arXiv subjects

Dmitry N. Tsigankov

Publications and source records attributed to Dmitry N. Tsigankov.

3 recordsLinked to original sources

arXiv2004

Can repulsion be induced by attraction: a role of ephrin-B1 in retinotectal mapping?

We study a role of EphB receptors and their ligand ephrin-B1 in dorsal-ventral retinotopic mapping. Earlier studies suggested that ephrin-B1 acts as an attractant for EphB expressing axons. We address the results of the recent experiment in chick tectum (McLaughlin et al., 2003b) in which axons of retinal ganglion cells were shown to be repelled by high ephrin-B1 density. Thus it was proposed that ephrin-B1 might act as both attractant and repellent. We show that the same axonal behavior may follow from attraction to ephrin-B1 density and axonal competition for space. Therefore, we show how apparent repulsive interaction can be induced by a combination of attraction to the target and competitive interactions between axons. We suggest an experimental test that may distinguish repulsive interaction with the target from repulsion induced by attraction and competition.

q-bio.NC↗

arXiv2004

How to find decision makers in neural circuits?

Neural circuits often face the problem of classifying stimuli into discrete groups and making decisions based on such classifications. Neurons of these circuits can be distinguished according to their correlations with different features of stimulus or response, which allows defining sensory or motor neuronal types. In this study we define the third class of neurons, which is responsible for making decision. We suggest two descriptions for contribution of units to decision making: first, as a spatial derivative of correlations between neural activity and the decision; second, as an impact of variability in a given neuron on the response. These two definitions are shown to be equivalent, when they can be compared. We also suggest an experimental strategy for determining contributions to decision making, which uses electric stimulation with time- varying random current.

q-bio.NC↗

arXiv2003

A stochastic model for retinocollicular map development

We present a theoretical model for retinocollicular map development, which can account for intriguing behaviors observed in gain-of-function experiments in knock-in mice by Brown et al., including bifurcation in heterozygous Isl2/EphA3 knock-ins. The model is based on known chemical labels, axonal repulsion/competition, stochasticity and uses Markov chain description. Our model suggests that the map in heterozygotes is single-valued in the temporal region of retina due to reduced gradient of ephrin in the corresponding region of SC. The remaining map is double-valued since the gradient of ephrin is high there. We predict therefore that if gradient of ephrin is reduced by a genetic manipulation, the single-valued region of the map should occupy a larger portion of temporal retina, i.e. the point of transition between single- and doulble-valued maps should move to a more nasal position in Isl2-EphA3 heterozygotes. We also discuss the importance of inhomogeneous EphA gradient and mapping in Isl2/EphB knock-ins.

physics.bio-ph↗