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Stimulus Trains (stimulus + trains)

Distribution by Scientific Domains

Life Sciences	100%

Selected Abstracts

Presynaptic inhibition of Schaffer collateral synapses by stimulation of hippocampal cholinergic afferent fibres

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 3 2003
David Fernández de Sevilla
Abstract It has been known for decades that muscarinic agonists presynaptically inhibit Schaffer collateral synapses contacting hippocampal CA1 pyramidal neurons. However, a demonstration of the inhibition of Schaffer collateral synapses induced by acetylcholine released by cholinergic hippocampal afferents is lacking. We present original results showing that electrical stimulation at the stratum oriens/alveus with brief stimulus trains inhibited excitatory postsynaptic currents evoked by stimulation of Schaffer collaterals in CA1 pyramidal neurons of rat hippocampal slices. The increased paired-pulse facilitation and the changes in the variance of excitatory postsynaptic current amplitude that paralleled the inhibition suggest that it was mediated presynaptically. The effects of oriens/alveus stimulation were inhibited by atropine, and blocking nicotinic receptors with methyllycaconitine was ineffective, suggesting that the inhibition was mediated via the activation of presynaptic muscarinic receptors. The results provide a novel demonstration of the presynaptic inhibition of glutamatergic neurotransmission by cholinergic fibres in the hippocampus, implying that afferent cholinergic fibres regulate the strength of excitatory synaptic transmission. [source]

Naturalistic stimulus trains evoke reproducible subicular responses both within and between animals in vivo

HIPPOCAMPUS, Issue 2 2010
Beth Tunstall
Abstract Previous investigation of CA1-evoked subicular responses has used either single low-frequency pulses (LF), paired-pulses (PP), or high-frequency bursts. Here we test for the first time how subiculum responds to naturalistic stimulation trains (NSTs). We recorded CA1-evoked field potentials from dorsal rat subiculum in response to LF, PP, and two NST patterns. The latter were derived from CA1 place cell activity; NST1 contained bursts of stimuli presented in two main episodes, while the burst-patterned stimuli in NST2 were spaced more evenly. NSTs generated significantly greater field responses compared with LF or PP patterns. Response patterns to either NST were significantly correlated across trial repeats in 9 out of 10 rats, supporting a robust postsynaptic encoding of CA1 input by subiculum. Correlations between NST responses were also observed across experiments; however, these were more variable than those within experiments. The relationship between response magnitude and activation history revealed a strong correlation between magnitude and NST instantaneous frequency for NST1 but was weaker for NST2. In addition, the number of stimuli within a prior 500 ms window was a determining factor for response magnitude for both NSTs. Overall, the robust reproducibility in subicular responses within rats suggests that information within NSTs is faithfully transmitted through the CA1-subiculum axis. However, variation in response sequences across rats suggests that encoding patterns to the same input differ across the subiculum. Changes in the ratio of target bursting and regularly spiking neurons along the subicular proximodistal axis may account for this variation. The activation history of this connection also appears to be a strong determining factor for response magnitude. © 2009 Wiley-Liss, Inc. [source]

Learning to breathe: control of the inspiratory,expiratory phase transition shifts from sensory- to central-dominated during postnatal development in rats

THE JOURNAL OF PHYSIOLOGY, Issue 20 2009
Mathias Dutschmann
The hallmark of the dynamic regulation of the transitions between inspiration and expiration is the timing of the inspiratory off-switch (IOS) mechanisms. IOS is mediated by pulmonary vagal afferent feedback (Breuer,Hering reflex) and by central interactions involving the Kölliker,Fuse nuclei (KFn). We hypothesized that the balance between these two mechanisms controlling IOS may change during postnatal development. We tested this hypothesis by comparing neural responses to repetitive rhythmic vagal stimulation, at a stimulation frequency that paces baseline breathing, using in situ perfused brainstem preparations of rats at different postnatal ages. At ages < P15 (P, postnatal days), phrenic nerve activity (PNA) was immediately paced and entrained to the afferent input and this pattern remained unchanged by repetitive stimulations, indicating that vagal input stereotypically dominated the control of IOS. In contrast, PNA entrainment at > P15 was initially insignificant, but increased after repetitive vagal stimulation or lung inflation. This progressive adaption of PNA to the pattern of the sensory input was accompanied by the emergence of anticipatory centrally mediated IOS preceding the stimulus trains. The anticipatory IOS was blocked by bilateral microinjections of NMDA receptor antagonists into the KFn and PNA was immediately paced and entrained, as it was seen at ages < P15. We conclude that as postnatal maturation advances, synaptic mechanisms involving NMDA receptors in the KFn can override the vagally evoked IOS after ,training' using repetitive stimulation trials. The anticipatory IOS may imply a hitherto undescribed form of pattern learning and recall in convergent sensory and central synaptic pathways that mediate IOS. [source]

Kinetics of both synchronous and asynchronous quantal release during trains of action potential-evoked EPSCs at the rat calyx of Held

THE JOURNAL OF PHYSIOLOGY, Issue 2 2007
V. Scheuss
We studied the kinetics of transmitter release during trains of action potential (AP)-evoked excitatory postsynaptic currents (EPSCs) at the calyx of Held synapse of juvenile rats. Using a new quantitative method based on a combination of ensemble fluctuation analysis and deconvolution, we were able to analyse mean quantal size (q) and release rate (,) continuously in a time-resolved manner. Estimates derived this way agreed well with values of q and quantal content (M) calculated for each EPSC within the train from ensemble means of peak amplitudes and their variances. Separate analysis of synchronous and asynchronous quantal release during long stimulus trains (200 ms, 100 Hz) revealed that the latter component was highly variable among different synapses but it was unequivocally identified in 18 out of 37 synapses analysed. Peak rates of asynchronous release ranged from 0.2 to 15.2 vesicles ms,1 (ves ms,1) with a mean of 2.3 ± 0.6 ves ms,1. On average, asynchronous release accounted for less than 14% of the total number of about 3670 ± 350 vesicles released during 200 ms trains. Following such trains, asynchronous release decayed with several time constants, the fastest one being in the order of 15 ms. The short duration of asynchronous release at the calyx of Held synapse may aid in generating brief postsynaptic depolarizations, avoiding temporal summation and preserving action potential timing during high frequency bursts. [source]