Spatiotemporal Properties of the Action Potential Propagation in the Mouse Visual Cortical Slice Analyzed by Calcium Imaging

The calcium ion (Ca2+) is an important messenger for signal transduction, and the intracellular Ca2+ concentration ([Ca2+]i) changes in response to an excitation of the cell. To reveal the spatiotemporal properties of the propagation of an excitatory signal with action potentials in the primary visual cortical circuit, we conducted a Ca2+ imaging study on slices of the mouse visual cortex. Electrical stimulation of layer 4 evoked [Ca2+]i transients around the stimulus electrode. Subsequently, the high [Ca2+]i region mainly propagated perpendicular to the cortical layer (vertical propagation), with horizontal propagation being restricted. When the excitatory synaptic transmission was blocked, only weak and concentric [Ca2+]i transients were observed. When the action potential was blocked, the [Ca2+]i transients disappeared almost completely. These results suggested that the action potential contributed to the induction of the [Ca2+]i transients, and that excitatory synaptic connections were involved in the propagation of the high [Ca2+]i region in the primary visual cortical circuit. To elucidate the involvement of inhibitory synaptic connections in signal propagation in the primary visual cortex, the GABAA receptor inhibitor bicuculline was applied. In this case, the evoked signal propagated from layer 4 to the entire field of view, and the prolonged [Ca2+]i transients were observed compared with the control condition. Our results suggest that excitatory neurons are widely connected to each other over the entire primary visual cortex with recurrent synapses, and inhibitory neurons play a fundamental role in the organization of functional sub-networks by restricting the propagation of excitation signals

Subdivisions of the Auditory Midbrain (N. Mesencephalicus Lateralis, pars dorsalis) in Zebra Finches Using Calcium-Binding Protein Immunocytochemistry

The midbrain nucleus mesencephalicus lateralis pars dorsalis (MLd) is thought to be the avian homologue of the central nucleus of the mammalian inferior colliculus. As such, it is a major relay in the ascending auditory pathway of all birds and in songbirds mediates the auditory feedback necessary for the learning and maintenance of song. To clarify the organization of MLd, we applied three calcium binding protein antibodies to tissue sections from the brains of adult male and female zebra finches. The staining patterns resulting from the application of parvalbumin, calbindin and calretinin antibodies differed from each other and in different parts of the nucleus. Parvalbumin-like immunoreactivity was distributed throughout the whole nucleus, as defined by the totality of the terminations of brainstem auditory afferents; in other words parvalbumin-like immunoreactivity defines the boundaries of MLd. Staining patterns of parvalbumin, calbindin and calretinin defined two regions of MLd: inner (MLd.I) and outer (MLd.O). MLd.O largely surrounds MLd.I and is distinct from the surrounding intercollicular nucleus. Unlike the case in some non-songbirds, however, the two MLd regions do not correspond to the terminal zones of the projections of the brainstem auditory nuclei angularis and laminaris, which have been found to overlap substantially throughout the nucleus in zebra finches

Multidimensional Characterization and Differentiation of Neurons in the Anteroventral Cochlear Nucleus

Multiple parallel auditory pathways ascend from the cochlear nucleus. It is generally accepted that the origin of these pathways are distinct groups of neurons differing in their anatomical and physiological properties. In extracellular in vivo recordings these neurons are typically classified on the basis of their peri-stimulus time histogram. In the present study we reconsider the question of classification of neurons in the anteroventral cochlear nucleus (AVCN) by taking a wider range of response properties into account. The study aims at a better understanding of the AVCN's functional organization and its significance as the source of different ascending auditory pathways. The analyses were based on 223 neurons recorded in the AVCN of the Mongolian gerbil. The range of analysed parameters encompassed spontaneous activity, frequency coding, sound level coding, as well as temporal coding. In order to categorize the unit sample without any presumptions as to the relevance of certain response parameters, hierarchical cluster analysis and additional principal component analysis were employed which both allow a classification on the basis of a multitude of parameters simultaneously. Even with the presently considered wider range of parameters, high number of neurons and more advanced analytical methods, no clear boundaries emerged which would separate the neurons based on their physiology. At the current resolution of the analysis, we therefore conclude that the AVCN units more likely constitute a multi-dimensional continuum with different physiological characteristics manifested at different poles. However, more complex stimuli could be useful to uncover physiological differences in future studies

Cochlea-Implantate in älteren Menschen: Heidelberger Erfahrungen

Einleitung: Bei der Behandlung von hochgradigen Schwerhörigkeiten, ob angeboren oder erworben, spielt das Cochlea-Implantat (CI) eine immer größere Rolle. Etwa 9% aller Deutschen sind von hochgradiger Schwerhörigkeit bis hin zu Taubheit betroffen. 54% aller Deutschen >70 Jahre geben eine subjektive Hörbeeinträchtigung an. Es existieren jedoch wenige Informationen hinsichtlich der Hörentwicklung älterer Patienten mit CI. Unser Ziel war es, durch den Vergleich von prä- und postoperativer Einsilberverständlichkeit die Hörentwicklung nach Implantation eines CI in älteren Patienten darzustellen.Methoden: Mit Hilfe des Freiburger Sprachverständlichkeitstests wurde die Einsilberverständlichkeit bei 42 Patienten (> 80 Jahre) vor und nach CI-Versorgung gemessen. Ausgeschlossen wurden Patienten mit neu (<5 Wochen) implantiertem CI, sowie Patienten ohne Kenntnisse der deutschen Sprache.Ergebnisse: Das Kollektiv umfasste 17 weibliche und 25 männliche Patienten mit durchschnittlich 4,2 Jahren CI-Erfahrung (Median: 3,8 Jahre). Das Patientenalter lag bei 84 ± 3,2 Jahren (mean ± SD) (Median: 82,8 Jahre). Der Mittelwert des Erstanpassungsalters lag bei 78,5 ± 5,9 Jahren (mean ± SD) (Median: 79 Jahre). Die Einsilberverständlichkeit betrug präoperativ durchschnittlich 11,9% (Median: 0%). Postoperativ konnten die Patienten nach Implantation im Durchschnitt 56,4% (Median: 60%) der Wörter richtig zuordnen.Schlussfolgerung: Die Einsilberverständlichkeit war postoperativ deutlich größer als vor CI-Versorgung. Zusammenfassend zeigen unsere Ergebnisse, dass eine deutliche Zunahme des Sprachverstehens auch bei Patienten älter als 80 Jahre nach CI-Implantation zu erwarten ist. Weitere Untersuchungen auch in Hinblick auf den zeitlichen Verlauf dieser Hörverbesserung sind erforderlich.Der Erstautor gibt keinen Interessenkonflikt an