bluuebunny/crossref_metadata_2025 huggingface dataset:
Aziridines. IX—Mise en évidence du phénomène d'inversion de l'azote dans les aziridines secondaires par RMN de 13C
Authors: Martino R. , Mison P. , Wehrli F. W. , Wirthlin T.
Published: May 2005

L'effet d'inversion de l'azote sur les déplacements chimiques en Résonance Magnétique Nucléaire de carbone‐13 a été observé avec la diphényl‐2,2‐aziridine, la diméthyl‐2,2 diphényl‐3,3 aziridine et la phényl‐2 méthyl‐2 aziridine, sous des conditions d'échange lent du proton du NH. De plus, nous avons pu déceler des variations de déplacements chimiques dǔes à un échange isotopique lent HD.
Long range 13C1H coupling constants. III—methylpyridines
Authors: Takeuchi Yoshito
Published: May 2005

Proton coupled carbon‐13 NMR spectra of eleven mono‐, di‐ and trimethylpyridines were analysed on a first order basis. The long range 13C1H coupling constants are similar to those observed for pyridine and cyanopyridines.
Carbon‐13 nuclear magnetic resonance spectra of some methyl and phenyl substituted 2H‐azirines
Authors: Isomura Kazuaki , Taniguchi Hiroshi , Mishima Masaaki , Fujio Mizue , Tsuno Yuho
Published: May 2005

Carbon‐13 n.m.r. spectra have been obtained for some methyl and phenyl substituted 2H‐azirines. The higher field resonance of C‐2 than that of the corresponding aziridine carbon is interpreted in terms of ring strain. Substituent effects on the chemical shifts of the azirine ring carbons are discussed. A set of additivity parameters for the methyl and phenyl groups are obtained which can be used for the calculation of the chemical shifts of the azirine ring carbons. The substituent effect of an azirine ring on the chemical shift of benzene is also discussed in comparison with those of some other substituents. A high degree of s character (48.5%) in the exocyclic orbital of C‐3 is indicated by a large J(13C‐3,H) value (242.5 Hz).
Carbon‐13 n.m.r. spectroscopy of some Strychnos alkaloids
Authors: Verpoorte R. , Hylands P. J. , Bisset N. G.
Published: May 2005

13C N.m.r. spectra have been determined for strychnine and a series of fourteen derivatives. The assignments are based on previously established data and on off‐resonance decoupled spectra. The shifts resulting from the alterations in molecular structure are discussed and explained, in part, as a consequence of conformational changes. This detailed study indicates that changes are required in some previously published assignments.
Application of 13C and 15N spectroscopy to the study of electronic delocalization in NN bonds: Nitrosamines, hydrazones, triazenes and related protonated species
Authors: Gouesnard J. P. , Martin G. J.
Published: May 2005

13C and 15N spectroscopies at natural abundance have been applied to the study of nitrogen lone‐pair delocalization in NN containing compounds: nitrosamines, nitramines, hydrazines, hydrazones and triazenes. Structure‐chemical shift correlations have been derived for nitrosamines; the 13C upfield effect of a γ substituent has been used for assigning the configuration of both diastereoisomers in N,N‐unsymmetrically substituted nitrosamines. Equations have been computed which permit the prediction of the electronic delocalization, expressed in terms of free enthalpy of activation ΔG, as a function of δ15N and of the length of the NN bond. 15N spectroscopy has also been applied to the study of the protonated species of nitrosamines and of acceptor‐donor complexes of nitrosamines with Lewis acids. The behaviour of such NN containing compounds is compared to that of amides.
An NMR structural study of 2‐fluoropyridine dissolved in a nematic solvent
Authors: Burnell E. E. , Marshall A. G. , Roe D. C.
Published: May 2005

The proton NMR spectrum of 2‐fluoropyridine partially oriented in a nematic phase has been analyzed, and the geometry of the proton and fluorine skeleton and the order matrix have been determined. The structure does not differ significantly from that of pyridine in a nematic solvent, and the largest positive order parameter axis lies approximately along the CF bond direction in the molecule.
Carbon‐13 nuclear magnetic resonance spectra and conformations of cis,cis‐1,5‐cyclooctadiene monoepoxide and cis, syn,cis‐1,5‐cyclooctadiene diepoxide
Authors: Anet Frank A. L. , Easton N. Roy , Yavari Issa
Published: May 2005

The natural‐abundance 13C NMR spectra of cis,cis‐1,5‐cyclooctadiene monoepoxide and cis,syn,cis‐1,5‐cyclooctadiene diepoxide have been investigated over the temperature range of – 10 to – 180°C. Whereas the spectra of the former showed no dynamic NMR effect, two different conformations in the ratio of 3:1 were observed at low temperatures for the latter. The free‐energy barrier (ΔG≠) for conversion of the major conformation to the minor conformation is calculated to be 5.9°0.2 kcal mol−1 from a line‐shape analysis of spectra obtained at intermediate temperatures. It is shown that cis,syn,cis‐1,5‐cyclooctadiene diepoxide exists in solution in chair (major) and in twist‐boat (minor) conformations of slightly different energies. Interconversion paths between these conformations are discussed. The monoepoxide is suggested to have a twist‐boat conformation that is rapidly pseudorotating via a boat conformation even at – 180°C.
Calculation of 1H chemical shifts of [n]annuleno[m]annulenes and [n]annulenyl[m]annulenes
Authors: Vogler H.
Published: May 2005

