Modification of cyclical activity in the spinal cord of the 16- to 20-day-old chick embryo due to changes in Ca2+ and Mg2+ concentrations

In isolated segments of the 16- to 20-day old chick embryo, increasing the Mg²⁺ concentration from 1.3 to 5.0 mmoles/liter in the superfusate caused complete suppression of spontaneous rhythmic activity that appeared as synchronous cyclical oscillations of electrotonic potentials in the dorsal and ventral roots. A similar change was recorded when the Ca²⁺ concentration was decreased from 2.6 to 1.0 mmole/liter, but in this case tonic discharges of impulses (spikes) could occur. Further, during the disappearance of the spontaneous activity due to changing the concentration of Ca²⁺ or Mg²⁺, in six out of eight experiments another type of rhythmic activity was seen, appearing as oscillations of electrotonic potentials in the ventral roots that were independent of oscillations in the dorsal roots. The amplitude of these oscillations of potential in the ventral roots was up to 200 µV, and their duration was up to 400 msec. The highest frequency of this activity was 0.4 sec^–1. The possible functional significance of the observed patterns of activity is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 3, pp. 333–338, May–June, 1991.     

Single nucleotide polymorphism rs1800872 in the promoter region of the IL10 gene is associated with predisposition to chronic hepatitis C in Russian population

Previously, we studied an association of two IL28B gene single nucleotide polymorphisms (SNPs) and three IL10 gene SNPs with predisposition to tick-borne encephalitis in a Russian population. In this study, a possible involvement of these SNPs in the development of predisposition to chronic hepatitis C (caused by structurally similar, related virus from the Flaviviridae family) was investigated in the same population. Only the IL10 promoter rs1800872 SNP was associated with predisposition to chronic hepatitis C. This SNP seems to be a common genetic marker of predisposition to two diseases caused by hepatitis C and tick-borne encephalitis viruses in Russian population.     

Basic principles of terminal flower formation

Studies of efflorescences of the mutants bractea and terminal flower1 and double mutant bra tfl1 of Arabidoipsis thaliana (L.) Heynh. have shown that the presence of a developed leaf in the node preceding the terminal flower is a necessary condition for the formation of the terminal flower perianth. This means that perianth cannot develop in an abracteose efflorescence of terminal flower. The second necessary condition for the terminal flower formation is a sufficient level of expression of the genes responsible for floral morphogenesis. Combination of these two conditions suffices for the development of a terminal flower with perianth. Since the general principles of organization are close for most flower plants, it can be stated that if the abracteose efflorescence is terminated by a flower with perianth, this is a consequence of forcing the lateral flower into the terminal position.     

The Principles of Data Formalization for Building Biological Model of Shoot Development in Flowering Plants

Shoot system of a plant can be divided into elementary molecules composed of phyllome, internode, and meristem of the lateral bud. The capacity of plants for open growth is manifested as multiple reproductions of the modules. These main principles of plant structural organization can be used to formalize and integrate the data from various disciplines studying shoot development—genetics of development, morphology, etc. At the example of a model species Arabidopsis thaliana we show that the data on genetic control of shoot development can be considered in terms of rearrangement of individual modules. Several variants of the module structural reorganization are allowed: reduction or transformation of phyllome, change in the internode length, and triggering active/inactive status of the lateral shoot meristem. Each variant of module structure corresponds to specific pattern of genes activity. Such integration of the data on genetic and structural aspects of morphogenesis can form a basis for mathematical modeling of plant development.     

Structure of flower in Arabidopsis thaliana: spatial pattern formation

Morphological analysis of flowers was carried out in Arabidopsis thaliana wild type plants and agamous and apetala2 mutants. No direct substitution of organs takes place in the mutants, since the number and position of organs in them do not correspond to the structure of wild type flower. In order to explain these data, a notion of spatial pattern formation in the meristem was introduced, which preceded the processes of appearance of organ primordia and formation of organs. Zones of acropetal and basipetal spatial pattern formation in the flower of wild type plants were postulated. It was shown that the acropetal spatial pattern formation alone took place in agamous mutants and basipetal spatial pattern formation alone, in apetala2 mutants. Different variants of flower structure are interpreted as a result of changes in the volume of meristem (space) and order of spatial pattern formation (time).     

