The composition of the vagus nerve of the cat

Summary The number and caliber of myelinated and non-myelinated fibers of entire and sensory vagal nerves of cats were studied by means of light and electron microscopy. The results obtained with electron microscopy show that the non-myelinated component is particularly rich (about 40,000 elements at the cervical level), with clearly higher numbers of fibers than demonstrated thus far with light microscopy. The ratio of myelinated to non-myelinated fibers is on the average 1 4 for the total vagi and only 1 8 for the sensory vagal component. The comparison of the nerve above and below the level of the nodose ganglion shows that (1) mean fiber diameter is usually greater at the infranodose than at the supranodose level, and (2) some myelinated fibers of small diameter occurring below the nodose ganglion become non-myelinated above it. Additionally, the number of non-myelinated fibers per Schwann cell is greater at the supranodose than at the infranodose level; this speaks in favor of a reorganization of the C-fiber population from one level to the other.     

Neocortical Dynamics: Implications for Understanding the Role of Neurofeedback and Related Techniques for the Enhancement of Attention

For nearly 25 years, EEG biofeedback (neurofeedback) has been utilized in research and clinical settings for the treatment and investigation of a number of disorders ranging from attention deficit hyperactivity disorder to seizure disorders as well as many other established and investigational applications. Until recently, mechanisms underlying the generation and origins of EEG have been poorly understood but now are beginning to become much more clarified. Now it is important to combine the information gathered on the genesis of EEG and neocortical dynamics with the findings from neurofeedback investigations. This will help us to develop models of how neurofeedback might operate in producing the changes in EEG and in clinical symptomatology. We know that the cortex operates in terms of resonant loops between neocortical columns of cells known as local, regional, and global resonances. These resonances determine the specific EEG frequencies and are often activated by groups of cells in the thalamus known as pacemakers. There are complex excitatory and inhibitory interactions within the cortex and between the cortex and the thalamus that allow these loops to operate and provide the basis for learning. Neurofeedback is a technique for modifying these resonant loops, and hence, modifying the neurophysiological and neurological basis for learning and for the management of a number of neurologically based disorders. This paper provides an introduction to understanding EEG and neocortical dynamics and how these concepts can be used to explain the results of neurofeedback training and other interventions particularly in the context of understanding attentive mechanisms and for the management of attention deficit/hyperactivity disorders.     

Excitation of cat spinal cord dorsal column fibers during stimulation of different fiber groups of cutaneous and somatic nerves

The effects of electrically stimulating different groups of nerve fibers supplying the skin and muscle on evoked potentials in cat spinal cord dorsal columns were studied. Significant differences in the configuration of dorsal column potentials recorded in response to stimulation of these nerves were found. It was shown that cutaneous nerve unmyelinated fibres were connected to unmyelinated dorsal column fibers. In addition, excitation of cutaneous C-fibers lead to activation of dorsal column fibers with the maximum conduction velocity. The somatic nerve was only connected to myelinated dorsal column fibers, and excitation of its non-myelinated fibers did not cause other types of dorsal column fibers to be activated. It is suggested that the acceleration of cutaneous signal transmission in the dorsal column system may be brought about by the necessity for rapid warning of potentially harmful stimuli.Medical Institute, Russian Federation Ministry of Public Health, Nizhny Novgorod. Translated from Neirofiziologiya, Vol. 24, No. 5, pp. 625–635, September–October, 1992.     

Ultrastructure of the rat pineal stalk

The ultrastructure of the rat pineal stalk was described. The pineal stalk contained few pinealocytes, glial cells and numerous nerve fibers. The last were mostly non-myelinated axons, although a few myelinated ones were also observed. Glial cells showed many filaments, mostly in the processes which presented a longitudinal orientation. Other more lamellar processes were found enclosing the axons. The pineal stalk became wider as it reached the body of the gland. Ultrastructurally, this wide region resembled more the pineal body. Bundles of non-myelinated nerve fibers were seen around the pineal stalk.     

Visual inter-hemispheric processing: constraints and potentialities set by axonal morphology.

