibers is down‐regulated by activity and perhaps other factors; and (3) an intrinsic tendency of motor neurons to withdraw some connections while allowing others to grow.
Role of postnatal androgens in sexual differentiation of the lordosis‐inhibiting effect of central injections of cholecystokinin
Authors: Ulibarri Catherine , Popper Paul , Micevych Paul E.
Published: May 2005

The neuropeptide cholecystokinin (CCK) inhibits lordosis behavior when infused into the ventromedial nucleus of the hypothalamus (VMN) of female rats and has no effect when infused into the VMN of male rats. To test whether this sex difference develops under the control of perinatal steroids, male rats were castrated or given sham surgeries within 3 h of birth and female rats were injected with either 0 or 100 μg testosterone propionate on postnatal day 5. As adults, these rats were castrated as necessary, implanted with unilateral cannulae directed at the VMN, and tested for their ability to display female sexual behavior and to respond to CCK. Neonatal castration of males prevented defeminization of this response. When treated with 5 μg estradiol benzoate (EB), neonatally castrated males showed both lordosis behavior and a profound inhibition of that behavior after infusions of CCK. Neonatally castrated males did not display lordosis behavior when treated with 2 μg EB. Control males showed no lordosis behavior and, therefore, no response to CCK. Both doses of EB induced lordosis behavior in neonatally androgenized females. Significantly, these neonatally androgenized females were less responsive to CCK's inhibition of lordosis and were also anovulatory. These results imply that androgens alter the development of CCK responsive circuits as well as defeminize cyclic gonadotropin release. Levels of 125I‐sCCK‐8 binding in the VMN were correlated closely with an individual's ability to respond to sCCK‐8. In summary, the inhibition of female sexual behavior caused by exogenously administered CCK in normal adult female rats appears to be controlled at least partially by levels of CCK receptors in the VMN and to differentiate under the control of perinatally present testosterone.
Cytochrome oxidase activity as a measure of synaptogenesis by mutifunctional neuron L7 of Aplysia
Authors: Ambron Richard T. , Dotty Stephen B. , Goldberg Daniel J. , Smedman Marilyn
Published: May 2005

Neuron L7 of the marine mollusc, Aplysia californica, is unique in that it innervates five different target tissues in the animal. We show that when L7 is grown in vitro with two of these targets, that is, muscle cells isolated from the auricle or the gill vein, newly formed L7 neurites contact the muscle cells. Chemical synapses are formed since intracellular stimulation of L7 elicits contraction of individual muscle cells. Interestingly, auricle muscles are also innervated by neuron RBhe and co‐cultures of RBhe and auricle muscle cells also exhibit synapse formation. To explore the molecular basis for synaptogenesis between L7 and its targets, it would be useful to quantify the extent of synapse formation in vitro, that is, to determine how many muscle cells can be innervated by a single L7. We show that this can be attained by staining for cytochrome oxidase activity. Cultures of auricle and gill vein muscles were exposed to the appropriate neurotransmitter in order to elicit contraction. The cells were then fixed and stained. In both cases, only cells that contracted were stained and electron microscopy showed reaction product associated with the cristae of mitochondria. When this procedure was applied to cultures of L7 and muscle cells, 38 ± 2.8% (S.E.M.;n=7) of the cells on the neurites were stained and therefore responded to L7 stimulation. Thus, part of the L7‐RBhe circuit can be assembled in vitro and the extent of synaptogenesis can be accurately quantitated.
Agrin induces α‐actinin, filamin, and vinculin to co‐localize with AChR clusters on cultured chick myotubes
Authors: Shadiack Annette M. , Nitkin Ralph M.
Published: May 2005

