Cortical Auditory-Evoked Responses in Preterm Neonates: Revisited by Spectral and Temporal Analyses.

Characteristic preterm EEG patterns of "Delta-brushes" (DBs) have been reported in the temporal cortex following auditory stimuli, but their spatio-temporal dynamics remains elusive. Using 32-electrode EEG recordings and co-registration of electrodes' position to 3D-MRI of age-matched neonates, we explored the cortical auditory-evoked responses (AERs) after 'click' stimuli in 30 healthy neonates aged 30-38 post-menstrual weeks (PMW). (1) We visually identified auditory-evoked DBs within AERs in all the babies between 30 and 33 PMW and a decreasing response rate afterwards. (2) The AERs showed an increase in EEG power from delta to gamma frequency bands over the middle and posterior temporal regions with higher values in quiet sleep and on the right. (3) Time-frequency and averaging analyses showed that the delta component of DBs, which negatively peaked around 550 and 750 ms over the middle and posterior temporal regions, respectively, was superimposed with fast (alpha-gamma) oscillations and corresponded to the late part of the cortical auditory-evoked potential (CAEP), a feature missed when using classical CAEP processing. As evoked DBs rate and AERs delta to alpha frequency power decreased until full term, auditory-evoked DBs are thus associated with the prenatal development of auditory processing and may suggest an early emerging hemispheric specialization.

[DETECTION OF OPTICAL INTRINSIC SIGNAL IN SOMATOSENSORY CORTEX OF NEONATAL RATS USING PRINCIPAL COMPONENT ANALYSIS].

Recordings of the intrinsic optical signal (IOS) are widely used in the functional imaging of the central nervous system in vivo. However, the IOS technique has been mainly described in the adult brain and the possibility of using IOS for the robust functional imaging of the immature brain and the optimal parameters for IOS recording and analysis in the analysis in the immature brain tissue remain largely unknown. Here, we show that the use of the near to infrared light and automatic PCA enable efficient detection of IOS in the neonatal rat pups' whisker-related somato- sensory cortex during the first three weeks after the birth. IOS detection using automatic PCA survived fourfold artificial noise increase in the baseline, indicating on the robustness of this approach. Thus, our findings indicate that IOS imaging using near infrared light and automatic PCA is efficient technique for the functional imaging of somatosensory cortex in the neonatal rats.

Selective suppression of excessive GluN2C expression rescues early epilepsy in a tuberous sclerosis murine model.

Tuberous sclerosis complex (TSC), caused by dominant mutations in either TSC1 or TSC2 tumour suppressor genes is characterized by the presence of brain malformations, the cortical tubers that are thought to contribute to the generation of pharmacoresistant epilepsy. Here we report that tuberless heterozygote Tsc1(+/-) mice show functional upregulation of cortical GluN2C-containing N-methyl-D-aspartate receptors (NMDARs) in an mTOR-dependent manner and exhibit recurrent, unprovoked seizures during early postnatal life (

Gamma oscillations in the somatosensory cortex of newborn rats.

Here we addressed a question of whether gamma oscillations previously described in the whisker-related barrel cortex are a universal pattern of activity in the somatosensory cortex of newborn rats. Intracortical recording of local field potentials and action potentials in neurons using multisite silicon electrodes in 2-7-day-old rats showed that mechanical stimulation of single fingers or specific areas on the plantar or back side of the foot evoked early gamma oscillations followed by spindle-burst oscillations in the corresponding regions of the somatosensory cortex. Early gamma oscillations had maximum amplitude in layer IV of the somatosensory cortex and effectively synchronized action potentials in layer IV neurons. It was concluded that early gamma oscillations evoked by activation of the topographic sensory input are a universal activity pattern of the entire somatosensory cortex of newborn rats.

Early gamma oscillations.

Gamma oscillations have long been considered to emerge late in development. However, recent studies have revealed that gamma oscillations are transiently expressed in the rat barrel cortex during the first postnatal week, a "critical" period of sensory-dependent barrel map formation. The mechanisms underlying the generation and physiological roles of early gamma oscillations (EGOs) in the development of thalamocortical circuits will be discussed in this review. In contrast to adult gamma oscillations, synchronized through gamma-rhythmic perisomatic inhibition, EGOs are primarily driven through feedforward gamma-rhythmic excitatory input from the thalamus. The recruitment of cortical interneurons to EGOs and the emergence of feedforward inhibition are observed by the end of the first postnatal week. EGOs facilitate the precise synchronization of topographically aligned thalamic and cortical neurons. The multiple replay of sensory input during EGOs supports long-term potentiation at thalamocortical synapses. We suggest that this early form of gamma oscillations, which is mechanistically different from adult gamma oscillations, guides barrel map formation during the critical developmental period.

Effect of blockers of potential-dependent and calcium-activated K+-channels on facilitation of neuromuscular transmission.

