bluuebunny/crossref_metadata_2025 huggingface dataset:
Developmental study of afferented and deafferented bee antennal lobes
Authors: Gascuel Jean , Masson Claudine
Published: May 2005

The role of antennal sensory projections on the ontogeny of the bee antennal lobe was analyzed using both light and transmission electron microscopy. Normal and deafferented developing antennal lobes were examined. The results obtained show that (1) initiation of synaptogenesis in the antennal lobe is independent of the arrival of sensory inputs; (2) sensory inputs are necessary for setting up the glomerular antennal lobe organization; (3) regressive events, such as the reduction of synapse density, occur during the development of the antennal lobe; and (4) glomeruli formation appears as related to glia development.
Migration patterns of sympathetic preganglionic neurons in embryonic rat spinal cord
Authors: Markham Jeffrey A. , Vaughn James E.
Published: May 2005

The displacement of immature neurons from their place of origin in the germinal epithelium toward their adult positions in the nervous system appears to involve migratory pathways or guides. While the importance of radial glial fibers in this process has long been recognized, data from recent investigations have suggested that other mechanisms might also play a role in directing the movement of young neurons. We have labeled autonomic preganglionic cells by microinjections of horseradish peroxidase (HRP) into the sympathetic chain ganglia of embryonic rats in order to study the migration and differentiation of these spinal cord neurons. Our results, in conjunction with previous observations, suggest that the migration pattern of preganglionic neurons can be divided into three distinct phases. In the first phase, the autonomic motor neurons arise in the ventral ventricular zone and migrate radially into the ventral horn of the developing spinal cord, where, together with somatic motor neurons, they form a single, primitive motor column (Phelps P. E., Barber R. P., and Vaughn J. E. (1991). J. Comp. Neurol. 307:77–86). During the second phase, the autonomic motor neurons separate from the somatic motor neurons and are displaced dorsally toward the intermediate spinal cord. When the preganglionic neurons reach the intermediolateral (IML) region, they become progressively more multipolar, and many of them undergo a change in alignment, from a dorsoventral to a mediolateral orientation. In the third phase of autonomic motor neuron development, some of these cells are displaced medially, and occupy sites between the IML and central canal. The primary and tertiary movements of the preganglionic neurons are in alignment with radial glial processes in the embryonic spinal cord, an arrangement that is consistent with a hypothesis that glial elements might guide autonomic motor neurons during these periods of development. In contrast, during the second phase, the dorsal translocation of preganglionic neurons occurs in an orientation perpendicular to radial glial fibers, indicating that glial elements are not involved in the secondary migration of these cells. The results of previous investigations have provided evidence that, in addition to glial processes, axonal pathways might provide a substrate for neuronal migration. Logically, therefore, it is possible that the secondary dorsolateral translocation of autonomic preganglionic neurons could be directed along early forming circumferential axons of spinal association interneurons, and this hypothesis is supported by the fact that such fibers are appropriately arrayed in both developmental time and space to guide this movement.
Influence of altered afferent input on the number of trochlear motor neurons during development
Authors: Sohal G. S. , Hirano S. , Kumaresan K. , Ali M. M.
Published: May 2005

A loss of about half of the trochlear motor neurons occurs during the course of normal development. The present investigation was undertaken to examine the role of afferent input in regulating the number of surviving or dying trochlear motor neurons. A majority of the afferent input to the trochlear nucleus comes from the vestibular nuclei of the hindbrain via the medial longitudinal fasciculus. Portions of the hindbrain were lesioned in duck embryos on embryonic day 3, considerably prior to the time motor neurons send their axons out and cell death begins. The effectiveness of hindbrain lesion was verified by electron microscopical examination of synapses. There was a significant decrease in the number of synapses on trochlear motor neurons following hindbrain lesion. Cell counts made after the period of cell death indicated a significant decrease in the final number of surviving trochlear motor neurons. Cell counts made prior to the onset of cell death indicated that there was a drastic reduction in the initial number of trochlear motor neurons produced in hindbrain lesion embryos. In spite of a significant reduction in the initial number of neurons, the percentage loss of neurons was about the same as during normal development. Since trochlear motor neurons are generated prior to the formation of afferent synapses on them, it is unlikely that the reduction in the number of motor neurons initially produced is due to reduced afferent synaptic input. Since the percentage of cell loss in hindbrain lesion and normal embryos is about the same, it seems that the magnitude of cell death is genetically programmed. These observations suggest that the afferent synaptic input to the trochlear motor neurons may not be as important as previously thought in regulating cell number during development. They also suggest that some afferent input, of nonsynaptic type, available at very early stages of development may specify the initial number of trochlear motor neurons produced and that a fixed percentage of that number is programmed to die during development. It is suggested that this early influence may be provided by the embryonic medial longitudinal fasciculus.
Reorganization of sensory regulation of locust flight after partial deafferentation
Authors: Büschges Ansgar , Ramirez Jan‐Marino , Pearson Keir G.
Published: May 2005