The ring current and local anisotropic contributions to the 1H chemical shifts of [n]annuleno[m]annulenes and [n]annulenyl[m]annulenes with n, m = 12, 14, 18 and n, m = 13, 15 are calculated. The agreement between experimental and calculated shifts for the few known compounds is very good so that the predictions for the as yet unknown compounds are reliable. The effect of an annulene ring on the shifts of the protons at the other ring in these bicyclic compounds is discussed for several types of fusion of the two constituent annulenes.
1H‐, 31P‐ and 13C‐NMR spectra of some 2‐arylsulphonylamido‐2‐thiono‐5‐methyl‐1,3,2‐dioxaphospholanes
Authors: Barabás A. , Mureşan V. , Almási L.
Published: May 2005

Some 2‐arylsulphonylamido‐2‐thiono‐5‐methyl‐1,3,2‐dioxaphospholanes (1), containing two chiral centres, give NMR spectra in which splittings of the 1H and 13C signals of the 5‐methyl substituent and of the 31P signal indicate that they exist in an approximately 70:30% ratio of two racemic mixtures, Z and E respectively, diastereomeric to each other. These splittings were invariably observed for compounds 1a, containing a monosubstituted sulphonylamido group (Y = H) and various substituents at position 4′ of the aryl group, X = H, CH3, OCH3, F, CI and Br. The methylenic protons in position 4 of the phospholane ring are diastereotopic and therefore magnetically non‐equivalent. Benzene‐induced shifts were measured for the Z isomers of compounds 1a, X = H, F and for compound 1b, containing an N‐disubstituted sulphonylamido group (Y = CH3) and X = H; the tentative interpretation of these shifts places the more shielded diastereotopic methylene proton on the same side of the ring as the 5‐methyl substituent. The HP and HH coupling constants indicate that the preferred conformation of the dioxaphospholane ring should be a ‘twisted envelopey’ shape with the 5‐methyl substituent in the equatorial position.
A13C NMR investigation of restricted rotation and dimerization inp‐substituted nitrosobenzenes
Authors: Cox Richard H. , Hamada Masao
Published: May 2005

The barrier to internal rotation in a series ofp‐substituted nitrosobenzenes has been determined by means of variable temperature13C NMR. Substituent (X) effects on the barrier are similar to those observed for acetophenones and benzaldehydes. In addition, dimerization of the nitrosobenzenes was observed at low temperature for X = CH3, CI and H. The barrier height is discussed in terms of contributions from resonance effects.
Prediction of proton magnetic resonance shifts: The dependence on hydrogen charges obtained by iterative partial equalization of orbital electronegativity
Authors: Gasteiger Johann , Marsili Mario
Published: May 2005

Proton chemical shifts correlate linearly with charges on hydrogen obtained by a method for iterative partial equalization of orbital electronegativity. The compounds studied comprise a wide variety of classes of molecules; all points fall on a single correlation line, showing the general importance of electronic effects in proton chemical shifts and the physical significance of the atomic charges. On the other hand, as there is no general correlation between charges on carbon and on hydrogen atoms, proton chemical shifts cannot be used as probes for charge densities on carbon atoms. Deviations from the correlation line can be attributed to anisotropy effects and provide an estimate for their magnitude.
The conformations of bicyclo[3.1.0]hexane derivatives by 1H and 13C NMR
Authors: Rees John C. , Whittaker David
Published: May 2005

The 1H and 13C spectra of bicyclo[3.1.0]hexanes and thujanes have been recorded and assigned. Application of the Karplus equation has yielded dihedral angles, and a computer calculation of the angle of ring buckle as a function of the main dihedral angles has been carried out. The calculated angles of ring buckle agree well with known values in the bicyclo[3.1.0]hexanes, but for 1‐methylbicyclo[3.1.0]hexanes and thujanes the results are not self consistent. It is suggested that the bridgehead substituent causes the boat to twist, although the twist can be reduced by an axial methyl substituent on C‐4.
14N nuclear quadrupole resonance in nicotinic acid derivatives
Authors: Kim N. S. , Bray P. J.
Published: May 2005

Nitrogen‐14 nuclear quadrupole resonance (NQR) spectra of nicotinic acid derivatives, known as antitumor agents, are reported and analyzed in the framework of the Townes and Dailey theory. A strong correlation exists between the charge difference σNC − π at the pyridinic nitrogen and the inhibition of acetylcholinesterase by nicotinic acid derivatives, in which the inhibition potency (pI50) increases as the charge difference σNC − π increases. There are significant differences between 14N NQR spectra for the pyridinic nitrogen sites of nicotinic acid and nicotinamide; these can be explained in terms of the differences in hydrogen bond lengths.
Carbon‐13 NMR spectroscopy of some pentacyclic triterpenoids
Authors: Patra Amarendra , Mitra Alok K. , Ghosh Saroj , Ghosh Amitava , Barua A. K.
Published: May 2005

Carbon‐13 NMR signal assignment of a number of polyoxygenated triterpenes of the olean‐12‐ene and urs‐12‐ene series, carried out by considering the changes in chemical shift produced by the change of oxygenation pattern(s), and using methyl oleanolate as a model, are reported.
Sulphur‐33 nuclear magnetic resonance studies of sulphur compounds with sharp resonance lines. 33S NMR spectra of some sulphones and sulphonic acids
Authors: Faure R. , Vincent E. J. , Ruiz J. M. , Léna L.
Published: May 2005