The largest bundle of axonal fibers in the entire mammalian brain, namely the corpus callosum, is the pathway through which almost half a billion neurons scattered over all neocortical areas can exert an influence on their contralateral targets. These fibers are thus crucial participants in the numerous cortical functions requiring collaborative processing of information across the hemispheres. One of such operations is to combine the two partial cortical maps of the visual field into a single, coherent representation. This paper reviews recent anatomical, computational and electrophysiological studies on callosal connectivity in the cat visual system. We analyzed the morphology of individual callosal axons linking primary visual cortices using three-dimensional light-microscopic techniques. While only a minority of callosal axons seem to perform a strict 'point-to-point' mapping between retinotopically corresponding sites in both hemispheres, many others have widespread arbors and terminate into a handful of distant, radially oriented tufts. Therefore, the firing of a single callosal neuron might influence several cortical columns within the opposite hemisphere. Computer simulation was then applied to investigate how the intricate geometry of these axons might shape the spatio-temporal distribution of trans-callosal inputs. Based on the linear relation between diameter and conduction velocity of myelinated fibers, the theoretical delays required for a single action potential to reach all presynaptic boutons of a given arbor were derived from the caliber, g-ratio and length of successive axonal segments. This analysis suggests that the architecture of callosal axons is, in principle, suitable to promote the synchronous activation of multiple targets located across distant columns in the opposite hemisphere. Finally, electrophysiological recordings performed in several laboratories have shown the existence of stimulus-dependent synchronization of visual responses across the two hemispheres. Possible implications of these findings are discussed in the context of temporal tagging of neuronal assemblies.     

Role of myelinated and unmyelinated fibers of the vagus nerve in the development of ischemic fibrillation of the heart]

The effect of nn. vagi on ischemic heart arrhythmia was studied in acute experiments on cats. It was shown that thick myelinated fibers do not significantly alter the rate of onset of such arrhythmias. On the contrary, where the nn. vagi were cooled to 0 degree C, which entrained the block of non-myelinated fibers as well, the rate of ischemic heart arrhythmias (including heart fibrillation) drastically increased.     

High diversity,abundance and distinct fish assemblages on submerged coral reef pinnacles compared to shallow emergent reefs

Coral Reefs - Coral reefs exhibit consistent patterns in biodiversity across multiple spatial scales, from local to global clines in species richness, abundance and community structure. Knowledge...     

Understanding extinction debts: spatio–temporal scales,mechanisms and a roadmap for future research

Extinction debt refers to delayed species extinctions expected as a consequence of ecosystem perturbation. Quantifying such extinctions and investigating long‐term consequences of perturbations has proven challenging, because perturbations are not isolated and occur across various spatial and temporal scales, from local habitat losses to global warming. Additionally, the relative importance of eco‐evolutionary processes varies across scales, because levels of ecological organization, i.e. individuals, (meta)populations and (meta)communities, respond hierarchically to perturbations. To summarize our current knowledge of the scales and mechanisms influencing extinction debts, we reviewed recent empirical, theoretical and methodological studies addressing either the spatio–temporal scales of extinction debts or the eco‐evolutionary mechanisms delaying extinctions. Extinction debts were detected across a range of ecosystems and taxonomic groups, with estimates ranging from 9 to 90% of current species richness. The duration over which debts have been sustained varies from 5 to 570 yr, and projections of the total period required to settle a debt can extend to 1000 yr. Reported causes of delayed extinctions are 1) life‐history traits that prolong individual survival, and 2) population and metapopulation dynamics that maintain populations under deteriorated conditions. Other potential factors that may extend survival time such as microevolutionary dynamics, or delayed extinctions of interaction partners, have rarely been analyzed. Therefore, we propose a roadmap for future research with three key avenues: 1) the microevolutionary dynamics of extinction processes, 2) the disjunctive loss of interacting species and 3) the impact of multiple regimes of perturbation on the payment of debts. For their ability to integrate processes occurring at different levels of ecological organization, we highlight mechanistic simulation models as tools to address these knowledge gaps and to deepen our understanding of extinction dynamics.     