Rhythmic stimulation of nerve-muscle preparation of frog sternal muscle bathed in low-Ca(2+) saline increased the release of neurotransmitter (facilitation) and modified the shape of extracellular response of nerve terminal (decreased phase III amplitude). Iberiotoxin and 4-aminopyridine modified the dynamics these processes. We conclude that inactivation of potential-dependent K(+)-channels and activation of calcium-dependent K(+)-channels in frog motor nerve terminals during rhythmic activity modulate Ca(2+) influx into nerve terminals and contribute into facilitation of neurotransmitter secretion. The degree of these mechanisms depends on the rate of synaptic rhythmic activity.

Transmitter secretion in the frog neuromuscular synapse after prolonged exposure to calcium-free solutions.

Experiments on neuromuscular synapses from frog skin/chest muscle preparations in conditions of extracellular recording addressed changes in the spontaneous and evoked transmitter secretion after long-term (1.5-6 h) maintenance of preparations in calcium-free solution containing EGTA. Use of three microelectrodes for recording of single-quantum postsynaptic signals showed that calcium-free solution altered the characteristic topography of transmitter secretion in nerve terminals, with widening and fusion of groups of transmitter release. These changes persisted after preparations were returned to the initial solution. These data suggest that calcium-free solutions lead to disorganization of the active zones of nerve endings, At initially low extracellular Ca ion concentrations (0.15-0.4 mM), disorganization of active zones induced by prolonged maintenance of preparations in calcium-free solutions led to decreases in the mean amplitude of endplate currents (EPC) because of decreases in their quantum composition, increases in the time course of transmitter secretion, and decreases in the frequency of miniature endplate currents. The relationship between quantum composition of EPC and the extracellular Ca ion concentration showed a sharp displacement towards higher concentrations, without significant changes in the slope of the relationship. At high initial Ca concentrations (1.8 mM), long-term exposure to calcium-free solutions led to a less marked decrease in EPC amplitude. It is suggested that the extra- and intracellular Ca ion concentrations support the maintenance of the characteristic morphofunctional organization of the apparatus responsible for transmitter secretion in frog nerve endings. Disorganization of the active zones leads to disruption of elements involved in transmitter secretion and decreases in the efficiency of secretion.

[Analysis of living motor nerve ending of a frog by endocytotic fluorescent marker FM 1-43]. / Prizhiznennoe fluorestsentnoe issledovanie dvigatel'nogo nervnogo okonchaniia liagushki s ispol'zovaniem éndotsitoznogo markera FM 1-43.

In our experiments on motor nerve endings of the frog cutaneous pectoris muscle, using fluorescent marker FM 1-43, the intensity and topography of endocytosis were investigated after the initiation of massive exocytosis of synaptic vesicles by increasing the extracellular potassium concentration. Using FM 1-43, fluorescent spots were shown to appear, looking as accumulations of synaptic vesicles in the active zone region. The forms and sizes of luminous spots and the distances between them were analysed. Considerable variations in brightness and total areas of fluorescent spots per a length unit in different regions of the nerve ending were revealed in addition to a proximal-distal gradient of these parameters along the nerve terminal. Peculiarities of topography and intensities of luminescence in the most terminal regions of the nerve ending are described. The obtained data are discussed in terms of the exo- and endocytosis cycle of synaptic vesicles in the active zone region, and from the point of view of the plasticity of the motor nerve ending and active zones. The factors involved in the transmitter release nonuniformity are analysed.

[Mediator secretion in the nerve-muscle synapse in the frog following long-term effect of calcium-free solutions]. / Sekretsiia mediatora v nervno-myshechnom sinapse u liagushki posle dlitel'nogo vozdeistviia beskal'tsievykh rastvorov.

The changes of spontaneous and evoked transmitter release in condition of long time (1-4 hours) incubation in Ca-free solution with EGTA adding, were investigated with extracellular recordings in experiments on the nerve-muscular junction of the frog cutaneous-pectoris muscle. Using the method of three extracellular microelectrodes recordings of the monoquantal postsynaptic signals, it was shown that during action of Ca-free solutions the topography of transmitter release changed, the specific spatial organization of points of transmitter release was disrupted. These changes remained after returning to the initial solution. The obtained data suggest that the Ca2+ free solution leads to disruption of active zones of nerve ending. In condition of low initial extracellular Ca2+ concentrations (0.15-0.4 mmol/l), the active zones disorganization led to decreasing of average amplitude of the end-plate currents (EPC) by decreasing their quantal content, increasing their time-course and decreasing the frequency of the miniature end-plate currents (MEPC). The sharp displacement of dependence of quantal contents of EPC in extracellular Ca2+ concentration to a higher Ca2+ concentration without significant changes of slope was revealed. In condition of high (1.8 mmol/l) concentration of Ca2+, the long action of Ca-free solutions leads to decreasing of amplitude of EPC too, but it was less obvious than in condition of initial low Ca2+ concentration. It is supposed that intra- and extracellular Ca concentration provides the support of the typical morpho-functional organization of the mechanisms of transmitter release at the nerve ending of the frog. The disorganization of active zones leads to separation of the elements, which take part at the transmitter release process and reduces the efficiency of secretion.