33S NMR spectra have been obtained in the FT mode for some sulphones and sulphonic acids. The investigated compounds show narrow resonance lines. In the case of sulphones, the range of 33S chemical shifts is sufficiently wide, i.e. the effects due to changes in substituents are significant enough to allow further use of the 33S NMR of sulphones for quantitative analysis in petroleum chemistry.
Carbon‐13 NMR spectra of a series of para‐substituted phenyl isothiocyanates. Linear free energy relationships for carbon‐13 substituent chemical shifts
Authors: Jones Ronald G. , Allen Grace
Published: May 2005

Carbon‐13 chemical shifts are reported for 16 para‐substituted phenyl isothiocyanates measured at 1 and 10 mol % in chloroform‐d solution. Data for the NCS group were not obtained at 1 mol %, but concentration effects for the other resonances were negligible. Hammett, dual substituent parameter (DSP) and DSP‐nonlinear resonance (DSP‐NLR) analyses were used to evaluate substituent effects on the substituent chemical shifts (SCS) for the ipso‐carbon (C‐1), C‐2, and the NCS carbon atoms. A good Hammett correlation was observed for C‐1 (νp+ = 8.1 ppm, r = 0.98 at 1 mol %) but was improved for the higher order correlations with the following results, DSP:ρ I = 5.4, ρR° = 22.2, r = 0.998; DSP‐NLR: ρI = 5.6, ρR° = 20.5, ϵ = −0.22, r = 0.999. The 10 mol % data were very similar except the value of ϵ was −0.26 and confirms the phenyl‐bonded NCS moiety as a mild electron acceptor substituent. Hammett correlations were unsuccessful for the C‐2 data, but fairly good results were obtained from the higher order analyses. For the 1 mol % data, DSP: νI = 1.6, νR° = −2.0, r = 0.976; DSP‐NLR: νI = 1.8, νR° = −2.6, ϵ = 1.1, r = 0.982. Excellent correlations were obtained for the 10 mol % NCS carbon data. Hammett: νp° = 6.2, r = 0.997; DSP: νI = 5.9, νR° = 7.0, r = 0.997; DSP‐NLR: νI = 5.8, νR° = 7.6, ϵ = 0.25, r = 0.997. The positive ν values in these three correlations contrast the negative values usually observed for carbonyl and thiocarbonyl carbons, and more closely parallel results previously reported for the β‐carbon of styrenes and benzylidene anilines with para‐substituents in the aniline ring.
The use of lanthanide‐induced shifts for conformational and structural studies of (R)‐MTPA (α‐methoxy‐α‐trifluoromethyl‐α‐phenylacetic acid) esters. 2—Complexes of the (R)‐MTPA esters of 4‐tert‐butylcyclohexanols with Eu(fod)3
Authors: Vanhoeck L. , Bossaerts J. , Dommisse R. A. , Lepoivre J. A. , Alderweireldt F. C.
Published: May 2005

It is shown that the complexation of the (R)‐MTPA (α‐methoxy‐α‐trifluoromethyl‐α‐phenylacetic acid) ester ofcis‐4‐tert‐butylcyclohexanol with Eu(fod)3is very similar to that of the correspondingtrans‐ester and ketones with Eu(fod)3. Further evidence is provided that the MTPA moiety exists as two different rotamers. The LIS technique, used as a tool for structure and conformation elucidation, was found by means of a Monte Carlo error analysis not to be dependent on small experimental errors.
Structural and spectral assignment of three forskolin‐like diterpenoids isolated from Plectranthus ornatus
Authors: Rijo Patrícia , Fátima Simões M. , Rodríguez Benjamín
Published: May 2005

Three labdane diterpenoids were isolated from an acetone extract of Plectranthus ornatus. Their structures, closely related to that of forskolin, were determined by NMR studies. Unambiguous and complete assignments of the 1H and 13C NMR chemical shifts for these substances are presented. The assignments are based on 2D shift‐correlated [1H, 1H‐COSY, 1H, 13C‐gHSQC‐1J (C,H), 1H, 13C‐gHMBC‐nJ (C,H) (n = 2 and 3)] and NOE experiments. Copyright © 2005 John Wiley & Sons, Ltd.
Habituation of the motion detectors of the crayfish optic nerve: Their relationship to the visually evoked defense reflex
Authors: Glantz Raymon M.
Published: May 2005

Examination of sustaining units, dimming units, and motion detectors under stimulus conditions associated with defense reflex habituation revealed that only the motion detectors exhibit a response decrement with stimulus repetition. Motion detector habituation was specific to the retinal locus of the repetitive stimulus and thus can provide a basis for the spatially specific component of defense reflex habituation. When stimulated at low repetition rates (2‐‐4 min) the motion detectors exhibited a time course of habituation and spontaneous recovery similar to that observed behaviorally. At high repetition rates (20/mm) the motion detectors exhibited a more rapid rate of habituation than was observed for the defense reflex. Simultaneous recordings of motion detector and cheliped levatory muscle activity revealed consistently significant and frequently substantial positive correlations. Both defense reflex and motion detector habituation were transiently reversed by treatment with the GABA antagonist, picrotoxin (1.8 2.8 mg kg body weight). The action of picrotoxin is likely to be mediated via mechanisms controlling the general level of arousal. It was concluded that the response variations of motion detectors subjected to repetitive stimuli contribute to the habituation of the visually evoked defense refle.
The morphology of cricket giant interneurons
Authors: Mendenhall Barbara , Murphey R. K.
Published: May 2005