Previous investigations have shown that the flight motor pattern of the mature locust (Locusta migratoria L.) relies heavily on the input of the hindwing tegulae. Removal of the hindwing tegulae results in an immediate change in the motor pattern: the wingbeat frequency (WBF) decreases and the interval between the activity of depressor and elevator muscles (D–E interval) increases. In contrast, removal of the forewing tegulae has little effect on the motor pattern. Here we report adaptive modifications in the flight system that occur after the removal of the hindwing tegulae. Over a period of about 2 weeks following hendwing tegula removal, the flight motor pattern progressively returned towards normal, and in about 80% of the animals recovery of the flight motor pattern was complete. We describe the changes in the activity pattern of flight muscles and in the patterns of depolarizations in flight motoneurons and flight interneurons associated with this recovery. In contrast to the situation in the intact animal, the activity of the forewing tegulae is necessary in recovered animals for the generation of the motor pattern. Removal of the forewing tegulae in recovered animals resulted resulted in similar changes in the flight motor pattern as were observed in intact animals after the removal of the hindwing tegulae. Furthermore, electrical stimulation of forewing tegula afferents in recovered animals produced similar resetting effects on the motor pattern as electrical stimulation of the hindwing tegulae afferents in intact animals. From these observations we conclude that recovery is due to the functional replacement of the removed hindwing tegulae by input from the forewing tegulae.
History of the discovery of neuronal death in embryos
Authors: Hamburger Viktor
Published: May 2005

The German anatomists, M. Ernst and A. Glücksmann, deserve credit for the discovery of widespread cell death in embryonic tissues, including the nervous tissue. In 1934, V. Hamburger described a significant hypoplasia in dorsal root ganglia (DGR) and lateral motor columns, following the extirpation of limb buds in chick embryos. In the early 1940s, Dr. Rita Levi‐Montalcini in Turin (Italy) repeated the experiment and suggested that the hypoplasia might result from the death of young differentiated neurons. In a joint reinvestigation, published in 1949, large numbers of degenerating neurons were described in brachial DRG, following wing bud extirpations. In the same embryos, Dr. Levi‐Montalcini observed massive neuronal death in cervical and thoracic DRG which had not been affected by the operation. This was the discovery of naturally occurring neuronal death. Long after the discovery of Nerve Growth Factor (NGF) it was recognized that NGF and natural neuronal death are two sides of the same coin: the latter results from an insufficient supply of the former by the target tissues. © 1992 John Wiley & Sons, Inc.
The role of target size in neuronal survival
Authors: Sohal G. S.
Published: May 2005

A loss of about half of the trochlear motor neurons occurs during the course of normal development in duck and quail embryos. The role of the size of the target muscle in controlling the number of surviving motor neurons was examined by making motor neurons innervate targets either larger or smaller in size than their normal target. In one experiment the smaller trochlear motor neuron pool of the quail embryo was forced to innervate the larger superior oblique muscle of the duck embryo. This was accomplished by grafting the midbrain of a quail embryo in the place of the midbrain of a duck embyro. Results indicated that no additional quail trochlear motor neurons were rescued in spite of a considerable increase in target size. In another experiment the larger trochlear motor neuron pool of the duck embryo was made to innervate the smaller superior oblique muscle of the quail embryo. This resulted in loss of some additional neurons; however, the number of surviving motor neurons was not proportionate to the reduction in target size. These experiments failed to provide support for the hypothesis that the size of the target muscle controls the number of surviving motor neurons. Although contact with target is necessary for survival of neurons, factors other than the number or size of target cells are involved in the control of motor neuron numbers during development. © 1992 John Wiley & Sons, Inc.
Excitotoxic cell death
Authors: Choi Dennis W.
Published: May 2005

Excitotoxicity refers to the ability of glutamate or related excitatory amino acids to mediate the death of central neurons under certain conditions, for example, after intense exposure. Such excitotoxic neuronal death may contribute to the pathogenesis of brain or spinal cord injury associated with several human disease states. Excitotoxicity has substantial cellular specificity and, in most cases, is mediated by glutamate receptors. On average, NMDA receptors activation may be able to trigger lethal injury more rapidly than AMPA or kainate receptor activation, perhaps reflecting a greater ability to induce calcium influx and subsequent cellular calcium overload. It is possible that excitotoxic death may share some mechanisms with other forms of neuronal death. © 1992 John Wiley & Sons, Inc.
Programmed neuronal death in insect development
Authors: Truman James W. , Thorn Robert S. , Robinow Steven
Published: May 2005

Programmed death in the developing nervous system of insects serves to remove obsolete neurons, generate segmental specializations and sexual dimorphism, as well as adjust neuronal number. This diversity is also reflected in the mechanisms which control the death of these neurons. In general, but not without exception, these deaths occur independent of target fate, while endocrine cues, segmental identity, and neural signalling often play critical roles. In addition, the programmed death of at least some neurons can be delayed by behavioral feedback. The study of neuronal death in Drosophila and the cloning of an ecdysteroid receptor bring the promise of understanding the genetic factors and molecular events that regulate this phenomenion. © 1992 John Wiley & Sons, Inc.
Molecular genetics of cell death in the nematode Caenorhabditis elegans
Authors: Driscoll Monica
Published: May 2005

In C. elegans, cell death can be readily studied at the cellular, genetic, and molecular levels. Two types of death have been characterized in this nematode: (1) programmed cell death, which occurs as a normal component in development; and (2) pathological cell death which occurs aberrantly as a consequence of mutation. Analysis of mutations that disrupt programmed cell death in various ways has defined a genetic pathway for programmed cell death which includes genes that perform such functions as the determination of which cells die, the execution of cell death, the engulfment of cell corpses, and the digestion of DNA from dead cells. Molecular analysis is providing insightinto the nature of the molecules that function in these aspects of programmed cell death. Characterization of some genes that mutate to induce abnormal cell death has defined a novel gene family called degenerins that encode putative membrane proteins. Dominant alleles of at least two degenerin genes, mec‐4 and deg‐1, can cause cellular swelling and late onset neurodegeneration of specific groups of cells. © 1992 John Wiley & Sons, Inc.
Neuroethology of olfactory preference development
Authors: Leon Michael
Published: May 2005

