The aim of this study was to characterize the effect of γ-aminobutyric acid (GABA) in the resting multiunit activity of the vestibular afferents during development using the isolated inner ear of embryonic and postnatal chickens (E15-E21 and P5). GABA (10(-3) to 10(-5) M; n = 133) and muscimol (10(-3) M) elicited an increase in the frequency of the basal discharge of the vestibular afferents. We found that GABA action was dose-dependent and inversely related to animal age. Thus, the largest effect was observed in embryonic ages such as E15 and E17 and decreases in E21 and P5. The GABAA receptor antagonists, bicuculline (10(-5) M; n = 10) and picrotoxin (10(-4) M; n = 10), significantly decreased the excitatory action of GABA and muscimol (10(-3) M). Additionally, CNQX 10(-6) M, MCPG 10(-5) M and 7ClKyn 10(-5) M (n = 5) were co-applied by bath substitution (n = 5). Both the basal discharge and the GABA action significantly decreased in these experimental conditions. The chloride channel blocker 9-AC 0.5 mM produced an important reduction in the effect of GABA 10(-3) (n = 5) and 10(-4) M (n = 5). Thus, our results suggest an excitatory role of GABA in the resting activity of the vestibular afferents that can be explained by changes in the gradient of concentration of Cl(-) during development. We show for the first time that the magnitude of this GABA effect decreases at later stages of embryonic and early postnatal development. Taking into account the results with glutamatergic antagonists, we conclude that GABA has a presynaptic action but is not the neurotransmitter in the vestibular afferent synapses, although it could act as a facilitator of the spontaneous activity and may regulate glutamate release.

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Here, we report for the first time developmental changes in spontaneous activity and in response properties of single nerve fibers from the macular chick lagena. Such aspects are important in order to get insight into the functional role of the lagena which remains undetermined. For this purpose, we used intracellular and extracellular single-unit recording techniques in an isolated inner ear preparation from the chicken at ages E15 and P1. At E15, afferent fibers displayed a low irregular spontaneous discharge rate (41 +/- 14 spikes/s, CV = 1.17 +/- 0.1), which was replaced by regular high frequency spontaneous activity at P1 (CV = 0.48 +/- 0.8, 89 +/- 27 spikes/s). During the developmental period including E15, the percentage of silent neurons was 60% while that of P1 was 40%. The synaptic activity was higher at E15 than at P1. The action potential waveform generated at E15 had small amplitude and derivative depolarization, and consequently, a large duration in correlation with respect to action potential waveform at P1 (respectively: 53 +/- 2 vs. 65 +/- 3 mV, 60 +/- 11 vs. 109 +/- 20 mV/ms, 3.6 +/- 0.4 vs. 1.1 +/- 0.12 ms). In addition, we recognized two response dynamics to the injection of current steps: phasic, or rapidly adapting neurons and tonic, or slowly adapting neurons. Our results indicate similar developmental processes for the lagena as described for the vestibular system in other species, in agreement with the known morphological characteristics of this otholitic end organ. The presence of more than one subtype of afferent neuron also correlates with previous reports on vestibular afferents with analogous electrophysiological properties, strongly suggesting the vestibular nature of the lagena.

We performed intracellular and single-unit extracellular recordings of neurons from different regions of the basilar papilla in the isolated chicken inner ear. We compared the spontaneous activity and the response properties of these neurons in embryos at E15 versus posthatching animals at P1. The recordings were carried out from the apical (position 0) to the basal extension at three positions of the basilar papilla, at 5%, 10% and 40% of the entire length of the cochlea. We found that the neurons at E15 recorded from these three regions exhibited a significant higher coefficient of variation compared with those neurons at P1 recorded in the same positions. This shows that in the posthatching age P1 the neurons from the whole basilar papilla become less irregular. We found that the intracellular action potential waveforms generated at E15 had small amplitudes and small depolarization slopes in comparison to those recorded at P1, respectively (53 ± 1 mV vs. 62 ± 2 mV; 66 ± 12 mV/msec vs. 166 ± 23 mV/msec). Furthermore, we also found that the response patterns to injection of current steps were phasic, tonic, or in the form of a not yet reported "burst" pattern. Our study shows that the low irregular discharge, the immature action potential waveforms, and the differences in the response patterns to current injection, highlights the important differences between neurons at E15 and P1, consistent with the incapacity of auditory neurons at embryonic age E16, to respond at sound levels <100 decibels.

Abstract. The relaxation time of collective electronic states in a 2D distribution of quantum dots is investigated theoretically by simulating EELS experiments. From the numerical calculation of the probability of energy loss of an electron beam, traveling parallel to the distribution, it is possible to estimate the damping time of ferroelectric-like states. We generate this collective response of the distribution by introducing a mean field interaction among the quantum dots, and then, the model is extended incorporating effects of long-range correlations through a Bragg-Williams approximation. The behavior of the dielectric function, the energy loss function, and the relaxation time of ferroelectric-like states is then investigated as a function of the temperature of the distribution and the damping constant of the electronic states in the single quantum dots. The robustness of the trends and tendencies of our results indicate that this scheme of analysis can guide experimentalists to develop tailored quantum dots distributions for specific applications.