N-methyl-D-aspartate effect on spontaneous activity of 16–20-day-old chick embryo spinal cord

The effects of N-methyl-D-aspartate (NMDA) and the NMDA receptor antagonist, 2-amino-5-phosphonovaleric acid (2-APV), on spontaneous activity of dorsal and ventral roots (DR and VR, respectively) generated by isolated spinal cord from 16–20-day-old chick embryo were studied. This activity was synchronous oscillations of electrotonic potentials in DR and VR. There was no impulse activity in the VR. When NMDA was applied at 2–25 µM, the amplitudes of the oscillations increased, the impulse activities in VR and DR developed, and the tonic component of electrotonic potentials appeared. At 20 µM, 2-APV decreased both, the spontaneous and NMDA induced activity. After sectioning of the spinal cord, the neuronal network of the isolated dorsal arm conserved the capacity to generate spontaneous activity in the DR which increased after NMDA application. There was no rhythm in the ventral part of the spinal cord. The localization of the NMDA-sensitive neuronal network, generator of the rhythmic (motor) activity, in the spinal cord is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 2, pp. 205–213, March–April, 1991.     

Mechanisms of spontaneous activity in developing spinal networks

Developing networks of the chick spinal cord become spontaneously active early in development and remain so until hatching. Experiments using an isolated preparation of the spinal cord have begun to reveal the mechanisms responsible for this activity. Whole-cell and optical recordings have shown that spinal neurons receive a rhythmic, depolarizing synaptic drive and experience rhythmic elevations of intracellular calcium during spontaneous episodes. Activity is expressed throughout the neuraxis and can be produced by different parts of the cord and by the isolated brain stem, suggesting that it does not depend upon the details of network architecture. Two factors appear to be particularly important for the production of endogenous activity. The first is the predominantly excitatory nature of developing synaptic connections, and the second is the presence of prolonged activity-dependent depression of network excitability. The interaction between high excitability and depression results in an equilibrium in which episodes are expressed periodically by the network. The mechanism of the rhythmic bursting within an episode is not understood, but it may be due to a “fast” form of network depression. Spontaneous embryonic activity has been shown to play a role in neuron and muscle development, but is probably not involved in the initial formation of connections between spinal neurons. It may be important in refining the initial connections, but this possibility remains to be explored. © 1998 John Wiley & Sons, Inc. J Neurobiol 37: 131–145, 1998

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Effects of dopamine on spontaneous activity generated by isolated spinal cord in 16- to 20-day-old chick embryos

The effects were investigated of applying L-DOPA, dopamine (DA), and noradrenaline (NA) on spontaneous activity (cyclic fluctuations in electrotonic dorsal and ventral root (DR and VR) potentials generated by a section of spinal cord isolated from 16 to 20-day-old chick embryos. A low concentration of L-DOPA (30–150 µm) intensified operation of the spinal generator, giving rise to above-threshold rhythm (i.e., spike activity in the DR and the VR). At a high concentration, L-DOPA produced inhibition of generator operation, although spontaneous activity did intensify during subsequent washout of the substance, with the onset of above-threshold rhythm. Both DA and NA failed to affect spontaneous activity in the VR and the DR at a concentration to 50 µM but a concentration of 100 µM produced inhibition. Application of 20 µM 2-amino-5-phosphonovaleric acid blocked the reinforced spontaneous activity produced by low L-DOPA concentrations. Activity generated by the neuronal network of the isolated dorsal horn rose under the effects of low L-DOPA concentrations; rhythmic activity was observed neither before nor after applying this substance in isolated ventral horn. Findings obtained would point to the occurrence of a direct (i.e., non-catecholamine dependent) excitatory influence of L-DOPA on the neuronal network of the chick embryo dorsal horn.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 3, pp. 338–343, May–June, 1991.     

Population behavior and self-organization in the genesis of spontaneous rhythmic activity by developing spinal networks

During development spinal networks generate recurring episodes of rhythmic bursting that can be recorded from motoneurons and interneurons. Optical imaging has identified a set of propriospinal interneurons that may be important in the production of this activity. These neurons are rhythmically active, are recurrently interconnected and have powerful projections to motoneurons. The excitability of this propriospinal network is depressed by activity and recovers in the interval between episodes. These and other observations have been formulated into a qualitative model in which population behavior and self-organization are responsible for the spontaneous activity generated by developing spinal networks.     

Imaging the spatiotemporal organization of neural activity in the developing spinal cord

In this review, we discuss the use of imaging to visualize the spatiotemporal organization of network activity in the developing spinal cord of the chick embryo and the neonatal mouse. We describe several different methods for loading ion- and voltage-sensitive dyes into spinal neurons and consider the advantages and limitations of each one. We review work in the chick embryo, suggesting that motoneurons play a critical role in the initiation of each cycle of spontaneous network activity and describe how imaging has been used to identify a class of spinal interneuron that appears to be the avian homolog of mammalian Renshaw cells or 1a-inhibitory interneurons. Imaging of locomotor-like activity in the neonatal mouse revealed a wave-like activation of motoneurons during each cycle of discharge. We discuss the significance of this finding and its implications for understanding how locomotor-like activity is coordinated across different segments of the cord. In the last part of the review, we discuss some of the exciting new prospects for the future.