Young mammals come to approach the odor of their mother, a response that facilitates their survival during early life. Young rats induce a cascade of events in their mother to induce the emission of her odor. The pups increase circulating prolactin levels, which increases food intake and the emission of large quantities of cecotrophe containing the maternal odor. This odor is synthesized by the action of cecal microorganisms and changes with maternal diet. The diet‐dependence of the odor requires the pups to acquire their attraction to the odor postnatally. The acquisition of this preference occurs when an odor is paired with the tactile stimulation that pups receive during maternal care. The action of the tactile stimulation appears to be mediated by noradrenaline. The development of this type of olfactory attraction is accompanied by changes in the regions of the olfactory bulb that are responsive to the attractive odor. Metabolic, anatomical, and neurophysiological changes in response to the attractive odor emerge in such regions of the bulb after early olfactory preference training. © 1992 John Wiley & Sons, Inc.
Brachially innervated ectopic hindlimbs in the chick embryo. I. Limb motility and motor system anatomy during the development of embryonic behavior
Authors: Kitchener P. D. , Laing N. G.
Published: May 2005

The functional status of brachially innervated hindlimbs, produced by transplanting hindlimb buds of chick embryos in place of forelimb buds, was quantified by analyzing the number and temporal distribution of spontaneous limb movements. Brachially innervated hindlimbs exhibited normal motility until E10 but thereafter became significantly less active than normal limbs and the limb movements were more randomly distributed. Contrary to the findings with axolotls and frogs, functional interaction between brachial motoneurons and hindlimb muscles cannot be sustained in the chick embryo. Dysfunction is first detectable at E10 and progresses to near total immobility by E20 and is associated with joint ankylosis and muscular atrophy. Although brachially innervated hindlimbs were virtually immobile by the time of hatching (E21), they produced strong movements in response to electrical stimulation of their spinal nerves, suggesting a central rather than peripheral defect in the motor system. The extent of motoneuron death in the brachial spinal cord was not significantly altered by the substitution of the forelimb bud with the hindlimb bud, but the timing of motoneuron loss was appropriate for the lumbar rather than brachial spinal cord, indicating that the rate of motoneuron death was dictated by the limb. Measurements of nuclear area indicated that motoneuron size was normal during the motoneuron death period (E6‐E10) but the nuclei of motoneurons innervating grafted hindlimbs subsequently became significantly larger than those of normal brachial motoneurons. Although the muscle mass of the grafted hindlimb at E18 was significantly less than that of the normal hindlimb (and similar to that of a normal forelimb), electronmicroscopic examination of the grafted hindlimbs and brachial spinal cords of E20 embryos revealed normal myofiber and neuromuscular junction ultrastructure and a small increase in the number of axosomatic synapses on cross‐sections of motoneurons innervating grafted hindlimbs compared to motoneurons innervating normal forelimbs. The anatomical data indicate that, rather than being associated with degenerative changes, the motor system of the brachial hindlimb of late‐stage embryos is intact, but inactive. © 1993 John Wiley & Sons, Inc.
Selective fasciculation as a mechanism for the formation of specific chemical connections between Aplysia neurons in vitro
Authors: Hawver David B. , Schacher Samuel
Published: May 2005

Selective fasciculation of growth cones along preestablished axon pathways expressing matching or complementary adhesion molecules is thought to be an important strategy in axon guidance. Growth cone inhibiting factors also appear to influence pathfinding decisions. We have used identified Aplysia neurons in vitro to explore the hypothesis that similar mechanisms could be involved in target selection. Co‐cultures of L10 neurons with RB neuron targets or R2 neurons with RUQ neuron targets reliably formed chemical connections. In contrast, co‐cultures of L10 with RUQ targets usually failed to form detectable chemical connections unless cell–cell contact was forced during plating by intertwining the major axons. These data suggested that differences in the ability to form cell–cell contacts might underlie the observed synaptic specificity. This notion was supported when fluorescent dye fills of L10 and R2 revealed a positive correlation between the amount of target contact and the frequency of synapse formation: L10–RUQ cultures showed much less target contact than L10–RB or R2–RUQ cultures. To examine the cellular mechanisms of these differences in target contact, presynaptic growth cones were observed as they interacted with target processes. L10–RUQ cultures showed much less fasciculation and more avoidance behavior compared to L10–RB and R2–RUQ cultures. This initial specificity suggested that the differences in amount of target contact arose through selective fasciculation and avoidance rather than through selective elimination after indiscriminate fasciculation. Selective fasciculation and avoidance might, therefore, aid in target selection by regulating the amount of contact between presynaptic processes and potential target cells. © 1993 John Wiley & Sons, Inc.
Formation of functional synapses by regenerating adult rat retinal ganglion cell axons in midbrain target regions in vitro
Authors: Bähr Mathias , Eschweiler Gerhard W.
Published: May 2005