Agrin induces discrete high‐density patches of acetylcholine receptors (AChRs) and other synaptic components on cultured myotubes in a manner that resembles synaptic differentiation. Furthermore, agrin‐like molecules are present at developing neuromuscular junctions in vivo. This provides us with a unique opportunity to manipulate AChR patching in order to examine the role of cytoskeletal components. Cultured chick myotubes were fixed and labeled to visualize the distributions of actin, α‐actinin, filamin, tropomyosin, and vinculin. Overnight exposure to agrin caused a small amount of α‐actinin, filamin, and vinculin to reorganize into discrete clusters. Double‐labeling studies revealed that 78% of the AChR clusters were associated with detectable concentrations of filamin, 70% with α‐actinin, and 58% with vinculin. Filamin even showed congruence to AChRs within clustered regions. By contrast, actin (visualized with fluorescein‐phalloidin) and tropomyosin did not show specific associations with agrin‐induced AChR clusters. The accumulation of cytoskeletal components at AChRs clusters raised the possibility that cytoskeletal rearrangements direct AChR clustering. However, a time course of agrin‐induced clustering that focused on filamin revealed that most of the early AChR clusters (3–6 h) were not associated with detectable amounts of cytoskeletal material. The accumulation of cytoskeletal material at later times (12–18 h) may imply a role in maintenance and stabilization, but it appears unlikely that these cytoskeletal elements initiate AChR clustering on myotubes.
Remodeling of retinal ganglion cell dendrites in the absence of action potential activity
Authors: Wong Rachel O. L. , Herrmann Kathrin , Shatz Carla J.
Published: May 2005

The dendrites of ganglion cells in the retina have an excess number of spines and branches that are normally lost during the first postnatal month of development. We investigated whether this dendritic remodeling can be prevented when the action potential activity of ganglion cells is abolished by chronic intraocular injections of tetrodotoxin (TTX) during the first 4 or 5 postnatal weeks in the cat. Dendritic tree morphologies of alpha and beta ganglion cells from TTX‐treated, non‐TTX‐treated (contralateral eye), and normal control retinae were compared after intracellular filling with Lucifer yellow. Qualitative observations and quantitative measurements indicate that TTX treatment does not prevent the normally occurring loss of spines and dendritic branches. Indeed, the dendritic trees of both alpha and beta cells in TTX injected eyes actually have even fewer spines and branches than normal cells at equivalent ages. However, because the total dendritic lengths of these cells are also reduced after TTX blockade, spine density is indistinguishable from untreated animals at the same age. In addition, although dendritic field areas are not altered with treatment, the complexity of the dendritic trees is reduced. These observations suggest that dendritic remodeling can occur in the absence of ganglion cell action potential activity. Thus, the factors that influence the dendritic and axonal development of retinal ganglion cells must differ, because similar TTX treatment during the period of axonal remodeling does have profound effects on the final pattern of terminal arborizations.
Isolation and partial characterization of neuropeptides that mimic prolonged inhibition produced by bag cell neurons in Aplysia
Authors: Eliassen James C. , Rajpara Sanjay M. , Mayeri Earl
Published: May 2005

The bag cell neurons of the marine mollusk Aplysia are part of a neural system that utilizes four neuropeptides as neurotansmitters. The peptides, derived from the egglaying hormone/bag cell peptide (ELH/BCP) precursor protein, are released during a 20‐min burst discharge of the bag cells and produce several types of responses in various abdominal ganglion neurons. In the identified neurons L3 and L6, bag cell activity produces prolonged inhibition that lasts for more than 2 h. One of the bag cell peptides, alpha‐BCP, mediates an early component of the inhibition in these neurons. To identify the co‐transmitter mediating the prolonged component of inhibition, we purified material from an acid extract of abdominal ganglia using molecular sizing high‐pressure liquid chromatography (HPLC) on TSK 250‐125 followed by two steps of reverse‐phase HPLC on C4 or C18. We isolated three inhibitory factors that mimic the prolonged component of inhibition. Mass spectroscopy and partial amino acid sequence analysis indicate one factor is ELH [2‐36], that is, ELH that lacks the first, N‐terminal amino acid. This inhibitory activity was similar in potency to that of ELH and is the first to be described for an ELH related peptide. The two other factors were approximately 3,300 and 4,700 Da and were effective at 10‐ and 50‐fold lower concentration, respectively, than ELH or its fragment. Amino acid composition analysis suggests that they are not derived from the ELH/BCP precursor protein. The 4,700 Da factor is effective at the lowest concentration and produces an effect that lasts as long as 100 min. Therefore, it is the best candidate for the true inhibitory transmitter. Because the inhibited neurons in nervate the kidney, the function of prolonged inhibition may be to regulate kidney function during egg laying.
Interactions of Schwann cells with neurites and with other Schwann cells involve the calcium‐dependent adhesion molecule, N‐cadherin
Authors: Letourneau Paul C. , Roche Florence K. , Shattuck Terri A. , Lemmon Vance , Takeichi Masatoshi
Published: May 2005

