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

Mean Field Theory of enhanced defect formation in AgCl and AgBr

L'anomalie marquante de la conductivité qui est observée aux températures hautes indique une augmentation considérable de la formation des défauts près du point de fusion Tm. Puisque ni les corrections de Debye-Hückel ni la théorie classique diélectrique ne produisent une dépendance convenable sur la température, on introduit une théorie du champ moyen (MFT), dans laquelle l'énergie de formation se réduit par une quantité en proportion immédiate avec la concentration des défauts. La MFT simple donne certainement un accroissement rapide de la concentration des défauts aux températures hautes, mais quand on choisit la constante de force pour convenir à Tm, les concentrations calculées aux températures plus basses sont trop petites.The large conductivity anomaly observed at high temperatures indicates substantial enhancement of defect formation near the melting point Tm. Since neither Debye-Hückel corrections nor the classical continuum theory yield a suitable temperature dependence, a mean field theory is introduced in which the formation energy is reduced by an amount directly proportional to the defect concentration. The simple MFT does gives a rapid rise in defect concentration at high T, but when the strength constant is chosen to match Tm the predicted concentrations are too small at lower temperatures

APPLICATION OF CHI SQUARE TESTS TO FITTING OF IONIC CONDUCTIVITY

En relation avec une étude de l'anomalie de la conductivité à haute température dans les halogénures d'argent, plusieurs formes de tests de chi carré ont été appliquées pour déterminer la validité statistique des résultats. En premier lieu est décrit le processus habituel pour obtenir un lissage par moindres carrés de la conductivité en fonction de la température. Ensuite une discussion des erreurs expérimentales montre que les incertitudes sur la résistance, les dimensions de l'échantillon et la mesure de la température peuvent donner une erreur totale de 0,5 % et que cette erreur doit être indépendante, avec une bonne approximation, de la température. Un test de chi carré est alors décrit pour la distribution des déviations dans un intervalle intermédiaire de température. Dans les cas favorables, les erreurs peuvent être décrites par une moyenne égale à 0 et une déviation standard de 0,39% dans AgCl et 0,43 % dans AgBr. Enfin, une deuxième forme de test de chi carré est décrite pour mesurer la validité de lissage de la fonction à adapter basée sur le modèle de conductivité par défauts de réseau. La valeur de chi carré croît rapidement lorsque le domaine de température est étendu vers les hautes températures où se produit l'anomalie, fournissant une limite supérieure de température nécessaire à un lissage satisfaisant. On conclut que l'utilisation du test de chi carré a joué un rôle important dans la présente étude et que des utilisations semblables devraient être valables dans le cadre d'autres études de diffusion et conductivité ionique.In connection with a study of the high temperature conductivity anomaly for the silver halides, several forms of chi square tests have been applied to determine the statistical validity of the results. First the usual procedure for obtaining a least squares fit of conductivity us. temperature is described. Next a discussion of experimental errors shows that uncertainties in resistance, sample dimensions, and temperature measurements may give an accumulated error of around 0.5 %, and that this per cent error should be independent of temperature to a good first approximation. A chi square test is then described for the distribution of deviations in an inter-mediate temperature range, and it is shown that in favorable cases the errors can be described satisfactorily by a normal error distribution with a mean of zero and a standard deviation of 0.39 % for AgCl and 0.43 % for AgBr. Finally a second form of chi square test is described to measure the goodness of fit of the fitting function based on the defect model for the conductivity. It is shown that the value of chi square increases rapidly as the upper end of the intermediate temperature region is extended into the higher temperature region where the anomaly occurs, thereby providing a rather clearly defined upper temperature limit for an acceptable fit. It is concluded that these uses of the chi square test have played an important role in the present study, and that similar uses should be valuable for analyzing the experimental results of other studies of diffusion and ionic conductivity