Axonal iontophoresis of cobalt chloride was used to describe the morphology of the seven largest interneurons in the abdominal nervous system of the cricket Acheta domesticus. The somata of these neurons are all found in the terminal (5th) abdominal ganglion. This ganglion is derived from four primitive segmental ganglia (the 7th–10th primitive segments) and the morphology of the interneurons within this ganglion suggests that the neurons are derived from different primitive segments. Furthermore, some of the neurons appear to be serially homologous elements. Three aspects of the morphology support these suggestions: (1) soma position, (2) relative positions of commissural processes, and (3) the general shape and extent of dendritric fields.
Neuromuscular transmission in an insect visceral muscle
Authors: Orchard Ian , Lange Angela B.
Published: May 2005

The electrical properties of the muscles of locust oviduct have been examined using intracellular recordings. The muscle cells are both dye and electrically coupled. They possess a wide array of spontaneous electrical activity ranging from slow oscillations of membrane potential to action potentials. In addition to possessing spontaneous electrical activity, certain regions of the oviduct are under motor control. The amplitude of evoked excitatory junction potentials (EJPs) increased step wise revealing innervation from a maximum of three motor units. These EJPs underwent summation and facilitation, and reached a critical threshold at which point the membrane revealed an active response. Bath applied glutamate, aspartate, proctolin, and octopamine were tested for their ability to alter resting potential and EJPs. L‐glutamate (1.6 × 10−5 M and above) produced a dose‐dependent depolarization of membrane potential accompanied by a reduction in amplitude of EJPs. Although L‐aspartate resulted in similar effects, the concentrations required were higher than those for glutamate. Proctolin (6.3 × −11 M − 6.0 × 10−9 M) resulted in a dose‐dependent depolarization but had little or no effect on amplitude of EJPs. Application of D, L‐octopamine (3.2 × 10−5 M − 1.7 × 10−4 M) induced a small hyperpolarisation and a reduction in amplitude of EJP. It is suggested that contractions of locust oviduct appear to be regulated by a combination of a classical neurotransmitter such as glutamate, along with the neuromodulators octopamine and proctolin.
Differential time course of the response to axotomy induced by cut or crush in the leech AP cell
Authors: Matteoli Michela , Nencioni Brunetta , Pellegrino Mario
Published: May 2005

The time course of the reaction to axotomy in the leech AP cell was determined by measuring the duration of the spontaneous spikes at different times after the operation. The axotomy performed by section of the segmental roots containing the AP axon induced an increase of the spike duration, which persisted over 30 days. A different time course was found when the axotomy was performed by nerve crush: the changes in duration of the spontaneous spikes, which occurred during the early 2 weeks, were significantly reduced afterwards. Dye staining of some cells axotomized by crushing revealed that the reversion of the changes, which had been set up by axotomy, was in some cases concomitant with the reconnection between proximal and distal axon stumps. The section of a single axonal branch was never sufficient to affect the membrane properties of the AP cells.

It is concluded that the changes observed in axotomized AP cells are not produced by simple axonal injury and that the maintainance of normal properties in the somatic membrane requires the presence of at least part of the distal axon arborization.
Microtubule stability along mammalian peripheral nerves
Authors: Donoso J. Alejandro
Published: May 2005

Microtubule (MT) number, axonal area, and MT density were examined in unmyelinated axons of rat cervical vagus nerve. Study of nerve regions proximal (1–5 mm) and distal (35–40 mm) to the nodosum ganglion in controls (incubation at 37°C for 1 h) showed that the number of MT per axon is significantly less in distal than in proximal nerve regions. Cooling (incubation at 0°C for 1 h) caused a significant reduction in the number of MT per axon in both nerve regions. The unmyelinated axons from both nerve regions showed a comparable reduction in MT number by cooling, indicating that axonal MT stability to cold was not significantly different between these two nerve regions. In these nerves no detectable changes were found in cross‐axonal area of unmyelinated axons between distal and proximal nerve regions. In another experimental series, in distal nerve regions (35–40 mm from the nodosum ganglion) the number of MT was not further reduced in nerves incubated at 0°C by increasing the incubation time. Similar results were obtained from colchicine treated nerves (incubation at 37°C, with 10 mM colchicine for 1 and 2 h). Distal nerve regions (35–40 mm from the nodosum ganglion) showed a similar reduction in the number of MT per axon when nerves were incubated at 0°C or with colchicine, suggesting that this drug, as well as cold, may be affecting a similar population of axonal MT, i.e., MT susceptible to anti‐MT agents. These results indicate that approximately one‐half of the axonal MT are stable to cold as well as to colchicine in rat unmyelinated axons.
Changes in intra‐axonal calcium distribution following nerve crush
Authors: Mata Marina , Staple Julie , Fink David J.
Published: May 2005

We used the oxalate‐pyroantimonate method to demonstrate the ultrastructural distribution of calcium within rat sciatic nerve 4 h after a crush injury. In normal nerve there are discrete gradients of axoplasmic calcium precipitate with the amount of precipitate decreasing in the axoplasm beneath the Schmidt Lantermann clefts and in the paranodal regions at the node of Ranvier. Near the crush site a marked increase in endoneurial and intra‐axonal calcium precipitate correlated with morphologic evidence of axonal degeneration. More distant from the crush site, both in the distal segment destined to degenerate and in the proximal segment destined to regenerate, the most prominent finding was a loss of the normal gradient of precipitate beneath the Schmidt Lantermann clefts. The calcium influx at the crush site corresponds to the known role of calcium in triggering degeneration. The alterations in the distal axon may be an early stage leading to degeneration. Alteration in calcium distribution in the proximal nerve stump may play a role in the regulation of the response to injury.
Discriminative behavior and pavlovian conditioning in the mollusc Pleurobranchaea
Authors: Mpitsos George J. , Cohan Christopher S.
Published: May 2005