The ability of adult rat retinal ganglion cell (RGC) axons to reinnervate normal target regions was examined in vitro. In co‐culture experiments, adult rat retinal explants were placed adjacent to fetal rat midbrain sections that contained the superior colliculus (SC) which is the main target for RGC axons. Adult rat RGCs regrew axons over more than 500 μm on a polylysine‐laminin substrate to reach the co‐cultured explants. By using neurofilament immunohistochemistry and the fluorescent dye Dil for anterograde and retrograde tracing, it was shown that (1) adult rat RGCs with a stereotyped morphology survived in explant cultures for more than 4 weeks in the presence of fetal midbrain explants, (2) regenerating RGC axons preferentially terminated within midbrain target regions, and (3) RGCs formed functional synapses. In addition, the maturation of the SC region in midbrain explants was examined histologically and ultrastructurally to demonstrate appropiate target development. © 1993 John Wiley & Sons, Inc.
Amitriptyline inhibits neurite outgrowth in chick cerebral neurons: A possible mechanism
Authors: Wong Ka L. , Chuang Tzu Y. , Bruch Richard C. , Farbman Albert I.
Published: May 2005

Previous studies showed that amitriptyline (AMI), a tricyclic antidepressant, inhibited neurite outgrowth from chick embryonic cerebral explants and inhibited adenylyl cyclase activity in cerebral membrane preparations. In the present study, we have investigated the possibility that AMI may have additional effects on cellular metabolism and signal transduction that underlie AMI‐mediated inhibition of neurite outgrowth. In vitro AMI inhibited phospholipase C in a dose‐ and GTP‐dependent manner in membranes from 8‐day‐old chick forebrain. Brain homogenates from 8‐day‐old chick embryos, treated in vivo for 6 days with AMI (20 μg/g/day), showed significant reductions in (1) phosphorylation of two polypeptides (49 and 105 kD), and (2) levels of three polypeptides (43, 53, and 92 kD). Western blots showed that the 43‐ and 53‐kD polypeptides corresponded to actin and tubulin, respectively. Diolein and dilinolein, potent activators of protein kinase C, stimulated neurite outgrowth and reversed the inhibitory effects of AMI. Sphingosine, a protein kinase C inhibitor, significantly inhibited neurite outgrowth and eliminated the stimulatory effects of diolein and dilinolein on neurite outgrowth. These data suggest that AMI‐mediated inhibition of neurite outgrowth involves multiple effects on cellular metabolism and signal transduction. A hypothesis consistent with our data is that AMI interferes in some manner with the action of G proteins in the signal transduction cascade. © 1993 John Wiley & Sons, Inc.
NGF and the local control of nerve terminal growth
Authors: Campenot Robert B.
Published: May 2005

It is generally believed that the mechanism of action of neurotrophic factors involves uptake of neurotrophic factor by nerve terminals and retrograde transport through the axon and back to the cell body where the factor exerts its neurotrophic effect. This view originated with the observation almost 20 years ago that nerve growth factor (NGF) is retrogradely transported by sympathetic axons, arriving intact at the neuronal cell bodies in sympathetic ganglia. However, experiments using compartmented cultures of rat sympathetic neurons have shown that neurite growth is a local response of neurites to NGF locally applied to them which does not directly involve mechanisms in the cell body. Recently, several NGF‐related neurotrophins have been identified, and several unrelated molecules have been shown to act as neurotrophic or differentiation factors for a variety of types of neurons in the peripheral and central nervous systems. It has become clear that knowledge of the mechanisms of action of these factors will be crucial to understanding neurodegenerative diseases and the development of treatments as well as the means to repair or minimize neuronal damage after spinal injury. The concepts derived from work with NGF suggest that the site of exposure of a neuron to a neurotrophic factor is important in determining its response. 1994 John Wiley & Sons, Inc.
Target‐derived molecules that influence the development of neurons in the avian ciliary ganglion
Authors: Nishi Rae
Published: May 2005

The developing avian ciliary ganglion has been a particularly amenable system for the identification, isolation, and characterization of putative target‐derived molecules that mediate retrograde interaction. To date a number of biochemically distinct activities that regulate neuronal survival, transmitter phenotype, and chemosensitivity of ciliary ganglion neruons have been identified. Of these, only two survival‐promoting molecules have been purified to homogeneity: ciliary neurotrophic factor and a related molecule, growth‐promoting activity. A somatostatin‐inducing activity found in cultured choroid cells is very likely to be chick activin A. Other molecules that regulate acetylcholine and acetylcholine receptor expression comigrate on a gel filtration column at a molecular weight of 50–60 kD, but they have yet to be isolated. Once molecules that mimic retrorgrade influences are identified, a number of criteria must be met before their physiological significance can be established. These criteria are (1) availability of the molecule from the target at the appropriate time in development: (2) ability of the neurons to respond to the molecule at the appropriate time in development: (3) demonstration that blocking the activity or availability of the molecule is able to block the target‐derived developmental change expressed in the neurons. Of the molecules that are thought to retrogradely influence ciliary neuron development, only growth‐promoting activity is known to meet criteria 1 and 2, and experiments of growth‐promoting activity in vivo will exacerbate normal cell death. 1994 John Wiley & Sons, Inc.
Voltage‐activated lonic currents in differentiating rat cerebellar granule neurons cultured from the external germinal layer
Authors: Stewart Randall R. , Bossu Jean‐Louis , Muzet Muriel , Dupont Jean‐Luc , Feltz Anne
Published: May 2005