EEG simulation: variation of spectral envelope, pulse synchrony and ≈40 Hz oscillation

 Macroscopic EEG travelling wave phenomena and cortical pulse synchronisation effects are related within a single simple simulation. Non-specific activation acts to control the transfer function of the simulated cortex, and thus determines the relative amplitude of macroscopic EEG waves generated by rhythmic inputs. When concurrent asynchronous excitatory inputs to separate, local, cortical sites are introduced, the simulation reproduces both gamma-band (40 Hz) electrocorticogram (ECoG) activity and synchronous oscillation of action potential pulse density at the separate sites. The gamma-band ECoG and pulse synchrony effects depend on different mechanisms: the former upon local excitatory/inhibitory interactions, and the latter on cortico-cortical interactions. The pattern of synchronous activity depends upon both structural and dynamic aspects of gain, and is sustained by linearised versions of the simulation’s state equations. Dynamic properties of the simulation, which are independent of scale, describe both microscopic and macroscopic phenomena, all in accord with physiological findings. Received: 25 June 1996 / Accepted in revised form: 29 November 1996     

Ultrastructural observations on the central innervation of the guinea-pig pineal gland

Summary In the present study the central innervation of the guinea-pig pineal gland was investigated. The habenulae and the pineal stalk contain myelinated and non-myelinated nerve fibres with few dense-cored and electron-lucent vesicles. Some myelinated fibres leave the main nerve fibre bundles, lose their myelin-sheaths and terminate in the pineal gland. Although direct proof is lacking, the non-myelinated fibres appear to end near the site where the bulk of the myelinated fibres are located. Here a neuropil area exists where synapses between non-myelinated fibre elements are abundant. Neurosecretory fibres were also seen. The results support the concept of functional interrelationships between hypothalamus, epithalamus and the pineal gland.     

Meta-ecosystems: a theoretical framework for a spatial ecosystem ecology

This contribution proposes the meta‐ecosystem concept as a natural extension of the metapopulation and metacommunity concepts. A meta‐ecosystem is defined as a set of ecosystems connected by spatial flows of energy, materials and organisms across ecosystem boundaries. This concept provides a powerful theoretical tool to understand the emergent properties that arise from spatial coupling of local ecosystems, such as global source–sink constraints, diversity–productivity patterns, stabilization of ecosystem processes and indirect interactions at landscape or regional scales. The meta‐ecosystem perspective thereby has the potential to integrate the perspectives of community and landscape ecology, to provide novel fundamental insights into the dynamics and functioning of ecosystems from local to global scales, and to increase our ability to predict the consequences of land‐use changes on biodiversity and the provision of ecosystem services to human societies.     

A Novel Approach for Studying the Physiology and Pathophysiology of Myelinated and Non-Myelinated Axons in the CNS White Matter

Advances in brain connectomics set the need for detailed knowledge of functional properties of myelinated and non-myelinated (if present) axons in specific white matter pathways. The corpus callosum (CC), a major white matter structure interconnecting brain hemispheres, is extensively used for studying CNS axonal function. Unlike another widely used CNS white matter preparation, the optic nerve where all axons are myelinated, the CC contains also a large population of non-myelinated axons, making it particularly useful for studying both types of axons. Electrophysiological studies of optic nerve use suction electrodes on nerve ends to stimulate and record compound action potentials (CAPs) that adequately represent its axonal population, whereas CC studies use microelectrodes (MEs), recording from a limited area within the CC. Here we introduce a novel robust isolated "whole" CC preparation comparable to optic nerve. Unlike ME recordings where the CC CAP peaks representing myelinated and non-myelinated axons vary broadly in size, "whole" CC CAPs show stable reproducible ratios of these two main peaks, and also reveal a third peak, suggesting a distinct group of smaller caliber non-myelinated axons. We provide detailed characterization of "whole" CC CAPs and conduction velocities of myelinated and non-myelinated axons along the rostro-caudal axis of CC body and show advantages of this preparation for comparing axonal function in wild type and dysmyelinated shiverer mice, studying the effects of temperature dependence, bath-applied drugs and ischemia modeled by oxygen-glucose deprivation. Due to the isolation from gray matter, our approach allows for studying CC axonal function without possible "contamination" by reverberating signals from gray matter. Our analysis of "whole" CC CAPs revealed higher complexity of myelinated and non-myelinated axonal populations, not noticed earlier. This preparation may have a broad range of applications as a robust model for studying myelinated and non-myelinated axons of the CNS in various experimental models.     

