Computational modeling of an early evolutionary stage of the nervous system

The object of this work is to create a computational model that examines the early evolution of the nervous system in relation to adaptive behavior. The main questions are: how did the nervous system and the most primitive forms of intelligence came into being, how a system can be organized during evolution that is able to ensure the adaptive behavior of a being, what are the basic rules of construction that are sufficient to create a workable nervous system without specifying the details of the construction. The biological bases of the model are the phyla Cnidaria and Porifera as they stand at the beginning of the genesis of nervous organization. We found in our model that in a network of homogenous epithelial-like cells, which is considered the starting point of the genesis of the nervous system, the changes that have positive influence on the behavior are those that make the spreading of the electric potential more efficient. It can cause the increase of the effectiveness of the behavior by itself without creating new specific cell-types. There are some alternatives to increasing the effectiveness of spreading of stimuli, for example increasing the value of biophysical parameters of the cells, or increasing the density of nerve cells and the number of synapses. If during the evolution a sort of cell comes into being that is able to conduct electrical stimuli--even in a rudimentary way--it can increase the adaptivity of behavior by itself without the need for specific information of how to organize the construction of this system.     

Involvement of novel feeding-related peptides in neuroendocrine response to stress

Various stressors are known to cause eating disorders. However, it is not known in detail about the neural network and molecular mechanism that are involved in the stress-induced changes of feeding behavior in the central nervous system. Many novel feeding-regulated peptides such as orexins/hypocretins and ghrelin have been discovered since the discovery of leptin derived from adipocytes as a product of the ob gene. These novel peptides were identified as endogenous ligands of orphan G protein-coupled receptors. The accumulating evidence reveals that these peptides may be involved in stress responses via the central nervous system, as well as feeding behavior. The possible involvement of novel feeding-related peptides in neuroendocrine responses to stress is reviewed here.     

Neurotoxicology:From the Whole Animal toMolecules

Neurotoxicity induced by a chemical in vivo is usually produced when the target site within the nervous system is exposed to a sufficient amount of the chemical or its toxic metabolite(s) for a duration of time that is sufficient to result in biological changes. These may be seen as changes in behavior, neurochemistry, neurophysiology, or neuropathology.     

Drugs,flies, and videotape: the effects of ethanol and cocaine on Drosophila locomotion

Drosophila melanogaster has been introduced recently as a model organism in which to study the mechanisms by which drugs of abuse change behavior and by which the nervous system changes upon repeated drug exposure. Surprising similarities between flies and mammals have begun to emerge at the behavioral, neurochemical and molecular levels.     

Network, cellular and molecular mechanisms of plasticity in simple nervous systems

In the present study we will try to single out several principles of the nervous system functioning essential for describing mechanisms of learning and memory basing on our own experimental investigation of cellular mechanisms of memory in the nervous system of gastropod molluscs and literature data: main changes in functioning due to learning occur in effectivity of synaptic inputs and in the intrinsic properties of postsynaptic neurons; due to learning some synaptic inputs of neurons selectively change its effectivity due to pre- and postsynaptic changes, but the induction of plasticity always starts in postsynapse, maintaining of long-term memory in postsynapse is also shown; reinforcement is not related to activity of the neural chain receptor-sensory neuron-interneuron-motoneuron-effector; reinforcement is mediated via activity of modulatory neurons, and in some cases can be exerted by a single neuron; activity of modulatory neurons is necessary for development of plastic modifications of behavior (including associative), but is not needed for recall of conditioned responses. At the same time, the modulatory neurons (in fact they constitute a neural reinforcement system) are necessary for recall of context associative memory; changes due to learning occur at least in two independent loci in the nervous system. A possibility for erasure of memory with participation of nitroxide is experimentally and theoretically based.     