During embryogenesis, Schwann cells interact with axons and other Schwann cells, as they migrate, ensheath axons, and participate in organizing peripheral nervous tissues. The experiments reported here indicate that the calcium‐dependent molecule, N‐cadherin, mediates adhesion of Schwann cells to neurites and to other Schwann cells. Cell cultures from chick dorsal root ganglia and sciatic nerves were maintained in media containing either 2mM Ca++ or 0.2 mM Ca++, a concentration that inactivates calcium‐dependent cadherins. When the leading lamellae of Schwann cells encountered migrating growth cones in medium with 2 mM Ca++, they usually remained extended, and the growth cones often advanced onto the Schwann cell upper surface. In the low Ca++ medium, the frequency of withdrawal of the Schwann cell lamella after contact with a growth cone was much greater, and withdrawal was the most common reaction to growth cone contact in medium with 2 mM Ca++ and anti‐N‐cadherin. Similarly, when motile leading margins of two Schwann cells touched in normal Ca++ medium, they often formed stable areas of contact. N‐cadherin and vinculin were co‐concentrated at these contact sites between Schwann cells. However, in low Ca++ medium or in the presence of anti‐N‐cadherin, interacting Schwann cells usually pulled away from each other in a behavior reminiscent of contact inhibition between fibroblasts. In cultures of dissociated cells in normal media, Schwann cells frequently were aligned along neurites, and ultrastructural examination showed extensive close apposition between plasma membranes of neurites and Schwann cells. When dorsal root ganglia explants were cultured with normal Ca++, Schwann cells migrated away from the explants in close association with extending neurites. All these interactions were disrupted in media with 0.2 mM Ca++. Alignment of Schwann cells along neurites was infrequent, as were extended close apposition between axonal and Schwann cell plasma membranes. Finally, migration of Schwann cells from ganglionic explants was reduced by disruption of adhesive contact with neurites. The addition of antibodies against N‐cadherin to medium with normal Ca++ levels had similar effects as lowering the Ca++ concentration, but antibodies against the neuronal adhesive molecule, L1, had no effects on interactions between Schwann cells and neurites.
Lack of evidence for cell death among avian spinal cord interneurons during normal development and following removal of targets and afferents
Authors: McKay Sharen E. , Oppenheim Ronald W.
Published: May 2005

Chick embryos and posthatched chicks were examined at several ages for the presence of pyknotic interneurons in the lumbar spinal cord. Because no pyknotic interneurons were found, direct cell counts of healthy interneurons were carried out and a comparison made between early‐and late‐stage embryos and hatchlings. There was no decrease in the number of interneurons in the ventral intermediate gray matter of the spinal cord between embryonic day (E) 8 and 2 weeks posthatching (PH) or in the dorsal horn between E10 and 2 weeks PH. To study whether interneuron survival is regulated by targets or afferents, a situation known to exist in other developing neural populations, early embryos were subjected to (1) removal of one limb, resulting in the loss of lateral motor column motoneurons and dorsal root ganglion sensory afferents; (2) transection of the thoracic spinal cord, thereby removing both descending afferents and rostral targets of spinal interneurons, or (3) a combination of the two operations. No reductions in interneuron numbers were found as a result of these operations. Furthermore, morphometric analysis also revaled no change in neuronal size following these experimental manipulations. By contrast, there was a slight decrease in the total area of spinal gray matter that was most prominent in the dorsal region following limb bud removal. Our results indicate (1) that spinal interneurons fail to exhibit the massive naturally occurring death of postmitotic neurons that has been observed for several other populations of spinal neurons, and (2) spinal interneurons appear to be relatively resistant to induced cell death following the removal of substantial numbers of afferent inputs and targets.
Clonal cells from embryonic retinal cell lines express qualitative electrophysiological differences
Authors: Lenzi David , Radke Kathryn , Wilson Martin
Published: May 2005