The electrical properties of the precursor cells of the external germinal layer of rat cerebellum were assessed during their differentiation in control medium (Dulbecco's modified Eagle's medium) supplemented or not with either basic fibroblast growth factor (bFGF) or 25 mM potassium chloride (KCI). Resting potential was shown to be –10 mV in all three conditions 3 hours after plating [days in vitro (DIV)0]. By DIV 5, it reached ‐63 mV for cells cultured in 25 mM KCI but only –28 mV in control and bFGF media. The main voltage‐sensitive ionic current measured at DIV 0 under all conditions was a composite Ik consisting in a sustained K+ current blocked by tetraethylammonium (Ik(TEA)), plus a rapidly activating and inactivating TEA‐insensitive Ik(A). Both currents increased with time in all conditions, but after 5 days IK(A) became dominant in terms of density. IK(TEA) is likely an IK(Ca), since it was blocked by 67% in 1 mM TEA. On DIV O, INa and ICa were absent or small in amplitude. By DIV 3, 80% of the cells had currents able to generate a spike. Interestingly, ICa mean amplitude and current density measured at –10 mV in control condition on DIV 1 was singnificantly larger than those recorded in bFGF and 25 mM KCI. The order of appearance of the ionic currents, IK, ICa, and INa, leads directly to fast spike activity allowing for poor calcium entry. Firing rate likely depends on IK(A), which increased during the first 6 days of development but could be differentially regulated by bFGF. © 1995 John Wiley & Sons, Inc.
Gap junctions are required for the propagation of spreading depression
Authors: Nedergaard Maiken , Cooper Arthur J. L. , Goldman Steven A.
Published: May 2005

Spreading depression (SD) is a slowly propagating depression of cerebral neuronal activity and transmembrance ionic gradients, that arises in response to a variety of noxious stimuli. SD bears a strong resemblance to gap junction‐mediated calcium waves among cultured astrocytes. Here, we show that gap junction‐mediated intercellular diffusion is necessary for the generation of SD. Waves of SD in the isolated chicken retina were blocked by five different inhibitors of gap junctional coupling, which was assessed by the intercellular transit of Lucifer Yellow (LY). Each of these gap junction blockers inhibited both the migration of SD and the diffusion of LY in a dose‐dependent manner. In contrast, glutamate‐evoked calcium influx into retinal cells was not affected by these compounds. The results indicate that intercellular coupling through gap junctions is required for SD. Gap junction‐mediated communication might therefore constitute an important mechanism in both normative and pathological brain function. © 1995 John Wiley & Sons, Inc.
Modulation of transmitter release from the terminals of the locust wing stretch receptor neuron by muscarinic antagonists
Authors: Leitch Beulah , Pitman Robert M.
Published: May 2005

The forewing stretch receptor (SR) neuron makes monosynaptic connections with wing depressor motoneruons; in this article the pharmacology of its output onto the first baslar motoneuron (BA1) has been investigated. The SR, like other insect afferents that have been studied so far, appears to be cholinergic; transmission was suppressed reversibly by the nicotinic antagonist gallamine (10−4M) and irreversibly by α‐bungarotoxin (10−6 M). The choline reuptake blocker hemicholinium‐3 (10−4 M) also caused a reversible reduction in the amplitude of SR excitatory postsynaptic potentials (EPSPs) recorded in BA1. The receptor subtype nonselective muscarinic antagonists atropine (10−4 M), scopolamine (10−4 M), and quinuclidinyl benzilate (10−5 M), unlike nicotinic antagonists, caused an augmentation in EPSP amplitude. This effect does not appear to be caused by an increase in sensitivity of the motoneuron to acetylcholine (ACh), since atropine produced a marked reduction rather than an increase in the amplitude of responses to ACh pressure applied to the soma of BA1. Scopolamine only caused a modest reduction in the amplitude of ACh somatic responses. The simplest explanation for these observations is that muscarinic antagonists bring about an increase in EPSP amplitude by blockade of presynaptic autoreceptors that normally down‐regulate the release of ACh from SR terminals. The effects of muscarinic receptor subtype‐selective antagonists indicate that presynaptic receptors in this preparation may have a pharmacological profile more similar to that of vertebrate M2 receptors than to that of M1 or M2 subtypes. The functional significance of autoreceptors in this preparation are discussed. © 1995 John Wiley & Sons, Inc.
Synthesis and dynamic NMR studies of the 3,7‐diazabicyclo[4.1.0]heptane system
Authors: Majchrzak Michal W. , Kotełko Antoni , Lambert Joseph B.
Published: May 2005

A new bicyclic system, 3,7‐diazabicyclo[4.1.0]heptane, has been prepared from 3‐(ethoxycarbonyl)‐7,3‐oxazabicyclo[4.1.0]heptane by reaction with sodium azide and reduction of the resulting tosyloxy azide with lithium aluminum hydride. The molecule can exist in four stereoisomeric half‐chairs, depending on the configuration of the two nitrogen atoms. Half‐chair ring reversal and piperidine nitrogen inversion are fast on the NMR time scale at all observed temperatures. Inversion of the secondary aziridine nitrogen becomes slow as the temperature is lowered (Tc= −10°C). Complete analysis of the 1H spectrum was possible with the 1,5,5‐trideuteriated analog. At slow exchange, two aziridine invertomers are present with an exo/endo ratio of approximately 0.7 in toluene‐d8, 0.7 in CH2Cl2 and 1.7 in CHCl3/CH2Cl2. The free energy of activation for nitrogen inversion is 13.2 kcal mol−1 at −10°C in CHCl3/CH2Cl2.
Elucidation of the structure of alkane chains in solution by means of 1H NMR
Authors: Nikki Kunio , Nakagawa Naoya
Published: May 2005

