FENS-2014-Milan 5-9 июля 2014 года Милан, Италия «FENS Forum of Neuroscience»

 

 

 

 

На форуме были представлены четыре постера:

  • OPTOGENETIC APPROACH FOR INVESTIGATION OF GABA ACTIONS IN THE NEURONAL NETWORKS

Presenter: G. Valeeva

We present a novel approach for non-invasive investigation of gamma-aminobutyric acid (GABA) actions in neuronal networks of cerebral cortex. It does not require using any pharmacological agents and preserves native intracellular ion composition as well as intact membrane potential of cells affected by GABA. A mice line expressing channelrhodopsin-2 (ChR2) in GABAergic interneurons was used to monitor developmental changes in GABA-mediated responses characteristic for rodents? brain early in postnatal life. ChR2 is a light-gated cation-permeable membrane receptor which allows Na+ influx to depolarize and excite cells when illuminated by blue (~ 470 nm) light. Patch-clamp recordings were performed during laser stimulation of ChR2 expressing interneurons in hippocampal and neocortical slices obtained from P (postnatal day) 2-15 mice. Starting from P2 onwards, laser light excited interneurons to release GABA and to evoke postsynaptic GABAergic currents. Excitatory/inhibitory GABA actions on pyramidal cells were further assessed by monitoring EPSCs frequency alteration during photoactivation of interneurons. Until P8, photoactivation of interneurons caused an increase in EPSCs frequency, whereas in older animals a decrease in EPSCs frequency was observed. Thus, the timing of the developmental switch obtained using this technique matches the developmental changes in GABA actions previously reported using traditional electrophysiological and imaging methods. This study demonstrates a utility of presented optogenetics based approach for investigation of GABA actions during development. It can also be employed for exploration of GABAergic function in other physiological or pathological conditions where an assessment of GABA actions is required.

  • DEVELOPMENTAL SWITCH FROM ELECTRICAL TO SYNAPTIC COUPLING BETWEEN LAYER 4 EXCITATORY NEURONS IN THE NEONATAL RAT BARREL CORTEX

Presenter: F. Valiullina

In adult somatosensory cortex, only 10% of excitatory inputs to L4 cortical neurons are provided by thalamic inputs. The remaining 90% of synapses are of intracortical origin, largely representing recurrent excitatory connections between neighboring neurons within a single barrel which enables amplification of the thalamic inputs. Our aim was to characterize the development of excitatory connections between L4 neurons during the postnatal period. Using dual patch-clamp recordings from the neurons in slices of postnatal days (P4-15) rat somatosensory barrel cortex we analyzed 128 neuronal pairs at different ages. We found two types of connections between barrel cells during the postnatal development: (i) electrical connections and (ii) chemical glutamatergic synapses. These were identified on the basis of their electrical coupling and sensitivity to carbenoxolone. Electrical synapses were observed in 10-15% of recorded pairs during the first postnatal week, and their expression progressively decreased with age. Glutamatergic synapses showed an inverse developmental profile: no glutamatergic connections were detected until the postnatal age P5, and their incidence progressively increased with age, reaching nearly 20% probability of all pairs by the end of the second postnatal week. Thus, the development of connectivity between barrel neurons is characterized by a developmental switch from electrical to chemical connectivity and this transition coincides with a switch in sensory mode processing from bursting to acuity. We hypothesize that electrical synapses between barrel cells support their synchronization during generation of the early oscillatory activity patterns that are characteristic of the developing thalamocortical networks during the first postnatal week.

  • SENSORY FEEDBACK BY SPONTANEOUS MUSCLE TWITCHES IN NEONATAL RATS

Presenter: A. INACIO

FENS-2014-Ana-Rita-Lourenco-InacioDuring the critical period for development of sensorimotor function, sleep is a predominant state, and behavior is dominated by spontaneous muscle twitches, short contractions in atonic muscles. Twitches participate in activity-dependent formation of spinal cord circuits and trigger oscillatory patterns in the developing somatosensory cortex, delta-brushes in human fetuses and neonates, as well as spindle-bursts and early gamma oscillations in neonatal rats. It has thus been proposed that twitches originate sensory feedback, but this hypothesis has not been directly tested. By simultaneously recording neuronal activity at the population level across all spinal cord laminae and limb twitches and movements of neonatal rats, we demonstrate the following network dynamics: activity bursts in the ventral horn (motor) -> twitching -> dorsal horn activity (sensory). This phenomenon is disrupted following transection of sensory afferents: while bursts at the level of the ventral horn precede twitches and twitching frequency remains unaltered, activity at the level of the spinal dorsal horn is abolished. Our results provide direct evidence for twitches-triggered sensory feedback in activation of spinal dorsal neurons.

  • POSTNATAL EMERGENCE OF TOPOGRAPHIC WHISKER MAP IN THE RAT BARREL CORTEX

Presenter: M. Minlebaev

Somatosensory barrel cortex in rodents is organized in a topographic map of the facial whiskers in which each barrel is tuned to a single whisker at the snout. However, it remains unknown when this correspondence is established during early development, or functionally protomap is precise before formation of anatomical barrels. Here, we addressed this question by using a combination of extracellular and whole-cell recordings from the barrel cortex of 0-7 day old (P0-7) rat pups in vivo. At P0-1 the level of whisker tuning in cortical neurons was low, with multiple adjacent whiskers evoking large multiunit responses and excitatory postsynaptic currents, however cortical neurons showed maximal responses to a single (principal) whisker. Along with these findings, projection fields of neighbour whiskers in barrel cortex were broad and largely overlapped in P0-1 rats. Starting from P2-3, segregated whisker map emerged, characterized by preferential single whisker tuning and segregated whisker projection fields comparable to that in adult rats. These results indicate that functional whisker protomap in somatosensory cortex is imprecise at birth. During the two-three days after birth, a "critical" period in the barrel map formation, whiskers compete for the cortical territories to form segregated whisker map, which formation coincides with an emergence of the anatomical barrel map.