The buccal motor system in the sea slug Pleurobranchaea californica is multifunctional; similar sets of neurons and muscles generate different behaviors through similar electrophysiological motor patterns. Such multifunctional systems compromise the traditional practice of identifying a motor pattern and then using that pattern to indicate the behavior in reduced preparations. We address this issue in a series of experiments leading to the comparison of differential Pavlovian conditioning in whole animals with the conditioned behavior of the same animals during electrophysiological recording. Because differential conditioning requires two conditioned stimuli (CSs), we show here that each of two CSs activated the conditioned response from animals after they received the stimulus (CS+) paired with an unconditioned stimulus (UCS). Conditioning sessions consisted of 5 training trials with a 2‐h intertrial interval. In one study, experimental animals received a 60‐s CS+, derived from beer (Sbr), paired with a 50‐s electrical shock UCS whose onset occurred 10 s after the CS+ onset; control animals received the Sbr and UCS explicitly unpaired. In a second study, animals received similar procedures as in the first but with a CS+ consisting of squid homogenate (Ssq). Tests with both CSs showed that animals did not discriminate between Sbr and Ssq before beginning conditioning, but did so afterward. Experimental animals exhibited robust food aversion (withdrawal and suppressed feeding) to the CS+, but retained strong appetitive responses to the CS they did not receive in training; response thresholds to the CS+ changed as much as 1000‐fold by comparison to the preconditioning values. Control animals exhibited similar though significantly smaller behavioral changes as the experimental animals. Both stimuli evoked associatively learned responses, but Sbr produced greater experimental‐control differences than Ssq did. Two accompanying papers show the results of using both CSs in differential conditioning, and describe the behavioral/electrophysiological comparisons.
Convergence in a distributed nervous system: Parallel processing and self‐organization
Authors: Mpitsos George J. , Cohan Christopher S.
Published: May 2005

The present findings show that the motor system of the carnivorous sea slug Pleurobranchea californica consists of parallel, distributed, and interconnected neuronal channels by which motor activity may emerge from the dynamics of the system rather than from “switchboard” circuitry. The findings are shown primarily through the properties of the buccal‐cerebral neurons (BCNs) that extensively converge and diverge monosynaptically and polysynaptically onto brain motoneurons, providing them with drive and patterned activity. The motoneurons, some of which are electrically coupled, feed back onto the BCNs. The BCNs are functionally heterogeneous both as a group and individually. Many are multifunctional in that they take part in the generation of different behaviors, and some also appear to change their timing with respect to the phase of the pattern generator in the different motor patterns. In the buccal ganglion, the BCNs affect the characteristics of the pattern generator and may be part of the pattern generator itself. By sending axons to buccal roots and to the brain, some BCNs may act as motoneurons and also integrate the activity of brain motoneurons. Because of the effects produced by the extensive interconnections among such functionally heterogeneous and nonlinerar elements, and because the “history” of activity in the system can bias subsequent activity, there is ambiguity in assessing the response properties of neurons by examining them individually or in pairs. Such an assessment requires, first, an understanding of the context of activity in which a neuron becomes coactive, and, second, because of inherent variability in the system, it is necessary to consider the temporal, nonlinear computations of the system as a whole. We discuss the findings with regard to the attractor theory that has been used to study complex mammalian systems but that does not rely on modeling of any neuronal activity. The Pleurobranchaea nervous system may provide the means for studying individual neurons within such analyses of global activity.
Adult‐specific neurons in the nervous system of the moth, Manduca sexta: Selective chemical ablation using hydroxyurea
Authors: Truman James W. , Booker Ronald
Published: May 2005

The segmental ganglia of adults of the moth, Manduca sexta, are constructed both from remodeled larval neurons and from adult‐specific cells. The latter are produced by identified stem cells (neuroblasts) during larval life and then differentiate to form functional neurons during metamorphosis. The mitotic activity of the larval neuroblasts could be irreversibly blocked by the DNA‐synthesis inhibitor hydroxyurea (HU). Treatment on day 1 of the third larval stage resulted in 80–90% of the neuroblasts being blocked before they produced any progeny while leaving the functional larval neurons unaffected. Treated larvae finished growth, underwent metamorphosis, and produced an adult CNS that contained the normal set of remodeled larval neurons but lacked most of the new adult‐specific cells. When HU treatment was delayed until the start of the fourth or fifth larval stage, the neuroblasts produced the early portions of their respective lineages before they were blocked. The immature neurons that were generated prior to treatment survived to contribute adult‐specific neurons to the moth CNS, but the remainder of each lineage was missing. This technique therefore enables one to produce adult nervous systems containing the basic set of remodeled larval cells plus defined sets of adult‐specific neurons.
Skin sensory innervation patterns in embryonic chick hindlimb following dorsal root ganglion reversals
Authors: Scott Sheryl A.
Published: May 2005