Solvent shifts of a series of alkanes have been studied in perfluorohexane, carbon tetrachloride and diiodomethane. The methylene proton resonances for longer alkyl chains are shifted downfield in perfluorohexane, but upfield in diiodomethane. It is suggested that n‐alkanes have a tendency to adopt folded structures in solution, the degree of folding for n‐alkane chains in perfluorohexane being larger than that in diiodomethane.
15N NMR studies of amino acids and their reaction products with formaldehyde
Authors: Naulet N. , Tomé D. , Martin G. J.
Published: May 2005

Natural abundance 15N NMR spectroscopy has been used to investigate the effect of pH on the 15N chemical shifts of lysine and of ε‐hydroxymethyllysine. A computer calcualtion which fits the chemical shifts of both α‐and ε‐nitrogen atoms versus pH has been used to predict the pKa values. 15N chemical shifts and some 1J(15NH) values of some other amino acids and of their reaction products with formaldehyde are also reported.
Silicon‐29 NMR spectroscopy in carbohydrate chemistry: Galactose derivatives
Authors: Gale D. J. , Evans N. A.
Published: May 2005

29Si NMR spectra of the O‐trimethylsilyl (OTMS) derivatives of various methyl α‐ and β‐D‐galactopyranosides have been recorded. The effect of changes in the anomeric configuration provides a means of assigning the resonance of the 2‐OTMS substituent. Whereas the signal of the OTMS group attached at the 6‐position can be assigned readily, those of the OTMS group at the 3‐ or 4‐position cannot be assigned unequivocally.
Carbon‐13 NMR study of substituted benzyl N,N‐dimethylcarbamates
Authors: Yamagami Chisako , Takao Narao , Takeuchi Yoshito
Published: May 2005

The 13C NMR chemical shifts of m‐ and p‐substituted benzyl N,N‐dimethylcarbamates were measured in CDCl3. The meta and para 13C substituent chemical shifts were analysed by means of dual substituent parameter (DSP) equations. Good correlations were obtained, especially for the para‐carbon substituent chemical shifts. The computed transmission coefficients, ρI and ρR, are consistent with the general features of the fitting parameters. It has been shown that no significant electron demand is imposed by the CH2OCON(CH3)2 substituent.
Gas‐phase NMR studies of chemical equilibria: 1—Methodology
Authors: Harris Robin K. , Rao Renée C.
Published: May 2005

Methods for obtaining 1H NMR spectra of gases are discussed. Particular attention is paid to the nature of the tube and to the use of ‘second sample’ field/frequency locking. The question of the chemical shift reference is examined, and some results for tetramethylsilane gas are presented. Representative spectra are shown for three types of organic equilibria in the gas phase: keto‐enol tautomerism, addition of methanol to acetaldehyde and Z‐E isomerism of acetaldoxime.
The mass spectra of some alkyl and aryl imidazolines
Authors: Ohashi M. , Ohno N. , Kakisawa H. , Tatematsu A. , Yoshizumi H.
Published: May 2005

The mass spectra of mono‐ and di‐substituted alkyl and aryl imidazolines have been measured and the spectra analysed with the aid of deuterium labelling and high resolution techiques.

In contrast to the fragmentation of thiazolines, all principal fragments of the imidazoline ring contain one nitrogen with or without hydrogen migration. In the case of 2,4‐disubstituted imidazolines, the presence of two tautomeric molecular ions are suggested.
Electron‐impact studies of organometallic molecules—VIII: Some transition metal derivatives of polyfluorobenzenes
Authors: Bruce M. I. , Thomas Mair A.
Published: May 2005

The mass spectra of (π‐C5H5)2Ti(C6F5)X (X  Cl and C6F5), C6F5Re(CO)5, RfFe(CO)2(π‐C5H5) (Rf  C6F5, 4‐HC6F4, and three isomeric H2C6F3), and C6F5Ru(CO)2(π‐C5H5) are compared to those of C6F5X (X  F, Cl, Br, I) and the three isomers of C6F4H2. Significant differences occur, apparently depending on the relative thermodynamic stabilities of the various fragments which may be formed. Comparison of the mass spectra of pentafluorophenyl‐ and pentafluorobicyclo[2.2.0]hexa‐2,5‐dien‐2‐yl‐Re(CO)5 show that similar ions are produced by both complexes, perhaps because of thermal isomerisation before ionisation.
The elimination of small neutral molecules and fragments in mass spectra—I. Substituted salicylic acids and their derivatives
Authors: Scott Ward M. , Wacks Morton E. , Eskelson C. D. , Towne J. C. , Cazee C.
Published: May 2005

The mass spectra of various ring‐substituted salicylic acids and derivatives thereof have been examined. Fragmentation pathways for derivatives of salicylic acid; 3‐NO2 salicylic acid; 5‐I salicylic acid; 3‐NO2, 5‐I salicylic acid; and 3‐NH2, 5‐I salicylic acid are suggested. The major dissociations of these compounds are by elimination of the elements of neutral molecules, e.g. water, methanol, ketene (from the acetylated compounds) carbon monoxide, nitric oxide and nitrogen dioxide, leading to (iodo) phenoxy and (iodo) quinone type ion structures. These ions further decompose to yield the corresponding substituted cyclopentadienyl and cyclopropylium ions.
Mass spectral studies on thiobenzoates and thioacetates
Authors: Ohno A. , Koizumi T. , Ohnishi Y. , Tsuchihashi G.
Published: May 2005