Spontaneous hemodynamic oscillations during human sleep and sleep stage transitions characterized with near-infrared spectroscopy

Understanding the interaction between the nervous system and cerebral vasculature is fundamental to forming a complete picture of the neurophysiology of sleep and its role in maintaining physiological homeostasis. However, the intrinsic hemodynamics of slow-wave sleep (SWS) are still poorly known. We carried out 30 all-night sleep measurements with combined near-infrared spectroscopy (NIRS) and polysomnography to investigate spontaneous hemodynamic behavior in SWS compared to light (LS) and rapid-eye-movement sleep (REM). In particular, we concentrated on slow oscillations (3-150 mHz) in oxy- and deoxyhemoglobin concentrations, heart rate, arterial oxygen saturation, and the pulsation amplitude of the photoplethysmographic signal. We also analyzed the behavior of these variables during sleep stage transitions. The results indicate that slow spontaneous cortical and systemic hemodynamic activity is reduced in SWS compared to LS, REM, and wakefulness. This behavior may be explained by neuronal synchronization observed in electrophysiological studies of SWS and a reduction in autonomic nervous system activity. Also, sleep stage transitions are asymmetric, so that the SWS-to-LS and LS-to-REM transitions, which are associated with an increase in the complexity of cortical electrophysiological activity, are characterized by more dramatic hemodynamic changes than the opposite transitions. Thus, it appears that while the onset of SWS and termination of REM occur only as gradual processes over time, the termination of SWS and onset of REM may be triggered more abruptly by a particular physiological event or condition. The results suggest that scalp hemodynamic changes should be considered alongside cortical hemodynamic changes in NIRS sleep studies to assess the interaction between the autonomic and central nervous systems.     

Hormonally mediated changes in simple reflex circuits during metamorphosis in Manduca

During insect metamorphosis, the nervous system must be reorganized to allow the production of unique behaviors during each life stage. In the hawkmoth, Manduca sexta, it has been possible to follow this postembryonic phase of neuronal development at the level of identified neurons. Of particular interest in the present context are sensory neurons, motoneurons, and interneurons which persist through metamorphosis, but participate in different types of behavior at different stages of life. Many of these neurons undergo striking changes in their dendritic arborizations and axonal projection patterns, which can be correlated with changes in their synaptic interactions with other neurons. Manipulations of the ecdysteroid and juvenile hormone titers, both in vivo and in vitro, implicate these hormones in the regulation of metamorphic changes within the nervous system. Taking advantage of this endocrine control, it has been possible to create heterochronic mosaic animals that allow the relationship between specific cellular changes and behavioral alterations to be tested directly.     

Selective versus total insulin resistance: a pathogenic paradox

When food becomes scarce, animals undergo distinct metabolic, behavioral, and physiological changes that allow them to survive. In this issue, Greer et al. (2008) take advantage of the relatively simple and well-characterized nervous system of C. elegans to elucidate a neural circuit regulating feeding behavior and fat storage.     

The evolution of neuronal circuits underlying species-specific behavior.

The nervous system is evolutionarily conservative compared to the peripheral appendages that it controls. However, species-specific behaviors may have arisen from very small changes in neuronal circuits. In particular, changes in neuromodulatory systems may allow multifunctional circuits to produce different sets of behaviors in closely related species. Recently, it was demonstrated that even species differences in complex social behavior may be attributed to a change in the promoter region of a single gene regulating a neuromodulatory action.     

Polypocephalus sp. infects the nervous system and increases activity of commercially harvested white shrimp (Litopenaeus setiferus)

Larval tapeworms (Polypocephalus sp.) reside within the central nervous system of decapod crustaceans. Living within the nervous system would seem to create an excellent opportunity for the parasites to manipulate the behavior of their hosts, so we tested the hypothesis that behavior of white shrimp ( Litopenaeus setiferus ) would be correlated with the level of parasitic infection. We videorecorded the behavior of L. setiferus for 8 hr, then examined the nervous system and digestive glands for parasite infection. Larval Polypocephalus sp. were found in the nerve cord, often in large numbers, but only very rarely in the digestive gland, which was typically infected by the larval stage of the nematode, Hysterothylacium sp. There were significantly more Polypocephalus larvae in the abdominal and thoracic ganglia than the subesophageal ganglia and brain. Walking, but not swimming, was significantly and positively related to the number of Polypocephalus sp. lodged in nervous tissue, as well as shrimp carapace length. Polypocephalus sp. is 1 of only a few parasites residing inside the host nervous system and it may, therefore, be suitable for investigating mechanisms of parasite manipulation of invertebrate host behavior.     