During embryonic development skin sensory neurons in lumbosacral dorsal root ganglia (DRGs) establish their dermatomes and axonal projections in a precise, orderly fashion in the chick. To investigate mechanisms responsible for this specific outgrowth, the rostrocaudal order of DRGs T7‐LS3 was reversed by rotating the corresponding segments of neural crest, either alone or together with the underlying neural tube in St.15–16 embryos. The resulting skin sensory innervation patterns, mapped physiologically or an‐atomically at St.29–40, differed between the two experimental groups. Following neural tube rotations DRGs tended to establish innervation patterns that were consonant with their original position in the embryo. Axons from these rotated DRGs generally projected into the appropriate pathways and innervated the appopriate region of skin. Neural crest rotations left the ventral neural tube (including the motor neuron precursors) largely intact. In this case rotated DRGs tended to establish innervation patterns in accordance with their new position in the embryo, almost as if no rotation had been made. These results cannot be explained solely by the inherent specificity of sensory neurons. Instead, the results are largely consistent with the suggestion (Honig et al., 1986; Landmesser and Honig, 1986) that motor axons can direct the outgrowth of sensory axons and thereby influence the establishment of sensory innervation patterns. Other mechanisms that may also affect the development of sensory innervation patterns are discussed.
Diffusional and electrokinetic redistribution at the synapse: A physicochemical basis of synaptic competition
Authors: Poo Mu‐Ming , Young Steven H.
Published: May 2005

Coinnervating nerve terminals may compete for “stabilizing factors” confined within the postsynaptic cell. The competition could be achieved through a diffusion‐mediated trapping the factor, facilitated by an activity‐dependent electrokinetic migration of the factor toward the synaptic site. We have examined the evidence for diffusional and electrokinetic motions of cell surface and cytoplasmic components, the profile and magnitude of the electric field produced by the synaptic current, and the plausibility that these motions underlie the process of synaptic competition.
Evidence for androgen receptors in sexually dimorphic perineal muscles of neonatal male rats. Absence of androgen accumulation by the perineal motoneurons
Authors: Fishman Renata B. , Chism Leila , Firestone Gary L. , Breedlove S. Marc
Published: May 2005

During development, survival of the sexually dimorphic spinal nucleus of the bulbocavernosus (SNB) and its target perineal muscles, the bulbocavernosus (BC) and the levator ani (LA) is androgen‐dependent. To define androgen's site of action in masculinizing SNB system structures, we examined whether or not androgen receptors are present in SNB motoneurons and/or BC/LA muscles of neonatal male rats. Using a receptor binding assay, we have identified androgen‐binding factors in the neonatal BC/LA (Bmax = 13.5 fmol/mg protein; Kd = 4.69 nM) for the first time. In contrast, androgen autoradiography provided no evidence that neonatal spinal motoneurons accumulate androgens. These results support the hypothesis that BC/LA muscles are a primary site of androgen action for masculinizing SNB system structures, and that androgen need not interact with SNB motoneurons directly to sexually differentiate them.
Hormonal control of neuron number in sexually dimorphic spinal nuclei of the rat: IV. Masculinization of the spinal nucleus of the bulbocavernosus with testosterone metabolites
Authors: Goldstein L. A. , Sengelaub D. R.
Published: May 2005

The spinal nucleus of the bulbocavernosus (SNB) is a sexually dimorphic motor nucleus in the rat lumbar spinal cord. SNB motoneurons and their perineal target muscles are present in adult males but reduced or absent in females. This sexual dimorphism is due to the presence of androgen during development; females treated with testosterone (T) perinatally have a masculine SNB system. To assess whether masculinization of the SNB could involve the conversion of testosterone into its active metabolites, dihydrotestosterone (DHT) and estrogen, we examined the development of the SNB in females treated perinatally with estrogen alone or in combination with dihydrotestosterone.

Counts of motoneurons in the developing SNB in all groups showed the typical prenatal increase followed by a differential postnatal decline; the incidence of degenerating cells reflected this decline. Motoneuron numbers and the frequency of degenerating cells in females treated with estrogen (E) alone did not differ from those of normal females, with both groups losing large numbers of motoneurons and having a high incidence of degenerating cells. In contrast, females treated with both estrogen and dihydrotestosterone did not show the female‐typical decline in motoneuron number and had a low, masculine incidence of degenerating cells. By postnatal day 10, females treated with estrogen and dihydrotestosterone had a fully masculine SNB motoneuron number, suggesting that dihydrotestosterone alone or in conjunction with estrogen may be involved in the development of the sexually dimorphic SNB system.
Hormonal regulation of adult sympathetic neurons: The effects of castration on neuropeptide Y, norepinephrine, and tyrosine hydroxylase activity
Authors: Hamill Robert W. , Schroeder Barbara
Published: May 2005

Previous studies utilizing the hypogastric ganglia (HG) have indicated that gonadal steroids exert organizational and activational effects on noradrenergic biochemistry. Bilateral castration of male rodents at birth prevents the normal maturation of tyrosine hydroxylase (T‐OH) activity in the HG; castration during adulthood results in a progressive decline in T‐OH activity. Testosterone replacement corrects both the ontogenetic and adult functional alterations in the neurotransmiter‐synthesizing enzyme. The present studies in adult male rats extend these previous observations and asked the question whether gonadal steroids regulate the neurotransmitters neuropeptide Y (NPY) and norepinephrine (NE) in the HG. Adult rodents were castrated and ganglia T‐OH, NPY, and NE were examined at various time points after surgery. All three indices of sympathetic neuron biochemistry declined following castration, but they exhibited different profiles. It appears that hormones may affect enzyme activity and neurotransmitter pools differently within neurons. Testosterone replacement therapy fully restored T‐OH activity, and NPY and NE levels in the HG. These studies extend the activational role of testosterone in regulating sympathetic neuron neurotransmitter and neuropeptide levels as well as neurotransmitter‐synthesizing enzymes.
Critical period for the androgenic block of neuromuscular synapse elimination
Authors: Jordan Cynthia L. , Letinsky Michael S. , Arnold Arthur P.
Published: May 2005