The formation of free axonal sprouts from a dorsal root ganglion-nerve preparation maintained in organotypic culture,and the effects of demecolcine

Summary Nerve-ganglion preparations from rat dorsal spinal nerve roots were maintained in organotypic culture for 20 h. Free axonal sprouts formed at the cut tips. Clear and dense-core vesicles, mitochondria and smooth endoplasmic reticulum accumulated in the axons for a distance of 500 m behind the cut, as has previously been described in dorsal roots sectioned in vivo. Sprouting did not occur in dorsal roots maintained in culture without their ganglia attached. Sprouting was also prevented by demecolcine (3 × 10^-7 M) which reduced the number of microtubules in non-myelinated, small myelinated and large myelinated axons to respectively 45, 30 and 20% of control values. The sprouts contained several types of vesicle including small clear vesicles, large and small dense-core vesicles and flattened vesicles. The possible relevance of the vesicles to transmitter mechanisms in these neurones is discussed.I.R.D. is supported by the Medical Research Council; P.K. thanks the Mental Health Trust for a project grant     

Escape reaction performance of myelinated and non-myelinated calanoid copepods

Calanoid copepods from seven families in three superfamilies were exposed to a controlled near-field hydrodynamic stimulus and their escape reactions were recorded using high-speed videographic techniques. Copepod species have two distinct mechanisms for increasing conduction speed of neural signals: larger diameter nerve axons and insulated axons, i.e., myelination. Myelinated axons have been found in certain species of the more recently-evolved calanoid superfamilies. Copepod representatives from these superfamilies were expected to have shorter response latencies than species from more ancestral superfamilies due to the increased conduction speed of nerve impulses in myelinated neurons. Using frame-by-frame playback and computerized motion analysis techniques, response latency, jump speed, and acceleration were measured. Kinetic performance of copepods was highly variable, with mean escape speeds ranging between 100-250 mm s^− 1 and accelerations of 9-230 m s^− 2. Minimum behavioral response latencies of 2 ms were recorded for both myelinated and non-myelinated calanoids. There was no significant difference between the response latencies of copepods from the myelinated and non-myelinated superfamilies. Furthermore, no relationships were found between copepod latency and size for either myelinated or non-myelinated species. Previous research may suggest that myelin may shorten the response latencies of certain calanoid species. However, our results show that non-myelinated copepods are also capable of responding rapidly, within as few as 2 ms, to hydrodynamic stimuli and produce similar kinetic performance to myelinated species. The main advantage of myelination over giant nerve axons is their more efficient transfer of nerve impulses resulting in a metabolic energy savings. Although this energetic reward would be important for copepods in food-limited environments, for coastal copepods, in food-rich habitats, either mechanism is a viable solution.     

家兔主动脉神经低阈压力感受反射快速重调中枢过程的特征

40只家兔,乌拉坦静脉麻醉。切断双侧主动脉神经(AN)、窦神经及迷走神经。以选择兴奋 AN 有髓传人纤维的条件刺激(0.02ms,50Hz,4—6V,5min)给予切断的 AN 中枢段,模拟导致低阈压力感受反射快速重调的保持压背景,借以诱导快速重调的中枢过程。实验表明:该中枢过程使 AN 有髓纤维传入所激发的压力感受反射降压效应衰减41.82%(P<0.01),肾交感神经活动抑制效应衰减19.31%(P相似文献   

Modeling microdamage behavior of cortical bone

Bone is a complex material which exhibits several hierarchical levels of structural organization. At the submicron-scale, the local tissue porosity gives rise to discontinuities in the bone matrix which have been shown to influence damage behavior. Computational tools to model the damage behavior of bone at different length scales are mostly based on finite element (FE) analysis, with a range of algorithms developed for this purpose. Although the local mechanical behavior of bone tissue is influenced by microstructural features such as bone canals and osteocyte lacunae, they are often not considered in FE damage models due to the high computational cost required to simulate across several length scales, i.e., from the loads applied at the organ level down to the stresses and strains around bone canals and osteocyte lacunae. Hence, the aim of the current study was twofold: First, a multilevel FE framework was developed to compute, starting from the loads applied at the whole bone scale, the local mechanical forces acting at the micrometer and submicrometer level. Second, three simple microdamage simulation procedures based on element removal were developed and applied to bone samples at the submicrometer-scale, where cortical microporosity is included. The present microdamage algorithm produced a qualitatively analogous behavior to previous experimental tests based on stepwise mechanical compression combined with in situ synchrotron radiation computed tomography. Our results demonstrate the feasibility of simulating microdamage at a physiologically relevant scale using an image-based meshing technique and multilevel FE analysis; this allows relating microdamage behavior to intracortical bone microstructure.     