Differential modulation of the expression of axonal proteins by non-neuronal cells of the peripheral and central nervous system.

Axonal behavior during the formation of the neuronal network of the nervous system has been shown to be under environmental control. Hence, as a first step in a project aiming to elucidate the molecular basis of axonal functions, we have identified axonal proteins whose synthesis is subject to environmentally induced changes. Neurons from chicken embryonic dorsal root ganglia (DRG) were grown in a compartmental cell culture system that allows selective examination of axonal proteins. Non-neuronal cells of the peripheral or central nervous system were co-cultured with the DRG axons. The axonal proteins expressed under these different environmental conditions were examined by metabolic labeling and two-dimensional SDS-polyacrylamide gel electrophoresis. Computerized quantification revealed that 12 out of 400 axonal proteins responded to changes in the local axonal environment by a change in their relative abundance. Some proteins changed in response to both types of co-cultures whereas some changed specifically under the influence of either peripheral or central non-neuronal cells.     

家蚕神经系统研究进展

家蚕Bombyx mori神经系统属于腹神经索型, 构造简单, 却能产生丰富的行为, 是研究神经生物学的理想实验材料。研究表明： 家蚕神经系统由中枢神经系统、 外周神经系统和交感神经系统构成, 通过信号传递在调节家蚕视觉、 嗅觉、 取食、 结茧、 交配、 排泄等生命活动中发挥作用。家蚕具有编码乙酰胆碱、 γ-氨基丁酸、 多巴胺等多种神经递质及其受体和促前胸腺激素（prothoracicotropic hormone, PTTH）、 滞育激素（diapause hormone, DH）等神经肽的基因。家蚕神经系统发育受到许多基因和bmo-miR-92等小分子RNA的调控。目前研究家蚕神经的方法主要有触角电位技术、 免疫细胞化学法、 转基因方法、 神经信息学及计算机三维重建等。对家蚕神经系统的研究有助于阐明神经系统的信号传递机制和生物神经网络的形成机制。     

Substance P in the central mechanism of the rabbit feeding response evoked by stimulation of the lateral hypothalamus

The effects of substance P on the central mechanisms of food motivation elicited by electrical stimulation of the lateral hypothalamus were studied in chronic experiments on rabbits. Intravenous injection of substance P (30 micrograms/kg) brought about a dramatic reduction in the excitability of the "food center" in the hypothalamus, which returned to normal 45-60 minutes after injection. Higher concentrations of substance P provoked food behavior inversion up to the replacement of food motivation by avoidance behavior. Intravenous injections of substance P disturbed the relationships between the hippocamp, midbrain reticular formation and hypothalamus seen in health. This manifested in complete cessation of the inhibitory effects of the dorsal hippocamp and facilitating influences of the midbrain reticular formation on the excitability of the hypothalamic "food center". It is assumed that disorders of the central mechanisms of food motivation may arise from the effects produced by substance P directly on the central nervous system or on the brain via changes in the hormonal balance and responses of the autonomous nervous system.     