Cells from the embryonic quail retina were immortalized with the v‐mil oncogene and cloned by limiting dilution. Their phenotype was examined using the whole‐cell patch clamp method. Three membrane currents, Ik(IR), INa and IK, were found at different frequencies within a sample of 170 cells drawn from a large clone. Nearly all combinations of these three markers were found and the frequency of combinations showed that the markers assorted independently. Examination of clones of less than 10 cells showed that heterogeneity originates with a high probability within clones, arguing that chromosomal mutation, for example, is unlikely to account for phenotypic diversity. A possible explanation is that phenotypic differences between cells might reflect the local exchange of instructive signals. If so, then the genes for the three phenotypic markers are controlled independently.
Phosphatases modulate transmission and serotonin facilitation at synapses: Studies with the inhibitor okadaic acid
Authors: Swain James E. , Robitaille Richard , Dass Gavin R. , Charlton Milton P.
Published: May 2005

We examined the role of phosphatases in synaptic transmission using the permeant phosphatase inhibitor okadaic acid (OA). In the crayfish neuromuscular junction (NMJ), postsynaptic effects including increases in input resistance occurred at doses greater than 5 μM OA. At lower doses (0.5–5 μM) the effects were solely presynaptic and transmitter release increased over three‐fold despite small reductions in amplitude and duration of presynaptic action potentials. Potentiating effects of serotonin on transmitter release, Which depend on phosphorylation, were increased by OA. Frequency facilitation was reduced but its decay was not affected. In frog NMJs, OA increased spontaneous and evoked release two‐fold through presynaptic mechanisms. An inactive analog of OA, OA tetra‐acetate, had no effect on transmitter release at frog and crayfish NMJ. Therefore, phosphatases have a strong modulating influence on synaptic transmission.
Reinnervation of murine muscle following fetal sciatic nerve transection
Authors: Mallonga Rosa L. , Ontell Marcia
Published: May 2005

A technique is reproted that permits transection of the sciatic nerve of mouse fetuses without interfering with fetal viability. Sciaticotomy was performed on Swiss Webster mice at day 17 of gestation; the contralateral side served as a control. Six weeks later the extensor digitorum longus (EDL) muscles on both sides were injected with horseradish peroxidase (HRP). Examination of the lumbar spinal cord revealed that while a substantial number of motor neurons in the region of the spinal cord giving rise to the sciatic nerve died, the EDL muscle did become reinnervated. The size of the EDL motor neuron pool on the denervated‐reinnervated side was ∼43% of that seen on the control side. While the control EDL motor neuron pool was located in lumbar segments L3–L5, the location of the pool to the denervated‐reinnervated EDL was shifted cranially to L2–L4. Denervated‐reinnervated EDL muscles were analyzed immunohistochemically to study the effect of fetal denervation on the neuronal cell adhesion molecule (N‐CAM) expression. At 2 weeks postnatal, N‐CAM immunoreactivity in control muscle was segregated to the motor end plate region, while fetally denervated muscle continued to express N‐CAM along the length of the sarcolemma. Thus fetally denervated muscle does not develop the same pattern of N‐CAM expression as normal, innervated muscle. By 6 weeks of age, the denervated‐reinnervated muscle showed the same level and distribution of N‐CAM immunoreactivity as did age‐matched control muscle, indicating that most, if not all, of its myofibers had been reinnervated.