The mass spectra of O‐methyl and O‐ethyl thiobenzoates and their derivatives have been recorded together with those of the corresponding S‐alkyl thiobenzoates. The direct fragmentations of the O‐alkyl thiobenzoates are almost identical to those of alkyl benzoates and of S‐alkyl thio‐benzoates. Several important differences in rearrangements upon electron‐impact can be observed between them, however. These are the migration of the alkyl group from the alkoxy oxygen to the thiocarbonyl sulphur and the migration of a hydrogen from the alkoxy group to the thiocarbonyl group. O‐methyl and O‐ethyl thioacetates behave similarly. The mass spectra of the thioesters obtained with low electron‐accelerating voltages have also been studied.
Mass spectrometric studies of phenoxarsine derivatives
Authors: Tou James C. , Wang C. S.
Published: May 2005

Nine phenoxarsine derivatives with arsenic in the trivalent state and the pentavalent state are synthesized and studied by mass spectrometry. Their characteristic fragmentation modes and the fragment ions with common structures are discussed. Phenoxarsinic acids are found to be unstable in the gaseous phase at the temperatures studied and tend to form their corresponding anhydrides.
Ion‐molecule reactions in alkyl cyanides: Identification of reactive hydrogen in precursor ions
Authors: Heerma W. , Dijkstra G.
Published: May 2005

The relative abundance of [M + H]+ ions in the spectra of different nitriles depends on the nature of the nitrile. A new method for the identification of ion‐molecule reactions has been applied, by determining the [M + D]+ ion intensity with respect to the [M + H]+ ion intensity in the spectra of partially deuteriated alkyl cyanides. This intensity ratio is correlated with the hydrogen‐deuterium content of the suspected primary ions. In addition not only the reacting primary ions, but also the reactive hydrogen atom in the primary ion could be indicated. There is clear evidence that the proton attached to the nitrogen atom in the H2CCN+˙H rearrangement ion is transferred to the nitrile molecule.
Mass spectrometry of aralkyl compounds with a functional group—VIII: Comparison of the breakdown of 3‐phenylnitropropane with that of 3‐phenylpropyl nitrite upon electron‐impact
Authors: Nibbering N. M. M. , De Boer Th. J.
Published: May 2005

Mass spectra of 3‐phenylnitropropane and of its analogues, specifically deuterated in the aliphatic chain and in the phenyl ring, show that the molecular ion loses a molecule of water in two different modes, viz. either with both α‐hydrogen atoms or with a γ‐ and an ortho‐hydrogen atom. Moreover, a molecule of nitric oxide is eliminated from the molecular ion and the resulting [M ‐ NO]+‐ion appears to decompose further in many complicated ways. This loss of nitric oxide does not arise from an isomerization of the nitro group to a nitrite group, because the [M ‐ NO]+‐ion of 3‐phenylpropyl nitrite breaks down in an altogether different manner than that of 3‐phenylnitropropane. This is demonstrated by the spectra of specifically deuterated analogues of 3‐phenylpropyl nitrite.
Mass spectrometry in the investigation of β‐lysine‐containing peptides
Authors: Rostovtseva L. I. , Kiryushkin A. A.
Published: May 2005

Mass spectrometry can be used for amino acid sequence determination in β‐lysine‐containing peptides and for the identification of α‐ and β‐lysine residues in peptides, as well as for amide bond type determination in β‐lysine peptides. The peptide bond in streptothricin D is shown to be formed through the participation of an ε‐amino group of the L‐β‐lysine residue.
A novel fragmentation of trimethylsilyl ethers of 3β‐hydroxy‐Δ5‐steroids
Authors: Björkhem Ingemar , Gustafsson Jan‐Årke , Sjövall Jan
Published: May 2005

An ion formed by loss of 56 mass units from the molecular ion is often seen in mass spectra of trimethylsilyl ethers of C19 and C21 steroids having a 3β‐hydroxy‐Δ5 structure and an oxo group at C‐17 or C‐20. The nature of this fragment was investigated by the use of perdeuteriotrimethylsilyl ether derivatives and of [4‐14C], [3‐18O], [4,4‐2H2] and [2,2,4,4‐2H] labelled derivatives of 3β‐hydroxy‐5‐androsten‐17‐one and 3β‐hydroxy‐5‐pregnen‐20‐one. Evidence is presented to show that the neutral fragment of mass 56 is composed of carbon atoms 1, 2 and 3, the oxygen at C‐3 and four hydrogen atoms. During the fragmentation process, the trimethylsilyl group and one of the hydrogens at C‐2 are transferred to the fragment that carries the charge.
Substituent effects in mass spectrometry—III: Substituent effects in the dissociation of the molecular ions of para and meta substituted benzoic acids
Authors: Benoit F.
Published: May 2005