Neural sites and pathways regulating food intake in birds: a comparative analysis to mammalian systems

The paper reviews hypotheses explaining the regulation of food intake in mammals that have addressed specific anatomical structures in the brain. An hypothesis, poikilostasis, is introduced to describe multiple, homeostatic states whereby the regulation of metabolism and feeding occur in birds. Examples are given for both wild and domestic avian species, illustrating dynamic shifts in homeostasis responsible for the changes in body weights that are seen during the course of an annual cycle or by a particular strain of bird. The following neural structures are reviewed as each has been shown to affect food intake in birds or in mammals: ventromedial hypothalamic nucleus (n.), lateral hypothalamic area, paraventricular hypothalamic n., n. tractus solitarius and area postrema, amygdala, parabrachial n., arcuate n. and bed n. of the stria terminalis. Two neural pathways are described which have been proposed to regulate feeding. The trigeminal sensorimotor pathway is the most complete neural pathway characterized for this behavior and encompasses the mechanics of pecking, grasping and mandibulating food particles from the tip of the bill to the back of the buccal cavity. A second pathway, the visceral forebrain system (VFS), affects feeding by regulating metabolism and the balance of the autonomic nervous system. Wild, migratory birds are shown to exhibit marked changes in body weight which are hypothesized to occur due to shifts in balance between the sympathetic and parasympathetic nervous systems. Domestic avian species, selected for a rapid growth rate, are shown to display a dominance of the parasympathetic nervous system. The VFS is the neural system proposed to effect poikilostasis by altering the steady state of the autonomic nervous system in aves and perhaps is applicable to other classes of vertebrates as well.     

Glial cell regulation of neurotransmission and behavior in Drosophila

Mounting evidence demonstrates that glial cells might have important roles in regulating the physiology and behavior of adult animals. We summarize some of this evidence here, with an emphasis on the roles of glia of the differentiated nervous system in controlling neuronal excitability, behavior and plasticity. In the review we highlight studies in Drosophila and discuss results from the analysis of mammalian astrocytes that demonstrate roles for glia in the adult nervous system.     

Proteomic analysis in the neurosciences

Proteomics is a field of study directed toward providing a comprehensive view of the characteristics and activity of every cellular protein. Rapid innovations in the core technologies required to characterize proteins on a global scale are poised to bring about a comprehensive understanding of how dynamic changes in protein expression, post-translational modification, and function affect complex signaling and regulatory networks. These advances have significant implications for understanding the multitude of pathways that govern behavior and cognition and the response of the nervous system to injury and disease.     

Diet, central nervous system, and aging.

A variety of morphological, structural, and chemical changes have been described in the central nervous systems of aging humans and animals. Brain size and volume decline during senescence, and the brain atrophy is accompanied by changes in the number, size, and ultrastructural characteristics of nerve and glial cells. Moreover, recent evidence suggests that the ability of central nervous system cells to communicate with one another via the release of neurotransmitter compounds might be impaired in the elderly. Nutritional factors may play important roles in the aging process of the central nervous system by influencing brain neurotransmission, or by accelerating or retarding geriatric changes in central nervous system structure.     

Sleep, learning, and birdsong

Neuroethological research combines approaches derived from animal behavior and neurobiology to examine the neuronal mechanisms of behavior, often in the context of laboratory experiments on species chosen for particular adaptations. Typically, these species are not traditional laboratory animals yet they contribute greatly to a broad, evolutionarily diverse view of nervous system function. The surprising role of sleep in the vocal learning process of songbirds is one such example, described here. Juvenile zebra finches show sleep-dependent daytime fluctuations in their patterns of singing starting after their first exposure to tutor songs. Nighttime bursting activity in the vocal control song system also changes after the onset of tutoring, with the neuronal changes preceding the changes in objective behavior (daytime singing). After tutoring, the nighttime bursting increases and exhibits structure that depends on the particular tutor song, and the nighttime expression of these changes requires normal auditory feedback during daytime singing. These observations shed light on the information carried in neuronal activity during sleep and on the adaptive plastic mechanisms engaged during sleep. They suggest a new hypothesis of sensorimotor learning, whereby sensory memories act indirectly on sensorimotor feedback by modifying networks through plastic changes at night. Sleep may also contribute to adult song maintenance, with nighttime neuronal replay conveying information about songs produced during the day and possibly mediating daily changes in the structure of premotor bursts. Collectively, these insights contribute a comparative perspective to theories of sleep and memory, which also help to inform a developing understanding of how humans acquire and retain memories.