Juvenile androgen treatment during developmental synapse elimination changes the pattern of innervation in the adult levator ani (LA), an androgen‐sensitive muscle (Jordan, Letinsky, and Arnold, 1989b). Most notably, such adult muscles contain an unusually high number of muscle fibers that are innervated by two or more axons indicating that these fibers are multiply innervated. Juvenile androgen treatment also increases the adult level of preterminal branching, the number of junctional sites per adult fiber, and the size of adult LA muscle fibers and motoneurons in the spinal nucleus of the bulbocavernosus (SNB). The present study was designed to determine when in development androgen treatment is most effective in maintaining multiple innervation in adulthood and whether there are different critical periods for the different effects of juvenile androgen treatment. Male rats were castrated on 7, 21, or 34 days after birth (roughly corresponding to the beginning, middle, and end of synapse elimination in the LA muscle) and treated daily with testosterone propionate for the next 2 weeks. All rats were sacrificed at 9 weeks and their spinal cords and LA muscles were stained and analyzed. Only during the first treatment period (7–20) did androgen treatment result in increased levels of multiple innervation at 9 weeks. During this period, androgen also increased the number of junctional sites per fiber and the size of SNB somata but did not influence the adult level of preterminal branching or the diameter of adult LA muscle fibers. Androgen treatment during the two later periods increased the level of preterminal branching and the size of LA muscle fibers without influencing the level of multiple innervation. These results suggest that androgen maintains multiple innervation independent of its effects on preterminal branching and muscle fiber size and that motoneuron soma size may be related importantly to the long‐term maintenance of multiple innervation. Androgen treatment during but not after synapse elimination results in elevated levels of multiple innervation in adulthood, suggesting that androgen maintains multiple innervation in adult LA muscle by preventing its normal elimination in development.
Immunocytochemical colocalization of progestin receptors and β‐endorphin or enkephalin in the hypothalamus of female guinea pigs
Authors: Olster Deborah H. , Blaustein Jeffrey D.
Published: May 2005

Double‐label immunocytochemistry was used to determine whether estradiol‐induced progestin receptors and either β‐endorphin or leucine‐enkephalin are colocalized in female guinea pig brain. Ovariectomized, adult guinea pigs were implanted with capsules containing estradiol‐17β to induce high levels of progestin receptors, and injected intracerebroventricularly with co chicine to improve visualization of the opiate peptides. Sections through the hypothalamus and preoptic area were processed for progestin receptor, followed by β‐endorphin or leucine‐enkephalin immunocytochemistry. As reported previously, high concentrations of progestin receptor‐immunoreactive (PR‐IR) cells were found in the preoptic area (medial and periventricular portions, medial preoptic nucleus) and hypothalamus (anterior hypothalamic and arcuate nuclei, ventrolateral area). Many β‐endorphin‐IR cells contained PR‐IR in the arcuate nucleus and its surroundings (33%) and in the dorsomedial area of the hypothalamus (64%). Scattered enkephalin‐IR cells were found in the septal nucleus, medial and lateral preoptic area, bed nucleus of the stria terminalis, and the arcuate nucleus. The ventromedial nucleus of the hypothalamus and dorsolateral magnocellular nucleus, respectively, contained moderate and heavy concentrations of enkephalin‐IR cells. Although some of these areas also contained PR‐IR, enkephalin‐IR was colocalized consistently with PR‐IR only in a small number of cells in the arcuate nucleus and ventromedial/ventrolateral area of the hypothalamus. These data, taken together with earlier observations that virtually all cells containing estradiol‐induced PR‐IR also contain estrogen receptor‐IR, provide neuroanatomical evidence that hypothalamic actions of progesterone and estradiol may be mediated by β‐endorphin and/or enkephalin.
Onset of the hormone‐sensitive perinatal period for sexual differentiation of the sexually dimorphic nucleus of the preoptic area in female rats
Authors: Rhees Reuben W. , Shryne James E. , Gorski Roger A.
Published: May 2005

The volume of the sexually dimorphic nucleus of the preoptic area (SDN‐POA) of the rat brain is severalfold larger in males than in females. The volume of the SDN‐POA can be influenced significantly by the hormonal milieu during the perinatal “critical period” of sexual differentiation of the brain. The purpose of the present study was to determine the onset of this period of sexual differentiation of the SDN‐POA. Pregnant rats received no treatment or were injected subcutaneously with oil on day 17, 18, or 20, or testosterone (T;5 mg) on days 16‐22 of gestation. On postnatal day 15, unilateral SDN‐POA volumes from female offspring prenatally exposed to testosterone on day 16 or 17 were not different from values of control (untreated or oil‐injected) offspring. Female offspring from mothers treated with testosterone on day 18, 19, or 20 of gestation showed a significant and similar increase in SDN‐POA volume over values from control animals. SDN‐POA volumes from female offspring exposed to testosterone on day 21 or 22, although larger than those of controls, were not different statistically. We conclude that with the specific paradigm used in this study SDN‐POA development is insensitive prior to day 18 of gestation, the day on which the onset of the hormone‐sensitive period occurs.
Effects of castration and testosterone treatment on the activity of testosterone‐metabolizing enzymes in the brain of male and female zebra finches
Authors: Vockel A. , Pröve E. , Balthazart J.
Published: May 2005