The effect of substituents on the electron‐impact‐induced fragmentation of the molecular ions of para and meta substituted benzoic acids has been examined. The substituent is observed to exert an effect on the ionisation potential of the molecular ion, on the appearance potentials of the primary daughter ions and on the amount of H/D scrambling in the molecular ion of the carboxyl‐d1 analogues prior to the loss of hydroxyl therefrom. The energy of activation for the loss of hydroxyl from the molecular ion is in general dependent upon the nature but not the position of the substituent, while the amount of H/D scrambling in the molecular ion of the carboxyl‐d1 derivative is dependent upon both the nature and the position of the substituent. No correlation of the relative ion abundances with σ+ constants was observed. The results are consistent with the molecular ions of each compound having a dissimilar energy distribution, which could arise either by different energy transfers from the electron beam to the molecule or by the participation of different isolated electronic excited states (or similar states but to varying extents) in the dissociation of the molecular ions.
Field ionization mass spectrometry—IV. Isotopically labeled heptanals
Authors: Brown Peter , Fenselau Catherine
Published: May 2005

The field ionization (FI) mass spectra of n‐heptanal and a series of deuterium labeled analogs have been studied, with the objectives of initiating systematic investigations of reaction mechanisms of FI produced ions and to permit comprison with those found for other ionization processes. It is now recognized that FI ions have: (a) lower average internal energies and (b) shorter residence times than similar ions generated by electron‐impact (EI), and the possibility exists of H/D‐randomization occuring in ions formed by desorption from the emitter, by unimolecular decomposition close to the emitter and by either ‘fast’ or ‘slow’ metastable decompositions.

In this study only the peak shifts of normal ions could be utilized; accurate mass measurements of all major ions revealed elemental compositions similar to EI. A site‐specific McLafferty rearrangement gave the base peak at m/e 44 ([C2H4O]+.), although the apparently complementary ion at m/e 70 ([C5H10]+.) arose in a less specific process. Ions at m/e 43 ([C3H7]+) and 71 ([C5H11]+ 80%; [C4H7O]+ 20%) were apparantly generated without significant H/D‐scrambling. Of special interest was the observation of the rearrangement ion at m/e 86 ([C5H10O]+.) caused by loss of C‐2 and C‐3 as C2H4, as found for EI.

It is concluded that at least in this system, decomposing molecular ions formed: (a) in the gas phase extremely close to the emitter and/or (b) on the emitter surface, have lifetimes sufficiently short to preclude complete H/D randomization. The results also provide evidence for common fragmentation mechanisms for heptanal molecular ions at both the low end and the high end of the energy distribution.
Mass spectrometry of heterocyclic compounds—III. Electron‐impact‐induced fragmentation of 1,2‐benzisothiazole and some 3‐substituted derivatives
Authors: Selva Antonio , Gaetani Enrico
Published: May 2005

The mass spectra of fifteen 1,2‐benzisothiazoles are reported; their fragmentation patterns have been investigated by labelling experiments, high resolution mass measurements and defocused metastable ion detection. The parent compound of the series, 1,2‐benzisothiazole, eliminates HCN after partial inter‐ring hydrogen scrambling. The extent of scrambling has been determined for normal daughter ions produced at different electron beam energies and also for metastable daughter ions, and is compared with the data reported for benzothiazole. Some 3‐substituted derivatives show unusual fragmentation patterns. The mechanisms of these processes are under further investigation.
Mass spectrometry in structural and stereochemical problems—CCXXII: Delineation of competing fragmentation pathways of complex molecules from a study of metastable ion transitions of deuterated derivatives
Authors: Smith D. H. , Duffield A. M. , Djerassi Carl
Published: May 2005

Data on defocused metastable ions have been obtained for a series of structurally significant fragment ions in the mass spectra of the estrogenic steroid, estrone methyl ether and the alkaloid tropine. These data, in conjunction with measurements on defocused metastable ions in the mass spectra of isotopically labeled analogs and complete high resolution mass spectra provide important insights into the details of fragmentation processes, specifically: (a) an enumeration and determination of the frequent multiple origins of fragment ions in the mass spectra of such complex molecules, (b) specification of skeletal atoms lost and retained in concerted (one step) processes, and at each step of stepwise processes, leading to a particular fragment ion and (c) information on the relative contributions of concerted and stepwise processes resulting in the genesis of a given ion.
High resolution mass spectrometry in molecular structure studies—V: The fragmentation of amaryllis alkaloids in the crinine series
Authors: Longevialle P. , Smith D. H. , Burlingame A. L. , Fales H. M. , Highet R. J.
Published: May 2005

High resolution mass spectral fragmentation patterns of Amaryllidaceae alkaloids in the crinine series have been investigated as well as those of certain isotopically labeled derivatives. Attention is directed to the particular importance of employing entire high resolution mass spectra in attempting the elucidation of structural correlations in compounds which display few significant relative intensity variations in a complex fragmentation pattern.
Mass spectra of polymeric thioformaldehydes (CH2S)3, (CH2S)4, (CH2S)5 and (CH2S)x
Authors: Peach Michael E. , Weissflog Eckhard , Pelz Norbert
Published: May 2005

The mass spectral fragmentations of various thioformaldehydes, 1,3,5‐trithiacyclohexane, 1,3,5,7‐tetrathiacyclooctane, 1,3,5,7,9‐pentathiacyclodecane and a polymeric form (CH2S)x have been examined. The principal features of the spectra are reported. The fragmentation occurred by fracture of the ring in the cyclic compounds with or without rearrangement.
The analysis of mixtures: IV
Authors: Halket J. McK. , Reed R. I.
Published: May 2005

The analysis of mixtures has been re‐examined and extended. The results have been applied to several mixtures, including steroids, distilled from a direct insertion probe with promising results. An experimental scheme is described to enable the determination of the number of components in a mixture by two distinct methods. This work forms an early stage in a general mixtures analysis system.