Electrophysiology of the peripheral effect of two analgesics: aspirin and dibencozide

The peripheral effect of two analgesics (aspirin and dibencozide) was studied on anaesthetized cats. Several types of neurons and stimulations were performed in this work: traction for periodontal mechanoreceptors connected to small-sized trigeminal fibres, distension for the muscular intestinal mechanoreceptors connected to non-myelinated vagal fibres, chemical stimulation by means of phenyldiguanide for the non-myelinated vagal fibres, electrical stimulation of the myelinated and non-myelinated vagal fibres. In all cases, unitary activities were recorded into corresponding ganglia (nodose or gasserian) with extracellular glass microelectrodes. After injection of analgesics, a decrease of control responses were observed till 30 minutes but the maximum occurred between 1 and 5 minutes. This effect concerned the non-myelinated neurones as well as the myelinated ones. It can be explained by a direct action of analgesics on the ending excitability.     

Assessment of the reflex vagal origin of broncho-constrictor effects of hypercapnia in cats (author's transl)

Breath-by-breath measurements of pulmonary resistance (RL) were used to study the bronchomotor effects produced by the inhalation of a CO2-enriched gas mixture in anaesthetized, spontaneously breathing cats. A significant increase in RL occurred from the second inhalation of the hypercapnic gas mixture. This bronchoconstrictor effect lasted about 18 seconds, then a marked decrease in RL was observed. The secondary bronchodilatation persisted during the entire hypercapnic test (4 min). After surgical suppression of the sensory vagal component at the level of the nodose ganglion (bilateral sensory vagotomy), the early bronchoconstrictor effect of CO2 disappeared, but the secondary bronchodilatation was unchanged. In other experiments, after procaine block of the nervous conduction in non-myelinated vagal fibers, the bronchomotor effects of CO2 were the same as those observed after sensory vagotomy. In contrast, an electrotonic block of both vagus nerves, which abolished nervous conduction in myelinated fibers, did not suppress the bronchoconstrictor response to hypercapnia. Thus, the early increase in RL, which follows inhalation of a hypercapnic gas mixture, seems to be reflexly mediated by vagal afferents, especially by non-myelinated fibers.     

Using ecological networks to answer questions in global biogeography and ecology

Ecological networks have classically been studied at site and landscape scales, yet recent efforts have been made to collate these data into global repositories. This offers an opportunity to integrate and upscale knowledge about ecological interactions from local to global scales to gain enhanced insights from the mechanistic information provided by these data. By drawing on existing research investigating patterns in ecological interactions at continental to global scales, we show how data on ecological networks, collected at appropriate scales, can be used to generate an improved understanding of many aspects of ecology and biogeography—for example, species distribution modelling, restoration ecology and conservation. We argue that by understanding the patterns in the structure and function of ecological networks across scales, it is possible to enhance our understanding of the natural world.     

The influence of multiple dispersal mechanisms and landscape structure on population clustering and connectivity in fragmented artesian spring snail populations

Many organisms occupy heterogeneous landscapes that contain both barriers to movement as well as corridors that facilitate dispersal. The extent to which such features determine population connectivity will depend on the mechanisms utilized by organisms to disperse. Here we examined the interaction between landscape structure and dispersal in the endemic aquatic snail, Fonscochlea accepta , in the fragmented artesian spring ecosystem of arid central Australia. We used frequentist and Bayesian analyses of microsatellite data to identify population structure and immigration for 1130 snails sampled from 50 springs across an entire spring complex. We introduce a modified isolation-by-distance analysis to test hypotheses about how populations are clustered and to distinguish the most likely dispersal pathways within and between those clusters. Highly significant differences in F _ST values and significant isolation-by-distance patterns were detected among springs across the entire complex, while Bayesian assignment tests revealed the presence of two hierarchical levels of spring clustering. Clusters were defined by the spatial aggregation of springs, dynamic aquatic habitat connections between springs and the ecology of the snails. Bayesian immigrant identification and our modified isolation-by-distance analysis revealed that dispersal occurs at two geographical scales via two very different mechanisms. Short range dispersal (usually ≤ 300 m) occurs via active movement facilitated by aquatic connections among springs while long-range dispersal (≥ 3 km) is likely facilitated by an animal vector (phoresy). These results underline the importance of both dispersal mode and landscape structure in influencing connectivity rates and patterns among populations.