Recently, we described the distribution of testosteronemetabolizing enzymes (i.e., aromatase, 5α‐ and 5β‐reductases) in the zebra finch (Taeniopygia guttata) brain using a sensitive radioenzyme assay combined to the Palkovits punch method. A number of sex‐differences in the activity of these enzymes were observed especially in nuclei of the song‐control system. The hormonal controls of these differences have now been analyzed by gonadectomizing birds of both sexes and by giving them a replacement therapy with silastic implants of testosterone (T). Five nuclei of the song system (Area X [X], nucleus magnocellularis of the anterior neostriatum [MAN], nucleus robustus archistriatalis [RA], nucleus intercollicularis [ICo], hyperstriatum ventrale, pars caudalis [HVc]) and three preoptic‐hypothalamic areas (preoptic anterior [POA], periventricular magnocellular nucleus [PVM], and posterior medial hypothalamic nucleus [PMH]) were studied as well as other limbic and control non‐steroid‐sensitive areas. The activity of the 5β‐reductase was higher in males than in females for the five song‐control nuclei and was not affected by the hormonal treatments. The overall activity of this enzyme was not sexually dimorphic in POA and PVM. It was higher in males than in females in intact birds only, and was reduced by gonadectomy and enhanced by T. The activity of the 5β‐reductase was higher in females than in males in all nuclei of the song system and in POA, but was not influenced by the changes in T level. Both sex and treatment effects were observed in the control of aromatase. The production of estrogens was dimorphic (females > males) in RA and PMH. It was increased by T in POA, PVM, and PMH, and also in RA. These data show that some of the sex differences in T‐metabolizing enzymes result from the exposure to different levels of T in adulthood (e.g., 5α‐reductase in POA and PVM or aromatase in PVM), whereas others persist even if birds are exposed to the same hormonal conditions. These are presumably the result of organizational effects of steroids. The steroid modulation of the aromatase might be related directly to the activation of sexual, aggressive, and nest‐building behaviors, whereas the stable dimorphism in 5α‐and 5β‐reductase observed in the nuclei of the song system might be one of the neurochemical bases of the sex differences in the vocal behavior of the zebra finch.
Morphology of pioneer and follower growth cones in the developing cerebral cortex
Authors: Kim Gina J. , Shatz Carla J. , McConnell Susan K.
Published: May 2005

In the developing nervous systems of both invertebrates and vertebrates, neurons must develop precise sets of axonal connections. One strategy used by both orders of animals is to generate a special class of neurons whose axons “pioneer” the first pathways between these cells and their targets. In the developing mammalian telencephalon, the subplate neurons (which are among the first neurons to be generated in development) extend axons to long‐distance subcortical targets before the neurons of the deep cortical layers 5 and 6 have been generated. The axons of layer 5 and 6 neurons later follow a similar pathway to form permanent subcortical projections to the thalamus and tectum, and thereafter the vast majority of subplate neurons die. These results have generated the hypothesis that subplate axons may actually be required for the axons of layer 5 and 6 neurons to innervate their appropriate subcortical targets. The complexity of growth cones has previously been correlated with axonal decision making: differences in growth cone morphologies have been noted in comparisons of leading versus following axons (LoPresti, Macagno, and Levinthal, 1973; Nordlander, 1987; Yaginuma, Homma, Kunzi, and Oppenheim, 1991), and at choice points along axon pathways (Raper, Bastiani, and Goodman, 1983; Tosney and Landmesser, 1985; Caudy and Bentley, 1986a, b; Bovolenta and Mason, 1987; Holt, 1989; Bovolenta and Dodd, 1990; Yaginuma et al., 1991). Thus, as a first step toward addressing the question of whether the axons of deep‐layer neurons simply follow subplate axons to their targets, we have studied the morphology of cortical growth cones at various points along the corticothalamic pathway and at different stages of development. We examined the brains of fetal ferrets and cats at ages ranging from embryonic days (E) 24 to E50, using the fluorescent lipophilic tracer 1,1‐dioctadecyl‐3,3,3′,3′‐tetramethyl indocarbocyanine perchlorate (Dil) to reveal the axons and growth cones of cortical neurons. Growth cones were drawn, and quantitative measurements of their complexity were made by counting filopodia and calculating their surface area. No morphological differences were found among growth cones at different points along the corticothalamic pathway at a given age. However, growth cones belonging to early‐generated cells (likely to be subplate neurons) are significantly larger and more complex than are the growth cones of later‐generated cortical neurons. This evidence is consistent with the suggestion that subplate growth cones actively pioneer the corticothalamic pathway, and that the axons of layer 5 and 6 neurons follow it.
Patterns of cell division and interkinetic nuclear migration in the chick embryo hindbrain
Authors: Guthrie Sarah , Butcher Matthew , Lumsden Andrew
Published: May 2005

Early in its development, the chick embryo hindbrain manifests an axial series of bulges, termed rhombomeres. Rhombomeres are units of cell lineage restriction, and both they and their intervening boundaries form a series that reiterates various features of neuronal differentiation, cytoarchitecture, and molecular character. The segmented nature of hindbrain morphology and cellular development may be related to early patterns of cell division. These were explored by labeling with BrdU to reveal S‐phase nuclei, and staining with basic fuchsin to visualise mitotic cells. Whereas within rhombomeres, S‐phase nuclei were located predominantly toward the pial surface of the neuroepithelium, at rhombomere boundaries S‐phase nuclei were significantly closer to the ventricular surface. The density of mitotic figures was greater toward the centres of rhombomeres than in boundary regions. Mitotic cells did not show any consistent bias in the orientation of division, either in the centres of rhombomeres, or near boundaries. Our results are consistent with the idea that rhombomeres are centres of cell proliferation, while boundaries contain populations of relatively static cells with reduced rates of cell division.